Welcome to the Hitachi Medical Systems America, Inc. MRI Anatomy and Positioning Series. Over the coming months, we will be offering teaching modules to allow users of Hitachi MRI scanners to advance their positioning skills and review the anatomy that should be seen on some common MRI exams. Our intention is to discuss and review the anatomy that is most often seen, and the positioning that is most often used in your MRI studies. Good positioning skills are needed to ensure the best possible image quality for your studies.
In this fifth module, we will discuss the anatomy and positioning of the bony pelvis, as well as the anatomy and positioning of the abdominal and pelvic organs that are protected by the pelvic bones. We will review the functioning of the organs found in the true pelvis, including their relevant muscles, ligaments, arterial and venous systems, and nerve supply. We will also discuss the relevance of MRI in the characterization and diagnosis of pathology and disease in the pelvic region, to include specialized imaging for males and females.
Within our modules, we will offer suggestions as to appropriate RF coils to be used for various MRI exams. The RF coils that are recommended for pelvic imaging are part of the standard group of coils that are furnished with your magnet. Regardless of the RF coil that is being used, every attempt should be made to route the coil cable(s) in a manner that will avoid contact with the patient.
We will also discuss the use of the various pads that are furnished with our MRI systems (trough pads, table pads, accessory pads, coil cable pads, etc.). It is important to use the various pads that are provided to assist in eliminating, or at least minimizing, the amount of each patient’s skin-to-skin, skin-to-bore, or skin-to-cable contact. Reducing the amount of each of the aforementioned contacts reduces the patient’s chances of thermal injury. Please refer to the MR Patient Warming Prevention Plan published by Hitachi Medical Systems America, Inc. for more information concerning the prevention of patient warming.
The bony pelvic girdle consists of the innominate bones bilaterally, and the sacrum and coccyx posteriorly. In an adult, the innominate bones consist of the fused ilium, ischium, and pubis (Figure 1). The main purposes of the pelvic girdle are to support and protect the abdominal and pelvic organs, and to connect the trunk and lower limbs. Differences between the male and female bony pelvis include the observations that female pelvic bones are typically thinner, smaller and lighter; the female sacrum is typically shorter and wider than the male sacrum; the obturator foramen may be oval or triangular in the female, and round in the male; the female pelvic cavity is typically wider and shallower than that of the male.
To further differentiate this anatomical region by function, the pelvis is often divided into two parts. The greater or false pelvis acts like a basin to support the abdominal organs (area above Line 1 in Figures 2 and 3). Due to the upright position of humans, the false pelvis is large and flared. The lesser or true pelvis contains and protects the pelvic organs, and is the link between the trunk and the lower extremities. (Area between lines 1 and 2 in Figures 2 and 3) The true pelvis acts as a framework — it is hollow, in order to contain and protect the pelvic organs, yet strong, in order to support the weight of the body on the legs. The male’s sacral promontory juts out into this lesser or true pelvis. In Figures 2 and 3, Lines 1 and 2 delineate the pelvic inlet and pelvic outlet, respectively. Line 1, which marks the pelvic inlet, travels from the sacral promontory to the upper pubic symphysis. In males, the pelvic inlet is heart-shaped, while in females, it is oval-shaped. Line 2, which marks the pelvic outlet, travels from the coccyx to the lower border of the pubic symphysis. The pelvic outlet is larger in females, which is necessary for childbirth.
The joints of the pelvis include the lumbosacral, sacrococcygeal, sacroiliac, and pubic symphysis. The lumbosacral joint is between the fifth lumbar vertebrae and the sacrum. This joint has intervertebral discs and joints between the articular processes. The sacrococcygeal joint often exhibits bony fusion. An intervertebral disc is found between the sacrum and coccyx, in addition to accessory ligaments. The sacroiliac joints have a synovial articulation between the sacral and iliac surfaces. These joints are further strengthened posteriorly by the interosseous dorsal sacroiliac ligaments. Strong sacroiliac joints are important, as our body weight is transmitted through the sacrum and ilia, to the femora during standing, and to the ischial tuberosities for sitting. The pubic symphysis is a cartilaginous joint located between the pubic bones. This symphysis is united by an interpubic disc of fibrocartilage. The ligament around this joint relaxes during pregnancy.
The pelvic girdle differs from other bony anatomical regions because it protects and supports abdominal and pelvic organs. MRI of the pelvis may be more focused on the organs, soft tissues, and vessels, rather than on the bones themselves. In many instances, MRI may be used to further clarify or confirm a diagnosis from another imaging modality. MRI of the pelvis is also beneficial for pre-op planning and cancer staging. We will be concentrating on the anatomy of the true or lesser pelvis, as the false or greater pelvis serves mainly as support for the ileum and sigmoid colon.
The true pelvis contains and protects the urinary bladder, rectum, and female and male internal reproductive organs. The fibromuscular urinary bladder typically lies midline, and is covered superiorly by parietal peritoneum. It can contain 50-1000 ml of urine, which produces high signal on T2-weighted images in MRI. In most cases, the patient should be instructed to empty their bladder before the start of their MRI exam, in order to reduce artifacts and increase patient comfort.
The organs of the internal female reproductive system found in the true pelvis include the uterus, uterine (fallopian) tubes, ovaries, and vagina (Figure 4). The uterus is a hollow-pear shaped organ where fetal development occurs. It lies midline, posterior to the bladder, anterior to the rectum, and is typically tilted anteriorly. The uterine tubes are lateral extensions of the uterus, and assist in moving the ovum to the uterus, although they have no direct connection to the ovaries. These tubes open into the peritoneal cavity from their lateral aspects, and into the uterus from their medial aspects. The ovaries are oval and almond-sized with ligamentous attachments on either side of the uterus. They are responsible for the production, maturation and discharge of ova, as well as the secretion of estrogen and progesterone. The vagina connects with the uterus at the cervix, and is the birth canal. It is a musculomembranous tube or sheath, which passes through both the muscular urogenital and pelvic diaphragms of the pelvic floor.
MRI is extremely important as an imaging tool for the organs and pathologies of the female pelvis. In many cases, ultrasound will be the primary imaging modality, but MRI may be added to confirm the origin of pathology, to assist in determining if pathology is benign or malignant, for pre-op planning purposes, as well as for cancer staging. MRI has become the modality of choice in the evaluation of leiomyomas, commonly known as fibroids. When fibroids are treated using uterine artery embolization, MRI is performed both before the procedure, to localize and characterize the fibroids, and after the procedure, to help determine the success of the treatment (Figure 5).
The anatomy of the internal male reproductive system found in the true pelvis includes the prostate gland, ejaculatory ducts, seminal vesicles, and portions of the vas deferens and urethra (Figure 6). The prostate gland is the largest accessory gland of the reproductive system. It is cone-shaped, approximately the size of a chestnut, and consists of connective tissue and smooth muscle. It lies inferior to the bladder, and closer to the bladder’s posterior aspect. The urethra passes through the center of the prostate gland, carrying urine and semen. Enlargement or pathology in certain prostate lobes can hinder or obstruct the passage of urine through the urethra. The prostate gland is made up of 5 lobes — one each anterior, middle and posterior, and 2 lateral lobes. The middle lobe is frequently the site of adenomas, which can encroach on the urethra. Enlarged mucous glands of this lobe can also lead to urethral obstruction. The posterior lobe is the lobe that is felt on rectal exam. Enlargement of the lateral lobes can also cause obstruction of the urethra. The bilateral vas deferens bring mature sperm superiorly from the epididymis, across the superior aspect of the bladder, then curve inferiorly along the posterior aspect of the bladder to enter the ejaculatory ducts. The seminal vesicles, located posterior to the bladder, supply fluid for sperm energy, and also connect to the ejaculatory ducts. The ejaculatory ducts pass through the prostate, and empty into the urethra.
MRI of the male pelvis is most often ordered to diagnose, rule out, or follow-up treatment of prostate cancer (Figure 7). When paired with a contrast injection, and a CAD (computer-aided detection) system, similar to those often used with breast MRI, analysis of the kinetics of blood flow through the prostate can be performed. CAD systems can offer a higher sensitivity for the detection of abnormal sites of blood flow that may represent sites of cancer in the prostate gland, as well as more accurate biopsies. Due to the proximity and inter-relationships of the male internal reproductive anatomy, MRI of the prostate should include evaluation of the reproductive anatomy as well.
The muscles of the pelvis help to form the pelvic walls and the pelvic floor. The female and male pelvic muscles have the same names, but have different organs to support, and some differences in functions (strong female muscles are important for childbirth). Pelvic wall muscles include the anterior and inferior obturator internus, and the posterior iliacus, piriformis, and psoas major (Figures 8 and 9). The pelvic floor muscles, which are located in the pelvic outlet, make up the pelvic diaphragm, which separates the pelvic viscera from the more inferior perineal structures. Pelvic floor muscles must be strong to support the midline pelvic organs and structures, to counter abdominal pressure (from a cough or sneeze), and to assist in urination, defecation and childbirth. The pelvic diaphragm closes the pelvic outlet posteriorly. However, the pelvic outlet must remain open anteriorly as an exit for the urethra, vagina and anal canal. The main muscles of the pelvic diaphragm are the bilateral levator ani and coccygeus muscles. The levator ani is made up of the pubococcygeus and iliococcygeus muscles. The anteromedial border of the pubococcygeus surrounds the levator or urogenital hiatus, an opening that allows for passage of the urethra, vagina, and rectum. The medial aspect of the pubococcygeus muscle is termed the puborectalis muscle. The puborectalis wraps around the posterior aspect of the rectum to form a sling that holds the rectum forward in the pelvis. The puborectalis also provides support for the female vagina and bladder, as well as for the male seminal vesicles, prostate and bladder. The posterior and lateral aspects of the levator ani are formed by the iliococcygeus muscles. These muscles fan out horizontally, inserting on the pelvic sidewalls. The iliococcygeus muscle and posterior fibers of the pubococcygeus fuse at midline to form the levator plate. This plate acts as a shelf on which the pelvic organs rest. Weakening of the levator ani muscle can cause sagging of the levator plate. This “sagging” allows for increased opening of the levator or urogenital hiatus, which predisposes the patient to pelvic organ prolapse, and urinary or fecal incontinence. The coccygeus muscle is the most posterior muscle of the pelvic diaphragm.
The ligaments of the pelvis include the articular type, that hold bone to bone, bone to cartilage, or hold a joint together, as well as the various “fascial condensations” and membranous folds that support organs and keep them in the correct position. We will discuss both types, as the ligaments of both the bony pelvis and the pelvic organs are important in MRI.
The ligaments of the bony pelvis hold the sacrum and pelvis together. Both the sacroiliac and sacrococcygeal ligaments are found anteriorly and posteriorly. The anterior longitudinal ligament covers the anterior aspect of the lumbar vertebral bodies (Figure 10). The iliolumbar ligament connects the fifth lumbar vertebrae to the ilium. On the anterior border of the pelvis, the inguinal ligament attaches at the anterior superior iliac spine. Posteriorly, the sacrotuberous ligaments connect the sacrum to the ischial tuberosities bilaterally, and convert the sciatic notches to foramina (Figure 11). The sacrospinous ligaments connect the sacrum to the ischial spines bilaterally, separating the greater and lesser sciatic foramina, which transmit specific nerves and vessels. Together, the bilateral sacrotuberous and sacrospinous ligaments, and the greater and lesser sciatic foramina serve to separate the lateral and posterior walls of the pelvic cavity.
There is an extensive network of fascial ligaments, folds, and pouches amongst the pelvic organs, especially in the female. Although these ligaments may not be seen on MRI, it is important to understand their locations and functions with respect to the pelvic organs, as secondary signs may infer damage to these fascial ligaments. Fascia refers to a layer of fibrous tissue that permeates the body. It functions as a connective tissue that surrounds muscles, blood vessels, and nerves to bind them together. In certain anatomical regions, localized thickenings or “condensations” of this fascia occur, which are termed ligaments. The fascia and ligaments are made up of collagen fibers, so they remain somewhat flexible. The endopelvic fascia is a system of connective tissue that attaches the bladder, urethra, vagina and uterus to the pelvic walls. It is continuous with the visceral fascia, which is the capsule that contains the organs.
One of the largest of the fascial ligaments is the broad ligament of the uterus (Figure 12). It suspends the uterus, covers the uterine tubes, and suspends the ovaries. It is technically two layers of peritoneum, extending from the lateral margin of the uterus to the lateral pelvic wall, helping to hold the uterus in place. The broad ligament contains the round and ovarian ligaments, as well as the uterine tubes, uterine vessels, and lower part of the ureter. The round ligament is attached to the uterus in front of and below the attachment of the uterine tube. It assists in keeping the uterus anteverted and anteflexed. The ovarian ligament attaches the ovary to the lateral wall of the uterus. The suspensory ligament of the ovary is a band of peritoneum that extends upward from the ovary to the pelvic wall, for transmission of ovarian nerves, vessels and lymphatics. Additional peritoneal folds that are part of the broad ligament attach to the ovary (mesovarium) and suspend the uterine tubes (mesosalpinx). Endopelvic fasciae called the paracolpium and parametrium surround and support the uterus and vagina, and assist in preventing genital organ prolapse. Additional support for the uterus comes from the cardinal ligament, which is continuous medially with the pubocervical ligament, and the previously mentioned paracolpium and parametrium. The cardinal ligament extends laterally below the base of the broad ligament, and serves to hold the uterus and upper vagina in their proper places over the levator plate.
The female endopelvic fascia condenses to form three distinct ligaments that function as support for the bladder and urethra (Figure 13). The pubourethral ligament is the most anterior, extending from the urethra to the pubic bone, and helping to stabilize the urethra. The urethropelvic ligament, which can be seen on MRI, is a little more posterior, supporting the bladder neck and the urethra. The pubocervical fascia or ligaments extend from the posterior surface of the pubis to the cervix and offer additional support for the bladder. Loss of support from this ligament can lead to incontinence and hypermobility of the urethra. These three ligaments attach to the side wall of the urethra and the pelvic wall, forming a “hammock” behind the urethra. When intra-abdominal pressure increases (such as during sneezing, coughing, or exercise) the urethra is forced closed against this posterior “hammock”. Additional bladder support comes from the female pubovesical ligament, and the male puboprostatic ligament. Both attach to the pubic bone, with the pubovesical ligament extending from the neck of the bladder, and the puboprostatic ligament extending from the prostate gland.
The ovarian/testicular arteries are branches from the abdominal aorta, while the main arterial supply to the pelvis and perineum comes from the internal iliac arteries (Figure 14). There are also collateral arteries from the inferior mesenteric and femoral arteries. The pelvic arteries can be organized into posterior and anterior divisions. The posterior division includes the iliolumbar, superior gluteal and lateral sacral arteries. The iliolumbar artery supplies muscles in the lumbar region, the superior gluteal artery supplies the gluteal muscles, and the lateral sacral arteries branch off the superior gluteal to supply the structures of the vertebral canal and related bones and soft tissue. The anterior, or visceral, arteries include the inferior gluteal, pudendal, and four branches from the anterior trunk of the internal iliac artery. The inferior gluteal artery supplies the buttocks and posterior thigh. The pudendal arteries supply the external genital structures. The four branches from the internal iliac artery, from superior to inferior location, include the superior vesical, obturator, uterine (female) or inferior vesical (male), and middle rectal. The superior vesical artery supplies the bladder and male ductus deferens. The obturator artery goes to the medial thigh area. The uterine artery supplies the uterus in females, has a branch to the vaginal artery, and forms a strong anastamosis with the ovarian artery. The inferior vesical artery in males is similar in position to the female uterine artery. It supplies the bladder, and has branches to the prostate and seminal vesicles. The fourth artery of the anterior division is the middle rectal, which supplies blood to the rectum.
The internal iliac vein drains the majority of the pelvic organs and the perineum. The blood then flows to the common iliac vein and on to the inferior vena cava. Variations from this occur with the ovarian/testicular veins and the superior rectal vein. The right ovarian/testicular (gonadal) vein drains into the inferior vena cava. The left ovarian/testicular (gonadal) vein drains into the left renal vein, which in turn drains into the inferior vena cava (Figure 15). The superior rectal vein is actually the starting point for the inferior mesenteric vein. It flows from the rectum, across the left common iliac vein, and continues upward as the inferior mesenteric vein. It then flows into the splenic vein, which joins the hepatic portal system (Figure 16).
The majority of nerves that innervate the pelvic region are from the sacral plexus, the coccygeal plexus, and the sacral sympathetic chain (Figure 17). The term “plexus” refers to a structure in the form of a network, in this case the interconnecting nerves of the pelvis and perineum. The sacral plexus includes the lumbosacral trunk (merging of nerves from L4 and L5), and the nerves arising from S1 through S4. The sciatic nerve, the largest nerve in the body, is formed by the L4 through S3 nerves (Figure 18). It runs through the buttocks and down the lower limb, supplying most of the skin of the leg, muscles of the back of the thigh, and muscles of the lower leg and foot. Compression or irritation of this nerve causes sciatica, which can result in pain in the lower back, buttock, leg, or foot, depending on the site of the nerve injury. Treatment for sciatica differs widely, depending on the site and severity of symptoms. Nerves from S2 through S4 join to form the pudendal nerve, which innervates the sphincters of the bladder and rectum, the external genitalia, and the muscles of the perineum. A pudendal nerve block is a type of anesthesia given in the perineum when women are in labor for childbirth. This nerve can become stretched or compressed during difficult childbirth, as well as during activities such as bicycling. Loss of function of the pudendal nerve from these activities is typically temporary. Permanent nerve damage can result from a pelvic tumor, or from the surgery required to remove a pelvic tumor. Sacral plexus branches from the S1 through S3 area form the superior and inferior gluteal nerves, which innervate the gluteal region. Additional nerves from the sacral plexus innervate the piriformis muscle of the pelvis, the quadratus femoris muscle of the hip, and the pelvic diaphragm. The coccygeal plexus sends nerves to the levator ani and coccygeus muscles of the pelvis.
The sacral sympathetic chain, a part of the peripheral nervous system, supplies autonomic innervations through three pairs of sacral splanchnic nerves (splanchnic meaning of or relating to the viscera or organs). These nerves serve to induce contractions of sphincters, decrease intestinal motility, relax the bladder muscle, constrict the urinary sphincter, and stimulate uterine contractions or male ejaculation. Sympathetic nerves are typically those involved in the fight or flight response, while parasympathetics maintain homeostasis of the body (Figure 19). Parasympathetic fibers from the sacral spinal nerves at S2 through S4 form the pelvic splanchnic nerves. These nerves travel bilaterally to the inferior hypogastric plexus, also known as the pelvic plexus. Nerves from the inferior hypogastric plexus assist with contraction of the urinary bladder and rectal muscles, and vasodilation of vessels. Branches from the pelvic plexus reach the pelvic organs by way of additional nerve plexuses, including the vesical, prostatic, uterovaginal, and middle rectal.
The prostate gland is a small walnut-shaped gland that is part of the male reproductive system (Figure 20). It produces the seminal fluid that nourishes and transports sperm. The prostate is located anterior to the rectum, and inferior to the bladder. It surrounds the first part of the urethra, which connects the bladder with the tip of the penis, and carries urine and other fluids out of the body.
MRI of the prostate is most commonly performed to evaluate prostate cancer. Additional indications for prostate MRI include infection (prostatitis) or prostate abscess, enlarged prostate (benign prostatic hypertrophy or BPH), congenital abnormalities, as well as complications after pelvic surgery.
Prostate cancer is the most common malignancy among men in the US, with an estimated 217,730 new cases and 32,050 prostate cancer-related deaths in 2010. Most men diagnosed with prostate cancer have localized disease confined to this gland, which has a better chance of successful treatment, and does not ultimately cause their death. A small percentage of patients with aggressive tumors will progress to develop local, extracapsular tumor extension and distant metastases. The overall 5-year survival rate is 99% for all stages, but only 34% in cases involving distant metastases. The aim of prostate cancer management is to identify and treat those patients with aggressive disease before they develop locally advanced or metastatic disease, and to avoid over treating “idle” tumors, which are unlikely to be life threatening. MRI is valuable in the local staging of prostate cancer, and as an aid to the management of clinically significant disease.
The incidence of prostate cancer increases with age, and it is most commonly found in men over the age of sixty five. Risk factors for prostate cancer are also higher for males that are African American, for those that have a family history of prostate or breast cancer, or men that are obese. Early prostate cancer is usually asymptomatic, but may be accompanied by nonspecific symptoms that mimic benign prostatic disease. Patients with metastatic disease may present with pelvic or back pain, difficulty urinating, hematuria, and/or blood in the semen. More men are requesting screening for this disease, as their longevity and disease awareness both increase, leading to an expected increase in prostate cancer diagnoses in the future.
A blood test that measures prostate-specific antigen (PSA) is used as a screening tool for prostate cancer, although it is neither 100% sensitive nor specific. PSA gives a range of risk for prostate cancer, not an absolute level. Men diagnosed with prostate cancer usually have an abnormal digital rectal exam, and/or raised PSA. Diagnosis may be confirmed by transrectal prostate biopsy, which is typically performed under ultrasound guidance. Prostate tumors are also given a Gleason score, which combines two numbers and grades their pathological appearance. High Gleason scores indicate aggressive tumors with increased potential for local and distant spread. Gleason grading can provide a spectrum of risk for all patients, ranging from 2 (nonaggressive cancer) to 10 (very aggressive cancer).
Once the prostate cancer diagnosis is made, additional testing is performed to determine the stage of the cancer, which helps in deciding treatment options. This testing may include bone scans, ultrasounds, CT, MRI, and/or PET scans. Prostate cancer stages are:
Various types of imaging have proven to be valuable in not only the local staging of prostate cancer, but also in the management of clinically significant disease in intermediate and high-risk patients. Modern imaging techniques, including MRI, can identify the site of the tumor within the prostate, allow targeted biopsy, optimize planning for patients that are proceeding to radical surgical treatment or focal therapy, and improve the management of low-risk patients on active surveillance strategies. Very early stages of prostate cancer may not need immediate treatment, or may never need treatment at all. These cases would be placed in active surveillance, where regular follow-up blood tests, rectal exams, and possibly biopsies are performed to monitor progression of the cancer. If the cancer is progressing, other treatment options may be advised.
Prostate MRI is an effective diagnostic tool for men with:
The zones of the prostate are best demonstrated on MRI (Figures 21-23). On T2-weighted sequences of the normal prostate, the peripheral zone shows high signal intensity due to its high water content. The central gland, which is comprised of the central and transition zones, has lower signal intensity on T2-weighted images. Prostate cancer is often seen as an area of low signal abnormality in the peripheral zone, but some cancers are isointense and cannot be seen on standard MRI. Conditions such as prostatitis, atrophy, and calcifications may also cause low signal intensity, and result in false positives. Areas of hemorrhage secondary to biopsy can also be confused with tumor on T2-weighted sequences. This problem emphasizes the importance of performing a T1-weighted sequence to demonstrate high signal blood products. Recommendations are that prostate MRI should not be performed until 8 weeks post-biopsy to minimize image interpretation interference from hemorrhage.
A solitary fibrous tumor (SFT) of the prostate can be confused with prostatic carcinoma. SFTs are rare, and typically benign, but are similar to prostatic cancer with their peripheral location and solid hypoechoic appearance on transrectal ultrasound (TRUS). The mass seen in the images below was diffusely hyperintense on T1-weighted images, and mildly hyperintense on T2-weighted images (Figures 24, 25). When contrast was administered, there was gradual enhancement from the periphery to the center of the tumor (Figure 26). Larger lesions can have heterogeneous T2 signal, with variations dependent on the differences in the main components of the tumor. These tumors can have histologically malignant components, and deserve close follow-up after surgical treatment.
MRI has an established role for patients who are at intermediate or high risk for localized disease progression and who are being considered for radical treatments (surgical prostatectomy or brachytherapy). Extracapsular tumor extension can be identified as an abnormal low signal mass that extends through the prostate pseudocapsule into the periprostatic fat or into the seminal vesicles. Additional signs of extracapsular spread include loss of the rectoprostatic angles, and retraction or bulge of the prostate capsule. The sensitivity of MRI in detecting extra-capsular extension or seminal vesicle invasion has improved to a range of 73-80%, with a high specificity of 97-100%. Extracapsular tumor extension as small as 0.5mm (as determined in histopathology) has been accurately detected.
MR has taken on an emerging role in tumor localization within the prostate gland. Patients with suspected prostate cancer and negative systematic biopsies may benefit from an MRI examination aimed at locating the tumor. MR has detected prostate cancer in approximately a third of patients with one or more negative systematic biopsies. Tumors in the transitional zone of the prostate are uncommon and can be challenging to diagnose due to the coexistence of nodular BPH (benign prostatic hyperplasia), which is quite common in older men.
MR has also shown excellent results in assisting with surgical planning. The surgical technique will be influenced by the position of the tumor within the gland. MR findings have changed the surgical plan in 78% of patients, and were accurate in 93% of patients. Newer MR techniques, such as dynamic contrast-enhanced imaging, diffusion-weighted imaging, and magnetic resonance spectroscopy allow the potential for improved prostate tumor detection, when added to standard MRI protocols.
In dynamic contrast-enhanced MRI, prostate cancer demonstrates increased enhancement compared with normal prostatic tissue (Figure 27). Tumoral enhancement tends to be most prominent with higher grades, which are more clinically significant tumors. Prostatic cancers are characterized by their early enhancement and early washout, but can be mimicked by benign prostatic nodules, prostatitis, and hemorrhage. Benign prostatic nodules enhance early, but have a slower washout than prostate cancers. When added to T2-weighted sequences, dynamic contrast-enhanced sequences have resulted in significant improvement in the detection of extracapsular extension. Dynamic contrast-enhanced sequences are also useful in the detection of local tumor recurrence following radiotherapy.
Using diffusion-weighted imaging (DWI), normal prostate glandular tissue displays a higher water diffusion rate than cancerous tissue, as diffusion is restricted in tightly packed cancer cells (Figure 28). DWI is an inherently T2-weighted sequence but, unlike conventional T2-weighted imaging, prostate cancer often demonstrates increased signal intensity on DWI. Cancerous tumors may then be difficult to visualize within the normally high signal peripheral zone of the prostate. Calculation of the apparent diffusion coefficient (ADC) and ADC mapping displays prostate cancer as a low-signal region, due to the restricted diffusion of water in cancer cells. The sensitivity of DWI is better in the peripheral zone than the central gland. DWI offers the advantages of high-contrast resolution between normal prostate and cancerous tissue, as well as a short acquisition time. Its disadvantages include low spatial resolution, increased susceptibility to artifacts, and an overlap of diffusion values between benign and malignant lesions. DWI has been shown to be helpful in the identification of prostate cancer in patients with previous negative biopsies and persistently elevated PSA as well as in differentiating between low-, intermediate-, and high-risk patients. A significant correlation has been found between the Gleason score of the tumor and the ADC value, while an inverse relationship is seen between the ADC value and the percentage of tumor involvement in core biopsies. For patients being monitored by active surveillance, reduction of the ADC value by 10% or more indicates disease progression. ADC values can also be used to assess response to treatment for pre- and post-radiotherapy.
Magnetic resonance spectroscopy imaging (MRSI) has a potential use as a noninvasive method to assess prostate cancer aggressiveness. The most commonly detected metabolites in the prostate include choline, creatine, polyamines, and citrates. Healthy prostates have low levels of choline and high levels of citrates; the opposite of each is found with prostate cancer. Polyamines are increased with benign prostatic hyperplasia, but reduced with cancer. A ratio of choline-plus-creatine to citrate has been used to help differentiate benign from malignant lesions. This ratio also tends to increase with tumors of high grade. MRSI has been found to be beneficial in the characterization of prostate nodules within the peripheral zone, and can be used to predict cancer recurrence and response to therapy.
For the last two decades, transrectal ultrasound (TRUS) guided biopsy has been the most common method used to diagnose prostate malignancy. This is referred to as a “blind” procedure because specific prostate tumors, especially very small tumors, cannot always be distinguished due to ultrasound’s poor resolution of soft tissue. TRUS biopsies also follow a systematic approach, which tends to target the peripheral aspects of the prostate gland, typically sampling 12-14 sites. With this approach, they are likely to omit 30-40% of prostate cancers that are located in the anterior, midline transition zone, or apex of the gland. In addition, a negative TRUS biopsy does not ensure the absence of disease. For those men with persistently elevated PSA levels, subsequent biopsies are performed with an associated decrease in the rate of cancer detection. With multiple site sampling, there are also increased risks of infection, pain, and bleeding.
Advances in MRI technology have led to the development of MRI-guided targeted biopsy methods. One method involves the performance of the targeted biopsy within the MRI bore, also known as TRIM (Trans-Rectal Interventional MRI). A more recent development is the fusion biopsy, in which stored MRI data is fused with real-time ultrasound to guide the physician to the suspicious targets. Targeted prostate biopsy has the potential to improve the diagnosis of prostate cancer, as well as to aid in the selection of patients for active surveillance and focal therapy.
The direct “in-bore” biopsy is typically performed by an interventional radiologist. MR images should be obtained immediately preceding the biopsy to provide precise current details about the size and dimensions of the prostate gland, and to identify the location and size of potential cancerous tumors. Pre-biopsy imaging may include routine scans, as well as DWI and contrast-enhanced imaging. Since the potential cancerous cells within the prostate can be precisely pinpointed with MRI, typically only 2-3 biopsy samples need to be taken vs. the 12-14 samples done with TRUS biopsies. A biopsy device is inserted into the rectum to guide the biopsy needle to the targeted area for tissue sampling (Figures 29, 30). This highly targeted approach assures both the physician and the patient that tissue samples are coming from the locations identified on the MR image as having the most likely chance of containing cancer. Radiologists are better able to identify and characterize any prostate malignancy. Correlations between targeted biopsies and final pathology have improved when comparing the “in-bore” or TRIM biopsy method to TRUS biopsies.
Information concerning the fusion biopsy method is from UCLA, where the Artemis device (a 3D prostate biopsy system) was installed in 2009 (Figure 31). MR images are fused with real-time ultrasound to provide a 3D image, similar to a roadmap, for biopsy guidance. The process begins with a patient that has a “suspected” prostate cancer diagnosis — this includes men with prior negative biopsies, but persistently elevated PSA levels, as well as those with slow-growing cancers. The patient receives an MRI of the prostate, which is reviewed and “scored” for cancer risk. Using UCLA-created software, a 3D image of the prostate is generated using the data and scores from the MRI prostate scan. The 3D image should clearly show the locations of any suspicious areas. The information is transferred to a CD, which is loaded into the Artemis system during the prostate biopsy procedure. The Artemis system allows the stored MRI images to be electronically transferred and fused with real-time ultrasound. The resultant 3D image provides a roadmap to help guide the biopsy needle into the targeted areas (Figure 32).
Results of early studies that involved the fusion targeted biopsy reveal that this may be the next step in the evolution of the prostate biopsy. Lesions seen on the MRI, with a corresponding positive biopsy, are associated with a higher grade cancer, and increased amount of cancer sampled. High-grade cancers are typically more life-threatening. This results in improved information for both the patient and the clinician, and reduces the chances that a man will undergo unnecessary treatment. This method may also aid in the selection of patients for active surveillance and focal therapy. Targeted fusion biopsies can be performed in an outpatient setting with local anesthesia, in time periods as short as twenty minutes. The overall added cost of the MRI may be offset by a reduction in the number of biopsy procedures that will need to be performed.
A variety of methods exist for the treatment of prostate cancer. The decision as to which treatment method is used should factor in the rate of growth of the prostate cancer, existence of metastasis, the patient’s overall health, as well as the benefits and potential side effects of the recommended treatment.
Radiation therapy can be delivered as external beam radiation, or as brachytherapy. External beam radiation uses high-powered energy x-ray or proton beams to deliver the radiation. Brachytherapy involves the placement of radioactive seeds in the prostate tissue, where the seeds deliver a low dose of radiation over a long time period. Side effects of radiation therapy may include painful, frequent and/or urgent urination, rectal symptoms, and erectile dysfunction.
Hormone therapy treatment will stop the body from producing the male hormone testosterone, which prostate cancer cells rely on for their growth. Cutting off the hormone supply causes the cancer cells to die, or at least slow their growth rate. Medications can be provided to either stop the body’s testosterone production, or block the testosterone from reaching the cancer cells. Orchiectomy is the surgical removal of the testicles, which serves to reduce testosterone levels very quickly. Hormone therapy may be used with early-stage prostate cancer in order to shrink tumors before radiation therapy, as well as with more advanced cases of this disease to shrink and slow the growth rate of tumors. Hormone therapy may also be used post-surgery or post-radiation therapy to slow the growth of any residual cancer cells. Side effects of this treatment may include erectile dysfunction, hot flashes, loss of bone mass, reduced sex drive, and weight gain.
Radical prostatectomy is the surgical removal of the prostate gland, some surrounding tissue, and some lymph nodes. Surgical methods are varied, as are their risks and benefits. The routine laparoscopic prostatectomy is now more commonly performed with the assistance of a robot, providing more precise movement of surgical tools. In retropubic surgery, the prostate gland is removed through an incision in the lower abdomen. This method may carry a lower risk of nerve damage, which can lead to problems with bladder control and erections. Perineal surgery involves an incision between the scrotum and the anus for prostate removal. This method may allow for faster recovery times, but adds difficulty to both lymph node removal and the avoidance of nerve damage. All forms of radical prostatectomy carry the risks of urinary incontinence and erectile dysfunction.
Cryosurgery or cryoablation involves killing cancer cells by freezing tissue. Ultrasound images are used to guide the insertion of small needles into the prostate. A very cold gas is placed in the needles, which causes the surrounding tissue to freeze. A second gas is then placed in the needles to reheat the tissue. The cycles of freezing and thawing kill the cancer cells, as well as some surrounding healthy tissue. At its inception, cryosurgery had high complication rates and unacceptable side effects. However, with newer technologies, complication rates have been lowered, and cancer control has improved. This treatment method may be an option for men who have not been helped by radiation therapy.
Chemotherapy may be an option for men whose prostate cancer has metastasized, or those with cancers that do not respond to hormone therapy. A form of immunotherapy has also been developed to treat advanced recurrent prostate cancer. The patient’s immune cells are removed and genetically engineered to fight prostate cancer. The cells are then replaced in the body intravenously. Some men respond to this therapy, but it requires multiple visits and is reported to be expensive.
An advanced therapy method being investigated in clinical trials in the U.S. is high-intensity focused ultrasound treatment. A small probe inserted in the rectum focuses ultrasound energy at precise points in the prostate. The powerful sound waves heat the prostate tissue, causing cancer cells to die.
MRI is leading the way in a recent non-surgical prostate cancer treatment: MRI-guided laser ablation. In reports from the University of Texas Medical Branch at Galveston, advanced MRI that can identify cancer-suspicious areas in the prostate has been paired with advanced laser technology to remove these suspicious areas, without damaging surrounding tissue. In most cases, images of aggressive prostate cancer are distinctly different from slow-growing prostate cancer. MRI enables men that are engaging in “active surveillance”, or watchful waiting, to be observed over time with improved results as to what their prostate cancer looks like, and how far or fast it is, or is not, spreading. National standards and expert advice concerning prostate cancer screening have changed dramatically in the last few years. Results have shown that “standard” treatment for prostate cancer — surgical prostate removal — often causes more damage than the disease ever would have. The most common and devastating side effects associated with surgical prostate removal, which are impotence and incontinence, have been eliminated with this new method. MRI-guided laser ablation may not be the recommended treatment for prostate cancer that is large, aggressive, or that has metastasized outside of the pelvis.
The uterus is a dynamic reproductive organ that is responsible for several reproductive functions. It must adapt to the different stages of a woman’s reproductive life. Specific MRI weightings and techniques are used to gain important information concerning the uterus, as well as the pathologies of the female pelvis. Axial T1-weighted images may be obtained to evaluate the uterine contour, lymph nodes, and bone marrow. Fat-suppressed T1-weighted images can be used to differentiate between pelvic masses that contain fat and those that contain protein or hemorrhage. T2-weighted imaging may be performed in 3 orthogonal planes. One plane typically gives good visualization of the endometrial complex and the long and short axis of the uterus. Contrast enhancement is used to document the extent of endometrial carcinoma invasion, or to detect the presence of necrosis in uterine leiomyomas (commonly called fibroids) after uterine artery embolization. Dynamic contrast injections can be used prior to uterine artery embolization to evaluate the uterine arteries and the collateral artery supply.
The uterus is divided into three layers — endometrium, myometrium, and serosa or perimetrium (Figure 33). The endometrium is the inner layer and the most active layer. It responds to cyclic ovarian hormone changes, and is essential to menstrual and reproductive function. The endometrium varies in thickness with the menstrual cycle and menopausal status. The central endometrium has high signal intensity due to its mucinous rich glands and connective tissue. The middle layer, or myometrium, makes up most of the uterine volume. It is the muscular layer, and is composed of mainly smooth muscle cells. It can be further separated into the inner myometrium, or junctional zone, and the outer myometrium. The junctional zone contains compact smooth muscle with little intercellular matrix, and has a relatively low T2 signal intensity. The outer myometrium has more intercellular matrix and vessels, and less compact smooth muscle, resulting in a higher T2 signal intensity. These T2 signal intensity differences are best visualized during the reproductive years. T1-weighted images typically show poor contrast distinction between the endometrium and the myometrium, but these layers display a tri-level appearance on T2-weighted images (Figure 34). The outer layer of the uterus is the serosa or perimetrium, which is a thin layer of tissue made up of epithelial cells that envelops the uterus.
MRI is often used to exclude malignancy in the diagnosis of cystic adnexal masses that persist or increase in size on follow-up ultrasounds. The term “adnexal” refers to anatomy that adjoins organs; i.e. uterine adnexa include the ovaries and uterine tubes. MRI has demonstrated 91-93% accuracy in characterizing adnexal masses as benign or malignant. The accuracy rate for identifying lesions such as hemorrhagic cysts and endometriomas is higher with MRI than with transvaginal ultrasound. The MR characteristics of hemorrhagic cysts may vary, depending on the age and amount of hemorrhagic component. Typically, they tend to be of relatively high signal intensity on T1-weighted images, intermediate-to-high intensity on T2-weighted images, and often reveal a fluid-fluid level. Hemorrhagic cysts should maintain relatively high signal intensity on T1-weighted images with fat suppression, which helps differentiate them from other types of cysts. Post-contrast imaging should not show enhancement of the internal components of these cysts, but their walls may enhance (Figure 35).
Endometriosis occurs when the presence of endometrial glands and tissue are present outside the uterus. MRI has a sensitivity of 90%, specificity of 98%, and overall accuracy of 96% for the identification of endometriomas in patients with clinically suspected adnexal masses. Similar to hemorrhagic cysts, the MR appearance of endometriomas is variable, depending on their stage and the amount of blood products present. Typically, they have high signal on T1-weighted images and intermediate to low signal intensity on T2-weighted images (Figure 36). The lower T2-weighted signal intensity is secondary to methemoglobin, protein and iron from repeated episodes of hemorrrhage. Endometriosis implants on serosal or peritoneal surfaces will display with high T1 signal on nonenhanced fat-suppressed images. Endometriomas are frequently bilateral and numerous.
Endometrial carcinoma is the most common gynecologic malignancy, and the fourth most common cancer in women. Approximately 75% of these cancers occur in postmenopausal women, typically affecting those in their sixties and seventies. The most common symptom is postmenopausal bleeding. As a result of this early clinical symptom, patients typically present with early-stage disease. Excessive estrogen stimulation is the most recognized association with endometrial cancer. MRI is an important tool for the staging of known endometrial carcinoma. With its ability to demonstrate cervical invasion, MRI can influence pre-operative and surgical decisions. It has also been shown to be superior to both CT and ultrasound in assessing myometrial invasion, cervical extension, and nodal involvement. Endometrial cancer appears isointense to the myometrium and endometrium on T1-weighted images. On T2-weighted images, this cancer is typically hyperintense, but this signal intensity can be variable. Myometrial invasion is best seen on T2-weighted images, appearing as a disruption or irregularity of the junctional zone (Figure 37). When dynamic contrast-enhanced MR scanning is performed, endometrial cancer usually enhances less than the myometrium. Protocols that include both T2-weighted and contrast-enhanced scans offer better opportunities for differentiation between superficial and deep muscle invasive tumors.
Women taking tamoxifen for the treatment of breast cancer may have endometrial thickening, and are at an increased risk for endometrial cancer, endometrial hyperplasia, and endometrial polyps (Figure 38). Tamoxifen exhibits antiestrogenic effects within the breast, but can show proestrogenic activity within the endometrium.
Ovarian carcinoma is the leading cause of gynecological cancer-related deaths in the United States, but it accounts for only about 3% of all cancers in women. In 2010, approximately 20,000 women in the U.S. were diagnosed with ovarian cancer, and approximately 14,500 female deaths were attributed to ovarian cancer. With no truly effective screening method, approximately 75% of women have advanced disease at the time of diagnosis, with a 5-year survival rate of 29% in those with metastases. MR has superior accuracy over CT and Doppler sonography in diagnosing ovarian malignancy. Gadolinium-enhanced MRI has depiction rates of 93% for benign lesions and 95% for malignant lesions (Figure 39). In addition to characterization of ovarian masses, MRI can be used for staging when a mass has malignant features. Predictors of malignancy include ascites, peritoneal or serosal metastases, and hydronephrosis. One study found the two most significant predictors of malignancy to be the presence of vegetations in a cystic lesion, and the presence of necrosis in a solid lesion. On T2-weighted images, an ovarian mass of high signal intensity found in conjunction with implants in the abdomen and pelvis is suggestive of mucinous cystadenocarcinoma, with peritoneal metastatic disease.
Uterine leiomyomas are benign uterine neoplasms, derived from the smooth muscle cells of the myometrium. They are the most common tumors of the female genital tract, occurring in more than twenty percent of women over the age of thirty. Most women with uterine leiomyomas or “fibroids”, as they are commonly called, are asymptomatic; however, amongst those with symptoms, the most common complaints are dysmenorrhea and irregular menstrual bleeding. Uterine leiomyomas are classified based on their location within the uterus, where they may be intramural, subserosal, or submucosal (Figure 40). The most common subtype is intramural, meaning they are centered in the uterine wall. Subserosal leiomyomas are centered external to the uterus. Submucosal leiomyomas have a component in the endometrial canal, with a further subset called intracavitary tumors that are found almost entirely within the endometrial canal (Figure 41). MRI is considered to be superior to transvaginal ultrasound for mapping of individual myomas. A uterus that contains leiomyomas will appear enlarged, and have abnormal contours on MRI. Nondegenerated uterine leiomyomas are typically well circumscribed, exhibit lower T2 signal intensities than the outer myometrium, and enhance homogeneously. As they degenerate, these fibroids have more heterogeneous signal on T2-weighted images, and display less enhancement. They may also contain calcifications, which display as signal voids on MRI. Intramural or subserosal leiomyomas often display a high signal intensity rim. Subserosal fibroids can also simulate fibrous or smooth muscle ovarian masses, but can be differentiated due to the presence of a normal ovary on the same side as the fibroid, as well as the presence of a bridging vessel from the uterus to the fibroid (Figure 42). Submucosal leiomyomas can simulate endometrial masses. It is reported that both submucosal and intracavitary fibroids are common causes of infertility or miscarriage. They can create an adverse environment for implantation and/or they prohibit sufficient blood flow to support a developing embryo.
MRI is the modality of choice for the evaluation of leiomyomas both before and after their treatment using uterine artery embolization (UAE) (Figure 43). Embolization is performed to block the blood supply to uterine fibroids when they become symptomatic. Prior to the embolization procedure, MRI can offer accurate information concerning the size, location, and vascularity of leiomyomas. Additional uterine abnormalities need to be identified or excluded, as some abnormalities can impact or preclude UAE treatment. Large intracavitary fibroids are considered a contraindication for this procedure, as are submucosal fibroids, which may be expelled from the uterus. These conditions may be better treated with hysteroscopic resection. Specific imaging characteristics can be used as “predictors” of a fibroid’s response to UAE. High signal intensity on T1-weighted imaging may indicate a pre-existing hemorrhagic infarction, which results in a poor outcome secondary to insufficient reduction in fibroid volume. Fibroids that do not enhance after contrast injections are considered nonviable, and do not respond to treatment. The best response to UAE treatment is seen with those fibroids that display high signal intensity on T2-weighted images and homogeneous contrast enhancement pre-operatively. MR protocols should include MRA scans to evaluate the uterine arteries, and identify collateral feeding vessels that may require embolization. Post-embolization images should be compared to pre-embolization images, with success measured as an overall reduction in uterine size, and a reduction in the mean leiomyoma volume. Treatment is successful if the post-op images display high signal intensity on T1-weighted images, homogeneously decreased T2 signal intensity, a decrease in enhancement of fibroids, preserved enhancement of the remainder of the uterus, and a lack of visualization of the uterine arteries. Fibroids that still enhance after UAE treatment are viable, and usually grow and cause a recurrence of symptoms. Post-embolization MRA images should be closely examined for causes of treatment failure, which would include revascularization of the uterine artery, or collateral arterial supply from the ovarian arteries (Figure 44).
The UAE procedure is performed to block the blood supply to uterine fibroids. These fibroids or leiomyomas are hypervascular, meaning they use more blood than normal tissue. The abnormal arteries that supply the fibroids are larger than the arteries supplying the normal uterine tissue. The embolization process consists of the injection of multiple tiny inert polyvinyl particles into the uterine artery. The particles are sized to tumble into the abnormal large fibroid arteries, while sparing the tiny vessels that feed the uterus (Figure 45). Deprived of blood, nutrition, and oxygen, the fibroids shrink following embolization, and the patient’s symptoms should lessen. Short-term and long-term follow-up MRI examinations are typically performed to monitor the success of the embolization treatment (Figure 46).
MRI is also being combined with ultrasound in a non-invasive treatment to eliminate fibroids called MRgFUS (MR-guided Focused Ultrasound Surgery). This method destroys tissues by focusing a high-energy beam on a specific point, and raising its temperature to 60-85°C (140-185°F). Multiple focal deliveries of energy are required to ablate a specific tissue. The MR system can provide high-resolution 3D imaging of the location of the tumor and internal organs, as well as real-time temperature feedback indicating the degree of tissue heating and coagulation. The physician can then adjust treatment parameters and control the treatment, ensuring a high level of safety and efficacy. Contrast-enhanced T1-weighted images are acquired to assess the treatment outcome. The treated fibroid should not enhance on post-treatment images (Figure 47).
MRI is quickly becoming the modality of choice for the evaluation of pelvic floor dysfunction in women. Up to 50% of women over the age of 50 that have had children have some degree of abnormal descent of the bladder, uterus, vagina, small bowel, or rectum. Approximately 10-20% of the aforementioned group has signs or symptoms of abnormal descent problems, including pelvic pressure, tissue protrusion and incontinence. Risk factors for pelvic floor dysfunction in women are age, multiparity, obesity, and menopause. Faster MRI sequences offer a quick evaluation of pelvic organ prolapse and /or pelvic floor relaxation with an increase in patient comfort, and a decrease in exam complexity and invasiveness. Dynamic MRI exams have an important role in pre-op planning for pelvic floor dysfunction surgeries. One study detailed changes in 41% of initial surgical plans after reviewing the information gained from dynamic MRI studies. Dynamic images can be acquired with the patient at rest, then with the patient performing the Valsalva maneuver. A healthy female at rest should have contracted levator ani muscles. These muscles keep the rectum, vagina, and urethra elevated and closed by pressing them anteriorly, toward the pubic symphysis. While interpreting MRI images, the radiologist may add lines and perform measurements between specific areas of the pelvic anatomy to determine pelvic organ movement, and the degree of pelvic floor dysfunction (Figure 48). The pubococcygeal line (from inferior border of pubic symphysis to inferior joint of coccyx) designates the level of the pelvic floor. Organ descent greater than 2 cm below the pubococcygeal line could require surgical intervention (Figure 49). The levator plate, which is a transverse portion of the levator ani, is inferior to the pubococcygeal line. The levator plate should remain parallel to the pubococcygeal line, both when the patient is at rest and when straining. The H line, which extends from the pubic symphysis to the posterior wall of the rectum, indicates the A-P width of the levator hiatus. This measurement should be no greater than 5 cm. on a sagittal image. The M line, which extends from the posterior aspect of the H line to the pubococcygeal line, indicates the vertical descent of the levator hiatus. This measurement should be no greater than 2 cm. on a sagittal image. The measurements of both the H and the M lines will be elongated during the Valsalva maneuver in patients with pelvic floor laxity.
Before positioning a patient for a pelvis scan in an open MRI system, it is important to consider the anatomy that is to be included on the images, the coil options, and the use of table and accessory pads. Proper patient positioning, with both the coil and the anatomy at isocenter in all three planes, results in improved image quality.
Body habitus will play a key role in both coil selection and table pad choices. Hitachi’s systems offer flexible body coils, which can be more accommodating for larger patients. The Oasis and Altaire systems also feature a Transmit/Receive body coil, which is the inherent or “built-in” coil located in the magnet bore. Keep in mind that parameter adjustments should be made when the T/R body coil is used. One must be aware of how the use of trough pads, table pads, or no pads will affect the coronal positioning of both the patient and the coil. Hitachi also offers an extensive inventory of accessory pads and sponges, which are helpful for patient stability, comfort, and safety (Figure 50). When positioning your patient for scanning on an open MRI system, it is extremely important to have the anatomy of interest and the coil centered in the laser lights in all three directions: head-to-foot (axial or transverse plane), right-to-left (sagittal plane), and anterior-to-posterior (coronal plane) (Figure 51).
The coil of choice for a study of the pelvis is the RAPID body coil (Figures 52, 53). Fit the base of the coil in the table trough. The longitudinal center mark on the coil will be centered at the midline of the table. The horizontal center of the coil should be between the marking on the patient table and the end of the table nearest the magnetic field. This will allow for sufficient table travel while still achieving isocenter positioning. The patient should be positioned on the base portion of the coil so that the horizontal center mark on the coil passes through a point midway between the symphysis pubis and the iliac crests. The coil pads and additional table pads can be adjusted to help achieve coronal centering of the pelvis. The upper portion of the coil is then placed on the base and pushed firmly into place to lock the coil (Figure 56). The midline of the patient’s body should be aligned with the longitudinal center mark on the upper portion of the coil. The patient should now be centered in all three planes — centered on the pelvis in the coronal and axial planes, and centered midline in the sagittal plane.
The flexible body coils can be used for pelvis scanning to accommodate larger patients (Figures 54, 55). However, they do not have RAPID capabilities, and should not be used with protocols that are labeled as “RAPID”. Trough and/or table pads should be placed on the table to help center the flexible coil in the coronal plane. The horizontal center of the coil should be between the marking on the patient table and the end of the table nearest the magnetic field. This will allow for sufficient table travel while still achieving isocenter positioning. The longitudinal center of the coil should be aligned with the sagittal laser light. Position the patient on the flexible coil so that the horizontal center mark on the coil passes through a point midway between the symphysis pubis and the iliac crests. Depending on the patient’s body habitus, table and/or accessory pads may need to be adjusted to maintain coronal centering. Close the flexible body coil around the patient and secure the latches. Accessory pads can be placed between the flex coil and the patient to maintain the anterior portion of the coil in a level position, which will minimize stress on the latches. The midline of the patient’s body should be aligned with the longitudinal center mark or stitching found on the anterior aspect of the coil (Figures 57, 58). The patient should now be centered in all three planes — centered on the pelvis in the coronal and axial planes, and centered midline in the sagittal plane.
A T/R Body coil is available on the Altaire and Oasis systems. This integrated coil is the coil of choice for very large patients, as well as high-anxiety or claustrophobic patients. These patients can be scanned without a coil being placed over or around their bodies. However, use of the T/R body coil in this manner is not recommended for routine day-to-day scanning. Specific parameter changes should be made before using the integrated coil. Trough and/or table pads should be placed on the table, depending on the patient’s size and body habitus. If the patient cannot be accommodated with any pads, a sheet should be placed on the table underneath them. Position the patient on the table so that the marking on the patient table passes through a point midway between the symphysis pubis and the iliac crests. This will allow for sufficient table travel while still achieving isocenter positioning. The patient’s midline should be centered in the sagittal laser light. The axial laser light should be centered at a point midway between the symphysis pubis and the iliac crests. The coronal laser light should be positioned along the center of the patient’s coronal dimension.
The patient’s arms and hands can be placed at their sides, above their head, or on their chest, with no interlocking of their fingers. Their arms and hands should remain outside of the RAPID or flex coils. The table straps may be used to further secure both the RAPID and flexible coils. Figure 58 demonstrates use of the table strap with the flexible coil. Patients will typically be positioned on the table feet first, in consideration of the table travel limitation mark found on vertical field systems. Use of the large knee bolster cushion for patient comfort may be determined by individual facilities, as its placement could interfere with the required positioning of the pelvis.
The 1.5T Echelon system comes equipped with a variety of trough and table pads, as well as various positioning pads and sponges (Figure 59). These positioning aids can be used to support the position of both the patient and the coil, as well as to keep your patient comfortable and secure. The magnet bore of the Echelon does not permit lateral patient table movement. However, accurate patient and coil positioning, and correct use of the sagittal and axial laser lights (Figure 60) to center the patient’s anatomy ensures that high quality images will be acquired with isocenter scanning.
The coil of choice for a study of the pelvis is the RAPID Torso/Body coil (Figure 61). Trough and/or table pads are placed on the table as needed, depending on the patient’s size and body habitus. The lower portion of the coil should be positioned in the middle of the table on top of the pads. The exact placement of the coil on the table, and the direction it faces, are based on the patient’s preference to enter the scanner head first or feet first. The patient should be in a supine position on the lower portion of the coil, positioned so that the horizontal center mark on the coil passes through a point midway between the symphysis pubis and the iliac crests. Their feet should be pointed in the same direction as the coil cables and plugs. The upper portion of the coil is then placed on the base and secured with the Velcro® straps (Figure 62). The midline of the patient’s body should be aligned with the longitudinal center mark on the upper portion of the coil. Plug the coil in to the nearest table connector, and cover the coil cable with the cylindrical cable cover padding.
This integrated coil is the coil of choice for very large patients, as well as high-anxiety or claustrophobic patients. These patients can be scanned without a coil being placed over or around their bodies. However, use of the T/R body coil in this manner is not recommended for routine day-to-day scanning. Specific parameter changes should be made before using the integrated coil. Trough and/or table pads should be placed on the table, depending on the patient’s size and body habitus. If the patient cannot be accommodated with any pads, a sheet should be placed on the table underneath them. The patient can be positioned on the table either head first or feet first. The patient’s midline should be centered in the sagittal laser light. The axial laser light should be centered at a point midway between the symphysis pubis and the iliac crests.
The patient’s arms and hands can be placed at their sides, above their head, or on their chest, with no interlocking of their fingers. Their arms and hands should remain outside of the RAPID Torso/Body coil. Use of the large knee bolster cushion for patient comfort may be determined by individual facilities, as its placement could interfere with the required positioning of the pelvis.
The 1.5T Echelon OVAL system incorporates the WIT (Workflow Integrated Technology) RF coils for scanning. Eight element and twelve element WIT Spine coils are integrated in the table. The WIT Spine coils are used in combination with the eight element WIT Torso coil to provide uniform, volumetric coverage over a large field of view for scanning of the pelvis. RAPID is available for use with the WIT coils. The Echelon OVAL system incorporates table pads that are always in place between the Posterior WIT spine coils and the patient’s body (Figure 63D), as well as between the WIT Torso coil and the patient. Numerous positioning pads, sponges, and straps are furnished with the OVAL system and should be used for patient comfort and safety (Figures 63A, B, C).
These three coils are the recommended coil combination for pelvis scanning, whether for general purposes, female pelvis, or male pelvis (Figures 64, 65, 66). Pelvis scanning, like most scanning on the Echelon OVAL, can be done head first or feet first. The WIT Spine 8 coil should be plugged into the center table connector, with its “Gantry” label oriented toward the MR gantry. For feet first pelvis scanning, which is probably the most common method, the WIT Spine 12 coil should be plugged into the table connector closest to the gantry (Figure 67). The large table pad is placed on the portion of the table nearest the table handle, where the patient will place his or her head. The spine coil pad is placed over the WIT Spine 8 and WIT Spine 12 coils, with its notched area fit into the large table pad. The medium notched pad fits in at the gantry end of the table, with the notched areas aligned so that the table connectors are accessible.
If the patient chooses to be scanned head first, the WIT Spine 12 coil should be plugged into the table connector farthest away from the gantry. The large table pad will then be placed on the end of the table closest to the gantry, where the patient will place his or her head. The spine coil pad is placed over the WIT Spine 8 and Spine 12 coils, with its notched area fit into the large table pad. The medium notched pad fits in at the end of the table nearest the table handle, with the notched areas aligned so that the table connectors are accessible. Place a pillow at the end of the table where the patient’s head will be, and place the long rectangular pads at the end of the table where their legs will be for comfortable support. Whether they are head first or feet first, the patient should be positioned on the table so that a point midway between the symphysis pubis and the iliac crests is at the center of the spine coil pad. This positioning will result in proper centering of the pelvis over the WIT Spine 8 and WIT Spine 12 coils. Adjust the patient so that their midline is in the center of the table. Place the Torso pad on the patient, centered over the patient’s pelvis (Figure 68A). Place the WIT Torso coil on the Torso pad, using two Velcro straps on each side to attach the WIT Torso coil to the WIT Spine coil wings. Adjust the WIT Torso coil so that its center is aligned longitudinally with the midline of the patient. Plug the coil in to the nearest table connector, and cover the coil cable with the cylindrical cable cover padding (Figure 68B).
This integrated coil is the coil of choice for very large patients, as well as high-anxiety or claustrophobic patients. These patients can be scanned without a coil being placed over or around their bodies. However, use of the T/R body coil in this manner is not recommended for routine day-to-day scanning. Specific parameter changes should be made before using the integrated coil. The WIT Spine 8 and WIT Spine 12 coils can remain plugged in to the table, with the appropriate table pads placed over them, depending on the patient’s size and body habitus. The T/R Body coil can be used in conjunction with the WIT Spine coils, in cases where the WIT Torso coil cannot be used. For cases when the patient cannot be accommodated with any pads or any WIT coils, and only the T/R Body coil will be used, the connector covers should be placed over the WIT Spine connectors in the table. A sheet should be placed on the table underneath the patient. The patient can be positioned on the table either head first or feet first. The patient’s midline should be centered in the sagittal laser light. The axial laser light should be centered at a point midway between the symphysis pubis and the iliac crests.
The patient’s arms can be placed at their sides, above their head, or on their chest, with no interlocking of their fingers. When possible, have the patient keep their arms and hands over their head to prevent wrap artifacts, especially when performing RAPID sequences. Additional pads can be placed under and/or alongside the patient’s arms for their comfort, as well as to prevent contact with the magnet bore.
The following are HMSA suggestions for imaging of the pelvis. Always check with your radiologist for his/her imaging preferences. Sequence types, imaging planes, angulation of slices, and use of presat bands will be site and radiologist specific. Specific scan setups for prostate imaging and female pelvis imaging are included.
Axial slices of the pelvis can be set up using coronal and sagittal images or scanograms. Slices should be prescribed to include the area from the pelvic floor to the iliac crests (Figure 69).
Coronal slices of the pelvis can be set up using axial and sagittal images or scanograms. Slices should be prescribed to include the area from the coccyx to the anterior aspect of the symphysis pubis (Figure 70). Coverage should include the area from the symphysis pubis to the iliac crests.
Sagittal slices of the pelvis can be set up using coronal and axial images or scanograms. Slices should be prescribed to include the area from the left to the right pelvic side walls (Figure 71).
Axial slices of the prostate can be set up using coronal and sagittal images. Slices should be prescribed parallel to the base of the bladder, and should provide coverage of the prostate and seminal vesicles (Figure 72). Presat bands may be included to decrease artifacts from breathing and arterial pulsation. A large FOV axial image may be requested to check the para-aortic and pre-sacral lymph nodes. Coverage should then include from the middle of the kidneys inferiorly to the symphysis pubis. Axial slices on a large FOV image should be aligned parallel to the right and left iliac crests.
Coronal slices of the prostate can be set up using axial and sagittal images. Slices should be prescribed parallel to a line from the right hip joint to the left hip joint on an axial image, and should provide coverage of the prostate and seminal vesicles (Figure 73). Presat bands may be included to decrease artifacts from breathing and arterial pulsation. A large FOV coronal image may be requested to check the para-aortic and pre-sacral lymph nodes. Coverage should then include from mid abdomen to the sacrum. Coronal slices on a large FOV image can be planned on a sagittal image, where they should be aligned parallel to the lumbar spine.
Sagittal slices of the prostate can be set up using axial and coronal images. Slices should be prescribed parallel to the line along the interpubic fibrocartilage and the anal canal on an axial image. Slices should be parallel to the interpubic fibrocartilage in the coronal plane. The area of coverage should include the prostate and seminal vesicles, as well as the region from the right acetabulum to the left acetabulum (Figure 74). Presat bands placed superiorly and anteriorly to the sagittal slices may be included to decrease artifacts from breathing and arterial pulsation.
Axial slices of the female pelvis can be set up using coronal and sagittal images. Slices should be prescribed parallel to the line along the right and left iliac crest, and perpendicular to the lumbar spine in the sagittal plane. The area of coverage should include the uterus and ovaries (Figure 75). Presat bands may be included to decrease artifacts from breathing and arterial pulsation. A large FOV axial image may be requested to check the para-aortic and pre-sacral lymph nodes. Coverage should then include from the middle of the kidneys inferiorly to the symphysis pubis. Axial slices on a large FOV image should also be aligned parallel to the right and left iliac crests.
Coronal slices of the female pelvis can be set up using axial and sagittal images. Slices should be prescribed parallel to a line from the right hip joint to the left hip joint on an axial image, and should provide coverage of the entire uterus and ovaries (Figure 76). Presat bands may be included to decrease artifacts from breathing and arterial pulsation. Your radiologist may request a coronal oblique scan, where the slices are aligned parallel to the endometrium. Angulation of slices for a coronal oblique will vary, according to the pathology that may be involved. A large FOV coronal image may be requested to check the para-aortic and pre-sacral lymph nodes. Coverage should then include from mid abdomen to the sacrum. Coronal slices on a large FOV image can be planned on a sagittal image, where they should be aligned parallel to the lumbar spine.
Sagittal slices of the female pelvis can be set up using axial and coronal images. Slices should be prescribed perpendicular to the sacrum in the axial plane. Slices should be parallel to the lumbosacral spine in the coronal plane. The area of coverage should include the entire pelvis, from the right acetabulum to the left acetabulum (Figure 77). Presat bands placed superiorly and anteriorly to the sagittal slices may be included to decrease artifacts from breathing and arterial pulsation.
This concludes the Pelvis Imaging module of the Hitachi Medical Systems America’s MRI Anatomy and Positioning Series. You must complete the post-test for this activity in order to receive your Continuing Education credits.