Protocol
•Axial, coronal and sagittal T2 whole pelvis
•Sagittal midline T2 -3 images
–At rest
–Squeezing/Clenched
–Straining/Bearing down
•Sagittal T2 Bearing down 15 images
•Sagittal T2 single slice 1/second during evacuation
•Sagittal T2 post evacuation Valsalva
Imaging Protocol
Imaging with the patient in the supine position has been shown to be perfectly satisfactory for evaluating symptomatic pelvic floor weakness, despite the fact that defects are most easily identified when patients are upright . The MR imaging protocol requires no oral or intravenous contrast agents, and the examination can be completed in 15 minutes. Once familiar with signs of pelvic descent, the radiologist can complete the interpretation in 5–10 minutes.
After the patient has voided, she is positioned on the MR imager table with a multicoil array wrapped low around the pelvis. Scout images are obtained to identify a midline sagittal section that shows the pubic symphysis, urethra, vagina, rectum, and coccyx. Next, 10-mm-thick sagittal images of the midline are obtained with a rapid half-Fourier T2-weighted imaging sequence, such as single-shot fast spin echo (SSFSE; GE Medical Systems, Milwaukee, Wis) or half-acquisition single-shot turbo spin echo (HASTE; Siemens, Iselin, NJ), and a 30-cm field of view. These images are obtained while the patient is at rest and during the Valsalva maneuver. Many patients require coaching to achieve maximal pelvic strain. Next, 5-mm-thick axial T2-weighted images of the pelvic floor centered on the puborectal muscle are obtained with a 20-cm field of view and a standard high-resolution sequence such as fast spin echo. Coronal images are optional.
Imaging Technique:
In MRI of the pelvis, adequate patient preparation and a good technique with fast acquisition time are required to achieve maximum patient comfort and hence better patient compliance. The patient will be asked to void partially before the dynamic examination in order to prevent a distended urinary bladder from obscuring the pelvic structures and masking pelvic organ prolapse. Maintaining a small amount of urine in the urinary bladder improves visualization of the bladder and anterior vaginal wall prolapse. The examination is performed with a torso phased-array coil wrapped around the pelvis. Although use of an endovaginal coil may improve the spatial resolution of the fine supporting ligaments in the pelvis, it is invasive and may diminish patient acceptance and compliance [9]. The use of an endovaginal coil may distort the pelvic tissues in patients with a small pelvis. The field of view is small and often inadequate for visualization of the puborectalis. To improve visualization of the vagina and rectum, a small volume of intraluminal ultrasonic gel that has a hyperintense T2 signal may be instilled. Via a small-caliber catheter-tip syringe, 20 mL of gel may be instilled into the vagina and approximately 60–120 mL into the rectum. Although the dynamic MRI examination may be performed without endoluminal gel, doing so results in suboptimal straining that masks the degree of pelvic organ prolapse and results in inconspicuity of visceral descent.
Ultrafast, large-field-of-view, T2-weighted sequences such as single-shot fast spin-echo (SSFSE, GE Healthcare scanners) or half-Fourier acquisition turbo spin-echo (HASTE, Siemens Medical Solutions scanners) are frequently described in dynamic MRI of the pelvic floor and are performed at our institution. Alternatively, true fast imaging in steady-state precession may be performed. The patient should be given instructions as to the proper performance of straining before the examination. Specifically, she should be told to keep her sacrum on the table and strain using only the internal organs. The images are acquired in the sagittal plane and can be viewed in a cine loop to visualize the pelvic floor and the degree of prolapse of the pelvic organs.
For patients with a rectocele, these images should be repeated after the patient evacuates the rectal contents. The evacuation sequence can be obtained with the patient in the magnet and recorded if the magnet has been adequately prepared and the patient is able to cooperate with instructions. However, if the patient cannot evacuate in the magnet, evacuation in the commode followed by repeated imaging may be necessary. Residual contrast material will define a significant rectocele. In patients with pelvic organ prolapse, static images may be acquired in the coronal plane. These images show ballooning of the iliococcygeus muscle that often occurs with chronic constipation and perineal hernias.
After the dynamic examination is completed, small-field-of-view (20–24 cm) T2-weighted axial fast spin-echo (FSE, GE Healthcare scanners) or axial turbo spin-echo (TSE, Siemens Medical Solutions scanners) sequences are acquired to obtain high-resolution images of the muscles and fascia of the pelvic floor and the fascial condensations supporting the urethra. Although this set of images requires approximately 4 minutes to acquire, images of the lower pelvis are resistant to breathing motion artifacts. These high-resolution axial images of the pelvis are useful in showing the relationship between the pelvic side wall and the urethra and vagina. Fat saturation is generally not applied to these sequences because the hyperintense signal of fat in the pelvis provides good contrast to the hypointense signal of the adjacent muscles, fascia, and pubic bones. The entire examination is typically completed in 20 minutes.
Imaging Technique:
Pelvic coil and fast T2-weighted (T2W) sequences, such as single-shot fast spin echo, half Fourier
acquisition turbo spin echo, or steady-state free precession sequences (true FISP) are typically used for dynamic pelvic floor MR imaging. On the T2W images, the fluid in the bowel and urine in the bladder, as well as pelvic fat have bright signal, which allows clear delineation of the pelvic organs. To achieve good visualization of the vagina and rectum, intraluminal gel (sterile lubricating gel), which gives high T2 signal, should be instilled. About 120 cc of warmed gel is instilled into the rectum, and 20 cc into the vagina. MR imaging of the pelvic floor can be performed without endoluminal contrast, however lack of vaginal and rectal distention may lead to suboptimal evaluation . Vaginal gel allows better visualization of the anterior and posterior vaginal walls, therefore improves detection of the apex of the vagina and its inversion, if present, which can be difficult to reveal otherwise. Without rectal distension with gel, adequate straining, evacuation, and rectal emptying cannot be properly documented and recto-vaginal septum defects and posterior rectal wall laxity and intrarectal intussusception may not be visualized during the exam while contributing to defecatory dysfunction in the real life. Also, non-emptying of a large rectocele may obscure an enterocele. Over distention of the bladder can mask prolapse in other compartments, therefore patients are asked to void prior to the study.Imaging is usually performed in three planes (axial, sagittal, and coronal). Images acquired in the sagittal plane at midline can be viewed in a cine loop to visualize pelvic organs descent during strain maneuvers and Valsalva. Sagittal images are used to evaluate and measure pelvic organ position at rest and their descent during strain. Coronal images are used to assess the symmetry of the levator ani muscles. Axial images are important in the assessment of the levator hiatus, the shape of the vagina, and lateral defects. Patients are imaged in the supine position or in the left lateral decubitus position in the standard closed magnet configuration. For the patients to be imaged in the upright position, the open magnet system can be used. Patients are instructed to perform different maneuvers during the scanning, such as Kegel squeeze or strain and defecation, to allow the dynamic evaluation of the pelvic floor function. The combination of gravity and rectal evacuation maximizes the stress on the pelvic floor. Rectal evacuation during MR scan in supine position is especially important due to diminished effects of gravity in this body orientation. Majority of patients can defecate in the supine position. Some patients need to have their knees bent over the pillow to
facilitate rectal emptying. Typically, the study is completed in less than 20 minutes.
Dynamic pelvic MR imaging technique
Dynamic pelvic MR imaging may be performed in either closed or open-configuration MR systems and allows for the evaluation of the pelvic floor in different positions.Al though open- conf igur a t ion MR systems in sitting position enable a more physiological approach to defecation, the use of such systems is limited by the lack of their world wide availability. Since Bertschinger et al (10) have shown that no clinical significant findings were missed when comparing dynamic pelvic MR in supine position with dynamic pelvic MR in sitting position, MR in supine position may be considered a reliable imaging modality for imaging the pelvic floor. In our experience, performing the examination using state-of-the-art technique, which means MR imaging at rest, at maximal contraction of the anal sphincter ( squeezing) , at straining,as well as imaging during evacuation is probably more important than the patient position. In particular, MR imaging during defecation is of paramount importance since relevant findings may be missed when dynamic pelvic MR encompasses imaging at rest, at squeeze and at straining only . Although there is general agreement that no premedication nor oral or intrarectal preparation for bowel cleansing is necessary when dynamic pelvic MR imaging is performed, there is considerable variation in the literature with regard to the optimal examination protocol. For evaluation of the posterior compartment (i.e. the anorectum) all authorities agree that the rectum should be filled with contrast agent. The viscosity of the enema should be somehow similar to that of a normal rectum content because the manifestations of outlet obstruction may vary with fecal consistency . Hence, when performing dynamic pelvic MR, most authors use ultrasound gel for rectal enema . Other authors have proposed the use of mashed-potatoes spiked with a small amount of gadolinium-chelate for filling the rectum .The increasing use of dynamic MR imaging has shown that patients with abnormalities of the posterior pelvic compartment often reveal concomitant disorders involving the anterior as well as the middle com-partment . Therefore some authors have proposed also to tag the vagina (i.e. the middle compartment) and/or the bladder (i.e. the anterior pelvic compartment) in order to clearly delineate the anterior and the middle pelvic compart - ments . In our experience, there is no need for contrast agent administration neither in the vagina nor in the bladder since MR imaging allows easily the identification of all the anatomical landmarks of the three pelvic compartments.
Drawing of the sagittal midline view of the female pelvis shows bony landmarks and the puborectal muscle, also called the levator sling. The pubococcygeal, H, and M lines and the levator plate are delineated in red.
Advanced Imaging Techniques
The MR imaging protocol described above is all that is required for preoperative evaluation of the symptomatic patient with pelvic floor weakness. Several authors have described the use of upright imaging in an open-configuration MR imaging unit . Although this technique does maximize the evidence of all weakness, it rarely helps identify new defects or changes the therapeutic approach. Three-dimensional imaging has also been explored as a tool for determining levator ani volume in an attempt to select patients for either conservative therapy or surgery . At present, it remains a research technique.
Dynamic pelvic MR imaging in sitting position
Dynamic MR imaging of the pelvic floor in sitting position is performed in a vertically open-configuration MR s y s t e m s u c h a s t h e 0 . 5 T s u p e r c o n d u c t i n g o p e n -
configuration MR system Signa SP (GE Medical Systems, Milwaukee, Wis). A wooden chair, which fits into the open space between the two magnet rings, allows imaging in the sitting position . Before the subject is placed on the seat, the rectum is filled with 300 mL of a contrast agent solution which consists of a suspending agent (mashed potatoes) spiked with 1.5 mL of an extracellular 0.5 M gadolinium-chelate contrast agent . A flexible transmit/receive radiofrequency coil is wrapped around the pelvis. On the basis of axial localizing images, a 15-mm thick multiphase T1-weighted spoiled gradient-recalled echo (GRE) sequence which transverses the rectal canal in the midsagittal plane is planned. An image update is provided every 2 seconds. Images are obtained at rest, at maximal sphincter contraction, during straining, and during defecation in the midsagittal plane. The images are analysed on a workstation in cine loop presentation. Additional gradient-echo (GRE) images are used in axial and coronal planes when a lateral rectocele or an internal rectal prolapse is suspected. Dynamic pelvic MR imaging in supine position Dynamic pelvic MR imaging may also be performed in supine position using nearly all commercially available closed- or open-configuration MR systems with horizontal access. When dynamic pelvic imaging is performed in these MR systems the patient is placed in supine position and a pelvic phased-array coil is used for signal transmission and/ or reception. For dynamic MR imaging in the different positions various MR sequences can be used with similar results. The basic requirement for the sequence is the necessity for a fast imaging update. Some authors have used T2-weighted single-shot fast spin-echo sequences (SSFSE) in the midsagittal plane obtained at rest, at squeezing, at straining and during defecation . Al t e r n a t i v e l y, s t e a d y s t a t e f r e e p r e c e s s i o n ( S S F P )sequences may be used for this purpose. Our current protocol includes (SSFP) sequences obtained at rest, at squeezing, straining, and after evacuation. For assessment of the defecation we prefer the use of a T1-weighted multiphase GRE sequence since this sequence offers an imaging window long enough for continuous imaging of t h e e v a c u a t i o n , e v e n i n p a t i e n t s wi t h a p r o l o n g e d evacuation time. The choice of the enema depends on the MR sequence which is used for dynamic imaging of the pelvic floor. For SSFSE and SSFP sequences ultrasound gel is most suitable (10,13, 22, 23). If the dynamic sequences are performed with some sort of T1 weightening the rectum
is filled with an enema which consists of ultrasound gel or mashed potatoes mixed with a small amount of gadoliniumchelate as described above. MR findings in patients with outlet obstruction Rectocele An anterior rectocele is the most frequent anatomical abnormality in patients with pelvic floor disorders and is defined as a rectal wall protrusion or bulging during defecation. The anterior wall is most commonly involved but a rectocele may also be located in the posterior rectal wall. Posterior rectoceles are also referred as a posterior perineal hernia by some authors based on the fact that the bulging is through a puborectalis muscle defect . Two pathogenetic mechanisms are involved in the formation of rectoceles: (a) the weakness of the rectovaginal septum either congenital or after an obstetric trauma, and (b) chronic straining at defecation in constipated patients. Rectoceles may occur in up to 20% of asymptomatic women . However, there is general agreement that only rectoceles with a sagittal diameter of more than 2 cm may result in outlet obstruction, and/or the need of digital manoeuvres to empty the rectum . A clinical significant rectocele should be considered based on the following criteria: patient history, size exceeding 2 cm in sagittal diameter, retention of contrast medium, reproducibility of the patient’s symptoms, and the need for evacuation assistance . Most of the rectoceles are diagnosed during physical examination but a reliable classification with regard to the size, emptying, and associated abnormalities are only provided by imaging examinations. Dynamic MR enables an accurate assessment of the size, location and degree of emptying of a rectocele. Using dynamic pelvic MR imaging, an anterior rectocele may be classified with regard to its size, expressed as the depth of wall protrusion beyond the expected margin of the normal anterior rectal wall into small < 2 cm, moderate 2-4 cm, and large > 4 cm . In addition, rectoceles are classified into those with complete evacuation and those with incomplete evacuation depending on the presence or absence of contrast material retention at the end of defecation. Small rectoceles do not trap contrast material at the end of evacuation and are asymptomatic while most of the rectoceles exceeding 2 cm in sagittal diameter do not completely evacuate the contrast material and are usually symptomatic . The treatment decision in patients with rectocele highly depends on associated imaging findings. It is known that anterior rectocele as a solitary finding is rare . Anismus, internal rectal prolapse and enterocele are often associated with the presence of a rectocele and therefore the treatment should be tailored according to the,imaging findings in order to achieve an optimal outcome
T2 SAGITAL
