MRI Protocol for Peritoneal Tumors

Our MR imaging exam for patients with peritoneal disease includes breath-hold, fat-suppressed T2-weighted imaging and fat-suppressed, gadolinium-enhanced SGE imaging of the abdomen and pelvis in the axial and coronal planes.

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T2-weighted MR images. For the fat-suppressed T2-weighted imaging, the examiner may use a single-shot rapid acquisition relaxation-enhanced (RARE) technique, such as single-shot fast spin-echo (SSFSE) or half-Fourier acquired single-shot turbo spin-echo (HASTE), to rapidly acquire T2-weighted images. Since each image is acquired independently, there is minimal or no motion artifact. Both SSFSE and HASTE acquisitions use half-Fourier techniques, which reduce signal-to-noise ratio. The addition of fat suppression brings a further reduction in signal, making these images less useful for body coil imaging. For body coil imaging of the abdomen and pelvis, we prefer a fat-suppressed, breath-hold fast spin-echo acquisition. The time of breath-holding is 25 seconds for each of the 12 slices. These images have better SNR than the fat-suppressed SSFSE images but exhibit more artifact from bowel peristalsis.

Gadolinium-enhanced SGE MR images. The key images for evaluating peritoneal disease are the fat-suppressed, gadolinium-enhanced SGE MR images (Figure 1). Due to the slow accumulation of gadolinium within the eritoneal tumor, a delayed set of images obtained five minutes after injection of gadolinium is most sensitive in 

depicting peritoneal disease.We obtain two sets of axial SGE MR images at zero and approximately five minutes after injection of 0.2 mmol/kg gadolinium. A set of coronal SGE MR images is also obtained. Fat suppression is a critical element in this protocol as it accentuates subtle peritoneal enhancement by suppressing the competing high signal of subcutaneous, retroperitoneal, and mesenteric fat. Since the SGE MR images are sensitive to bowel peristalsis, we administer 1 mg IV glucagon at the time of the gadolinium injection. In our experience, this improves depiction of peritoneal tumor involving bowel serosa and mesentery.

The specific parameters for SGE MR images will vary with the vendor. On our LX GE 1.5-tesla MR imager, we use the parameters described in Figure 2 for the gadolinium-enhanced SGE MR images. Selecting minimum TE will improve fat suppression when combined with chemical fat suppression, as well as shortening the time of breath-hold. The receiver bandwidth should be kept as low as possible to maintain image quality.

Bowel preparation. Depiction of peritoneal disease in the middle abdomen requires distention and separation of bowel loops (Figure 3). This can be easily accomplished by having the patient drink two to three bottles of ReadiCat 2, starting 30 minutes prior to the MR examination.⁶ From experience we have found that drinking the barium more rapidly and then scanning immediately provides better distention of small bowel. The dilute barium serves as a positive oral contrast agent on the T2-weighted images and as a negative oral contrast agent on the T1-weighted SGE images.
We have begun to use rectal water for distention of the colon. We administer 500 to 1000 cc of rectal water via an enema tip just prior to the gadolinium injection. Distending the rectosigmoid colon is particularly important in patients with ovarian cancer who may have primary or recurrent pelvic tumor involving the rectum, sigmoid colon, or bladder.

Gadolinium injection. We inject a double dose of gadolinium 0.2 mmol/kg via either hand or power injection. Since the delayed gadolinium-enhanced images are most important, the rate and timing of injection are not critical. At the time of gadolinium injection, 1 mg IV glucagon is also administered to reduce bowel peristalsis.