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Diffusion-Weighted MRI of Peritoneal Tumors: Comparison With Conventional MRI and Surgical and Histopathologic Findings—A Feasibility Study

¹ Sharp and Children's MRI Center, 7901 Frost St., San Diego, CA 92123.
² San Diego Imaging, Inc., San Diego, CA.
³ Department of Surgical Oncology, Sharp Memorial Hospital, San Diego, CA.
⁴ Department of Pathology, Sharp Memorial Hospital, San Diego, CA.

OBJECTIVE. The purpose of our study was to evaluate the utility of single-shot spinecho echo-planar diffusion-weighted imaging (DWI) using a b value of 400–500 s/mm² for depicting peritoneal tumors.

MATERIALS AND METHODS. Thirty-four consecutive oncology patients underwent preoperative abdominal and pelvic MRI for tumor staging. MRI included breath-hold DWI with a b value of 400–500 s/mm², T1-weighted spoiled gradient-echo, T2-weighted fast spin-echo, and 0- and 5-minute delayed gadolinium-enhanced imaging. At three separate sessions, two observers independently reviewed images for peritoneal tumors at 16 anatomic sites. First DWI alone was reviewed, followed by conventional MRI alone, and then conventional MRI, including DWI, was reviewed. Results of laparotomy and histopathologic evaluation were compared with MRI results. Sensitivity, specificity, and accuracy were calculated for DWI, conventional MRI, and combined DWI and conventional MRI for peritoneal tumor depiction.

RESULTS. Two-hundred fifty-five sites of peritoneal tumor were proven by surgical and histopathologic findings. The combination of DWI and conventional MRI was most sensitive and accurate for peritoneal tumors, depicting 230 and 214 tumor sites for the two observers (sensitivity, 0.90, 0.84; and accuracy, 0.91, 0.88) compared with DWI alone, which depicted 182 and 182 tumor sites with sensitivity (0.71, 0.71; and accuracy, 0.81, 0.81), and conventional MRI alone, which depicted 185 and 132 tumor sites (sensitivity, 0.73, 0.52; and accuracy, 0.81, 0.72). Peritoneal tumor showed restricted diffusion on DWI and ascites was of low signal intensity, increasing tumor conspicuity.

CONCLUSION. Adding DWI to routine MRI improves the sensitivity and specificity for depicting peritoneal metastases. Breath-hold DWI is now routinely used in all oncology patients referred for abdominal MRI at our institution.

Keywords: colorectal • diffusion • MRI • ovary • pseudomyxoma peritonei

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