PET/MR enterography is technically feasible as an imaging technique to assess bowel lesions in malignant and inflammatory disease. The radiation exposure to a patient having this procedure is reduced by at least half and up to four times less than a comparable PET/CT exam.
A proof-of-concept study published in the February 2016 issue of the European Journal of Radiology describes the protocol developed and used to image 19 patients with bowel malignancies, Crohn’s disease, or an unknown focus of inflammation at the University Hospital Essen in Essen, Germany. The image quality of all 19 PET/MR enterography exams enabled excellent visualization of both intestinal and extra-intestinal pathologies, according to lead author Karsten Beiderwellen, M.D., professor of radiology of the Department of Diagnostic and Interventional Radiology and neuroradiology, and colleagues.
While endoscopy is the usual method to evaluate pathologies of the large bowel and terminal ileum, portions of the small bowel – specifically the proximal ileum and the distal – are inaccessible. MRI has the ability to evaluate the small bowel, providing excellent soft tissue contrast. 18-FDG PET can detect and quantify increased glucose metabolism inherent to both malignant and inflammatory processes. Additionally, when used with other radiotracers, PET can detect neuroendocrine tumors of the gastrointestinal tract. But because the fusion of MRI and PET datasets are prone to misregistration, they are impractical to use together. The commercial availability of integrated PET/MR scanners changes this.
For this reason, the authors developed and tested a four-sequence protocol for PET/MR enterography that used a low-attenuation oral contrast medium that would not interfere with the PET attenuation correction. After image post-processing and fusion, all datasets were reviewed by two experienced radiologists with respect to co-registration of anatomical structures based on a 3-point scale, to image quality on a 1(poor) -to-4(excellent) -point scale. Additionally, the radiologists also scored overall bowel distension, visualization of the intestinal pathologies, and depiction of peri-intestinal lymph nodes.
Scores ranged from acceptable to good, but all acquired and fused images were of diagnostic quality. The authors reported that a significantly higher image quality was obtained for the fast, free-breathing sequences of MRI, and that TrueFISP and T2w HASTE sequences varied according to patient compliance. Overall bowel distension was acceptable, but bowel collapse in two of the patients indicated a necessity to improve the oral contrast intake procedure or use of a different oral contrast solution. Both inflammatory and malignant lesions were detected in the patient cohort, and the authors suggest that stenotic lesions may be able to be characterized with higher accuracy by multimodal imaging.
The authors’ protocol supports the technical feasibility of PET/MR enterography to produce high quality images that can be accurately co-registered. They believe that the combination of morophological and metabolical information will enable both inflammatory and malignant disease of the bowel to be visualized. Additionally, the use of PET/MR exposes a patient to a fraction of the radiation dose (5-7 mSv) compared to PET/CT (up to 25 mSv).They recommend that future trials of PET enterography should be prospectively evaluated for different intestinal pathologies and to monitor the results of different types of therapy for patients with small and large bowel disease.
PET/MR enterography is feasible for evaluation of bowel lesions. Appl Radiol.