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Utility of simultaneous T1 and T2 mapping with MR Fingerprinting (MRF) for bowel wall imaging in Crohn’s Disease1Radiology, Case Western Reserve University, Cleveland, OH, United States, 2Diagnostic, Interventional and Pediatric Radiology, Inselspital, Bern, Switzerland, 3School of Medicine, Case Western Reserve University, Cleveland, OH, United States, 4Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States, 5Radiology, Mayo Clinic, Rochester, MN, United States, 6Gastroenterology and Digestive Health, University Hospitals Cleveland Medical Center, Cleveland, OH, United States, 7Biostatistics, Case Western Reserve University, Cleveland, OH, United States
Synopsis
The feasibility of using MRF to assess T1 and T2 relaxation times in the intestine for the evaluation of inflammatory bowel disease was explored. 52 patients with Crohn’s Disease underwent MR enterography with MRF acquisitions through the bowel. T1 relaxation times allowed quantitative differentiation between unaffected segments and inflamed segments, p = 0.004. T2 relaxation times further allowed distinction between segments with active and chronic fibrotic changes, p = 0.003.
Introduction
Crohn’s disease (CD) is a common inflammatory disease of the bowel which carries significant and lifelong morbidity (1). While the upper and lower ends of bowel are easily evaluated endoscopically, much of the small bowel presents a greater challenge, with few reliable methods of assessment. To evaluate the extent and location of disease, especially in small bowel, recent guidelines recommend comprehensive cross-sectional imaging with MR enterography (MRE) (2). There are several qualitative findings in identifying affected bowel loops. However, all these are difficult to compare quantitatively, especially in the assessment of treatment response were quantitative parameters are desirable. MR Fingerprinting (MRF) (3) enables quantitative mapping of T1 and T2 of a tissue from a single acquisition, making a fully quantitative MR exam clinically feasible. A hallmark of inflammation is bowel wall edema, which manifests as increased signal intensity (SI) on T2w imaging in the bowel wall (4). Edema would be expected to have decreased SI on T1w imaging due to increase fluid content, though hypointensity on T1-weighted imaging is not typically evaluated in bowel imaging. Thus it may be postulated that T1 and T2 mapping could provide quantitative assessment of bowel inflammation in Crohn’s Disease. The purpose of this study was to evaluate the feasibility of MRF-based relaxometry in the bowel for evaluation of inflammatory bowel disease.Methods
Normative testing of coronal and axial MRF-FISP acquisitions was performed on the ISMRM-NIST System Phantom and normal subjects (5) (data not shown for brevity). In this IRB approved, HIPAA compliant study, 52 patients (27:25 M:F median age 27 years with range 11-77 years) undergoing complete MR enterography exams including pre contrast T2w, TRUEFISP and T1w images as well as dynamic enhanced post contrast T1w images at 1.5T (Aera, Siemens Healthineers, Erlangen, Germany) were included. Three axial and three coronal 2D-MRF-FISP slices were acquired through the bowel, each with a 24s breath-hold. Sequence settings: FOV 400 mm, in-plane spatial resolution 1.6x1.6 mm2, slice thickness 5mm, TRs: 11.2 to 15.5 ms, variable flip angles: 5 to 55° (modified from (6)). The raw data were reconstructed online using the GADGETRON pipeline to generate T1 and T2 maps (7). Regions of interest (ROIs) were drawn in the wall of small bowel and colon to assess T1 and T2 relaxation times of unaffected, active (wall edema with high T2w SI, stratified or layered enhancement, presence of adjacent mesenteric edema) and/or chronic inflamed segments (fibrotic wall thickening with low T2 signal intensity ± fatty infiltration, diffuse or low-level inhomogeneous enhancement, fat wrapping), for each patient. Information from weighted clinical images and endoscopy were used to identify affected segments. Additional ROI were drawn in the solid organs of the abdomen with known relaxation parameters for sequence validation. Mann-Whitney-U and Kruskal-Wallis-Test with Dunn-Bonferroni post-hoc-tests were used to assess differences in T1 and T2 values between unaffected, acutely, and chronically inflamed bowel.Results
Comparison with relaxometry in known values of other abdominal organs revealed liver T1 683±84 ms, literature 568-678 ms T2 36±32 ms, literature 32-107 ms; pancreas T1 651±110 ms, literature 584 ms, T2 49±59 ms, literature 46 ms; kidney cortex T1 106±133 ms, literature 827-1083 ms; T2 95±116 ms, literature 87-112 ms. There were 17 segments with chronic disease and 20 with acute inflammation. T1 relaxation times were significantly longer in unaffected segments (1428±327 ms, n=76) versus inflamed segments (active 1309±322 ms and chronic 12138±301 ms), p = 0.004. T2 relaxation times were longer in segments with active inflammation (67±20 ms) versus chronic fibrotic segments (44±19 ms), p = 0.003 (Figure 1). Figure 2 shows differences in a patient with chronic inflammation in the terminal ileum compared to unaffected segments.Discussion
This study demonstrates feasibility of T1 and T2 mapping in the bowel using MR Fingerprinting and potential utility in quantifying disease activity. The results from T2 mapping confirm qualitative findings from T2w images with the presence of edema in active inflammation and fibrotic changes in chronic disease stages. The observed significant differences in T1 relaxation times is a new finding that has not been described previously. Currently one key sequence in disease activity assessment with MRE is the contrast enhanced T1w sequence (8). Given ongoing discussions about potential tissue deposition of gadolinium based contrast agents, an approach without the use of IV contrast would be desirable. Given experience in other organs (9, 10), combination of multiple quantitative approaches, for example MRF with perfusion or diffusion, could be a route to explore in the future to objectively assess disease severity and treatment response.Conclusion
Initial application of MRF in bowel imaging is presented, with promising results for quantitative differentiation of unaffected, actively inflamed and chronically diseased bowel.Acknowledgements
This work was supported by a Swiss National Science Fund mobility stipend and Siemens Healthineers.References
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