Diffusion Weighted Imaging in IBD: An Update Ethan A. Smith, MD Section of Pediatric Radiology C.S. Mott Children s Hospital University of Michigan ethans@med.umich.edu
Disclosures Royalties from Elsevier (book chapters) No relevant financial disclosures
Overview Background Does DWI help in IBD imaging? Why does it work? How might we use it in the future? Beyond the bowel Use in clinical practice
Diffusion Weighted Imaging Imaging the motion of water molecules Random motion versus impeded motion First applications in neuro-imaging Stroke imaging, CNS infections, tumors Now widely used in body MRI Especially oncology
Diffusion Weighted Imaging DWI in oncologic imaging Most tumors are highly cellular MORE CELLS MORE CELL MEMBRANES IMPEDED DIFFUSION HIGH SIGNAL ON DWI
Background What else can DWI be used for? Started to be used in body protocols, including MRE Noticed that bowel segments with other evidence of inflammation also impede diffusion
Oto, et al 2009 Research 11 adult patients MRE and surgery within 4 weeks Found ADC in inflamed segments DWI detected 94.7% of inflamed segment ROC = 0.938 Oto A, et al. Acad Radiol 2009
Research Ream, et al 2013 46 MRE exams Mean age 14.3 Terminal ileal pathology vs. DWI 41 biopsy proven TI disease ACD correlated with: Bowel wall thickening Arterial enhancement Mesenteric inflammation Stricture Ream JM, et al. Pediatr Radiol 2013
Tielback, et al 2014 Research 27 adult patients MRE vs. resected specimens ADC correlation was not significant but very strong trend toward correlation Underpowered? Tielback JA, et al. Eur Radiol 2014
Why? How does bowel inflammation lead to impeded diffusion? No one really knows Cellular theory Fibrosis theory Perfusion theory Oto A, et al. Acad Radiol 2009 Morani A, et al. AJR 2015
Cellular theory Why? Inflammation = increased cellularity Impeded diffusion reported in other inflammation e.g., encephalitis, pyelonephritis, etc inflammatory cells cellularity impedes diffusion of water Oto A, et al. Acad Radiol 2009 Morani A, et al. AJR 2015
Fibrosis theory Why? Fibrosis has been shown to impede diffusion in cirrhotic livers Inflammation and fibrosis co-exist Adler, et al
Perfusion theory Why? DWI information comes from 2 sources Intravascular (perfusion) Extravascular Intravoxel Incoherent Motion (IVIM) Le Bihan D, et al. Radiology 1986
DWI - Perfusion Intravoxel incoherent motion (IVIM) DWI with multiple b-values Takes into account micro-capillary perfusion and diffusion within a voxel May allow a more accurate and reproducible assessment of ADC values
ADC DWI - Perfusion Perfusion b-value
Perfusion theory Why? Inflammation increased blood flow blood flow = micro-capillary perfusion perfusion may contribute significant DWI signal
Why? High signal on DWI images ( ADC) probably comes from all 3 sources cellularity Perfusion Fibrosis Could this be useful?
Future Possibilities Figure out sources for DWI signal Separate signal from fibrosis vs. inflammation? Could allow better treatment planning Can we evaluate healing Mucosal healing = biomarker for treatment response and prognosis Could DWI signal changes be a quantitative imaging marker?
Future Possibilities Non-contrast MRE? Do we need gadolinium based contrast? Deposition Rare allergic like reactions Renal dysfunction/nsf Is DWI specific enough to be relied on? Sensitivity doesn t seem to be an issue Is spatial resolution adequate? Can artifacts be overcome?
Non-contrast MRE? Can DWI replace contrast enhanced imaging? Neubauer et al, 2013 33 Crohn disease patients vs. 27 controls DWI correctly identified 32 patients All small bowel lesions detected by both methods Slightly more false positives with DWI CE MR better spatial resolution Neubauer H, et al. Pediatr Radiol 2013
Non-contrast MRE? Seo et al, 2016 50 adult Crohn disease patients All had MRE and endoscopy within 7 days Compared CE MR to DWI Agreement in 91.8% of segments Correlation coefficient 0.937 (p<0.001) Conclusion: DWI was non-inferior to CE MR in well distended small bowel segments Seo N, et al. Radiology 2016
Additional Uses for DWI Penetrating complications Fistula, abscess Schmid-Tannwald, et al 2012 Addition of DWI increased detection of intra-loop fistulas and sinus tracts in adults with IBD Lymph nodes Reactive Infection Malignancy risk of lymphoma due to therapy Schmid-Tannwald C, et al. J Magn Reson Imaging 2012
So, where do we stand?
Practical Uses How do I use DWI in practice? Qualitative assessment Screening Think CAD Increase reader confidence Extra-intestinal manifestations Abscesses and penetrating disease Perianal disease Lymph nodes
Take Home Points Diffusion weighted imaging is useful in pediatric IBD Should be included in MRE protocols Current clinical uses are qualitative Detect involved segments, reader confidence Extra-intestinal manifestations
Take Home Points Potential future directions Defining sources of signal Fibrosis vs. inflammation Qualitative imaging biomarker for mucosal healing? Avoiding gadolinium contrast?
Thank You
Selected References: 1. Oto A, Zhu F, Kulkami K, et al. Evaluation of diffusion-weighted MR imaging for detection of bowel inflammation in patients with Crohn s disease. Acad Radiol 2009; 16: 597-603 2. Ream JM, Dillman JR, Adler J, et al. MRI diffusion-weighted imaging (DWI) in pediatric small bowel Crohn disease: correlation with MRI findings of active bowel wall inflammation. Pediatr Radiol 2013; 43: 1077-1085 3. Tielback JAW, Ziech MLW Li Z, et al. Evaluation of conventional, dynamic contrast enhanced and diffusion weighted MRI for quantitative Crohn s disease assessment with histopathology of surgical specimens. Eur Radiol 2014; 24: 619-629 4. Schmid-Tannwald C, Agrawal G, Dahi F, et al. Diffusion-weighted MRI: Role in detecting abdominopelvic internal fistulas and sinus tracts. J Magn Reson Imaging 2012; 35: 125-131 5. Le Bihan D, Breton E, Lallemand D, et al. MR imaging of intravoxel incoherent motions: Applications to diffusion and perfusion in neurologic disorders. Radiology 1986; 161: 401-407 6. Neubauer H, Pabst T, Dick A, et al. Small-bowel MRI in children and young adults with Crohn disease: retrospectve head-to-head comparison of contrast-enhanced and diffusion weighted MRI. Pediatr Radiol 2013; 43: 103-114 7. Seo N, Park SH, Kim KJ, et al. MR Enterography for the evaluation of small bowel inflammation in Crohn disease by using diffusion-weighted imaging without intravenous contrast material: A prospective non-inferiority study. Radiology 2016; 278: 762-772