W170 AJR:200, February 2013 MRI), images are acquired during the delivery of the contrast agent to the tissue of interest, re- flecting the dynamic response of the tissue to the inflow of blood. The signal intensity of tis- sue on a T1-weighted MR image increases as a result of the leakage of contrast material from the capillaries into the extracellular extravascu- lar space. By use of dynamic acquisition, time- intensity curves (TICs) are acquired. These curves represent the signal intensity at each moment before and during contrast injection. DCE-MRI parameters such as TIC shape and the volume transfer constant (K trans ) have often been considered a mirror of the physiologic pa- rameters of the tissue (e.g., capillary permea- bility, tissue vascularization) that change in in- flammatory conditions [4]. In a previous study [5], semiquantitative DCE-MRI was used for evaluation of perianal fistulas, and significant correlations were found between the absolute number of certain TIC shapes and perianal dis- ease activity index (PDAI). However, quantita- tive information on fistula perfusion (i.e., K trans ) Dynamic Contrast-Enhanced MRI in Determining Disease Activity in Perianal Fistulizing Crohn Disease: A Pilot Study Manon L. W. Ziech 1 Cristina Lavini 1 Shandra Bipat 1 Cyriel Y. Ponsioen 2 Anje M. Spijkerboer 1 Pieter C. F. Stokkers 3 Aart J. Nederveen 1 Jaap Stoker 1 Ziech MLW, Lavini C, Bipat S, et al. 1 Department of Radiology, Academic Medical Center, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands. Address correspondence to M. L. W. Ziech (m.l.ziech@amc.uva.nl). 2 Department of Gastroenterology, Academic Medical Center, Amsterdam, The Netherlands. 3 Department of Gastroenterology, Sint Lucas Andreas Ziekenhuis, Amsterdam, The Netherlands. Gastrointestinal฀Imaging฀•฀Original฀Research WEB This is a Web exclusive article. AJR 2013; 200:W170–W177 0361–803X/13/2002–W170 © American Roentgen Ray Society P erianal fistulas are a common find- ing in patients with Crohn disease [1]. To determine treatment strate- gy and response, the course of the perianal fistula and its inflammatory activity have to be evaluated, and MRI is the recom- mended initial examination [2]. For assessing active inflammation, a T1-weighted contrast- enhanced sequence can be performed. This is especially important in patients with fistulizing Crohn disease because they are usually medi- cally, not surgically, treated and therapeutic re- sponse is the clinical question for these patients. Enhancement indicates active inflammation be- cause it reflects increased tissue perfusion and vascular permeability [3]. Enhancement is usu- ally assessed only on conventional contrast- enhanced images at one time point, and the grading is subjective. Subjective grading has intrinsic limitations, and conventional contrast- enhanced imaging at one time point does not give information about microvascularization. In dynamic contrast-enhanced MRI (DCE- Keywords: anti–tumor necrosis factor α, Crohn disease, dynamic contrast-enhanced MRI, perianal fstula, pharmacokinetic modeling DOI:10.2214/AJR.11.8276 Received November 18, 2011; accepted after revision June 13, 2012. OBJECTIVE. The objective of our study was to perform a semiquantitative analysis of dynamic contrast-enhanced MRI for the evaluation of disease activity and therapeutic re- sponse in patients with perianal fistulizing Crohn disease. SUBJECTS฀ AND฀ METHODS. Sixteen consecutively registered patients with peri- anal Crohn disease underwent pelvic MRI. A dynamic contrast-enhanced sequence was per- formed at 3 T (temporal resolution, 4.2 seconds) during IV contrast injection. Maximum en- hancement, initial slope of increase, volume transfer constant (K trans ), and the extravascular space fractional volume (υ e ) were calculated in a region of interest drawn around the fistula. Perianal disease activity index, C-reactive protein concentration, and an MRI-based activity score were calculated as reference standards. Six patients underwent a second MRI examina- tion 6 weeks after starting treatment with anti–tumor necrosis factor α (anti–TNF-α). RESULTS. Perianal disease activity index moderately correlated with maximum en- hancement (r = 0.67, p = 0.005), initial slope of increase (r = 0.58, p = 0.018), and volume of enhancing pixels (r = 0.79, p < 0.001) but not with K trans or υ e . Volume of enhancing pixels also correlated with C-reactive protein concentration and the MRI-based score (r = 0.52, p = 0.041; r = 0.79, p < 0.001). The K trans values had decreased significantly 6 weeks after the start of anti–TNF-α therapy. CONCLUSION. Maximum enhancement and initial slope of increase correlate with disease activity in perianal Crohn disease. K trans may be an indicator of the effect of therapy on patients starting anti–TNF-a treatment. Ziech et al. MRI of Crohn Disease Gastrointestinal Imaging Original Research Downloaded from www.ajronline.org by 52.73.204.196 on 05/16/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved