ORIGINAL RESEARCH Changes in Apparent Diffusion Coefficient (ADC) during Cardiac Cycle of the Brain in Idiopathic Normal Pressure Hydrocephalus Before and After Cerebrospinal Fluid Drainage Tomoshi Osawa, MD, 1† Naoki Ohno, PhD, 2† Mitsuhito Mase, MD, PhD, 1 * Tosiaki Miyati, PhD, DMSc, 2 Ryoko Omasa, MS, 3 Shota Ishida, PhD, 4 Hirohito Kan, PhD, 5 Nobuyuki Arai, MS, 6 Harumasa Kasai, PhD, 7 Yuta Shibamoto, MD, PhD, 7 Satoshi Kobayashi, MD, PhD, 2,8 and Toshifumi Gabata, MD, PhD 8 Background: The causative mechanisms of idiopathic normal-pressure hydrocephalus (iNPH) symptoms are currently unknown. Purpose: To assess the dynamic changes in the apparent diffusion coefficient (ADC) during the cardiac cycle (ΔADC) of the brain before and after the lumbar tap and shunt surgery for the purpose of determining changes in hydrodynamic and biomechanical properties in the brain after cerebrospinal fluid (CSF) drainage for iNPH. Study Type: Retrospective. Subjects: Overall, 22 patients suspected to have iNPH were examined before and after the lumbar tap and were divided into patients who showed symptomatic improvements (positive group, n= 17) and those without improvement (negative group, n= 5) after the lumbar tap. Seven patients in the positive group were examined after the shunt surgery. Field Strength/Sequence: 1.5T, electrocardiographically synchronized single-shot diffusion echo-planar imaging. Assessment: The frontal white matter ΔADC and mean ADC (ADC mean ) were compared between before and 24 hours after lumbar tap and from 1 week to 1 month after the shunt surgery. Statistical Tests: Wilcoxon signed-rank test was used. P < 0.05 was considered statistically significant. Results: The ΔADC after the lumbar tap in the positive group was significantly lower than that before (P < 0.05), whereas no significant difference was found in the negative group (P = 0.23). After the lumbar tap, ΔADC decreased in 16 of 17 patients in the positive group, whereas ADC mean did not significantly change (P = 0.96). After the shunt surgery, ΔADC decreased in all seven patients (P < 0.05), whereas ADC mean did not significantly change (P = 0.87). Data Conclusion: The frontal white matter ΔADC in iNPH decreased after the lumbar tap and shunt surgery. ΔADC analysis may provide detailed information regarding changes in the hydrodynamic and biomechanical properties through CSF drainage. Level of Evidence: 4. Technical Efficacy Stage: 4. J. MAGN. RESON. IMAGING 2020. View this article online at wileyonlinelibrary.com. DOI: 10.1002/jmri.27412 Received Jul 8, 2020, Accepted for publication Oct 9, 2020. *Address reprint requests to: M.M., Department of Neurosurgery, Nagoya City University Graduate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya, Aichi 4678601, Japan. E-mail: mitmase@med.nagoya-cu.ac.jp † The authors equally contributed to this work Contract grant sponsor: JSPS KAKENHI; Contract grant number 18KK0450. From the 1 Department of Neurosurgery, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan; 2 Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Japan; 3 Department of Medical Technology, Ishikawa Prefectural Central Hospital, Kanazawa, Japan; 4 Radiological Center, University of Fukui Hospital, Fukui, Japan; 5 Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, Nagoya, Japan; 6 Department of Radiological Technology, Suzuka University of Medical Science, Suzuka, Japan; 7 Department of Radiology, Nagoya City University Hospital, Nagoya, Japan; and 8 Department of Radiology, Kanazawa University Hospital, Kanazawa, Japan © 2020 International Society for Magnetic Resonance in Medicine 1