Practice guidelines suggest most patients should wait at least 28 days from the onset of low back pain before receiving imaging. This study evaluates a nondenial prior authorization program's performance in modifying lower back imaging orders. Ordering physicians were asked by a consulting physician to modify any order that did not meet guidelines through collaborative consultation. If original orders were not reinitiated, it could signify that modified orders met clinical objectives. Prior authorization and claims data from 2014 to 2017 were analyzed to determine the rate of reinitiation within 28 days for modified computed tomography and magnetic resonance imaging orders. Chi-square tests were used to evaluate whether modification or reinitiation was associated with several factors. Across the four sequences of interaction between ordering physicians and the program examined, 533,768 orders were placed, leading to 6855 completed consultations (1.3% of orders), 1380 modifications (20.1% of consultations), and 224 reinitiations (16.2% of modifications). Modification led to reinitiation 7.1%-20.6% of the time, depending upon the sequence. Orders from primary care physicians were significantly more likely to be modified. Reinitiation was significantly more likely for urban orders. Low back imaging orders modified by the program were infrequently reinitiated within 28 days. Some reinitiation may have been consistent with evidence-based practice, as orders may have been placed after the onset of pain. Copyright © 2018 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.