AUA QI Summit 2017: Multispecialty Collaboration on Best Imaging Practices in Renal Colic: Radiologist’s Perspective

Linthicum, Maryland (UroToday.com) Dr. Erick Remer from the Cleveland Clinic discussed best practice imaging practices from the radiologist’s perspective. An abdominal CT scan is universally acknowledged as the most accurate imaging exam for stone detection, localization and size determination, however for any one patient there are multiple competing considerations in determining appropriate imaging techniques. Certainly, not all flank pain CT studies are positive with study estimates ranging from 6-40% for having a negative imaging study. As was mentioned in Dr. Moore’s talk, utilization of the STONE score more accurately predicts ureteral stone presence and decreases the likelihood of an alternative diagnosis [1].

The concept of low-dose radiation exposure for CT imaging is important, but no quantitative definition exists. There is variability over time with hardware and software changes, geographical variability based on different regulatory bodies and patient body habitus, and conceptual imprecision. Furthermore, the AUA definition of low-dose CT scan is 4 mSv, while the American College of Radiology (ACR) definition is 3 mSV.

According to Dr. Remer, there are several ways to reduce radiation exposure:

  • Reduce coverage – only image the top of the kidneys to the bladder base
  • Increase slice thickness from 1-3 mm to 5 mm and add coronal reformatted imaging (reduces dose 30-50%)
  • Decrease tube current (mAs) – use automated modulation, particularly in obese patients. Small retrospectives studies have shown no significant differences with 50% or 75% mAs reduction for detection of >3mm stones.
  • Lower tube voltage (kVp) – dose reduction of 35-75%, although with increased degradation (“noise”)
Several studies have suggested that adherence to low-dose protocols is poor at <10%, so why don’t more sites modify their CT protocols? First, it takes effort, according to Dr. Remer, including many enterprises having multiple scanner models from different vendors. Second, renal colic CTs are used inexactly by some practitioners and the emergency physicians are in need of patient disposition. Third, radiologists aren’t used to reading reduced dose images, and Dr. Remer notes that there is a learning curve with reading these images.

Dr. Remer concluded with several goals moving forward for renal colic imaging: (i) minimizing unnecessary imaging, (ii) shared-decision making, and (iii) facilitate prompt evaluation. Continued refinement of algorithms for acute colic/known stone formers is necessary and important.

Speaker(s): Erick Remer, Cleveland Clinic Foundation, Cleveland, OH, USA

Written by: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre, Twitter: @zklaassen_md, at the AUA Quality Improvement Summit - October 21, 2017- Linthicum, Maryland

References:
1. Moore CL, et al. Derivation and validation of a clinical prediction rule for uncomplicated ureteral stone – the STONE score: retrospective and prospective observational cohort studies. BMJ 2014;348:g2191.`
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