Imaging Guidelines for Kidney Stone Evaluation

Introduction to Imaging Modalities

The American College of Radiology recommends non-contrast CT scans of the abdomen and pelvis as the gold standard for kidney stone evaluation, with 97% sensitivity and 95% specificity 1, 2, 3

Non-contrast CT achieves 94-98% sensitivity for detecting renal stones, compared to only 19% sensitivity for ultrasonography, making it the preferred imaging modality for kidney stone detection 4, 5, 6
The American Urological Association recommends non-contrast CT for its ability to detect virtually all stone compositions, accurately measure stone size and location, and identify secondary signs of obstruction 1, 2, 3

Detects virtually all stone compositions regardless of radiopacity 1
Accurately measures stone size and location, which is critical for determining whether intervention is needed 1, 3
Identifies secondary signs of obstruction including hydronephrosis, periureteral inflammation, and perinephric fluid 1, 2
Provides multiplanar reformations for precise anatomic localization 1

The American College of Radiology recommends a low-dose protocol (<3 mSv) to reduce radiation while maintaining 97% sensitivity and 95% specificity 1, 2, 3
Non-contrast technique is preferred, as contrast obscures stones within the collecting system and should NOT be used as first-line imaging 1, 2, 3
Thin slice acquisition (1-1.5mm) is recommended for optimal stone detection 1
Helical (spiral) technique is preferred for precise measurements and multiplanar reformations 1

For pregnant patients, the American College of Obstetricians and Gynecologists recommends starting with renal ultrasound, and if inconclusive, considering MRI without contrast rather than CT 2, 3
For recurrent stone formers, the American Urological Association recommends using ultra-low-dose CT protocols or limiting scanning to the area of interest to reduce cumulative radiation exposure 1, 2, 3

The American College of Radiology advises against ordering contrast-enhanced CT as the initial test, as it can obscure small stones within the collecting system and potentially lead to missed diagnoses 1, 2, 3
The American Urological Association recommends against relying solely on ultrasound for acute stone evaluation, unless the patient is pregnant or a child, due to its low sensitivity (19-57%) 4, 5, 6, 2