What is the imaging study of choice for diagnosing kidney stones?

The imaging study of choice for diagnosing kidney stones is non-contrast helical CT. This modality is highly sensitive and specific for detecting urinary calculi, providing detailed cross-sectional images of the kidneys, ureters, and bladder. Non-contrast CT is especially advantageous because it can identify stones of various compositions and sizes without the interference of intravenous contrast, which can complicate the evaluation in some patients, particularly those with kidney impairment.

Additionally, non-contrast helical CT can rapidly assess other causes of abdominal or flank pain, which is valuable in acute settings. Its speed and accuracy make it the preferred imaging technique when there is a suspicion of nephrolithiasis, particularly in emergency departments.

Other imaging modalities, such as X-rays, are limited in sensitivity for detecting small stones or those not radiopaque. Ultrasound can be beneficial, especially in pediatric patients or pregnant women, but it may miss smaller stones or those that are not causing obstruction. CT angiography is focused on vascular structures and does not provide the necessary detail for evaluating kidney stones specifically, thus is not appropriate for this indication.