What imaging modalities are used to diagnose kidney stones (nephrolithiasis)?

From the Guidelines

Non-contrast CT (NCCT) is the imaging study of choice for initial evaluation of patients with acute onset of flank pain and suspicion of stone disease. This recommendation is based on the most recent and highest quality study, which suggests that NCCT can reliably characterize the location and size of an offending ureteral calculus, identify complications, and diagnose alternative etiologies of abdominal pain 1.

Key Considerations

• NCCT is preferred due to its high sensitivity and specificity for detecting stones, allowing for accurate diagnosis and treatment planning.
• Ultrasound may have a role in evaluating for signs of obstruction, although it is less sensitive than NCCT 1.
• Radiography, such as X-ray (KUB), has a limited role due to its lower sensitivity compared to NCCT, but may be useful in specific situations, such as follow-up of radio-opaque stones.
• For patients with known disease and recurrent symptoms of urolithiasis, NCCT remains the test of choice 1.
• Other imaging modalities, such as CT urography (CTU), MR urography (MRU), and digital tomosynthesis (DT), may be considered in specific situations, but are not the primary choice for initial evaluation 2.

Special Considerations

• Low-dose CT examinations can replace traditional noncontrast CT examinations to minimize patient radiation dose 2.
• Dual-energy CT allows for the characterization of stone composition and the generation of virtual unenhanced images simulating noncontrast CT images 2.
• MRU is tailored to improve visualization of the urinary system, but is not the primary choice for initial evaluation 2.
• DT may be useful for detecting intrarenal stones, but its availability and accuracy for ureteral stones are limited 2.

From the Research

Imaging Modalities for Kidney Stones

• Non-contrast CT scans are commonly used to diagnose kidney stones, especially in patients with limited renal function or an allergy to iodinated contrast 3.
• Low-dose CT scans can be effective in detecting kidney stones, with a good detection rate for all types of stones, even small ones 4.
• Non-contrast enhanced multi-slice CT-KUB is a useful imaging modality for diagnosing renal colic, with high sensitivity and specificity for detecting stones 5.

Advantages and Limitations of Imaging Modalities

• CT scans have the advantage of showing alternate causes of pain other than stones, but radiation dose is a major limitation 5.
• Low-dose CT scans can reduce radiation exposure, but may not be effective in detecting small uric acid fragments 4.
• Ultrasound is recommended as the initial imaging modality for suspected renal colic in pregnant women and children, but low-dose CT scans may be safe in pregnancy 6.

Imaging Protocols and Stone Composition

• The minimum radiation dose capable of detecting stone fragments depends on the stone composition, with calcium-based stones having a higher Hounsfield unit (HU) than non-calcium-based stones 4.
• Knowing the stone composition after surgery can help suggest the most appropriate CT scan setting for follow-up 4.
• Current research aims to develop a micro-CT scan and coherent-scatter analysis to determine stone composition in vivo, which may impact the future clinical management of renal calculi 6.