What are the imaging modalities for diagnosing kidney (renal) stones (nephrolithiasis)?

From the Guidelines

Non-contrast CT scan is the preferred imaging method for diagnosing kidney stones due to its high sensitivity and specificity, as recommended by the most recent study 1. This is because it can detect stones as small as 1mm, identify their exact location, and determine stone density which helps predict treatment success. For patients with recurrent stones or those who need repeated imaging, low-dose CT protocols should be used to reduce radiation exposure while maintaining diagnostic accuracy, as suggested by 1. Some of the key points to consider when choosing an imaging method include:

• Ultrasound is a reasonable alternative for pregnant women, children, and in follow-up situations, though it's less sensitive and can miss ureteral stones, as noted in 1 and 1.
• In cases where intravenous contrast is needed to evaluate for complications or other conditions, a CT urogram may be performed, as described in 1.
• X-ray (KUB) has limited value as a primary diagnostic tool since it only detects radio-opaque stones and misses uric acid stones completely, as stated in 1 and 1.
• MRI has a limited role in kidney stone imaging but may be used when radiation exposure must be avoided and ultrasound is insufficient, as mentioned in 1. The choice of imaging should consider the patient's clinical presentation, likelihood of stone disease, radiation exposure concerns, and availability of imaging modalities, as emphasized in 1 and 1. It's also important to note that the use of digital tomosynthesis (DT) and MR urography (MRU) may provide additional benefits in certain situations, as discussed in 1. However, the most recent and highest quality study 1 recommends non-contrast CT scan as the imaging study of choice for initial evaluation of patients with acute onset of flank pain and suspicion of stone disease. Overall, the goal is to prioritize the patient's morbidity, mortality, and quality of life when choosing an imaging method for kidney stone diagnosis. Some key considerations include:
• The patient's symptoms and medical history
• The likelihood of stone disease
• The potential risks and benefits of each imaging method
• The availability of imaging modalities and expertise. By considering these factors and following the recommendations of the most recent and highest quality study 1, healthcare providers can make informed decisions about the best imaging method for each patient.

From the Research

Kidney Stone Imaging Techniques

• Noncontrast-enhanced computer tomography (CT) is considered the most accurate imaging technique for identifying urinary stones 2
• Dual-energy CT can specifically assess stone composition 2
• CT with contrast injection is recommended when information about the anatomy of the renal collecting system is required or alternative pathologies are suspected 2

Radiation Exposure and Low-Dose Protocols

• Low-dose protocols can drastically reduce the effective dose administered to the patient, limiting the biological risk due to ionising radiations 2
• Strategies such as dual-split bolus dual energy CT and adaptive statistical image reconstruction can help contain radiation exposure 2
• Abdomen ultrasound may be a valid alternative as an initial approach, especially in children and pregnant women, as it does not change the outcome of patients compared with CT 2, 3

Evaluation of Diuresis Enhanced Non-Contrast Computed Tomography

• A novel protocol, including oral hydration and an oral diuretic, can increase the distention of the renal collecting system, allowing for more reliable preoperative planning for stone removal 4
• The DRINK protocol significantly increased the visible collecting system volume and surface area, and expanded the upper and lower pole infundibular widths and the width of the renal pelvis in the majority of cases 4

National Trends and Diagnostic Accuracy

• The utilization of CT scans for suspected urolithiasis has increased significantly over the years, without a corresponding change in diagnosis rates or hospitalization rates 5
• Initial ultrasonography is associated with lower cumulative radiation exposure than initial CT, without significant differences in high-risk diagnoses with complications or serious adverse events 3

Contrast-Associated Nephropathy

• The true risk attributable to intravenous contrast media for the occurrence of contrast-induced nephropathy (CIN) has become debatable, with new studies challenging the previously held paradigm 6