CT, MRI, X-ray
and sonography: Diagnostic procedures for kidney and
ureteral stones
Kidney and ureteral stones are common medical problems that can cause severe pain and other serious complications. A quick and accurate diagnosis is therefore crucial in order to initiate appropriate treatment and minimize potential risks. Imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI), X-ray and sonography play a central role in the diagnosis of these diseases, as they help to define the size, location and composition of the stones and determine the appropriate therapy.
Further information on the individual examination methods
Computed tomography (CT): CT is considered the gold standard for urinary and kidney stone diagnostics. It is a special X-ray procedure for producing cross-sectional images of the body. Ionizing radiation is used to create the images. If kidney or ureteral stones are suspected, a native low-dose CT scan of the abdomen is often performed. The CT urogram enables stones to be imaged precisely and their density to be measured as well as providing better visualization of the anatomy through 3D reconstruction of the urinary tract. This method is particularly effective as it can visualize urinary stones very accurately. The sensitivity of CT ranges from 94 to 100 %, depending on the size and composition of the stone.
Magnetic resonance imaging (MRI): MRI is used less frequently for the diagnosis of stones, as it requires longer examination times. Using magnetic fields and radio waves, detailed cross-sectional images can be generated. MRI is useful if further imaging of the urinary tract is necessary after negative CT results. MRI can provide indirect evidence of stones and is particularly helpful in identifying other possible causes of narrowing or stenosis. One advantage of MR urography is the visualization of kidney function. Following the administration of contrast media, renal function and outflow conditions can be assessed.
X-ray: Formerly the standard procedure for diagnosing stones, today X-rays are mainly used to monitor stone fragmentation after lithotripsy or to plan treatment for known, calcified urinary calculi. It can show concretions as shadowing structures (calcareous) or non-shadowing, but with lower sensitivity and specificity compared to CT.
Sonography: As a radiation-free method, sonography (ultrasound examination) is often used as the primary diagnostic tool for suspected urinary stones. By emitting sound waves that are reflected by the body structures, images of organic structures can be generated. Sonography is good at detecting enlargement of the renal pelvicalyceal system and the presence of stones, above a stone size of 2 mm. It does not allow reliable exclusion of stones, as stones made of organic material, for example, cannot be visualised.
How exactly does the examination work?
CT: The patient lies on an examination couch, which moves slowly through a ring-shaped scanner. The examination only takes a few minutes. The images generated provide detailed visualization of anatomical structures. No special preparation of the patient is required for the examination. However, a well-filled bladder can make it easier to distinguish between small ureteral stones and certain calcifications.
MRI: This examination requires the patient to lie still for an extended period of time while the scanner produces detailed images. Contrast agents can be used to emphasize certain structures.
X-ray: A quick and simple examination in which the patient is placed in different positions to obtain the best images. About 90 % of kidney stones are cast an acoustic shadow (calcium oxalate and calcium oxalate/calcium phosphate), while the remaining 10 % consist of non-shadowing stones (uric acid and cystine stones as well as struvite or matrix stones).
Sonography: The examiner uses a hand-held device. The waves emitted by the ultrasound device are reflected to varying degrees at the junctions between different organs and tissues. Based on these reflected waves, the device then generates an image that allows conclusions to be drawn about the presence of urinary stones. This method is painless and radiation-free.
Summary
Selection of the appropriate imaging procedure depends on various factors, including the suspected stone composition, the size of the stones, the symptoms and the patient’s overall health situation. While CT offers the highest accuracy, sonography is a safe and radiation-free alternative, especially for initial diagnostics. MRI offers specific advantages in complex cases or when detailed visualization of the urinary tract is required. X-rays are an important tool for monitoring progress and planning treatment.