IQon Spectral CT in the Detection, Diagnosis of Gallstones

A middle-aged male presented with left flank pain. A computed tomography (CT) scan with IV contrast was performed on the IQon Spectral CT scanner (Philips, The Netherlands). Conventional images revealed the left kidney to be clearly hydronephrotic with less enhancement compared to the right kidney.

Magnification depicted a large stone in the left renal pelvis. Spectral CT enable visualization of the composition of the stone by comparing the uric acid-removed image to the uric acid image. This indicated the stone comprised two components: A dense, central component not composed of uric acid, and a less dense, peripheral component composed of uric acid on the uric acid-removed image..

Additionally detected in the left kidney were small stones, some of which were made of uric acid and others that were not, identifying them as calcium stones. Upon removal, the stones were determined to be a mix of both calcium and uric acid stones.

Evaluation of the gallbladder on the effective atomic number image showed small filling defects consistent with gallstones. These are negative gallstones, as they don’t appear on conventional images because their density is identical on conventional CT. Further examination of specific regions of interest on the gallstones and bile in the gallbladder on the conventional images showed similar density; however, the spectral plots were strikingly different. There was an overlap at about 70 Houndsfield units, which explains why these gallstones cannot be visualized on conventional CT.

This case highlights the use of spectral CT to identify the composition of the stones in the left kidney and to detect unsuspected gallstones.