Novel computed tomography characteristics of dust as well as tiny and small fragments in laser lithotripsy

To evaluate the appearance of dust and stone fragments in the upper urinary tract after retrograde intrarenal surgery (RIRS) on computed tomography (CT) imaging.

Human renal stones were implanted into porcine kidneys to assess the characteristics of dust and small fragments on CT imaging. Stone samples were classified as small fragments (2.00-2.36 mm), tiny fragments (1.00-1.40 mm) or dust (≤ 250 μm). Each group was divided into multiple 0.25-g dry weight samples. Twenty-four samples were placed in the upper poles of porcine kidneys with a ureteroscope and characterized using CT. The reconstructed images were evaluated with volume analyzer software to determine stone volume, maximum and mean attenuation values, and standard deviation of the stone attenuation value.

The mean stone volume decreased with increasing stone size (p < 0.001). The mean attenuation value (depicted in Hounsfield units [HU]) significantly increased with increasing stone size: dust (309.9), tiny fragments (401.2), and small fragments (474.5). The maximum attenuation value (HU) of small fragments (1430.0) was significantly greater than those of tiny fragments (1126.3) and dust (1039.8). As the stone size decreased from the small fragment size to the dust size, the standard deviation of the stone attenuation value significantly decreased.

As the stone size approaches the that of dust particles, the mean and maximum attenuation values decrease and become more homogeneous. CT and volume analyzer software can be used to distinguish dust from small fragments and assess small residual stones after RIRS.