Characterization of Human Renal Stones with MDCT: Advantage of Dual Energy and Limitations Due to Respiratory Motion

Abstract

monohydrate stones are more resistant to extracorporeal lithotripsy [16] than are the other types of stones we describe. Failure of extracorporeal shock wave lithotripsy increases medical costs, necessitates alternative treatment, and results in undesirable exposure of the renal parenchyma to shock waves. For these reasons, pretreatment determination of the composition of stones is essential. Since the early 1980s, studies have been conducted to determine stone composition on the basis of X-ray attenuation of stones in vitro [17][18][19][20][21][22] and in vivo [23][24][25].Organs in the upper part of the abdomen, including the liver, kidneys, and spleen, move considerably as a result of respiration [26] MATERIALS AND METHODS. The stones were placed in a jelly simulating the X-ray attenuation of the kidneys. A dynamic platform was used to apply to the phantom free-breathing motion (sinusoidal motion in z-axis) and motion due to lack of maintenance of a breath-hold (5 mm·s −1 in z-axis). Determination of the chemical composition was performed with mean CT attenuation values obtained at 80 and 120 kV and with dual-energy CT attenuation values. G e n it o u r i n a r y I m ag i ng • O r ig i n a l R e s e a rc hRESULTS. Two hundred forty-one human urinary stones were classified into six groups: uric acid, cystine, struvite, weddellite (calcium oxalate dihydrate), whewellite (calcium oxalate monohydrate), and brushite. With no motion, the use of dual energy enabled differentiation of all of the types of stones with statistically significant differences. Uric acid (-20 ± 22 H), cystine (106 ± 19 H), struvite (271 ± 16 H), weddellite (323 ± 5 H), brushite (415 ± 30 H), and whewellite (510 ± 17 H) were identified as distinct groups. Motion-induced mean CT attenuation values were significantly different from those obtained with no motion. With motion, dual-energy CT attenuation values did not allow differentiation of all stone types.CONCLUSION. Dual-energy CT attenuation values can be used to predict the chemical composition of stones in vitro. However, when slight motion is applied to renal stones during image acquisition, the values become significantly different from those obtained with no motion. Consequently, confusion arises in differentiating stone types. A perfect breath-hold has to be performed for in vivo use of attenuation value to discern stone type.

Feasibility of Single-Source Dual-Energy Computed Tomography for Urinary Stone Characterization and Value of Iterative Reconstructions

“…23,24 For example, Boulay et al 25 and Mostafavi et al 26 showed promising initial results in their in vitro studies using phantoms with urinary stones. However, an in vivo study by Grosjean et al 27 showed that when slight motion was applied to renal stones during image acquisition, the HU values become significantly different from those obtained without motion, rendering an accurate differentiation of urinary stones impossible. This problem of misregistration was overcome in 2006 by the introduction of dual-source CT enabling simultaneous acquisition of images at 2 x-ray spectra.…”

Dual-energy CT revisited by multidetector ct: review of principles and clinical applications

“…The effective dose ranges from 22.5 to 36.4 mSv and from 9.4 to 13.8 mSv for DECT and single-energy CT imaging, respectively. An increased radiation dose can be justified when unenhanced CT images are eliminated from the CT protocols, which may result in an overall radiation dose saving (92,93,105,106). Beam-hardening artifacts can be observed in thorax perfusion DECT due to the dense contrast in the superior vena cava, which can mimic an embolus.…”

Dual-energy CT for the characterization of urinary calculi: In vitro and in vivo evaluation of a low-dose scanning protocol

“…Immediately after reconstruction, the images can be postprocessed semi-automatically, offering the radiologist a fast diagnosis. The material decomposition algorithm has recently been tested in vitro and in vivo, showing a high accuracy for the discrimination of uric acid calculi from other calculus types [13][14][15]). However, all three studies used dedicated high-quality CT examination protocols, featuring relatively high tube currents and a narrow detector collimation and resulting in longer CT acquisition times and a higher radiation dosage compared to conventional low-dose CT.…”