Dual-Energy CT Iodine-Subtraction Virtual Unenhanced Technique to Detect Urinary Stones in an Iodine-Filled Collecting System: A Phantom Study

Abstract

OBJECTIVE-The objective of our study was to evaluate the feasibility of virtual unenhanced images reconstructed from a dual-energy CT scan to depict urinary stones in an iodine solution in a phantom study. MATERIALS AND METHODS-Twentyurinary stones of different sizes (1.4-4.2 mm in shortaxis diameter) were placed in plastic containers. The containers were consecutively filled with different concentrations of iodine solution (21, 43, 64, 85, and 107 mg/dL; CT attenuation value range, 510-2,310 H at 120 kVp). Dual-energy CT was repeated with 80-140 and 100-140 kVp pairs, two collimation-slice thickness combinations, and the presence or absence of a 4-cm-thick oil gel around the phantom. The iodine-subtraction virtual unenhanced images were reconstructed using commercial software. The images were evaluated by three radiologists in consensus for the visibility of the stones and the presence of residual nonsubtracted iodine. Stone visibility rates were compared between the 80-140 and 100-140 kVp pairs and the five different iodine concentrations.RESULTS-Stone visibility rates with the 80-140 kVp pair were 99%, 93%, 96%, 94%, and 3% and those with the 100-140 kVp pair were 98%, 95%, 99%, 94%, and 99% for an iodine concentration of 21, 43, 64, 85, and 107 mg/dL, respectively. The poor visibility rate with 80-140 kVp and 107 mg/dL iodine concentration was due to the failure of iodine subtraction.CONCLUSION-Dual-energy CT iodine-subtraction virtual unenhanced technique is capable of depicting urinary stones in iodine solutions of a diverse range of concentrations in a phantom study. Keywords dual-energy CT; genitourinary imaging; iodine-subtraction imaging technique; reconstructed images; urinary stonesCharacterization of tissue and materials using dual-energy CT was first described in the late 1970s when CT technology was still in its infancy [1,2]. The technique was not adapted widely for clinical use except for bone densitometry [3] due to immature CT technology. With new dual-source CT systems, dual-energy CT scans can be obtained simultaneously using two orthogonally positioned X-ray tube and detector sets. This capability eliminates the need for © American Roentgen Ray Society Address correspondence to N. Takahashi. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript two separate scans with two different energy X-ray spectra and, therefore, eliminates misregistration due to patient motion or change in the contrast distribution between the two scans [4,5].The use of dual-source CT scanners has been shown to be effective in improving temporal resolution in coronary CT angiography [4,[6][7][8]. Subtraction of bone or calcium plaques from vessels on CT angiography using the dual-energy CT technique also appears promising [4]. Outside the realm of cardiovascular imaging, little experimentation with current dual-energy scanning techniques and subtraction imaging has been performed.As a routine component of CT urograms for hematuria or suspected urothelial tumor, unenhanced...

Evaluation of virtual unenhanced CT obtained from dual-energy CT urography for detecting urinary stones

“…In addition, 45-62% of stones measuring #3.2 mm in diameter on UCT images were invisible on VUCT images owing to complete subtraction. This stone detection rate in our study is much lower than that of the previous studies, probably because of different stone sizes [11,12]. The mean diameter (8.0 mm) of stones in Scheffel et al's study was much larger than the stones in our study (4.6 mm) [11].…”

“…The mean diameter (8.0 mm) of stones in Scheffel et al's study was much larger than the stones in our study (4.6 mm) [11]. Takahashi et al measured the short axis of the stone in an in vitro study setting while we measured the longest diameter in an in vivo study setting [12].…”

“…DECT is also useful in evaluating composition of urinary stones, uric acid stones can be differentiated from calcified stones [6][7][8][9][10]. However, there are few in vitro or in vivo reports about the validity of VUCT in detecting urinary stones [11][12][13]. Still, it is unclear whether or not VUCT can be an alternative imaging to UCT for diagnosing urolithiasis.…”

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

“…The addition of a spectral filter to the dual-source CT did not improve the subgroup characterization of calcium-containing stones (110,111). Furthermore, dual-energy techniques have been used for the diagnosis of renal stones on CT pyelography images through the use of virtual non-contrast images; however, this technique is limited for the diagnosis of small (<2 mm) renal stones (112,113).…”

Noise suppression for dual-energy CT via penalized weighted least-square optimization with similarity-based regularization

“…Dual-energy CT (DECT) has been increasingly used for iodine quantification, 1 kidney stone characterization, [2][3][4] virtual monochromatic imaging, 5,6 lung perfusion/ventilation studies, 7 and virtual nonenhanced images [8][9][10] among a growing list of diagnostic applications. However, material differentiation via DECT still suffers from noise amplification during the signal decomposition process.…”