Ryo Itatani

Reduction in radiation and contrast medium dose via optimization of low-kilovoltage CT protocols using a hybrid iterative reconstruction algorithm at 256-slice body CT: Phantom study and clinical correlation

AIM To optimize low-kilovoltage (kV) computed tomography (CT) protocols using a hybrid iterative reconstruction (HIR) algorithm at 256-detector-row body CT. MATERIALS AND METHODS Based on preliminary phantom studies, three different tube voltage protocols with an equal contrast-to-noise ratio (CNR) were developed. They were a conventional 120 kV protocol with filtered back-projection (FBP), an 80 kV protocol with HIR (a 160% increase in the tube current-time product and a 40% reduction in the contrast medium dose), and a 100 kV protocol with HIR (a 20% reduction in the tube current-time product and the contrast medium dose). The clinical study included 70 patients (34 women, 36 men; mean age 70.5 ± 9.1 years, range 44-92 years) who had undergone CT at 120 kV a mean of 148 ± 137 days before undergoing low kV contrast-enhanced body CT (80 kV with HIR, n = 35; 100 kV with HIR, n = 35). The estimated effective radiation dose (ED), image noise, and CNR were calculated and the visual image quality was scored on a four-point scale. RESULTS Mean ED was 12.3, 8.4, and 15.4 mSv for the 80, 100, and 120 kV protocol, respectively, and significantly lower using the low kV protocols. There was no significant difference in the image noise and CNR between the low kV protocols with HIR and the 120 kV protocol with FBP, or in the visual scores among the three protocols. CONCLUSION Without ensuing image-quality degradation, the radiation and contrast medium dose can be reduced with optimal contrast-enhanced CT protocols using a low kV technique and an HIR algorithm.

Characterization of Liver Tumors by Diffusion-Weighted Imaging: Comparison of Diagnostic Performance Using the Mean and Minimum Apparent Diffusion Coefficient.

Purpose To determine the minimum apparent diffusion coefficient (ADCmin) values of benign and malignant hepatic lesions based on diffusion-weighted imaging and to compare the diagnostic performance of ADCmin and mean ADC (ADCmean) values for differentiating between benign and malignant tumors of the liver. Materials and Methods We retrospectively subjected 240 patients with 195 malignant (hepatocellular carcinoma [HCC], n = 137; metastases, n = 44; cholangiocellular carcinoma [CCC], n = 14) and 45 benign tumors (hemangiomas, n = 37; focal nodular hyperplasia [FNH], n = 8). Both ADCmean and ADCmin were evaluated independently by 2 readers, the sensitivity and specificity for the detection of malignancy were calculated, and receiver operating characteristic (ROC) curves were generated. To determine interobserver agreement, we calculated the Pearson correlation coefficient. Results Mean ADC (×10−3 mm2/s) was 1.19 for malignant (HCC, 1.15; metastasis, 1.23; CCC, 1.51) and 2.01 for benign tumors (hemangioma, 2.09; FNH, 1.52; P < 0.001). Minimum ADC was 0.81 for malignant (HCC, 0.79; metastasis, 0.81; CCC, 0.91) and 1.62 for benign tumors (hemangioma, 1.66; FNH, 1.28; P < 0.001). The sensitivity, specificity, and the calculated area under the ROC curve for diagnosing malignant lesions were 86.2%, 86.7%, and 0.942 (reader 1) and 88.7%, 88.9%, and 0.939 (reader 2) for ADCmean; they were of 92.3%, 97.8%, and 0.984 (reader 1) and 94.9%, 97.8%, and 0.983 (reader 2) for ADCmin. Conclusions Mean ADC and ADCmin were valuable for differentiating between malignant and benign hepatic lesions. The area under the ROC curve of ADCmin was significant higher than that of ADCmean.

Clinical impact of 3-dimensional balanced turbo-field-echo magnetic resonance cholangiopancreatography at 3 T: prospective intraindividual comparison with 3-dimensional turbo-spin-echo magnetic resonance cholangiopancreatography.

Objective The objective of this study was to evaluate the clinical utility of 3-dimensional (3D) balanced turbo-field-echo (BTFE) magnetic resonance cholangiopancreatography (MRCP) with gate and track acquisition at 3 T. Methods Using a 3-T unit, we subjected 52 consecutive patients to 3D BTFE MRCP with the navigator-gated technique and 3D turbo-spin-echo volume isotropic T2-weighted acquisition (VISTA) MRCP with the navigator-triggered technique. Two radiologists independently rated the image quality and visibility of the right and left hepatic duct, cystic duct, common bile duct, gallbladder, and main pancreatic duct using a 4-point scale. The signal-to-noise ratio, contrast-to-noise ratio, and the acquisition time were evaluated by quantitative analysis. Results The visual scores of the cystic duct, common bile duct, gallbladder, and overall image quality were significantly higher for BTFE than VISTA MRCP (P < 0.01). The score for the main pancreatic duct was significantly higher with VISTA MRCP (P < 0.01). The image acquisition time was significantly shorter with BTFE than VISTA MRCP (139.8 ± 45.4 vs 416.9 ± 108.3 seconds, P < 0.01). There was no significant difference in signal-to-noise ratio and contrast-to-noise ratio. Conclusions Three-dimensional BTFE MRCP yields significantly better image quality and visibility of large biliary structures than VISTA MRCP at a significantly shorter acquisition time. Volume isotropic T2-weighted acquisition MRCP provides detailed information on the main pancreatic duct that tends to be obscure on the 3D BTFE sequence.

Usefulness of the Short-Echo Time Cube Sequence at 3-T Magnetic Resonance Cholangiopancreatography: Prospective Comparison With the Conventional 3-Dimensional Fast Spin-Echo Sequence.

Objectives We evaluated prospectively the clinical use of the short–echo time (TE) Cube sequence for magnetic resonance cholangiopancreatography (MRCP) at 3 T. Methods Using a 3-T unit, we subjected 41 consecutive patients to short-TE Cube MRCP and conventional 3-dimensional fast spin-echo (3D-FSE) MRCP. Two radiologists independently rated the image quality and the visibility of the right and left hepatic, cystic, common bile, and main pancreatic ducts and the gallbladder on a 4-point scale. The averaged visual scores by 2 readers for the image quality were calculated, and the artifacts were evaluated in cases with relatively lower (<3) score. The signal-to-noise ratio, contrast-to-noise ratio, and acquisition time were evaluated by quantitative analysis. Results The visual scores of the common bile duct (P < 0.05), cystic duct (P < 0.01), and gallbladder (P < 0.01) were significantly higher for Cube than 3D-FSE MRCP. Signal-to-noise ratio was also significantly higher for Cube than 3D-FSE MRCP (P < 0.01). There was no significant difference in the image acquisition time (352.1 ± 93.0 vs 314.1 ± 126.2 seconds, P = 0.059). Four cases on 3D-FSE MRCP and 2 cases on Cube MRCP have relatively lower image quality; however, the difference was not significant (P = 0.18). Conclusions The visibility of biliary structures is significantly better on short-TE Cube MRCP than conventional 3D-FSE MRCP images at a clinically acceptable acquisition time.

Extracapsular extension of prostate cancer: diagnostic value of combined multiparametric magnetic resonance imaging and isovoxel 3-dimensional T2-weighted imaging at 1.5 T.

Objective The objective of this study was to assess whether adding isovoxel 3-dimensional T2-weighted imaging (volume isotropic T2-weighted acquisition [VISTA]) to multiparametric magnetic resonance imaging (mp-MRI) improves the ability to diagnose the extracapsular extension (ECE) of prostate cancer. Methods Two radiologists independently evaluated ECE on images acquired with mp-MRI only (method A) and mp-MRI plus VISTA (method B) in 50 men who had undergone prostatectomy. We also compared the signal-to-noise ratio of the tumor on T2WI and VISTA scans. Results Sensitivity, specificity, and accuracy were higher with method B. For both readers, specificity, accuracy, and the area under the receiver operating characteristic curve of method B were significantly higher than those of method A (reader 1: P = 0.028, 0.025, and 0.006; reader 2: P = 0.017, 0.0071, and 0.018). The signal-to-noise ratio was significantly higher on T2-weighted imaging than VISTA images (9.21 [SD, 2.46] vs 7.30 [SD, 1.87], P < 0.01). Conclusions The addition of VISTA to mp-MRI improves the diagnostic value for ECE significantly.