Yoshinori Funama

Combination of a low-tube-voltage technique with hybrid iterative reconstruction (iDose) algorithm at coronary computed tomographic angiography.

We compare the performance of low tube voltage with the hybrid iterative reconstruction (iDose) with standard and low tube voltage with the filtered backprojection (FBP) using phantoms at computed tomographic coronary angiography. In computed tomographic coronary angiography, application of the combined low tube voltage with iDose resulted in significant image quality improvements compared to the low tube voltage with FBP. Image quality was the same or better despite a reduction in the radiation dose by 76% compared with standard tube voltage with FBP.

Low Contrast Agent and Radiation Dose Protocol for Hepatic Dynamic CT of Thin Adults at 256–Detector Row CT: Effect of Low Tube Voltage and Hybrid Iterative Reconstruction Algorithm on Image Quality

PURPOSE To evaluate the effect on image quality of a low contrast agent dose and radiation dose protocol at abdominal dynamic computed tomography (CT) with a low tube voltage, hybrid iterative reconstruction algorithm, and a 256- detector row scanner. MATERIALS AND METHODS This prospective study received institutional review board approval, and prior informed written consent was obtained from all patients. Seventy-four patients undergoing hepatic dynamic CT were randomly assigned to one of two protocols: Thirty-nine patients underwent scanning with the conventional 120-kVp protocol and the other 35 patients underwent scanning with an 80-kVp tube voltage and a 40% reduction in contrast agent dose. The 80-kVp images were also postprocessed with a hybrid iterative reconstruction algorithm. The estimated effective radiation dose of each protocol was compared and the image noise and contrast-to-noise-ratio (CNR) of the 120-kVp, 80-kVp, and hybrid iterative reconstructed 80-kVp images were evaluated by using the Student t test. RESULTS The effective radiation dose was 51% lower during the hepatic arterial phase (HAP) and 48% lower during the portal venous phase (PVP) with the 80-kVp protocol than with the 120-kVp protocol (HAP: 5.6 mSv ± 1.0 [standard deviation] vs 11.6 mSv ± 3.3; PVP: 5.8 mSv ± 0.7 vs 11.2 mSv ± 3.2, respectively). The hybrid iterative reconstruction decreased image noise by 23% during the HAP (9.2 ± 1.9 vs 12.0 ± 2.6) and by 24% during the PVP (9.4 ± 1.8 vs 12.3 ± 2.6). There were no significant differences in the CNR of any of the regions of interest between 80-kVp with iterative reconstruction and 120-kVp protocols (P = .46-.85). CONCLUSION A low tube voltage and the hybrid iterative reconstruction algorithm can dramatically decrease radiation and contrast agent doses with adequate image quality at hepatic dynamic CT of thin adults with use of a 256-detector row scanner.

Improvement of low-contrast detectability in low-dose hepatic multidetector computed tomography using a novel adaptive filter : Evaluation with a computer-simulated liver including tumors

Purpose:The purpose of this study was to investigate how much radiation dose can be reduced without loss of low-contrast detectability with a newly developed adaptive noise reduction filter in hepatic multidetector computed tomography (MDCT) scans by using a computer-simulated liver phantom. Materials and Methods:Simulated CT images, including liver and intrahepatic tumors, were mathematically constructed using a computer workstation to evaluate low-contrast detectability by the observer performance test. Milliampere second for construction of simulated images were 60, 80, 100, and 120 mAs (low dose) and 160 mAs (standard dose) at 120 kVp. Images with 60, 80, 100, and 120 mAs were postprocessed with the adaptive noise reduction filter. A total of 432 images were prepared and receiver operating characteristic (ROC) analysis was performed by 5 radiologists. The detectability of simulated tumor by radiologists was estimated with the area under the ROC curves (Az values). In addition, we visually evaluated CT images of 15 patients with chronic liver damage for graininess of the liver parenchyma, sharpness of the liver contour, conspicuity and marginal sharpness of the liver tumors, and overall image quality. Results:The mean Az value at 0.777 (60 mAs), 0.828 (80 mAs), and 0.844 (100 mAs) without filter was significantly lower than that of 160 mAs without filter (P < 0.001, 60 mAs; P = 0.010, 80 mAs; P = 0.040, 100 mAs). There was no statistical difference between the mean Az value at 80 mAs with and 160 mAs without the adaptive noise reduction filter (P = 0.220) and 100 mAs with and 160 mAs without the adaptive noise reduction filter (P = 0.979). In the visual evaluation of patient livers, there was no statistical difference in the graininess and sharpness of the liver, the conspicuity and marginal sharpness of the tumor, and the overall image quality between standard-dose and filtered low-dose images (Wilcoxon signed rank test, P > 0.05). Conclusion:The radiation dose can be reduced by 50% without loss of nodule detectability by applying the adaptive noise reduction filter to simulated and patient liver images obtained at MDCT.

Low-kilovoltage, high-tube-current MDCT of liver in thin adults: pilot study evaluating radiation dose, image quality, and display settings.

OBJECTIVE The purpose of our study was to evaluate the effect of a low tube voltage-high tube current-time product technique for portal phase abdominal CT of thin adults. SUBJECTS AND METHODS This study included 25 patients who had undergone portal phase abdominal CT at 120 kVp in the preceding 6 months. All were scanned using 80 kVp and high tube-current time products. We assessed the estimated effective dose (ED), image noise, attenuation, contrast-to-noise ratio (CNR), and figure of merit of the liver and portal vein. Two radiologists evaluated the quality of scans for image contrast and streak artifacts at 80 kVp, 120 kVp, and 80 kVp with wide window width display presets (W-80). RESULTS The estimated ED was 33% lower at 80 than at 120 kVp. CNR of the portal vein was 36.8% higher at 80 than 120 kVp, and for the liver it was 17.7% higher at 80 than 120 kVp. The visual score of image contrast was significantly higher for W-80 than for 120 kVp; however, there was no significant difference in the visual score of streak artifacts. CONCLUSION At portal phase abdominal CT, 80 kVp and a high tube current-time product setting significantly improved image quality and reduced the radiation dose compared with 120 kVp.

Effect of Contrast Injection Protocols with Dose Adjusted to the Estimated Lean Patient Body Weight on Aortic Enhancement at CT Angiography

OBJECTIVE The objective of our study was to investigate the effect on aortic enhancement of iodine doses adjusted for the patient estimated lean body weight (LBW) at CT angiography (CTA). SUBJECTS AND METHODS CTA for the whole aorta using a 64-MDCT scanner was performed in 97 patients (mean age, 67.4 years) with confirmed or suspected aortoiliac disease. The patients were divided into two groups: a total body weight (TBW) group (n = 49) and an estimated LBW group (n = 48). LBW was estimated from the patient weight (TBW) and height. The TBW and estimated LBW groups received 360 mg I/kg of TBW and 450 mg I/kg of estimated LBW of contrast medium, respectively. The relative dose ratio for the estimated LBW group versus the TBW group was based on the fact that the standard percentage of body fat in Japanese adults with an average TBW of 60 kg is 20% (360 = 0.8 x 450). Differences in the degree of aortic enhancement and interpatient variability in aortic enhancement between the estimated LBW and TBW group were evaluated. RESULTS Mean aortic enhancement was 308.9 HU for the estimated LBW group and 314.1 HU for the TBW group, indicating no significant difference in the degree of enhancement (Welchs t test, p = 0.61). The interquartile range was smaller for the LBW group than the TBW group (52.8 vs 79.1 HU, respectively); interpatient variability was lower in the estimated LBW group. The aortic attenuation gradient in the TBW group and estimated LBW group was 20.7 and 25.8 HU, respectively; the difference was not statistically significant. CONCLUSION The CTA protocol using an estimated LBW-tailored dose yielded more consistent aortic enhancement with reduced interpatient variability than the CTA protocol using a TBW-based dose.

Detection of nodules showing ground-glass opacity in the lungs at low-dose multidetector computed tomography: phantom and clinical study.

To investigate the effect of the radiation dose (tube current second product) and the attenuation value of nodules with ground-glass opacity (GGO) on their detectability at multidetector computed tomography (MDCT). Methods: We scanned a chest CT phantom that included simulated GGO nodules with an MDCT scanner. The attenuation value of the simulated lung parenchyma was −900 Hounsfield units (HU); it was −800 and −650 HU for the simulated GGO nodules. We used a tube current second product of 180 mA as the standard and 21, 45, 60, and 90 mAs as the low-dose and performed receiver operating characteristic analysis to compare the performance of 5 radiologists in detecting GGO nodules at each milliampere. To assess the detectability of GGO nodules on human lung images, the observers were presented with 38 GGO nodules from 15 patients. The 5 radiologists independently reviewed chest CT images at 21 and 45 mAs. Results: In the phantom study, the Az value for GGO nodules with a CT number of −800 HU was significantly lower at 21 than 180 effective mA (0.86 vs. 0.96; P < 0.01). There was no statistically significant difference in the Az value of GGO nodules with a CT number of −650 HU, irrespective of milliamperes used (P = 0.165). In the clinical study, 39.5% and 25.8% of GGO were missed at 21 and 45 mAs, respectively. Conclusions: At MDCT, GGO nodules with a CT number of −650 HU or less were difficult to detect at the lower milliampere settings (21 and 45 mAs).

Performance of radiologists in detection of small pulmonary nodules on chest radiographs: Effect of rib suppression with a massive-training artificial neural network

OBJECTIVE A massive-training artificial neural network is a nonlinear pattern recognition tool used to suppress rib opacity on chest radiographs while soft-tissue contrast is maintained. We investigated the effect of rib suppression with a massive-training artificial neural network on the performance of radiologists in the detection of pulmonary nodules on chest radiographs. MATERIALS AND METHODS We used 60 chest radiographs; 30 depicted solitary pulmonary nodules, and 30 showed no nodules. A stratified random-sampling scheme was used to select the images from the standard digital image database developed by the Japanese Society of Radiologic Technology. The mean diameter of the 30 pulmonary nodules was 14.7 +/- 4.1 (SD) mm. Receiver operating characteristic analysis was used to evaluate observer performance in the detection of pulmonary nodules first on the chest radiographs without and then on the radiographs with rib suppression. Seven board-certified radiologists and five radiology residents participated in this observer study. RESULTS For all 12 observers, the mean values of the area under the best-fit receiver operating characteristic curve for images without and with rib suppression were 0.816 +/- 0.077 and 0.843 +/- 0.074; the difference was statistically significant (p = 0.019). The mean areas under the curve for images without and with rib suppression were 0.848 +/- 0.059 and 0.883 +/- 0.050 for the seven board-certified radiologists (p = 0.011) and 0.770 +/- 0.081 and 0.788 +/- 0.074 for the five radiology residents (p = 0.310). CONCLUSION In the detection of pulmonary nodules, evaluation of a combination of rib-suppressed and original chest radiographs significantly improved the diagnostic performance of radiologists over the use of chest radiographs alone.

Optimal Contrast Dose for Depiction of Hypervascular Hepatocellular Carcinoma at Dynamic CT Using 64-MDCT

OBJECTIVE The objective of our study was to investigate prospectively the optimal contrast dose for the depiction of hypervascular hepatocellular carcinoma (HCC) during the hepatic arterial phase (HAP) at dynamic CT using a 64-MDCT scanner. SUBJECTS AND METHODS The study included 135 patients with known or suspected HCC who underwent dynamic CT on a 64-detector scanner and 47 were found to have 71 hypervascular HCCs. The patients were randomly assigned to one of three protocols: A contrast dose of 450, 525, or 600 mg I/kg of body weight was delivered over 30 seconds in protocols A, B, and C, respectively. We measured the tumor-liver contrast (TLC) during HAP in the three groups and compared the results. Two radiologists qualitatively evaluated tumor conspicuity during HAP using a 3-point scale; their results were compared. RESULTS The TLC in protocols A, B, and C was 26.5, 38.4, and 52.3 H, respectively; the difference was significant between protocols A and B (p = 0.05), A and C (p < 0.01), and B and C (p = 0.02). In our qualitative analysis of tumor conspicuity, the mean score for protocols A, B, and C was 1.6, 2.3, and 2.7, respectively; there was a significant difference between protocols A and B and A and C, but not between protocols B and C. CONCLUSION The administration of a total iodine dose of 525 mg or more per kilogram of body weight is desirable for the good or excellent depiction of hypervascular HCC, although the administration of 450 mg I/kg of body weight can depict hypervascular HCC.

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.

A Low Tube Voltage Technique Reduces the Radiation Dose at Retrospective ECG-gated Cardiac Computed Tomography for Anatomical and Functional Analyses

RATIONALE AND OBJECTIVES To investigate the effect of low-tube-voltage technique on a cardiac computed tomography (CT) for coronary arterial and cardiac functional analyses and radiation dose in slim patients. MATERIALS AND METHODS We enrolled 80 patients (52women, 28 men; mean age, 68.7 ± 8.9 years) undergoing retrospective electrocardiogram-gated 64-slice cardiac CT. Forty were subjected to the low (80-kV) and 40 to the standard (120-kV) tube-voltage protocol. Quantitative parameters of the coronary arteries (ie, CT attenuation, image noise, and the contrast-to-noise ratio [CNR]) were calculated, as were the effective radiation dose and the figure of merit (FOM). Each coronary artery segment was visually evaluated using a 5-point scale. Cardiac function calculated by using low-tube-voltage cardiac CT was compared with that on echocardiographs. RESULTS CT attenuation and image noise were significantly higher at 80- than 120-kV (P < .01). CNR of the left and right coronary artery was 18.4 ± 3.8 and 18.5 ± 3.3, respectively, at 80 kV; these values were 19.7 ± 2.7 and 19.8 ± 2.8 at 120 kV; the difference was not significant. The estimated effective radiation dose was significantly lower at 80 than 120 kV (6.3 ± 0.6 vs. 13.9 ± 1.1 mSv, P < .01) and FOM was significantly higher at 80 than 120 kV (P < .01). At visual assessment, 99% of the coronary segments were diagnostic quality; the two protocols did not differ significantly. We observed a strong correlation and good agreement between low-tube-voltage cardiac CT and echocardiography for cardiac functional analyses. CONCLUSION Low-tube-voltage cardiac CT significantly reduced the radiation dose by approximately 55% in slim patients while maintaining anatomical image quality and accuracy of cardiac functional analysis.