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Background: To determine whether machine learning with histogram analysis of coronary CT angiography (CCTA) yields higher diagnostic performance for coronary plaque characterization than the conventional cut-off method using the median CT number., Methods: We included 78 patients with 78 coronary plaques who had undergone CCTA and integrated backscatter intravascular ultrasound (IB-IVUS) studies. IB-IVUS diagnosed 32 as fibrous- and 46 as fatty or fibro-fatty plaques. We recorded the coronary CT number and 7 histogram parameters (minimum and mean value, standard deviation (SD), maximum value, skewness, kurtosis, and entropy) of the plaque CT number. We also evaluated the importance of each feature using the Gini index which rates the importance of individual features. For calculations we used XGBoost. Using 5-fold cross validation of the plaque CT number, the area under the receiver operating characteristic curve of the machine learning- (extreme gradient boosting) and the conventional cut-off method was compared., Results: The median CT number was 56.38 Hounsfield units (HU, 8.00-95.90) for fibrous- and 1.15 HU (-35.8-113.30) for fatty- or fibro-fatty plaques. The calculated optimal threshold for the plaque CT number was 36.1 ± 2.8 HU. The highest Gini index was the coronary CT number (0.19) followed by the minimum value (0.17), kurtosis (0.17), entropy (0.14), skewness (0.11), the mean value (0.11), the standard deviation (0.06), and the maximum value (0.05), and energy (0.00). By validation analysis, the machine learning-yielded a significantly higher area under the curve than the conventional method (area under the curve 0.92 and 95%, confidence interval 0.86-0.92 vs 0.83 and 0.75-0.92, p = 0.001)., Conclusion: The machine learning-was superior the conventional cut-off method for coronary plaque characterization using the plaque CT number on CCTA images., (Copyright © 2018. Published by Elsevier Inc.)

Objective:: To evaluate the effects of virtual monochromatic imaging (VMI) using dual-layer spectral detector CT on the image quality of coronary CT angiography (CCTA) acquired by using a low contrast material (CM) dose., Methods:: We used a VMI 50keV protocol with a 50%  CM dose (140  mgI kg -1 ) to scan 30 patients with renal insufficiency and a 120 kVp with the standard CM dose (280  mgI kg -1 ) to scan 30 controls without renal insufficiency. Quantitative parameters, including CT attenuation, image noise, and contrast-to-noise ratio (CNR), were measured. The visual image quality factors of contrast enhancement, image noise, beam-hardening artefact, vessel sharpness, and overall image quality were scored on a 4-point scale., Results:: The mean CT attenuation of the ascending aorta was significantly higher for 50 keV VMI than for 120 kVp. Image noise was significantly lower under the 50 keV VMI. CNR and the mean visual score for contrast enhancement were significantly higher for 50 keV VMI. There were no significant differences in the other visual image quality parameters between the two protocols., Conclusion:: Dual-layer spectral detector CT using 50 keV VMI enabled reducing the CM dose by 50 % without CCAT image quality degradation in patients with renal insufficiency., Advances in Knowledge:: The VMI 50 keV protocol using dual-layer spectral detector CT and a CM dose reduced by 50 % (140 mgI kg -1 ) can improve the diagnostic image quality of CCTA.

Objective:: To compare the ability of test scans with undiluted and diluted contrast medium (CM) to predict contrast enhancement (CE) on cardiovascular CT angiography (CCTA) images of infants., Methods:: We divided 120 consecutive infants who had undergone CCTA on a 64-MDCT scanner into two equal groups. In one group, the test bolus consisted of undiluted CM [protocol 1 (P1): injection volume = total  body weight × 1.2  ml, injection time 5  s], in the other (P2) it was total  body weight × 4.0  ml (CM 15%, saline 85%, injection time 16  s). CE on the test scans was recorded on a 3-point visual scale. We investigated the relation for CE in the pulmonary artery and ascending aorta between the P1 or P2 test scans and CCTA images., Results:: While peak CE was observed on all test scans performed with P2, in approximately 10 % of test scans obtained under P1, peak CE was not visualized. There was a strong positive linear correlation for CE of the pulmonary artery and ascending aorta on P2 images (r = 0.61  and r = 0.63, p < 0.01); under P1 the correlation was weak (r = 0.26  and r = 0.33, p < 0.01)., Conclusion:: Test-scanning with diluted CM revealed the optimal CE peak time and was useful for predicting CE on CCTA scans of the pulmonary artery and ascending aorta in infants with congenital heart disease., Advances in Knowledge:: Diluted test scans help to select the optimal scan parameters for the CCTA study of infants by using contrast-to-noise-based scanning.

Background: Coronary Computed Tomography Angiography (CTA) has become one of the most important diagnostic imaging modalities for the evaluation of coronary artery diseases. During coronary computed CTA, sufficient vascular enhancement is essential for the accurate detection and evaluation of lesions in the coronary arteries. To obtain optimal contrast enhancement and perform appropriate clinical coronary CTA, physicians, radiologists, and radiology technologists should acquire a basic knowledge of contrast injection protocols., Conclusion: This review article summarizes the basic concepts of contrast injection protocols for coronary CTA., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

Purpose: A three-dimensional (3D) image from computed tomography (CT) angiography is a useful method for evaluation of complex anatomy such as congenital heart disease. However, 3D imaging requires high contrast enhancement for distinguishing between blood vessels and soft tissue. To improve the contrast enhancement, many are increasing the injection rate. However, one method is the use of fenestrated catheters, it allows use of a smaller gauge catheter for high-flow protocols. The purpose of this study was to compare the pressure of injection rate and CT number of a 24-gauge fenestrated catheter with an 22-gauge non-fenestrated catheter for i.v. contrast infusion during CT., Methods: Between December 2014 and March 2015, 50 newborn patients were randomly divided into two protocols; 22-gauge conventional non-fenestrated catheter (24 newborn; age range 0.25-8 months, body weight 3.6±1.2 kg) and 24-gauge new fenestrated catheter (22 newborn; age range 0.25-12 months, body weight 3.3±0.9 kg). Helical scan of the heart was performed using a 64-detector CT (LightSpeed VCT, GE Healthcare) (tube voltage 80 kV; detector configuration 64×0.625 mm, rotation time 0.4 s/rot, helical pitch 1.375, preset noise index for automatic tube current modulation 40 at 0.625 mm slice thickness)., Results: We compared the maximum pressure of injection rate, CT number of aortic enhancement, and CT number of pulmonary artery enhancement between both protocols. The median injection rate, CT number of aortic enhancement, and CT number of pulmonary artery enhancement were 0.9 (0.5-3.4) ml/s, 455.5 (398-659) HU, and 500.0 (437-701) HU in 22-gauge conventional non-fenestrated catheter and 0.9 (0.5-2.0) ml/s, 436.5 (406-632) HU, and 479.5 (445-695) HU in the 24-gauge fenestrated catheter, respectively. There are no significantly different between a 24-gauge fenestrated catheter and 22-gauge non-fenestrated catheters at injection rate and CT number. Maximum pressure of injection rate was lower with 24-gauge non-fenestrated catheters (0.33 kg/cm 2 ) than 22-gauge non-fenestrated catheters (0.55 kg/cm 2 ) (p<0.01Conclusion: A 24-gauge fenestrated catheter performs similarly to an 22-gauge non-fenestrated catheter with respect to i.v. contrast infusion and aortic enhancement levels and can be placed in most subjects whose veins are deemed insufficient for an 22-gauge catheter.

Repeatability of quantitative assessment of atherosclerotic plaques is important for the accurate detection of high-risk plaques in coronary CT angiography (CTA). We assessed the effect of heart rate (HR) on plaque CT number using a coronary artery model and a cardiac phantom capable of simulating cardiac motion. The coronary artery model with luminal stenosis on a cardiac phantom was imaged with a simulated HR of 0, 50, 60, and 70 beats per minute using a 320-row CT scanner. We reconstructed CT images for cardiac diastolic phases (for 75% R-R interval) using filtered back projection (FBP), hybrid iterative reconstruction (AIDR3D), and model-based iterative reconstruction (FIRST). Two observers measured plaque attenuation in the lesion with 75% stenosis. The coefficient of determination (R 2 ) was obtained to evaluate interobserver agreement. At HR 70, FIRST improved the correlation between two observers compared with FBP and AIDR3D (FIRST: R 2  = 0.68, p < 0.05; FBP: R 2  = 0.29, p = 0.31; AIDR3D: R 2  = 0.22, p = 0.18). These R 2 at HR 70 were lower compared with at HR 50 (FIRST: R 2  = 0.92, p < 0.05; FBP: R 2  = 0.83, p < 0.05; AIDR3D: R 2  = 0.87, p < 0.05) and HR 0 (FIRST: R 2  = 0.97, p < 0.05; FBP: R 2  = 0.89, p < 0.05; AIDR3D: R 2  = 0.95, p < 0.05). Higher HR affected plaque measurement repeatability in coronary CTA. FIRST may improve plaque measurement repeatability at the higher HR compared with FBP and AIDR3D.

Objective: We evaluated the effect of various patient characteristics and time-density curve (TDC)-factors on the test bolus-affected vessel enhancement on coronary computed tomography angiography (CCTA). We also assessed the value of generalized linear regression models (GLMs) for predicting enhancement on CCTA., Materials and Methods: We performed univariate and multivariate regression analysis to evaluate the effect of patient characteristics and to compare contrast enhancement per gram of iodine on test bolus (ΔHUTEST) and CCTA (ΔHUCCTA). We developed GLMs to predict ΔHUCCTA. GLMs including independent variables were validated with 6-fold cross-validation using the correlation coefficient and Bland-Altman analysis., Results: In multivariate analysis, only total body weight (TBW) and ΔHUTEST maintained their independent predictive value ( p < 0.001). In validation analysis, the highest correlation coefficient between ΔHUCCTA and the prediction values was seen in the GLM ( r = 0.75), followed by TDC ( r = 0.69) and TBW ( r = 0.62). The lowest Bland-Altman limit of agreement was observed with GLM-3 (mean difference, -0.0 ± 5.1 Hounsfield units/grams of iodine [HU/gI]; 95% confidence interval [CI], -10.1, 10.1), followed by ΔHUCCTA (-0.0 ± 5.9 HU/gI; 95% CI, -11.9, 11.9) and TBW (1.1 ± 6.2 HU/gI; 95% CI, -11.2, 13.4)., Conclusion: We demonstrated that the patient's TBW and ΔHUTEST significantly affected contrast enhancement on CCTA images and that the combined use of clinical information and test bolus results is useful for predicting aortic enhancement.

Objective: To assess the utility of virtual monochromatic imaging (VMI) using a dual-layer spectral detector CT for electronic cleansing in fecal-tagging CT colonography (CTC)., Methods: This study included 35 patients who underwent fecal-tagging CTC with a dual-layer detector spectral CT scanner. Conventional images at 120 kVp and VMI at 40, 50, and 60 keV were reconstructed. Quantitative image quality parameters, i.e., tagging density and image noise, were compared and the visual image quality was scored on a four-point scale. We recorded the number of the colon segments with appropriate tagging density (≥300 HU) for each patient and used these data to compare the reconstructions. In addition, electronic cleansing performance was semi-quantitatively assessed using a four-point scale., Results: The mean tagging density on VMI was significantly higher than that on conventional 120 kVp images. The number of colon segments with appropriate tagging density on VMI were significantly higher than that on conventional 120 kVp images. There was no significant difference among the reconstructed images with respect to image noise. Scores for subjective image quality and electronic cleansing performance on VMI were significantly higher than those on conventional 120 kVp images., Conclusion: With dual-layer spectral detector CT, VMI can yield significantly better fecal-tagged CTC image quality and improve electronic cleansing performance., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Introduction: The aim of this study was to evaluate the radiation dose and image quality at low tube-voltage pediatric chest computed tomographic angiography (CTA) that applies the same contrast-to-noise ratio (CNR) index as the standard tube voltage technique., Materials and Methods: Contrast-enhanced chest CTA scans of 100 infants were acquired on a 64-row multidetector computed tomography (MDCT) scanner. In the retrospective study, we evaluated 50 images acquired at 120 kVp; the image noise level was set at 25 Hounsfield units. In the prospective study, we used an 80-kVp protocol; the image noise level was 40 Hounsfield units because the iodine contrast was 1.6 times higher than on 120-kVp scans; the CNR was as in the 120-kVp protocol. We compared the CT number, image noise, CT dose index volume (CTDI vol ), and the dose-length product on scans acquired with the 2 protocols. A diagnostic radiologist and a pediatric cardiologist visually evaluated all CTA images., Results: The mean CTDI vol and the mean dose-length product were 0.5 mGy and 7.8 mGy-cm for 80- and 1.2 mGy and 20.8 mGy-cm for 120-kVp scans, respectively (P < .001). The mean CTDI vol was 42% lower at 80 kVp than at 120 kVp, and there was no significant difference in the visual scores assigned to the CTA images (P = .28)., Conclusions: With the CNR index being the same at 80-kVp and 120-kVp imaging, the radiation dose delivered to infants subjected to chest CTA can be reduced without degradation of the image quality., (Copyright © 2018 Canadian Association of Radiologists. Published by Elsevier Inc. All rights reserved.)

Rationale and Objectives: We compared the radiation dose and diagnostic accuracy on 120- and 100-kVp coronary computed tomography angiography (CCTA) scans whose contrast-to-noise ratio (CNR) was the same., Materials and Methods: We studied 1311 coronary artery segments from 100 patients. For 120-kVp scans, the targeted image level was set at 25 Hounsfield units (HU). For 100-kVp scans, the targeted noise level was set at 30 HU to obtain the same CNR as at 120 kVp. We compared the CNR and the radiation dose on scans acquired at 120 and 100 kVp. Invasive coronary angiography (ICA) images were evaluated by an interventional coronary angiography specialist, and CCTA images were evaluated by a radiologist. Coronary artery disease was defined as a luminal narrowing ≧50% for ICA and CCTA. With ICA considered the gold standard, the diagnostic accuracy (sensitivity, specificity, positive predictive value, and negative predictive value) was analyzed on both 120- and 100-kVp CCTA images. We also compared the diagnostic accuracy for area under the receiver operating characteristic curve of the ICA and CCTA performed at 120 and 100 kVp. Two blinded observers visually evaluated the septal branch., Results: The mean dose-length product was 48% lower at 100 kVp than at 120 kVp (P < .01). Under the 120-kVp CCTA protocol, the area under the curve, 95% confidence interval, sensitivity, specificity, positive predictive value, and negative predictive value were 0.94%, 0.91%-0.96%, 94.0%, 93.0%, 82.3%, and 98.1%, respectively; at 100 kVp these values were 0.94%, 0.92%-0.97%, 96.1%, 92.0%, 85.2%, and 98.0%, respectively. Area under the receiver operating characteristic curve analysis revealed no significant difference in diagnostic accuracy between the two protocols (P = .87)., Conclusions: At the same CNR, the 100-kVp CCTA protocol may help to reduce the radiation dose by approximately 50% compared to the 120-kVp protocol without degradation of diagnostic accuracy., (Copyright © 2018 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.)

Given the growing awareness of and concern for potential carcinogenic effects of exposure of children to ionizing radiation at CT, optimizing acquisition parameters is crucial to achieve diagnostically acceptable image quality at the lowest possible radiation dose. Among currently available dose reduction techniques, recent technical innovations have allowed the implementation of low tube voltage scans and iterative reconstruction (IR) techniques into daily clinical practice for pediatric CT. The benefits of lowering tube voltage include a considerable reduction in radiation dose and improved contrast on images, especially when an iodinated contrast medium is used. The increase in noise, which is attributed to decreased photon penetration, is a major drawback but is not as severe as that at adult CT because of the small body size of children. In addition, use of IR algorithms can suppress increased noise, yielding wider applicability for low tube voltage scans. However, a careful implementation strategy and methodologic approach are necessary to maximize the potential for dose reduction while preserving diagnostic image quality under each clinical condition. The potential pitfalls of and topics related to these techniques include (a) the effect of tube voltage on the surface radiation dose, (b) the effect of window settings, (c) accentuation of metallic artifacts, (d) deterioration of low contrast detectability at low-dose settings, (e) interscanner variation of x-ray spectra, and (f) a comparison with the use of a spectral shaping technique. Appropriate use of low tube voltage and IR techniques is helpful for radiation dose reduction in most applications of pediatric CT. Online DICOM image stacks are available for this article . © RSNA, 2018.

We aimed to evaluate the image quality performance of coronary CT angiography (CTA) under the different settings of forward-projected model-based iterative reconstruction solutions (FIRST).Thirty patients undergoing coronary CTA were included. Each image was reconstructed using filtered back projection (FBP), adaptive iterative dose reduction 3D (AIDR-3D), and 2 model-based iterative reconstructions including FIRST-body and FIRST-cardiac sharp (CS). CT number and noise were measured in the coronary vessels and plaque. Subjective image-quality scores were obtained for noise and structure visibility.In the objective image analysis, FIRST-body produced the significantly highest contrast-to-noise ratio. Regarding subjective image quality, FIRST-CS had the highest score for structure visibility, although the image noise score was inferior to that of FIRST-body.In conclusion, FIRST provides significant improvements in objective and subjective image quality compared with FBP and AIDR-3D. FIRST-body effectively reduces image noise, but the structure visibility with FIRST-CS was superior to FIRST-body.

Purpose: To investigate the image quality characteristics for virtual monoenergetic images compared with conventional tube-voltage image with dual-layer spectral CT (DLCT)., Methods: Helical scans were performed using a first-generation DLCT scanner, two different sizes of acrylic cylindrical phantoms, and a Catphan phantom. Three different iodine concentrations were inserted into the phantom center. The single-tube voltage for obtaining virtual monoenergetic images was set to 120 or 140 kVp. Conventional 120- and 140-kVp images and virtual monoenergetic images (40-200-keV images) were reconstructed from slice thicknesses of 1.0 mm. The CT number and image noise were measured for each iodine concentration and water on the 120-kVp images and virtual monoenergetic images. The noise power spectrum (NPS) was also calculated., Results: The iodine CT numbers for the iodinated enhancing materials were similar regardless of phantom size and acquisition method. Compared with the iodine CT numbers of the conventional 120-kVp images, those for the monoenergetic 40-, 50-, and 60-keV images increased by approximately 3.0-, 1.9-, and 1.3-fold, respectively. The image noise values for each virtual monoenergetic image were similar (for example, 24.6 HU at 40 keV and 23.3 HU at 200 keV obtained at 120 kVp and 30-cm phantom size). The NPS curves of the 70-keV and 120-kVp images for a 1.0-mm slice thickness over the entire frequency range were similar., Conclusion: Virtual monoenergetic images represent stable image noise over the entire energy spectrum and improved the contrast-to-noise ratio than conventional tube voltage using the dual-layer spectral detector CT., (Copyright © 2018 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Purpose: We investigated the feasibility of single breath hold unenhanced coronary MRA using multi-shot gradient echo planar imaging (MSG-EPI) on a 3T-scanner., Methods: Fourteen volunteers underwent single breath hold coronary MRA with a MSG-EPI and free-breathing turbo field echo (TFE) coronary MRA at 3T. The acquisition time, signal to noise ratio (SNR), and the contrast of the sequences were compared with the paired t-test. Readers evaluated the image contrast, noise, sharpness, artifacts, and the overall image quality., Results: The acquisition time was 88.1% shorter for MSG-EPI than TFE (24.7 ± 2.5 vs 206.4 ± 23.1 sec, P < 0.01). The SNR was significantly higher on MSG-EPI than TFE scans (P < 0.01). There was no significant difference in the contrast on MSG-EPI and TFE scans (1.8 ± 0.3 vs 1.9 ± 0.3, P = 0.24). There was no significant difference in image contrast, image sharpness, and overall image quality between two scan techniques. The score of image noise and artifact were significantly higher on MSG-EPI than TFE scans (P < 0.05)., Conclusion: The single breath hold MSG-EPI sequence is a promising technique for shortening the scan time and for preserving the image quality of unenhanced whole heart coronary MRA on a 3T scanner.

Objectives: To evaluate the image quality and lesion conspicuity of virtual-monochromatic-imaging (VMI) with dual-layer DECT (DL-DECT) for reduced-iodine-load multiphasic-hepatic CT., Methods: Forty-five adults with renal dysfunction who had undergone hepatic DL-DECT with 300-mgI/kg were included. VMI (40-70-keV, DL-DECT-VMI) was generated at each enhancement phase. As controls, 45 matched patients undergoing standard 120-kVp protocol (120-kVp, 600-mgI/kg, and iterative reconstruction) were included. We compared the size-specific dose estimate (SSDE), image noise, CT attenuation, and contrast-to-noise ratio (CNR) between protocols. Two radiologists scored the image quality and lesion conspicuity., Results: SSDE was significantly lower in DL-DECT group (p < 0.01). Image noise of DL-DECT-VMI was almost constant at each keV (differences of ≤15%) and equivalent to or lower than of 120-kVp. As the energy decreased, CT attenuation and CNR gradually increased; the values of 55-60 keV images were almost equivalent to those of standard 120-kVp. The highest scores for overall quality and lesion conspicuity were assigned at 40-keV followed by 45 to 55-keV, all of which were similar to or better than of 120-kVp., Conclusions: For multiphasic-hepatic CT with 50% iodine-load, DL-DECT-VMI at 40- to 55-keV provides equivalent or better image quality and lesion conspicuity without increasing radiation dose compared with standard 120-kVp protocol., Key Points: • 40-55-keV yields optimal image quality for half-iodine-load multiphasic-hepatic CT with DL-DECT. • DL-DECT protocol decreases radiation exposure compared with 120-kVp scans with iterative reconstruction. • 40-keV images maximise conspicuity of hepatocellular carcinoma especially at hepatic-arterial phase.

Rationale and Objectives: To assess the effect of model-based iterative reconstruction (MBIR) on image quality and diagnostic performance of low-radiation-dose computed tomography colonography (CTC) in the preoperative assessment of colorectal cancer., Materials and Methods: This study included 30 patients with colorectal cancer referred for surgical treatment. All patients underwent CTC with a standard dose (SD) protocol in the supine position and a low-dose (LD; radiation dose reduction of approximately 85%) protocol in the prone position. The SD protocol images were post-processed using filtered back projection (FBP), whereas the LD protocol images were post-processed using FBP and MBIR. Objective and subjective image quality parameters were compared among the three different methods. Preoperative evaluations, including site, length, and tumor and node staging were performed, and the findings were compared to the postsurgical findings., Results: The mean image noise of SD-FBP, LD-FBP, and LD-MBIR images was 17.3 ± 3.2, 40.5 ± 10.9, and 11.2 ± 2.0 Hounsfield units, respectively. There were significant differences for all comparison combinations among the three methods (P < .01). For image noise, the mean visual scores were significantly higher for SD-FBP and LD-MBIR than for LD-FBP, and the scores for SD-FBP and LD-MBIR were equivalent (3.9 ± 0.3 [SD-FBP], 2.0 ± 0.5 [LD-FBP], and 3.7 ± 0.3 [LD-MBIR]). Preoperative information was more accurate under SD-FBP and LD-MBIR than under LD-FBP, and the information was comparable between SD-FBP and LD-MBIR., Conclusion: MBIR can yield significantly improved image quality on low-radiation-dose CTC and provide preoperative information equivalent to that of standard-radiation-dose protocol., (Copyright © 2018 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.)

Objective: To evaluate the effect of patient characteristics on popliteal aortic contrast enhancement at lower extremity CT angiography (LE-CTA) scanning., Materials and Methods: Prior informed consent to participate was obtained from all 158 patients. All were examined using a routine protocol; the scanning parameters were tube voltage 100 kVp, tube current 100 mA to 770 mA (noise index 12), 0.5-second rotation, 1.25-mm detector row width, 0.516 beam pitch, and 41.2-mm table movement, and the contrast material was 85.0 mL. Cardiac output (CO) was measured with a portable electrical velocimeter within 5 minutes of starting the CT scan. To evaluate the effects of age, sex, body size, CO, and scan delay on the CT number of popliteal artery, the researchers used multivariate regression analysis., Results: A significant positive correlation was seen between the CT number of the popliteal artery and the patient age ( r = 0.39, p < 0.01). A significant inverse correlation was observed between the CT number of the popliteal artery and the height ( r = -0.48), total body weight ( r = -0.52), body mass index ( r = -0.33), body surface area (BSA) ( r = -0.56), lean body weight ( r = -0.56), and CO ( r = -0.35) ( p < 0.001 for all). There was no significant correlation between the enhancement and the scan delay ( r = 0.06, p = 0.47). The BSA, CO, and age had significant effects on the CT number (standardized regression: BSA -0.42, CO -0.22, age 0.15; p < 0.05, respectively)., Conclusion: The BSA, CO, and age are significantly correlated with the CT number of the popliteal artery on LE-CTA.

Objective: Different CT scanners have different X-ray spectra and photon energies indicating that contrast enhancement vary among scanners. However, this issue has not been fully validated; therefore, we performed phantom and clinical studies to assess this difference., Methods: Two scanners were used: scanner-A and scanner-B. In the phantom study, we compared the contrast enhancement between the scanners at tube voltage peaks of 80, 100 and 120 kVp. Then, we calculated the effective energies of the two CT scanners. In the clinical study, 40 patients underwent abdominal scanning with scanner-A and another 40 patients with scanner-B, with each group using the same scanning protocol. The contrast enhancement of abdominal organs was assessed quantitatively (based on the absolute difference between the attenuation of unenhanced scans and contrast-enhanced scans) and qualitatively. A two-tailed independent Student's t-test and or the Mann-Whitney U test were used to compare the discrepancies., Results: In the phantom study, contrast enhancement for scanner-B was 36.9, 32.6 and 30.8% higher than that for scanner-A at 80, 100 and 120 kVp, respectively. The effective energies were higher for scanner-A than for scanner-B. In the quantitative analysis for the clinical study, scanner-B yielded significantly better contrast enhancement of the hepatic parenchyma, pancreas, kidney, portal vein and inferior vena cava compared with that of scanner-A. The mean visual scores for contrast enhancement were also significantly higher on images obtained by scanner-B than those by scanner-A., Conclusion: There were significant differences in contrast enhancement of the abdominal organs between the compared CT scanners from two different vendors even at the same scanning and contrast parameters. Advances in knowledge: Awareness of the impact of different X-ray energies on the resultant attenuation of contrast material is important when interpreting clinical CT images.

Objective: We compared the effect of a dual-region-of-interest (ROI) bolus-tracking technique on interpatient variability of arterial contrast enhancement with that of the conventional bolus-tracking technique in coronary computed tomographic angiography (CTA) on a 320-row scanner., Methods: This study included 100 patients who underwent coronary CTA using one of two protocols: (1) 50 patients underwent scanning using a conventional single-ROI bolus-tracking technique (P-single) with an ROI placed in the ascending aorta, and (2) 50 patients underwent scanning using a dual-ROI technique (P-dual) with two ROIs placed in the pulmonary trunk and the ascending aorta. CT attenuation in the ascending aorta and coronary arteries, and the interpatient variability were compared between the two scanning protocols., Results: The mean CT attenuation of the ascending aorta and coronary arteries tended to be higher for P-dual than for P-single, but the difference was not significant (p = 0.08-0.30). The interpatient variability of contrast enhancement (SD of the CT attenuation) was significantly smaller for P-dual than for P-single (p < 0.01)., Conclusion: The dual-ROI bolus-tracking technique can reduce interpatient variability of arterial contrast enhancement in coronary CTA on a 320-row scanner. Advances in knowledge: The use of a dual-ROI bolus-tracking technique can provide sufficient and consistent arterial enhancement of coronary CTA.

Purpose: The purpose of this study was to compare scan time and image quality between magnetic resonance angiography (MRA) of the thoracic aorta using a multi-shot gradient echo planar imaging (MSG-EPI) and MRA using balanced steady-state free precession (b-SSFP)., Materials and Methods: Healthy volunteers (n=17) underwent unenhanced thoracic aorta MRA using balanced steady-state free precession (b-SSFP) and MSG-EPI sequences on a 3T MRI. The acquisition time, total scan time, signal-to-noise ratio (SNR) of the thoracic aorta, and the coefficient of variation (CV) of thoracic aorta were compared with paired t-tests. Two radiologists independently recorded the images' contrast, noise, sharpness, artifacts, and overall quality on a 4-point scale., Results: The acquisition time was 36.2% shorter for MSG-EPI than b-SSFP (115.5±14.4 vs 181.0±14.9s, p<0.01). The total scan time was 40.4% shorter for MSG-EPI than b-SSFP (272±78 vs 456±144s, p<0.01). There was no significant difference in mean SNR between MSG-EPI and b-SSFP scans (17.3±3.6 vs 15.2±4.3, p=0.08). The CV was significantly lower for MSG-EPI than b-SSFP (0.2±0.1 vs. 0.5±0.2, p<0.01). All qualitative scores except for image noise were significantly higher in MSG-EPI than b-SSFP scans (p<0.05)., Conclusion: The MSG-EPI sequence is a promising technique for shortening scan time and yielding more homogenous image quality in MRA of thoracic aorta on 3T scanners compared with the b-SSFP., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Background: Cardiac computed tomography (CT) has the potential for fully four-dimensional (4D for 3D plus time) motion analysis of the heart. We aimed at developing a method for assessment and presentation of the 4D motion for multi-phase, contrast-enhanced cardiac CT data sets and demonstrating its clinical applicability., Methods: Four patients with normal cardiac function, old myocardial infarction (OMI), takotsubo cardiomyopathy, and hypertrophic cardiomyopathy (HCM) underwent contrast-enhanced cardiac CT for one heartbeat using a 320-row CT scanner with no tube current modulation. CT images for 10 cardiac phases (with a 10%-increment of the R-R interval) were reconstructed with the isotropic effective resolution of (0.5 mm) 3 An image-based motion-estimation (iME) algorithm, developed previously, has been used to estimate a time series of 3D cardiac motion, from the end-systole to the other nine phases. The iME uses down-sampled images with a resolution of (1.0 mm) 3 deforms the end-systole images non-rigidly to match images at other phases. Once the agreement is maximized, iME outputs a 3D motion vector defined for each voxel for each phase, that smoothly changes over voxels and phases. The proposed visualization method, which is called "vectors through a cross-sectional image (VCI)," presents 3D vectors from the end-diastole to the end-systole as arrows with an end-diastole CT slice. We performed visual assessment of the VCI with calculated the mean vector lengths to evaluate regional left ventricular (LV) contraction., Results: The VCI images showed the magnitude and direction of systolic 3D vectors, including the through-plane motion, and successfully visualized the relations of LV wall segments and abnormal regional wall motion. Decreased regional motion and asymmetric motion due to hypokinetic infarct segment, takotsubo cardiomyopathy, and hyper trophic cardiomyopathy was clearly observed. It was easy to appreciate the relation of the abnormal regional wall motion to the affected LV wall segments. The mean vector lengths of the affected segments with pathologies were clearly smaller than the other unaffected segments (1.2-1.7 mm versus 2.5-4.7 mm)., Conclusions: VCI images could capture the magnitude and direction of through-plane motion and show the relations of LV wall segments and abnormal wall motion., (Copyright © 2017 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.)

To compare the radiation dose and image noise of nonenhanced CT scans performed at 80, 100, and 120 kVp with tube current modulation (TCM) we used anthropomorphic phantoms of newborn, 1-year-old, and 5-year-old children. The noise index was set at 12. The image noise in the center of the phantoms at the level of the chest and abdomen was measured within a circumscribed region of interest. We measured the doses in individual tissues or organs with radio-photoluminescence glass dosimeters for each phantom. Various tissues or organs were assigned and the radiation dose was calculated based on the international commission on radiological protection definition. With TCM the respective radiation dose at tube voltages of 80, 100, and 120 was 29.71, 31.60, and 33.79 mGy for the newborn, 32.00, 36.79, and 39.48 mGy for the 1-year-old, and 32.78, 38.11, and 40.85 mGy for the 5-year-old phantom. There were no significant differences in the radiation dose among the tube voltages and phantoms (P > 0.05). Our comparison of the radiation dose using anthropomorphic phantoms of young children showed that the radiation dose of nonenhanced CT performed at different tube voltages with TCM was not significantly different., (© 2017 Hiroshima University. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)

Objectives: The objective of this study is to evaluate the usefulness of iterative model reconstruction designed for brain computed tomography (CT) (IMR-Neuro) for the diagnosis of acute ischemic stroke., Methods: This retrospective study included 20 patients with acute middle cerebral artery infarction who have undergone brain CT and 20 nonstroke patients (control). We reconstructed axial images with filtered back projection (FBP) and IMR-Neuro (slice thickness, 1 and 5 mm). We compared the CT number of the infarcted area, the image noise, contrast, and the contrast to noise ratio of the infarcted and the noninfarcted areas between the different reconstruction methods. We compared the performance of 10 radiologists in the detection of parenchymal hypoattenuation between 2 techniques using the receiver operating characteristic (ROC) techniques with the jackknife method., Results: The image noise was significantly lower with IMR-Neuro [5 mm: 2.5 Hounsfield units (HU) ± 0.5, 1 mm: 3.9 HU ± 0.5] than with FBP (5 mm: 4.9 HU ± 0.5, 1 mm: 10.1 HU ± 1.4) (P < 0.01). The contrast to noise ratio was significantly greater with IMR-Neuro (5 mm: 2.6 ± 2.1, 1 mm: 1.6 ± 1.3) than with FBP (5 mm: 1.2 ± 1.0; 1 mm: 0.6 ± 0.5) (P < 0.01). The value of the average area under the receiver operating curve was significantly higher with IMR-Neuro than FBP (5 mm: 0.79 vs 0.74, P = 0.04; 1 mm: 0.76 vs 0.69, P = 0.04)., Conclusions: Compared with FBP, IMR-Neuro improves the image quality and the performance for the detection of parenchymal hypoattenuation with acute ischemic stroke.

Rationale and Objectives: To investigate the stabilities of plaque attenuation and coronary lumen for different plaque types, stenotic degrees, lumen densities, and reconstruction methods using coronary vessel phantoms and the visualization of coronary plaques in clinical patients through coronary computed tomography (CT) angiography., Materials and Methods: We performed 320-detector volume scanning of vessel tubes with stenosis and a tube without stenosis using three types of plaque CT numbers. The stenotic degrees were 50% and 75%. Images were reconstructed with filtered back projection (FBP) and two types of iterative reconstructions (AIDR3D and FIRST [forward-projected model-based iterative reconstruction solution]), with stenotic CT number of approximately 40, 80, and 150 HU (Hounsfield unit), respectively. In each case, the tubing of the coronary vessel was filled with diluted contrast material and distilled water to reach the target lumen CT numbers of approximately 350 HU and 450 HU, and 0 HU, respectively. Peak lumen and plaque CT numbers were measured to calculate the lumen-plaque contrast. In addition, we retrospectively evaluated the image quality with regard to coronary arterial lumen and the plaque in 10 clinical patients on a 4-point scale., Results: At 50% stenosis, the plaque CT number with contrast enhancement increased for FBP and AIDR3D, and the difference in the plaque CT number with and without contrast enhancement was 15-44 HU for FBP and 10-31 HU for AIDR3D. However, the plaque CT number for FIRST had a smaller variation and the difference with and without contrast enhancement was -12 to 8 HU. The visual evaluation score for the vessel lumen was 2.8 ± 0.6, 3.5 ± 0.5, and 3.7 ± 0.5 for FBP, AIDR3D, and FIRST, respectively., Conclusions: The FIRST method controls the increase in plaque density and the lumen-plaque contrast. Consequently, it improves the visualization of coronary plaques in coronary CT angiography., (Copyright © 2017 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.)

We describe a case of ischemia complicating acute small-bowel obstruction in which retrospective on-demand spectral analysis using dual-layer spectral detector computed tomography (CT) provided a higher degree of confidence pertaining to the diagnosis. Dual-layer spectral detector CT enables retrospective on-demand spectral analysis, including virtual monochromatic imaging, iodine mapping, and determining the effective atomic number Z, without the need of a pre-scan setting requiring a special protocol, particularly facilitating emergency situations. Retrospective on-demand spectral analysis could improve the accuracy and diagnostic confidence in cases with ischemia complicating small-bowel obstruction.

Objective: To investigate the usefulness of modifying scanning parameters based on the size-specific dose estimate (SSDE) for a breast-dose reduction for chest CT., Materials and Methods: We scanned 26 women with a fixed volume CT dose index (CTDI vol ) (15 mGy) and another 26 with a fixed SSDE (15 mGy) protocol (protocol 1 and 2, respectively). In protocol 2, tube current was calculated based on the patient habitus obtained on scout images. We compared the mean breast dose and the inter-patient breast dose variability and performed linear regression analysis of the breast dose and the body mass index (BMI) of the two protocols., Results: The mean breast dose was about 35 % lower under protocol 2 than protocol 1 (10.9 mGy vs. 16.8 mGy, p < 0.01). The inter-patient breast dose variability was significantly lower under protocol 2 than 1 (1.2 mGy vs. 2.5 mGy, p < 0.01). We observed a moderate negative correlation between the breast dose and the BMI under protocol 1 (r = 0.43, p < 0.01); there was no significant correlation (r = 0.06, p = 0.35) under protocol 2., Conclusion: The SSDE-based protocol achieved a reduction in breast dose and in inter-patient breast dose variability., Key Points: • CT scan parameters can be modified based on the pre-scan SSDE. • The pre-scan SSDE is useful for a breast dose reduction. • The fixed SSDE protocol reduced individual variations in the breast dose.

Objective: The aim of this study was to evaluate the effect of cardiac output (CO) on aortic peak enhancement using protocols with different contrast material (CM) injection durations., Methods: We used a flow phantom that simulated the human circulatory system. Contrast material was injected at a rate of 4.0 mL/s for a period of 2.5, 5, 10, 15, or 20 seconds for a CO of 2.8, 4.2, and 5.6 L/min. Single-level serial computed tomography scans of the simulated aorta were acquired after the start of CM delivery, and aortic peak enhancement was recorded under the different injection protocols., Results: Under a long injection duration protocol (20 seconds), a decrease in CO increased aortic peak enhancement proportionally (CO of 2.8 L/min, 420 Hounsfield units [HU]; CO of 4.2 L/min, 365 HU; CO of 5.6 L/min, 291 HU). However, this effect was decreased under shorter injection duration protocols (5, 10, and 15 seconds); under the shortest (2.5-second) injection duration protocol, a decrease in CO resulted in a decrease in aortic peak enhancement (CO of 2.8 L/min, 36 HU; CO of 4.2 L/min, 51 HU; CO of 5.6 L/min, 55 HU)., Conclusions: The magnitude of the effect of CO on aortic peak enhancement depends on the CM injection duration.

Objective: The objective of our study was to compare contrast enhancement on CT angiography (CTA) images of the lower extremity in patients with suspected peripheral artery disease who did not undergo hemodialysis (HD) and patients who were scanned before or after HD., Materials and Methods: We divided 287 consecutive patients who underwent CTA of the lower extremity on a 64-MDCT scanner into three groups: group 1 patients (n = 151) were not dependent on HD, group 2 patients (n = 70) were dependent on HD and underwent HD less than 24 hours after CTA, and group 3 (n = 66) were dependent on HD and underwent HD less than 24 hours before CTA. We then compared the CT number in the popliteal artery at the level of the patella on all CTA images. A cardiologist and a radiology technologist visually evaluated the depiction of the descending genicular artery (DGA) on the CTA images and assigned a visualization score., Results: The median CT number was lowest in group 2 patients (373 HU vs 429 [group 1] and 418 [group 3] HU). The score for visualization of the DGA was significantly lower in group 2 than in group 1 (p = 0.02) and group 3 (p = 0.04)., Conclusion: At CTA, arterial enhancement decreases with the passage of time after HD likely because of the increase in intravascular volume. CTA that is performed within 24 hours after HD generates higher-quality images of the lower extremities than CTA that is performed within 24 hours before HD.

Rationale and Objectives: We compared the effect of iterative model reconstruction (IMR), filtered back projection (FBP), and hybrid iterative reconstruction (HIR) on coronary artery calcium (CAC) scoring., Materials and Methods: CAC scans of 30 consecutive patients (18 men and 12 women, age 70.1 ± 12.2 years) were reconstructed with FBP, HIR, and IMR, and the image noise was measured on all images. Two radiologists independently measured the CAC scores using semiautomated software, and interobserver agreement was evaluated. Statistical analysis included the Spearman correlation coefficient and Bland-Altman analysis., Results: The mean image noise on FBP, HIR, and IMR images was 48.0 ± 7.9, 29.6 ± 4.8, and 9.3 ± 1.3 Hounsfield units, respectively. The difference among all reconstruction combinations was significant (P < .01). The CAC score on HIR and IMR scans was 4.2% and 8.9% lower, respectively, than the CAC score on FBP images. There was no significant difference in the mean CAC score among the three reconstructions. The interobserver correlation was excellent for all three reconstructions (r 2  = 0.96 FBP, 0.99 HIR, 0.99 IMR); the best Bland-Altman measure of agreement was with IMR, followed by HIR and FBP., Conclusion: For CAC scoring, IMR can reduce the image noise and blooming artifacts, and consequently lowers the measured CAC score. IMR can lessen measurement variability and yield stable, reproducible measurements., (Copyright © 2017 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.)

Objective: We evaluated the effect of the age, sex, total body weight (TBW), height (HT) and cardiac output (CO) of patients on aortic and hepatic contrast enhancement during hepatic-arterial phase (HAP) and portal venous phase (PVP) computed tomography (CT) scanning., Methods: This prospective study received institutional review board approval; prior informed consent to participate was obtained from all 168 patients. All were examined using our routine protocol; the contrast material was 600 mg/kg iodine. Cardiac output was measured with a portable electrical velocimeter within 5 minutes of starting the CT scan. We calculated contrast enhancement (per gram of iodine: [INCREMENT]HU/gI) of the abdominal aorta during the HAP and of the liver parenchyma during the PVP. We performed univariate and multivariate linear regression analysis between all patient characteristics and the [INCREMENT]HU/gI of aortic- and liver parenchymal enhancement., Results: Univariate linear regression analysis demonstrated statistically significant correlations between the [INCREMENT]HU/gI and the age, sex, TBW, HT, and CO (all P < 0.001). However, multivariate linear regression analysis showed that only the TBW and CO were of independent predictive value (P < 0.001). Also, only the CO was independently and negatively related to aortic enhancement during HAP and to liver parenchymal enhancement when the contrast material injection protocol was adjusted for the TBW (P < 0.001)., Conclusion: By multivariate linear regression analysis only the TBW and CO were significantly correlated with aortic and liver parenchymal enhancement; the age, sex, and HT were not. The CO was the only independent factor affecting aortic and liver parenchymal enhancement at hepatic CT when the protocol was adjusted for the TBW.

Objective: A 320-row multidetector CT (MDCT) is expected for a good artery-vein separation in terms of temporal resolution. However, a shortened scan duration may lead to insufficient vascular enhancement. We assessed the optimal scan timing for the artery-vein separation at whole-brain CT angiography (CTA) when bolus tracking was used at 320-row MDCT., Methods: We analyzed 60 patients, who underwent whole-brain four-dimensional CTA. Difference in CT attenuation between the internal carotid artery (ICA) and the superior sagittal sinus (D att ) was calculated in each phase. Using a visual evaluation score for the depiction of arteries and veins, we calculated the difference between the mean score for the intracranial arteries and the mean score for the veins (D score ). We assessed the time at which the maximum D att and D score were simultaneously observed., Results: The maximum D att was observed at 6.0 s and 8.0 s in the arterial-dominant phase and at 16.0 s and 18.0 s in the venous-dominant phase after the contrast media arrival time at the ICA (T aa ). The maximum D score was observed at 6.0 s and 8.0 s in the arterial-dominant phase and at 16.0 s in the venous-dominant phase after the T aa . There were no statistically significant differences in D att (p = 0.375) or D score (p = 0.139) between these scan timings., Conclusion: The optimal scan timing for artery-vein separation at whole-brain CTA was 6.0 s or 8.0 s for the arteries and 16.0 s for the veins after the T aa . Advances in knowledge: Optimal scan timing allowed us to visualize intracranial arteries or veins with minimal superimposition.

Objectives: We evaluated the effects of a low contrast material (CM) dose protocol using 80-kVp on the image quality of hepatic multiphasic CT scans acquired on a 320-row CT scanner., Methods: We scanned 30 patients with renal insufficiency (eGFR < 45 mL/min/1.73 m 2 ) using 80-kVp and a CM dose of 300mgI/kg. Another 30 patients without renal insufficiency (eGFR > 60 mL/min/1.73 m 2 ) were scanned with the conventional 120-kVp protocol and the standard CM dose of 600mgI/kg. Quantitative image quality parameters, i.e. CT attenuation, image noise, and the contrast-to-noise ratio (CNR) were compared and the visual image quality was scored on a four-point scale. The volume CT dose index (CTDI vol ) and the size-specific dose estimate (SSDE) recorded with the 80- and the 120-kVp protocols were also compared., Results: Image noise and contrast enhancement were equivalent for the two protocols. There was no significant difference in the CNR of all anatomic sites and in the visual scores for overall image quality. The CTDI vol and SSDE were approximately 25-30 % lower under the 80-kVp protocol., Conclusion: Hepatic multiphase CT using 80-kVp on a 320-row CT scanner allowed for a decrease in the CM dose and a reduction in the radiation dose without image quality degradation in patients with renal insufficiency., Key Points: • The 80-kVp CT protocol enabled reduction of contrast dose by 50 % • The 80-kVp CT protocol reduced the radiation dose by 25-33 % • There was no degradation in the image quality of the 80-kVp protocol.

Background: An optimal metal artifact reduction (MAR) technique is needed for a reliable and accurate image-based diagnosis., Purpose: Using a 320-row scanner, we compared the dual-energy computed tomography (CT)-based monochromatic and the single-energy metal artifact reduction (SEMAR) techniques for CT venography (CTV) to identify the better imaging method for diagnosing deep vein thrombosis (DVT) in patients who had undergone knee replacement surgery., Material and Methods: Twenty-three consecutive patients with suspected DVT after unilateral knee replacement surgery underwent dual-energy CT (135/80 kVp). Monochromatic images of 35-135 keV were generated; the monochromatic image with the best signal-to-noise ratio (SNR) of the popliteal vein near the metal prosthesis were selected. The projection data of 80 kVp were reconstructed using MAR algorithm. The mean SNR ON MAR and the best SNR ON monochromatic images were compared. Two radiologists evaluated visualization of the metal artifacts on a four-point scale where 1 = extensive artifacts, 2 = strong artifacts, 3 = mild artifacts, and 4 = minimal artifacts., Results: The mean SNR was significantly higher on the MAR than the monochromatic images (12.8 ± 4.7 versus 7.7 ± 5.1, P  < 0.01) and the visual scores were significantly higher for MAR than monochromatic images (2.6 ± 0.8 versus 1.3 ± 0.4, P  < 0.01)., Conclusion: For CTV after knee replacement surgery, the MAR technique is superior to the monochromatic imaging technique.

It is well known that head computed tomography (CT) examination is an area affected by beam hardening because the brain parenchyma surrounded by thick bones is an object to be imaged. Therefore, it is essential to use the beam hardening correction process. However, the beam hardening correction processing varies depending on the apparatus. The purpose of this study is to verify the influence on the image by the difference of the beam hardening correction method from the CT value of the phantom and to prove the effect of the beam hardening correction method. We obtained CT value fluctuation amount, CT value correction amount, and CT value correction effect by the beam hardening from the CT value measurement result of phantom imaging. This was compared with 1 st pass method, 2 nd pass method, and Brain forward projected model-based iterative reconstruction solution. From the results, it was confirmed that the intensity and precision of the beam hardening correction process differ depending on the correction method. As a result, in the head CT examination, even if the same subject is imaged, there is a possibility of a difference in CT value due to the beam hardening correction method.

Background: To figure out the relationship between image noise and contrast noise ratio (CNR) at different tube voltages, using anthropomorphic new-born and 1-year-old phantoms, and to discuss the feasibility of radiation dose reduction, based on the obtained CNR index from image noise. We performed helical scans of the anthropomorphic new-born and 1-year-old phantoms. The CT numbers of the simulated aorta and image noise of the simulated mediastinum were measured; then CNR was calculated on 80, 100, and 120-kVp images reconstructed with filtered back projection (FBP) and iterative reconstruction (IR). We also measured the center and surface dose in the case of CNR of 14 using radio-photoluminescence glass dosimeters., Results: The CT number of the simulated aorta was increased with decreasing tube voltage from 120 to 80 kVp (362.5-535.1 HU for the new-born, 358.9-532.6 HU for the 1-year-old). At CNR of 14, the center dose was 0.4, 0.6 and 0.9 mGy at FBP and 0.5, 0.6 and 0.9 mGy at IR and with the new-born phantom acquired at 80, 100 and 120 kVp, respectively. The center dose for FBP image was reduced by 56% at 80 kVp, 34% at 100 kVp for the new-born and 36% at 80 kVp, 22% at 100 kVp for the 1-year-old compared with that at 120 kVp. We obtained a relationship between image noise and CNR at different tube voltages using the anthropomorphic new-born and 1-year-old phantoms., Conclusion: The use of index of CNR with low-tube voltage may achieve further radiation dose reduction in pediatric CT examination.

Purpose: Transluminal-attenuation-gradient (TAG) may reflect patient characteristics and physiological parameters. Furthermore, TAG may be affected by factors such as the CT scanner speed, scanning method, scan timing after contrast-medium (CM) injection, and the injection methods. The purpose of our study was to investigate quantitative TAG at different scan timing points after CM injection for coronary CT angiography., Materials and Methods: Using a CM flow phantom and two types of connecting tube mimicking 0% and 70% coronary artery stenosis, we performed 320-detector volume scanning. The heart rate was set at 60bpm and cardiac-output (CO) at 2.0 and 4.0 l/min, respectively. The acquisition time repeated at 0.5-s intervals for 40 and 25s at a CO of 2.0- and 4.0 l/min. We measured the CT number on the same slice level, calculated the time-density-curve (TDC) and the TAG at each time point., Results: At COs of 2.0 and 4.0 l/min at 0% stenosis, TAG exhibited smaller variations (-3.02 to +0.55HU/cm at 2.0 l/min, -2.63 to +0.43HU/cm at 4.0 l/min) than at 70% stenosis at each time point along the TDC. Compared with a CO at 2.0 l/min with 70% stenosis, the TAG curve for a CO at 4.0 l/min gradually changed with time (-6.64 to +1.18HU/cm at 2.0 l/min vs. -3.46 to +2.75HU/cm at 4.0 l/min)., Conclusion: The TAG value was affected by scan timing after CM injection and by CO although the size of the connecting tube with and without stenosis was identical., (Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Rationale and Objectives: We investigated the effects of small focal spot (SFS) imaging and iterative model reconstruction (IMR) on the image quality of computed tomography angiographs (CTA) in patients with peripheral arterial disease., Materials and Methods: We divided 60 consecutive patients with suspected or confirmed peripheral artery disease into two equal groups. One group underwent large focal spot scanning under our standard CTA protocol with hybrid iterative reconstruction (iDose(4)) (protocol 1), and the other underwent scanning with the SFS protocol and IMR (protocol 2). Quantitative image quality parameters, ie, arterial computed tomography attenuation, image noise, and the contrast-to-noise ratio, were compared and the visual image quality (depiction of each vessel) was scored on a 5-point scale., Results: There was no significant difference in the arterial attenuation among all evaluated slice levels. The mean image noise was significantly lower under protocol 2 and the contrast-to-noise ratio was significantly higher at all slice levels. The visual scores assigned to the two protocols for the depiction of large vessels, such as the abdominal aorta and iliac artery, were comparable. However, the mean visual scores for small vessels in the lower extremities were significantly higher under protocol 2., Conclusion: CTA with SFS and IMR yielded significantly better qualitative and quantitative image quality especially for small vessels., (Copyright © 2016 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.)

Objectives: We evaluated the effect of a single-energy metal artefact reduction (SEMAR) algorithm for metallic coil artefact reduction in body imaging., Methods: Computed tomography angiography (CTA) was performed in 30 patients with metallic coils (10 men, 20 women; mean age, 67.9 ± 11 years). Non-SEMAR images were reconstructed with iterative reconstruction alone, and SEMAR images were reconstructed with the iterative reconstruction plus SEMAR algorithms. We compared image noise around metallic coils and the maximum diameters of artefacts from coils between the non-SEMAR and SEMAR images. Two radiologists visually evaluated the metallic coil artefacts utilizing a four-point scale: 1 = extensive; 2 = strong; 3 = mild; 4 = minimal artefacts., Results: The image noise and maximum diameters of the artefacts of the SEMAR images were significantly lower than those of the non-SEMAR images (65.1 ± 33.0 HU vs. 29.7 ± 10.3 HU; 163.9 ± 54.8 mm vs. 10.3 ± 19.0 mm, respectively; P < 0.001). Better visual scores were obtained with the SEMAR technique (3.4 ± 0.6 vs. 1.0 ± 0.0, P < 0.001)., Conclusions: The SEMAR algorithm significantly reduced artefacts caused by metallic coils compared with the non-SEMAR algorithm. This technique can potentially increase CT performance for the evaluation of post-coil embolization complications., Key Points: • The new algorithm involves a raw data- and image-based reconstruction technique. • The new algorithm mitigates artefacts from metallic coils on body CT images. • The new algorithm significantly reduced artefacts caused by metallic coils. • The metal artefact reduction algorithm improves CT image quality after coil embolization.

Background: Model-based type iterative reconstruction algorithms with fast reconstruction times are now available. The clinical feasibility of their reconstruction has not been evaluated adequately., Purpose: To investigate the effects of model-based type iterative reconstruction, i.e. iterative model reconstruction (IMR), with fast reconstruction time on the qualitative and quantitative image quality at low-dose chest computed tomography (CT)., Material and Methods: Thirty-one patients undergoing low-dose screening chest CT were enrolled. Images were reconstructed using filtered back projection (FBP), hybrid iterative reconstruction (HIR), and IMR algorithms. The CT attenuation and image noise for all reconstructions were calculated at the lung apex, middle, and base. Using a 4-point scale, two reviewers visually evaluated the image quality with respect to vessel sharpness, streak artifact, the mediastinum, and the overall image quality of each reconstruction method., Results: The mean estimated effective dose was 1.0 ± 0.3 mSv. There was no significant difference in the CT attenuation among the three reconstructions. The mean image noise of FBP, HIR, and IMR images was 124.3 ± 57.3, 34.8 ± 10.2, and 22.9 ± 5.8 HU, respectively. There were significant differences for all comparison combinations among the three methods (P < 0.01). The best subjective overall image quality for the lung and mediastinum was obtained with IMR (P < 0.01). The reconstruction time for IMR was within 3 min in all cases., Conclusion: At low-dose chest CT, IMR can improve the qualitative and quantitative visualization of both lung and mediastinal structures especially in the lung apex at a clinically acceptable reconstruction time. Its application may improve diagnostic performance., (© The Foundation Acta Radiologica 2015.)

Rationale and Objectives: The characterization of plaques based on their computed tomography (CT) number is important for the detection of vulnerable atherosclerotic plaques. An earlier in vitro study showed that intravascular attenuation affected the attenuation of coronary atherosclerotic plaques. We attempted to validate this finding in vivo and here we introduce a dual-phase coronary CT angiography (CCTA) technique to address this issue., Materials and Methods: Institutional ethics committee approval and informed consent were obtained. Thirty patients (30 noncalcified plaques) underwent dual-phase CCTA. Two CT datasets were obtained, one with coronary artery enhancement and the other without coronary artery enhancement. The CT number of the plaque and the adjacent vessel lumen was measured in a circular region of interest on curved planar reconstruction images. The region of interest setting was consistent between the two CT datasets. We performed linear regression analysis of the changes in the CT numbers (ΔHounsfield unit), calculated by subtracting the two CT datasets, for the lumen and for the plaque. We also evaluated the relationship between plaque attenuation on nonenhanced coronary artery images and luminal attenuation with and without contrast enhancement., Results: The ΔHounsfield unit for the plaque and the lumen showed a strong correlation (r = 0.61). There was no significant correlation between plaque attenuation on nonenhanced coronary artery images and luminal attenuation with and without contrast enhancement (r = 0.23 and 0.24, respectively)., Conclusions: Intravascular attenuation changed the attenuation of coronary atherosclerotic plaques. Using the copy-paste technique, the CT number of identical plaques can be measured in registered dual-phase CCTA images for the evaluation of coronary plaques., (Copyright © 2015 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.)

Background: The epicardial fat volume (EFV) measured by cardiac CT has emerged as an important parameter for understanding the pathophysiology of coronary atherosclerosis., Objective: We investigated the variability and reproducibility of EFV measurements and evaluated the effect of model-based type iterative reconstruction (M-IR) on measurement results., Methods: Non-contrast cardiac CT data (tube voltage 120-kVp, tube current time product 32 mAs) of 30 consecutive patients were reconstructed with filtered back projection (FBP), hybrid type iterative reconstruction (H-IR), and M-IR using a slice thickness of 3.0 mm. CT attenuation and image noise was measured for all reconstructions. Two observers independently quantified EFV using semi-automated software and interobserver agreement was evaluated., Results: There was no significant difference in the CT attenuation of the ascending aorta among the three reconstructions. The mean image noise on FBP-, H-IR-, and M-IR images was 48.0 ± 7.9 HU, 29.6 ± 4.8 HU, and 9.3 ± 1.3 HU, respectively; there was a significant difference among all comparison combinations for the three reconstructions (p < 0.01). FBP yielded the highest EFV among the three reconstructions (171.0 ± 54.9 cm(3) [FBP], 153.8 ± 53.1 cm(3) [H-IR], and 134.0 ± 46.4 cm(3) [M-IR]). For all three reconstructions, interobserver correlations were excellent (r = 0.91 [FBP], 0.93 [H-IR], and 0.96 [M-IR]). Interobserver comparisons showed that the lowest Bland-Altman limit of agreement was with M-IR (mean difference 2.0 ± 4.9%, 95% limit of agreement, -24.0 to 28.0%) followed by H-IR (-2.6 ± 7.1%, -39.8 to 34.6%) and FBP (-0.2 ± 8.6%, -45.3- to 45.0%)., Conclusion: For the quantification of epicardial fat by cardiac CT, model-based iterative reconstruction can improve the image quality and lessen measurement variability., (Copyright © 2016 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.)

Rationale and Objectives: The purpose of this study was to assess the effect of a low-tube-voltage technique and iterative reconstruction (IR) on the radiation dose and image quality of computed tomography colonography (CTC)., Materials and Methods: We studied 30 patients (14 women and 16 men; mean age, 64.5 ± 13.1 years; range, 39-90 years) with colorectal cancer referred for surgical treatment. All underwent CTC with fecal tagging under a standard 120-kVp protocol in the supine position and a 100-kVp protocol in the prone position. The 120-kVp images were reconstructed with filtered back projection (FBP). The 100-kVp images were postprocessed using FBP and a hybrid type of IR (adaptive iterative dose reduction 3D). The effective radiation dose (ED), image noise, and contrast-to-noise ratio (CNR) were compared among the three protocols. The visual image quality was scored on a four-point scale., Results: The mean ED was significantly lower under the 100-kVp protocol than the 120-kVp protocol, resulting in a 27% radiation dose decrease (3.5 ± 2.0 vs 2.5 ± 1.5 mSv; P < .01). Image noise decreased by 48%, and the mean attenuation of tagged fluid increased from 452 to 558 HU on images acquired at 100 kVp with IR compared to that in the 120-kVp protocol; these differences were significant. The mean CNR was significantly higher under the 100 kVp with IR than the other two protocols. We found no significant differences in the visual scores for diagnostic utility between the 100 kVp with IR and the 120 kVp with FBP protocol (P = .10)., Conclusions: Low-tube-voltage CTC reduced the radiation dose by approximately 27% while maintaining the image quality., (Copyright © 2016 AUR. Published by Elsevier Inc. All rights reserved.)

Purpose: We used pediatric and adult anthropomorphic phantoms to compare the radiation dose of low- and standard tube voltage chest and abdominal non-contrast-enhanced computed tomography (CT) scans. We also discuss the optimal low tube voltage for non-contrast-enhanced CT., Methods: Using a female adult- and three differently-sized pediatric anthropomorphic phantoms we acquired chest and abdominal non-contrast-enhanced scans on a 320-multidetector CT volume scanner. The tube voltage was set at 80-, 100-, and 120 kVp. The tube current was automatically assigned on the CT scanner in response to the set image noise level. On each phantom and at each tube voltage we measured the surface and center dose using high-sensitivity metal-oxide-semiconductor field-effect transistor detectors., Results: The mean surface dose of chest and abdominal CT scans in 5-year olds was 4.4 and 5.3 mGy at 80 kVp, 4.5 and 5.4 mGy at 100 kV, and 4.0 and 5.0 mGy at 120 kVp, respectively. These values were similar in our 3-pediatric phantoms (p > 0.05). The mean surface dose in the adult phantom increased from 14.7 to 19.4 mGy for chest- and from 18.7 to 24.8 mGy for abdominal CT as the tube voltage decreased from 120 to 80 kVp (p < 0.01)., Conclusion: Compared to adults, the surface and center dose for pediatric patients is almost the same despite a decrease in the tube voltage and the low tube voltage technique can be used for non-contrast-enhanced chest- and abdominal scanning., (Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Size-specific dose estimate (SSDE) takes into account the patient size but remains to be fully validated for adult coronary computed tomography angiography (CCTA). We investigated the appropriateness of SSDE for accurate estimation of patient dose by comparing the SSDE and the volume CT dose index (CTDIvol) in adult CCTA. This prospective study received institutional review board approval, and informed consent was obtained from each patient. We enrolled 37 adults who underwent CCTA with a 320-row CT. High-sensitivity metal oxide semiconductor field effect transistor dosimeters were placed on the anterior chest. CTDIvol reported by the scanner based on a 32-cm phantom was recorded. We measured chest diameter to convert CTDIvol to SSDE. Using linear regression, we then correlated SSDE with the mean measured skin dose. We also performed linear regression analyses between the skin dose/CTDIvol and the body mass index (BMI), and the skin dose/SSDE and BMI. There was a strong linear correlation (r = 0.93, P < 0.001) between SSDE (mean 37 ± 22 mGy) and mean skin dose (mean 17.7 ± 10 mGy). There was a moderate negative correlation between the skin dose/CTDIvol and BMI (r = 0.45, P < 0.01). The skin dose/SSDE was not affected by BMI (r = 0.06, P > 0.76). SSDE yields a more accurate estimation of the radiation dose without estimation errors attributable to the body size of adult patients undergoing CCTA.

Rationale and Objectives: We delivered the saline chaser via a spiral flow-generating tube or a conventional connecting tube and compared arterial enhancement at computed tomography angiography (CTA) of the lower extremities., Materials and Methods: We randomly assigned 100 patients whose ankle bronchial pressure index or clinical symptoms were suspect of peripheral arterial disease to a spiral flow-generating tube (protocol A) or a conventional connecting-tube protocol (protocol B) and performed CTA of the lower extremities. The test bolus was delivered under protocol A or B, and the CT numbers recorded for each protocol were compared. Two radiological technologists visually evaluated the descending genicular artery., Results: In the test injection, the median CT number for the popliteal artery was significantly higher with protocol A than B (204.5 HU vs. 170.5 HU, P = 0.03). For CTA of the lower extremities, the median CT number for the popliteal artery at the level of the patella was 436.1 HU (range, 259-608 HU) under protocol A; with protocol B, it was 382.9 HU (range, 244-564 HU) (P = 0.02). The visual score assigned in the descending genicular artery was statistically significantly higher under protocol A than B (P = 0.03)., Conclusions: Use of the spiral flow-generating tube increased the effect of the saline chaser and significantly improved arterial enhancement from the abdominal aorta to the arteries of the foot at CTA of the lower extremities.

Purpose: To investigate differences in image-to-image variations between full- and half-scan reconstruction on myocardial CT perfusion (CTP) study., Methods: Using a cardiac phantom we performed ECG-gated myocardial CTP on a second-generation 320-multidetector CT volume scanner. The heart rate was set at 60 bpm; once per second for a total of 24 s were performed. CT images were acquired at 80- and 120 kVp and subjected to full- and half-scan reconstruction. On images acquired at the same slice level we then measured image-to-image variations, coefficients of variance (CV), and image noise., Results: The image-to-image variations with full- and half-scan reconstruction were 1.3 HU vs. 27.2 HU at 80 kVp (p < 0.001) and 0.70 HU vs. 9.3 HU at 120 kVp (p < 0.001) even though the mean HU value was almost the same for both reconstruction methods. The CV of 80- and 120-kVp images of the left ventricular cavity decreased by 0.16% and 0.17%, respectively, with full-scan reconstruction; with half-scan reconstruction it decreased by 3.34% and 2.30%, respectively. Compared with half-scan reconstruction, the image noise was reduced by 27.2% at 80 kVp and by 28.0% at 120 kVp with full-scan reconstruction., Conclusion: Myocardial CTP with full-scan reconstruction substantially decreased image-to-image variations and provided accurate CT attenuation., (Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Background: Body weight, body mass index (BMI), and scout X-ray radiographic attenuation can be used to predict image noise on computed tomographic coronary angiography (CTCA) images., Purpose: To use a formula to predict patient-specific image noise and then select an appropriate CTCA patient-specific tube voltage for better radiation control., Material and Methods: Forty-eight patients who underwent CTCA imaging at 120 kVp were reviewed, and their patient information and scouting X-ray radiographic attenuations were recorded to identify the best correlations between patient data and image noise and to develop a predicted image noise formula. Subsequently, 54 patients subjected to scanning at 100 or 120 kVp, depending on the noise predicted by our formula, were prospectively studied. Two radiologists visually assessed the image quality of the right coronary artery (RCA), left anterior descending artery (LAD), and left circumflex artery (LCX) by consensus readings., Results: The predicted image noise = 0.939 BMI + 0.025 scouting attenuation + 20.16. The median value of the overall image noise was 30.55 HU at 120 kVp and 29.85 HU at 100 kVp. The mean visual evaluation scores at 100 and 120 kVp were 3.25 and 3.24 for the proximal RCA, 3.40 and 3.26 for the proximal LAD, and 3.30 and 3.15 for the proximal LCX, respectively., Conclusion: The BMI and scouting X-ray radiographic attenuation can be combined to predict the CTCA image noise. Our prediction formula is useful for deciding when to switch from the 120- to the 100-kVp technique., (© The Foundation Acta Radiologica 2014.)

Purpose: The purpose of our study was to investigate the added value of the single-energy projection-based metallic artifact reduction (SEMAR) technique on the visualization and diagnostic confidence of oral cavity cancers., Materials and Methods: Contrast-enhanced CT was performed on 40 patients with dental metalwork. Of these, 18 patients had pathologically confirmed oral cavity cancer, and the other 22 patients had no lesions. CT attenuation and noise in the oral cavity were compared between the conventional and SEMAR images. Two radiologists visually graded the diagnostic confidence on a 5-point scale from 1 (definitely absent) to 5 (definitely present). The value of the SEMAR was assessed in a receiver-operating characteristic curve analysis., Results: The artifact of the SEMAR images was significantly lower than that of the conventional images (38.4 ± 18.0 HU vs. 187.7 ± 162.7 HU; P < 0.01). Reviewers 1 and 2 detected 10 and 7 more lesions with the SEMAR, respectively. Areas under the curve for the conventional and SEMAR reconstruction were 0.761 and 0.942, respectively, for reviewer 1 and 0.701 and 0.864, respectively, for reviewer 2., Conclusion: The SEMAR significantly improved the oral cavity cancer visualization and diagnostic confidence.

The influence of newer-generation CT on the clinical indications and appropriateness of cardiac CT has not been adequately surveyed. We aimed to evaluate the distribution of appropriateness ratings and test the outcomes of cardiac CT using second-generation 320-row CT. The 2010 appropriate use criteria (AUC) were applied at the point of service to a consecutive series of patients (N = 309) who were referred for cardiac CT. The CT indication was determined based on interviews and medical records. The proportions of patients within the categories of appropriate (A), uncertain (U), inappropriate (I), and not covered were described. The prevalence of significant coronary artery disease (CAD) was also compared among the categories. The proportions were 49.2%, 25.9%, and 20.7% for appropriate, uncertain, and inappropriate indication, respectively. The indication that was not covered was only 4.2%. Significant CAD was more frequently observed for uncertain- than appropriate indication (42.5% vs 27.6%; P = 0.03), although the number of significant stenosed segments was not different (P = 0.13). The recent advancement of cardiac CT increased the proportion of uncertain scans, which were associated with a high prevalence of significant CAD.

Purpose: To investigate whether a newly-developed single-energy metal artifact reduction (SEMAR) algorithm applied to images acquired on a 320-MDCT volume scanner reduces image artifacts from dental metal., Methods: We inserted the lower right teeth covered with a dental metal alloy and crown in a skull phantom and performed single-volume scanning on a second-generation 320-MDCT scanner. A 12-mm diameter spherical lesion was placed either close to or far from the dental metal. The tube voltage and current were 120 kVp and 80 or 155 mA, respectively. Images were reconstructed with filtered back projection (FBP) or iterative reconstruction (IR), with or without SEMAR. We calculated the signal-to-artifact ratios (SAR) to quantify the visibility of the lesion. Two radiologists inspected 96 images (48 with lesion and 48 without) for the presence or absence of the lesion using a 5-point ordinal scale (1 = definitely absent to 5 = definitely present)., Results: On images reconstructed with FPB and IR with SEMAR, streak artifacts from the dental metal were reduced substantially compared to images without SEMAR. At 155 mA with the lesion near the dental metal, the SARs were better on FBP and IR images (FBP: 1.7 and 0.5 with and without SEMAR, respectively; IR: 1.6 and 0.9 with and without SEMAR, respectively). The observer visual scores improved with SEMAR (FBP: 4.2 and 3.2 with and without SEMAR, respectively; IR: 4.2 and 3.0)., Conclusion: The SEMAR algorithm reduces dental metal artifacts and improves lesion detectability and image quality in patients with oral cavity lesions., (Copyright © 2014 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)