Yutaka Tanami

Virtual Monochromatic Spectral Imaging with Fast Kilovoltage Switching: Improved Image Quality as Compared with That Obtained with Conventional 120-kVp CT

PURPOSE To compare image quality obtained in phantoms with virtual monochromatic spectral (VMS) imaging with that obtained with conventional 120-kVp computed tomography (CT) for a given radiation dose. MATERIALS AND METHODS Three syringes were filled with a diluted contrast medium (each syringe contained a contrast medium with a different iodine concentration [5, 10, or 15 mg of iodine per milliliter]), and a fourth syringe was filled with water. These syringes were placed in a torso phantom meant to simulate the standard human physique. The phantom was examined with a CT system and use of the fast kilovoltage switching (80 and 140 kVp) and conventional (120 kVp) modes. Image noise and contrast-to-noise (CNR) ratio were analyzed on VMS images and 120-kVp CT images. RESULTS Image noise on VMS images in the range of 67-72 keV was significantly lower than that on the 120-kVp CT images (P < .014). Image noise was lowest at 69 keV and was 12% lower when compared with that on 120-kVp CT images. CNR on the VMS images was highest at 68 keV. CNR on the VMS images obtained at 68 keV in the syringes filled with diluted contrast material (5, 10, and 15 mg of iodine per milliliter) was 28%, 31%, and 30% higher, respectively, compared with that on the 120-kVp CT images (P < .001). CONCLUSION VMS imaging at approximately 70 keV yielded lower image noise and higher CNR than did 120-kVp CT for a given radiation dose. VMS imaging has the potential to replace 120-kVp CT as the standard CT imaging modality, since optimal VMS imaging may be expected to yield improved image quality in a patient with standard body habitus.

Model-based iterative reconstruction technique for ultralow-dose computed tomography of the lung: a pilot study.

ObjectivesThe aim of this study was to assess the effectiveness of a model-based iterative reconstruction (MBIR) in improving image quality and diagnostic performance of ultralow-dose computed tomography (ULDCT) of the lung. Materials and MethodsThe institutional review board approved this study, and all patients provided written informed consent. Fifty-two patients underwent low-dose computed tomography (LDCT) (screening-dose, 50 mAs) and ULDCT (4 mAs) of the lung simultaneously. The LDCT images were reconstructed with filtered back projection (LDCT-FBP images) and ULDCT images were reconstructed with both MBIR (ULDCT-MBIR images) and FBP (ULDCT-FBP images). On all the 156 image series, objective image noise was measured in the thoracic aorta, and 2 blinded radiologists independently assessed subjective image quality. Another 2 blinded radiologists independently evaluated the ULDCT-MBIR and ULDCT-FBP images for the presence of noncalcified and calcified pulmonary nodules; LDCT-FBP images served as the reference. Paired t test, Wilcoxon signed rank sum test, and free-response receiver-operating characteristic analysis were used for statistical analysis of the data. ResultsCompared with LDCT-FBP and ULDCT-FBP, ULDCT-MBIR had significantly reduced objective noise (both P <; 0.001). Subjective noise on the ULDCT-MBIR images was comparable with that on the LDCT-FBP images but lower than that on the ULDCT-FBP images (P <; 0.001). Artifacts on ULDCT-MBIR images were more numerous than those on the LDCT-FBP images (P = 0.007) but fewer than those on the ULDCT-FBP images (P <; 0.001). Compared with the LDCT-FBP images, ULDCT-MBIR and ULDCT-FBP images showed reduced image sharpness (both P <; 0.001). All the ULDCT-MBIR images showed a blotchy pixelated appearance; however, the performance of ULDCT-MBIR was significantly superior to that of ULDCT-FBP for the detection of noncalcified pulmonary nodules (P = 0.002). The average true-positive fractions for significantly sized noncalcified nodules (≥4 mm) and small noncalcified nodules (<;4 mm) on the ULDCT-MBIR images were 0.944 and 0.884, respectively, when LDCT-FBP images were used as reference. All of the calcified nodules were detected by both the observers on both the ULDCT-MBIR and ULDCT-FBP images. ConclusionAs compared with FBP, MBIR enables significant reduction of the image noise and artifacts and also better detection of noncalcified pulmonary nodules on ULDCT of the lung. Compared with LDCT-FBP images, ULDCT-MBIR images showed significantly reduced objective noise and comparable subjective image noise. Almost all of the noncalcified nodules and all of the calcified nodules could be detected on the ULDCT-MBIR images, when LDCT-FBP images were used as the reference.

Dose reduction in chest CT: Comparison of the adaptive iterative dose reduction 3D, adaptive iterative dose reduction, and filtered back projection reconstruction techniques

OBJECTIVES To assess the effectiveness of adaptive iterative dose reduction (AIDR) and AIDR 3D in improving the image quality in low-dose chest CT (LDCT). MATERIALS AND METHODS Fifty patients underwent standard-dose chest CT (SDCT) and LDCT simultaneously, performed under automatic exposure control with noise index of 19 and 38 (for a 2-mm slice thickness), respectively. The SDCT images were reconstructed with filtered back projection (SDCT-FBP images), and the LDCT images with FBP, AIDR and AIDR 3D (LDCT-FBP, LDCT-AIDR and LDCT-AIDR 3D images, respectively). On all the 200 lung and 200 mediastinal image series, objective image noise and signal-to-noise ratio (SNR) were measured in several regions, and two blinded radiologists independently assessed the subjective image quality. Wilcoxons signed rank sum test with Bonferronis correction was used for the statistical analyses. RESULTS The mean dose reduction in LDCT was 64.2% as compared with the dose in SDCT. LDCT-AIDR 3D images showed significantly reduced objective noise and significantly increased SNR in all regions as compared to the SDCT-FBP, LDCT-FBP and LDCT-AIDR images (all, P ≤ 0.003). In all assessments of the image quality, LDCT-AIDR 3D images were superior to LDCT-AIDR and LDCT-FBP images. The overall diagnostic acceptability of both the lung and mediastinal LDCT-AIDR 3D images was comparable to that of the lung and mediastinal SDCT-FBP images. CONCLUSIONS AIDR 3D is superior to AIDR. Intra-individual comparisons between SDCT and LDCT suggest that AIDR 3D allows a 64.2% reduction of the radiation dose as compared to SDCT, by substantially reducing the objective image noise and increasing the SNR, while maintaining the overall diagnostic acceptability.

Virtual monochromatic spectral imaging for the evaluation of hypovascular hepatic metastases: the optimal monochromatic level with fast kilovoltage switching dual-energy computed tomography.

Objectives:The purpose of this study was to select the optimal monochromatic level for virtual monochromatic spectral (VMS) imaging to minimize the image noise of the liver parenchyma and to acquire a high contrast-to-noise ratio (CNR) of hypovascular hepatic metastases in the portal-dominant phase. Materials and Methods:This study was conducted with the approval of our institutional review board, and written informed consent was obtained from all the participating patients. Ninety patients with hepatic metastases were scanned by fast kilovoltage switching dual-energy computed tomography in the portal-dominant phase. One hundred one sets of VMS images in the range of 40 to 140 keV at 1-keV intervals were reconstructed. The image noise of the liver parenchyma in each patient and the CNR of each metastasis (n = 303) were measured on all the 101 VMS image sets. Data were analyzed by the paired t test and mixed-effects model. Bonferronis method was used for multiple comparisons. Results:The lowest noise of the liver parenchyma was obtained in 6, 15, 31, 29, 7, 1, and 1 patient at 67, 68, 69, 70, 71, 72, and 73 keV, respectively. The mean noise of the liver parenchyma on the 69-keV VMS images in all 90 patients was significantly lower than that on the 67-, 68-, 71-, 72-, and 73-keV VMS images (P < 0.001); however, there was no significant difference in the mean noise of the liver parenchyma between the 69-keV and 70-keV VMS images (P = 0.279). For 95% of the hepatic metastases (288/303 metastases), the highest metastasis-to-liver CNR was obtained in the 66- to 71- keV VMS images. The mean metastasis-to-liver CNR for the 303 metastases was numerically highest at 68 keV; however, there was no significant difference in the mean metastasis-to-liver CNR between the 68-keV and 69-keV images (P = 0.737) or between the 68-keV and 70-keV images (P = 0.103). Conclusions:VMS imaging at approximately 70 keV (69–70 keV) yielded the lowest image noise of the liver parenchyma and a high CNR for hypovascular hepatic metastases in the portal-dominant phase.

Computed Tomographic Attenuation Value of Coronary Atherosclerotic Plaques With Different Tube Voltage: An Ex Vivo Study

Objectives: To compare the diagnostic performance of computed tomographic (CT) attenuation and CT attenuation ratio at different tube voltages for ex vivo plaque characterization. Materials and Methods: Human coronary arteries were obtained at the time of autopsy in 15 subjects. The coronary arteries were serially cut into 5-mm-long segments and scanned ex vivo using 4 sets of tube voltages and tube currents (80 kV, 660 mA; 100 kV, 500 mA; 120 kV, 400 mA; and 140 kV, 340 mA). The CT attenuation value at the center of each plaque was obtained, and the ratio of the CT attenuation value at the 80-kV setting divided by that at the 140-kV setting (Hounsfield ratio [HR], 80:140) was calculated. Separate receiver operating characteristic (ROC) analyses were used to assess the usefulness of the CT attenuation value and the 80:140 HR for the differential diagnosis of lipid-rich plaques from other types of plaques. Results: A total of 93 coronary plaques were detected macroscopically. Histological examination revealed 39 lipid-rich, 24 calcified, and 30 fibrotic plaques. At all the tube voltages, the CT attenuation values of the lipid-rich plaques were lower than those of the calcified plaques, whereas the CT attenuation values of the lipid-rich and fibrotic plaques overlapped. An ROC analysis showed that the area under the curve (AUC) for the differential diagnosis of lipid-rich plaques from fibrotic plaques was 0.813 at 80 kV, 0.772 at 100 kV, 0.682 at 120 kV, or 0.651 at 140 kV. Regarding the 80:140 HR, the AUC was 0.952 (0.029). The AUC was significantly larger at 80 and 100 kV and 80:140 HR compared with the AUC at 120 kV. Conclusions: The diagnostic performance of CT analysis for ex vivo plaque characterization was superior at lower energy settings and using the dual-energy method.

Abdominal CT: an intra-individual comparison between virtual monochromatic spectral and polychromatic 120-kVp images obtained during the same examination

OBJECTIVES To compare quantitative and subjective image quality between virtual monochromatic spectral (VMS) and conventional polychromatic 120-kVp imaging performed during the same abdominal computed tomography (CT) examination. MATERIALS AND METHODS Our institutional review board approved this prospective study; each participant provided written informed consent. 51 patients underwent sequential fast kVp-switching dual-energy (80/140 kVp, volume CT dose index: 12.7 mGy) and single-energy (120-kVp, 12.7 mGy) abdominal enhanced CT over an 8 cm scan length with a random acquisition order and a 4.3-s interval. VMS images with filtered back projection (VMS-FBP) and adaptive statistical iterative reconstruction (so-called hybrid IR) (VMS-ASIR) (at 70 keV), as well as 120-kVp images with FBP (120-kVp-FBP) and ASIR (120-kVp-ASIR), were generated from dual-energy and single-energy CT data, respectively. The objective image noises, signal-to-noise ratios and contrast-to-noise ratios of the liver, kidney, pancreas, spleen, portal vein and aorta, and the lesion-to-liver and lesion-to-kidney contrast-to-noise ratios were measured. Two radiologists independently and blindly assessed the subjective image quality. The results were analyzed using the paired t-test, Wilcoxon signed rank sum test and mixed-effects model with Bonferroni correction. RESULTS VMS-ASIR images were superior to 120-kVp-FBP, 120-kVp-ASIR and VMS-FBP images for all the quantitative assessments and the subjective overall image quality (all P<0.001), while VMS-FBP images were superior to 120-kVp-FBP and 120-kVp-ASIR images (all P<0.004). CONCLUSIONS VMS images at 70 keV have a higher image quality than 120-kVp images, regardless of the application of hybrid IR. Hybrid IR can further improve the image quality of VMS imaging.

Lack of Association Between Epicardial Fat Volume and Extent of Coronary Artery Calcification, Severity of Coronary Artery Disease, or Presence of Myocardial Perfusion Abnormalities in a Diverse, Symptomatic Patient Population Results From the CORE320 Multicenter Study

Background—Epicardial fat may play a role in the pathogenesis of coronary artery disease (CAD). We explored the relationship of epicardial fat volume (EFV) with the presence and severity of CAD or myocardial perfusion abnormalities in a diverse, symptomatic patient population. Methods and Results—Patients (n=380) with known or suspected CAD who underwent 320-detector row computed tomographic angiography, nuclear stress perfusion imaging, and clinically driven invasive coronary angiography for the CORE320 international study were included. EFV was defined as adipose tissue within the pericardial borders as assessed by computed tomography using semiautomatic software. We used linear and logistic regression models to assess the relationship of EFV with coronary calcium score, stenosis severity by quantitative coronary angiography, and myocardial perfusion abnormalities by single photon emission computed tomography (SPECT). Median EFV among patients (median age, 62.6 years) was 102 cm3 (interquartile range: 53). A coronary calcium score of ≥1 was present in 83% of patients. Fifty-nine percent of patients had ≥1 coronary artery stenosis of ≥50% by quantitative coronary angiography, and 49% had abnormal myocardial perfusion results by SPECT. There were no significant associations between EFV and coronary artery calcium scanning, presence severity of ≥50% stenosis by quantitative coronary angiography, or abnormal myocardial perfusion by SPECT. Conclusions—In a diverse population of symptomatic patients referred for invasive coronary angiography, we did not find associations of EFV with the presence and severity of CAD or with myocardial perfusion abnormalities. The clinical significance of quantifying EFV remains uncertain but may relate to the pathophysiology of acute coronary events rather than the presence of atherosclerotic disease.

OATP1B3 expression is strongly associated with Wnt/β-catenin signalling and represents the transporter of gadoxetic acid in hepatocellular carcinoma

BACKGROUND & AIMS In the current era of emerging molecular targeted drugs, it is necessary to identify before treatment the specific subclass to which a tumour belongs. Gadoxetic acid is a liver-specific contrast agent that is preferentially taken up by hepatocytes. Therefore, gadoxetic acid-enhanced magnetic resonance imaging (EOB-MRI) should provide precise molecular information about hepatocellular carcinomas (HCCs). The aim of this study was to investigate the transporters of gadoxetic acid in HCC comprehensively and to analyse the molecular regulatory mechanism of such transporters. METHODS Expression levels of transporters, transcriptional factors and Wnt target genes in clinical samples were examined by quantitative real-time reverse transcription polymerase chain reaction and immunohistochemistry. LiCl treatment of the HCC cell line KYN-2 was conducted in vitro to assess the effects of Wnt signalling activity. RESULTS Comprehensive analyses of transporter mRNAs and protein expressions revealed that the organic anion transporting polypeptide 1B3 (OATP1B3) had the strongest correlation with tumour enhancement in hepatobiliary-phase images of EOB-MRI. Association analysis with OATP1B3 expression revealed significant correlation with the expression of Wnt/β-catenin target genes. Further, LiCl treatment induced OATP1B3 mRNA expression in KYN-2 cells, indicating a strong association between OATP1B3 expression and Wnt/β-catenin signalling. The sensitivity and specificity to predict Wnt/β-catenin-activated HCC using tumour enhancement in EOB-MRI were 78.9% and 81.7%, respectively. CONCLUSIONS OATP1B3 was confirmed as the most important transporter mediating HCC enhancement in EOB-MRI. OATP1B3 expression showed a strong association with the expression of Wnt/β-catenin target genes, therefore, OATP1B3-upregulated HCC likely represents a specific subclass of Wnt/β-catenin-activated HCC.

Feasibility of coronary artery calcium scoring on virtual unenhanced images derived from single-source fast kVp-switching dual-energy coronary CT angiography

BACKGROUND Dual-energy CT technology enables acquisition of virtual unenhanced (VUE) images from contrast-enhanced scans. OBJECTIVE To assess the feasibility of coronary artery calcium (CAC) scoring on VUE images derived from fast kVp-switching dual-energy coronary CT angiography. METHODS Twenty-seven patients underwent true noncontrast CAC-scoring CT followed by routine single-energy (120-kVp) and fast kVp-switching dual-energy coronary CT angiography, in a random acquisition order on the same day. We calculated the CAC scores on true noncontrast and VUE images. The image noises and the signal-to-noise and contrast-to-noise ratios of the aorta and coronary arteries were measured on both the single-energy coronary CT angiography images and dual-energy coronary CT angiography images (70 keV virtual monochromatic spectral images). The Pearson correlation coefficient test and paired t test were used for statistical analysis. RESULTS Excellent correlation was observed between the CAC scores on the true noncontrast and those on the VUE images (r = 0.88; P < .001). Compared with single-energy coronary CT angiography, dual-energy coronary CT angiography showed significantly reduced image noise and increased signal-to-noise and contrast-to-noise ratios in all regions (all P < .001). The effective dose of dual-energy coronary CT angiography (4.3 ± 0.3 mSv) was significantly lower than that of true noncontrast CAC-scoring CT plus single-energy coronary CT angiography (5.4 ± 0.7 mSv; P < .0001). CONCLUSIONS Excellent correlation was observed between the CAC scores on the VUE images and true noncontrast images. Thus, fast kVp-switching dual-energy coronary CT angiography could allow prediction of the true CAC scores, potentially reducing the total radiation exposure and image acquisition time by obviating the need for true noncontrast CAC-scoring CT.

Detection of a coronary artery vessel wall: performance of 0.3 mm fine-cell detector computed tomography--a phantom study.

The purpose of this study was to evaluate whether experimental fine-cell detector computed tomography with a 0.3125 mm cell (0.3 mm cell CT) can improve the detection of coronary vessel walls compared with conventional 64-slice computed tomography with a 0.625 mm cell (0.6 mm cell CT). A coronary vessel wall phantom was scanned using 0.6 mm cell CT and 0.3 mm cell CT. The data for 0.3 mm cell CT were obtained using four protocols: a radiation dose equal, double, triple or quadruple that were used in the 0.6 mm cell CT protocol. The detectable size of the vessel wall was assessed based on the first and second derivative functions, and the minimum measurable values were compared using a paired t-test. As a result, the minimum detectable wall thickness of 0.6 mm cell CT (1.5 mm) was significantly larger than that of 0.3 mm cell CT performed using the triple- and quadruple-dose protocols (0.9 mm) and the double-dose protocol (1.1 mm). The difference in the minimum detectable vessel wall thickness measured using 0.6 mm cell CT (1.5 ± 0.1 mm) and 0.3 mm cell CT (0.9 ± 0.1 mm, 1.1 ± 0.2 mm) was significant (p < 0.01). We concluded that 0.3 mm cell CT improved the detection of coronary vessel walls when a more than double-dose protocol was used compared with 0.6 mm cell CT.