Masatoshi Kondo

Volumetric measurement of artificial pure ground-glass nodules at low-dose CT: Comparisons between hybrid iterative reconstruction and filtered back projection

PURPOSE To compare hybrid iterative reconstruction (HIR) with filtered back projection (FBP) in the volumetry of artificial pure ground-glass nodules (GGNs) with low-dose computed tomography (CT). MATERIALS AND METHODS Artificial GGNs (10 mm-diameter, 523.6 mm(3), -660 HU) in an anthropomorphic chest phantom were scanned by a 256-row multi-slice CT with three dose levels (10, 30, 100 mAs). Each scan was repeated six times. Each set was reconstructed by FBP and HIR at 0.625-mm thickness. The volumes of artificial GGNs placed at the lung apex and middle lung field of the chest phantom were measured by two observers. Semi-automated measurements were performed by clicking the cursor in the center of GGNs, and manual measurements were performed by tracing GGNs on axial section. Modification of the trace was added on a sagittal or coronal section if necessary. Measurement errors were calculated for both the FBP and HIR at each dose level. We used the Wilcoxon signed rank test to identify any significant difference between the measurement errors of the FBP and HIR. Inter-observer, intra-observer, and inter-scan variabilities were evaluated by Bland Altman analysis with limits of agreements given by 95% confidence intervals. RESULTS There were significant differences in measurement errors only at the lung apex between FBP and HIR with 10 mAs in both the semi-automated (observer 1, -37% vs. 7.2%; observer 2, -39% vs. 1.9%) and manual methods (observer 1, -29% vs. 7.5%; observer 2, -30% vs. 1.1%), respectively (P<0.05). HIR provided each variability equal to or less than one half of that of FBP at 10 mAs in both methods. In the semi-automated method, the inter-observer and intra-observer variabilities obtained by HIR at 10 mAs were -11% to 17% and -6.7% to 6.7%, whereas those for FBP at 10 mAs were -29% to 30% and -38% to 20%, respectively. The inter-scan variability for FBP at 100 mAs vs. HIR at 10 mAs was -9.5% to 11%, and that for FBP at 100 mAs vs. FBP at 10 mAs was -73% to 32%. In the manual method, the inter-observer and intra-observer variabilities for HIR at 10 mAs were -14% to 22% and -9.8% to 22%, and those for FBP at 10 mAs were -45% to 36% and -31% to 28%, respectively. The inter-scan variability for FBP at 100 mAs vs. HIR at 10 mAs was -7.4% to 23%, and that for FBP at 100 mAs vs. FBP at 10 mAs was -52% to 26%. CONCLUSION HIR is superior to FBP in the volumetry of artificial pure GGNs at lung apex with low-dose CT.

Improvement of Automated Right Ventricular Segmentation Using Dual-bolus Contrast Media Injection with 256-slice Coronary CT Angiography

RATIONALE AND OBJECTIVES To investigate the effect of dual-bolus contrast media injection (dual-CM) on the accuracy of automated right ventricular (RV) segmentation on coronary computed tomography angiography (CCTA). MATERIALS AND METHODS A total of 104 patients with suspected and known coronary artery disease underwent 256-slice CCTA with retrospective electrocardiographic (ECG) gating. The patients were divided into 51 patients who underwent single-bolus CM injection (single-CM) and 53 patients who underwent dual-CM. The dual-CM method consisted of an initial bolus of CM followed by an injection of dilute CM with saline (CM:saline, 1:9). Three-dimensional CCTA images were automatically segmented into the RV, left ventricle (LV), and myocardium using commercially available software (Comprehensive Cardiac Analysis; Philips Medical Systems, Cleveland, OH). Prevalence and locations of segmentation errors were compared between single-CM and dual-CM. Segmentation errors were defined as segment deviation of >1 cm from the actual ventricular margin. RESULTS Prevalence of segmentation errors was significantly lower with dual-CM than with single-CM in the diastolic phase (4/41 vs. 20/41, respectively; P < .01), and there was no difference between the two methods in the systolic phase (2/12 vs. 2/10, respectively). With dual-CM and single-CM, the locations of segmentation errors were mostly the RV wall (4/53 and 18/51, respectively) and secondly the LV wall (2/53 and 9/51, respectively). CONCLUSIONS Dual-CM improved the accuracy of automated ventricular segmentation using diastolic data from 256-slice CCTA.

Dynamic flow imaging using 320-detector row CT and motion coherence analysis in coronary aneurysms associated with Kawasaki disease

Introduction We propose a new dynamic flow imaging using 320-detector row CT, and investigate the assessment of coronary flow in aneurysms of Kawasaki disease in adulthood. METHODS Six patients with Kawasaki disease and coronary aneurysms associated (26.7 years old) and six controls were enrolled. Dynamic coronary CT angiography with 320-row CT was continuously performed at mid-diastole throughout 15-25 cardiac cycles with prospective Electrocardiogram gating after injection of contrast media. Dynamic data sets of 15-25 cycles were computed into 90-100 data sets by motion coherence image processing. Next, time-density curves for coronary arteries were calculated for all the phases. On the basis of the maximum slope method, coronary flow index was defined as the ratio of the maximum upslope of the attenuation of coronary arteries to the upslope of the attenuation of ascending aorta on the time-density curves. Coronary flow indexes for the proximal and distal sites of coronary arteries and intra-aneurysm were measured.

Optimal scan timing for artery–vein separation at whole-brain CT angiography using a 320-row MDCT volume scanner

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 (Datt) 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 (Dscore). We assessed the time at which the maximum Datt and Dscore were simultaneously observed. RESULTS The maximum Datt 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 (Taa). The maximum Dscore 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 Taa. There were no statistically significant differences in Datt (p = 0.375) or Dscore (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 Taa. Advances in knowledge: Optimal scan timing allowed us to visualize intracranial arteries or veins with minimal superimposition.

Low-dose CT screening using hybrid iterative reconstruction: confidence ratings of diagnoses of simulated lesions other than lung cancer

OBJECTIVE To evaluate the confidence ratings of diagnoses of simulated lesions other than lung cancer on low-dose screening CT with hybrid iterative reconstruction (IR). METHODS Simulated lesions (emphysema, mediastinal masses and interstitial pneumonia) in a chest phantom were scanned by a 320-row area detector CT. The scans were performed by 64-row and 160-row helical scans at various dose levels and were reconstructed by filtered back projection (FBP) and IR. Emphysema, honeycombing and reticular opacity were visually scored on a four-point scale by six thoracic radiologists. The ground-glass opacity as a percentage of total lung volume (%GGO), CT value and contrast-to-noise ratio (CNR) of mediastinal masses were calculated. These scores and values were compared between FBP and IR. Wilcoxons signed-rank test was used (p < 0.05). Interobserver agreements were evaluated by κ statistics. RESULTS There were no significant differences in visual assessment. Interobserver agreement was almost perfect. CT values were almost equivalent between FBP and IR, whereas CNR with IR was significantly higher than that with FBP. %GGO significantly increased at low-dose levels with FBP; however, IR suppressed the elevation. CONCLUSION The confidence ratings of diagnoses of simulated lesions other than lung cancer on low-dose CT screening were not degraded with hybrid IR compared with FBP. ADVANCES IN KNOWLEDGE Hybrid IR did not degrade the confidence ratings of diagnoses on visual assessment and differential diagnoses based on CT value of mediastinal masses, and it showed the advantage of higher GGO conspicuity at low-dose level. Radiologists can analyse images of hybrid IR alone on low-dose CT screening for lung cancer.

Impact of hybrid iterative reconstruction on unenhanced liver CT

OBJECTIVE To clarify the impact of hybrid iterative reconstruction (HIR) and filtered back projection (FBP) on unenhanced liver CT. METHODS 30 patients with hepatocellular carcinoma (HCC) underwent unenhanced CT. The images were reconstructed with FBP and weak (Level 1), mild (Level 4) and strong (Level 7) levels of HIR (iDose4; Philips Medical Systems, Cleveland, OH). Quantitatively, attenuations of the HCC (with the largest lesion in each case), hepatic parenchyma (the average of four segments) and image noise (standard deviation of the attenuations in hepatic parenchyma) were compared between the four kinds of reconstruction using the two-tailed paired t-test. Qualitatively, liver lesion conspicuity and characterization were also compared using the Wilcoxon signed-rank test. RESULTS Attenuation of the liver lesion with the strong level of HIR was significantly higher than that with FBP (p = 0.0005). Attenuations of hepatic parenchyma with all three HIR levels were significantly lower than that with FBP (p ≤ 0.0002 in all comparisons). Image noise with each of the three HIR levels was significantly smaller than that with FBP (p < 0.0001 in any comparison). There was no significant difference in lesion conspicuity and characterization between FBP and each HIR level (p ≥ 0.0819 in all comparisons). CONCLUSION Although attenuations of the liver lesion and hepatic parenchyma were significantly different between HIR and FBP, HIR had no significant effect on lesion conspicuity and characterization. Advances in knowledge: Attenuations of liver lesions and hepatic parenchyma differ significantly between HIR and FBP images.

Additive value of “otosclerosis-weighted” images for the CT diagnosis of fenestral otosclerosis:

Background Otosclerotic foci are usually seen as minute low-density lesions and this may be attributed to relatively low sensitivity on visual assessment using computed tomography (CT). Otosclerotic foci can be detected by using the accurate region of interest (ROI) setting, while small ROI settings by less-experienced radiologists may result in false negative findings. Purpose To evaluate the diagnostic ability of our proposed method (“otosclerosis-weighted” imaging [OWI]), which is based on reversing the density, compared with conventional CT (CCT) imaging alone. Material and Methods Temporal bone CTs of consecutive patients with otosclerosis were analyzed. Gender- and age-matched control participants were also included. All CT images were obtained using a 64-detector row scanner. OWI was obtained by extracting the temporal bone region using the threshold technique and reversing the density (black to white). Four independent radiologists took part in two reading sessions. In the first session, the observers read only CCT imaging. In the second session, they read OWI along with the CCT imaging. Sensitivity was assessed for the four readers. Results Thirty temporal bones of 25 patients with otosclerosis (3 men, 22 women; mean age, 53.9 ± 9.0 years) and 30 temporal bones of 30 control participants (4 men, 26 women; mean age, 44.0 ± 16.2 years) were included. For all observers, reading with a combination of the two methods was associated with a higher sensitivity (63.3–80.0%) than with conventional CT images alone (30.0–60.0%; P < 0.05, each). Conclusion Application of our proposed method based on threshold value may help detect foci of fenestral otosclerosis.

Prognostic utility of computed tomography histogram analysis in patients with post-cardiac arrest syndrome: Evaluation using an automated whole-brain extraction algorithm

Objective The aim of the study was to evaluate the prognostic utility of computed tomography (CT) histogram analysis with an automated whole-brain extraction algorithm in patients with post–cardiac arrest syndrome (PCAS). Methods Computed tomography data from consecutive patients between January 2009 and February 2012 were obtained and retrospectively analyzed. All CT images were obtained using a 64-detector-row CT scanner with a slice thickness of 4.0 mm. A brain region was extracted from the whole-brain CT images using our original automated algorithm and used for the subsequent histogram analysis. The obtained histogram statistics (mean brain tissue CT value, kurtosis, and skewness), as well as clinical parameters, were compared between the good and poor outcome groups using the Student t test. In addition, receiver operating characteristic curve analysis was performed for the discrimination between the 2 groups for each parameter. Results One hundred thirty-eight consecutive PCAS patients were enrolled. The patients were classified into good (n = 47) and poor (n = 91) outcome groups. The mean brain tissue CT value was significantly higher in the good outcome group than in the poor outcome group (P < 0.05). Kurtosis, skewness, and age were significantly lower in the good outcome group than in the poor outcome group (P < 0.0001, P < 0.05, and P < 0.05, respectively). The area-under-the-curve values for kurtosis, mean brain tissue CT value, skewness, and age were 0.751, 0.639, 0.623, and 0.626, respectively. A combination of the 4 parameters increased the diagnostic performance (area under the curve = 0.814). Conclusions Histogram analysis of whole-brain CT images with our automated extraction algorithm is useful for assessing the outcome of PCAS patients.