Liang-Kuang Chen

Retrospective gating vs. prospective triggering for noninvasive coronary angiography: Assessment of image quality and radiation dose using a 256-slice CT scanner with 270 ms gantry rotation.

OBJECTIVE To report our clinical experience with a 256-slice multidetector computed tomography (MDCT) with a 270-ms gantry rotation system in performing CT coronary angiograms (CTCA) using both prospectively gated step and shoot (PGSS) and retrospectively gated helical (RGH) techniques. MATERIALS AND METHODS We studied 252 patients who received CTCA; 126 patients having mean heart rate (HR) of 72.1 were imaged with RGH CTCA and 126 patients having mean HR of 58.7 were imaged with PGSS CTCA. For patients with a prescan HR ≤70 beats/min, a PGSS acquisitions trigger was used, whereas patients whose prescan HR was >70 beats/min were imaged using an RGH acquisition. The blood vessel accessibility of both PGSS and RGH techniques was evaluated by grading the image quality score from 1 (no motion artifacts) to 4 (severe motion artifacts preventing diagnosis) for each coronary artery segment. Radiation doses of the techniques were also compared. RESULTS In both groups, more than 50% of segments received the best imaging score. The overall image quality scores for RGH and PGSS groups were 1.522 ± 0.317 and 1.500 ± 0.374, respectively. There was no significant difference in right coronary artery, left anterior descending artery, and left circumflex artery image quality between the two groups. Only 0.1% of segments were nonevaluative with the PGSS technique and all segments were evaluative with RGH. PGSS was associated with a 62% reduction in effective radiation dose as compared to RGH (PGSS, 5.1 mSv; RGH, 13.2 mSv). CONCLUSIONS There is no significant difference in image quality between PGSS and RGH in this study. Although providing similar image quality as RGH, PGSS was associated with a 62% reduction in effective radiation dose. Further study to confirm the diagnostic accuracy as compared to coronary artery angiography is warranted.

Optimal Systolic and Diastolic Image Reconstruction Windows for Coronary 256-Slice CT Angiography

RATIONALE AND OBJECTIVES The aims of this study were to determine the optimal image reconstruction intervals for the systolic and diastolic phases of coronary computed tomographic angiography on 256-slice computed tomography and to assess their associated motion artifacts. MATERIALS AND METHODS One hundred twenty-six patients were recruited (mean heart rate [HR], 72.1 beats/min; heart rate variability, 1.3 beats/min). Twenty data sets were reconstructed in 5% steps through 0% to 95% of the R-R interval. Two reviewers discriminated optimal reconstruction intervals for 15 segments distributed in three coronary arteries on the basis of motion artifacts, which were graded from 1 (no motion artifacts) to 4 (severe motion artifacts preventing diagnosis). Patients were then stratified into four HR groups for motion score comparison according to the results of a correlation analysis of HR and motion scores. RESULTS The optimal systolic and diastolic reconstruction intervals were 44.4 ± 3.8% and 77.4 ± 3.7%, respectively. The mean motion scores for systolic, diastolic, and combined systolic and diastolic (S+D) reconstructions were 1.8 ± 0.3, 1.8 ± 0.5, and 1.5 ± 0.3, respectively. Combined S+D reconstruction improved diagnostic evaluability to 100% and showed fewer motion artifacts compared to single-phase reconstructions for all HR ranges (S+D vs systolic, P < .05 for HR < 85 beats/min; S+D vs diastolic, P < .05 for HRs of 73-84 beats/min). For HRs of 60 to 72 beats/min, motion artifacts were significantly lower for diastole (1.6 ± 0.3) than systole (1.8 ± 0.4) (P < .001), and vice versa for HRs of 73 to 84 beats/min (1.7 ± 0.3 for systole vs 2.0 ± 0.5 for diastole, P < .01). CONCLUSIONS Optimal systolic and diastolic reconstruction intervals were determined for this 256-slice coronary computed tomographic angiographic study. Combined reconstruction showed fewer motion artifacts compared to single-phase reconstruction. In conclusion, 256-slice computed tomography has the potential to improve the diagnostic accuracy of coronary computed tomographic angiography.

Evaluation of the screening power of Cognitive Abilities Screening Instrument for probable Alzheimer's disease using voxel-based morphometry ☆

OBJECTIVE The aim of this study was to compare two screening methods, total score of the Cognitive Abilities Screening Instrument (CASI(T)) and the combined score for the short-term memory and orientation domains (CASI(R)) for screening and grading probable Alzheimers disease (AD), based on their correlations with voxel-based morphometry (VBM). MATERIALS AND METHODS Forty-five subjects with probable AD and normal controls underwent magnetic resonance imaging and CASI testing. Their corresponding T1-weighted magnetic resonance images were analyzed using VBM. RESULTS VBM results showed that in moderate-to-severe AD subgroups, significant whole-brain gray matter loss was detected using both CASI(T) and CASI(R). Significantly more voxels were detected using the CASI(T) compared with the CASI(R) system in mild AD subjects (P<.05). CONCLUSIONS Based on their correlations with VBM results, there is no significant difference for CASI(R) and CASI(T) for grading moderate-to-severe AD subgroups, and CASI(R) scoring system may be more accurate and effective than the CASI(T) for screening mild AD.

Potential Dose Reduction of Optimal ECG-controlled Tube Current Modulation for 256-Slice CT Coronary Angiography

RATIONALE AND OBJECTIVES The purpose of this study was to design an optimized heart rate (HR)-dependent electrocardiogram (ECG) pulsing protocol for computed tomography coronary angiography (CTCA) on a 256-slice CT scanner and to assess its potential dose reduction retrospectively, based on the retrospective ECG gating data without dose modulation. MATERIALS AND METHODS A total of 137 patients were enrolled to perform CTCA with a 256-slice scanner. Two independent radiologists graded image quality of coronary artery segments (1 = excellent, no motion artifacts; 4 = poor, severe motion artifacts) to define optimal reconstruction window in end-systolic phase, mid-diastolic phase, and the combination of both cardiac phases. According to statistical analysis for HR against image quality, four HR-depended ECG-pulsing protocols were proposed. We also demonstrated the potential dose reduction of the proposed technique. RESULTS For patients with HR <59 beats/min (group 1), 60-72 beats/min (group 2), 73-84 beats/min (group 3), and >85 beats/min (group 4), the optimal reconstruction windows were at 74.1-81.3%, 73.4-82.2%, 38.3-82.3%, and 37.2-61.6% of R-R interval, respectively. The ECG-pulsing protocols with minimal radiation dose (ie, no tube current outside the pulsing window) can reduce the effective dose of CTCA by 79.5%, 75.7%, 38.3%, and 57.4% for HR groups 1 to 4, respectively. The corresponding results for reducing tube current by 80% outside the pulsing window were 63.7%, 56.6%, 32.0%, and 46.0%. CONCLUSION Through the optimization of ECG-pulsed tube-current modulation, radiation exposure can be greatly reduced, especially in patients with HR <72 beats/min or >85 beats/min.

High-resolution gel dosimetry using flat-panel detector cone-beam computed tomography: preliminary study.

This study compares the dose response of irradiated polymer gel with acrylic and styrofoam housing while applying multi-detector CT (MDCT) and cone-beam CT (CBCT). The dose response for MDCT and CBCT, while using an acrylic phantom is 1.34 and 0.67 DeltaHU Gy(-1), respectively, and becomes 1.54 and 0.84 DeltaHU Gy(-1) while using styrofoam, suggesting styrofoam is the better housing material. While the dose response of MDCT is better than that of CBCT, CBCT is yet a promising 3D dosimetry technique, given its potentially better spatial resolution and sensitive dose interpretation capability.