Relationship between heart rate and optimal reconstruction phase in coronary CT angiography performed on a 256-slice multidetector CT.

OBJECTIVE: This study aimed to evaluate the relationship between heart rate (HR) and optimal reconstruction phase in prospectively electrocardiogram (ECG)-triggered coronary CT angiography (CCTA) performed on a newly introduced 256-slice multidetector CT (MDCT). METHODS: All the cases were selected retrospectively from the patients scheduled for CCTA in our department between January and April 2017. The scanner selected the optimal exposure phase based on 10 s ECG recordings. To ensure the success of CCTA, the operator also checked patient's age, breathing control, emotional status and past medical history to decide whether the automatically selected scan phase needs manual adjustment or not. Images were reconstructed in 1% steps of the R-R interval to determine the cardiac phase with least coronary motion. If CCTA images showed moderate motion blurring or discontinuity in the course of coronary segments, a cardiac motion correction algorithm was applied to the reconstructed images. Subjective diagnostic image quality was evaluated with 4-point grading scale. RESULTS: A total of 87 consecutive CCTA examinations were investigated in this study. Diastolic reconstruction was applied to all vessel segments in patients with HR <63 bpm, where 36.5 and 77.8% of vessel segments were reconstructed with the use of motion correction in HR ≤57 and 58-62 bpm, respectively. As for patients with HR ≥63 bpm, 89.3 and 71.7% of vessel segments were reconstructed in diastole in HR 63-67 and ≥68 bpm, respectively, while 81 and 100% of vessel segments were reconstructed with the use of motion correction in the same HR groups. CONCLUSION: Based on our results, a HR less than 67 bpm can be used to identify appropriate patients for diastolic reconstruction. Although the motion correction algorithm is an effective approach to reduce the impact of cardiac motion in CCTA, HR control is still important to optimize the image quality of CCTA. The relationship between HR and optimal reconstruction phase established in this study could be further used to tailor the ECG pulsing window for dose reduction in patients undergoing CCTA performed on the 256-slice MDCT. ADVANCES IN KNOWLEDGE: The HR thresholds to identify patients who are the best suitable candidates for diastolic or systolic reconstruction are scanner specific. This study investigated the relationship between HR and optimal reconstruction phase in prospectively ECG-triggered CCTA for a newly introduced 256-slice MDCT. Once the relationship is established, it could be used to tailor the ECG pulsing window for radiation dose reduction.

Quantitative evaluation of breast density using a dual-energy technique on a digital breast tomosynthesis system.

PURPOSE: Although breast density is considered a strong risk factor of breast cancer, its quantitative assessment is difficult. To investigate a quantitative method of measuring breast density using dual-energy mammographic imaging with central digital breast tomosynthesis in physically uniform and nonuniform phantoms. MATERIAL AND METHODS: The dual-energy imaging unit used a tungsten anode and silver filter with 30 kVp for high-energy images and 20 kVp for low-energy images. Uniform glandular-equivalent phantoms were used to calibrate a dual-energy based decomposition algorithm. The first study used uniform breast phantoms which ranged in thicknesses from 20 to 70 mm, in 10-mm increments, and which provided 30%, 50%, and 70% of breast density. The second study used uniform phantoms ranging from 10% to 90% of breast density. The third study used non-uniform phantoms (at an average density of 50%) with a thickness which ranged from 20 to 90 mm, in 10-mm increments. RESULTS: The root mean square error of breast density measurements was 2.64-3.34% for the uniform, variable thickness phantoms, 4.17% for the uniform, variable density phantoms, and 4.49% for the nonuniform, variable thickness phantoms. CONCLUSION: The dual-energy technique could be used to measure breast density with a margin of error of < 10% using digital breast tomosynthesis.

Effects of Analyzer Detection Method, Ethnicity, and Reference Individuals on Reference Interval of Immature Platelet Fraction.

BACKGROUND: Immature platelet fraction (IPF) is a new biomarker for thrombopoiesis and inflammation. However, the reference interval (RI) is wildly discrepant among published reports. This study aimed to establish the RI of IPF for a population in Taiwan and evaluate the effects the detection method of the analyzer, ethnicity, and reference individuals have on the RI of IPF. METHODS: The RI of absolute IPF (A-IPF) and IPF% were established with healthy subjects from the outpatient services of the Health Management Department of Taichung Veterans General Hospital between January 1, 2015 and March 1, 2016. These values were used along with published reports for meta-analysis. RESULTS: A-IPF (109/L) and IPF% of Taiwanese were 6.9 - 7.6 and 3.1 - 3.4, respectively. Significant differences were found when performing paired comparisons of the RI of A-IPF and IPF% published in reports. For A-IPF, there was only one paired comparison with a significant difference (Z > 1.96) across 6 reports. Thus, the contribution of the factors examined on the RI of IPF cannot be determined. For IPF%, there were 8 paired comparisons with significant differences across 10 reports. The discrepancy rates of RI for IPF% were 41.2%, 50.0%, and 25.0% with the difference of reference individuals, the analyzer method, and ethnicity, respectively. CONCLUSIONS: The RIs of Taiwanese for A-IPF and IPF% were established. Furthermore, the analyzer detection method and the reference individuals contribute to the discrepancy of the RI for IPF% and should be considered cautiously when the value of IPF is interpreted.

The feasibility of low-dose CT protocols for coronary artery calcium scoring and PET attenuation correction in cardiac PET/CT.

INTRODUCTION: The purpose of this study was to investigate the feasibility of using low-dose computed tomography (CT) in coronary artery calcium scoring and PET attenuation correction for patients in different weight categories undergoing cardiac PET/CT examinations. MATERIALS AND METHODS: Calcium scoring computed tomography (CSCT) scans and PET scans of anthropomorphic cardiac phantoms simulating normal-weight, mildly obese, and severely obese patients were acquired with a hybrid PET/CT scanner. CSCT images were acquired at 120 kVp, with tube current ranging from 10 to 550 mA. PET scans were performed in three-dimensional mode, with acquisition time of 3 min/bed position. The image quality of cardiac PET/CT was evaluated by assessing the signal-to-noise ratio. CT-based coronary artery calcium quantification was performed using the Agatston scoring system. RESULTS: On the basis of our results, the CSCT protocols using tube currents of 50 and 150 mA should be able to achieve the lowest possible radiation dose while maintaining the desired image quality for normal-weight and mildly obese patients undergoing cardiac PET/CT examinations, respectively. When the proposed low-dose CSCT protocols were performed, radiation dose could be reduced by 83.34 and 50% compared with those from CSCT scans acquired with standard tube current settings for normal-weight and mildly obese patients, respectively. In the scanning of severely obese patients, an increase in tube voltage or current would help improve the reliability of image information provided by cardiac PET/CT. CONCLUSION: Our study demonstrated the feasibility of low-dose CT protocols for coronary artery calcium scoring and PET attenuation correction in cardiac PET/CT to examine patients in different weight categories. The calculations performed in this work should be able to provide practical information to achieve necessary diagnostic information while keeping radiation dose as low as reasonably achievable.

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 Alzheimer's 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.

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.

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.