| Summary: | 碩士 === 慈濟科技大學 === 放射醫學科學研究所 === 107 === Purpose:
The first aim of this study investigated the effect of patient’ s body mass index (BMI) on radiation dose and image quality, the other aim of this study evaluate the relationship between heart rate (HR) and optimal reconstruction phase in prospectively ECG-triggered coronary CT angiography (CCTA) performed on a newly introduced 256-slice multi-detector CT.
Methods:
In this study there were 1098 coronary artery segments in 87 patients. Automatic exposure control (AEC) and iterative reconstruction (IR) techniques were used in this study. 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.
Results:
First part: The tube voltage, tube current and radiation dose increased as BMI increased (BMI < 25 kg/m2: 112.44 ± 9.81 kVp, 637.38 ± 92.17 mA, 4.25 ± 1.35 mSv; BMI ≥ 25 kg/m2: 120.95 ± 6.17 kVp, 701.67 ± 39.94 mA, 5.22 ± 1.27 mSv). However, there were CCTA scans exceeding the AEC modulation range because the maximum x-ray output was reached (BMI < 25 kg/m2: 40.0%; BMI ≥ 25 kg/m2 88.1%). Hence, it was found that the subjective image quality scores and objective noise measurements also increased with increasing BMI.
Second part: All segments shown acceptable diagnostic information. 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 bpm and 58-62 bpm, respectively. As for patients with HR ≥ 63 bpm, 72.4% and 39.2% of vessel segments were reconstructed in diastole in HR 63-67 bpm 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:
The first part explores the performance of BMI and image noise. AEC cannot always guarantee a consistent image quality for all patients. It was found that the image quality also increases with increasing BMI. IR techniques can reduce photon attenuation for better image quality.
The second part explores the impact of HR and motion artifacts. 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.
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