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.

Combined evaluation of myocardial perfusion and coronary morphology in the identification of subclinical CAD

Summary Purpose: To evaluate the mean effective radiation dose of 13N-ammonia PET/CT and ECGpulsing CT angiography (CTA) in the evaluation of myocardial perfusion, myocardial blood flow (MBF) and coronary morphology for the identification of subclinical CAD. Patients, material, methods: Following rest-stress 13N-ammonia PET/CT perfusion imaging and MBF quantification, ECG-pulsing CTA at a pulse window of 70% of the R-R cycle was performed in ten healthy controls and in sixteen individuals with cardiovascular risk factors. Individual radiation dose exposure for ECG-pulsing CTA was estimated from the dose-length product. Results: PET demonstrated normal perfusion in all study individuals, while hyperemic MBFs during dipyridamole stimulation and the myocardial flow reserve (MFR) in cardiovascular risk individuals were significantly lower than in healthy controls (1.34 ± 0.26 vs. 2.28 ± 0.47 ml/g/min and 1.48 ± 0.39 vs. 3.24 ± 0.81, both p . 0.0001). Further, ECG-pulsing CTA identified mild calcified and non-calcified coronary plaque burden in 7 (43%) individuals of the cardiovascular risk group. Rest-stress 13N-ammonia PET/CT perfusion study yielded a mean effective radiation dose of 3.07 ± 0.06 mSv (2.07 ± 0.06 mSv from the rest-stress 13N-ammonia injections and 1.0 mSv from the 2 CT transmission scans), while ECG-pulsing CTA was associated with 5.57 ± 2.00 mSv. The mean effective radiation dose of the combined 13N-ammonia PET/CT and ECG-pulsing CTA exams in the evaluation of myocardial perfusion and coronary morphology was 8.0 ± 1.5 mSv. Conclusion: 13N-ammonia PET/CT and ECG-pulsing CTA affords cardiac hybrid imaging studies in the evaluation of subclinical CAD with a relatively low mean effective radiation exposure of 8.0 ± 1.5mSv.