Prospective ECG-triggered coronary 64-MDCT has the potential to reduce radiation exposure while maintaining the diagnostic performance of retrospective ECG-gated coronary 64-MDCT.
Rationale and Objectives: To compare coronary artery calcium scores, the variability and radiation doses on 64-slice and 16-slice CT scanners by both prospective electrocardiograph (ECG)-triggered and retrospective ECG-gated scans. Materials and Methods: Coronary artery models (n=3) with different plaque CT densities (~240 HU, ~600 HU and ~1000 HU) of four sizes (1 mm, 3 mm, 5 mm and 10 mm in length) on a cardiac phantom were scanned three times in 5 heart rate sequences. The tube current-time-products were set to almost the same on all four protocols (32.7 mAs for 64-slice prospective and retrospective scans, 33.3 mAs for 16-slice prospective and retrospective scans). Slice-thickness was set to 2.5 mm in order to keep the radiation dose low. Overlapping reconstruction with 1.25 mm increment was applied on the retrospective ECG-gated scan. Results: The coronary artery calcium scores were not different between the four protocols (one-factor ANOVA, Agatston; p=0.32, volume; p=0.19 and mass; p=0.09). Two-factor factorial ANOVA test revealed that the interscan variability was different between protocols (p<0.01) and scoring algorithms (p<0.01). The average variability of Agatston/volume/mass scoring and effective doses were 64-slice prospective scan: 16%/15%/11% and 0.5 mSv, 64-slice retrospective scan: 11%/11%/8% and 3.7 mSv, 16-slice prospective scan: 20%/18%/13% and 0.6 mSv & 16-slice retrospective scan: 16%/15%/11% and 2.9 to 3.5 mSv (depending on the pitch). Conclusions: Retrospective ECG-gated 64-slice CT showed the lowest variability. Prospective ECG-triggered 64-slice CT, with low radiation dose, shows low variability 2 on coronary artery calcium scoring comparable to retrospective ECG-gated 16-slice CT.
The effect of heart rate and variation during cardiac computed tomography (CT) on the examination quality. The purpose of this study is to investigate whether it is possible to predict heart rate and range during enhanced cardiac computed CT scan from previous non-enhanced cardiac CT scan. Electrocardiograph (ECG) files from 112 patients on three types of cardiac 64-slice CT (nonenhanced, prospective ECG-triggered and retrospective ECG-gated enhanced scans) were recorded. The mean heart rate, range (defined as difference between maximal and minimal heart rates) and the range ratio (defined as maximal heart rate divided by minimal heart rate) during the scans were compared. Scan time was 4.8, 4.6, and 7.3 s on non-enhanced, prospective ECG-triggered and retrospective ECG-gated scans, respectively (pG0.0001). The heart rates were not significantly different (60±9 beats per minute (bpm), 60±9 and 61±10 bpm; p=0.64). Heart rate on the enhanced scan markedly correlated with that of the non-enhanced scan (r=0.78 and 0.74). In contrast, the ranges of heart rate were 2±5, 4±8, and 8± 21 bpm, with different range ratios (1.04, 1.07, and 1.14; pG0.0001). Correlation of heart rate ranges between nonenhanced scan versus prospective ECG-triggered scan was low (r=0.27) and that between non-enhanced scan versus retrospective ECG-gated scan negligible (r= −0.027).Heart rate on enhanced cardiac CT, in most cases, can be predicted from a non-enhanced scan. Heart rate range on enhanced cardiac CT, however, is hard to predict from the non-enhanced scan.
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