Accuracy and rate of coronary artery segment visualization with CT angiography for the non-invasive detection of coronary artery stenoses

[Usefulness of the Training of Trigger Point in Coronary CT Using Test Bolus Tracking Method]

BACKGROUND

Test bolus tracking (TBT) method has been used in coronary CT examination, because it is possible to examine the optimum contrast timing. However, the scan timing highly depends on an operators' recognition of peak in test bolus, thus there is a possibility of variation in contrast effect.

PURPOSE

The aim of this study is to improve the variation of contrast effect among the operators.

METHODS

The training for the operators was conducted to acknowledge them the optimal trigger points. The mean CT value and standard deviation of the ascending aorta were calculated to compare before and after the training.

RESULTS

The mean CT value of the ascending aorta after the training was 485.02±73.06 HU, compared to 462.53±78.26 HU before the training. Standard deviation was significantly lower than before the training.

CONCLUSION

The variation of contrast effect between the operators has been reduced by the training, and reproducibility of the examination has been improved.

Initial evaluation of coronary images from 320-detector row computed tomography

PURPOSE

To evaluate image quality and contrast opacification from coronary images acquired from 320-detector row computed tomography (CT). Patient dose is estimated for prospective and retrospective ECG-gating; initial correlation between 320-slice CT and coronary catheterization is illustrated.

METHODS

Retrospective image evaluation from forty consecutive patients included subjective assessment of image quality and contrast opacification (80 ml iopamidol 370 mg I/ml followed by 40 ml saline). Region of interest opacification measurements at the ostium and at 2.5 mm diameter were used to determine the gradient of contrast opacification (defined as the proximal minus distal HU measurements) in coronary arteries imaged in a single heartbeat. Estimated effective dose was compared for prospective versus retrospective ECG-gating, two body mass index categories (30 kg/m(2) cutoff), and single versus two heartbeat acquisition. When available, CT findings were correlated with those from coronary catheterization.

RESULTS

Over 89% of arterial segments (15 segment model) had excellent image quality. The most common reason for image degradation was cardiac motion. One segment in one patient was considered unevaluable. Contrast opacification was almost universally considered excellent. The mean Hounsfield units (HU) was greater than 350; the coronary contrast opacification gradient was 30-50 HU. Patient doses were greater for retrospective ECG-gating, larger patients, and those imaged with two heartbeats. For the most common (n=25) protocol (120 kV, 400 mA, prospective ECG-gating, 60-100% phase window, 16 cm craniocaudal coverage, single heartbeat), the mean dose was 6.8+/-1.4 mSv. All CT findings were confirmed in the four patients who underwent coronary catheterization.

CONCLUSION

Initial 320-detector row coronary CT images have consistently excellent quality and iodinated contrast opacification. These patients were scanned with conservative protocols with respect to iodine load, prospective ECG-gating phase window, and craniocaudal coverage. Future work will focus on lowering contrast and radiation dose while maintaining image quality.