Subtraction Coronary CT Angiography for the Evaluation of Severely Calcified Lesions Using a 320-Detector Row Scanner

Subtraction coronary CT angiography in patients with high heart rate

All the previous subtraction coronary CT angiography (CCTA) had strict heart rate (HR) inclusion criteria. In this study, a new subtraction method was applied to patients with various HR. The post-contrast scan time was respectively 3.5 s after ascending aorta peak enhancement while HR >80 bpm, 4 s while 65≤ HR ≤80 bpm and 4.5 s while HR <65 bpm. Forty-six patients who underwent the new subtraction protocol were enrolled and patients were stratified into the high HR group (≥70 bpm) and low HR group (<70 bpm). Eighteen patients with 15 severe calcification segments and 25 stent segments further received invasive coronary angiography (ICA). In all included patients, the coronary artery enhancement was compared between the high and low HR groups. In patients with ICA performed, the image quality improvement and diagnostic effectiveness for detection of significant coronary segments stenosis (>50%) were compared between the conventional CCTA and subtraction CCTA and between the high HR group and low HR group, respectively. All enrolled patients got sufficient coronary artery enhancement. In patients with ICA performed, receiver operating characteristic (ROC) curve analysis showed that the area under the curve (AUC) for the diagnosis of significant stenosis was 0.93 in subtraction CCTA and 0.73 in conventional CCTA (p < 0.05). Furthermore, there were no significant differences in image quality improvement, specificity, positive predictive value and accuracy between the high HR group and low HR group. The new subtraction CCTA method broadened the clinical availability for patients with high HR.

Clinical Applications of Wide-Detector CT Scanners for Cardiothoracic Imaging: An Update

Technical developments in multidetector computed tomography (CT) have increased the number of detector rows on the z-axis, and 16-cm wide-area-coverage CT scanners have enabled volumetric scanning of the entire heart. Beyond coronary arterial imaging, such innovations offer several advantages during clinical imaging in the cardiothoracic area. The wide-detector CT scanner markedly reduces the image acquisition time to less than 1 second for coronary CT angiography, thereby decreasing the volume of contrast material and radiation dose required for the examination. It also eliminates stair-step artifacts, allowing robust improvements in myocardial function and perfusion imaging. Additionally, new imaging techniques for the cardiothoracic area, including subtraction imaging and free-breathing scans, have been developed and further improved by using the wide-detector CT scanner. This article investigates the technical developments in wide-detector CT scanners, summarizes their clinical applications in the cardiothoracic area, and provides a review of the recent literature.

Subtraction CT angiography improves evaluation of significant coronary artery disease in patients with severe calcifications or stents-the C-Sub 320 multicenter trial

OBJECTIVES

Diagnostic accuracy of conventional coronary CT angiography (CCTA_conv) may be compromised by blooming artifacts from calcifications or stents. Blooming artifacts may be reduced by subtraction coronary CT angiography (CCTA_sub) in which non-contrast and contrast CT data sets are subtracted digitally. We tested whether CCTA_sub in patients with severe coronary calcification or stents reduces the number of false-positive stenosis evaluations compared with CCTA_conv.

METHODS

In this study, 180 symptomatic patients scheduled for invasive coronary angiography (ICA) were prospectively enrolled and CT scanned (2013-2016) at three international centers. CCTA_conv, and CCTA_sub data sets were reconstructed. Target segments were defined as motion-free coronary segments with a suspected stenosis (> 50% of lumen) potentially due to blooming of either calcium or stents. Target segments were evaluated with respect to misregistration artifacts from the CCTA_sub reconstruction process, in which case evaluation was omitted. CCTA_sub and CCTA_conv were compared with ICA. Primary outcome measure was the frequency of false positives by CCTA_conv versus CCTA_sub to identify > 50% coronary stenosis by ICA on a per-segment level.

RESULTS

After exclusion of 76 patients, 104 (14% females) with mean age 67 years and median Agatston score 852 were included. There were 136 target segments with misregistration and 121 target segments without. Accuracy calculations in target segments without misregistration showed a reduction of the false positives from 72% [95% confidence interval (CI): 63-80%] in CCTA_conv to 33% (CI:25-42%) in CCTA_sub, at the expense of 7% (CI:3-14%) false negatives in CCTA_sub.

CONCLUSIONS

In severely calcified coronary arteries or stents, CCTA_sub reduces the false-positive rate in well-aligned, calcified or stent segments suspected of significant stenosis on CCTA_conv. Nevertheless, misregistration artifacts are frequent in CCTA_sub.

KEY POINTS

• A high calcium-score reduces the diagnostic accuracy in patients scanned with cardiac CT. • These patients would normally need an invasive angiogram for diagnosis. • In this prospective, multicenter study, subtraction CT, when evaluable, reduces false-positive stenosis evaluations. • Subtraction coronary CT angiography may, when evaluable, reduce excessive downstream testing.

Feasibility of coronary calcium and stent image subtraction using 320-detector row CT angiography

BACKGROUND

The reader confidence and diagnostic accuracy of coronary CT angiography (CCTA) can be compromised by the presence of calcified plaques and stents causing blooming artifacts. Compared to conventional invasive coronary angiography (ICA), this may cause an overestimation of stenosis severity leading to false-positive results. In a pilot study, we tested the feasibility of a new coronary calcium image subtraction algorithm in relation to reader confidence and diagnostic accuracy.

METHODS

Forty-three patients underwent clinically indicated ICA and CCTA using a 320-detector row CT. Median Agatston score was 510. Two data sets were reconstructed: a conventional CCTA (CCTAconv) and a subtracted CCTA (CCTAsub), where calcifications detected on noncontrast images were subtracted from the CCTA. Reader confidence and concordance with ICA for identification of >50% stenosis were recorded. We defined target segments on CCTAconv as motion-free coronary segments with calcification or stent and low reader confidence. The effect of CCTAsub was assessed. No approval from the ethics committee was required according to Danish law.

RESULTS

A total of 76 target segments were identified. The use of coronary calcium image subtraction improved the reader confidence in 66% of these segments. In target segments, specificity (86% vs 65%; P < .01) and positive predictive value (71% vs 51%, P = .03) were improved using CCTAsub compared to CCTAconv without loss in negative predictive value.

CONCLUSIONS

Our initial experience with coronary calcium image subtraction suggests that it is feasible and could lead to an improvement in reader confidence and diagnostic accuracy for identification of significant coronary artery disease.