Korean J Radiol.  2019 Jul;20(7):1146-1155. 10.3348/kjr.2018.0845.

Modified Subtraction Coronary CT Angiography with a Two-Breathhold Technique: Image Quality and Diagnostic Accuracy in Patients with Coronary Calcifications

• Guo W
• Tripathi P
• Yang S
• Qian J
• Rai B
• Zeng M

• KMID: 2467025
• DOI: http://doi.org/10.3348/kjr.2018.0845

Abstract

OBJECTIVE
To evaluate a modified subtraction coronary computed tomography angiography (CCTA) technique with a two-breathhold approach in terms of image quality and stenosis grading of calcified coronary segments and in the detection of significant coronary stenosis in segments with severe calcification.
MATERIALS AND METHODS
The institutional board approved this study, and all subjects provided written consent. A total of 128 patients were recruited into this trial, of which 32 underwent subtraction CCTA scans and invasive coronary angiography (ICA). The average Agatston score was 356 ± 145. In severely calcified coronary segments, the presence of significant (> 50%) stenosis was assessed on both conventional CCTA and subtraction CCTA images, and the results were finally compared with ICA findings as the gold standard.
RESULTS
For severely calcified segments, the image quality in conventional CCTA significantly improved from 2.51 ± 0.98 to 3.12 ± 0.94 in subtraction CCTA (p < 0.001). In target segments, specificity (70% vs. 87%; p = 0.005) and positive predictive value (61% vs. 79%, p < 0.01) were improved using subtraction CCTA in comparison with conventional CCTA, with no loss in the negative predictive value. The segment-based diagnostic accuracy for detecting significant stenosis was significantly better in subtraction CCTA than in conventional CCTA (area under the receiver operating characteristic curve, 0.94 vs. 0.85; p = 0.03).
CONCLUSION
This modified subtraction CCTA method showed lower misregistration and better image quality in patients with limited breathhold capability. In comparison with conventional CCTA, modified subtraction CCTA would allow stenosis regrading and improve the diagnostic accuracy in coronary segments with severe calcification.

Keyword

320-detector row CT; Coronary CT angiography; Plaque calcification; Subtraction

MeSH Terms

Angiography*
Constriction, Pathologic
Coronary Angiography
Coronary Stenosis
Humans
Methods
ROC Curve
Sensitivity and Specificity

Figure

• 

  Fig. 1 Scan protocol for imaging acquisition for modified subtraction CCTA.BH time is interval between end of BH announcement to end of contrast scan, and also to end of mask scan respectively. BH = breath-holding, CCTA = coronary computed tomography angiography

• 

  Fig. 2 Examples of coronary atherosclerotic plaque calcification by CT images.A. Mildly calcified (cross-sectional arc calcium < 90°). B. Moderately calcified (cross-sectional arc calcium 90°–180°). C, D. Severely calcified (cross-sectional arc calcium > 180°) segments. Segment calcification was measured by using cross-sectional arc method.

• 

  Fig. 3 Image quality of conventional and subtraction computed tomography angiography in different degrees of segment-based plaque calcifications.Image quality in subtraction CCTA is significantly improved in segments with severe calcification (2.51 ± 0.98 to 3.12 ± 0.94, p < 0.001). However, image quality is only slightly improved in segments with mild calcification (3.68 ± 0.54 to 3.71 ± 0.49) and segments with moderate calcification (3.49 ± 0.65 to 3.56 ± 0.59), but not significantly (p = 0.68 and p = 0.48, respectively). Image quality score: 1 = uninterpretable, 2 = poor image quality, 3 = adequate image quality, 4 = good image quality.

• 

  Fig. 4 Case showing stenosis regrading in conventional CCTA and subtraction.A, B. Moderate calcification is observed in left ascending artery on conventional images. C. After performing subtraction, calcification is eliminated. D–F. Degree of stenosis is assessed as mild in both subtraction and conventional CCTA. Corresponding subtraction process for severe plaque calcification at left anterior descending coronary artery from another patient. Moderate stenosis can be seen in subtraction CCTA, while severe stenosis is rated in conventional CCTA.

• 

  Fig. 5 Area under receiver operating characteristic curves of conventional CCTA and subtraction CCTA versus invasive coronary angiography: AUC for conventional CCTA is 0.85 (95% CI, 0.74–0.96).AUC for subtraction CCTA is 0.94 (95% CI, 0.86–1.00). ACU = area under curve, CI = confidence interval

• 

  Fig. 6 68-year-old man with suspected coronary artery disease.From CPR image (A) and cross-sectional image (B) in conventional CCTA, severe calcification is observed in proximal portion of left anterior descending artery, which makes it difficult to assess lumen (arrow). In cross-sectional image (C) and CPR cross-sectional image (D) after subtraction, no significant stenosis is depicted (arrow). There is no significant stenosis determined by invasive coronary angiography (arrow) (E). CPR = curved planar reformation

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