Reproducibility in the assessment of noncalcified coronary plaque with 256-slice multi-detector CT and automated plaque analysis software

Computed tomographic angiography measures of coronary plaque in clinical trials: opportunities and considerations to accelerate drug translation

Atherosclerotic coronary artery disease (CAD) is the causal pathological process driving most major adverse cardiovascular events (MACE) worldwide. The complex development of atherosclerosis manifests as intimal plaque which occurs in the presence or absence of traditional risk factors. There are numerous effective medications for modifying CAD but new pharmacologic therapies require increasingly large and expensive cardiovascular outcome trials to assess their potential impact on MACE and to obtain regulatory approval. For many disease areas, nearly a half of drugs are approved by the U.S. Food & Drug Administration based on beneficial effects on surrogate endpoints. For cardiovascular disease, only low-density lipoprotein cholesterol and blood pressure are approved as surrogates for cardiovascular disease. Valid surrogates of CAD are urgently needed to facilitate robust evaluation of novel, beneficial treatments and inspire investment. Fortunately, advances in non-invasive imaging offer new opportunity for accelerating CAD drug development. Coronary computed tomography angiography (CCTA) is the most advanced candidate, with the ability to measure accurately and reproducibly characterize the underlying causal disease itself. Indeed, favourable changes in plaque burden have been shown to be associated with improved outcomes, and CCTA may have a unique role as an effective surrogate endpoint for therapies that are designed to improve CAD outcomes. CCTA also has the potential to de-risk clinical endpoint-based trials both financially and by enrichment of participants at higher likelihood of MACE. Furthermore, total non-calcified, and high-risk plaque volume, and their change over time, provide a causally linked measure of coronary artery disease which is inextricably linked to MACE, and represents a robust surrogate imaging biomarker with potential to be endorsed by regulatory authorities. Global consensus on specific imaging endpoints and protocols for optimal clinical trial design is essential as we work towards a rigorous, sustainable and staged pathway for new CAD therapies.

Comparison of Two Contemporary Quantitative Atherosclerotic Plaque Assessment Tools for Coronary Computed Tomography Angiography: Single-Center Analysis and Multi-Center Patient Cohort Validation

BACKGROUND

Coronary computed tomography angiography (CCTA) provides non-invasive quantitative assessments of plaque burden and composition. The quantitative assessment of plaque components requires the use of analysis software that provides reproducible semi-automated plaque detection and analysis. However, commercially available plaque analysis software can vary widely in the degree of automation, resulting in differences in terms of reproducibility and time spent.

AIM

To compare the reproducibility and time spent of two CCTA analysis software tools using different algorithms for the quantitative assessment of coronary plaque volumes and composition in two independent patient cohorts.

METHODS

The study population included 100 patients from two different cohorts: 50 patients from a single-center (Siemens Healthineers, SOMATOM Force (DSCT)) and another 50 patients from a multi-center study (5 different > 64 slice CT scanner types). Quantitative measurements of total calcified and non-calcified plaque volume of the right coronary artery (RCA), left anterior descending (LAD), and left circumflex coronary artery (LCX) were performed on a total of 300 coronaries by two independent readers, using two different CCTA analysis software tools (Tool #1: Siemens Healthineers, syngo.via Frontier CT Coronary Plaque Analysis and Tool #2: Siemens Healthineers, successor CT Coronary Plaque Analysis prototype). In addition, the total time spent for the analysis was recorded with both programs.

RESULTS

The patients in cohorts 1 and 2 were 62.8 ± 10.2 and 70.9 ± 11.7 years old, respectively, 10 (20.0%) and 35 (70.0%) were female and 34 (68.0%) and 20 (40.0%), respectively, had hyperlipidemia. In Cohort #1, the inter- and intra-observer variabilities for the assessment of plaque volumes per patient for Tool #1 versus Tool #2 were 22.8%, 22.0%, and 26.0% versus 2.3%, 3.9%, and 2.5% and 19.7%, 21.4%, and 22.1% versus 0.2%, 0.1%, and 0.3%, respectively, for total, noncalcified, and calcified lesions (p < 0.001 for all between Tools #1 and 2 both for inter- and intra-observer). The inter- and intra-observer variabilities using Tool #2 remained low at 2.9%, 2.7%, and 3.0% and 3.8%, 3.7%, and 4.0%, respectively, for total, non-calcified, and calcified lesions in Cohort #2. For each dataset, the median processing time was higher for Tool #1 versus Tool #2 (459.5 s IQR = 348.0-627.0 versus 208.5 s; IQR = 198.0-216.0) (p < 0.001).

CONCLUSION

The plaque analysis Tool #2 (CT-guided PCI) encompassing a higher degree of automated support required less manual editing, was more time-efficient, and showed a higher intra- and inter-observer reproducibility for the quantitative assessment of plaque volumes both in a representative single-center and in a multi-center validation cohort.

Quantitative plaque assessment by coronary computed tomography angiography: An up-to-date review

Coronary computed tomography angiography has an emerging role in the diagnostic workup of coronary artery disease. Due to its high sensitivity and negative predictive value, coronary computed tomography angiography can rule out obstructive coronary artery diseases and substitute invasive coronary angiography in many cases. In addition, coronary computed tomography angiography provides a unique information beyond stenosis grading as it can visualize atherosclerosis and quantify its extent. Qualitative and quantitative plaque assessment provides an incremental value in the prediction of future major adverse cardiac events. Moreover, determining adverse plaque features has a potential to identify advanced atherosclerosis and patients at increased risk of acute coronary syndrome. Nevertheless, challenges may emerge with the process of quantifying coronary plaques due to limited reproducibility, lack of automated, standardized and validated techniques. Therefore, reliable quantified data are scarce due to the various computed tomography scanners and software platforms and investigations with small sample sizes. Radiomics and machine learning-based image processing methods are relatively new in the field of cardiovascular plaque imaging. These techniques hold the promise to improve diagnostic performance, reproducibility and prognostic value of computed tomography based plaque assessment.

Iterative model reconstruction reduces calcified plaque volume in coronary CT angiography

OBJECTIVE

To assess the impact of iterative model reconstruction (IMR) on calcified plaque quantification as compared to filtered back projection reconstruction (FBP) and hybrid iterative reconstruction (HIR) in coronary computed tomography angiography (CTA).

METHODS

Raw image data of 52 patients who underwent 256-slice CTA were reconstructed with IMR, HIR and FBP. We evaluated qualitative, quantitative image quality parameters and quantified calcified and partially calcified plaque volumes using automated software.

RESULTS

Overall qualitative image quality significantly improved with HIR as compared to FBP, and further improved with IMR (p<0.01 all). Contrast-to-noise ratios were improved with IMR, compared to HIR and FBP (51.0 [43.5-59.9], 20.3 [16.2-25.9] and 14.0 [11.2-17.7], respectively, all p<0.01) Overall plaque volumes were lowest with IMR and highest with FBP (121.7 [79.3-168.4], 138.7 [90.6-191.7], 147.0 [100.7-183.6]). Similarly, calcified volumes (>130 HU) were decreased with IMR as compared to HIR and FBP (105.9 [62.1-144.6], 110.2 [63.8-166.6], 115.9 [81.7-164.2], respectively, p<0.05 all). High-attenuation non-calcified volumes (90-129 HU) yielded similar values with FBP and HIR (p=0.81), however it was lower with IMR (p < 0.05 both). Intermediate- (30-89 HU) and low-attenuation (<30 HU) non-calcified volumes showed no significant difference (p=0.22 and p=0.67, respectively).

CONCLUSIONS

IMR improves image quality of coronary CTA and decreases calcified plaque volumes.

Coronary CT Angiography: Variability of CT Scanners and Readers in Measurement of Plaque Volume

Purpose To determine reader and computed tomography (CT) scan variability for measurement of coronary plaque volume. Materials and Methods This HIPAA-compliant study followed Standards for Reporting of Diagnostic Accuracy guidelines. Baseline coronary CT angiography was performed in 40 prospectively enrolled subjects (mean age, 67 years ± 6 [standard deviation]) with asymptomatic hyperlipidemia by using a 320-detector row scanner (Aquilion One Vision; Toshiba, Otawara, Japan). Twenty of these subjects underwent coronary CT angiography repeated on a separate day with the same CT scanner (Toshiba, group 1); 20 subjects underwent repeat CT performed with a different CT scanner (Somatom Force; Siemens, Forchheim, Germany [group 2]). Intraclass correlation coefficients (ICCs) and Bland-Altman analysis were used to assess interreader, intrareader, and interstudy reproducibility. Results Baseline and repeat coronary CT angiography scans were acquired within 19 days ± 6. Interreader and intrareader agreement rates were high for total, calcified, and noncalcified plaques for both CT scanners (all ICCs ≥ 0.96) without bias. Scanner variability was ±18.4% (coefficient of variation) with same-vendor follow-up. However, scanner variability increased to ±29.9% with different-vendor follow-up. The sample size to detect a 5% change in noncalcified plaque volume with 90% power and an α error of .05 was 286 subjects for same-CT scanner follow-up and 753 subjects with different-vendor follow-up. Conclusion State-of-the-art coronary CT angiography with same-vendor follow-up has good scan-rescan reproducibility, suggesting a role of coronary CT angiography in monitoring coronary artery plaque response to therapy. Differences between coronary CT angiography vendors resulted in lower scan-rescan reproducibility. ^© RSNA, 2016 Online supplemental material is available for this article.

Quantitative analysis of coronary plaque composition by dual-source CT in patients with acute non-ST-elevation myocardial infarction compared to patients with stable coronary artery disease correlated with virtual histology intravascular ultrasound

RATIONALE AND OBJECTIVES

To quantitatively assess coronary atherosclerotic plaque composition in patients with acute non-ST elevation myocardial infarction (NSTEMI) and patients with stable coronary artery disease (CAD) by coronary computed tomography angiography (cCTA) correlated with virtual histology intravascular ultrasound (VH-IVUS).

MATERIALS AND METHODS

Sixty patients (35 with NSTEMI) were included. Corresponding plaques were assessed by dual-source cCTA and VH-IVUS regarding volumes and percentages of fatty, fibrous, and calcified component; overall plaque burden; and maximal percent area stenosis. Possible differences between patient groups were investigated. Concordance between cCTA and VH-IVUS measurements was validated by Bland-Altman analysis.

RESULTS

Forty corresponding plaques (22 of patients with NSTEMI) were finally analyzed by cCTA and VH-IVUS. cCTA plaque analysis revealed no significant differences between plaques of patients with NSTEMI and stable CAD regarding absolute and relative amounts of any plaque component (fatty: 20 mm³/13% versus 17 mm³/14%; fibrous: 81 mm³/63% versus 80 mm³/53%; calcified: 16 mm³/14% versus 26 mm³/26%; all P > .05) or overall plaque burden (153 mm³ versus 165 mm³; P > .05), nor did VH-IVUS plaque analysis. VH-IVUS measured a higher area stenosis in patients with NSTEMI compared to patients with stable CAD (76% versus 68%, P = .01; in cCTA 69% versus 65%, P = .2). Volumes of fatty component were measured systematically lower in cCTA, whereas calcified and fibrous volumes were higher. No significant bias was observed comparing volumes of overall noncalcified component and overall plaque burden.

CONCLUSION

Plaques of patients with acute NSTEMI and of patients with stable CAD cannot be differentiated by quantification of plaque components. cCTA and VH-IVUS differ in plaque component analysis.

Asymptomatic subjects with zero coronary calcium score: coronary CT angiographic features of plaques in event-prone patients

The aims of this study were: (a) to assess clinical predictors and coronary computed tomography angiography (CCTA) characteristics of noncalcified coronary plaques (NCP) in subjects who had cardiac events despite a zero coronary artery calcium score (CACS), and (b) to describe computed tomography (CT) plaque characteristics in subjects with cardiac events. A total of 7,961 subjects with zero CACS were evaluated; 6,531 subjects underwent CCTA as part of a health check-up. Those who had zero CACS were included in our mid-term follow-up study. Cardiac events included cardiac death, acute coronary syndrome or revascularization with stable angina. More than one NCP was identified in 441 subjects with zero CACS, including 48 subjects with obstructive coronary artery disease (CAD) caused by NCPs. Age, male gender, hypertension, diabetes and low density lipoprotein were independent predictors of obstructive CAD. Among subjects with obstructive CAD, young adults were classified into low (79.2 %) or moderate (72.9 %) risk groups by the National Centers for Environmental Prediction III guidelines. Approximately 0.2 % of subjects had cardiac events during our follow-up period. All patients with cardiac events had NCPs with significantly lower mean CT numbers, higher remodeling indexes and worse degree of stenosis. In asymptomatic subjects with zero CACS, NCP was associated with cardiac events. CCTA might be useful for risk stratification among select populations with CAD and zero CACS who have certain plaque characteristics associated with cardiac events.

Additive value of semiautomated quantification of coronary artery disease using cardiac computed tomographic angiography to predict future acute coronary syndrome

OBJECTIVES

The purpose of this study was to investigate whether the use of a semiautomated plaque quantification algorithm (reporting volumetric and geometric plaque properties) provides additional prognostic value for the development of acute coronary syndromes (ACS) as compared with conventional reading from cardiac computed tomography angiography (CCTA).

BACKGROUND

CCTA enables the visualization of coronary plaque characteristics, of which some have been shown to predict ACS.

METHODS

A total of 1,650 patients underwent 64-slice CCTA and were followed up for ACS for a mean 26 ± 10 months. In 25 patients who had ACS and 101 random controls (selected from 993 patients with coronary artery disease but without coronary event), coronary artery disease was evaluated using conventional reading (calcium score, luminal stenosis, morphology), and then independently quantified using semiautomated software (plaque volume, burden area [plaque area divided by vessel area times 100%], noncalcified percentage, attenuation, remodeling). Clinical risk profile was calculated with Framingham risk score (FRS).

RESULTS

There were no significant differences in conventional reading parameters between controls and patients who had ACS. Semiautomated plaque quantification showed that compared to controls, ACS patients had higher total plaque volume (median: 94 mm(3) vs. 29 mm(3)) and total noncalcified volume (28 mm(3) vs. 4 mm(3), p ≤ 0.001 for both). In addition, per-plaque maximal volume (median: 56 mm(3) vs. 24 mm(3)), noncalcified percentage (62% vs. 26%), and plaque burden (57% vs. 36%) in ACS patients were significantly higher (p < 0.01 for all). A receiver-operating characteristic model predicting for ACS incorporating FRS and conventional CCTA reading had an area under the curve of 0.64; a second model also incorporating semiautomated plaque quantification had an area under the curve of 0.79 (p < 0.05).

CONCLUSIONS

The semiautomated plaque quantification algorithm identified several parameters predictive for ACS and provided incremental prognostic value over clinical risk profile and conventional CT reading. The application of this tool may improve risk stratification in patients undergoing CCTA.