Single-phase coronary artery CT angiography extracted from stress dynamic myocardial CT perfusion on third-generation dual-source CT: Validation by coronary angiography

Dynamic myocardial CT perfusion imaging-state of the art

In patients with suspected coronary artery disease (CAD), dynamic myocardial computed tomography perfusion (CTP) imaging combined with coronary CT angiography (CTA) has become a comprehensive diagnostic examination technique resulting in both anatomical and quantitative functional information on myocardial blood flow, and the presence and grading of stenosis. Recently, CTP imaging has been proven to have good diagnostic accuracy for detecting myocardial ischemia, comparable to stress magnetic resonance imaging and positron emission tomography perfusion, while being superior to single photon emission computed tomography. Dynamic CTP accompanied by coronary CTA can serve as a gatekeeper for invasive workup, as it reduces unnecessary diagnostic invasive coronary angiography. Dynamic CTP also has good prognostic value for the prediction of major adverse cardiovascular events. In this article, we will provide an overview of dynamic CTP, including the basics of coronary blood flow physiology, applications and technical aspects including protocols, image acquisition and reconstruction, future perspectives, and scientific challenges. KEY POINTS: • Stress dynamic myocardial CT perfusion combined with coronary CTA is a comprehensive diagnostic examination technique resulting in both anatomical and quantitative functional information. • Dynamic CTP imaging has good diagnostic accuracy for detecting myocardial ischemia comparable to stress MRI and PET perfusion. • Dynamic CTP accompanied by coronary CTA may serve as a gatekeeper for invasive workup and can guide treatment in obstructive coronary artery disease.

Low-dose CT perfusion with combined use of CTP and CTP-derived coronary CT angiography at 70 kVp: validation with invasive fractional flow reserve

OBJECTIVES

To investigate the diagnostic performance of 70-kVp stress dynamic myocardial CT perfusion (CTP) as a low-dose, one-stop cardiac CT examination in clinical application.

MATERIALS AND METHODS

Consecutive symptomatic patients were prospectively recruited and scanned with stress dynamic myocardial CTP. The CTP phase with the best enhancement of the coronary arteries was selected and extracted as the CTP-derived single-phase coronary CT angiography (SP-CTA). The diagnostic performance of CTP and CTP+SP-CTA for functionally significant CAD was assessed. Invasive coronary angiography and fractional flow reserve were used as the reference standard for the myocardial ischemia evaluation.

RESULTS

In total, 71 patients (43 men and 28 women; 63.6 ± 8.8 years old) underwent the stress dynamic myocardial CTP; 63 vessels (36.2%) from 42 of the patients (59.2%) were identified as causing ischemia. On a per-vessel basis, the sensitivity, specificity, PPV, NPV, and diagnostic accuracy for CTP and CTP+SP-CTA were 77.8%, 93.7%, 87.5%, 88.1%, and 87.9% and 84.1%, 93.7%, 88.3%, 91.2%, and 90.2%, respectively. The area under the curve (AUC) of CTP+SP-CTA (AUC = 0.963; 95%CI, 0.938-0.989) was significantly superior to that of CTP (AUC = 0.922; 95%CI, 0.880-0.964) and that of SP-CTA (AUC = 0.833; 95%CI, 0.765-0.900) alone (all p < 0.01). The mean radiation dose of the CTP examination was 3.8 ± 1.4 mSv.

CONCLUSION

CTP-derived SP-CTA improved the diagnostic value of CTP. With a promising performance of myocardial ischemia detection and low radiation dose, the innovative low-dose, one-stop CTP examination is clinically feasible for patients who need to receive a myocardial perfusion assessment.

KEY POINTS

• Myocardial CTP performed well in the evaluation of hemodynamically significant CAD. • CTP-derived single-phase CCTA improved the diagnostic value of CTP. • The combined use of low-dose CTP and CTP-derived CCTA at 70 kVp is clinically feasible for CAD patients who need to receive a myocardial perfusion assessment.

Incremental Image Noise Reduction in Coronary CT Angiography Using a Deep Learning-Based Technique with Iterative Reconstruction

Objective

To assess the feasibility of applying a deep learning-based denoising technique to coronary CT angiography (CCTA) along with iterative reconstruction for additional noise reduction.

Materials and Methods

We retrospectively enrolled 82 consecutive patients (male:female = 60:22; mean age, 67.0 ± 10.8 years) who had undergone both CCTA and invasive coronary artery angiography from March 2017 to June 2018. All included patients underwent CCTA with iterative reconstruction (ADMIRE level 3, Siemens Healthineers). We developed a deep learning based denoising technique (ClariCT.AI, ClariPI), which was based on a modified U-net type convolutional neural net model designed to predict the possible occurrence of low-dose noise in the originals. Denoised images were obtained by subtracting the predicted noise from the originals. Image noise, CT attenuation, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were objectively calculated. The edge rise distance (ERD) was measured as an indicator of image sharpness. Two blinded readers subjectively graded the image quality using a 5-point scale. Diagnostic performance of the CCTA was evaluated based on the presence or absence of significant stenosis (≥ 50% lumen reduction).

Results

Objective image qualities (original vs. denoised: image noise, 67.22 ± 25.74 vs. 52.64 ± 27.40; SNR [left main], 21.91 ± 6.38 vs. 30.35 ± 10.46; CNR [left main], 23.24 ± 6.52 vs. 31.93 ± 10.72; all p < 0.001) and subjective image quality (2.45 ± 0.62 vs. 3.65 ± 0.60, p < 0.001) improved significantly in the denoised images. The average ERDs of the denoised images were significantly smaller than those of originals (0.98 ± 0.08 vs. 0.09 ± 0.08, p < 0.001). With regard to diagnostic accuracy, no significant differences were observed among paired comparisons.

Conclusion

Application of the deep learning technique along with iterative reconstruction can enhance the noise reduction performance with a significant improvement in objective and subjective image qualities of CCTA images.

Myocardial Coverage and Radiation Dose in Dynamic Myocardial Perfusion Imaging Using Third-Generation Dual-Source CT

OBJECTIVE

Third-generation dual-source computed tomography (3rd-DSCT) allows dynamic myocardial CT perfusion imaging (dynamic CTP) with a 10.5-cm z-axis coverage. Although the increased radiation exposure associated with the 50% wider scan range compared to second-generation DSCT (2nd-DSCT) may be suppressed by using a tube voltage of 70 kV, it remains unclear whether image quality and the ability to quantify myocardial blood flow (MBF) can be maintained under these conditions. This study aimed to compare the image quality, estimated MBF, and radiation dose of dynamic CTP between 2nd-DSCT and 3rd-DSCT and to evaluate whether a 10.5-cm coverage is suitable for dynamic CTP.

MATERIALS AND METHODS

We retrospectively analyzed 107 patients who underwent dynamic CTP using 2nd-DSCT at 80 kV (n = 54) or 3rd-DSCT at 70 kV (n = 53). Image quality, estimated MBF, radiation dose, and coverage of left ventricular (LV) myocardium were compared.

RESULTS

No significant differences were observed between 3rd-DSCT and 2nd-DSCT in contrast-to-noise ratio (37.4 ± 11.4 vs. 35.5 ± 11.2, p = 0.396). Effective radiation dose was lower with 3rd-DSCT (3.97 ± 0.92 mSv with a conversion factor of 0.017 mSv/mGy·cm) compared to 2nd-DSCT (5.49 ± 1.36 mSv, p < 0.001). Incomplete coverage was more frequent with 2nd-DSCT than with 3rd-DSCT (1.9% [1/53] vs. 56% [30/54], p < 0.001). In propensity score-matched cohorts, MBF was comparable between 3rd-DSCT and 2nd-DSCT in non-ischemic (146.2 ± 26.5 vs. 157.5 ± 34.9 mL/min/100 g, p = 0.137) as well as ischemic myocardium (92.7 ± 21.1 vs. 90.9 ± 29.7 mL/min/100 g, p = 0.876).

CONCLUSION

The radiation increase inherent to the widened z-axis coverage in 3rd-DSCT can be balanced by using a tube voltage of 70 kV without compromising image quality or MBF quantification. In dynamic CTP, a z-axis coverage of 10.5 cm is sufficient to achieve complete coverage of the LV myocardium in most patients.

Myocardial blood flow analysis of stress dynamic myocardial CT perfusion for hemodynamically significant coronary artery disease diagnosis: The clinical value of relative parameter optimization

BACKGROUND

The methods for calculating the optimal myocardial blood flow (MBF) relative parameters in stress dynamic myocardial CT perfusion (CTP) in the detection of hemodynamically significant coronary artery disease (CAD) are non-uniform and lack standards.

METHODS

A total of 86 patients who were prospectively recruited underwent APT stress dynamic myocardial CTP. The relative MBF perfusion parameters were calculated as av_Ratio, Q3av_Ratio and hi_Ratio according to the three types of reference MBF values, respectively: (1) average segmental MBF value, (2) the third quartile of the average segmental MBF value, and (3) highest segmental MBF value. All the data were derived from both the endocardial and transmural layers of the myocardium. Invasive coronary angiography and fractional flow reserve (ICA/FFR) were used as the reference standards for myocardial ischemia evaluation.

RESULTS

A total of 151 vessels of 60 patients (43 men and 17 women; 61.38 ± 8.01 years) were enrolled in the analysis. The performance of the endocardial layer was superior to that of the transmural layer (all P < 0.05). The hi_Ratio of the endocardial myocardium (AUC = 0.906, 95% CI: 0.857-0.954), for which the highest segmental value was selected as the reference MBF, was superior to both av_Ratio and Q3av_Ratio for ischemia detection (AUC, 0.906 vs.0.879, P < 0.05; 0.906 vs.0.891, P = 0.18), and the sensitivity, specificity, PPV, NPV and diagnostic accuracy were 74.1%, 93.6%, 87.8%, 85.3% and 86.1%, respectively. The cutoff value of hi_Ratio was 0.675.

CONCLUSIONS

The relative MBF parameter of the endocardial myocardium using the highest segmental MBF value as a reference provided optimal diagnostic accuracy for the detection of hemodynamically significant CAD.