Transluminal attenuation gradient in coronary computed tomography angiography for determining stenosis severity of calcified coronary artery: a primary study with dual-source CT

Development and evaluation of a radiomics model of resting 13N-ammonia positron emission tomography myocardial perfusion imaging to predict coronary artery stenosis in patients with suspected coronary heart disease

BACKGROUND

Coronary angiography (CAG) is usually performed in patients with coronary heart disease (CHD) to evaluate the coronary artery stenosis. However, patients with iodine allergy and renal dysfunction are not suitable for CAG. We try to develop a radiomics machine learning model based on rest 13N-ammonia (13N-NH3) positron emission tomography (PET) myocardial perfusion imaging (MPI) to predict coronary stenosis.

METHODS

Eighty-four patients were included with the inclusion criteria: adult patients; suspected CHD; resting MPI and CAG were performed; and complete data. Coronary artery stenosis >75% were considered to be significant stenosis. Patients were randomly divided into a training group and a testing group with a ratio of 1:1. Myocardial blood flow (MBF), perfusion defect extent (EXT), total perfusion deficit (TPD), and summed rest score (SRS) were obtained. Myocardial static images of the left ventricular (LV) coronary segments were segmented, and radiomics features were extracted. In the training set, the conventional parameter (MPI model) and radiomics (Rad model) models were constructed using the machine learning method and were combined to construct a nomogram. The models' performance was evaluated by area under the curve (AUC), accuracy, sensitivity, specificity, decision analysis curve (DCA), and calibration curves. Testing and subgroup analysis were performed.

RESULTS

MPI model was composed of MBF and EXT, and Rad model was composed of 12 radiomics features. In the training set, the AUC/accuracy/sensitivity/specificity of the MPI model, Rad model, and the nomogram were 0.795/0.778/0.937/0.511, 0.912/0.825/0.760/0.936 and 0.911/0.865/0.924/0.766 respectively. In the testing set, the AUC/accuracy/sensitivity/specificity of the MPI model, Rad model, and the nomogram were 0.798/0.722/0.659/0.841, 0.887/0.810/0.744/0.932 and 0.900/0.849/0.854/0.841 respectively. The AUC of Rad model and nomogram were significantly higher than that of MPI model. The DCA curve also showed that the clinical net benefit of the Rad model and nomogram was similar but greater than that of MPI model. The calibration curve showed good agreement between the observed and predicted values of the Rad model. In the subgroup analysis of Rad model, there was no significant difference in AUC between subgroups.

CONCLUSIONS

The Rad model is more accurate than the MPI model in predicting coronary stenosis. This noninvasive technique could help improve risk stratification and had good generalization ability.

A Noninvasive Assessment of Flow Based on Contrast Dispersion in Computed Tomography Angiography: A Computational and Experimental Phantom Study

Transluminal attenuation gradient (TAG), defined as the gradient of the contrast agent attenuation drop along the vessel, is an imaging biomarker that indicates stenosis in the coronary arteries. The transluminal attenuation flow encoding (TAFE) equation is a theoretical platform that quantifies blood flow in each coronary artery based on computed tomography angiography (CTA) imaging. This formulation couples TAG (i.e., contrast dispersion along the vessel) with fluid dynamics. However, this theoretical concept has never been validated experimentally. The aim of this proof-of-principle phantom study is to validate TAFE based on CTA imaging. Dynamic CTA images were acquired every 0.5 s. The average TAFE estimated flow rates were compared against four predefined pump values in a straight (20, 25, 30, 35, and 40 ml/min) and a tapered phantom (25, 35, 45, and 55 ml/min). Using the TAFE formulation with no correction, the flow rates were underestimated by 33% and 81% in the straight and tapered phantoms, respectively. The TAFE formulation was corrected for imaging artifacts focusing on partial volume averaging and radial variation of contrast enhancement. After corrections, the flow rates estimated in the straight and tapered phantoms had an excellent Pearson correlation of r = 0.99 and 0.87 (p < 0.001), respectively, with only a 0.6%±0.2 mL/min difference in estimation of the flow rate. In this proof-of-concept phantom study, we corrected the TAFE formulation and showed a good agreement with the actual pump values. Future clinical validations are needed for feasibility of TAFE in clinical use.

Advances in CT Techniques in Vascular Calcification

Vascular calcification, a common pathological phenomenon in atherosclerosis, diabetes, hypertension, and other diseases, increases the incidence and mortality of cardiovascular diseases. Therefore, the prevention and detection of vascular calcification play an important role. At present, various techniques have been applied to the analysis of vascular calcification, but clinical examination mainly depends on non-invasive and invasive imaging methods to detect and quantify. Computed tomography (CT), as a commonly used clinical examination method, can analyze vascular calcification. In recent years, with the development of technology, in addition to traditional CT, some emerging types of CT, such as dual-energy CT and micro CT, have emerged for vascular imaging and providing anatomical information for calcification. This review focuses on the latest application of various CT techniques in vascular calcification.

The transluminal attenuation gradient does not add diagnostic accuracy to coronary computed tomography

BACKGROUND

A method for improving the accuracy of coronary computed tomography angiography (CCTA) is highly sought after as it would help to avoid unnecessary invasive coronary angiographies. Measurement of the transluminal attenuation gradient (TAG) has been proposed as an alternative to other existing methods, i.e. CT perfusion and CT fractional flow reserve (FFR).

PURPOSE

To evaluate the incremental value of three types of TAG in high-pitch spiral CCTA with invasive FFR measurements as reference.

MATERIAL AND METHODS

TAG was measured using two semi-automatic methods and one manual method. A receiver operating characteristic (ROC) analysis was made to determine the usefulness of TAG alone as well as TAG combined with CCTA for detection of significant coronary artery stenoses defined by an invasive FFR value ≤0.80.

RESULTS

A total of 51 coronary vessels in 37 patients were included in this retrospective study. Hemodynamically significant stenoses were found in 13 vessels according to FFR. The ROC analysis TAG alone resulted in areas under the curve (AUCs) of 0.530 and 0.520 for the semi-automatic TAG and 0.557 for the manual TAG. TAG and CCTA combined resulted in AUCs of 0.567, 0.562 for semi-automatic TAG, and 0.569 for the manual TAG.

CONCLUSION

The results from our study showed no incremental value of TAG measured in single heartbeat CCTA in determining the severity of coronary artery stenosis degrees.

Diagnostic performance of corrected FFRCT metrics to predict hemodynamically significant coronary artery stenosis

OBJECTIVES

To determine the diagnostic performance of the fractional flow reserve (FFR) derived from coronary computed tomography angiography (CCTA) (FFR_CT) difference across the lesion (ΔFFR_{CT lesion}) or the vessel (ΔFFR_{CT vessel}) and the gradient of FFR_CT for the identification of hemodynamically significant coronary stenosis.

METHODS

From June 2016 to December 2018, 73 patients suspected of having coronary artery disease who underwent CCTA followed invasive coronary angiography (ICA) within 1 month were retrospectively included. ΔFFR_{CT lesion}, ΔFFR_{CT vessel}, and FFR_CT gradient were calculated. Performance characteristics of different corrected FFR_CT metrics in detecting ischemic stenosis were analyzed. Impacts of coronary calcification and lesion length on the corrected FFR_CT metrics were also analyzed.

RESULTS

The diagnostic sensitivities, specificities, and accuracies of 94.4%, 88.7%, and 91.0% with ΔFFR_{CT lesion}, 57.1%, 72.3%, and 65.2% with ΔFFR_{CT vessel}, and 50.0%, 85.1%, and 68.5% with FFR_CT gradient, respectively, were detected. There was higher specificity, accuracy, and area under the curve (AUC) for ΔFFR_{CT lesion} compared with CCTA (p < 0.05 for all). The specificity and AUC of FFR_CT gradient and ΔFFR_{CT vessel} were significantly higher than CCTA (p < 0.05 for all). Coronary calcification showed no impact on corrected FFR_CT metrics. ΔFFR_{CT lesion} for lesion length ratio (LLR) < 1/10 was significantly lower than that for LLR 1/10 to 3/10 and LLR > 3/10.

CONCLUSIONS

ΔFFR_{CT lesion} was significantly correlated with the hemodynamically significant coronary artery stenosis. ΔFFR_{CT lesion} had the potential to be immediately used in real-world practice to discriminate ischemic coronary artery stenosis.

KEY POINTS

• The difference of FFR_CT across the lesion or the vessel and the gradient of FFR_CT was related to the hemodynamically significant coronary artery stenosis. • The difference of FFR_CT across the lesion showed the best diagnostic performance in detecting the hemodynamically significant coronary artery stenosis. • Coronary calcification showed no impact on corrected FFR_CT metrics, while lesion length related to the difference of FFR_CT across the lesion.

New transluminal attenuation gradient derived from dynamic coronary CT angiography: diagnostic ability of ischemia detected by 13N-ammonia PET

Coronary computed tomography angiography (CCTA) has low specificity for detecting significant functional coronary stenosis. We developed a new transluminal attenuation gradient (TAG)-derived dynamic CCTA with dose modulation, and we investigated its diagnostic performance for myocardial ischemia depicted by ¹³N-ammonia positron emission tomography (PET). Data from 48 consecutive patients who had undergone both dynamic CCTA and ¹³N-ammonia PET were retrospectively analyzed. Dynamic CCTA was continuously performed in mid-diastole for five cardiac cycles with prospective electrocardiography gating after a 10-s contrast medium injection. One scan of the dynamic CCTA was performed as a boost scan for conventional CCTA at the peak phase of the ascending aorta. Absolute TAG values at five phases around the boost scan were calculated. The dynamic TAG index (DTI) was defined as the ratio of the maximum absolute TAG to the standard deviation of five TAG values. We categorized the coronary territories as non-ischemia or ischemia based on the ¹³N-ammonia PET results. A receiver operating characteristic (ROC) analysis was performed to determine the optimal cutoff of the DTI for identifying ischemia. The DTI was significantly higher for ischemia compared to non-ischemia (8.8 ± 3.9 vs. 4.6 ± 2.0, p < 0.01). The ROC analysis revealed 5.60 as the optimal DTI cutoff to detect ischemia, with an area under the curve of 0.87, 85.7% sensitivity, and 76.2% specificity. TAG provided no additional diagnostic value for the detection of ischemia. We propose the DTI derived from dynamic CCTA as a novel coronary flow index. The DTI is a valid technique for detecting functional coronary stenosis.

The effect of without using anisodamine during CT enterography on image quality, diagnostic performance and latent side effects

OBJECTIVE

To examine whether no anisodamine injection before CTE was feasible without impairing image quality and diagnostic performance.

MATERIALS

The change of mural thickness and luminal diameter were compared between using and no using anisodamine. The diagnostic performance of small-bowel disease was analyzed and compared.

RESULTS

No motion artifact was detected in two groups. There was no significant difference regarding the change of luminal diameter and mural thickness (all P>0.05). The diagnostic accuracy of small-bowel disease was no significant difference (P=0.63).

CONCLUSION

Lack of anisodamine injection before CTE did not impair image quality and diagnostic performance compared with CTEs performed with anisodamine injection.

Transluminal attenuation gradient and corrected models in coronary CT angiography for determining stenosis severity: a primary study using dual-source CT

AIM

To compare the incremental value of transluminal attenuation gradient (TAG), TAG with corrected contrast opacification (TAG-CCO), and TAG with exclusion of calcified coronary segments (TAG-ExC) in determining the stenosis severity of coronary arteries using coronary angiography (CAG) as the reference standard.

MATERIALS AND METHODS

One hundred and fifteen patients who underwent computed tomography coronary angiography (CTCA) and confirmed by coronary angiography (CAG) were included in the retrospective analysis. TAG, TAG-CCO, and TAG-ExC were calculated in 311 major epicardial coronary arteries. Changes in different TAG models were compared with corresponding stenosis severities ascertained by CAG. The diagnostic performances of TAG, TAG-CCO, TAG-ExC, and the TAG/CTCA, TAG-CCO/CTCA, and TAG-ExC/CTCA combinations over CTCA alone in evaluating stenosis severity were then analysed and compared. Furthermore, the incremental value of the TAG and the corrected models in the reclassification of CTCA-evaluated stenosis severity were calculated.

RESULTS

TAG, TAG-CCO, and TAG-ExC decreased gradually with increased stenosis severity (p<0.001 for all TAG models). TAG and TAG-ExC improved the diagnostic performance over CTCA in total vessel evaluation (c statistic= 0.926 versus 0.907, p=0.018; c statistic= 0.922 versus 0.907, p=0.030, respectively), but TAG-CCO did not. Meanwhile, adding TAG to CTCA enabled a significant reclassification in calcified vessels (n=95; net reclassification improvement = 0.143, p=0.038).

CONCLUSIONS

TAG and TAG-ExC improved the diagnostic performance of CTCA in all vessels. Adding TAG to CTCA significantly reclassified the calcified vessels. The additional value of TAG-CCO over CTCA alone in determining the stenosis severity is limited.

Functional Evaluation of Coronary Disease by CT Angiography

In recent years, several technical developments in the field of cardiac computed tomography (CT) have made possible the extraction of functional information from an anatomy-based examination. Several different lines have been explored and will be reviewed in the present paper, namely: 1) myocardial perfusion imaging; 2) transluminal attenuation gradients and corrected coronary opacification indexes; 3) fractional flow reserve computed from CT; and 4) extrapolation from atherosclerotic plaque characteristics. In view of these developments, cardiac CT has the potential to become in the near future a truly 2-in-1 noninvasive evaluation for coronary artery disease.

Non-invasive imaging of myocardial bridge by coronary computed tomography angiography: the value of transluminal attenuation gradient to predict significant dynamic compression

OBJECTIVES

To study the diagnostic value of transluminal attenuation gradient (TAG) measured by coronary computed tomography angiography (CCTA) for identifying relevant dynamic compression of myocardial bridge (MB).

METHODS

Patients with confirmed MB who underwent both CCTA and ICA within one month were retrospectively included. TAG was defined as the linear regression coefficient between luminal attenuation and distance. The TAG of MB vessel, length and depth of MB were measured and correlated with the presence and degree of dynamic compression observed at ICA. Systolic compression ≧50 % was considered significant.

RESULTS

302 patients with confirmed MB lesions were included. TAG was lowest (-17.4 ± 6.7 HU/10 mm) in patients with significant dynamic compression and highest in patients without MB compression (-9.5 ± 4.3 HU/10 mm, p < 0.001). Linear correlation revealed relation between the percentage of systolic compression and TAG (Pearson correlation, r = -0.52, p < 0.001) and no significant relation between the percentage of systolic compression and MB depth or length. ROC curve analysis determined the best cut-off value of TAG as -14.8HU/10 mm (area under curve = 0.813, 95 % confidence interval = 0.764-0.855, p < 0.001), which yielded high diagnostic accuracy (82.1 %, 248/302).

CONCLUSIONS

The degree of ICA-assessed systolic compression of MB significantly correlates with TAG but not MB depth or length.

KEY POINTS

• TAG is associated with the extent of dynamic compression of MB. • TAG is superior to depth and length for identifying dynamic compression. • Cut-off value of TAG as -14.8HU/10 mm yielded high predictive value.