Noninvasive physiologic assessment of coronary stenoses using cardiac CT

Cardiovascular Computed Tomography in the Diagnosis of Cardiovascular Disease: Beyond Lumen Assessment

Cardiovascular CT is being widely used in the diagnosis of cardiovascular disease due to the rapid technological advancements in CT scanning techniques. These advancements include the development of multi-slice CT, from early generation to the latest models, which has the capability of acquiring images with high spatial and temporal resolution. The recent emergence of photon-counting CT has further enhanced CT performance in clinical applications, providing improved spatial and contrast resolution. CT-derived fractional flow reserve is superior to standard CT-based anatomical assessment for the detection of lesion-specific myocardial ischemia. CT-derived 3D-printed patient-specific models are also superior to standard CT, offering advantages in terms of educational value, surgical planning, and the simulation of cardiovascular disease treatment, as well as enhancing doctor-patient communication. Three-dimensional visualization tools including virtual reality, augmented reality, and mixed reality are further advancing the clinical value of cardiovascular CT in cardiovascular disease. With the widespread use of artificial intelligence, machine learning, and deep learning in cardiovascular disease, the diagnostic performance of cardiovascular CT has significantly improved, with promising results being presented in terms of both disease diagnosis and prediction. This review article provides an overview of the applications of cardiovascular CT, covering its performance from the perspective of its diagnostic value based on traditional lumen assessment to the identification of vulnerable lesions for the prediction of disease outcomes with the use of these advanced technologies. The limitations and future prospects of these technologies are also discussed.

Evaluation of the Relationship between Left Coronary Artery Bifurcation Angle and Coronary Artery Disease: A Systematic Review

Recent studies have suggested a relationship between wide left coronary artery bifurcation (left anterior descending [LAD]-left circumflex [LCx]) angle and coronary artery disease (CAD). Current literature is multifaceted. Different studies have analysed this relationship using computational fluid dynamics, by considering CAD risk factors, and from simple causal-comparative and correlational perspectives. Hence, the purpose of this systematic review was to critically evaluate the current literature and determine whether there is sufficient evidence available to prove the relationship between LAD-LCx angle and CAD. Five electronic databases (ProQuest, Scopus, PubMed, CINAHL Plus with Full Text, and Emcare) were used to locate relevant texts, which were then screened according to predefined eligibility criteria. Thirteen eligible articles were selected for review. Current evidence suggests individuals with a wide LAD-LCx angle experience altered haemodynamics at the bifurcation site compared to those with narrower angles, which likely facilitates a predisposition to developing CAD. However, further research is required to determine causality regarding relationships between LAD-LCx angle and CAD risk factors. Insufficient valid evidence exists to support associations between LAD-LCx angle and degree of coronary stenosis, and future haemodynamic analyses should explore more accurate coronary artery modelling, as well as CAD progression in already stenosed bifurcations.

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.

Synchrotron radiation computed tomography assessment of calcified plaques and coronary stenosis with different slice thicknesses and beam energies on 3D printed coronary models

Background

To investigate the effect of different slice thicknesses and beam energies on the visualization and assessment of coronary artery stenosis caused by calcified plaques using synchrotron radiation computed tomography (CT) based on 3D printed coronary artery models.

Methods

Patient-specific 3D coronary models were created based on 3 sample coronary CT angiographic cases with calcified plaques in the left coronary arteries. In addition to the original significant coronary stenosis (>70%) shown on these CT images, stenoses of <50% and >90% were created in the segmented coronary models for simulation of different degrees of stenosis. The coronary lumen and calcification were printed with soft and rigid materials to simulate properties of coronary wall and calcified plaque, respectively. The models were scanned with synchrotron radiation CT with beam energies of 30, 40 and 50 keV and spatial resolution of 0.019×0.019×0.019 mm³ voxel size. Original high-resolution images were reconstructed with slice thicknesses of 0.095, 0.208, 0.302 and 0.491 mm to determine the effect of spatial resolution on plaque and coronary stenosis assessment based on 2D axial and 3D virtual intravascular endoscopy (VIE) images.

Results

Three coronary artery models were successfully printed with plaques placed in the coronary arteries to simulate different degrees of stenosis. 2D and 3D VIE images reconstructed with slice thicknesses of 0.095, 0.208 and 0.302 mm allowed for accurate assessment of coronary plaques and lumen stenosis with no significant differences (P>0.05). Synchrotron radiation CT images reconstructed with a slice thickness of 0.491 mm resulted in overestimation of coronary stenosis when compared to other images on 2D and 3D VIE views (<50% vs. 55-72%; 70-79% vs. 80-90%) with significant differences (P<0.05). Similarly, irregular plaque appearances were observed on 2D and 3D VIE images with a slice thickness of 0.491 mm when compared to others using thin slice thicknesses. The scanning protocol with beam energy of 30 keV provided optimal visualization of coronary lumen and plaque appearances.

Conclusions

This study shows the feasibility of using 3D printed coronary artery models to simulate calcifications and different degrees of coronary stenosis. High resolution synchrotron radiation CT imaging with the 30 keV beam energy enables accurate assessment of coronary stenosis in the presence of calcification, thus highlighting the importance of high spatial resolution in the diagnosis of calcified coronary plaques.

CT Myocardial Perfusion Imaging: A New Frontier in Cardiac Imaging

The past two decades have witnessed rapid and remarkable technical improvement of multidetector computed tomography (CT) in both image quality and diagnostic accuracy. These improvements include higher temporal resolution, high-definition and wider detectors, the introduction of dual-source and dual-energy scanners, and advanced postprocessing. Current new generation multidetector row (≥64 slices) CT systems allow an accurate and reliable assessment of both coronary epicardial stenosis and myocardial CT perfusion (CTP) imaging at rest and during pharmacologic stress in the same examination. This novel application makes CT the unique noninvasive "one-stop-shop" method for a comprehensive assessment of both anatomical coronary atherosclerosis and its physiological consequences. Myocardial CTP imaging can be performed with different approaches such as static arterial first-pass imaging, and dynamic CTP imaging, with their own advantages and disadvantages. Static CTP can be performed using single-energy or dual-energy CT, employing qualitative or semiquantitative analysis. In addition, dynamic CTP can obtain quantitative data of myocardial blood flow and coronary flow reserve. The purpose of this review was to summarize all available evidence about the emerging role of myocardial CTP to identify ischemia-associated lesions, focusing on technical considerations, clinical applications, strengths, limitations, and the more promising future fields of interest in the broad spectra of ischemic heart disease.

Coronary Computed Tomography Angiography in Combination with Coronary Artery Calcium Scoring for the Preoperative Cardiac Evaluation of Liver Transplant Recipients

Liver transplantation is the best treatment option for early-stage hepatocellular carcinoma, liver cirrhosis, fulminant liver failure, and end-stage liver diseases. Even though advances in surgical techniques and perioperative care have improved postoperative outcomes, perioperative cardiovascular complications are a leading cause of postoperative morbidity and mortality following liver transplantation. Ischemic coronary artery disease (CAD) and cardiomyopathy are the most common cardiovascular diseases and could be negative predictors of postoperative outcomes in liver transplant recipients. Therefore, comprehensive cardiovascular evaluations are required to assess perioperative risks and prevent concomitant cardiovascular complications that would preclude good outcomes in liver transplant recipients. The two major types of cardiac computed tomography are the coronary artery calcium score (CACS) and coronary computed tomography angiography (CCTA). CCTA in combination with the CACS is a validated noninvasive alternative to coronary angiography for diagnosing and grading the severity of CAD. A CACS > 400 is associated with significant CAD and a known important predictor of posttransplant cardiovascular complications in liver transplant recipients. In this review article, we discuss the usefulness, advantages, and disadvantages of CCTA combined with CACS as a noninvasive diagnostic tool for preoperative cardiac evaluation and for maximizing the perioperative outcomes of liver transplant recipients.

Evidence for myocardial CT perfusion imaging in the diagnosis of hemodynamically significant coronary artery disease

This editorial discusses a recent paper published in the August issue of Radiology about the diagnostic value of myocardial computer tomography (CT) perfusion imaging in the detection of hemodynamically significant coronary stenosis when compared to single-photon emission CT (SPECT) imaging based on a secondary analysis of CORE320 study. Three aspects including high diagnostic sensitivity of CT perfusion imaging, moderate specificity of SPECT imaging and lack of use of attenuation correction in SPECT imaging have been discussed with reference to the current literature, and some suggestions have been highlighted for future studies to improve the diagnostic performance of CT perfusion and SPECT imaging in the diagnostic evaluation of coronary artery disease.