ICTpost Radiology Bureau
CT analysis software allows visualization and quantification of perfusion in the myocardium with images similar to nuclear studies, but with a highly accurate anatomic image base
A study, led by researchers from Wake Forest School of Medicine has indicated that computed tomography (CT) scanning of the heart and measuring the coronary artery calcium (CAC) score is the most accurate predictor of cardiovascular disease for individuals at intermediate risk for heart disease.
The study included 1,300 individuals with intermediate cardiovascular risk factors (excluding diabetes) based on the Framingham Risk Score (FRS), who were followed over a period of seven years as part of the National Heart, Lung and Blood Institute’s Multi-Ethnic Study of Atherosclerosis (MESA). MESA is an observational study of cardiovascular disease.
Six novel or established markers of heart disease risk were directly compared. These included the CT CAC score, ankle-brachial index, brachial flow mediated dilation, carotid intima-media thickness, high sensitivity C-reactive protein and family history of heart disease. CAC score, determined by CT scan, held the highest predictive association for cardiovascular disease.
Cardiac Imaging Modality
Cardiac computed tomography (CT), magnetic resonance imaging (MRI), echocardiography and nuclear myocardial perfusion imaging each offer advantages and disadvantages, and frequently at least two of these tests are required to get the full picture of a patient’s cardiac health. However, in this age of cutting healthcare costs, declining reimbursements and improving efficiency, it would be advantageous to have a single gold standard exam. Technology advances are now making that possibility.
MRI is ideal because it uses zero radiation, offers higher contrast and clarity than CT, can image without contrast and performs perfusion exams. But, its limitation remains its expense, ferrous metal and implantable device safety issues and the complexity of its operation.
Nuclear imaging is limited because it fails to provide detailed anatomical information and uses ionizing radiation. It also is expensive, and short half-life radiotracers limit its hours of operations and on-demand use.
Software advances have improved 3-D echo image quality to the point where it appears like a CT reconstruction. It uses no radiation and offers immediate images of anatomy inside the body. But, echo has a limited ability to image the function of the heart. It also requires highly trained operators to ensure precise positioning of the transducer and interpretation can be subjective.
CT has the major disadvantage of high radiation doses compared to other modalities, but technical advances make CT the most likely dominant cardiac imaging technology in the next decade. The rapid expansion and decreasing cost of computing power has enabled fast iterative reconstruction software for lower dose scans. New detector technology is reducing the amount of electronic noise in lower-dose scans and new ECG gating technology has helped cut dose. Combined, these advances have reduced CT dose by more than 50 percent compared to doses a few years ago.
CT analysis software now allows visualization and quantification of perfusion in the myocardium with images similar to nuclear studies, but with a highly accurate anatomic image base.
Coronary CT Angiography Software
FFR-CT
One of the exciting, next-step technologies for CCTA is FFR-CT developed by HeartFlow. This automated software can quantify the blood flow in each coronary segment, displaying it in a color-coded map on a 3-D coronary tree. If validated, the software may drastically reduce the need for diagnostic catheter angiography procedures. It also promises to pinpoint the specific culprit lesions in patients with myocardial ischemia.
Fractional flow reserve (FFR) has become a popular tool in interventional cardiology to measure the impact of a lesion on coronary blood flow. Although a lesion may look severe on CT or during invasive angiography, clinical research has found that the hemodynamic flow might not be significantly impacted. Stenting hemodynamically insignificant lesions does not impact patient outcomes, decreases future revascularization options of that lesion, and significantly increases healthcare costs. Using a catheter wire to measure flow before and after a lesion in a vessel, a cardiologist can compute an FFR number. If 0.8 or higher, the lesion does not significantly impact flow. If less than 0.8, the flow is considered restricted and revascularization is required. Use of FFR has helped target only lesions causing ischemia, reducing the number of stents implanted.
Advanced Visualization of the Coronaries
Mild plaques are the cause of many heart attacks, not heavily stenosed lesions, Min said. CT technology is getting to the point where it can help evaluate the composition of plaques, vessel remodeling and the level of stenosis, leading to virtual vessel biopsies.
All the major CT system manufacturers and third-party advanced visualization software vendors offer plaque assessment software. They all classify plaque make up based on the Hounsfield unit (HU) returns in each pixel of the CT image matrix. The software can auto-shade or outline the vessel wall, patent lumen (highlighted by contrast) and the different types of plaque detected. The basic detection level on all the software on the market is for calcified, non-calcified and mixed plaques.