Having more patient specific information about the coronary arteries may allow for more patient specific management of coronary artery disease. The next generation of CT scanners may give physicians a golden opportunity to do this. by Ella A. Kazerooni, MD*


Cardiac risk factor stratification uses information such as age, gender, family history, hypertension, diabetes and smoking history to determine a patient's risk of heart disease and coronary events. This approach is based on the relative risk of coronary events for these and other risk factors, as determined from the study of populations of patients with and without these risk factors. By the nature in which the data is collected and applied, it is population based. As we are moving further into the era of patient-based medicine, in which preventive medical strategies and disease treatments are tailored to individuals, having more patient specific information about the coronary arteries may allow for more patient specific management of coronary artery disease. The next generation of CT scanners, which will bring a better image resolution, may give physicians a golden opportunity to do this.

ECG-gated cardiac CT has brought tremendous innovation to imaging. Prior to CT, the only way to visualize atherosclerotic plaques clinically was invasively, using intravascular ultrasound (IVUS) as part of a cardiac catherization procedure. IVUS is generally used to better evaluate coronary artery lesions in determining the need for and planning of percutaneous coronary intervention, and is not a stand alone procedure. Now coronary CT allows atherosclerotic plaques to bee seen non-invasively. CT has the potential to provide phenomenal insights the character of plaques, distinguishing not only calcified from non calcified, but potentially identifying the vulnerable plaques that place patients at greatest risk of an acute coronary event.

Traditionally, cardiac CT has been limited to calcium scoring, which quantifies the calcified or healed plaques, which represents the tip of the iceberg of a patients total plaque burden, and correlates with future cardiac events. With coronary CT angiography on the current generation of 64-slice CT scanners, atherosclerotic plaque can be detected and grossly characterized. Many commercial and independent groups have and are working on plaque quantification and characterization software. However the input data that comes from the CT scanners is currently of insufficient spatial resolution, which limits the reliability and reproducibility of such measurements currently.

With the next generation of CT scanners, that further improve spatial resolution by the use of smaller detectors (less than 0.5 mm), as well as further gains in temporal resolution, the CT data should be more robust, allowing reproducible plaque characterization and quantification. With such a tool, it would be possible to follow a patients plaque non-invasively, and determine if drugs designed to stabilize or shrink plaque are working, allowing a tailoring of the drug regimen to the individual’s plaque type and response.

Another current limitation to the widespread use of coronary CT in this way is the radiation dose of 10-12 mSv, which prevents its use in screening or following patients and their plaque. Newer tools, such as prospective triggering at fixed points in the cardiac cycle only, instead of the retrospective gating used currently across the entire cardiac cycle, may allow significant dose reductions down to 3 mSv or less by only turning on the x-ray beam during the part of the cardiac cycle that is the most motion free, rather than having it on across the entire cycle. GE Healthcare is among the companies testing this new generation of scanners, which should be robust enough to be used in clinical setting within the year, with research to follow on the robustness of the new CT scanners together with software to characterize and quantify plaque. While it will take several more years to know who should undergo coronary CT as part of a tailored coronary artery disease management strategy, it appears that advances in coronary CT may make it part of an individualized approach to coronary risk stratification and disease management,




* Dr. Ella A. Kazerooni is Professor and Director of Cardiothoracic Radiology at the Department of Radiology of the University of Michigan