Focus Section: Cardiac Computed Tomography

Cardiac computed tomography (CT) really arrived on the cardiology scene at the dawn of the 21st century. Though much important work on cardiac CT had been taking place for years before that time, the publication of a few key articles documenting the ability of 16-slice multidetector CT to reliably perform noninvasive coronary angiography and accurately identify coronary stenosis initiated wider interest in the technology. Since then, the technology has advanced considerably. Increased detector coverage to 40, 64 and 256 slices has now reduced 30-second scan times down to 5 seconds and improved scan reliability. At the same time, a near-doubling in gantry rotation speed from 120 rpm to the new benchmark of 222 rpm (or 270 ms per rotation) has improved temporal resolution. Advancements in X-ray tubes, detector elements and electronics, as well as faster processors, increases in data bandwidth and better scanner software have brought us today’s highly reliable and accurate coronary CT angiography (CTA).
The performance of coronary CTA requires iodinated contrast and X-ray radiation. The latter has been a source of much of the criticism of cardiac CT, but this will change. The future will see significant radiation dose reductions thanks to the development of wide-area-detector scanners in combination with what is called prospective, ECG-triggered acquisition, which uses bursts of X-ray rather than the conventional continuous irradiation.¹ The confluence of these two advances in particular will dramatically reduce radiation and contrast dosage requirements, such that coronary CTA in the near future will be performed with less radiation and contrast than a traditional invasive coronary angiogram. Still, physicians should educate and monitor themselves to ensure that the technology is used appropriately and not abused. The medical societies have provided guidance along these lines in the form of Appropriateness Criteria for cardiac CT.^2,3
In this emerging era of cardiac CT, coronary CTA should begin to take the role that has traditionally been filled by invasive diagnostic coronary angiography. It is likely that in the future, coronary interventions will be planned on CTA data as much as angiographic data, and cath labs will see almost all their time slots used for interventions and almost none for diagnostic-only catheterizations. While some might see these as competing technologies, in fact, thefuture will most likely see cardiac CT and cardiac catheterization moving closer together, even to the point of merging their images on-screen.
This issue of the Journal of Invasive Cardiology is focused on Cardiac CT, and in the lead investigative article by Alasnag et al, the authors describe the ability of coronary CTA to accurately classify coronary lesions according to the SCAI lesion classification scheme, a nice demonstration of the potential for coronary CTA to preview the invasive angiogram and provide relevant data for interventions. This issue also contains a number of clinical images which demonstrate the capabilities of cardiac CT to image beyond the coronary arteries. Gopal et al describe a case of left ventricular pseudoaneurysm following anterior myocardial infarction, and provide a brief synopsis of the entity’s clinical and imaging characteristics. Cardiac CT provides exquisite anatomical information about these lesions because of its excellent spatial resolution. Makaryus et al describe a case of congenital left ventricular diverticulum, an entity which must be carefully distinguished from ventricular septal defect. The growth of cardiac CT will surely lead to the increased discovery of such congenital variants, and reports like these improve our understanding of the significance of these lesions and understanding that further testing is not required. In a case of incredible timing, Kristensen et al provide the first description of CT angiography of acute stent thrombosis following bifurcation stenting. Stent visualization by coronary CTA can be challenging, and cases of bifurcated stents can be especially difficult to image because of the increased metal artifact from the abundance of stent material.
Namboodiri et al describe an unusual finding of dual anterior descending arteries. These anomaly cases can be especially bothersome in the cath lab, where coronary intubation and angiography can be tricky and time-consuming. Coronary CTA visualizes these anomalies readily, and the CTA information can prove extremely valuable to the interventionalist who can use it to plan the angiographic and interventional strategy.
I hope you enjoy these reports, and if you were not familiar with cardiac CT before reading them, that their images and findings inspire you to learn more about this promising and rapidlyadvancing field of cardiology.

References

1. Earls JP, Berman EL, Urban BA, et al. Prospectively gated transverse coronary CT angiography versus retrospectively gated helical technique: Improved image quality and reduced radiation dose. Radiology 2008;246:742–753.
   
2. Greenland P, Bonow RO, Brundage BH, et al. ACCF/AHA 2007 clinical expert consensus document on coronary artery calcium scoring by computed tomography in global cardiovascular risk assessment and in evaluation of patients with chest pain: A report of the American College of Cardiology Foundation Clinical Expert Consensus Task Force (ACCF/AHA Writing Committee to Update the 2000 Expert Consensus Document on Electron Beam Computed Tomography) developed in collaboration with the Society of Atherosclerosis Imaging and Prevention and the Society of Cardiovascular Computed Tomography. J Am Coll Cardiol 2007;49:378–402.
   
3. Hendel RC, Patel MR, Kramer CM, et al. ACCF/ACR/SCCT/SCMR/ ASNC/NASCI/SCAI/SIR 2006 appropriateness criteria for cardiac computed tomography and cardiac magnetic resonance imaging: A report of the American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group, American College of Radiology, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, American Society of Nuclear Cardiology, North American Society for Cardiac Imaging, Society for Cardiovascular Angiography and Interventions, and Society of Interventional Radiology. J Am Coll Cardiol 2006;48:1475–1497.