How did cardiac CT begin? How do you see the technology evolving?
| Dr Lawrence Boxt |
Cardiac CT (CCTA), as we practice it now, really began after 1999-2000, with the commercial introduction of 64-detector scanners. In a dramatic advance over recent, kindred technology (i.e., 4-, 8, 16-detector scanners), the 64-detector scanner produced isotropic voxels. That is, the imaging elements obtained from a scan are cubes; equal length on all sides. Thus, digital imagery of the epicardial coronary arteries reconstructed from these volume elements is of adequate spatial resolution to be artifact-free, and thus reliable for detection and quantitation of coronary artery calcium and the detection of significant coronary stenosis. Prior to 2001, the electron beam CT (EBCT) scanner developed at The University of California should have “revolutionised” cardiac imaging. It produced cine cardiac examinations of adequate quality for evaluation of myocardial wall thickening and valvular function. However, it was limited in spatial resolution, and thus unable to visualise the epicardial coronary arteries. Also, CCTA became commercially available in the early 1980’s, at the same time when magnetic resonance imaging was becoming commercially available. Radiology department chairmen were uncomfortable supporting two new and expensive technologies at the same time. EBCT was seen as a cardiac imaging device, and radiology chairmen didn’t want to fight with chiefs of cardiology. Radiology went headlong into MRI, and the EBCT virtually evaporated.
As to the future; the spread of multidetector CT technology and the growth of 16- and 64-detector scanners were associated with a dramatic increase in the number of CT scans, and the cumulative patient radiation exposure from multiple scanning. An uproar over patient radiation dose and risk of developing new cancer provided a moment of clarity for the CT and CCTA communities. In a remarkable change in industrial philosophy, there began another “revolution” in CT technology. Conscious attention to dose lowering methods and technologies has lowered the CCTA dose by nearly an order of magnitude. This is the first area of change we will see in the near and intermediate future. We will continue to see advances in tube and detector materials, and continued lowering of patient radiation exposure. The second area of change we will see will come in the arena of computer-based image processing and image distribution algorithms and the network technology to connect scanners with workstations and physicians. We are already seeing “afterhour” exams in the US sent to India for review, and vice versa. Advanced display technology will allow us to visualise cardiac abnormalities rather than infer their presence. Furthermore, association of relevant databases will provide correlation with other tests, other clinical information, or other imaging studies. Association of particular characteristics of coronary arterial plaque with specific genetic loci on the individual’s genome will open new areas of clinical intervention based on the morphologic appearance of coronary plaque.
Under what circumstances is the prognostic value of CCTA best utilised?
CCTA is increasingly used as a clinical tool to visualise the coronary artery lumen and to identify coronary stenosis. That is, the foremost current use for CCTA is to exclude significant coronary artery disease, and avoid bringing the patient to the catheterisation laboratory for the performance of a diagnostic coronary catheterisation. The predictive power of coronary calcium quantitation, with regard to both future cardiovascular events and overall mortality has been well established. Given the significant contribution of underlying genetic mechanisms for the development of coronary atherosclerosis, and the high prevalence of asymptomatic individuals among those with coronary stenosis, the prognostic value of CCTA lies in the evaluation of asymptomatic or minimally symptomatic individuals with low or intermediate risk of coronary heart disease. These patients can be risk stratified, and directed toward aggressive risk lowering management in face of the presence of coronary calcium and mild-to-moderate arterial stenosis. The results of several prospective, multi-center trials has demonstrated that hospital costs are lowered and patient length of stay shortened when CCTA is performed in low-to-intermediate risk emergency department patients complaining of recent onset of chest pain, but without a known history of coronary heart disease. In these series, individuals in whom no significant coronary artery disease was demonstrated have a near zero cardiac event rate after emergency department discharge.
What is the growth rate of this segment in India and what would be the estimated size of the market in five years’ time?
Most CT scanners are installed in the US, Europe and Japan. The number of CT scanners at an institution, as well as the number of scans performed continues to increase (certainly in the US, and presumably in the other markets). Non-64 detector scanners continue to be sold in these markets because of the continued high CT utilisation, and their significant advantage over older (1-to-4-detector scanners) for non-cardiac use. However, nearly 40 per cent of CT scanners installed in the US in 2010 were 16-detector scanners.
India is a rapidly growing, emerging market for CT scanners; scanner sales and installations will follow an increasing population, domestic economic growth, and increasing healthcare spending, including new hospital construction. There is no reason to expect the demand for high technology to wane. Rapid expansion will be met with installation of conventional (<64-detector) and refurbished CT scanners, as well as the expansion of the 64-detector market. Approximately one-third of all new scanners in India are 64-detector devices; only about 4 per cent are “mega-scanners” (i.e., 128-256+ detectors). If I could predict the Indian market in 5-10 years, I would expect to see steady growth in the number of scanners and their utilisation. I would also expect to see growth in the >128-detector market, as older scanners become out of service and are replaced.
Tell us about your association with CT Fest 2012? What will be your area of focus while speaking at the CT Fest 2012?
This is my first time to India, much less speaking at CT Fest 2012. Actually, Dr Sanjeev Mani contacted me two years ago, inviting me to speak at the 2011 meeting, but I had a previous engagement, and couldn’t come. I implored him to please remember me for the 2012 meeting, which he did. I intend to discuss the utility CCTA to diagnose not only coronary, but other common, and less common forms of acquired valvular and myocardial heart disease. CCTA is a valuable diagnostic problem solver, and has, and will continue to help elucidate normal and pathologic anatomy and function in patients with difficult to interpret echocardiograms sand electrocardiograms, in a manner analogous to cardiac MRI. I will also point out the value of CCTA for the evaluation of adult patients with congenital heart disease. This growing population (there are now more adult patients than paediatric patients with congenital heart disease) is well-served by the speed, convenience, and accuracy of cardiac CTA.
There is a great deal of cardiac CTA performed in India today, and the attendees at the meeting will reflect a broad spectrum of awareness, experience, and utilisation of the technology. I hope to teach a little, reinforce a lot, and learn from my audience.
raelene.kambli@expressindia.com
*(Look out for the full interview in the forthcoming October issue of In Imaging.)