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Insights Health Care

Medical Technology

How and why CT scanners are evolving

The advent of dual-source CT scanners represents a significant step up in the evolution of CT machines. Designed with two X-ray tubes and two detector arrays, the dual-source scanner captures data nearly twice as fast as previous scanners.

The dual-source CT scanner is ideal for cardiac imaging, says Stefan Ruehm, M.D., Ph.D., associate professor of radiology at UCLA Medical Center. “It’s a rather noninvasive diagnostic tool that allows a physician, with a very high negative predictive value, to determine whether or not the patient has coronary artery disease,” he says.

Smart Business spoke with Ruehm about how the new scanner aids patients and doctors alike and what further developments he expects to see in the early detection of heart disease.

How does the dual-source CT differ from earlier CT scanners?

The main difference is that it’s about twice as fast as the previous generation of scanners known as 64-slice CT scanners. The dual-source CT has two X-ray sources and two 64-slice detector arrays as compared to the previous generation, which had just one X-ray source and one detector with 64 rows. There has been a development of CT technology from one row of detectors to four rows to 16 rows to 64 rows. The latest development, as seen in the dual-source CT, is putting two 64-row detectors into one scanner.

What advantages does the new scanner offer patients?

It is particularly well suited for cardiac imaging because it provides very fast data acquisition. If your data acquisition times are too long, you will end up with images that show motion artifacts. You want to have a very small window to collect data during your cardiac cycle. The big advantage of the dual-source CT is that it nearly doubles the speed that you can acquire data compared to the previous generation of scanners. You could do cardiac CT with the previous machines; however, you had to use beta-blockers to decrease the heart rate. With the dual-source CT you don’t need to give beta-blockers, you can scan patients independent of the heart rate.

How does the noninvasive nature of the dualsource CT scanners aid doctors?

In the past, if there was a question about coronary artery disease, you would have done a catheter angiogram study. In a certain percentage of patients, you would have done the study for diagnostic purposes because you would have seen on the invasive angiogram that there is no coronary artery disease. This process is not very beneficial to the patient because it’s a rather invasive procedure and if you do it just for diagnostic purposes it’s not appropriate. There has been a need for an alternative, and it appears with the dual-source scanners that you can get diagnostic information concerning the coronary arteries in a far less invasive manner.

How useful is the dual-source scanner in helping to identify medical problems at an early stage?

The main goal is to detect coronary artery disease at an early stage and to adapt certain therapeutic strategies. You want to do this early, because with certain medications, you can prevent progression of coronary artery disease. The problem so far has been that people were reluctant undergoing the types of invasive procedures that were previously available. With this technique, we have a rather noninvasive tool to detect coronary artery disease. If there are signs of disease, patients can undergo medical treatment at a very early stage and prevent further progression or complications.

In the future, what further developments do you expect to see in the early detection of heart disease?

One further development focuses on the exact and objective grading of the degree of vessel narrowing. However, it has been shown that the degree of the narrowing of the coronary arteries does not predict the likelihood of a cardiac complication.

What appears more important is the characterization of the plaque that causes the vessel to narrow. There may be a change of paradigm away from the quantification of the degree of the narrowing, or stenosis, towards the characterization of plaque. In general, there are two different types of plaques: unstable and stable. The unstable plaques are regarded as dangerous while stable plaque is usually calcified plaque.

With the invasive, conventional angiogram you can only see the stenosis, but you can’t tell anything about the vessel wall itself where the plaques develop. With these new cross-sectional techniques, you can quantify the degree of stenosis. Eventually, we hope to differentiate between a dangerous plaque and a stable plaque.

STEFAN RUEHM, M.D., Ph.D., is an associate professor of radiology and director of cardiovascular CT at UCLA Medical Center. Reach him at sruehm@mednet.ucla.edu or (310) 825- 0958.

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