“Coronary CTA is stretching the physical boundaries of CT in imaging to small and more rapidly moving anatomy,” said Stephan Achenbach, MD, president of the Society of Cardiovascular CT (SCCT) who spoke at the mid-July meeting held in Arlington, Va. He is an assistant professor of medicine at the University of Erlangen in Germany and was described at the meeting as the “grandfather of coronary CTA” by other leaders in the field.
Despite its recent advancements, temporal resolution is still a major obstacle to cardiac CT, Achenbach said. Invasive angiography still maintains the advantage over CCTA in both spatial and temporal resolution, offering spatial resolution of 0.2 mm vs. 0.4mm in CCTA, and temporal resolution of 8 milliseconds vs. 80 to 200 ms for CCTA. He also noted that there is a tendency for CCTA to overestimate the degree of stenosis when compared with MR angiography. Yet, CCTA is now achieving high sensitivity and specificity.
“We can see lumen reduction and plaque with CT, and there is the potential to view atherosclerotic plaque,” he said. “The negative predictive value is very high [with CCTA]. If the CT is normal, you can be certain there is no stenosis.” Achenbach also voiced hope of the technology’s potential in viewing and characterizing plaque, stents and bypass grafts.
Since image quality decreases when patient heart rate increases, optimum imaging is achieved when the heart rate is in the range of 60 to 65 beats per minute; regular cardiac rhythm, less than 500 millisecond rotation; and IV contrast and administration of nitrates just before the scan, unless the patient cannot tolerate them.
CCTA is challenged by several limitations such as calcium, motion in the image, and a combination of the two that often causes a blooming effect that impinges effective reading. To avoid motion in the data set, he suggested lowering the heart rate very carefully or using a newer scanner such as the new-generation Dual Source CT unit he uses.
Achenbach said he relies on 2D images in his diagnoses, adding “3D doesn’t add too much in my opinion. It provides the same information, not more.”
In closing, he urged physicians trying to decide if a CCTA is the right test to ask the scanner: “Is this a patient who does NOT need a cardiac cath?” If the CT is normal, he sees no reason for further workup.