RSNA: Cardiac CT could replace fluoroscopy for valves w/ less radiation dose
CHICAGO—Cardiac CT can advantageously replace fluoroscopy for evaluation of bileaflet valves, according to a prospective analysis that confirms recent retrospective studies, presented Sunday at the 2009 Radiological Society of North America (RSNA) meeting.

Time and radiation-intensive fluoroscopic evaluation of mechanical valves is often impaired by overlapping bony structures, according to lead author and study presenter Santiago P. Miro, MD, assistant professor of radiology at the University of Massachusetts Medical School in Worcester, Mass. He said that imaging mechanical valves with fluoroscopy is “tedious at best, and CT can resolve many of those visualization complications.”

Miro and colleagues evaluated the opening and closing angles of mechanical valves in a total of 416 consecutive patients by cardiac CT, and compared the results with vendors' specifications.

None of the patients enrolled in the study was receiving additional medication, including beta blockers. Miro said that the Institutional Review Board would never have allowed the study to continue if he added a medication to the treatment.

They prospectively included images of all 416 patients presenting for a clinically-indicated gated ascending aortic/cardiac scan on Siemens Healthcare’s dual-source CT (385 patients; 44 of whom had mechanical valves) or Philips Healthcare’s 64-slice CT (31 patients; two of whom had mechanical valves) between Feb. 1, 2008 and April 10, 2009.

Of a total of 51 valves, 41 patients had one mechanical valve and five patients had two prosthetic valves in place, Miro explained. There were 8/51 bioprostheses, with 37/43 aortic and 6/43 mitral mechanical valves.

The researchers performed 31 scans in end-systole, 12 in end-diastole and three in both cycles, as required by the clinical question. Thus, 34 image sets were available for end-systolic evaluation and 15 for end-diastolic evaluation. They acquired 20/49 sets at 24 percent of full radiation dose.

Miro insisted that their CT imaging method can be performed on “any patient that needs to be imaged, without the assistance of beta blockers.”

The researchers found that three patients had tilting-disk valves, and the struts on these tilting disk valves caused significant artifacts in all three patients, rendering the tilting disk barely discernable. Also, 42 patients had bileaflet pyrolitic carbon valves, either aortic or mitral, all of which were properly visualized.

For aortic valves, opening and closing angles could be evaluated in 33/37 end-systole image sets; opening angle only in 4/37; closing angle in 15/15 of end-diastole image sets. For mitral valves, opening and closing angles could be evaluated in 3/6 end-diastole image sets; opening angle only in 3/6; closing angle in 6/6 of end-systole image sets.

Atrial fibrillation was a limiting factor in 4/6, according to Miro.

More than 95 percent of measurements were within two degrees of manufacturer’s specifications, he said. Only 2/20 sets at 2 percent dose could not be evaluated. Single leaflet opening discrepancies were found in three asymptomatic patients. Miro said that those three patients are being followed.

He noted that their results with as low as 2 percent of full tube current “suggest that total radiation dose for a dedicated valvular CT would be less than from fluoroscopy,” adding that fluoroscopy administers 1 mSv per minute. “If you take just the valve CT scan, the patient should only receive 1-2 mSv for the whole valve part of the study,” Miro said. “It’s very clear that the radiation dose is much lower with CT than fluoroscopy.

“It’s also clear that CT is the way of the future of looking at valves, in replacement of fluoroscopy,” Miro concluded.