Strategies for Optimizing Image Quality

Careful patient preparation, data acquisition and data evaluation top the list of ways to optimize image and study quality in CCTA, 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.
   
Achieving a heart rate under 60 or 65 beats per minute is key to patient preparation since the lower the heart rate the better the scan. Beta blockers such as atenolol, metoprolol or diltiazem can substantially enhance the data set, he said. Patients (of reasonable body habitus) should be asked not to discontinue regular medications since they can often help in regulating heart rate, but they should be asked to avoid coffee and erectile disfunction medications on the day of the scan. Giving nitrates via sublingual spray or by pill (unless contraindicated) just prior to the scan is helpful and can bring on increased lumen diameter of 12 to 21 percent, according to a recently published study by Dewey et al. Patient preparation also is key, which includes explaining the procedure, making sure breath hold commands are practiced and followed (breath in, breath out, breath in and hold) and heart rate is continually monitored through scan time since it can increase with patient anxiety.
   
Good ECG trace in inspiration that is higher than the T wave, not noisy and has a consistent R wave throughout the scan is important to good data acquisition. ECG pulsing should be on for lower and regular heart rates and off for irregular and higher heart rates. The scan area should be as small as possible, with the pulmonary artery as the reference for the mid level section of the coronary artery. Contrast timing should include a test bolus as well as double-checking the position of the IV and starting level. Achenbach uses 5 ml/sec of contrast for the duration of the scan with a 50 ml chaser. Adding 20 percent contrast to the chaser bolus also allows viewing of the right heart. Don’t miss saline and water boluses.
   
Making sure the heart fills the field of view is key in optimizing image reconstruction as is choosing the best cardiac phase such as 30 percent, 40 percent or 70 percent. Usually 65 to 75 percent is the standard setting while 30 to 40 percent is used for faster heart rates. Under all circumstances, avoid the P wave. You need to balance slice thickness and kernel, resolution and noise. Vendors recommend standard settings but those can be changed, according to Achenbach. “Vendors tend to like soft kernels because images look nice with smooth surfaces, but sharper will increase noise but provide higher resolution,” he said. Sharp kernels are key if an area is calcified. Reconstruct diastoly and in the full radiation window, he recommends. The ECG trace can be manipulated after the scan for issues such as arrhythmias or an ectopic beat.