Body mass index-adapted prospective coronary computed tomography angiography. Determining the lowest limit for diagnostic purposes.

Purpose: To investigate the value of 4 different protocols for prospectively triggered 256-slice coronary computed tomography angiography (coronary CTA).

Methods: Two hundred and ten patients underwent prospectively triggered coronary CTA for suspected or known coronary artery disease (CAD). Patients with heart rate >75 bps before the scan despite ß-blocker administration and with arrhythmia were excluded. From January to September 2010, 60 patients underwent coronary CTA using a non-tailored protocol (120 kV; 200 mAs) and served as our 'control' group. From September 2010 to April 2012, based on the body mass index (BMI) of the examined patients (BMI subgroups of <25; 25-28; 28-30, and ≥ 30 kg/m(2)) current tube voltage and tube current were: (1) slightly, (2) moderately or (3) strongly reduced, resulting into the 3 following BMI-adapted acquisition groups: (1) a 'standard' (100/120 kV; 100-200 mAs; n=50), 2) a 'low dose' (100/120 kV; 75-150 mAs; n=50), and 3) an 'ultra-low dose' (100/120 kV; 50-100 mAs; n=50) protocol.

Results: Patients examined using the non-tailored protocol exhibited the highest radiation exposure (3.2 ± 0.4 mSv), followed by the standard (1.6 ± 0.7 mSv), low-dose (1.2 ± 0.6 mSv) and ultra-low dose protocol (0.7 ± 0.3 mSv) (radiation savings of 50%, 63% and 78% respectively). Overall image quality was similar with standard dose (1.9 ± 0.6) and low-dose (2.0 ± 0.5) compared to the non-tailored group (1.9 ± 0.5) (p=NS for all). In the ultra-low dose group however, image quality was significant reduced (2.7 ± 0.6), p<0.05 versus all other groups).

Conclusion: Using BMI-adapted low dose acquisitions image quality can be maintained with simultaneous radiation savings of ∼65% (dose of ∼1 mSv). This appears to be the lower limit for diagnostic coronary CTA, whereas ultra-low dose acquisitions result in significant image degradation.