Background: Dose reduction strategies for coronary CTA (CCTA) have been underutilized
in clinical practice given concern that the strategies may lower image quality. Objective:
To explore associations between dose reduction strategies and CCTA image quality in
real world clinical practice. Methods: This subanalysis of the PROTECTION VI (International
Prospective Multicenter Registry on Radiation Dose Estimates of Cardiac CT Angiography
in Daily Practice in 2017) study included 3725 patients (2109 male, 1616 female; median
age 59 years) who underwent CCTA for coronary artery evaluation, performed at 55 sites
from 32 countries. CCTA image sets were reviewed at a central core lab. A range of
patient and scan characteristics, including use of three dose reduction strategies
(prospective ECG triggering, low tube potential, and iterative image reconstruction)
as well as image dose were recorded. A single core lab member reviewed all examinations
for quantitative image quality measures, including signal-to-noise ratio (SNR) and
contrast-tonoise (CNR) ratio, and reviewed 50% of examinations to assign a qualitative
CCTA image quality score and a semiquantitative coronary calcification measure. Multivariable
logistic regression models were used to identify predictors of image quality. A second
core lab member repeated quantitative measures in 100 patients and the qualitative
measure in 383 (approximately 20%) patients to assess interreader agreement. Results:
Independent predictors (p<.05) of SNR were female sex (+2.70), lower body mass index
(+0.38 per 1 kg/m2 decrease), stable sinus rhythm (+1.71), and scanner manufacturer
(variable effect across manufacturers). These same factors were also the only independent
predictors of CNR. Independent predictors (p<.05) of CCTA image quality were heart
rate (+0.17 increase per 10 beat per minute reduction) and coronary calcification
(+0.15 per coronary calcification grade). None of the three dose savings strategies,
nor dose length product, were independent predictors of any image quality measure.
Interreader agreement analysis demonstrated intraclass correlation coefficient of
0.874 for SNR and 0.891 for CNR and kappa of 0.812 for the qualitative score. Conclusion:
This large international multicenter study demonstrates that three dose reduction
strategies were not associated with decreased CCTA image quality. Clinical impact:
The dose reduction strategies should be routinely implemented in clinical CCTA imaging.
