Assessment of left ventricular ejection fraction using low radiation dose computed tomography.

BACKGROUND: Cardiac CT is a non-invasive modality with the ability to estimate LVEF. However, given its limited temporal resolution and radiation, there has been initial resistance to use CT to measure LVEF. Developing an accurate, fast, low radiation dose protocol is desirable. OBJECTIVE: The objective of this study is to demonstrate that a 'low radiation dose' 64 slice cardiac computed tomography (CT) protocol is feasible and can accurately measure left ventricular ejection fraction (LVEF) while delivering a radiation dose lower than radionuclide angiography (RNA). METHODS: Patients undergoing RNA were prospectively screened and enrolled to undergo a 'low-dose' 64 slice CT LVEF protocol. LVEF measures, duration of each study and radiation dose between CT and RNA were compared. RESULTS: A total of 77 patients (mean age = 61.8 ± 12.2 years and 58 men) were analyzed. The mean LVEF measured by CT and RNA were 41.9 ± 15.2% and 39.4 ± 13.9%, respectively, (P = 0.154) with a good correlation (r = 0.863). Bland-Altman plot revealed a good agreement between the CT and RNA LVEF (mean difference of -2.4). There was good agreement between CT LVEF and RNA for identifying patients with LVEF ≤30% (kappa = 0.693) and LVEF ≥50% (kappa = 0.749). The mean dose estimated effective dose for CT and RNA were 4.7 ± 1.6 and 9.5 ± 1.0 mSv, respectively. The mean CT LVEF imaging duration (4:32 ± 3:05 minutes) was significantly shorter than the RNA image acquisition time (9:05 ± 2:36 minutes; p < 0.001). CONCLUSION: The results of our study suggest that low-dose CT LVEF protocol is feasible, accurate, and fast while delivering a lower radiation dose than traditional RNA.

Discordance between Framingham Risk Score and atherosclerotic plaque burden.

AIM: Clinical predictors are routinely used to identify individuals who may benefit from aggressive risk factor modification. However, clinical predictors cannot account for all genetic and environmental variables. The objective of this study is to investigate the association of Framingham Risk Score (FRS) with computed tomography angiography (CTA) measures of coronary atherosclerosis. METHODS AND RESULTS: Consecutive patients who underwent CTA were prospectively enrolled and categorized according to clinical predictors such as FRS and pre-test probability for obstructive coronary artery disease (CAD). Atherosclerotic calcific and non-calcific plaques were assessed. Of the 1507 patients without a history of diabetes mellitus, myocardial infarction, and not on statin therapy, coronary atherosclerosis was present in 63.5% of the patients. Of the 1173 patients with low and intermediate FRS, atherosclerotic plaque was visually present in 47.6 and 72.7% of the patients, respectively. A higher proportion of low FRS patients had isolated non-calcific plaque (14.8%) compared with patients in the intermediate (10.1%) or high (7.2%) FRS groups, and 11.7% of high FRS patients had no visual evidence of plaque. The correlation between FRS and plaque was fair (r = 0.48; P < 0.001). CONCLUSION: Although clinical variables are predictive of CAD events, CTA identified coronary atherosclerosis in a significant proportion of patients with low to intermediate FRS, and a small minority of patients with high FRS had no evidence of atherosclerosis. Prospective studies are required to determine the potential value of identifying coronary atherosclerosis using CTA and to assess whether modifying therapies based on these results are warranted.