This study assessed the feasibility of reducing radiation exposure during coronary CT angiography (CCTA) using only modified acquisition parameters on a 64-slice CT scanner. Over 85% of patients were able to undergo prospective CCTA, which significantly reduced radiation dose compared to historical levels and conventional angiography. Image quality remained high, with over 97% of coronary segments evaluated as having either excellent, good, or fair quality. The study demonstrated that very low dose CCTA is possible using standard equipment by optimizing acquisition settings.

1. In vivo reduction of radiation exposure
with a single-source coronary CT
angiography
effects of optimal parameters settings in
real life conditions
Alain Tavildari MD; François Vochelet MD; Luc Maillard MD PhD
Clinique AXIUM – Aix en Provence - FRANCE

2. FINANCIAL DISCLOSURES
 None

3. BACKGROUND
 Coronary computed tomographic
angiography (CCTA) has become a
common diagnostic test for evaluating
patients with coronary artery disease
 Radiation exposure has been deemed
too high

4. OBJECTIVES
 To assess the feasibility of in vivo radiation
reduction only by modifying acquisition
parameters in real life conditions with a
single source 64-slice CT
 Comparison of radiation exposure with
conventional angiography

5. METHOD
 Patients :
 Over 18 YO
 Co-morbidities including diabetes mellitus and
overweight were not excluded
 Coronary calcifications were not excluded
 All patients recieved sublingual nitrate
 Target heart rate was under 65 bpm at
acquisition time
 Atenolol intraveinously was given if needed
 Informed consent was obtained for all patients

6. METHOD
 Acquisition parameters :
 General Electric VCT Xte
 Prospective acquisition if heart rate (HR) under 65 bpm
 80 kV or 100 kV
 120 mA to 400 mA
 Acquisition at 75% of R-R intervall
 No padding
 Retrospective acquisition if HR between 65 and 75 bpm
 80 kV or 100 kV
 Modulation limited to 400 mA (maximum around
phase 75%)
 Reconstruction every 10% from phase 0% to phase 90%

7. METHOD
 Image quality :
 Evaluatued on a per-segment basis using the
American Heart Association coronary model
 Two independant observers gradded image quality
on a 4 point scale
 1 : excellent : vessel fully evaluable, no artifact
 2 : good : vessel fully evaluable, slight artifacts
 3 : fair : evaluable concerning the presence of
stenosis, blurred vessel margins
 4 : unevaluable
 Average quotation was taken into account if in case
of difference between the 2 observers

8. METHOD
 Radiation dose
 Based on the dose-lenght product (DLP,
mGy.cm), and effective dose (ED, mSv)
 ED derived from DLP using a conversion
factor of 0.014 for male and 0.017 for female

9. METHOD
 Conventional angiography
 Performed for patients with coronary stenosis on CT
 GE Innova® all-digital X-Ray system
 No ventriculography
 Radiation dose expressed with Dose Surface Product
 Conversion factor for ED = 0.2

10. IMAGE QUALITY = 1 (excellent)

11. IMAGE QUALITY = 2 (good)

12. IMAGE QUALITY = 3 (fair)

13. IMAGE QUALITY = 4 (unevaluable)

14. RESULTS : patients characteristics (n=137)

15. IMAGE QUALITY
 Over 2055 segments
 97.7 % were evaluable (quality score 1,2 or3)
 86 % were good or excellent (quality score 1 or 2)

16. RESULTS
 Prospective acquisition has been
performed for 85.4 % of patients (n=117)
 Conventional angiography done for 20
patients to confirm coronary stenosis
seen on CT

17. RESULTS
p < 0.0001
p < 0.0001

18. SUMMARY
 Our study was able to demonstrate that very low dose
coronary CT is feasible with a standard 64 slice CT
 Radiation dose was dramatically reduced in all
acquisition modes compared to historical data and to
conventional angiography
 Prefered mode is prospective

19. STUDY LIMITATION
 Non randomized study
 Single center
 Conventional angiography not made for all patients
 Subjective image quality evaluation

20. CONCLUSION
 These data may reconsider the decisional algorithm for
coronary artery stenosis detection
 Radiation dose for the whole studied population is nearly
as low as a mammogram
 CCTA could be proposed, with the parameter settings
used in this study, for screening asymptomatic patients
with high cardio-vascular risk factors