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 PhDClinique AXIUM – Aix en Provence - FRANCE

FINANCIAL DISCLOSURES

None

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

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

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

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%

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

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

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

IMAGE QUALITY = 1 (excellent)

IMAGE QUALITY = 2 (good)

IMAGE QUALITY = 3 (fair)

IMAGE QUALITY = 4 (unevaluable)

RESULTS : patients characteristics (n=137)

IMAGE QUALITY

Over 2055 segments 97.7 % were evaluable (quality score 1,2 or3) 86 % were good or excellent (quality score 1 or

2)

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

RESULTSp < 0.0001

p < 0.0001

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

STUDY LIMITATION

Non randomized study

Single center

Conventional angiography not made for all patients

Subjective image quality evaluation

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