Radiation dose is a concern for all cardiac imaging studies in wich ionizing radiation is used.
The reported effective radiation dose in conventional coronary angiography varies from 3,1 to 9,4 mSv, whereas in most studies the coronary CT angiography is higher [4,5].
Reported effective dose with the use of 64-multidetector row CT have ranged from 9,5 to 21,4 mSv.
Several approaches were adopted to reduce the high radiation doses with coronary Ct angiography such as :
1 - Decreasing the tube voltage:
This decrease allows a reduction in effective dose, as the radiation dose varies as the tube voltage increased by its value squared .
It has also the benefit of allowing an increase in opacification of blood vessels caused by a decrease in compton scattering .
2 - Optimization of the study height:
Realisation of an acquisition without injection, low dose in sequential mode with triple purpose :
- Calcium scoring: quantification of calcifications of coronary arteries.
- Adapting the volume of exploration.
- Study the whole pulmonary parenchyma.
3 - ECG-dependent dose modulation Fig. 6 :
The modulation according to the ECG corresponds to an automatic adaptation according to the movement of the heart cycle.
The most useful phase in the study of coronary arteries being the diastole: less movement thus less artufacts.
This technique is all more effecrive as the heart rate is low and the disatole is long.
4 - The prospectively gated tranverse technique:
Which as we have shown in our study, provides a 60,9% effective radiation dose reduction and good image quality under condition of a slow and regular heart beat.
But it has some limits such as it can't determine neither the global nor the regional cardiac function.
But our study has some limits:
- A mono centric recruitement of the studied population and a study stuff relatively small which has the consequences of a lack of power of statistical tests.
- The assessment of the quality of the image obtained was carried out visually to a pre-defined but subjectival score.
In summary, many techniques have proven their efficiency in reduction of radiation doses in coronary CT angiography, among of them the prospectively gated transverse technique that we believe has great promise to become a commonly used method.