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TA allows the proper visualization of main vascular structures and has several advantages: minimal invasiveness, with a lower complication rate than that of angiography; generation of high spatial resolution images of both the arterial wall and the lumen; availability of multiplanar reconstructions (MPR) and three-dimensional (3D) reconstructions; and short examination times, allowing extended scan ranges.
There is increasing concern regarding the risk benefit ratio for this examinations particularly in younger patients and in women who are at higher risk of carcinogenesis from diagnostic irradiation. Consequently, there has been considerable interest in the application of dose reduction techniques to CT angiographic examination including stratification of tube current, tube potential, or both to patient body weight and body mass index.
Reductions in tube potential have been shown to result in a greater decrease in radiation dose than similar proportional decreases in tube current. Furthermore, reductions in tube potential have the added benefit of improving intravascular image signal on CT scans obtained with iodinated contrast material.
The disadvantage of the low-energy technique is an increase in image noise, especially in areas with more attenuating tissue, such as in large patients. Low energy protocols may also deliver increased radiation to the skin. Image noise increases with low tube current settings and low peak voltage; however, this is only a minor problem in the lungs.
In our study we adopted the strategy of lowering tube voltage rather than tube current aiming for significant decrease in radiation burden in patients less than 100 kgm body weight
This lead to significant decrease in the radiation burden compared to similar studies and compared to the standard effective radiation doses without significantly affecting the image quality in term of no inter-observer major notices according to the 5 points scaling system, mostly got 4 or 5 points, moreover the higher vascular attenuation aided in increasing the accuracy of diagnosis despite the minor increase in images noise and minor decrease in SNR and CNR
In conclusion, lowering tube voltage from 120 Kvp to 100 Kvp resulted in significant decrease in estimated effective radiation dose for the selected CTA examinations without significant effect on the image quality objectively and subjectively.