Low Dose High Resolution Computed Tomography of Chest by Reduction of Effective mAs by 50%: A Prospective Study

Abstract

Introduction: The objective of our study was to evaluate diagnostic acceptability of image quality in High Resolution Computed Tomography (HRCT) of chest with 50% reduction in effective mAs. Materials and Methods: This prospective crosssectional study was done in 104 patients with BMI less than 30 kg/m2 who underwent HRCT chest examination in Tribhuvan University Teaching
Hospital (TUTH) for the period of 4 months from August to November 2017. CT scans were performed on the Siemens Somatom Definition AS+ 128 slice CT scanner. 52 patients were scanned with routine HRCT protocol of the department while another 52 patients were scanned reducing the effective mAs selected by CARE Dose4D by 50% (low dose HRCT chest protocol), keeping other parameters unchanged. The first patient was scanned with the routine protocol while the next patient was scanned reducing the effective mAs
by 50% and so on alternately. These images were evaluated by faculty radiologist and the overall image quality was assessed and scored on 4 point ~351~˷ Original Article Medical Journal of Pokhara Academy of Health Sciences Vol. 4 Issue 1 scale ranging from 1 to 4, (1= Excellent, 2= Very Good, 3= Fair, 4= Poor).

Results: There was no statistically significant difference between the images obtained by routine protocol and with low dose protocol across all BMI categories (p<0.05). Reduction of effective dose was found to be 50.71%, 47.52% and 45.94% in overweight (25-30 kg/m2), underweight (below 18.5 kg/m2) and normal (18.5-24.9 Kg/m2) BMI category respectively, with overall average dose
reduction of 48%.

Conclusion: Image quality of low dose protocol is acceptable for patients with BMI less than 30kg/m2. Thus, reduction in radiation dose by approximately 50% is possible by using a low dose HRCT chest protocol.