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 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.