Low-dose CT for quantitative analysis in acute respiratory distress syndrome
ARMY INST OF SURGICAL RESEARCH FORT SAM HOUSTON TX
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Introduction The clinical use of serial quantitative computed tomography CT to characterize lung disease and guide the optimization of mechanical ventilation in patients with acute respiratory distress syndrome ARDS is limited by the risk of cumulative radiation exposure and by the difficulties and risks related to transferring patients to the CT room. We evaluated the effects of tube current-time product mAs variations on quantitative results in healthy lungs and in experimental ARDS in order to support the use of low-dose CT for quantitative analysis. Methods In 14 sheep chest CT was performed at baseline and after the induction of ARDS via intravenous oleic acid injection. For each CT session, two consecutive scans were obtained applying two different mAs 60 mAs was paired with 140, 15 or 7.5 mAs. All other CT parameters were kept unaltered tube voltage 120 kVp, collimation 32x0.5 mm, pitch 0.85, matrix 512x512, pixel size 0.625x0.625 mm . Quantitative results obtained at different mAs were compared via Bland-Altman analysis. Results Good agreement was observed between 60 mAs and 140 mAs and between 60 mAs and 15 mAs all biases less than 1. A further reduction of mAs to 7.5 mAs caused an increase in the bias of poorly and non aerated tissue -2.9 and 2.4, respectively and determined a significant widening of the limits of agreement for the same compartments -10.5 - 4.8 for poorly aerated and -5.9 - 10.8 for non aerated tissue. Estimated mean effective dose at 140, 60, 15 and 7.5 mAs corresponded to 17.8, 7.4, 2.0 and 0.9 millisievert, respectively. Image noise of scans performed at 140, 60, 15 and 7.5 mAs corresponded to 10, 16, 38 and 74 Hounsfield Units, respectively.
- Anatomy and Physiology
- Medicine and Medical Research