RESUMO
High resolution Computed Tomography (HRCT), a technique for pulmonary parenchyma studies, has been for a long time performed with only few scans with a large interval in between: the reasons were the supposed increase in the dose to the patient after kVp and mAs increase, which is necessary to reduce background noise, and the characteristic distribution of most diffuse lung diseases. Of late, HRCT skin dose has been demonstrated to be markedly lower than that of conventional CT (8/10 mm contiguous slices). To evaluate organ doses to patients during HRCT, we compared conventional CT (10 mm slices), HRCT (1.5 mm slices) and chest X-ray doses, as measured on an anthropomorphous phantom. We tested several scan protocols, with different kVp and mAs values to simulate various clinical situations for the two techniques, always with both slice thickness values and both contiguous and non-contiguous (10 mm gap) slices for HRCT scans. Doses were substantially similar for the two methods with contiguous slices in every protocol. "Clinical" HRCT dose (non-contiguous slices with 10 mm gap) is much lower than that of conventional CT--i.e., about 13% of conventional CT dose. On the other hand, HRCT dose is still two orders of quantity higher than that of standard radiography. To conclude, the importance of HRCT in pulmonary parenchyma studies is confirmed.
