Study of CT Acquisition Protocols Using Two Head Phantoms

Abstract

Computed Tomography (CT) scans promote a higher dose deposition than conventional radiology exams. These exams have significantly increased patient and collective doses and have become a global public health concern. There is a great need to improve protocols to seek for lower doses while maintaining the diagnostic image quality. The development of phantoms allows the testing of different acquisition protocols. In this study were tested two cylindrical head phantoms of polymethylmethacrylate (PMMA). One CT head phantom is the head standard test with 16 cm in diameter and the other head phantom developed is smaller at 12 cm in diameter. Both phantoms are 15 cm long. Different acquisition protocols were performed on a Philips CT scanner, Access model with 16 channels. The central slice of the phantoms was irradiated successively and measurements were performed using a pencil ionization chamber to obtain the CT air Kerma indexes in PMMA (Ck,PMMA,100) and CT dose indexes (CTDI). From these results, the CT Dose Index values weighted and volumetric (CTDIw, CTDIvol) were obtained to 10 cm scans of the central region of the head phantoms, in helical mode. The scans were performed using different voltage values (80, 100 and 120 kV) and charge (mA.s). Dose values varied from 5.59 to 21.51 mGy. The highest recorded dose value was 21.51 mGy for the smaller head phantom and 19.25 mGy for the standard head phantom with 120 kV. Considering the generation of images with the same diagnostic objective, the results obtained showed that the volumetric dose index (CTDIvol) presented a higher dose value in the 12 cm diameter phantom. This phantom has smaller volume than the standard head phantom.