Volume computed tomography air kerma index and image quality evaluation in Brazil.

The aim of this study was to evaluate the image quality of 29 computed tomography (CT) scanners in Brazil and to perform estimations of patient dose and image quality of common CT examinations at these equipment. The volume CT air kerma indexes (C(VOL)) were estimated, using normalised weighted air kerma indexes, supplied by the ImPACT group. The image quality tests were performed using the phantom and accreditation protocol from the American College of Radiology (ACR). The C(VOL) values for head scans varied between 8.7 and 108 mGy. The Hi-res chest examinations presented C(VOL) values varying from 0.4 to 32 mGy. For abdominal scans, the estimated C(VOL) values varied between 4.1 and 94 mGy. This wide variation of air kerma between different centres is related to the scanner type and also to the scanning parameters. The results also showed that the image quality did not attend all ACR CT accreditation requirements.

The velocity of a radioactive bolus in the oesophagus evaluated by means of an image segmentation algorithm

Classical scintigraphic evaluation of a radioactive bolus through the oesophagus is based on regions of interest and time/activity curves, which only gives information about the total time required for it to cross the organ. Instantaneous parameters can be obtained if the exact position (centroid) of the bolus is known. For that, one needs to know the co-ordinates of the centre of mass of the bolus radioactivity distribution. From this, one can obtain velocity at each time. Obtaining such a new parameter would be important, to try to determine whether the anatomical differences among the 3 thirds of the oesophagus have a functional correspondence or not. We have studied 5 normal volunteers (4 males, 1 female, 33-68 yo). Each volunteer swallowed (unique swallowing) 40 MBq of 99mTc-phytate in 10 ml water. Eighty frames (0.3 sec) were acquired in a scintillation camera. External marks were used to separate the pharynx from the oesophagus. Images were transformed into bitmap by means of a Sophy Medical processing module and analysed by means of the algorithm, which determines the co-ordinates of the centroid (horizontal and vertical) for each frame and instant velocities through the organ. Different velocities were found in typical evaluations. Curves representing the different positions of the bolus C and the correspondent different Vs were obtained. Different velocities of the bolus were detected during the pharyngeal phase, and proximal, mid and distal parts of the oesophagus. Larger studies are necessary, but it seems that the velocity of a radioactive bolus changes in the different parts of the oesophagus. It is reasonable to say that there is a functional correspondence to the anatomical differences in the organ