Evaluation and optimization of administered activity, scanning parameters and hydration at (99m) Tc hydroxymethylene...

To find out the method of optimal activity administration and scanning parameters to fulfil guidelines and diagnostic reference levels and to reach a maximal contrast-to-noise ratio (CNR) in bone imaging. We also investigate the influence on CNR and bladder activity in well-hydrated patients.

A total of 225 patients were included. The first group of 101 patients was used to find out the optimal method to administer activity in terms of optimized CNR. The next two groups with 62 patients each were hydrated with 1500 ml water in two different time periods. CNR, bladder area and content were calculated.

An administrated activity per metre body height gave the highest CNR (5·43). A standard activity had the lowest percentage (2%) of images with < 1·5 million counts. Early hydration decreased CNR from 5·41 to 4·85 (P = 0·06), with late hydration to 5·29 (NS). Studies with too few pulses were increased from 2 to 11% to a level of 15-26% and 11-21%, respectively. Early hydration reduced the bladder activity from 20·7 to 10·1 MBq (P< 0·01), late hydration to 14·8 MBq (P = 0·08). The bladder size was enlarged from the no hydrated group (1406 mm(2) ) to the early hydrated group (2406 mm(2) , P< 0·000) and between the early and late hydrated group (3183 mm(2) , P< 0·05).

A standard activity in sufficient quantity is the most practical method, in addition to have the lowest percentage of images with too few pulses. A high fluid intake is not recommended because of problems with disturbing bladder content.