Optimizing radiation dose for thorax CT scan with bolus triggering activation delay setting (study at the radiology installation at DR Moewardi hospital)

Thorax CT examination in dr. Moewardi Hospital Surakarta is performed by bolus triggering technique. Bolus trigering activation delay is adjusted at 5 to10 second after contrast injection by automatic injector. Radiation dose can be minimize by using this technique, but inapropriate delay adjustment can reduce the image accuracy. Contrast media enhancement of region of interest can be missed due to very long activation delay. This reseach aims to find out the effect of activation delay of bolus trigerring toward the radiation dose and to determine its possible maximum value. This is experimental research. Eight patients were divided into eight groups by random group design. Eight variations of activation delay (0, 2, 4, 6, 8, 10, 12, and 14) were applied to the groups. The dose (CTDIvol) for every scan was calculated by the scanner system and displayed directly on the monitor. Data were analyzed using regression statistic. This research method has been reviewed and aproved by The Ethic Comittee of Health Polytechnic of Semarang. The result showed that there was very strong effect of the bolus triggering activation delay toward the radiation dose (r = 0,97) (p-value <0,001) and determination coeficient (R²) = 0,940. The radiation dose was affected 94% by the activation delay. The equation of Y = 308,252 - 18,821Time Delay indicated that there was 18,821 mGy dose reduction for 1 second activation delay increase. The possible maximum activation delay was 17 second. (author)