PURPOSE: To determine the dose characteristics of multi-detector row computed tomography (CT) and to provide tabulated dose values and rules of thumb that assist in minimizing the radiation dose at multi-detector row CT.
MATERIALS AND METHODS: Weighted CT dose index (CTDI100w) values were obtained from three multi-detector row CT scanners (LightSpeed; GE Medical Systems, Milwaukee, Wis) for both head and body CT modes by using standard CT-dose phantoms. The CTDI100w was determined as a function of x-ray tube voltage (80,100, 120,140 kVp), tube current (range, 50-380 mA), tube rotation time (0.5-4.0 seconds), radiation profile width (RPW) (5, 10, 15, 20 mm), and acquisition mode (helical high-quality and high-speed modes and axial one-, two-, and four-section modes). Statistical regression was performed to characterize the relationships between CTDI100w and various technique factors.
RESULTS: The CTDI100w (milligray) increased linearly with tube current: in head mode, CTDI100w = (0-391 mGy/mA � 0.004) x tube current (milliampere) (i2 = 0.999); in body mode, CTDI100w = (0.162 mGy/mA � 0.002) x tube current (milliampere) (r2 = 0.999). The CTDI100w increased linearly with rotation time: in head mode, CTDI100w = (34.7 mGy/sec � 0.2) x rotation time (seconds) (r2 = 1.0); in body mode, CTDI100w = (13.957 mGy/sec � 0.005) x rotation time (seconds) (r* = 1.0). The relationship of normalized CTD^ QQ^ (milligrays per 100 mAs) with tube voltage followed a power law: in head mode, CTDI100w = (0.00016 mGy/100 mAs � kVp � 0.00007) x (tube voltage)2 Siai) (r2 = 0.997); in body mode, CTDI100w = (0.000012 mGy/100 mAs � kVp � 0.000007) x (tube voltage)2 8-ai) (r2 = 0.996). In all scanning modes, CTDI100w decreased when RPW increased. CTDI100w was 10% higher in head mode and 13% lower in body mode compared with the value suggested by the manufacturer, which is displayed at the scanner console. When deposited power exceeded 24 kW, CTDI100w increased by 10% as a result of use of the large focal spot.
CONCLUSION: The authors provide a set of tables of radiation dose as a function of imaging protocol to facilitate implementation of radiation dose-efficient studies.