Digital Tomosynthesis of the Chest: Comparison of Patient Exposure Dose and Image Quality between Standard Default Setting and Low Dose Setting

Objective: To determine the optimum low dose (LD) digital tomosynthesis (DT) setting, and to compared the image quality of the LD DT with that of the standard default (SD) DT. Materials and Methods: Nine DT settings, by changing tube voltage, copper filter, and dose ratio, were performed for determining the LD setting. Among combinations of DT setting, a condition providing the lowest radiation dose was determined. Eighty artificial nodules Less than 1 cm in diameter (subcentimeter nodules: 40, micronodules less than 4 mm: 40) were attached to a Styrofoam and a diaphragm of the phantom. Among these, 38 nodules were located at the periphery of the lung (thin area) and 42 nodules were located at the paravertebral or sub-diaphragmatic area (thick area). Four observers counted the number of nodules detected in the thick and thin areas. The detection sensitivity in SD and LD settings were calculated separately. Data were analyzed statistically. Results: The lowest LD setting was a combination of 100 kVp, 0.3 mm additional copper filter, and a 1 : 5 dose ratio. The effective dose for the LD and SD settings were 62 mu Sv and 140 mu Sv, separately. A 56.7% dose reduction was achieved in the LD setting compared with the SD setting. Detection sensitivities were not different between the SD and the LD settings except between observers 1 and 2 for the detection of micronodules in the thick area. Conclusion: LD DT can be effective in nodule detection bigger than 4 mm without a significant decrease in image quality compared with SD DT.