(Tuesday, 7/16/2019) 1:15 PM - 1:45 PM
Room: Exhibit Hall | Forum 8
Purpose: A number of different target/filter combinations are currently being employed in mammography. When rhodium filters and targets were introduced in the early 1990s, a systematic look at CNR and dose as a function of kV, target/filter combinations and breast thickness was carried out. Since then the available and commonly used target/filter combinations have changed, and the purpose of the current study was to investigate the effect of these combinations on CNR and dose.
Methods: Target/filter combinations available are Mo/Mo, Mo/Rh, Rh/Rh, W/Rh, W/Ag, and Ag/Rh. The target/filter combinations for this study involved Rh/Rh and Ag/Rh on two different models. A phantom (CIRS, Model 011A) was used which contains embedded 1 cm thick areas of different ratios of glandular and adipose tissue. The nominal thickness of the phantom is 4.2 cm 50% adipose/50% glandular slabs were added to achieve additional phantom thicknesses of 6.4 cm and 7.9 cm. The three phantom thicknesses were imaged using the standard clinical AEC settings and the kV, target, filter, mAs and average glandular dose (AGD) were recorded. Using (flat field and gain corrected) raw images, contrast was measured as the average pixel value difference between 100 % glandular area and the phantom reference area for a 53 mm2 ROI. For each image a Figure-of-Merit (FOM) was calculated equal to (contrast-to-noise)²/AGD and noise was estimated to be the pixel standard deviation of the reference area.
Results: The FOM values for Rh/Ag at 4.2, 6.4 and 7.9 cm thicknesses were 105.6, 43.9, and 21.9, respectively. For Rh/Rh, the FOM values were 69.9, 27.7, 11.9, respectively.
Conclusion: For the phantom thicknesses studied the Rh/Ag target/filter combination at 34 kV resulted in the highest FOM, but does have a higher grid ratio 11:1 vs 5:1. Further study is ongoing to separate out the effects of target/filter combination.
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