Comparison of anode/filter combinations in digital mammography with respect to the average glandular dose.

PURPOSE: To investigate the average glandular dose (AGD) applied for clinical digital mammograms acquired with the anode/filter combinations molybdenum/molybdenum (Mo/Mo), molybdenum/rhodium (Mo/Rh), and tungsten/rhodium (W/Rh). MATERIALS AND METHODS: Using the method of Dance, the AGD was evaluated from the exposure data of 4867 digital mammograms at two sites equipped with a full-field digital mammography (FFDM) system based on an amorphous selenium detector. 1793 images were acquired and analyzed with Mo/Mo, 643 with Mo/Rh, and 2431 with W/Rh. RESULTS: In the Mo/Mo cases the mean compressed breast thickness was 46 +/- 10 mm with an average AGD of 2.29 +/- 1.31 mGy. For the Mo/Rh cases with a mean compressed thickness of 64 +/- 9 mm, we obtained 2.76 +/- 1.31 mGy. The W/Rh cases with a mean compressed thickness of 52 +/- 13 mm resulted in 1.26 +/- 0.44 mGy. The image quality was assessed as normal and adequate for diagnostic purposes in all cases. CONCLUSION: Applying a W/Rh beam quality permits the reduction of the patient dose by approximately 50 % when using an FFDM system based on amorphous selenium. The dose reduction becomes larger as the breast thickness increases. The results are in agreement with simulations and phantom studies known from the literature.

Experimental phantom lesion detectability study using a digital breast tomosynthesis prototype system.

PURPOSE: To compare the sensitivity of conventional two-dimensional (2D) projection imaging with tomosynthesis with respect to the detectability of mammographic phantom lesions. MATERIALS AND METHODS: Using a breast tomosynthesis prototype based on a commercial FFDM system (Siemens MAMMOMAT Novation), but modified for a wide angle tube motion and equipped with a fast read-out amorphous selenium detector, we acquired standard 2D images and tomosynthesis series of projection views. We used the Wisconsin mammographic random phantom, model RMI 152A. The anode filter combinations Mo/Mo and W/Rh at two different doses were used as typical radiographic techniques. Slice images through the phantom parallel to the detector were reconstructed with a distance of 1 mm employing a filtered back-projection algorithm. The image data sets were read by five radiologists and evaluated with respect to the detectability of the phantom details. RESULTS: For all studied radiographic techniques, the detection rate in the tomosynthesis mode was 100 %, i. e. 75 true positive findings out of 75 possible hits. In contrast, the conventional projection mode yielded a detection rate between 80 and 93 % (corresponding to 60 and 70 detected details) depending on the dose and X-ray spectrum. CONCLUSION: Tomosynthesis has the potential to increase the sensitivity of digital mammography. Overlapping structures from out-of-plane tissue can be removed in the tomosynthesis reconstruction process, thereby enhancing the diagnostic accuracy.