The effect of different exposure parameters on radiation dose in digital mammography and digital breast tomosynthesis: A phantom study.

INTRODUCTION: There are concerns regarding the increase in radiation dose among women undergoing both digital mammography (DM) and digital breast tomosynthesis (DBT). The aim of this study was to evaluate the effect of different exposure parameters on entrance skin dose (ESD) and average glandular dose (AGD) for DM and DBT using a phantom. METHODS: The ESD and AGD of 30 DM and DBT (cranio-caudal projection) examinations using a tissue equivalent phantom where acquired using a GE Senographe Essential DM unit. Commercial phantoms were used to simulate three different breast thicknesses and compositions. Tube potential, tube load, and target/filter combinations were also varied with ESD and AGD recorded directly from the DM unit. Comparisons were made using the non-parametric Kruskal Wallis, Mann-Whitney, and Wilcoxon signed rank tests. RESULTS: The individual ESD values for 4 cm, 5 cm, and 6 cm thick phantoms for DM and DBT at Rh/Rh target/filter combination and 30-32 kV/56 mAs levels were 5.06 and 4.18 mGy; 5.82 and 5.08 mGy; and 7.26 and 11.4 mGy, respectively; while AGDs were 1.57 and 1.30 mGy, 1.33 and 1.39 mGy; and 1.29 and 3.60 mGy, respectively. The Kruskal-Wallis test showed a statistically significant difference in AGD for DM (P = .029) but not for DBT (P = 0.368). The Mann-Whitney and Wilcoxon signed rank tests showed no statistically significant difference for ESD or AGD between both DM and DBT techniques (P = .827 and .513). The percentage differences in ESD for phantom thicknesses of 4 cm, 5 cm, and 6 cm between DBT and DM ranged between -21% and 36%; while for AGD between -21% and 64.2%. CONCLUSIONS: The ESD and AGD for single view projection in DM and DBT showed differences at 4 and 6 cm breast thicknesses and compositions but not at 5 cm thickness with 30-32 kV and a Rh/Rh target/filter combination. IMPLICATIONS FOR PRACTICE: A fibro-fatty breast results in less radiation dose variations in terms of ESD and AGD between DM and DBT techniques.

Comparison between image quality in electronic zoom and geometric magnification in digital mammography.

BACKGROUND: Magnification mammography is performed to enhance the visibility of small structures at the expense of relatively high radiation dose as a complementary examination to standard mammography. The introduction of post-processing capabilities and the widespread use of digital mammography has promoted some controversy in the last decade on whether similar visibility can be achieved using electronic zoom. The aim of this study is to compare the visibility of small structures in images obtained by the two techniques stated above for different exposure conditions. METHODS: Images of a Fluke Biomedical Model 18-220 Mammography Accreditation Phantom were obtained using standard techniques and geometric magnification, using a digital mammography unit, with different exposure factors. Three different target/filter combinations (Mo/Mo,Mo/Rh,Rh/Rh), variable kVp (26-32), and automatic exposure control were used. Images obtained using standard technique were electronically zoomed and compared to the corresponding magnification mammograms. Comparisons were based on the visibility of structures evaluated by five senior technologist with extensive experience in mammography. Statistical analysis was performed using non-parametric tests. RESULTS: Visibility of structures was not affected by the kV used for a given target/filter combination for both techniques (p > 0.065). Target/filter combination of Mo/Mo provided better visibility of micro-calcification and fibers (p < 0.026) in geometric magnification technique and Mo/Rh in the digital zoom technique. No significant differences were observed in the visibility of simulated breast masses. The overall image score was significantly higher (p < 0.001) for geometric magnification over the digital zoom for Mo/Mo & Rh/Rh combinations. CONCLUSION: Although sufficient image quality was maintained in electronically zoomed images, geometric magnification provided better overall visualization of structures in the phantom.

Is venous reflux a common disease in post-thrombotic patients with unilateral deep vein thrombosis episode?

OBJECTIVES: To investigate reflux development and changes in resting venous diameters in the DVT and the non-DVT lower limbs. METHODS: Twenty subjects (40 limbs) with acute unilateral proximal DVT diagnosed by ultrasound, who were treated with low-molecular-weight-heparin (LMWH), followed by at least three months of oral warfarin therapy, were enrolled in the study. The limbs were classified according to CEAP (clinical, aetiologic, anatomic, pathophysiology) clinical classification on a scale of 0-6. Duplex ultrasound (DUS) was employed to assess DVT resolution, vein diameter and venous reflux in both limbs at intervals of zero, three, six and 12 months. Venous reflux was defined as a valve closure time more than 1 s. RESULTS: There were 13 men and seven women, average age was 40.8 years and average body mass index 27.7 kg/m2. In the DVT limbs at three, six and 12 months, deep veins were non-occluded in 40%, 60% and 85%, respectively. By 12 months, 16 (80%) had developed venous reflux, mostly in the femoral (FV) and popliteal veins (PV); eight limbs (40%) were in clinical classes 4-6. In the contralateral 20 non-DVT limbs, four limbs developed borderline reflux at the sapheno-femoral junction (SFJ) after six months and mean diameters of SFJ, FV and PV increased significantly. CONCLUSIONS: Venous reflux is highly likely to occur in DVT limbs within a year follow-up period. Venous dilatation can occur in the contralateral unaffected lower limb, consistent with a systemic effect. Our results are suggestive and further studies are needed.