Modulation transfer function of digital breast tomosynthesis: a comparison of various edge devices.

The modulation transfer function (MTF) is a fundamental tool for assessing the sharpness of digital breast tomosynthesis (DBT) systems and is primarily measured using edge devices. We compared the MTF of a Senographe Pristina DBT system using four-edge devices. These devices were composed of stainless steel with a thickness of 0.6, 0.8, and 1.0 mm, and 1.0 mm tungsten, based on different international guidelines. We evaluated spatial frequencies at MTFs of 0.5 (MTF50%) and 0.1 (MTF10%). The collimator-equipped and non-collimator configurations of the DBT were compared. We found no appreciable differences between scan and chest wall-nipple directions. Both MTF50% (2.90-2.99 cycles/mm) and MTF10% (6.69-6.94 cycles/mm) demonstrated minimal variation across the different edge devices. The collimator-equipped system exhibited an MTF50% that was approximately 5% higher than that of the non-collimator configuration. The choice of the edge device did not appreciably impact the MTF.

[Assessment of the utility of digital subtraction in lacrimal passage contrasting].

The utility of lacrimal passage contrasting by a digital subtraction system (DS system) was assessed in comparison with a computed radiography system (CR system) by means of simulating the exposure dose of a patient's crystalline lens and measuring the image contrast of both systems. The exposure dose of the patient's crystalline lens in the DS system was an average of 45.8 mGy, which was 41.6 times higher than that of the CR system. Therefore, care must be taken to reduce the exposure dose of the crystalline lens because it is necessary to reduce the probability of radiation injuries such as cataracts. The average of the image contrast of the DS system at the lacrimal passage to other parts of the head radiograph was lower than that of the CR system, but the standard deviation of the DS system was 0.16, a value that was almost constant because the shadow of obstacles such as the facial bone was almost completely removed, and image contrast was improved. The area under the curve (AUC) of the DS and CR systems as determined by means of receiver operating characteristic (ROC) analysis by ten radiological technologists were 0.869+/-0.066 and 0.746+/-0.125, respectively, and statistical significance was shown for both systems, although the detectability of the DS system was superior to that of the CR system (p<0.05). Therefore, we concluded that the DS system was a useful radiographic technique for lacrimal passage contrasting, and its use in patients is predicted to increase in the future.