Comparison study of reconstruction algorithms for prototype digital breast tomosynthesis using various breast phantoms.

Digital breast tomosynthesis (DBT) is a recently developed system for three-dimensional imaging that offers the potential to reduce the false positives of mammography by preventing tissue overlap. Many qualitative evaluations of digital breast tomosynthesis were previously performed by using a phantom with an unrealistic model and with heterogeneous background and noise, which is not representative of real breasts. The purpose of the present work was to compare reconstruction algorithms for DBT by using various breast phantoms; validation was also performed by using patient images. DBT was performed by using a prototype unit that was optimized for very low exposures and rapid readout. Three algorithms were compared: a back-projection (BP) algorithm, a filtered BP (FBP) algorithm, and an iterative expectation maximization (EM) algorithm. To compare the algorithms, three types of breast phantoms (homogeneous background phantom, heterogeneous background phantom, and anthropomorphic breast phantom) were evaluated, and clinical images were also reconstructed by using the different reconstruction algorithms. The in-plane image quality was evaluated based on the line profile and the contrast-to-noise ratio (CNR), and out-of-plane artifacts were evaluated by means of the artifact spread function (ASF). Parenchymal texture features of contrast and homogeneity were computed based on reconstructed images of an anthropomorphic breast phantom. The clinical images were studied to validate the effect of reconstruction algorithms. The results showed that the CNRs of masses reconstructed by using the EM algorithm were slightly higher than those obtained by using the BP algorithm, whereas the FBP algorithm yielded much lower CNR due to its high fluctuations of background noise. The FBP algorithm provides the best conspicuity for larger calcifications by enhancing their contrast and sharpness more than the other algorithms; however, in the case of small-size and low-contrast microcalcifications, the FBP reduced detectability due to its increased noise. The EM algorithm yielded high conspicuity for both microcalcifications and masses and yielded better ASFs in terms of the full width at half maximum. The higher contrast and lower homogeneity in terms of texture analysis were shown in FBP algorithm than in other algorithms. The patient images using the EM algorithm resulted in high visibility of low-contrast mass with clear border. In this study, we compared three reconstruction algorithms by using various kinds of breast phantoms and patient cases. Future work using these algorithms and considering the type of the breast and the acquisition techniques used (e.g., angular range, dose distribution) should include the use of actual patients or patient-like phantoms to increase the potential for practical applications.

Effective DQE (eDQE) and dose to optimize radiographic technical parameters: a survey of pediatric chest X-ray examinations in Korea.

OBJECTIVE: The purpose of this study was to investigate the effect of various technical parameters for dose optimization in pediatric chest radiological examinations by evaluating effective dose and effective detective quantum efficiency (eDQE). MATERIALS AND METHODS: For tube voltages ranging from 40 to 90 kV in 10 kV increments at the focus-to-detector distance (FDD) of 100, 110, 120, 150, 180 cm, the eDQE was evaluated at same effective dose. RESULTS: The eDQE was considerably higher without the use of the grid on equivalent effective dose. This indicates that the reduction of scatter radiation did not compensate for the loss of absorbed effective photons in the grid. The eDQE increased with increasing FDD because of the greater effective modulation transfer function (eMTF) with lower focal spot blurring. However, most of the major hospitals in Korea employed a short FDD of 100 cm with the grid. The entrance surface air kerma values for the hospitals of this survey exceeded the Korean reference level of 100 µGy. CONCLUSIONS: The different reference levels might be appropriate for the same examination conducted on children of different ages. Also, it is necessary to refine the technical parameters to perform pediatric chest examinations.

Optimization of configuration parameters in a newly developed digital breast tomosynthesis system.

The purpose of the present work was to investigate the effects of variable projection-view (PV) and angular dose (AD) distributions on the reconstructed image quality for improving microcalcification detection. The PV densities at central and peripheral sites were varied through the distribution of 21 PVs acquired over ± 25° angular range. To vary the AD distribution, 7 PVs in the central region were targeted with two, four and six times the peripheral dose, and the number of central PVs receiving four times the peripheral dose was increased from 3 to 11. The contrast-to-noise ratio (CNR) for in-focus plane quality and the full width at half maximum (FWHM) of artifact spread function (ASF) for resolution in the z-direction were used. Although the ASF improved with increasing PV densities at two peripheral sites, the CNRs were inferior to those obtained with other subsets. With increasing PV density in the central area, the vertical resolution decreased but the CNR increased. Although increasing the central PV or AD concentrations improved image quality, excessive central densities reduced image quality by increasing noise in peripheral views.

Optimization of the key imaging parameters for detection of microcalcifications in a newly developed digital breast tomosynthesis system.

PURPOSE: The purpose of this study was to investigate the effect of different acquisition parameters and to characterize their relationships in order to improve the detection of microcalcifications using digital breast tomosynthesis (DBT). MATERIALS AND METHODS: DBT imaging parameters were optimized using 32 different acquisition sets with 6 angular ranges (± 5°, ± 10°, ± 13°, ± 17°, ± 21°, and ± 25°) and 8 projection views (PVs) (5, 11, 15, 21, 25, 31, 41, and 51 projections). To investigate the effects of variable angular dose distribution, the acquisition sets were evaluated with delivering more dose toward the central views. RESULTS: Our results show that a wide angular range improved the reconstructed image quality in the z-direction. If a large number of projections are acquired, then electronic noise may dominate the contrast-to-noise ratio (CNR) due to reduced radiation dose per projection. With delivering more dose toward the central views, it was found that the vertical resolution was reduced with increasing dose in the central PVs. On the other hand, the CNR clearly increased with increasing concentration of dose distribution in central views. CONCLUSIONS: Although it was found that increasing angular range improved the vertical resolution, it was also found that the image quality of microcalcifications in the in-focus plane did not improve by increasing the noise due to greater effective breast thickness. Angular dose distributions, with more dose delivered to the central views, generally yielded a higher quality factor than uniform dose distributions.

Effects of breast thickness and lesion location on resolution in digital magnification mammography.

This study aimed to examine the resolution effects of breast thickness and lesion location in magnification mammography by evaluating generalized modulation transfer function (GMTF) including the effect of focal spot, effective pixel size, and the scatter. Polymethyl methacrylate (PMMA) thicknesses ranging from 10 to 40 mm were placed on a standard supporting platform that was positioned to achieve magnification factors ranging from 1.2 to 2.0. As the magnification increased, the focal spot MTF degraded, while the detector MTF improved. The GMTF depended on the trade-off between the focal spot size and effective pixel size. Breast thickness and lesion location had little effect on the resolution at high frequencies. The resolution of small focal spot did improve slightly with increasing PMMA thickness for magnification factors less than 1.8. In contrast, system resolution decreased with increasing PMMA thickness for magnification factors greater than 1.8 since focal spot blur begins to dominate spatial resolution. In particular, breast thickness had a large effect on the resolution at lower frequencies. A low-frequency drop effect increased with increasing PMMA thickness because of the increase in scatter fraction. Hence, the effect of compressed breast thickness should be considered for the standard magnification factor of 1.8 that is most commonly used in clinical practice. Our results should provide insights for determining optimum magnification in clinical application of digital mammography, and our approaches can be extended to a wide diversity of radiological imaging systems.