Dinko Eduardo Gonzalez Trotter

Thickness-dependent scatter correction algorithm for digital mammography

We have implemented a scatter-correction algorithm (SCA) for digital mammography based on an iterative restoration filter. The scatter contribution to the image is modeled by an additive component that is proportional to the filtered unattenuated x-ray photon signal and dependent on the characteristics of the imaged object. The SCAs result is closer to the scatter-free signal than when a scatter grid is used. Presently, the SCA shows improved contrast-to-noise performance relative to the scatter grid for a breast thickness up to 3.6 cm, with potential for better performance up to 6 cm. We investigated the efficacy of our scatter-correction method on a series of x-ray images of anthropomorphic breast phantoms with maximum thicknesses ranging from 3.0 cm to 6.0 cm. A comparison of the scatter-corrected images with the scatter-free signal acquired using a slit collimator shows average deviations of 3 percent or less, even in the edge region of the phantoms. These results indicate that the SCA is superior to a scatter grid for 2D quantitative mammography applications, and may enable 3D quantitative applications in X-ray tomosynthesis.

3D Visualization of X-ray Tomosynthesis Digital Mammography Data: Preference Study

A 3D visualization preference study was conducted on digital mammography tomosynthesis datasets. Two volume rendering [VR] techniques were used in the preference study, the Maximum Intensity Projection [MIP] and the Composite Ray Casting [CRC]. These techniques were presented side by side to experts in the field of digital mammography on dual high resolution monitors. The two techniques were presented using each of three different modes, the thick slice VR, tumbling along the azimuth direction, and tumbling along the elevation direction. Several phantoms and mastectomy specimens were imaged and reconstructed for this study. The experts ranked MIP higher than CRC, and tumbling along the elevation direction was selected as the best mode. In addition, the experts indicated that the MIP technique is better in displaying microcalcifications, and the CRC technique is better in showing masses.

Response of a CsI/amorphous-Si flat panel detector as function of incident x-ray angle

Two mechanisms for MTF dependence on incident x-ray angle are demonstrated by an experimental technique that separates the two phenomena. The dominant effect is that travel of x-ray photons through the scintillator at non-normal incidence involves an in-plane component. This mechanism leads to a significant but deterministic blurring of the incident image, but has no effect on the noise transfer characteristics of the detector. A secondary effect is that at large angles to the surface normal, x-ray-to-optical conversion occurs at positions in the scintillator further away from the photodiode surface. This leads to a small net decrease in MTF and NPS at angles above 60 degrees. The deterministic character of the angular dependence of gain, MTF and NPS leads to the conclusion that sufficient angular range can be supported by this detector construction. Excellent functionality in the context of tomography is expected.

Scatter Correction in Tomosynthesis Imaging for Mamography

Scatter is a significant source of bias and contrast-degradation in X-ray mammography. Accurately scatter-corrected projection images in tomosynthesis are expected to improve the performance of advanced 3D quantitative applications, such as tissue decomposition. In standard 2D mammography, scatter grids typically mitigate the scatter signal to an acceptable level. A scatter-rejection grid is not a practical option in X-ray tomosynthesis, where the X-ray source moves with respect to the detector. We have developed a scatter-correction algorithm based on inverse filtering, including a priori information about the tomosynthesis acquisition system. We investigated the performance of our scatter-correction method on a series of x-ray projection images of anthropomorphic breast phantoms, with thickness ranging from 3.0 cm to 6.0 cm, and acquired at angles ranging from 0 to 16 degrees with respect to the normal to the detector plane. A comparison of the scatter-corrected projection images with the scatter-free signal acquired using a slit collimator showed mean deviations of ˜3% or less for all investigated phantom thicknesses and source angles. Because our scatter-correction method is almost entirely automated, we have readily incorporated it into the 3D breast tomosynthesis reconstruction procedure. We present the effect of scatter correction on breast phantom tomosynthesis projections.