Digital breast tomosynthesis promises solutions to many of the problems currently associated with projection mammography, including elimination of artifactual densities due to the superposition of normal tissues and increasing the conspicuity of true lesions that would otherwise be masked by superimposed normal tissue. We have investigated tomosynthesis using 45 photon counting, orientation sensitive, linear detectors which are precisely aligned with the focal spot of the x ray source. The x-ray source and the digital detectors are scanned in a continuous motion across the object (patient); each linear detector collecting an image at a distinct angle. Simulations of the imaging system were performed to evaluate the effect of: (1) the range of angles over which projection images are acquired; and (2) the number of projection images acquired used in the tomosynthetic reconstruction. Two different simulations were evaluated; the first was a numerical simulation of a tungsten wire; the second consisted of tomosynthetic reconstructions of a cadaveric rabbit, in which the number and/or range of projection angles was varied. We have shown, analytically and through these simulations, that both the use of more projection angles and the use of a larger range of projection angles improve the image quality of tomosynthetic image reconstructions. The use of a photon-counting x-ray detector system allows us to consider image acquisition geometries with a large number of projection angles, as there is no additive detector noise to degrade the projection or reconstructed images. The maximum number of projection angles and the range of projections angles do have upper practical limits; the range of projection angles is determined predominantly by the detector element size.
The purpose of this study was to investigate if the glandular dose to the breast in mammography can significantly be reduced without compromising image quality, when using photon counting technology, in a multi-slit scanning photon counting detector, compared to a conventional film mammography system and commercial available digital
mammography systems with TFT-array detectors. A CDMAM phantom study, with two different thicknesses of additional PMMA absorber, 4 cm and 7 cm respectively, has shown that multi-slit scanning photon counting detector technology can reduce the dose, without reducing the image quality. This comparison was made to two commercial available digital mammography systems Senographe 2000D (from GEMS) and Selenia (from Lorad). The results show that dose can be reduced with 63% to 77%, depending on object thickness, when using XCT for mammography. This dose reduction has also been verified clinically through a small pilot study with patients and specimen, where the comparison was made between XCT and film.
The most natural way of digital X-ray imaging is photon counting as the photon flux in itself is digital. In photon counting, the information in the X-ray flux is used more efficiently as the information carrying low-energy photons are given the same weight as higher energy photons carrying less image information. This is in contrast to all existing X-ray instruments, which are energy-integrating systems where the highest energy photons are given the highest weight. A novel technique for high resolution digital X-ray imaging, using gaseous avalanche detectors for photon counting with high signal-to-noise ratios for single X-ray photons, has been developed. The performance of this detector has been studied and compared to analogue film-screen system by imaging phantoms. Our results show that this technology can improve image quality while decreasing the glandular dose to the patient.
The detection characteristics of digital x-ray and film-screen mammography systems are different and thus current film-screen techniques are not ideal for digital mammography. Therefore optimum technical parameters required for digital mammography are likely to be different compared with film-screen mammography. The goal of this study is to evaluate the optimum technical parameters for full-field digital mammography by experimental and computer simulation methods. A General Electric Full Field Digital Mammography (FFDM) prototype unit using Cesium Iodide (CsI) on an amorphous Silicon photodiode array was used for the experimental measurements. Using breast equivalent phantoms, images were acquired for a set of x-ray target-filters for a range of peak kilovoltage, varying breast composition and thickness, with and without an anti-scatter grid. The signal-to-noise ratio (SNR) and figure-of-merit (FOM) were determined for simulated calcification and mass targets, independently by the two methods. The results for noise, contrast, SNR and FOM were compared and agree within 5% and 6% respectively. Combined results are presented for the case of 50% glandular - 50% adipose tissue breast composition using the grid and for the calcification target. Based on the FOM approach, preliminary results suggest that a Rhodium target-filter combination will be beneficial for higher breast thickness and for denser breasts.