We have developed a dual-energy subtraction technique for contrast-enhanced breast tomosynthesis. The imaging
system consists of 48 photon-counting linear detectors which are precisely aligned with the focal spot of the x-ray
source. The x-ray source and the digital detectors are translated across the breast in a continuous linear motion; each
linear detector collects an image at a distinct angle. A pre-collimator is positioned above the breast and defines 48 fan-shaped
beams, each aligned with a detector. Low- and high-energy images are acquired in a single scan; half of the
detectors capture a low-energy beam and half capture a high-energy beam, as alternating fan-beams are filtered to
emphasize low and high energies. Imaging was performed with a W-target at 45 and 49 kV. Phantom experiments and
theoretical modeling were conducted. Iodine images were produced with weighted logarithmic subtraction. The
optimal tissue cancellation factor, wt, was determined based on simultaneous preservation of the iodine signal and
suppression of simulated anatomic background. Optimal dose allocation between low- and high-energy images was
investigated. Mean glandular doses were restricted to ensure clinical relevance. Unlike other dual-energy approaches,
both spectra must have the same peak energy in this system design. We have observed that wt is mainly dependent on
filter combination and varies only slightly with kV and breast thickness, thus ensuring a robust clinical implementation.
Optimal performance is obtained when the dose fraction allocated to the high energy images ranges from 0.55 to 0.65.
Using elemental filters, we have been able to effectively suppress the anatomic background.
Andrew Maidment, Christer Ullberg, Karin Lindman, Leif Adelöw, Johan Egerström, Mathias Eklund, Tom Francke, Ulf Jordung, Tomas Kristoffersson, Lars Lindqvist, Daniel Marchal, Hans Olla, Erik Penton, Juha Rantanen, Skiff Solokov, Niclas Weber, Hans Westerberg
Digital breast tomosynthesis promises solutions to many of the problems 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 a digital camera containing 48 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. A preliminary assessment of tomosynthesis image quality has been performed with both qualitative and quantitative methods. Measured values of MTF and NPS appear concordant with theoretical values. The MTF in the scanning direction is dominated by scanning unsharpness and geometric factors, while the NPS is white. The MTF and NPS in the strip direction are somewhat lower than in the scan direction. The NPS of tomographic images show a slight decrease with increasing spatial frequency, related to the sampling and interpolation in the reconstruction process. A phase I clinical trial is ongoing; 9 women have been recruited. Breast positioning is comparable to other imaging systems. The visualization of breast anatomy appears to be superior to screen-film mammography, at the same average glandular dose. Examination of images reconstructed with a sub-sampled set of projection images appears to support the hypothesis that image quality is superior when more projection images are used in the reconstruction.
Andrew Maidment, Michael Albert, Stefan Thunberg, Leif Adelow, Ola Blom, Johan Egerstrom, Mathias Eklund, Tom Francke, Ulf Jordung, Tomas Kristoffersson, Karin Lindman, Lars Lindqvist, Daniel Marchal, Hans Olla, Erik Penton, Juha Rantanen, Skiff Solokov, Christer Ullberg, Niclas Weber
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.
Stefan Thunberg, Leif Adelow, Ola Blom, Anders Coster, Johan Egerstrom, Mathias Eklund, Per Egnell, Tom Francke, Ulf Jordung, Tomas Kristoffersson, Karin Lindman, Lars Lindqvist, Daniel Marchal, Hans Olla, Erik Penton, Vladimir Peskov, Juha Rantanen, Skiff Sokolov, Per Svedenhag, Christer Ullberg, Niclas Weber
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.
Stefan Thunberg, Tom Francke, Johan Egerstrom, Mathias Eklund, Leif Ericsson, Thomas Kristoffersson, Vladimir Peskov, Juha Rantanen, Skiff Sokolov, Per Svedenhag, Christer Ullberg, Niclas Weber
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.
Tom Francke, Mathias Eklund, Leif Ericsson, Thomas Kristoffersson, Vladimir Peskov, Juha Rantanen, Skiff Sokolov, Jan Soderman, Christer Ullberg, Niclas Weber
Radiation dose to the patient, contrast and position resolution are important quality factors in medical X-ray imaging. A novel technique for digital X-ray imaging has been developed, using photon counting with high signal-to-noise ratios for single X-ray photons. The novel technique allows a significant dose reduction over screen-film systems, as well as a high contrast and good position resolution. The novel technique is based on photon counting gaseous detectors. A high signal-to-noise ratio for single X-ray photons allows virtually noise-free counting of photons. Low noise together with a high contrast in the image allows a significant dose reduction compared to film-based systems. The new technique makes photon counting X-ray imaging possible, only limited by quantum fluctuations.
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