| 1. |
- Berggren, Karl, et al.
(författare)
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Physical characterization of photon-counting tomosynthesis
- 2015
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Konferensbidrag (refereegranskat)abstract
- Tomosynthesis is emerging as a next generation technology in mammography. Combined with photon-counting detectors with the ability for energy discrimination, a novel modality is enabled - spectral tomosynthesis. Further advantages of photon-counting detectors in the context of tomosynthesis include elimination of electronic noise, efficient scatter rejection (in some geometries) and no lag. Fourier-based linear-systems analysis is a well-established method for optimizing image quality in two-dimensional x-ray systems. The method has been successfully adapted to three-dimensional imaging, including tomosynthesis, but several areas need further investigation. This study focuses on two such areas: 1) Adaption of the methodology to photon-counting detectors, and 2) violation of the shift-invariance and stationarity assumptions in non-cylindrical geometries. We have developed a Fourier-based framework to study the image quality in a photon-counting tomosynthesis system, assuming locally linear, stationary, and shift-invariant system response. The framework includes a cascaded-systems model to propagate the modulation-transfer function (MTF) and noise-power spectrum (NPS) through the system. The model was validated by measurements of the MTF and NPS. High degrees of non-shift invariance and non-stationarity were observed, in particular for the depth resolution as the angle of incidence relative the reconstruction plane varied throughout the imaging volume. The largest effects on image quality in a given point in space were caused by interpolation from the inherent coordinate system of the x-rays to the coordinate system that was used for reconstruction. This study is part of our efforts to fully characterize the spectral tomosynthesis system, we intend to extend the model further to include the detective-quantum efficiency, observer modelling, and spectral effects.
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| 2. |
- Berggren, Karl, 1989-
(författare)
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Spectral image quality and applications in breast tomosynthesis
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the 1970s, it was determined that screening mammography is an efficient tool in fighting the increasing number of women dying from breast cancer, and many countries have established screening programs since then. Mammography systems have improved substantially over the years with one of the major advances being the transition from x-ray film to digital x-ray detectors. Following this development, the number of women dying from breast cancer has decreased, but there is still much room for improvement. One technology that is changing the breast imaging landscape is breast tomosynthesis; tomographic imaging with in-plane resolution similar to that of mammography, albeit limited height resolution. Breast tomosynthesis is commonly implemented with flat-panel detectors, but line detectors in a slit-scanning geometry can also be used. The latter configuration allows for more complex detector technologies, such as spectral photon-counting detectors that enable single-shot spectral imaging. The combination of spectral imaging and tomosynthesis opens up for a range of new applications, but the slit scanning geometry, which differs substantially from that of flat-panel tomosynthesis systems, and the factors affecting image quality have not been well understood. This thesis aims at filling this gap. Image quality and the parameters that influence image quality in spectral photon-counting slit-scanning breast tomosynthesis are characterized and analyzed using cascaded-systems modelling and linear image quality metrics. In addition, the thesis goes into characterizing the x-ray properties of breast tissue, an important input parameter for accurate material decomposition of in-vivo tissue. Material decomposition with spectral imaging opens up a range of applications, such as accurate measurement of volumetric breast density and spectral lesion characterization for decision support as part of mammography screening, and contrast-enhanced K-edge imaging for diagnostics. Tomosynthesis combined with material decomposition has the potential to improve these methods further by, for instance, separating lesions or regions of interest from surrounding fibro-glandular tissue in quantitative 3D maps of breast tissue.
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| 3. |
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| 4. |
- Bornefalk, Hans, et al.
(författare)
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Single-shot dual-energy subtraction mammography with electronic spectrum splitting : Feasibility
- 2006
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Ingår i: European Journal of Radiology. - : Elsevier BV. - 0720-048X .- 1872-7727. ; 60:2, s. 275-278
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Tidskriftsartikel (refereegranskat)abstract
- We present a single-shot dual-energy subtraction mammography technique using an energy sensitive photon counting detector. An electronic threshold near the middle of the X-ray spectrum discriminates between high- and low-energy photons, and allows the simultaneous acquisition of high- and low-energy images which can be combined to suppress anatomical clutter. By setting the electronic threshold close to 33.2 keV (the k-edge of iodine) the system is optimized for dual-energy contrast-enhanced imaging of breast tumors. This method eliminates the need for separate exposures which might otherwise lead to motion artifacts. The method is illustrated in phantom images.
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| 5. |
- Dahlman, Nils, et al.
(författare)
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Evaluation of photon-counting spectral breast tomosynthesis
- 2011
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Ingår i: Medical Imaging 2011. - : SPIE.
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Konferensbidrag (refereegranskat)abstract
- We have designed a mammography system that for the first time combines photon-counting spectral imaging with tomosynthesis. The present study is a comprehensive physical evaluation of the system; tomosynthesis, spectral imaging, and the combination of both are compared using an ideal-observer model that takes anatomical noise into account. Predictions of signal and noise transfer through the system are verified by contrast measurements on a tissue phantom and 3D measurements of MTF and NPS. Clinical images acquired with the system are discussed in view of the model predictions.
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| 6. |
- Danielsson, Mats, Professor, et al.
(författare)
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Method and arrangement relating to x-ray imaging
- 2008
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Patent (populärvet., debatt m.m.)abstract
- An X-ray apparatus is provided for acquisition of images containing spectral information. An X-ray source and a collimator having multiple slits are operable together with a set of line detectors, the line detectors including linear arrays of photon counting channels. Each of the channels includes a photon conversion channel element which is operable to convert photons to electric pulses. A plurality of pulse counters are operable to count pulses in a plurality of different ranges of pulse strength, where the strength of a pulse depends on the energy of the photon. Further, an arrangement is included for an energy subtracting operation.
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| 7. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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A photon-counting detector for dual-energy breast tomosynthesis
- 2009
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Ingår i: Medical Imaging 2009. - : SPIE. ; , s. 72581-
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Konferensbidrag (refereegranskat)abstract
- We present the first evaluation of a recently developed silicon-strip detector for photon-counting dual-energy breast tomosynthesis. The detector is well suited for tomosynthesis with high dose efficiency and intrinsic scatter rejection. A method was developed for measuring the spatial resolution of a system based on the detector in terms of the three-dimensional modulation transfer function (MTF). The measurements agreed well with theoretical expectations, and it was seen that depth resolution was won at the cost of a slightly decreased lateral resolution. This may be a justifiable trade-off as clinical images acquired with the system indicate improved conspicuity of breast lesions. The photon-counting detector enables dual-energy subtraction imaging with electronic spectrumsplitting. This improved the detectability of iodine in phantom measurements, and the detector was found to be stable over typical clinical acquisition times. A model of the energy resolution showed that further improvements are witn reach by optimization of the detector.
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| 8. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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Contrast-enhanced dual-energy subtraction imaging using electronic spectrum-splitting and multi-prism x-ray lenses
- 2008
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Ingår i: Medical Imaging 2008 - Physics of Medical Imaging. - San Diego, CA, USA : SPIE. - 9780819470973 ; , s. 91310-91310
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Konferensbidrag (refereegranskat)abstract
- Dual-energy subtraction imaging (DES) is a method to improve the detectability of contrast agents over a lumpy background. Two images, acquired at x-ray energies above and below an absorption edge of the agent material, are logarithmically subtracted, resulting in suppression of the signal from the tissue background and a relative enhancement of the signal from the agent. Although promising, DES is still not widely used in clinical practice. One reason may be the need for two distinctly separated x-ray spectra that are still close to the absorption edge, realized through dual exposures which may introduce motion unsharpness. In this study, electronic spectrum-splitting with a silicon-strip detector is theoretically and experimentally investigated for a mammography model with iodinated contrast agent. Comparisons are made to absorption imaging and a near-ideal detector using a signal-to-noise ratio that includes both statistical and structural noise. Similar to previous studies, heavy absorption filtration was needed to narrow the spectra at the expense of a large reduction in x-ray flux. Therefore, potential improvements using a chromatic multi-prism x-ray lens (MPL) for filtering were evaluated theoretically. The MPL offers a narrow tunable spectrum, and we show that the image quality can be improved compared to conventional filtering methods.
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| 9. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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Energy resolution of a photon-counting silicon strip detector
- 2010
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; , s. 156-162
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Tidskriftsartikel (refereegranskat)abstract
- A photon-counting silicon strip detector with two energy thresholds was investigated for spectral X-ray imaging in a mammography system. Preliminary studies already indicate clinical benefit of the detector, and the purpose of the present study is optimization with respect to energy resolution. Factors relevant for the energy response were measured, simulated, or gathered from previous studies, and used as input parameters to a cascaded detector model. Threshold scans over several X-ray spectra were used to calibrate threshold levels to energy, and to validate the model. The energy resolution of the detector assembly was assessed to range over ΔE/E=0.12–0.26 in the mammography region. Electronic noise dominated the peak broadening, followed by charge sharing between adjacent detector strips, and a channel-to-channel threshold spread. The energy resolution may be improved substantially if these effects are reduced to a minimum. Anti-coincidence logic mitigated double counting from charge sharing, but erased the energy resolution of all detected events, and optimization of the logic is desirable. Pile-up was found to be of minor importance at typical mammography rates.
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| 10. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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Imaging with multi-prism x-ray lenses
- 2008
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Ingår i: Medical Imaging 2008 - Physics of Medical Imaging. - : SPIE. - 9780819470973 ; , s. 91308-91308
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Konferensbidrag (refereegranskat)abstract
- The multi-prism lens (MPL) is a refractive x-ray lens consisting of two rows of prisms facing each other at an angle. Rays entering the lens at the periphery will encounter a larger number of prisms than will central ones, hence experiencing a greater refraction. The focusing effect of the MPL can be used to gather radiation from a large aperture onto a smaller detector, and accordingly to make better use of the available x-ray flux in medical x-ray imaging. Potential advantages of a better photon economy include shorter acquisition times, a reduced tube loading, or an improved resolution. Since the focusing effect is one-dimensional it matches the design of scanning systems. In this study we present the first images acquired with an MPL instead of the pre-breast slit collimator in a scanning mammography system. According to the measurements, the MPL is able to increase the flux 32% at equal resolution compared to the slit collimator, or to improve the resolution 2.4 mm(-1) at equal flux. If used with a custom-made absorption filter in a clinical set-up, the gain of flux of the MPL is expected to be at least 45%, and the corresponding improvement in resolution to be 3 mm(-1).
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