| 1. |
- Bakowski Holtryd, Mietek, et al.
(författare)
-
X-ray sensor, method for constructing an x-ray sensor and an x-ray imaging system comprising such an x-ray sensor
- 2020
-
Patent (populärvet., debatt m.m.)abstract
- An X-ray sensor (1) having an active detector region including a plurality of detector diodes (2) arranged on a surface region (3) of the X-ray sensor (1), a junction termination (4) surrounding the surface area (3) including the plurality of detector diodes (2), the junction termination (4) including a guard (5) arranged closest to the end of the surface region (3), a field stop (6) arranged outside the guard (2) and a number N of field limiting rings, FLRs (7) arranged between the guard (5) and the field stop (6), wherein each of the FLRs (7) are placed at positions selected so that distances between different FLRs (7) and between the guard and the first FLR lie within an effective area, the effective area being bounded by the lines α=(10+1.3×(n−1)) μm and β=(5+1.05×(n−1)) μm.
|
|
| 2. |
- Bakowski Holtryd, Mietek, et al.
(författare)
-
X-ray sensor, x-ray detector system and x-ray imaging system
- 2018
-
Patent (populärvet., debatt m.m.)abstract
- Disclosed is an x-ray sensor having an active detector region including a plurality of detector diodes at a first side of the sensor, and with placement of the junction termination at a second opposite side of the sensor. Normally, this implies that the junction termination is moved from the top side where the active detector area is located to the bottom side of the sensor, allowing for full utilization of the active detector area at the top side with detector diodes to the very edge of the sensor.
|
|
| 3. |
- Bakowski Holtryd, Mietek, et al.
(författare)
-
X-ray sensor, x-ray detector system and x-ray imaging system
- 2019
-
Patent (populärvet., debatt m.m.)abstract
- There is provided an x-ray sensor (21) comprising an active detector region including a plurality of detector diodes (22) at a first side of the sensor, and a common junction termination (23) at a second opposite side of the sensor. Normally, this implies that the junction termination (23) is moved from the top side where the active detector area is located to the bottom side of the sensor, allowing for full utilization of the active detector area at the top side with detector diodes to the very edge of the sensor.
|
|
| 4. |
- Berggren, Karl, et al.
(författare)
-
Physical characterization of photon-counting tomosynthesis
- 2015
-
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.
|
|
| 5. |
- Berggren, Karl, 1989-
(författare)
-
Spectral image quality and applications in breast tomosynthesis
- 2018
-
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.
|
|
| 6. |
- Bertilson, M., et al.
(författare)
-
Analyzer-free hard x-ray interferometry
- 2024
-
Ingår i: Physics in Medicine and Biology. - : Institute of Physics. - 0031-9155 .- 1361-6560. ; 69:4
-
Tidskriftsartikel (refereegranskat)abstract
- Objective. To enable practical interferometry-based phase contrast CT using standard incoherent x-ray sources, we propose an imaging system where the analyzer grating is replaced by a high-resolution detector. Since there is no need to perform multiple exposures (with the analyzer grating at different positions) at each scan angle, this scheme is compatible with continuous-rotation CT apparatus, and has the potential to reduce patient radiation dose and patient motion artifacts. Approach. Grating-based x-ray interferometry is a well-studied technique for imaging soft tissues and highly scattering objects embedded in such tissues. In addition to the traditional x-ray absorption-based image, this technique allows reconstruction of the object phase and small-angle scattering information. When using conventional incoherent, polychromatic, hard x-ray tubes as sources, three gratings are usually employed. To sufficiently resolve the pattern generated in these interferometers with contemporary x-ray detectors, an analyzer grating is used, and consequently multiple images need to be acquired for each view angle. This adds complexity to the imaging system, slows image acquisition and thus increases sensitivity to patient motion, and is not dose efficient. By simulating image formation based on wave propagation, and proposing a novel phase retrieval algorithm based on a virtual grating, we assess the potential of a analyzer-grating-free system to overcome these limitations. Main results. We demonstrate that the removal of the analyzer-grating can produce equal image contrast-to-noise ratio at reduced dose (by a factor of 5), without prolonging scan duration. Significance. By demonstrating that an analyzer-free CT system, in conjuction with an efficient phase retrieval algorithm, can overcome the prohibitive dose and workflow penalties associated grating-stepping, an alternative path towards realizing clinical inteferometric CT appears possible.
|
|
| 7. |
- Bornefalk, Hans
(författare)
-
Computer-aided detection and novel mammography imaging techniques
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents techniques constructed to aid the radiologists in detecting breast cancer, the second largest cause of cancer deaths for western women. In the first part of the thesis, a computer-aided detection (CAD) system constructed for the detection of stellate lesions is presented. Different segmentation methods and an attempt to incorporate contra-lateral information are evaluated. In the second part, a new method for evaluating such CAD systems is presented based on constructing credible regions for the number of false positive marks per image at a certain desired target sensitivity. This method shows that the resulting regions are rather wide and this explains some of the difficulties encountered by other researchers when trying to compare CAD algorithms on different data sets. In this part an attempt to model the clinical use of CAD as a second look is also made and it shows that applying CAD in sequence to the radiologist in a routine manner, without duly altering the decision criterion of the radiologist, might very well result in suboptimal operating points. Finally, in the third part two dual-energy imaging methods optimized for contrast-enhanced imaging of breast tumors are presented. The first is based on applying an electronic threshold to a photon-counting digital detector to discriminate between high- and low-energy photons. This allows simultaneous acquisition of the high- and low-energy images. The second method is based on the geometry of a scanned multi-slit system and also allows single-shot contrast-enhanced dual-energy mammography by filtering the x-ray beam that reaches different detector lines differently.
|
|
| 8. |
- Bornefalk, Hans, et al.
(författare)
-
Image quality in photon counting-mode detector systems
- 2013
-
Patent (populärvet., debatt m.m.)abstract
- The current invention applies to photon counting silicon x-ray detectors with energy discriminating capabilities and applications in x-ray imaging systems. The overall image quality produced by such a system is improved by the presented novel methods for optimally using the energy information in Compton events and making selective use of counts induced from charges collected in neighboring pixels. The pile-up problem during high-flux imaging regimes is reduced by a novel method for signal reset, which improves the count efficiency by reducing the risk of losing event due to signal pile-up in the read out electronics chain.
|
|
| 9. |
- Bornefalk, Hans, et al.
(författare)
-
Necessary forward model specification accuracy for basis material decomposition in spectral CT
- 2014
-
Ingår i: Medical Imaging 2014. - : SPIE - International Society for Optical Engineering. - 9780819498267 ; , s. 90332I-
-
Konferensbidrag (refereegranskat)abstract
- Material basis decomposition in the sinogram domain requires accurate knowledge of the forward model in spectral CT. Misspecifications over a certain limit will result in biased estimates and make quantum limited quantitative CT difficult. We present a method whereby users can determine the degree of allowed misspecification error in a spectral CT forward model, and still have quantification errors that are quantum limited.
|
|
| 10. |
- Bornefalk, Hans, et al.
(författare)
-
Photon-counting spectral computed tomography using silicon strip detectors : a feasibility study
- 2010
-
Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 55:7, s. 1999-2022
-
Tidskriftsartikel (refereegranskat)abstract
- We show how the spectral imaging framework should be modified to account for a high fraction of Compton interactions in low Z detector materials such as silicon. Using this framework, where deposited energies differ from actual photon energies, we compare the performance of a silicon strip detector, including the influence of scatter inside the detector and charge sharing but disregarding signal pileup, with an ideal energy integrating detector. We show that although the detection efficiency for silicon rapidly drops for the acceleration voltages encountered in clinical computed tomography practice, silicon detectors could perform on a par with ideal energy integrating detectors for routine imaging tasks. The use of spectrally sensitive detectors opens up the possibility for decomposition techniques such as k-edge imaging, and we show that the proposed modification of the spectral imaging framework is beneficial for such imaging tasks.
|
|
