Anders Persson | Linköping University (original) (raw)
Papers by Anders Persson
Joint Eurographics - IEEE TCVG Symposium on Visualization, 2006
The high complexity of Transfer Function (TF) design is a major obstacle to widespread routine us... more The high complexity of Transfer Function (TF) design is a major obstacle to widespread routine use of Direct Volume Rendering, particularly in the case of medical imaging. Both manual and automatic TF design schemes would benefit greatly from a fast and simple method for detection of tissue value ranges. To this end, we introduce the α-histogram, an enhancement that amplifies ranges corresponding to spatially coherent materials. The properties of the α-histogram have been explored for synthetic data sets and then successfully used to detect vessels in 20 Magnetic Resonance angiographies, proving the potential of this approach as a fast and simple technique for histogram enhancement in general and for TF construction in particular.
Journal of pathology informatics, 2015
Techniques for digital pathology are envisioned to provide great benefits in clinical practice, b... more Techniques for digital pathology are envisioned to provide great benefits in clinical practice, but experiences also show that solutions must be carefully crafted. The Nordic countries are far along the path toward the use of whole-slide imaging in clinical routine. The Nordic Symposium on Digital Pathology (NDP) was created to promote knowledge exchange in this area, between stakeholders in health care, industry, and academia. This article is a summary of the NDP 2014 symposium, including conclusions from a workshop on clinical adoption of digital pathology among the 144 attendees.
ABSTRACT PURPOSE To assess effect of image space iterative recontruction (IRIS) on visualization ... more ABSTRACT PURPOSE To assess effect of image space iterative recontruction (IRIS) on visualization of normal and abnormal lung and mediastinal soft tissues on chest CT acquired at 50, 100 and 200 mAs. METHOD AND MATERIALS 36 scan series were acquired in 12 patients (M:F 7:5, 29-85years) who gave informed consent for participation in an ongoing IRB approved prospective study. Scan series were acquired at our standard of care dose (100 reference mAs, Care Dose 4D) and, with 20% (80 reference mAs) and 60% (40 reference mAs) dose reduction on a 128-slice dual source MDCT scanner (Siemens Somatom Flash) over identical 10 cm scan length. All other scanning parameters were held constant. Projection data were exported from the scanner to offline image reconstruction workstation for creating filtered back projection (FBP) and four iterations of IRIS based reconstructions of low dose CT images. CT numbers and image noise was measure in the standard and low dose FBP (100, 80, 40 mAs FBP) and low dose IRIS (4 iteration for each of the 2 lower doses) images. Two chest radiologists assessed noise, visibility of small lung and mediastinal details, artifacts, and presence of lesions, their conspicuity, and diagnostic acceptability on all 121 image series. RESULTS Mean CT numbers were similar for FBP and IRIS images (p>.1). Both 40 and 80mAs IRIS image series had less quantitative noise compared to 100 mAs FBP images (p=.02-.0001). Subjective image noise for 40 (unacceptable noise) and 80 (suboptimal noise) mAs FBP images improved to acceptable and less than average on 40 and 80 mAs IRIS images (p=.04-.01) in all patients. Visibility of small lung and mediastinal structures as well as lesion conspicuity on low dose IRIS images were similar to that 100 mAs FBP on all but one high order iteration IRIS settings (p>.1). Average CTDI vol for 100, 80 and 40 mAs series were 7.5, 5.8 and 2.6 mGy (p<.0001). CONCLUSION For thoracic CT, objective and subjective image quality and lesion assessment at 40 and 80 mAs IRIS enabled CT image reconstruction is better than or equal to 100 mAs FBP images. With 40 mAs FBP, there is suboptimal visualization of normal and abnormal mediastinal soft tissues, which becomes acceptable with 40 mAs IRIS images. CLINICAL RELEVANCE/APPLICATION IRIS enabled chest CT image reconstructions allow radiation dose reduction of up to 60% or up to a CTDI vol of 2.6 mGy without compromising lesion conspicuity in the mediastinal soft tissues or lungs.
ABSTRACT PURPOSE To minimize radiation dose associated with whole spine CT in children with scoli... more ABSTRACT PURPOSE To minimize radiation dose associated with whole spine CT in children with scoliosis using low kVp, lowest tube current and high pitch and fast table speed. METHOD AND MATERIALS We performed whole spine CT for scoliosis in 19 children (age range 2-18 years, mean age 13 years, 12 girls, 7 boys) on 128-slice dual source MDCT (128-DSCT, Siemens Definition Flash). All scanning parameters were held constant at 3.0:1 pitch, 128x0.6mm detector collimation, 115.2mm table feed per gantry rotation, 0.28second gantry rotation time, 100kVp, and 1 and 3mm reconstructed sections at 50% overlap using B18f reconstruction kernel. Lowest possible quality reference mAs value (image quality factor for xyz- automatic exposure control or xyz-AEC, CARE Dose 4D) was selected on a per patient basis. Average mAs and projected estimated dose savings with xyz-AEC were recorded. CTDIvol and DLP were recorded. CT numbers and image noise were measured in vertebral bodies and air and signal to noise ratio (SNR) was estimated. Artifacts were graded on 4-point scale (1=no artifacts, 4=severe artifacts). Ability to identify vertebral and pedicular contours, and measure pedicular width and degree of vertebral rotation was graded on 3-point scale (1=reliable, 3=unreliable). RESULTS All whole spine CT were deemed as reliable for identifying vertebral and pedicular contours as well as for measuring pedicular width (5.4±0.9mm) and degree of vertebral rotation (19.3±9.3degrees). Mean objective image noise and SNR were 56.5±22.9 and 16.3±9.7, respectively. With a mean quality reference mAs of 13, the scanner employed an average actual effective mAs of 9.5±3.5 (range 6-17mAs) with an estimated radiation dose saving of 42.9±18.6% with xyz-AEC compared with fixed mAs. Mean CTDIvol, DLP and effective doses were 0.4±0.2mGy (0.2-0.7), 20±9mGy.cm (8-41) and 0.3±0.1mSv (0.12-0.61), respectively. CONCLUSION Radiation dose for whole spine CT for evaluation of scoliosis in children can be minimized to less than one-third of a milliSievert while maintaining diagnostic image quality with high pitch-high speed scanning using xyz-AEC and low kVp. CLINICAL RELEVANCE/APPLICATION Minimization of CT radiation dose for scoliosis evaluation can be achieved using high beam pitch, lowest possible tube current with xyz-AEC and low tube current on a 128-slice DSCT.
Miniaturization of sensitive magnetic sensors for nano- and picosatellites has come to the point ... more Miniaturization of sensitive magnetic sensors for nano- and picosatellites has come to the point where the traditional sensors with magnetic coils can soon be replaced. Thin film technology offers the possibility of making extremely small magnetic field sensors that employ the effect of anisotropic, giant and tunnelling magnetoresistance (AMR, GMR and TMR). In this paper, the development status of sensors
ABSTRACT A novel microplasma source, based on a microstrip split-ring resonator design with elect... more ABSTRACT A novel microplasma source, based on a microstrip split-ring resonator design with electrodes integrated in its silicon substrate, was designed, manufactured and evaluated. This device should offer straightforward integration with other MEMS components, and has a plasma discharge gap with a controlled volume and geometry, with potential for microfluidics. Two realized devices were resonant at around 2.9 GHz with quality factors of 26.6 and 18.7. Two different plasma ignition modes were observed, where the plasma at low pressures was not confined to the gap but rather appeared between the ends of the electrodes on the backside.
ABSTRACT Intracavity optogalvanic spectroscopy (ICOGS) has been proposed as a method for unambigu... more ABSTRACT Intracavity optogalvanic spectroscopy (ICOGS) has been proposed as a method for unambiguous detection of rare isotopes. Of particular interest is C-14, where detection of extremely low concentrations in the 1:10(15) range (C-14:C-12), is of interest in, e.g., radiocarbon dating and pharmaceutical sciences. However, recent reports show that ICOGS suffers from substantial problems with reproducibility. To qualify ICOGS as an analytical method, more stable and reliable plasma generation and signal detection are needed. In our proposed setup, critical parameters have been improved. We have utilized a stripline split-ring resonator microwave-induced microplasma source to excite and sustain the plasma. Such a microplasma source offers several advantages over conventional ICOGS plasma sources. For example, the stripline split-ring resonator concept employs separated plasma generation and signal detection, which enables sensitive detection at stable plasma conditions. The concept also permits in situ observation of the discharge conditions, which was found to improve reproducibility. Unique to the stripline split-ring resonator microplasma source in this study, is that the optogalvanic sample cell has been embedded in the device itself. This integration enables improved temperature control and more stable and accurate signal detection. Significant improvements are demonstrated, including reproducibility, signal-to-noise ratio, and precision.
ABSTRACT This paper describes the design, fabrication and characterization of a ceramic, heated c... more ABSTRACT This paper describes the design, fabrication and characterization of a ceramic, heated cold-gas microthruster device made with silicon tools and high temperature co-fired ceramic processing. The device contains two opposing thrusters, each with an integrated calorimetric propellant flow sensor and a heater in the stagnation chamber of the nozzle. The exhaust from a thruster was photographed using schlieren imaging to study its behavior and search for leaks. The heater elements were tested under a cyclic thermal load and to the maximum power before failure. The nozzle heater was shown to improve the efficiency of the thruster by 6.9%, from a specific impulse of 66 to 71 s, as calculated from a decrease of the flow rate through the nozzle of 13%, from 44.9 to 39.2 sccm. The sensitivity of the integrated flow sensor was measured to 0.15 mΩ sccm−1 in the region of 0–15 sccm and to 0.04 mΩ sccm−1 above 20 sccm, with a zero-flow sensitivity of 0.27 mΩ sccm−1. The choice of yttria-stabilized zirconia as a material for the devices makes them robust and capable of surviving temperatures locally exceeding 1000 °C.
ABSTRACT The demand for analysis of smaller samples in isotopic ratio measurements of rare isotop... more ABSTRACT The demand for analysis of smaller samples in isotopic ratio measurements of rare isotopes is continuously rising with the development of new applications, particularly in biomedicine. Interesting in this aspect are methods based on optogalvanic spectroscopy, which have been reported to facilitate both 13C-to-12C and 14C-to-12C ratio measurements with high sensitivity. These methods also facilitate analysis of very small samples, down to the microgram range, which makes them very competitive to other technologies, e.g., accelerator mass spectroscopy. However, there exists a demand for moving beyond the microgram range, especially from regenerative medicine, where samples consist of, e.g., DNA, and, hence, the total sample amount is extremely small. Making optogalvanic spectroscopy of carbon isotopes applicable to such small samples, requires miniaturization of the key component of the system, namely the plasma source, in which the sample is ionized before analysis. In this paper, a novel design of such a microplasma source based on a stripline split-ring resonator is presented and evaluated in a basic optogalvanic spectrometer. The investigations focus on the capability of the plasma source to measure the optogalvanic signal in general, and the effect of different system and device specific parameters on the amplitude and stability of the optogalvanic signal in particular. Different sources of noise and instabilities are identified, and methods of mitigating these issues are discussed. Finally, the ability of the cell to handle analysis of samples down to the nanogram range is investigated, pinpointing the great prospects of stripline split-ring resonators in optogalvanic spectroscopy.
A Co 60 Fe 20 B 20 -based tunneling magnetoresistance multilayer stack with an MgO barrier has be... more A Co 60 Fe 20 B 20 -based tunneling magnetoresistance multilayer stack with an MgO barrier has been exposed to 30 keV Ga ions at doses corresponding to ion etching and metal deposition in a focused ion beam (FIB) instrument, to study the applicability of these processes to magnetic tunnel junction (MTJ) fabrication. MTJs were fabricated and irradiated to investigate how the exposures affected their coercivity and magnetoresistance. Elemental depth profiles, acquired using electron spectroscopy for chemical analysis, showed that Ga gathered in and around the two Co 60 Fe 20 B 20 layers. Correlated with the results of the magnetic measurements, this Ga presence was found to cause a reduction of magnetoresistance and an increase in coercivity. Quantitatively, a dose of 10 14 Ga + cm 2 reduced the magnetoresistance by 60%, whereas a dose of 10 15 Ga + cm 2 reduced the magnetoresistance by 67% and also increased the coercivity by 2 mT and changed the dipole coupling between the sensing and the pinning layers by 1.6 mT. The latter was attributed to an imbalance in the synthetic antiferromagnetic structure, where the stack's Ru spacer served as an implantation barrier. The magnetoresistance was lost at a dose of 10 16 Ga + cm 2 . Annealing reduced the content of Ga around the magnetic layers but also caused diffusion of Cu from one of the layers in the stack. Apart from the observation and explanation of implantation damages in the multilayer, this work concludes on the applicability of FIB processes for prototyping of MTJs.
To compare three methods for standardizing volume rendering technique (VRT) protocols by studying... more To compare three methods for standardizing volume rendering technique (VRT) protocols by studying aortic diameter measurements in magnetic resonance angiography (MRA) datasets. Datasets from 20 patients previously examined with gadolinium-enhanced MRA and with digital subtraction angiography (DSA) for abdominal aortic aneurysm were retrospectively evaluated by three independent readers. The MRA datasets were viewed using VRT with three different standardized transfer functions: the percentile method (Pc-VRT), the maximum-likelihood method (ML-VRT), and the partial range histogram method (PRH-VRT). The aortic diameters obtained with these three methods were compared with freely chosen VRT parameters (F-VRT) and with maximum intensity projection (MIP) concerning inter-reader variability and agreement with the reference method DSA. F-VRT parameters and PRH-VRT gave significantly higher diameter values than DSA, whereas Pc-VRT gave significantly lower values than DSA. The highest interobserver variability was found for F-VRT parameters and MIP, and the lowest for Pc-VRT and PRH-VRT. All standardized VRT methods were significantly superior to both MIP and F-VRT in this respect. The agreement with DSA was best for PRH-VRT, which was the only method with a mean error below 1 mm and which also had the narrowest limits of agreement (95% of cases between 2.1 mm below and 3.1 mm above DSA). All the standardized VRT methods compare favorably with MIP and VRT with freely selected parameters as regards interobserver variability. The partial range histogram method, although systematically overestimating vessel diameters, gives results closest to those of DSA.
BMC Medical Imaging, 2006
Background: Computed Tomography Cholangiography (CTC) is a fast and widely available alternative ... more Background: Computed Tomography Cholangiography (CTC) is a fast and widely available alternative technique to visualise hepatobiliary disease in patients with an inconclusive ultrasound when MRI cannot be performed. The method has previously been relatively unknown and sparsely used, due to concerns about adverse reactions and about image quality in patients with impaired hepatic function and thus reduced contrast excretion. In this retrospective study, the feasibility and the frequency of adverse reactions of CTC when using a drip infusion scheme based on bilirubin levels were evaluated.
Joint Eurographics - IEEE TCVG Symposium on Visualization, 2006
The high complexity of Transfer Function (TF) design is a major obstacle to widespread routine us... more The high complexity of Transfer Function (TF) design is a major obstacle to widespread routine use of Direct Volume Rendering, particularly in the case of medical imaging. Both manual and automatic TF design schemes would benefit greatly from a fast and simple method for detection of tissue value ranges. To this end, we introduce the α-histogram, an enhancement that amplifies ranges corresponding to spatially coherent materials. The properties of the α-histogram have been explored for synthetic data sets and then successfully used to detect vessels in 20 Magnetic Resonance angiographies, proving the potential of this approach as a fast and simple technique for histogram enhancement in general and for TF construction in particular.
Journal of pathology informatics, 2015
Techniques for digital pathology are envisioned to provide great benefits in clinical practice, b... more Techniques for digital pathology are envisioned to provide great benefits in clinical practice, but experiences also show that solutions must be carefully crafted. The Nordic countries are far along the path toward the use of whole-slide imaging in clinical routine. The Nordic Symposium on Digital Pathology (NDP) was created to promote knowledge exchange in this area, between stakeholders in health care, industry, and academia. This article is a summary of the NDP 2014 symposium, including conclusions from a workshop on clinical adoption of digital pathology among the 144 attendees.
ABSTRACT PURPOSE To assess effect of image space iterative recontruction (IRIS) on visualization ... more ABSTRACT PURPOSE To assess effect of image space iterative recontruction (IRIS) on visualization of normal and abnormal lung and mediastinal soft tissues on chest CT acquired at 50, 100 and 200 mAs. METHOD AND MATERIALS 36 scan series were acquired in 12 patients (M:F 7:5, 29-85years) who gave informed consent for participation in an ongoing IRB approved prospective study. Scan series were acquired at our standard of care dose (100 reference mAs, Care Dose 4D) and, with 20% (80 reference mAs) and 60% (40 reference mAs) dose reduction on a 128-slice dual source MDCT scanner (Siemens Somatom Flash) over identical 10 cm scan length. All other scanning parameters were held constant. Projection data were exported from the scanner to offline image reconstruction workstation for creating filtered back projection (FBP) and four iterations of IRIS based reconstructions of low dose CT images. CT numbers and image noise was measure in the standard and low dose FBP (100, 80, 40 mAs FBP) and low dose IRIS (4 iteration for each of the 2 lower doses) images. Two chest radiologists assessed noise, visibility of small lung and mediastinal details, artifacts, and presence of lesions, their conspicuity, and diagnostic acceptability on all 121 image series. RESULTS Mean CT numbers were similar for FBP and IRIS images (p>.1). Both 40 and 80mAs IRIS image series had less quantitative noise compared to 100 mAs FBP images (p=.02-.0001). Subjective image noise for 40 (unacceptable noise) and 80 (suboptimal noise) mAs FBP images improved to acceptable and less than average on 40 and 80 mAs IRIS images (p=.04-.01) in all patients. Visibility of small lung and mediastinal structures as well as lesion conspicuity on low dose IRIS images were similar to that 100 mAs FBP on all but one high order iteration IRIS settings (p>.1). Average CTDI vol for 100, 80 and 40 mAs series were 7.5, 5.8 and 2.6 mGy (p<.0001). CONCLUSION For thoracic CT, objective and subjective image quality and lesion assessment at 40 and 80 mAs IRIS enabled CT image reconstruction is better than or equal to 100 mAs FBP images. With 40 mAs FBP, there is suboptimal visualization of normal and abnormal mediastinal soft tissues, which becomes acceptable with 40 mAs IRIS images. CLINICAL RELEVANCE/APPLICATION IRIS enabled chest CT image reconstructions allow radiation dose reduction of up to 60% or up to a CTDI vol of 2.6 mGy without compromising lesion conspicuity in the mediastinal soft tissues or lungs.
ABSTRACT PURPOSE To minimize radiation dose associated with whole spine CT in children with scoli... more ABSTRACT PURPOSE To minimize radiation dose associated with whole spine CT in children with scoliosis using low kVp, lowest tube current and high pitch and fast table speed. METHOD AND MATERIALS We performed whole spine CT for scoliosis in 19 children (age range 2-18 years, mean age 13 years, 12 girls, 7 boys) on 128-slice dual source MDCT (128-DSCT, Siemens Definition Flash). All scanning parameters were held constant at 3.0:1 pitch, 128x0.6mm detector collimation, 115.2mm table feed per gantry rotation, 0.28second gantry rotation time, 100kVp, and 1 and 3mm reconstructed sections at 50% overlap using B18f reconstruction kernel. Lowest possible quality reference mAs value (image quality factor for xyz- automatic exposure control or xyz-AEC, CARE Dose 4D) was selected on a per patient basis. Average mAs and projected estimated dose savings with xyz-AEC were recorded. CTDIvol and DLP were recorded. CT numbers and image noise were measured in vertebral bodies and air and signal to noise ratio (SNR) was estimated. Artifacts were graded on 4-point scale (1=no artifacts, 4=severe artifacts). Ability to identify vertebral and pedicular contours, and measure pedicular width and degree of vertebral rotation was graded on 3-point scale (1=reliable, 3=unreliable). RESULTS All whole spine CT were deemed as reliable for identifying vertebral and pedicular contours as well as for measuring pedicular width (5.4±0.9mm) and degree of vertebral rotation (19.3±9.3degrees). Mean objective image noise and SNR were 56.5±22.9 and 16.3±9.7, respectively. With a mean quality reference mAs of 13, the scanner employed an average actual effective mAs of 9.5±3.5 (range 6-17mAs) with an estimated radiation dose saving of 42.9±18.6% with xyz-AEC compared with fixed mAs. Mean CTDIvol, DLP and effective doses were 0.4±0.2mGy (0.2-0.7), 20±9mGy.cm (8-41) and 0.3±0.1mSv (0.12-0.61), respectively. CONCLUSION Radiation dose for whole spine CT for evaluation of scoliosis in children can be minimized to less than one-third of a milliSievert while maintaining diagnostic image quality with high pitch-high speed scanning using xyz-AEC and low kVp. CLINICAL RELEVANCE/APPLICATION Minimization of CT radiation dose for scoliosis evaluation can be achieved using high beam pitch, lowest possible tube current with xyz-AEC and low tube current on a 128-slice DSCT.
Miniaturization of sensitive magnetic sensors for nano- and picosatellites has come to the point ... more Miniaturization of sensitive magnetic sensors for nano- and picosatellites has come to the point where the traditional sensors with magnetic coils can soon be replaced. Thin film technology offers the possibility of making extremely small magnetic field sensors that employ the effect of anisotropic, giant and tunnelling magnetoresistance (AMR, GMR and TMR). In this paper, the development status of sensors
ABSTRACT A novel microplasma source, based on a microstrip split-ring resonator design with elect... more ABSTRACT A novel microplasma source, based on a microstrip split-ring resonator design with electrodes integrated in its silicon substrate, was designed, manufactured and evaluated. This device should offer straightforward integration with other MEMS components, and has a plasma discharge gap with a controlled volume and geometry, with potential for microfluidics. Two realized devices were resonant at around 2.9 GHz with quality factors of 26.6 and 18.7. Two different plasma ignition modes were observed, where the plasma at low pressures was not confined to the gap but rather appeared between the ends of the electrodes on the backside.
ABSTRACT Intracavity optogalvanic spectroscopy (ICOGS) has been proposed as a method for unambigu... more ABSTRACT Intracavity optogalvanic spectroscopy (ICOGS) has been proposed as a method for unambiguous detection of rare isotopes. Of particular interest is C-14, where detection of extremely low concentrations in the 1:10(15) range (C-14:C-12), is of interest in, e.g., radiocarbon dating and pharmaceutical sciences. However, recent reports show that ICOGS suffers from substantial problems with reproducibility. To qualify ICOGS as an analytical method, more stable and reliable plasma generation and signal detection are needed. In our proposed setup, critical parameters have been improved. We have utilized a stripline split-ring resonator microwave-induced microplasma source to excite and sustain the plasma. Such a microplasma source offers several advantages over conventional ICOGS plasma sources. For example, the stripline split-ring resonator concept employs separated plasma generation and signal detection, which enables sensitive detection at stable plasma conditions. The concept also permits in situ observation of the discharge conditions, which was found to improve reproducibility. Unique to the stripline split-ring resonator microplasma source in this study, is that the optogalvanic sample cell has been embedded in the device itself. This integration enables improved temperature control and more stable and accurate signal detection. Significant improvements are demonstrated, including reproducibility, signal-to-noise ratio, and precision.
ABSTRACT This paper describes the design, fabrication and characterization of a ceramic, heated c... more ABSTRACT This paper describes the design, fabrication and characterization of a ceramic, heated cold-gas microthruster device made with silicon tools and high temperature co-fired ceramic processing. The device contains two opposing thrusters, each with an integrated calorimetric propellant flow sensor and a heater in the stagnation chamber of the nozzle. The exhaust from a thruster was photographed using schlieren imaging to study its behavior and search for leaks. The heater elements were tested under a cyclic thermal load and to the maximum power before failure. The nozzle heater was shown to improve the efficiency of the thruster by 6.9%, from a specific impulse of 66 to 71 s, as calculated from a decrease of the flow rate through the nozzle of 13%, from 44.9 to 39.2 sccm. The sensitivity of the integrated flow sensor was measured to 0.15 mΩ sccm−1 in the region of 0–15 sccm and to 0.04 mΩ sccm−1 above 20 sccm, with a zero-flow sensitivity of 0.27 mΩ sccm−1. The choice of yttria-stabilized zirconia as a material for the devices makes them robust and capable of surviving temperatures locally exceeding 1000 °C.
ABSTRACT The demand for analysis of smaller samples in isotopic ratio measurements of rare isotop... more ABSTRACT The demand for analysis of smaller samples in isotopic ratio measurements of rare isotopes is continuously rising with the development of new applications, particularly in biomedicine. Interesting in this aspect are methods based on optogalvanic spectroscopy, which have been reported to facilitate both 13C-to-12C and 14C-to-12C ratio measurements with high sensitivity. These methods also facilitate analysis of very small samples, down to the microgram range, which makes them very competitive to other technologies, e.g., accelerator mass spectroscopy. However, there exists a demand for moving beyond the microgram range, especially from regenerative medicine, where samples consist of, e.g., DNA, and, hence, the total sample amount is extremely small. Making optogalvanic spectroscopy of carbon isotopes applicable to such small samples, requires miniaturization of the key component of the system, namely the plasma source, in which the sample is ionized before analysis. In this paper, a novel design of such a microplasma source based on a stripline split-ring resonator is presented and evaluated in a basic optogalvanic spectrometer. The investigations focus on the capability of the plasma source to measure the optogalvanic signal in general, and the effect of different system and device specific parameters on the amplitude and stability of the optogalvanic signal in particular. Different sources of noise and instabilities are identified, and methods of mitigating these issues are discussed. Finally, the ability of the cell to handle analysis of samples down to the nanogram range is investigated, pinpointing the great prospects of stripline split-ring resonators in optogalvanic spectroscopy.
A Co 60 Fe 20 B 20 -based tunneling magnetoresistance multilayer stack with an MgO barrier has be... more A Co 60 Fe 20 B 20 -based tunneling magnetoresistance multilayer stack with an MgO barrier has been exposed to 30 keV Ga ions at doses corresponding to ion etching and metal deposition in a focused ion beam (FIB) instrument, to study the applicability of these processes to magnetic tunnel junction (MTJ) fabrication. MTJs were fabricated and irradiated to investigate how the exposures affected their coercivity and magnetoresistance. Elemental depth profiles, acquired using electron spectroscopy for chemical analysis, showed that Ga gathered in and around the two Co 60 Fe 20 B 20 layers. Correlated with the results of the magnetic measurements, this Ga presence was found to cause a reduction of magnetoresistance and an increase in coercivity. Quantitatively, a dose of 10 14 Ga + cm 2 reduced the magnetoresistance by 60%, whereas a dose of 10 15 Ga + cm 2 reduced the magnetoresistance by 67% and also increased the coercivity by 2 mT and changed the dipole coupling between the sensing and the pinning layers by 1.6 mT. The latter was attributed to an imbalance in the synthetic antiferromagnetic structure, where the stack's Ru spacer served as an implantation barrier. The magnetoresistance was lost at a dose of 10 16 Ga + cm 2 . Annealing reduced the content of Ga around the magnetic layers but also caused diffusion of Cu from one of the layers in the stack. Apart from the observation and explanation of implantation damages in the multilayer, this work concludes on the applicability of FIB processes for prototyping of MTJs.
To compare three methods for standardizing volume rendering technique (VRT) protocols by studying... more To compare three methods for standardizing volume rendering technique (VRT) protocols by studying aortic diameter measurements in magnetic resonance angiography (MRA) datasets. Datasets from 20 patients previously examined with gadolinium-enhanced MRA and with digital subtraction angiography (DSA) for abdominal aortic aneurysm were retrospectively evaluated by three independent readers. The MRA datasets were viewed using VRT with three different standardized transfer functions: the percentile method (Pc-VRT), the maximum-likelihood method (ML-VRT), and the partial range histogram method (PRH-VRT). The aortic diameters obtained with these three methods were compared with freely chosen VRT parameters (F-VRT) and with maximum intensity projection (MIP) concerning inter-reader variability and agreement with the reference method DSA. F-VRT parameters and PRH-VRT gave significantly higher diameter values than DSA, whereas Pc-VRT gave significantly lower values than DSA. The highest interobserver variability was found for F-VRT parameters and MIP, and the lowest for Pc-VRT and PRH-VRT. All standardized VRT methods were significantly superior to both MIP and F-VRT in this respect. The agreement with DSA was best for PRH-VRT, which was the only method with a mean error below 1 mm and which also had the narrowest limits of agreement (95% of cases between 2.1 mm below and 3.1 mm above DSA). All the standardized VRT methods compare favorably with MIP and VRT with freely selected parameters as regards interobserver variability. The partial range histogram method, although systematically overestimating vessel diameters, gives results closest to those of DSA.
BMC Medical Imaging, 2006
Background: Computed Tomography Cholangiography (CTC) is a fast and widely available alternative ... more Background: Computed Tomography Cholangiography (CTC) is a fast and widely available alternative technique to visualise hepatobiliary disease in patients with an inconclusive ultrasound when MRI cannot be performed. The method has previously been relatively unknown and sparsely used, due to concerns about adverse reactions and about image quality in patients with impaired hepatic function and thus reduced contrast excretion. In this retrospective study, the feasibility and the frequency of adverse reactions of CTC when using a drip infusion scheme based on bilirubin levels were evaluated.