| 1. |
- Fredenberg, Erik, 1979-
(author)
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Spectral Mammography with X-Ray Optics and a Photon-Counting Detector
- 2009
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Doctoral thesis (other academic/artistic)abstract
- Early detection is vital to successfully treating breast cancer, and mammography screening is the most efficient and wide-spread method to reach this goal. Imaging low-contrast targets, while minimizing the radiation exposure to a large population is, however, a major challenge. Optimizing the image quality per unit radiation dose is therefore essential. In this thesis, two optimization schemes with respect to x-ray photon energy have been investigated: filtering the incident spectrum with refractive x-ray optics (spectral shaping), and utilizing the transmitted spectrum with energy-resolved photon-counting detectors (spectral imaging). Two types of x-ray lenses were experimentally characterized, and modeled using ray tracing, field propagation, and geometrical optics. Spectral shaping reduced dose approximately 20% compared to an absorption-filtered reference system with the same signal-to-noise ratio, scan time, and spatial resolution. In addition, a focusing pre-object collimator based on the same type of optics reduced divergence of the radiation and improved photon economy by about 50%. A photon-counting silicon detector was investigated in terms of energy resolution and its feasibility for spectral imaging. Contrast-enhanced tumor imaging with a system based on the detector was characterized and optimized with a model that took anatomical noise into account. Improvement in an ideal-observer detectability index by a factor of 2 to 8 over that obtained by conventional absorption imaging was found for different levels of anatomical noise and breast density. Increased conspicuity was confirmed by experiment. Further, the model was extended to include imaging of unenhanced lesions. Detectability of microcalcifications increased no more than a few percent, whereas the ability to detect large tumors might improve on the order of 50% despite the low attenuation difference between glandular and cancerous tissue. It is clear that inclusion of anatomical noise and imaging task in spectral optimization may yield completely different results than an analysis based solely on quantum noise.
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| 2. |
- Liu, Yuanhua, 1971, et al.
(author)
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Considering the importance of user profiles in interface design
- 2009
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In: User Interfaces. ; , s. 23-
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Book chapter (other academic/artistic)abstract
- User profile is a popular term widely employed during product design processes by industrial companies. Such a profile is normally intended to represent real users of a product. The ultimate purpose of a user profile is actually to help designers to recognize or learn about the real user by presenting them with a description of a real user’s attributes, for instance; the user’s gender, age, educational level, attitude, technical needs and skill level. The aim of this chapter is to provide information on the current knowledge and research about user profile issues, as well as to emphasize the importance of considering these issues in interface design. In this chapter, we mainly focus on how users’ difference in expertise affects their performance or activity in various interaction contexts. Considering the complex interaction situations in practice, novice and expert users’ interactions with medical user interfaces of different technical complexity will be analyzed as examples: one focuses on novice and expert users’ difference when interacting with simple medical interfaces, and the other focuses on differences when interacting with complex medical interfaces. Four issues will be analyzed and discussed: (1) how novice and expert users differ in terms of performance during the interaction; (2) how novice and expert users differ in the perspective of cognitive mental models during the interaction; (3) how novice and expert users should be defined in practice; and (4) what are the main differences between novice and expert users’ implications for interface design. Besides describing the effect of users’ expertise difference during the interface design process, we will also pinpoint some potential problems for the research on interface design, as well as some future challenges that academic researchers and industrial engineers should face in practice.
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| 3. |
- Fredenberg, Erik, PhD, 1979-, et al.
(author)
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A low-absorption x-ray energy filter for small-scale applications
- 2009
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In: Optics Express. - : The Optical Society. - 1094-4087. ; 17:14, s. 11388-11398
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Journal article (peer-reviewed)abstract
- We present an experimental and theoretical evaluation of an x-ray energy filter based on the chromatic properties of a prism-array lens (PAL). It is intended for small-scale applications such as medical imaging. The PAL approximates a Fresnel lens and allows for high efficiency compared to filters based on ordinary refractive lenses, however at the cost of a lower energy resolution. Geometrical optics was found to provide a good approximation for the performance of a flawless lens, but a field-propagation model was used for quantitative predictions. The model predicted a 0.29 ΔE/E energy resolution and an intensity gain of 6.5 for a silicon PAL at 23.5 keV. Measurements with an x-ray tube showed good agreement with the model in energy resolution and peak energy, but a blurred focal line contributed to a 29% gain reduction. We believe the blurring to be caused mainly by lens imperfections, in particular at the periphery of the lens.
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| 4. |
- Fredenberg, Erik, 1979-, et al.
(author)
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An efficient pre-object collimator based on an x-ray lens
- 2009
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In: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 36:2, s. 626-633
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Journal article (peer-reviewed)abstract
- A multiprism lens (MPL) is a refractive x-ray lens with one-dimensional focusing properties. If used as a pre-object collimator in a scanning system for medical x-ray imaging, it reduces the divergence of the radiation and improves on photon economy compared to a slit collimator. Potential advantages include shorter acquisition times, a reduced tube loading, or improved resolution. We present the first images acquired with a MPL in a prototype for a scanning mammography system. The lens showed a gain of flux of 1.32 compared to a slit collimator at equal resolution, or a gain in resolution of 1.31–1.44 at equal flux. We expect the gain of flux in a clinical setup with an optimized MPL and a custom-made absorption filter to reach 1.67, or 1.45–1.54 gain in resolution.
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| 5. |
- Buendia, Ruben, 1982, et al.
(author)
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A Novel Approach for Removing the Hook Effect Artefact from Electrical Bioimpedance Spectroscopy Measurements
- 2009
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In: Journal of Physics: Conference Series. - : Institute of Physics Publishing Ltd.. - 1742-6596.
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Conference paper (peer-reviewed)abstract
- Very often in Electrical Bioimpedance (EBI) spectroscopy measurements the presence of stray capacitances creates a measurement artefact commonly known as Hook Effect. Such an artefact creates a hook-alike deviation of the EBI data noticeable when representing the measurement on the impedance plane. Such Hook Effect is noticeable at high frequencies but it also causes a data deviation at lower measurement frequencies. In order to perform any accurate analysis of the EBI spectroscopy data, the influence of the Hook Effect must be removed. An established method to compensate the hook effect is the well known Td compensation, which consist on multiplying the obtained spectrum, Zmeas() by a complex exponential in the form of exp[jTd]. Such a method cannot correct entirely the Hook Effect since the hook-alike deviation occurs a broad frequency range in both magnitude and phase of the measured impedance, and by using a real value for Td. First, a real value only modifies the phase of the measured impedance and second, it can only correct the Hook Effect at a single frequency. In addition, the process to select a value for Td by an iterative process with the aim to obtain the best Cole fitting lacks solid scientific grounds. In this work the Td compensation method is revisited and a modified approach for correcting the Hook Effect that includes a novel method for selecting the correcting values is proposed. The initial validation results confirm that the proposed method entirely corrects the Hook Effect at all frequencies.
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| 6. |
- Candefjord, Stefan, et al.
(author)
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Evaluating the use of a Raman fiberoptic probe in conjunction with a resonance sensor for measuring porcine tissue in vitro
- 2009
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In: IFMBE Proceedings of the World Congress on Medical Physics and Biomedical Engineering. - Heidelberg : Springer. ; , s. 414-417, s. 414-417
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Conference paper (peer-reviewed)abstract
- Prostate cancer is the most common form of cancer and is the third leading cause of cancer-related death in European men. There is a need for new methods that can accurately localize and diagnose prostate cancer. In this study a new approach is presented: a combination of resonance sensor technology and Raman spectroscopy. Both methods have shown promising results for prostate cancer detection in vitro. The aim of this study was to evaluate the combined information from measurements with a Raman fiberoptic probe and a resonance sensor system. Pork belly tissue was used as a model system. A three-dimensional translation table was equipped with an in-house developed software, allowing measurements to be performed at the same point using two separate instruments. The Raman data was analyzed using principal component analysis and hierarchical clustering analysis. The spectra were divided into 5 distinct groups. The mean stiffness of each group was calculated from the resonance sensor measurements. One of the groups differed significantly (p < 0.05) from the others. A regression analysis, with the stiffness parameter as response variable and the principal component scores of the Raman data as the predictor variables, explained 67% of the total variability. The use of a smaller resonance sensor tip would probably increase the degree of correlation. In conclusion, Raman spectroscopy provides additional discriminatory power to the resonance sensor.
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| 7. |
- Jalkanen, Ville, 1978-, et al.
(author)
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Instrument towards faster diagnosis and treatment of prostate cancer : Resonance sensor stiffness measurements on human prostate tissue in vitro
- 2009
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In: IFMBE Proceedings of the World Congress on Medical Physics and Biomedical Engineering. - Heidelberg : Springer. ; , s. 145-148, s. 145-148
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Conference paper (peer-reviewed)abstract
- Prostate cancer is the most common cancer among men and the methods used to detect and diagnose prostate cancer are not sufficiently accurate. Radical prostatectomy is a surgical treatment of prostate cancer where the whole prostate is removed from the patient. Prostate tissue stiffness can be measured with a stiffness sensitive resonance sensor. The aim of this study was to measure the stiffness on the anterior and posterior side of fresh human prostate tissue in vitro and compare these two groups with each other and relate the findings with the prostate tissue histology. In a prostate tissue slice with mostly normal healthy tissue, the anterior side was significantly harder (p-value < 0.05) as expected. In a prostate tissue slice with areas of cancer tumors, no difference was found between the anterior and posterior sides. However, large stiffness variations were found within groups with measurements points on cancer tissue (coefficient of variation, CV = 42 and 85%), as opposed to groups without cancer tissue (CV = 27 and 28%). The large stiffness variations could be used as a sign for the presence of cancer. The results are promising for the development of an instrument and method for faster diagnosis on radical prostatectomy samples.
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| 8. |
- Lindberg, Peter L, et al.
(author)
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An image analysis method for prostate tissue classification : preliminary validation with resonance sensor data
- 2009
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In: Journal of Medical Engineering & Technology. - : Informa healthcare. - 0309-1902 .- 1464-522X. ; 33:1, s. 18-24
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Journal article (peer-reviewed)abstract
- Resonance sensor systems have been shown to be able to distinguish between cancerous and normal prostate tissue, in vitro. The aim of this study was to improve the accuracy of the tissue determination, to simplify the tissue classification process with computerized morphometrical analysis, to decrease the risk of human errors, and to reduce the processing time. In this article we present our newly developed computerized classification method based on image analysis. In relation to earlier resonance sensor studies we increased the number of normal prostate tissue classes into stroma, epithelial tissue, lumen and stones. The linearity between the impression depth and tissue classes was calculated using multiple linear regression (R(2) = 0.68, n = 109, p < 0.001) and partial least squares (R(2) = 0.55, n = 109, p < 0.001). Thus it can be concluded that there existed a linear relationship between the impression depth and the tissue classes. The new image analysis method was easy to handle and decreased the classification time by 80%.
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| 9. |
- Liu, Yuanhua, 1971
(author)
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Usability Evaluation of Medical Technology: Investigating the Effect of User Background and Users' Expertise
- 2009
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Doctoral thesis (other academic/artistic)abstract
- Medical devices play a major role in diagnosis and therapeutics in the healthcare systems. The basic features of medical devices concern safety and efficient clinical performance. Nowadays, usability evaluation is an important part of the design process of medical devices. The aims of this thesis work were to investigate the effect of user profiles on usability evaluation results and to provide practical advice on choice of users as test subjects when conducting usability evaluations of medical devices. Five studies, with analytical and empirical evaluation approaches with different foci, were included in the work. In the studies, consideration was given to user background and users’ expertise as well as to user interfaces of different levels of complexity. The user background aspect was taken as the focus for the analytical evaluation approach, while users’ expertise was taken as the focus for the empirical evaluation approach. Cognitive Walkthrough was employed as an example of an analytical evaluation method to investigate user background, while usability tests were used as an example of empirical evaluation method to investigate users’ expertise. The results showed that medical device user background settings can influence the outcome of an analytical evaluation results, i.e. when more ergonomic factors were included in the user background settings, a wider range of usability problems were detected. User expertise is an important factor for the results of empirical usability tests. Users’ familiarity with tasks can be used as an important criterion for classification of user expertise. The quantitative analysis of the empirical evaluations implies that the effect of users’ expertise may be invisible when interacting with a simple user interface, but visible when interacting with a more complex user interface. Expert users outperformed novice users when interacting with a complex interface but not when interacting with a simple interface.The qualitative analysis of verbal explanations and statements, causes of errors and redesign proposals stressed the differences between novice and expert users in terms of decision-making, presentation and judgment, which implied that expert users’ use experience and novice users’ interaction experience differ in contributing to product design and development. Insufficient domain and interaction knowledge were consistently identified as typical causes of errors for novice users. The differences of information organization between previously experienced user interfaces and the interfaces interacted in the usability tests affected expert users’ task completion. Expert users made task-related errors due to terminology issues and interaction-related errors due to their ‘old’ mental model of how to interact with the user interface. Based on the results, different strategies are suggested to be used when choosing test subjects for usability evaluations in different interaction situations. A guideline and some practical advices were proposed as well to medical industrial companies about how to conduct usability evaluations on medical devices.
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| 10. |
- Grishenkov, Dmitry, 1983-, et al.
(author)
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Acoustic properties of polymer-shelled ultrasound contrast agents. Bulk volume vs. microcapillary
- 2009
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In: 16th International Congress on Sound and Vibration 2009, ICSV 2009. - Krakow. - 9781615677368 ; , s. 2515-2522
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Conference paper (peer-reviewed)abstract
- The focus of contrast-enhanced ultrasound research has developed beyond detecting the blood pool to new areas such as perfusion imaging, drug and gene therapy, and targeted imaging. Polymer-shelled microbubbles are proposed as a new generation of ultrasound contrast agents (UCAs) which fulfil the requirements of these applications. With a shelf-life of several months and possibility to conjugate pharmacological molecules to their surface, these UCAs will allow not only to enhance the contrast of ultrasound images, but also to function as carriers of drugs to be delivered locally. In this study, the results of an experimental investigation of three types of UCAs stabilized by thick poly vinyl alcohol (PVA) shell are presented. These UCAs are synthesized from a PVA aqueous solution under varied pH values and temperature. The UCAs differ from each other in their average diameter, shell thickness and polydispersity. Knowledge of the peak negative pressure at which the solid shell fractures is paramount for a proper use of UCAs. Therefore, the dependence of this quantity on temperature and number of cycles in the incident pulse is examined. Much of the blood volume resides in the microcirculation, with capillaries playing a particularly important role in patho-physiology and drug delivery. In this sense in vitro characterization of the UCAs oscillation was moved from bulk volume to the capillary scale, where tissue-bubble interaction takes place. The main conclusion to be drawn from these results is that the shell of the UCAs begin to fracture at values of mechanical index (MI) approved for clinical applications. The fatigue, i.e. the accumulation of damage within the shell of the UCAs, is found to play an important role in fracturing the shell. Finally adhesion of the UCAs to the elastic wall is studied and correlated with estimates of the shell’s visco-elastic constants. Open questions arising from this comparison are briefly discussed.
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