| 1. |
- Bjarnegård, Niclas, et al.
(author)
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Age affects proximal brachial artery stiffness : differential behaviour within the length of the brachial artery?
- 2003
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In: Ultrasound in Medicine and Biology. - 0301-5629. ; 29:8, s. 1115-1121
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Journal article (peer-reviewed)abstract
- With increasing age, the diameter of central elastic arteries increases, whereas their distensibility decreases. The purpose of this study was to investigate the mechanical properties of the proximal brachial artery in relation to age and gender. Distensibility coefficient (DC), stiffness and compliance coefficient (CC) were calculated in 136 healthy males and females (range 9-82 y) using echo-tracking sonography. CC decreased with age in both genders, but CC was higher in males. Stiffness increased and DC decreased with age in an exponential manner, without any differences between genders. In conclusion, as in central elastic arteries, the distensibility of the proximal brachial artery decreases with age, in contrast to earlier reports on the muscular distal brachial artery. This may imply that the transition between elastic and muscular artery behavior is within the length of the brachial artery. In future studies using the brachial artery, the examination site needs to be defined.
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| 2. |
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| 3. |
- Debasso, Rachel, 1978-, et al.
(author)
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The popliteal artery, an unusual muscular artery with wall properties similar to the aorta : Implications for susceptibility to aneurysm formation?
- 2004
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In: Journal of Vascular Surgery. - : Elsevier BV. - 0741-5214 .- 1097-6809. ; 39:4, s. 836-842
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Journal article (peer-reviewed)abstract
- Objective: The popliteal artery is, after the aorta, the most common site for aneurysm formation. Why the popliteal artery is more susceptible than other peripheral muscular arteries is unknown. An important factor may be differences in arterial wall composition as compared with other peripheral muscular arteries, which in turn affect wall properties. These are however unknown. We studied the mechanical wall properties of the popliteal artery in healthy subjects. Material and Methods: An ultrasound echo-tracking system was used to measure pulsatile changes in popliteal diameter in 108 healthy subjects (56 female, 52 male, age range, 9-82 years). In combination with blood pressure, stiffness (β), strain, cross-sectional artery wall compliance coefficient (CC), and distensibility coefficient (DC) were calculated. Intima-media thickness (IMT) was registered with a Philips P700 ultrasound scanner. Results: The popliteal diameter increased with age, and was larger in male subjects than in female subjects (P < .001). Fractional diameter change (strain) decreased with age (P < .001), and strain values were lower in male subjects than in female subjects (P < .01). Accordingly, stiffness increased with age (P < .001), with higher stiffness values in male subjects (P < .01). DC decreased with age (P < .001), with lower DC values in male subjects (P < .01). CC decreased with age, with no difference between genders (P < .001). IMT increased with age (P < .001), with higher IMT values in male subjects (P < .001). The increase in IMT did not affect distensibility. Conclusion: The wall properties of the popliteal artery are affected by age and gender, not only with an increase in diameter, but also with an age-related decrease in distensibility, with male subjects having lower distensibility than in female subjects. This seems not to be the behavior of a true muscular artery, but of a central elastic artery, such as the aorta, and might have implications for susceptibility to arterial dilatation, as well as the association of aneurysm formation between the aorta and the popliteal artery.
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| 4. |
- Gudmundson, Erik, et al.
(author)
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Automatic Smoothing of Periodograms
- 2006
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In: Proceedings of the 2006 IEEE International Conference on Acoustics, Speech, and Signal Processing: May 14-19, 2006, Toulouse, France. ; , s. III-504-III-507
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Conference paper (peer-reviewed)abstract
- Thresholding the cepstrum associated with the periodogram is a smoothing technique that appears to be very useful for variance reduction. Here the thresholding is performed via the methods SThresh and EbayesThresh. They both work fine in the broadband spectra case, even if some of the data is missing. The SThresh method appears to be more efficient as it shows a smaller variance and is faster computationally. The smoothing methods are also shown to perform well on a real-life broadband signal.
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| 5. |
- Petersson, Linn, et al.
(author)
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Molecular design of recombinant scFv antibodies for site-specific photocoupling to β-cyclodextrin in solution and onto solid support.
- 2014
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In: Biochimica et Biophysica Acta - Proteins and Proteomics. - : Elsevier BV. - 1570-9639. ; 1844:12, s. 2164-2173
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Journal article (peer-reviewed)abstract
- The ability to design and tailor-make antibodies to meet the biophysical demands required by the vast range of current and future antibody-based applications within biotechnology and biomedicine will be essential. In this proof-of-concept study, we have for the first time tailored human recombinant scFv antibodies for site-specific photocoupling through the use of an unnatural amino acid (UAA) and the dock'n'flash technology. In more detail, we have successfully explored the possibility to expand the genetic code of E. coli and introduced the photoreactive UAA p-benzoyl-L-phenylalanine (pBpa), and showed that the mutated scFv antibody could be expressed in E. coli with retained structural and functional properties, as well as binding affinity. The pBpa group was then used for affinity capture of the mutated antibody by β-cyclodextrin (β-CD), which provided the hydrogen atoms to be abstracted in the subsequent photocoupling process upon irradiation at 365nm. The results showed that the pBpa mutated antibody could be site-specifically photocoupled to free and surface (array) immobilized β-CD. Taken together, this paves the way for novel means of tailoring recombinant scFv antibodies for site-specific photochemical-based tagging, functionalization and immobilization in numerous applications.
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| 6. |
- Sandgren, Niclas, 1977-
(author)
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Advanced Spectral Analysis with Applications
- 2007
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Doctoral thesis (other academic/artistic)abstract
- Spectral analysis has advanced the last decades as a signal processing tool to extract significant information about certain properties of measured data. The practical use of spectral analysis techniques in time-series analysis has been emphasized in the immense amount of previous literature in the field and by a rapidly growing number of applications. In this thesis, a variety of spectral analysis techniques are presented which address some fundamental problems in signal processing. The proposed methods are accompanied by several experimental and simulated data examples showing the advantages of the suggested approaches. The concept of spectral analysis is briefly introduced along with a condensed presentation of the area of magnetic resonance spectroscopy (MRS), which is an application area treated in several parts of the thesis. The technical contributions include several methods for frequency-selective analysis of exponentially damped sinusoidal signals, invocation of prior knowledge about the signal parameter relations in MRS multiplets for improved parametric spectral estimation, theoretical expressions for the lower error bounds on estimated signal parameters for damped sinusoidal components in the frequency-selective analysis framework, multichannel spectral analysis of MRS data, area-selective spectral analysis of two-dimensional data, spectral smoothing via cepstrum thresholding in one and two dimensions, and spectral analysis of irregularly sampled data. The majority of the presented techniques for magnetic resonance spectroscopy data are parametric methods where a certain amount of prior knowledge about the signal of interest is required, but alternative semi-parametric and non-parametric approaches are also suggested for some of the considered problems. The suggested cepstrum thresholding-based methods are non-parametric, and the analysis on unevenly sampled data contains a set of both non-parametric and parametric approaches.
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| 7. |
- Sandgren, Niclas, et al.
(author)
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Area-Selective Signal Parameter Estimation for Two-Dimensional MR Spectroscopy Data
- 2006
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In: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 183:1, s. 50-59
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Journal article (peer-reviewed)abstract
- We consider the problem of parametric spectral analysis of two-dimensional (2D) magnetic resonance spectroscopy (MRS) data. Estimating the signal components from 2D MRS data is becoming common practice in many clinical MR applications. The most frequently used signal processing tool for this estimation problem is the non-parametric 2D-FFT. There are several alternative parametric methods available to perform this analysis, yet their computational complexity is generally rather high and it becomes prohibitive when the number of points in the measured data matrix is large. In this paper, we propose a novel signal parameter estimation technique which operates on a pre-specified sub-area of the 2D spectrum. This area-selective approach can be used either to estimate only the signal components of main interest in the data, or to compute signal parameter estimates of all present signal components as the computational burden for each sub-area is low. In the numerical example section we consider both simulated data and in vitro H-1 data acquired from a 1.5 T MR scanner.
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| 8. |
- Sandgren, Niclas, et al.
(author)
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Frequency-Selective Analysis of Multichannel Magnetic Resonance Spectroscopy Data
- 2005
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In: Proceedings of the 27th Annual International Conference of the IEEE Engineering in Medicine and Biology Society.
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Conference paper (peer-reviewed)abstract
- In several practical magnetic resonance spectroscopy (MRS) applications the user is interested only in the spectral content of a specific frequency band of the spectrum. A frequency-selective (or sub-band) method estimates only the parameters of those spectroscopic components that lie in a preselected frequency band of the spectrum in a computationally efficient manner. Multichannel MRS is a technique that employs phased-array receive coils to increase the signal-to-noise ratio (SNR) in the spectra by combining several simultaneous measurements of the magnetic resonance (MR) relaxation of an excited sample. In this paper we suggest a frequency-selective multichannel parameter estimation approach that combines the appealing features (high speed and improved SNR) of the two techniques above. The presented method shows parameter estimation accuracies comparable to those of existing full-band multichannel techniques in the high SNR case, but at a considerably lower computational complexity, and significantly better parameter estimation accuracies in low SNR scenarios.
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| 9. |
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| 10. |
- Sandgren, Niclas, et al.
(author)
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Frequency-selective SVD-based magnetic resonance spectroscopy with prior knowledge
- 2004
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In: Conference Record of the 38th Asilomar Conference on Signals, Systems, and Computers.
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Conference paper (peer-reviewed)abstract
- We present a novel method for exploiting prior knowledge in magnetic resonance spectroscopy (MRS) based on the frequency-selective SELF-SVD method which was introduced in \cite{Sandgren}. More specifically, we use the common assumption that the magnetic resonance (MR) data is modeled by the superposition of a given number of exponentially damped sinusoids. As an application we consider the ATP (\textit{a}denosine \textit{t}ri\textit{p}hosphate) complex of an MRS signal and we use the fact that the dampings $\alpha_k$ and frequencies $\omega_k$ of the peaks of the ATP complex satisfy the following conditions: $\alpha_k = \alpha$ and $\omega_k = \omega + k\Delta$, where $\alpha$ and $\omega$ are unknown and $\Delta$ is known. Numerical examples mimicking $^{31}$P MRS data are included. The results show the superiority especially in speed of this new approach, which we will refer to as the FREEK (\textit{fre}quency-selective \textit{e}stimation with prior \textit{k}nowledge) method.
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