Biomedical subjects

Peter Lundberg

Publications and source records attributed to Peter Lundberg.

11 recordsLinked to original sources

PubMed2006

Optical measurements during experimental stereotactic radiofrequency lesioning.

The aim of this study was to evaluate in vivo a laser Doppler measurement system in porcine brain tissue during thermal lesioning. A 2-mm monopolar radiofrequency lesioning electrode was equipped with optical fibers in order to monitor the lesioning procedure. Laser Doppler and backscattered light intensity signals were measured along the electrode trajectory and during bilateral lesioning in the central gray (70, 80 and 90 degrees C, n = 14). The time course of the coagulation process could be followed by optical recordings. Two separate groups of tissue were identified from the intensity signals. The changes in the perfusion levels in both groups displayed significant changes (p < 0.05, n = 48) at all temperature settings, while backscattered light intensity was significant for only one group at the different temperatures (p < 0.05, n = 39). These results indicate that optical measurements correlate with lesion development in vivo. The study also indicates that it is possible to follow the lesioning process intra-operatively.

Animals↗

PubMed2005

Projection screen or video goggles as stimulus modality in functional magnetic resonance imaging.

The purpose of this study was to investigate the reliability of functional magnetic resonance imaging (fMRI) by using either a projection screen or video goggles as stimulus modality. A sequence of visual stimuli were presented to the same subject at different occasions. The sequence was optimized with a genetic algorithm. In five sessions the stimuli were presented using a projection screen viewed through a mirror in the head coil and in five sessions using video goggles. Failure to detect visual activation in the medial left hemisphere was observed in sessions using the projection screen as stimulus modality. Decreased thresholds for P values and cluster size resulted in activation outside the occipital lobe and did not significantly increase activated areas in this region. Results in this study indicate that presentation of fMRI tasks with visual routes is more reliable with direct input through video goggles than with the conventional use of projection screens. Failure to detect crucial visual areas has severe consequences for tumor surgery in the visual cortex. Inferior visual impression might also have negative consequences for cognitive tests with high demand on attention and perception.

Brain Mapping↗

PubMed2004

Paradigm design of sensory-motor and language tests in clinical fMRI.

Functional magnetic resonance imaging (fMRI) paradigms on sensory-motor and language functions are reviewed from a clinical user's perspective. The objective was to identify special requirements regarding the design of fMRI paradigms for clinical applications. A wide range of methods for setting up fMRI examinations were found in the literature. It was concluded that there is a need for standardised procedures adapted for clinical settings. Sensory-motor activation patterns do not vary much at different hand motion tasks. Nevertheless it is one of the most important clinical tests. In contrast, the language system is much more complex. In several studies it has been observed that word production tasks are preferable in determination of language lateralisation. Broca's area is activated by most tasks, whereas sentence processing and semantic decision also involve activation in temporoparietal and frontal areas. However, combined task analysis (CTA) of several different tasks has been found to be more robust and reliable for clinical fMRI compared to separate task analysis.

Brain Mapping↗

PubMed2004

Absolute quantification of human liver metabolite concentrations by localized in vivo 31P NMR spectroscopy in diffuse liver disease.

Phosphorus-31 NMR spectroscopy using slice selection (DRESS) was used to investigate the absolute concentrations of metabolites in the human liver. Absolute concentrations provide more specific biochemical information compared to spectrum integral ratios. Nine patients with histopathologically proven diffuse liver disease and 12 healthy individuals were examined in a 1.5-T MR scanner (GE Signa LX Echospeed plus). The metabolite concentration quantification procedures included: (1) determination of optimal depth for the in vivo measurements, (2) mapping the detection coil characteristics, (3) calculation of selected slice and liver volume ratios using simple segmentation procedures and (4) spectral analysis in the time domain. The patients had significantly lower concentrations of phosphodiesters (PDE), 6.3+/-3.9 mM, and ATP-beta, 3.6+/-1.1 mM, (P<0.05) compared with the control group (10.0+/-4.2 mM and 4.2+/-0.3 mM, respectively). The concentrations of phosphomonoesters (PME) were higher in the patient group, although this was not significant. Constructing an anabolic charge (AC) based on absolute concentrations, [PME]/([PME] + [PDE]), the patients had a significantly larger AC than the control subjects, 0.29 vs. 0.16 (P<0.005). Absolute concentration measurements of phosphorus metabolites in the liver are feasible using a slice selective sequence, and the technique demonstrates significant differences between patients and healthy subjects.

Adult↗

PubMed2004

Primary metabolism in N2-fixing Alnus incana-Frankia symbiotic root nodules studied with 15N and 31P nuclear magnetic resonance spectroscopy.

The primary nitrogen metabolism of the N2-fixing root nodule symbiosis Alnus incana (L.)- Frankia was investigated by 31P and 15N nuclear magnetic resonance (NMR) spectroscopy. Perfusion of root nodules in a pulse-chase approach with 15N- or 14N-labeled NH4+ revealed the presence of the amino acids alanine (Ala), gamma-amino butyric acid, glutamine (Gln), glutamic acid (Glu), citrulline (Cit) and arginine (Arg). Labeling kinetics of the Gln amide-N and alpha-amino acids suggested that the glutamine synthetase (GS; EC 6.3.1.2)-glutamate synthase (GOGAT; EC 1.4.1.13) pathway was active. Inhibition of the GS-catalyzed reaction by methionine sulphoximine abolished incorporation of 15N. Cit was labeled in all three N positions but most rapidly in the omega position, consistent with carbamoyl phosphate as the precursor to which Gln could be the amino donor catalyzed by carbamoyl phosphate synthase (CPS; EC 6.3.5.5). Ala biosynthesis occurred consistent with a flux of N in the sequence Gln-Glu-Ala. 31P NMR spectroscopy in vivo and of extracts revealed several metabolites and was used in connection with the 15N pulse-chase experiment to assess general metabolic status. Stable concentrations of ATP and UDP-glucose during extended perfusions showed that the overall root nodule metabolism appeared undisturbed throughout the experiments. The metabolic pathways suggested by the NMR results were confirmed by high activities of the enzymes GS, NADH-GOGAT and ornithine carbamoyltransferase (OCT; EC 2.1.3.3). We conclude that the primary pathway of NH4+ assimilation in A. incana root nodules occurs through the GS-GOGAT pathway. Biosynthesis of Cit through GS-CPS-OCT is important and is a link between the first amino acid Gln and this final transport and storage form of nitrogen.

Alnus↗

PubMed2004

Detection and detrending in fMRI data analysis.

This article addresses the impact that colored noise, temporal filtering, and temporal detrending have on the fMRI analysis situation. Specifically, it is shown why the detection of event-related designs benefit more from pre-whitening than blocked designs in a colored noise structure. Both theoretical and empirical results are provided. Furthermore, a novel exploratory method for producing drift models that efficiently capture trends and drifts in the fMRI data is introduced. A comparison to currently employed detrending approaches is presented. It is shown that the novel exploratory model is able to remove a major part of the slowly varying drifts that are abundant in fMRI data. The value of such a model lies in its ability to remove drift components that otherwise would have contributed to a colored noise structure in the voxel time series.

Brain↗

PubMed2004

A new method for monitoring long-term transport variability in the Baltic.

Direct measurements of the potential induced by motion of electrically conducting seawater through the earth's magnetic field may be used to estimate ocean transports. For the purpose of evaluating the feasibility of monitoring the Baltic climate, a number of temporary observational systems based on this principle have been established around the Swedish coast. Some results from these investigations are presented, and the study is concluded by an outlook towards the prospects for future work along these lines.

Baltic States↗

PubMed2003

Adaptive analysis of fMRI data.

This article introduces novel and fundamental improvements of fMRI data analysis. Central is a technique termed constrained canonical correlation analysis, which can be viewed as a natural extension and generalization of the popular general linear model method. The concept of spatial basis filters is presented and shown to be a very successful way of adaptively filtering the fMRI data. A general method for designing suitable hemodynamic response models is also proposed and incorporated into the constrained canonical correlation approach. Results that demonstrate how each of these parts significantly improves the detection of brain activity, with a computation time well within limits for practical use, are provided.

Algorithms↗

PubMed2002

Detection of neural activity in fMRI using maximum correlation modeling.

A technique for detecting neural activity in functional MRI data is introduced. It is based on a novel framework termed maximum correlation modeling. The method employs a spatial filtering approach that adapts to the local activity patterns, which results in an improved detection sensitivity combined with good specificity. A spatially varying hemodynamic response is simultaneously modelled by a sum of two gamma functions. Comparisons to traditional analysis methods are made using both synthetic and real data. The results indicate that the maximum correlation modeling approach is a strong alternative for analyzing fMRI data.

Brain↗

PubMed2002

Exploratory fMRI analysis by autocorrelation maximization.

A novel and computationally efficient method for exploratory analysis of functional MRI data is presented. The basic idea is to reveal underlying components in the fMRI data that have maximum autocorrelation. The tool for accomplishing this task is Canonical Correlation Analysis. The relation to Principal Component Analysis and Independent Component Analysis is discussed and the performance of the methods is compared using both simulated and real data.

Brain↗

PubMed2002

Experimental radiofrequency brain lesions: a volumetric study.

OBJECTIVE: This study describes the production, under strictly standardized and controlled conditions, of radiofrequency lesions with identical neurogenerator settings: in vitro in two different albumin solutions (nongelatinous and gelatinous) and in vivo in the thalamus of the pig. METHODS: The radiofrequency lesions were investigated in vitro by the use of a specially designed video system and in vivo by magnetic resonance imaging. Moreover, the size of the in vivo lesions was estimated with the use of histological sectioning. The statistical analysis included the calculation of a correlation coefficient for the length, width, and volume for each lesion estimation. RESULTS: A high correlation (R = 0.96, P < 0.005; n = 14) was found between clot sizes in the two albumin solutions. Albumin clots generated in gelatinous albumin showed systematically larger volumes. In the pig, two concentric zones were seen in all magnetic resonance images and all histological preparations. The width correlation of the completely coagulated brain tissue (inner zones) was R = 0.94, P < 0.005, and n = 7. The corresponding correlation between magnetic resonance images and gelatinous albumin was R = 0.93, P < 0.005, and n = 7. As a rule, the in vitro clots were smaller than the outer zone but larger than the inner zone of the magnetic resonance imaging-recorded lesions for all of the electrode and temperature combinations tested. In vivo lesions generated with the same electrode and parameter settings showed high reproducibility. CONCLUSION: The value of presurgical electrode tests to validate the electrode function and lesion size in vitro has become evident in this study, which shows a high correlation between the in vitro albumin clots and the in vivo lesions observed on magnetic resonance images.

Animals↗