Biomedical subjects

J L Andersson

Publications and source records attributed to J L Andersson.

At least 19 recordsLinked to original sources

PubMed2005

Free water surface wetlands for wastewater treatment in Sweden: nitrogen and phosphorus removal.

In South Sweden, free water surface wetlands have been built to treat wastewater from municipal wastewater treatment plants. Commonly, nitrogen removal has been the prime aim, though a significant removal of tot-P and BOD7 has been observed. In this study, performance data for 3-8 years from four large (20-28 ha) FWS wetlands have been evaluated. Two of them receive effluent from WWTP with only mechanical and chemical treatment. At the other two, the wastewater has also been treated biologically resulting in lower concentrations of BOD7 and NH4+-N. The wetlands performed satisfactorily and removed 0.7-1.5 ton N ha(-1) yr(-1) as an average for the time period investigated, with loads between 1.7 and 6.3 ton N ha(-1)yr(-1). Treatment capacity depended on the pre-treatment of the water, as reflected in the k20-values for N removal (first order area based model). In the wetlands with no biological pre-treatment, the k20-values were 0.61 and 1.1 m month(-1), whereas for the other two they were 1.7 and 2.5 m month(-1). P removal varied between 10 and 41 kg ha(-1) yr(-1), and was related to differences in loads, P speciation and to the internal cycling of P in the wetlands.

Biodegradation, Environmental↗

PubMed2001

Abnormal brain white matter in schizophrenia: a diffusion tensor imaging study.

Fractional anisotropy and the mean diffusion coefficient were measured in the cerebral volume in 20 schizophrenic and 24 healthy subjects, men and women, using diffusion tensor imaging. In addition, 3D SPGR was used for segmentation of brain tissue into grey and white matter and cerebrospinal fluid. In schizophrenic patients, fractional anisotropy was reduced in the splenium of the corpus callosum and in adjacent occipital white matter. The segmentation revealed no tissue deficits in the volume of reduced fractional anisotropy. The mean diffusion was increased in the total white and grey matter volume of the schizophrenic patients compared with the healthy subjects. The findings support the view that global and regional white matter abnormalities occur in chronic schizophrenia.

Adult↗

PubMed2001

Modeling geometric deformations in EPI time series.

Even after realignment there is residual movement-related variance present in fMRI time-series, causing loss of sensitivity and, potentially, also specificity. One cause is the differential deformation of the sampling matrix, by field inhomogeneities, at different object positions, i.e., a movement-by-inhomogeneity interaction. This has been addressed previously by using empirical field measurements. In the present paper we suggest a forward model of how data is affected by an inhomogeneous field at different object positions. From this model we derive a method to solve the inverse problem of estimating the field inhomogeneities and their derivatives with respect to object position, directly from the EPI data and estimated realignment parameters. The field is modeled as a linear combination of cosine basis fields, which facilitates a fast way of implementing the necessary matrix operations. Simulations suggest that the solution is tractable and that the fields are estimable given the deformed images and knowledge of the relative positions at which they have been acquired. An experiment on a subject performing voluntary movements in the scanner yielded plausible estimates of the deformation fields and their application to "unwarp" the time series significantly reduced movement-related variance.

Adult↗

PubMed2001

A global estimator unbiased by local changes.

The global activity is an important confound when analyzing PET data in that its inclusion in the statistical model can substantially reduce error variance and increase sensitivity. However, by defining global activity as the average over all voxels one introduces a bias that is collinear with experimental factors. This leads to an underestimation of true activations and the introduction of artefactual deactivations. We propose a novel estimator for the global activity based on the notion of finding a maximally nonlocal mode in a multivariate characterization of the data, while maximizing the locality of the remaining modes. The approach uses singular value decomposition (SVD) to find a provisional set of modes, which are subsequently rotated such that a metric based on the above heuristic is maximized. This metric is a version of the stochastic sign change (SSC) criterion that has been used previously for normalizing medical images with focal defects. The estimator was evaluated on simulated and real functional imaging (PET) data. The simulations show that the bias of the global mean, introduced by focal activations, is reduced by 80--90% with the new estimator. Comparison with a previous unbiased estimator, using the empirical data, yielded similar results. The advantage of the new estimator is that it is not informed of experimental design and relies only on general assumptions regarding the nature of the signal.

Brain↗

PubMed2001

On the effects of gating in diffusion imaging of the brain using single shot EPI.

To reduce image artifacts in diffusion tensor imaging using single shot EPI, cardiac gating may be performed to prevent brain motion induced signal void in the DWI data. In this work the necessity of performing cardiac gating with single shot echo planar imaging has been explored using F statistics of the variance in DWI data. Peripheral measurement of the cardiac cycle has been employed because of its greater convenience, and hence use, compared to ECG gating. Four volunteers have been studied. Six different trigger delays have been evaluated in the range 18-500 ms relative the peripheral pulse wave. Brain motion was found significant in and inferior to the corpus callosum area. A trigger delay of 500 ms was found to be optimal. However, a long delay allows only for one slice per R-R interval. Therefore, a minimum trigger delay may be the best choice in terms of SNR per unit of experiment time.

Artifacts↗

PubMed2000

Image registration using a symmetric prior--in three dimensions.

This paper describes a Bayesian method for three-dimensional registration of brain images. A finite element approach is used to obtain a maximum a posteriori estimate of the deformation field at every voxel of a template volume. The priors used by the MAP estimate penalize unlikely deformations and enforce a continuous one-to-one mapping. The deformations are assumed to have some form of symmetry, in that priors describing the probability distribution of the deformations should be identical to those for the inverses (i.e., warping brain A to brain B should not be different probablistically from warping B to A). A gradient descent algorithm is presented for estimating the optimum deformations.

Algorithms↗

PubMed2000

Improved efficiency for MRI-SPET registration based on mutual information.

Mutual information has been proposed as a criterion for image registration. The criterion is calculated from a two-dimensional grey-scale histogram of the image pair being registered. In this paper we study how sparse sampling can be used to increase speed performance using the registration algorithm of Maes et al. (IEEE Trans Med Imaging 1997; 16: 187-198) with a focus on registration of MRI-SPET brain images. In particular we investigate how sparse sampling and parameters such as the number of bins used for the grey-scale histograms and smoothing of the data prior to registration affect accuracy and robustness of the registration. The method was validated using both simulated and human data. Our results show that sparse sampling introduced local maxima into the mutual information similarity function when the number of bins used for the histograms was large. To speed up registration while retaining robustness, smoothing of the data prior to registration was used and a coarse to fine subsampling protocol, where the number of bins in the histograms were dependent on the subsampling factor, was employed, For the simulated data, the method was able to recover known transformations with an accuracy of about 1 mm. Using the human data, there were no significant differences in the recovered transformation parameters when the suggested subsampling scheme was used compared with when no subsampling was used, but there was a more than tenfold increase in speed. Our results show that, with the appropriate choice of parameters, the method can accurately register MRI-SPET brain images even when very efficient sampling protocols are used.

Algorithms↗

PubMed2000

A metabolic threshold of irreversible ischemia demonstrated by PET in a middle cerebral artery occlusion-reperfusion primate model.

OBJECTIVE: to evaluate the predictive value of measurements of regional cerebral blood flow (CBF), oxygen metabolism (CMRO2) and oxygen extraction ratio (OER) for assessment of the fate of ischemic brain tissue. MATERIALS AND METHODS: Sequential PET measurements were performed during middle cerebral artery occlusion (MCAO; 2 h) and 12-24 h (mean 18 h) of reperfusion in a primate model (Macaca mulatta, n = 8). A penumbra region was delineated on the MCAO PET image (OER > 125% and CMRO2> or = 45% of the values observed in the contralateral hemisphere, respectively) and an infarction region was delineated on the last PET image (CMRO2 <45% of the values observed in the contralateral hemisphere). The penumbra regions delineated during MCAO and the infarction regions delineated at the final PET, were copied on to the images from all other PET sessions for measurements of CBF, CMRO2 and OER. Ratios were calculated by dividing the mean values obtained by the values of the corresponding contralateral region. RESULTS: Histopathology verified the adequacy of the criteria applied in the last PET for delineation of the infarction region. The penumbra region and infarction region were separated in all cases, except in two cases where a minimal overlap was seen. CBF and OER showed considerable variation over time and there was no consistent difference between the penumbra and infarction regions. CMRO2 showed a more stable pattern and the difference between penumbra and infarction regions was maintained from the time of MCAO throughout the entire reperfusion phase. With CMRO2 as predictor, all 50 observations could be correctly predicted as penumbra or infarction when using an optimal threshold ratio value estimated to be in the interval of 61% to 69% of the corresponding contralateral region. CBF and OER proved to have low power as predictors. CONCLUSIONS: The results indicate that CMRO2 is the best predictor of reversible or irreversible brain damage and the critical metabolic threshold level appears to be a reduction of oxygen metabolism to between 61% and 69% of the corresponding contralateral region.

Animals↗

PubMed2000

Fear conditioning and brain activity: a positron emission tomography study in humans.

Regional cerebral blood flow (rCBF) was measured with H2 (15)O positron emission tomography in 8 healthy women before and after fear conditioning (i.e., paired shocks) and unpaired shocks to videotape cues. Conditioning was supported by enhanced peripheral nervous system recordings and subjective ratings. Fear conditioning increased rCBF in the central gray of the midbrain; bilaterally in the hypothalamus, the thalamus, and the left striatum; and in the right and left anterior cingulate and right prefrontal cortices. Regional CBF was attenuated bilaterally in the right and left prefrontal, temporal (including the amygdala), parietal, and occipital cortices, and in the left orbitofrontal cortex. When compared with unpaired shock presentations, fear conditioning resulted in elevated rCBF in the left cerebellum. Hence, in the present paradigm, only neural activity in the left cerebellum solely reflected processes associated with true Pavlovian conditioning.

Adult↗

PubMed2000

Registration of neuroimaging data: implementation and clinical applications.

Image registration brings images into a form in which each voxel corresponds to a predetermined anatomic entity and is necessary for comparisons of data across scans. Intrasubject registration is a matter of translating and rotating one image volume into correspondence with another. Intersubject registration is more difficult because it requires the removal of individual anatomy dependence from the data. This article describes, with the help of clinical examples, automated methods for intrasubject registration of scans within and between modalities, and intersubject registration used for registering a three-dimensional brain atlas with a patient's brain scan.

Adult↗

PubMed1999

Tyrosine transport is regulated differently in patients with schizophrenia.

Previous PET studies of tyrosine transport have suggested that the transport of tyrosine from blood to brain compartment is not dependent on its plasma concentration in patients with schizophrenia. In order to examine this relationship, the transport constant (K1) of tyrosine was determined in five patients with schizophrenia and five normals. L-[1-11C]Tyrosine was injected i.v. and arterial blood samples were taken during PET scanning. The tyrosine transport was assessed during baseline conditions and after oral administration of L-tyrosine at a dose (175 mg/kg) that significantly elevated the plasma levels. K1 was determined from tracer kinetic modelling. The transport rate dropped in the normals after tyrosine loading, which is consistent with the prevailing notion that the brain transport system for neutral amino acids works close to saturation, whereas it was virtually unchanged in the schizophrenics. The results demonstrated that tyrosine transport was not saturated in the patients with schizophrenia and thus could lead to elevated brain concentrations of tyrosine.

Biological Transport↗

PubMed1999

Brain regions associated with episodic retrieval in normal aging and Alzheimer's disease.

OBJECTIVE: To examine patterns of brain activation during verbal episodic retrieval in normal elderly subjects and patients in an early phase of AD. BACKGROUND: It is established that 1) a profound episodic memory impairment is a cardinal symptom of AD; and 2) some of the earliest brain changes in this disease occur in regions critical to episodic memory, such as the hippocampus and neighboring regions. Yet, it remains largely unknown whether the episodic memory deficit seen in AD is paralleled by concomitant alterations in brain activity during actual task performance in these or other brain areas. METHODS: Using PET, blood flow was assessed in normal elderly subjects and patients with early AD during two retrieval conditions involving completion of word stems: baseline and cued recall. RESULTS: The patients with AD showed a marked performance deficit in cued recall, although the two groups were indistinguishable in the baseline task condition. Both groups showed bilateral activity in orbital and dorsolateral prefrontal cortex, left precuneus, and right cerebellum, as well as decreased activity in distinct left temporal regions during cued recall. The normal elderly alone activated the left parietal cortex and the left hippocampal formation during episodic retrieval. By contrast, AD-related increases in activity during cued recall were observed in the left orbital prefrontal cortex and left cerebellum. CONCLUSIONS: The similar patterns of activations in the two groups suggest that a large distributed network involved in episodic memory retrieval functions relatively normally in early AD. Those retrieval activations seen in the normal elderly, as opposed to the patients, may reflect AD-related failures in semantic processing and successful recollection of the target information, respectively. Finally, the AD-related increases in activity were interpreted in terms of compensatory reactions to the difficulties in performing the episodic memory task.

Aged↗

PubMed1999

High-dimensional image registration using symmetric priors.

This paper is about warping a brain image from one subject (the object image) so that it matches another (the template image). A high-dimensional model is used, whereby a finite element approach is employed to estimate translations at the location of each voxel in the template image. Bayesian statistics are used to obtain a maximum a posteriori (MAP) estimate of the deformation field. The validity of any registration method is largely based upon the constraints or, in this instance, priors incorporated into the model describing the transformations. In this approach we assume that the priors should have some form of symmetry, in that priors describing the probability distribution of the deformations should be identical to those for the inverses (i.e., warping brain A to brain B should not be different probabilistically from warping B to A). The fundamental assumption is that the probability of stretching a voxel by a factor of n is considered to be the same as the probability of shrinking n voxels by a factor of n(-1). In the Bayesian framework adopted here, the priors are assumed to have a Gibbs form, where the Gibbs potential is a penalty function that embodies this symmetry. The penalty function of choice is based upon the singular values of the Jacobian having a lognormal distribution. This enforces a continuous one-to-one mapping. A gradient descent algorithm is presented that incorporates the above priors in order to obtain a MAP estimate of the deformations. We demonstrate this approach for the two-dimensional case, but the principles can be extended to three dimensions. A number of examples are given to demonstrate how the method works.

Bayes Theorem↗

PubMed1999

A multivariate approach to registration of dissimilar tomographic images.

We devised a method to allow for retrospective registration of tomographic images with very different information content, the main emphasis being on sets of positron emission tomography images obtained with different tracers. A multivariate cost-function based on information theory was used as an index of "goodness-of-alignment". The cost-function makes no assumptions regarding the form of the relationship between the two image sets, and is hence very general. Image volumes, with known relative spatial orientation, were simulated for tracers with different uptake patterns and the method was validated by assessing its ability to recover these known orientations. The method was able to recover the known transformations with an accuracy of about 1 mm and 1 degrees along and around all axes, even for tracer combinations with radically different uptake patterns and with large initial misalignment. With the suggested method it is feasible to retrospectively align examinations obtained with different tracers and/or modalities.

Adult↗

PubMed1999

Deletions of the heavy neurofilament subunit tail in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron degeneration resulting in paralysis and death, usually within 3 years of onset. Pathological and animal studies implicate neurofilament involvement in ALS, but whether this is primary or secondary is not clear. The heavy neurofilament subunit (NFH) tail is composed of a repeating amino acid motif, usually X-lysine-serine-proline-Y-lysine (XKSPYK), where X is a single amino acid and Y is one to three amino acids. There are two common polymorphic variants of 44 or 45 repeats. The tail probably regulates axonal calibre, with interfilament spacing determined by phosphorylation of the KSP motifs. A previous study suggested an association between sporadic cases of ALS and NFH tail deletions, but two subsequent studies have found none. We have analysed samples from two different populations (UK 207, Scandinavia 323) with age-matched controls for each group (UK 219, Scandinavia 228) and have found four novel NFH tail deletions, each involving a whole motif. These were found in three patients with sporadic ALS and a family with autosomal dominant ALS, although another was also found in two young controls. In all cases motif deletions were only associated with disease when paired with the long NFH allele. The deletions all occurred within a small region of the NFH tail. This has allowed us to propose a structural organization of the tail as well as allowing observed deletions both from this study and previous reports to be organized into logical groups. These results strongly suggest that NFH motif deletions can be a primary event in ALS but that they are not common.

Adult↗

PubMed1998

Brain correlates of an unexpected panic attack: a human positron emission tomographic study.

Previous brain imaging studies on symptom provocation in panic anxiety have used either drug-infusions or sensory related stimulation to induce panic attacks. We here report positron emission tomographic measurements of regional cerebral blood flow (rCBF) during an unexpected panic attack in a healthy female volunteer participating in a fear conditioning study. During a first but not a second run with electric shock presentations the woman unexpectedly experienced a panic attack that fulfilled the DSM-IV criteria. Panic was associated with decreased rCBF in the right orbitofrontal (Brodmann area 11), prelimbic (area 25), anterior cingulate (area 32) and anterior temporal cortices (area 15). These findings suggest that neural activity in brain regions previously associated with symptom provocation in specific phobics and subjects with posttraumatic stress disorder also are involved during panic in healthy individuals.

Adult↗

PubMed1998

Design, construction and six years' experience of an integrated system for automated handling of discrete blood samples.

The present paper describes the design of an integrated system to aid in the taking and measurement of manual blood samples during nuclear medical examinations requiring blood sampling. In contrast to previously published systems, the present system is not used in the actual sampling of the blood, but aims to aid in all other aspects of handling and measurement. It consists of two main parts. One part is a distributed software system running on the scanner host computer used to register sample times, to display information pertaining to the ongoing examination and to collect data from a number of well crystals. The other main part consists of an industrial robot used to perform the actual weighing, centrifugation, pipetting and measurement of the samples. The system has been operational for 6 years, during which time it has had an "up-time" in excess of 95% and has handled and measured the blood samples from more than 5000 examinations, each comprising an average of 15 blood samples. The throughput of the system is 50 whole blood samples or 21 plasma samples per hour. In addition it has to a large extent removed the "human factor" from the process, thereby increasing the reliability of the data.

Automation↗

PubMed1998

How to obtain high-accuracy image registration: application to movement correction of dynamic positron emission tomography data.

When registering dynamic positron emission tomography (PET) sequences, the time-dependent changes in uptake pattern prevent registration of all frames to the first frame in a straightforward manner. Instead, a sequential registration of each frame to its predecessor may be used, provided the registration algorithm is completely free of bias. It is shown that most existing algorithms introduce a bias, the size of which depends on the pixel size and the signal-to-noise ratio of the data. The bias is introduced by the pixelisation of the underlying continuous process. All existing cost-functions are more or less sensitive to noise, and the noise reduction resulting from translating one image set relative to the other means that a small movement will always be detected in the cases where no actual movement has occurred. The problem is solved by an initial resampling of the reference volume into a representation with another image and pixel size. If the new representation is sensibly chosen it means that all possible transforms applied to the other image volume will yield approximately the same noise reduction, thereby removing the source of the bias. The described effect is demonstrated on phantom data, and its impact is shown on human data.

Adult↗