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L Thurfjell

Publications and source records attributed to L Thurfjell.

13 recordsLinked to original sources
PubMed2001

A medical platform for simulation of surgical procedures.

Surgery simulation is a promising technique for training of surgical procedures. The overall goal for any surgical simulator is to allow for efficient training of the skills required and to improve learning by giving the user proper feedback. This goal is easier achieved if the training is performed in a realistic environment. Therefore functionality such as soft tissue deformation, tearing and cutting, penetration of soft tissue etc. is necessary. Furthermore, a realistic simulator must provide haptic feedback so that all senses match, that is, there should be a correspondence between what you see and what you feel with your hands. In this paper we describe a medical platform that provides all this functionality. It is based on the Reachln Magma API, which has been extended for surgery simulation. We describe the development of the platform and illustrate the use of it for the development of two different types of surgical simulators, both of which represents work in progress.

Computer Simulation↗
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

Validation of fully automatic brain SPET to MR co-registration.

Fully automatic co-registration of functional to anatomical brain images using information intrinsic to the scans has been validated in a clinical setting for positron emission tomography (PET), but not for single-photon emission tomography (SPET). In this paper we evaluate technetium-99m hexamethylpropylene amine oxime to magnetic resonance (MR) co-registration for five fully automatic methods. We attached six small fiducial markers, visible in both SPET and MR, to the skin of 13 subjects. No increase in the radius of SPET acquisition was necessary. Distortion of the fiducial marker distribution observed in the SPET and MR studies was characterised by a measure independent of registration and three subjects were excluded on the basis of excessive distortion. The location of each fiducial marker was determined in each modality to sub-pixel precision and the inter-modality distance was averaged over all markers to give a fiducial registration error (FRE). The component of FRE excluding the variability inherent in the validation method was estimated by computing the error transformation between the arrays of MR marker locations and registered SPET marker locations. When applied to the fiducial marker locations this yielded the surface registration error (SRE), and when applied to a representative set of locations within the brain it yielded the intrinsic registration error (IRE). For the best method, mean IRE was 1.2 mm, SRE 1.5 mm and FRE 2.4 mm (with corresponding maxima of 3.3, 4.3 and 5.0 mm). All methods yielded a mean IRE <3 mm. The accuracy of the most accurate fully automatic SPET to MR co-registration was comparable with that published for PET to MR. With high standards of calibration and instrumentation, intra-subject cerebral SPET to MR registration accuracy of <2 mm is attainable.

Algorithms↗
PubMed2000

Reproducibility and repeatability of 99Tcm-HMPAO rCBF SPET in normal subjects at rest using brain atlas matching.

The aim of this study was to assess regional cerebral blood flow (rCBF) in normal subjects at rest using 99Tcm-HMPAO single photon emission tomography (SPET). Analysis of reproducibility and repeatability was performed both before and after normalization of flow data. Six healthy volunteers were examined, three times each, according to a routine rCBF protocol. A computerized brain atlas was used to evaluate flow data in eight selected regions. The overall reproducibility of rCBF was evaluated from two scans performed at an average interval of 3 months. Repeatability was evaluated from two scans, 3 h apart and without re-injection of 99Tcm-HMPAO. For the normalized (relative) flow data, the reproducibility was +/- 1.3% and the repeatability +/- 2.2% (i.e. methodological errors dominate). For the non-normalized flow data, the corresponding values were +/- 14.8% and +/- 5.9%. rCBF SPET with 99Tcm-HMPAO is highly reproducible provided that the flow data are normalized. The variation in flow between individuals at one point in time and 3 months later was less than +/- 5% for all brain regions.

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

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↗
PubMed1998

Resting state rCBF mapping with single-photon emission tomography and positron emission tomography: magnitude and origin of differences.

Single-photon emission tomography (SPET), using technetium-99m hexamethylpropylene amine oxime, and positron emission tomography (PET), using oxygen-15 butanol were compared in six healthy male volunteers with regard to the mapping of resting state regional cerebral blood flow (rCBF). A computerized brain atlas was utilized for 3D regional analyses and comparison of 64 selected and normalized volumes of interest (VOIs). The normalized mean rCBF values in SPET, as compared to PET, were higher in most of the Brodmann areas in the frontal and parietal lobes (4.8% and 8.7% respectively). The average differences were small in the temporal (2. 3%) and occipital (1.1%) lobes. PET values were clearly higher in small VOIs like the thalamus (12.3%), hippocampus (12.3%) and basal ganglia (9.9%). A resolution phantom study showed that the in-plane SPET/PET system resolution was 11.0/7.5 mm. In conclusion, SPET and PET data demonstrated a fairly good agreement despite the superior spatial resolution of PET. The differences between SPET and PET rCBF are mainly due to physiological and physical factors, the data processing, normalization and co-registration methods. In order to further improve mapping of rCBF with SPET it is imperative not only to improve the spatial resolution but also to apply accurate correction techniques for scatter, attenuation and non-linear extraction.

Adult↗
PubMed1997

Construction of a standard reference for PET studies of methionine accumulation using a computerised brain atlas.

Positron emission tomography (PET) is valuable for assessing the biochemistry and physiology of the human brain. A computerised brain atlas has been developed which allows demonstration of anatomical regions of PET images and manipulation of these images into a standardised anatomical space. Once the images are in this standardised three-dimensional space it is possible to make comparisons between individuals and groups of individuals. We describe the use of this atlas in the generation of a set of mean reference images using methionine PET images of normal volunteers.

Adult↗
PubMed1995

CBA--an atlas-based software tool used to facilitate the interpretation of neuroimaging data.

CBA, a software tool used to improve quantification and evaluation of neuroimaging data has been developed. It uses a detailed 3-dimensional brain atlas that can be adapted to fit the brain of an individual patient represented by a series of displayed images. Anatomical information from the atlas can then be introduced into the images. If the patient has been imaged in different modalities, adaptation of the atlas to the different images will provide the transformation that brings the images into registration. CBA can thus be used as a tool for fusing multimodality information from the same patient. Furthermore, by applying the inverse atlas transformation, images from a patient can be transformed to conform to the anatomy of the atlas brain. This anatomical standardization, where the atlas brain itself serves as the anatomy standard, brings data from different individuals into a compatible form providing possibilities to perform individual-group and group-by-group comparisons between patients and normal controls.

Animals↗
PubMed1992

The role of anatomic information in quantifying functional neuroimaging data.

When using modern neuroimaging tools, such as CT, PET, SPECT, MRI and MEG, in brain research and brain diagnostics, there is a common need for including external anatomical information into the interpretation and analysis of data. This information may be used to aid the interpretation of structures in images from low resolution imaging tools. With high resolution tools it can help to identify resolved structures. It can also facilitate the merging of data from different modalities, or from different individuals. The anatomical information is often given as regions of interests (ROIs), which may be manually created from an anatomy rich image or automatically created from a standard template collection or from an atlas data base. Automatic methods will lead to a substantial reduction in bias and in size of the systematic errors. Functional ROIs can correspondingly be derived from functional images (usually PET or SPECT). Different aspects of these processes are discussed in the report.

Brain↗
PubMedDate not supplied

Implementation and validation of a fully automatic system for intra- and interindividual registration of PET brain scans.

PURPOSE: Stereotactic coordinate spaces and methods to adapt subjects to that space are required when performing averaging of functional studies across subjects. METHODS: A rapid and fully automatic method to perform intersubject registration and adaptation to a previously defined coordinate space has been developed and implemented. The implementation has been performed within an existing software developed to facilitate manual registration and adaptation, thus offering a versatile combination of automatic and manual tools. Furthermore, a novel measure, based on the F-statistic for intersubject (block) differences, for the assessment of intersubject goodness of fit was suggested and validated. RESULTS: The intra- and intersubject registration was validated by its application to data from six human subjects participating in an activation study. The registration was performed both manually and automatically, and the results indicated that the automatic method performed at least as well as the manual. The block F-statistic was lower for the automatic method, and the z-scores were not significantly different for the methods. The localization of activated regions showed good agreement and differed by an average of 6 mm between the methods. CONCLUSION: It is concluded that the suggested method is a valuable alternative to the current manual approach.

Adult↗
PubMedDate not supplied

Mapping pathological (99m)Tc-d,l-hexamethylpropylene amine oxime uptake in Alzheimer's disease and frontal lobe dementia with SPECT.

Seventeen patients with probable Alzheimer's disease (AD), 7 patients with frontal lobe dementia (FLD) and 19 control subjects (NOR) were examined by (99m)Tc-d,l- hexamethylpropylene amine oxime ((99m)Tc-HMPAO) SPECT. Images were standardised in the same 3D space and averaged within each group. After normalisation, the three sets of images were analysed in all cerebral lobes, hippocampus, thalamus and basal ganglia. In AD, the (99m)Tc-HMPAO uptake values were significantly reduced, as compared to NOR, in the parietal, temporal and insular lobes. In patients with FLD, the uptake was altered in all lobes with the exception of the parietal lobe. The uptake in the nucleus caudatus decreased significantly in both AD and FLD as compared to NOR. The uptake in the anterior cingulate cortex was significantly reduced in FLD. Subtraction images highlighted all significantly decreased areas. In conclusion, standardising SPECT in a common space and subtracting data from a control group improves the visual interpretation of images. In this study, the typical temporo-parietal and fronto-parietal (99m)Tc-HMPAO uptake reductions were found in AD and FLD, respectively. The uptake in the nucleus caudatus was found to decrease significantly in AD and FLD and the one in the anterior cingulate cortex was reduced in FLD.

Aged↗