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A method for attenuation and scatter correction of brain SPECT based on computed tomography images
Umeå University, Faculty of Medicine, Radiation Sciences, Radiation Physics.
Umeå University, Faculty of Medicine, Radiation Sciences, Radiation Physics.
Umeå University, Faculty of Medicine, Radiation Sciences, Diagnostic Radiology.
Umeå University, Faculty of Medicine, Radiation Sciences, Diagnostic Radiology.
2003 (English)In: Nuclear medicine communications, ISSN 0143-3636, Vol. 24, no 4, 411-420 p.Article in journal (Refereed) Published
Abstract [en]

A method for attenuation and scatter correction of brain single photon emission computed tomography (SPECT) is described where computed tomography (CT) images of the brain are used for the calculation of attenuation maps. The method is evaluated for the substance 99mTc hexamethylpropylene amine oxime. A transmission dependent scatter correction is utilized and is based on ray sums calculated through the attenuation map. A method based on external markers is used to align the SPECT and CT image volumes. The markers need only to be present during the SPECT acquisition since the corresponding landmarks can be found without markers on the CT images. The mismatching has been investigated for five patients who have undergone both a CT examination and a SPECT examination with markers. Twelve individuals from the staff have pointed out the landmarks on the CT images, with an average standard deviation of 3.4 mm. Reconstructions with an attenuation map shifted the corresponding 95% confidence interval have been performed to obtain an estimation of the quantitative uncertainty caused by the mismatching, and quantitative errors of up to 6.3% have been measured. At present the method is probably most useful when groups of patients are studied.

Place, publisher, year, edition, pages
2003. Vol. 24, no 4, 411-420 p.
Identifiers
URN: urn:nbn:se:umu:diva-5081DOI: 10.1097/01.mnm.0000068299.89730.b4PubMedID: 12673170OAI: oai:DiVA.org:umu-5081DiVA: diva2:144450
Available from: 2006-04-19 Created: 2006-04-19 Last updated: 2009-12-04Bibliographically approved
In thesis
1. Corrections for improved quantitative accuracy in SPECT and planar scintigraphic imaging
Open this publication in new window or tab >>Corrections for improved quantitative accuracy in SPECT and planar scintigraphic imaging
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A quantitative evaluation of single photon emission computed tomography (SPECT) and planar scintigraphic imaging may be valuable for both diagnostic and therapeutic purposes. For an accurate quantification it is usually necessary to correct for attenuation and scatter and in some cases also for septal penetration. For planar imaging a background correction for the contribution from over- and underlying tissues is needed. In this work a few correction methods have been evaluated and further developed. Much of the work relies on the Monte Carlo method as a tool for evaluation and optimisation.

A method for quantifying the activity of I-125 labelled antibodies in a tumour inoculated in the flank of a mouse, based on planar scintigraphic imaging with a pin-hole collimator, has been developed and two different methods for background subtraction have been compared. The activity estimates of the tumours were compared with measurements in vitro.

The major part of this work is attributed to SPECT. A method for attenuation and scatter correction of brain SPECT based on computed tomography (CT) images of the same patient has been developed, using an attenuation map calculated from the CT image volume. The attenuation map is utilised not only for attenuation correction, but also for scatter correction with transmission dependent convolution subtraction (TDCS). A registration method based on fiducial markers, placed on three chosen points during the SPECT examination, was evaluated.

The scatter correction method, TDCS, was then optimised for regional cerebral blood flow (rCBF) SPECT with Tc-99m, and was also compared with a related method, convolution scatter subtraction (CSS). TDCS has been claimed to be an iterative technique. This requires however some modifications of the method, which have been demonstrated and evaluated for a simulation with a point source.

When the Monte Carlo method is used for evaluation of corrections for septal penetration, it is important that interactions in the collimator are taken into account. A new version of the Monte Carlo program SIMIND with this capability has been evaluated by comparing measured and simulated images and energy spectra. This code was later used for the evaluation of a few different methods for correction of scatter and septal penetration of I-123 brain SPECT. The methods were CSS, TDCS and a method where correction for scatter and septal penetration are included in the iterative reconstruction. This study shows that quantitative accuracy in I-123 brain SPECT benefits from separate modelling of scatter and septal penetration.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2005. 88 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 983
Keyword
Quantitative SPECT, scintigraphic imaging, attenuation correction, scatter correction, collimator-detector response, septal penetration, background correction, Monte Carlo simulation
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:umu:diva-636 (URN)91-7305-938-2 (ISBN)
Public defence
2005-12-09, 244, 7, Norrlands Universitetssjukhus, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2005-11-17 Created: 2005-11-17 Last updated: 2012-04-03Bibliographically approved
2. Human brain function evaluated with rCBF-SPECT: memory and pain related changes and new diagnostic possibilities in Alzheimer’s disease
Open this publication in new window or tab >>Human brain function evaluated with rCBF-SPECT: memory and pain related changes and new diagnostic possibilities in Alzheimer’s disease
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this doctoral thesis was to study the influence of memory, pain, age and education on the regional cerebral blood flow (rCBF), i.e. brain function, in early Alzheimer's disease (AD) and in chronic neck pain patients in comparison to healthy controls and in healthy elderly per se. This was done by optimizing single photon emission computed tomography (SPECT) as a method to study rCBF with the tracer Technetium-99m (99mTc) hexamethylpropyleneamine oxime (HMPAO) and by matching all image data to a brain atlas before evaluation. The rCBF-SPECT was evaluated and developed to obtain higher diagnostic accuracy in AD and in chronic neck pain patients it was used to study basic pain related cerebral processes in chronic pain of different origin. A new semimanual registration method, based on fiducial marker, suitable for investigations with low spatial resolution was developed. The method was used to reconstruct images with an improved attenuation and scatter correction by using an attenuation-map calculated from the patients' previously acquired CT images.

The influence of age and education on rCBF was evaluated with statistical parametric mapping, SPM in healthy elderly. The main findings were age related changes in rCBF in regions close to interlobar and interhemispheric space but not in regions typically affected in early AD, except for the medial temporal lobe. The theory of a 'cognitive reserve' in individuals with a longer education was supported with findings in the lateral temporal lobe, a region related to semantic memory, and in the frontal lobe.

A cross-sectional study of chronic neck pain patients showed extensive rCBF changes in coping related regions in a non-traumatic pain patients compared to both healthy and a pain group with a traumatic origin, i.e. whiplash syndrome. The whiplash group displayed no significant differences in rCBF in comparison with the healthy controls. This suggests different pain mechanisms in these groups.

The AD-patients showed a significantly lower rCBF in temporoparietal regions including left hippocampus. These changes were associated to episodic memory performance, and especially to face recognition. The diagnostic sensitivity for AD was high. The face recognition test (episodic memory) was used in AD patients to improve the sensitivity of method, i.e. memory-provoked rCBF-SPECT (MP-SPECT). The results were compared to healthy controls and the reductions of rCBF in temporoparietal regions were more pronounced in mild AD during provocation. Memory provocation increased the sensitivity of AD-related rCBF changes at group level. If a higher sensitivity for AD at the individual level is verified in future studies, a single MP-SPECT study might then be of help to set diagnosis earlier.

In conclusion rCBF in temporoparietal regions are associated to an impaired episodic memory in early AD. Changes in these regions do not have a strong connection to chronological age. The diagnostic sensitivity of rCBF-SPECT in AD is high and there is a potentially higher sensitivity if memory provoked investigations are used. The findings in this thesis have given an increased knowledge of underlying cerebral pain processing in non-traumatic and traumatic (whiplash) neck pain. Preliminary results supporting the theory of 'cognitive reserve' by showing a correlation between long education and preserved rCBF was found in healthy elderly.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2006. 74 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1016
Keyword
brain imaging, rCBF, SPECT, early diagnosis, brain atlas, HMPAO, Alzheimer´s disease, Whiplash, neuropsychological function, episodic memory
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:umu:diva-761 (URN)91-7264-051-0 (ISBN)
Public defence
2006-05-05, sal 260 röntgen, 3A 2tr, Norrlands Universitetssjukhus, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2006-04-19 Created: 2006-04-19 Last updated: 2012-04-03Bibliographically approved

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Larsson, AnneJohansson, LennartSundström, TorbjörnRiklund Åhlström, Katrine

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