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Corrections for improved quantitative accuracy in SPECT and planar scintigraphic imaging
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
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 [en]
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: urn:nbn:se:umu:diva-636ISBN: 91-7305-938-2 (print)OAI: oai:DiVA.org:umu-636DiVA: diva2:144077
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
List of papers
1. Methods for estimating uptake and absorbed dose in tumours from I-125 labelled monoclonal antibodies, based on scintigraphic imaging of mice.
Open this publication in new window or tab >>Methods for estimating uptake and absorbed dose in tumours from I-125 labelled monoclonal antibodies, based on scintigraphic imaging of mice.
1999 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 38, no 3, 361-365 p.Article in journal (Refereed) Published
Abstract [en]

Monoclonal antibodies for radioimmunotargeting are often tested in tumour bearing nude mice. In vivo determination of the uptake of the monoclonal antibody in the tumour requires quantitative scintigraphy, and this in turn requires an adequate method for subtraction of radiation from the normal tissue. For this reason, two different methods for background subtraction were evaluated, a contralateral background region of interest or an irregular one, surrounding the tumour. A pinhole collimator was used for the scintigraphy and the monoclonal antibodies were labelled with 125I. Furthermore, a method was developed for estimation of the mean absorbed dose in the tumour from these repeated quantitative scintigraphic measurements. This requires that the tumour mass can be accurately estimated in vivo. Finally, the results were compared with in vitro measurements of the uptake.

Identifiers
urn:nbn:se:umu:diva-4822 (URN)10.1080/028418699431447 (DOI)10380828 (PubMedID)
Available from: 2005-11-17 Created: 2005-11-17 Last updated: 2011-03-21Bibliographically approved
2. A method for attenuation and scatter correction of brain SPECT based on computed tomography images
Open this publication in new window or tab >>A method for attenuation and scatter correction of brain SPECT based on computed tomography images
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.

Identifiers
urn:nbn:se:umu:diva-5081 (URN)10.1097/01.mnm.0000068299.89730.b4 (DOI)12673170 (PubMedID)
Available from: 2006-04-19 Created: 2006-04-19 Last updated: 2009-12-04Bibliographically approved
3. Transmission-dependent convolution subtraction of 99m-Tc-HMPAO rCBF SPECT - a Monte Carlo study
Open this publication in new window or tab >>Transmission-dependent convolution subtraction of 99m-Tc-HMPAO rCBF SPECT - a Monte Carlo study
2005 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 52, no 1, 231-237 p.Article in journal (Refereed) Published
Abstract [en]

Transmission-dependent convolution subtraction has been shown to be useful when correcting for malpositioned scattered events in single photon emission computed tomography (SPECT). The method is based on convolution subtraction but includes a matrix of scatter fractions instead of a global scatter fraction. In this study, this method is evaluated for regional cerebral blood flow SPECT with 99mTc-hexamethyl propylene-amine oxime (HMPAO) by using Monte Carlo simulations. Different geometries for generating the scatter fractions as a function of the attenuation path length are studied and compared. The most optimal value of the exponential describing the falloff of the monoexponential scatter kernel is determined for each geometry. The method is also compared with convolution subtraction with a global scatter fraction. It is shown that the most optimal of the tested geometries is a homogeneous activity distribution. A scatter kernel with an exponential of 0.15 pixel-1 is most optimal for this geometry. A comparison with convolution subtraction shows that transmission-dependent convolution subtraction can give more accurate results if used with optimal parameters.

Keyword
rCBF SPECT, scatter correction, TDCS, transmission-dependent convolution subtraction
Identifiers
urn:nbn:se:umu:diva-14159 (URN)10.1109/tns.2005.844441 (DOI)
Available from: 2006-11-08 Created: 2006-11-08 Last updated: 2011-03-21Bibliographically approved
4. Scatter-to-primary based scatter fractions for transmission dependent convolution subtraction of SPECT images
Open this publication in new window or tab >>Scatter-to-primary based scatter fractions for transmission dependent convolution subtraction of SPECT images
2003 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 48, no 22, N323-N328 p.Article in journal (Refereed) Published
Abstract [en]

In single photon emission computed tomography (SPECT), transmission-dependent convolution subtraction has been shown to be useful when correcting for scattered events. The method is based on convolution subtraction, but includes a matrix of scatter fractions instead of a global scatter fraction. The method can be extended to iteratively improve the scatter estimate, but in this note we show that this requires a modification of the theory to use scatter-to-total scatter fractions for the first iteration only and scatter-to-primary fractions thereafter. To demonstrate this, scatter correction is performed on a Monte Carlo simulated image of a point source of activity in water. The modification of the theory is compared to corrections where the scatter fractions are based on the scatter-to-total ratio, using one and ten iterations. The resulting ratios of subtracted to original counts are compared to the true scatter-to-total ratio of the simulation and the most accurate result is found for our modification of the theory.

Identifiers
urn:nbn:se:umu:diva-4825 (URN)10.1088/0031-9155/48/22/N03 (DOI)14680275 (PubMedID)
Available from: 2005-11-17 Created: 2005-11-17 Last updated: 2011-03-21Bibliographically approved
5. A new collimator simulation in SIMIND based on the delta-scattering technique
Open this publication in new window or tab >>A new collimator simulation in SIMIND based on the delta-scattering technique
2005 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 52, no 5, 1370-1375 p.Article in journal (Refereed) Published
Abstract [en]

To use conventional ray tracing methods in Monte Carlo simulation of the collimator in a scintillation camera system can be time consuming. It is however necessary to take collimator interactions into account when simulating radionuclides emitting high-energy photons that can penetrate the septa in the collimator. In this work a statistical collimator algorithm, based on the Delta-Scattering method, is evaluated using 123I. The evaluation is performed by comparing results from Monte Carlo simulations and measurements for a scintillation camera system, using point sources and a nonhomogeneous brain phantom. A good agreement can be seen for both images and energy spectra.

Keyword
Collimator, Monte Carlo, scattering, simulation, SPECT
Identifiers
urn:nbn:se:umu:diva-14024 (URN)10.1109/tns.2005.858252 (DOI)
Available from: 2006-11-08 Created: 2006-11-08 Last updated: 2011-03-21Bibliographically approved
6. Correction for scatter and septal penetration in 123I brain SPECT imaging: a Monte Carlo study
Open this publication in new window or tab >>Correction for scatter and septal penetration in 123I brain SPECT imaging: a Monte Carlo study
Show others...
(English)Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4827 (URN)
Available from: 2005-11-17 Created: 2005-11-17 Last updated: 2013-04-25Bibliographically approved

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