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Evaluation of reconstruction techniques for lung single photon emission tomography: A Monte Carlo study
Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics. Linköping University, Faculty of Health Sciences.ORCID iD: 0000-0002-1380-2497
Sahlgrenska universitetssjukhuset, Göteborg.
Göteborgs universitet, Göteborg.
Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.ORCID iD: 0000-0003-0209-498X
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2007 (English)In: Nuclear medicine communications, ISSN 0143-3636, Vol. 28, no 12, 929-936 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: In studies of the distribution of lung function, the image quality of lung single photon emission computed tomography (SPECT) is important and one factor influencing it is the reconstruction algorithm. AIM: To systematically evaluate ordered subsets expectation maximization (OSEM) and compare it with filtered back-projection (FBP) for lung SPECT with Tc. METHODS: The evaluation of the number of iterations used in OSEM was based on the image quality parameter contrast. The comparison between OSEM and FBP was based on trade-off plots between statistical noise and spatial resolution for different filter parameters, collimators and count-levels. A Monte Carlo technique was used to simulate SPECT studies of a digital thorax phantom containing two sets of activity: one with a homogeneous activity distribution within the lungs and the other with superposed high- and low-activity objects. Statistical noise in the reconstructed images was calculated as the coefficient of variation (CV) and spatial resolution as full width at half-maximum (FWHM). RESULTS: For the configuration studied, the OSEM reconstruction in combination with post-filtering should be used in lung SPECT studies with at least 60 MLEM equivalent iterations. Compared to FBP the spatial resolution was improved by about 1 mm. For a constant level of CV, a four-fold increase in count level resulted in an increased resolution of about 2 mm. Spatial resolution and cut-off frequency depends on what value of noise in the image is acceptable also increased by using a low-energy, high-resolution collimator for CV values above 3%. The choice of noise-reducing filter and cut-off frequency depends on what value of noise in the image is acceptable.

Place, publisher, year, edition, pages
United States: Lippincott Williams & Wilkins , 2007. Vol. 28, no 12, 929-936 p.
Keyword [en]
SPECT, Monte Carlo methods, image processing, lung
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-21152DOI: 10.1097/MNM.0b013e3282f1acacPubMedID: 18090220OAI: oai:DiVA.org:liu-21152DiVA: diva2:240758
Available from: 2009-09-29 Created: 2009-09-29 Last updated: 2015-03-20
In thesis
1. Quantification and optimisation of lung ventilation SPECT images
Open this publication in new window or tab >>Quantification and optimisation of lung ventilation SPECT images
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Currently, lung function tests are the gold standard for lung function measurements. Since the outcome of a lung function test is a summation of the status of the whole lung, significant changes in lung function may occur before a deviation from the norm can be identified. A method that can reliably detect lung abnormalities earlier in a disease process would therefore be beneficial. Regional differences in the lung are ideally studied by imaging methods. Heterogeneous ventilation in lungs of allergic individuals, cigarette smokers, asthmatics and chronic obstructive pulmonary disease (COPD) patients has been demonstrated using various imaging techniques such as single photon emission computer tomography, SPECT. The amount of heterogeneous ventilation is correlated to disease advancement. The CVT-method, that measures heterogeneity using the coefficient of variation (CV) caused by lung function reduction in lung SPECT images, was developed and optimised. Lung function in patients and healthy volunteers was evaluated using the CVT-method.

Monte Carlo simulated gamma camera projections were generated of activity distributions in two anthropomorphic phantoms. When comparing the two reconstruction algorithms, filtered back projection (FBP) and ordered subset expectation maximisation (OSEM), trade-off plots of spatial resolution, contrast and noise were used. Development and optimisation of the CVT-method was performed using activity distributions mimicking various degrees of COPD. The CVT-method itself was used when the optimal combination of acquisition, reconstruction and analysis parameter values was determined. The radioactive tracer 99mTc-Technegas was used for the ventilation examination on human subjects.

OSEM resulted in higher spatial resolution in combination with lower noise level compared to FBP and was therefore chosen. The optimal parameter values found were a total number of counts in the projections of at least 3.6 x 106 and a low energy highresolution collimator. The number of OSEM updates and cut-off frequency of the noise reduction filter depended on if the periphery of the lung was excluded or not. The CVT-method showed to be capable of identifying early COPD in computersimulated images (p<0.001). The CVT-method was also capable of correctly identifying patients with severe COPD (p<0.05). A compensation technique was implemented, making the heterogeneity values from healthy lung volumes of different subjects comparable. This adaptation made it possible to identify subjects who had normal lung function tests but with indications of conditions associated with ventilation disturbances. The results indicate that the present method has the capacity to identify minor lung function abnormalities earlier in a disease process than conventional lung function tests.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 79 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1403
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-106667 (URN)10.3384/diss.diva-106667 (DOI)978-91-7519-359-5 (ISBN)
Public defence
2014-06-05, Eken, ingång 65 (HU) plan 9, Campus US, Linköpings universitet, Linköping, 09:00 (Swedish)
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Available from: 2014-05-19 Created: 2014-05-19 Last updated: 2015-03-20Bibliographically approved

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Norberg, PernillaAlm Carlsson, GudrunGustafsson, Agnetha

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