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Quantification and optimisation of lung ventilation SPECT images
Linköping University, Department of Medical and Health Sciences, Division of Radiological Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Radiation Physics.ORCID iD: 0000-0002-1380-2497
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: urn:nbn:se:liu:diva-106667DOI: 10.3384/diss.diva-106667ISBN: 978-91-7519-359-5 (print)OAI: oai:DiVA.org:liu-106667DiVA: diva2:717934
Public defence
2014-06-05, Eken, ingång 65 (HU) plan 9, Campus US, Linköpings universitet, Linköping, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2014-05-19 Created: 2014-05-19 Last updated: 2015-03-20Bibliographically approved
List of papers
1. Evaluation of reconstruction techniques for lung single photon emission tomography: A Monte Carlo study
Open this publication in new window or tab >>Evaluation of reconstruction techniques for lung single photon emission tomography: A Monte Carlo study
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2007 (English)In: Nuclear medicine communications, ISSN 0143-3636, E-ISSN 1473-5628, 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
Keyword
SPECT, Monte Carlo methods, image processing, lung
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-21152 (URN)10.1097/MNM.0b013e3282f1acac (DOI)18090220 (PubMedID)
Available from: 2009-09-29 Created: 2009-09-29 Last updated: 2017-12-13
2. Quantitative lung SPECT applied on simulated early COPD and humans with advanced COPD
Open this publication in new window or tab >>Quantitative lung SPECT applied on simulated early COPD and humans with advanced COPD
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2013 (English)In: EJNMMI Research, ISSN 2191-219X, E-ISSN 2191-219X, Vol. 3, no 28Article in journal (Refereed) Published
Abstract [en]

BACKGROUND:Reduced ventilation in lung regions affected by chronic obstructive pulmonary disease (COPD), reflected as inhomogeneities in the single-photon emission computed tomography (SPECT) lung image, is correlated to disease advancement. An analysis method for measuring these inhomogeneities is proposed in this work. The first aim was to develop a quantitative analysis method that could discriminate between Monte Carlo simulated normal and COPD lung SPECT images. A second aim was to evaluate the ability of the present method to discriminate between human subjects with advanced COPD and healthy volunteers.

METHODS:In the simulated COPD study, different activity distributions in the lungs were created to mimic the healthy lung (normal) and different levels of COPD. Gamma camera projections were Monte Carlo simulated, representing clinically acquired projections of a patient who had inhaled 125 MBq 99mTc-Technegas followed by a 10-min SPECT examination. Reconstructions were made with iterative ordered subset expectation maximisation. The coefficient of variance (CV) was calculated for small overlapping volumes covering the 3D reconstructed activity distribution. A CV threshold value (CVT) was calculated as the modal value of the CV distribution of the simulated normal. The area under the distribution curve (AUC), for CV values greater than CVT, AUC(CVT), was then calculated. Moreover, five patients with advanced emphysema and five healthy volunteers inhaled approximately 75 MBq 99mTc-Technegas immediately before the 20-min SPECT acquisition. In the human study, CVT was based on the mean CV distribution of the five healthy volunteers.

RESULTS:A significant difference (p < 0.001) was found between the Monte-Carlo simulated normal and COPD lung SPECT examinations. The present method identified a total reduction of ventilation of approximately 5%, not visible to the human eye in the reconstructed image. In humans the same method clearly discriminated between the five healthy volunteers and five patients with advanced COPD (p < 0.05).

CONCLUSIONS:While our results are promising, the potential of the AUC(CVT) method to detect less advanced COPD in patients needs further clinical studies.

Place, publisher, year, edition, pages
Germany: SpringerOpen, 2013
Keyword
Quantitative lung SPECT, Ventilation, Iterative reconstruction, Lung disorder, Monte Carlo, COPD
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-96748 (URN)10.1186/2191-219X-3-28 (DOI)23597059 (PubMedID)
Available from: 2013-08-26 Created: 2013-08-26 Last updated: 2017-12-06
3. Optimisation of quantitative lung SPECT applied to mild COPD: a Monte Carlo-based analysis
Open this publication in new window or tab >>Optimisation of quantitative lung SPECT applied to mild COPD: a Monte Carlo-based analysis
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The amount of inhomogeneities in a single photon emission computed tomography (SPECT) lung image, caused by reduced ventilation in lung regions affected by chronic obstructive pulmonary disease (COPD), is correlated to disease advancement. A quantitative analysis method, the CVT-method, measuring these inhomogeneities was proposed in earlier work (Norberg et al., 2013). To detect mild COPD, which is a difficult task, optimized parameter values are needed. In this work, the CVT-method was optimized with respect to the parameter values of acquisition, reconstruction and analysis. The ordered subset expectation maximization (OSEM) algorithm was used for reconstructing the lung SPECT images. As a first step towards clinical application of the CVT-method in detecting mild COPD, this study was based on simulated SPECT images of an advanced anthropomorphic lung phantom including respiratory and cardiac motion, where the mild COPD lung had an overall ventilation reduction of 5%. The largest separation between healthy and mild COPD lung images as determined using the CVT-measure of ventilation inhomogeneity and 125 MBq 99mTc was obtained using a low-energy high-resolution collimator and a Butterworth postfilter with a cut-off frequency of 0.6-0.7 cm-1. Sixty-four reconstruction updates should be used when the whole lung is analysed and for the reduced lung a greater number of updates is needed.

National Category
Clinical Medicine
Identifiers
urn:nbn:se:liu:diva-106665 (URN)
Available from: 2014-05-19 Created: 2014-05-19 Last updated: 2015-03-31Bibliographically approved
4. Does quantitative lung SPECT detect lung abnormalities earlier than lung function tests?: Results of a pilot study
Open this publication in new window or tab >>Does quantitative lung SPECT detect lung abnormalities earlier than lung function tests?: Results of a pilot study
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2014 (English)In: EJNMMI Research, ISSN 2191-219X, E-ISSN 2191-219X, Vol. 4, no 39, 1-12 p.Article in journal (Refereed) Published
Abstract [en]

Background: Heterogeneous ventilation in lungs of allergic individuals, cigarette smokers, asthmatics and chronic obstructive pulmonary disease (COPD) patients has been demonstrated using imaging modalities such as PET, MR and SPECT. These individuals suffer from narrow and/or closed airways to various extents. By calculating regional heterogeneity in lung ventilation SPECT images as the coefficient of variation (CV) in small elements of the lung, heterogeneity maps and CV-frequency curves can be generated and used to quantitatively measure heterogeneity. This work explores the potential to use such measurements to detect mild ventilation heterogeneities in lung healthy subjects.

Method: Fourteen healthy subjects without documented lung disease or respiratory symptoms, and two patients with documented airway disease, inhaled on average approximately 90 MBq 99mTc-Technegas immediately prior to the 20 min SPECT acquisition. Variation in activity uptake between subjects was compensated for in resulting CV values. The area under the compensated CV frequency curve (AUC), for CV values greater than a threshold value CVT, AUC(CV> CVT), was used as the measure of ventilation heterogeneity.

Results: Patients with lung function abnormalities, according to lung function tests, generated higher AUC(CV>20%) values compared to healthy subjects (p=0.006). Strong linear correlations with the AUC(CV>20%) values were found for age (p=0.006) and height (p=0.001). These demonstrated that ventilation heterogeneities increased with age and that they depend on lung size. Strong linear correlations were found for the lung function value related to indices of airway closure/air trapping, RV/TLC (p=0.009), and DLCOc (p=0.009), a value partly related to supposed ventilation/perfusion mismatch. These findings support the association between conventional lung function tests and the AUC(CV>20%) value.

Conclusions: Among the healthy subjects there is a group with increased AUC(CV>20%) values, but with normal lung function tests, which implies that it might be possible to differentiate ventilation heterogeneities earlier in a disease process than by lung function tests.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2014
Keyword
Quantitative lung SPECT, ventilation heterogeneities, lung function tests
National Category
Clinical Medicine Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:liu:diva-106666 (URN)10.1186/s13550-014-0039-1 (DOI)000358049300001 ()26055938 (PubMedID)2-s2.0-84905881037 (Scopus ID)
Note

On the date of the defence date of the Ph.D. Thesis the status of this article was Manuscript.

Available from: 2014-05-19 Created: 2014-05-19 Last updated: 2017-12-05Bibliographically approved

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Norberg, Pernilla

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