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Optimization of Ordered Subset Expectation Maximization Reconstruction for Reducing Urinary Bladder Artifacts in Single-photon Emission Computed Tomography Imaging.

Katua AM, Ankrah AO, Vorster M, van Gelder A, Sathekge MM - World J Nucl Med (2011)

Bottom Line: Four iterations and 8 subsets yielded the best results in 48.5% of the images, whilst 2 iterations and 8 subsets yielded the best results in 33.8%.The number of reconstructed images which yielded the best results with 2 iterations and 8 subsets was the same as or more than those with 4 iterations and 8 subsets when the bladder/acetabulum ratio (A/B) was between 0.2 and 0.39.FBP) leads to better lesion detectability and characterization.

View Article: PubMed Central - PubMed

Affiliation: Department of Nuclear Medicine, University of Pretoria and Steve Biko Academic Hospital, Pretoria, South Africa.

ABSTRACT
Bladder artifact during bone single-photon emission computed tomography (SPECT) is a common source of error. The extent and severity of bladder artifacts have been described for filtered back projection (FBP) reconstruction. Ordered subset expectation maximization (OSEM) may help to address this problem of bladder artifacts, which render up to 20% of the SPECT images unreadable. The objective of this study was to evaluate the relationship of the bladder to acetabulum ratio in guiding the choice of the number of iterations and subsets used for OSEM reconstruction, for reducing bladder artifacts found on FBP reconstruction. One hundred five patients with various indications for bone scans were selected and planar and SPECT images were acquired. The SPECT images were reconstructed with both FBP and OSEM using four different combinations of iterations and subsets. The images were given to three experienced nuclear physicians who were blinded to the diagnosis and type of reconstruction used. They then labeled images from the best to the worst after which the data were analyzed. The bladder to acetabulum ratio for each image was determined which was then correlated with the different iterations and subsets used. The study demonstrated that reconstruction using OSEM led to better lesion detectability compared to FBP in 87.62% of cases. It further demonstrated that the iterations and subsets used for reconstruction of an image correlate with the bladder to acetabulum ratio. Four iterations and 8 subsets yielded the best results in 48.5% of the images, whilst 2 iterations and 8 subsets yielded the best results in 33.8%. The number of reconstructed images which yielded the best results with 2 iterations and 8 subsets was the same as or more than those with 4 iterations and 8 subsets when the bladder/acetabulum ratio (A/B) was between 0.2 and 0.39. A ratio below 0.2 or above 0.39 supports the usage of 4 iterations and 8 subsets over 2 iterations and 8 subsets. We conclude that bladder to acetabulum ratio can be used to select the optimum number of iterations and subsets for reconstruction of bone SPECT for accurate characterization of lesions. This study also confirms that reconstruction with OSEM (vs. FBP) leads to better lesion detectability and characterization.

No MeSH data available.


Representative images of pelvic SPECT obtained using FBP reconstruction method (a) and OSEM methods (b, c and d). Images (b), (c) and (d) were obtained using 2 × 8, 4 × 8 and 3 × 12 iterations × subsets, respectively. The results clearly demonstrate better quality images with OSEM reconstruction
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Figure 1: Representative images of pelvic SPECT obtained using FBP reconstruction method (a) and OSEM methods (b, c and d). Images (b), (c) and (d) were obtained using 2 × 8, 4 × 8 and 3 × 12 iterations × subsets, respectively. The results clearly demonstrate better quality images with OSEM reconstruction

Mentions: Patients were referred for various indications and we selected those where the primary region of interest was the pelvis or instances where pelvic lesions on planar images could not be confidently characterized in the absence of SPECT imaging. One hundred and five patients consented to the study; however, 25 were lost because of incomplete or lost SPECT images. Of the remaining 80 SPECT images, there was no clearly defined preference of one iterative and subset over the other in 12 patients. The standard departmental imaging protocol was followed for all patients (adapted from current SNM and EANM guidelines) starting with the acquisition of whole body planar/spot images and proceeding to SPECT image acquisition where needed.[78] The SPECT images were reconstructed with both FBP and OSEM using four different combinations of iterations and subsets [Figure 1].


Optimization of Ordered Subset Expectation Maximization Reconstruction for Reducing Urinary Bladder Artifacts in Single-photon Emission Computed Tomography Imaging.

Katua AM, Ankrah AO, Vorster M, van Gelder A, Sathekge MM - World J Nucl Med (2011)

Representative images of pelvic SPECT obtained using FBP reconstruction method (a) and OSEM methods (b, c and d). Images (b), (c) and (d) were obtained using 2 × 8, 4 × 8 and 3 × 12 iterations × subsets, respectively. The results clearly demonstrate better quality images with OSEM reconstruction
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198040&req=5

Figure 1: Representative images of pelvic SPECT obtained using FBP reconstruction method (a) and OSEM methods (b, c and d). Images (b), (c) and (d) were obtained using 2 × 8, 4 × 8 and 3 × 12 iterations × subsets, respectively. The results clearly demonstrate better quality images with OSEM reconstruction
Mentions: Patients were referred for various indications and we selected those where the primary region of interest was the pelvis or instances where pelvic lesions on planar images could not be confidently characterized in the absence of SPECT imaging. One hundred and five patients consented to the study; however, 25 were lost because of incomplete or lost SPECT images. Of the remaining 80 SPECT images, there was no clearly defined preference of one iterative and subset over the other in 12 patients. The standard departmental imaging protocol was followed for all patients (adapted from current SNM and EANM guidelines) starting with the acquisition of whole body planar/spot images and proceeding to SPECT image acquisition where needed.[78] The SPECT images were reconstructed with both FBP and OSEM using four different combinations of iterations and subsets [Figure 1].

Bottom Line: Four iterations and 8 subsets yielded the best results in 48.5% of the images, whilst 2 iterations and 8 subsets yielded the best results in 33.8%.The number of reconstructed images which yielded the best results with 2 iterations and 8 subsets was the same as or more than those with 4 iterations and 8 subsets when the bladder/acetabulum ratio (A/B) was between 0.2 and 0.39.FBP) leads to better lesion detectability and characterization.

View Article: PubMed Central - PubMed

Affiliation: Department of Nuclear Medicine, University of Pretoria and Steve Biko Academic Hospital, Pretoria, South Africa.

ABSTRACT
Bladder artifact during bone single-photon emission computed tomography (SPECT) is a common source of error. The extent and severity of bladder artifacts have been described for filtered back projection (FBP) reconstruction. Ordered subset expectation maximization (OSEM) may help to address this problem of bladder artifacts, which render up to 20% of the SPECT images unreadable. The objective of this study was to evaluate the relationship of the bladder to acetabulum ratio in guiding the choice of the number of iterations and subsets used for OSEM reconstruction, for reducing bladder artifacts found on FBP reconstruction. One hundred five patients with various indications for bone scans were selected and planar and SPECT images were acquired. The SPECT images were reconstructed with both FBP and OSEM using four different combinations of iterations and subsets. The images were given to three experienced nuclear physicians who were blinded to the diagnosis and type of reconstruction used. They then labeled images from the best to the worst after which the data were analyzed. The bladder to acetabulum ratio for each image was determined which was then correlated with the different iterations and subsets used. The study demonstrated that reconstruction using OSEM led to better lesion detectability compared to FBP in 87.62% of cases. It further demonstrated that the iterations and subsets used for reconstruction of an image correlate with the bladder to acetabulum ratio. Four iterations and 8 subsets yielded the best results in 48.5% of the images, whilst 2 iterations and 8 subsets yielded the best results in 33.8%. The number of reconstructed images which yielded the best results with 2 iterations and 8 subsets was the same as or more than those with 4 iterations and 8 subsets when the bladder/acetabulum ratio (A/B) was between 0.2 and 0.39. A ratio below 0.2 or above 0.39 supports the usage of 4 iterations and 8 subsets over 2 iterations and 8 subsets. We conclude that bladder to acetabulum ratio can be used to select the optimum number of iterations and subsets for reconstruction of bone SPECT for accurate characterization of lesions. This study also confirms that reconstruction with OSEM (vs. FBP) leads to better lesion detectability and characterization.

No MeSH data available.