Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2013
ABSTRACT Myocardial perfusion-gated-SPECT (MP-gated-SPECT) imaging often shows radiotracer uptake... more ABSTRACT Myocardial perfusion-gated-SPECT (MP-gated-SPECT) imaging often shows radiotracer uptake in abdominal organs. This accumulation interferes frequently with qualitative and quantitative assessment of the infero-septal region of myocardium. The objective of this study is to evaluate the effect of ingestion of different fat content on the reduction of extra-myocardial uptake and to improve MP-gated-SPECT image quality. In this study, 150 patients (65 ± 18 years) who were referred for MP-gated-SPECT underwent a 1-day-protocol including imaging after stress (physical or pharmacological) and resting conditions. All patients gave written informed consent. Patients were subdivided into five groups: GI, GII, GIII, GIV and GV. In the first four groups, patients ate two chocolate bars with different fat content. Patients in GV – control group (CG) – had just water. Uptake indices (UI) of myocardium (M)/liver(L) and M/stomach–proximal bowel(S) revealed lower UI of M/S at rest in all groups. Both stress and rest studies using different food intake indicate that patients who ate chocolate with different fat content showed better UI of M/L than the CG. The UI of M/L and M/S of groups obtained under physical stress are clearly superior to that of groups obtained under pharmacological stress. These differences are only significant in patients who ate high-fat chocolate or drank water. The analysis of all stress studies together (GI, GII, GIII and GIV) in comparison with CG shows higher mean ranks of UI of M/L for those who ate high-fat chocolate. After pharmacological stress, the mean ranks of UI of M/L were higher for patients who ate high- and low-fat chocolate. In conclusion, eating food with fat content after radiotracer injection increases, respectively, the UI of M/L after stress and rest in MP-gated-SPECT studies. It is, therefore, recommended that patients eat a chocolate bar after radiotracer injection and before image acquisition.
Compressed sensing (CS) is a new approach in medical imaging which allows a sparse image to be re... more Compressed sensing (CS) is a new approach in medical imaging which allows a sparse image to be reconstructed from undersampled data. Total variation (TV) based minimization algorithms are the one CS technique that has achieved great success due to its virtue of preserving edges while reducing image noise. The purpose of this work is to implement and evaluate the performance of a TV minimization filter able to increase the signal difference to noise ratio (SDNR) of digital breast tomosynthesis (DBT) images. Assuming a Poisson noise model, the authors present a practical methodology, based on Rudin, Osher, and Fatemi model, which directly applies a TV minimization filter to real phantom and clinical DBT images. Different moments of filter application (before and after image reconstruction) and the suitable Lagrange multiplier (λ) to be used in filter equation are studied. Also, the relationship between background standard deviation (σB) of unfiltered images and optimal λ values is det...
In this work we use the NEC transformation method in the OSEM reconstruction technique as a proce... more In this work we use the NEC transformation method in the OSEM reconstruction technique as a procedure to partially restore the Poisson characteristics of 3D whole-body PET precorrected data. We compare the use of FORE+NEC-OSEM with a fully 3D implementation of NEC-OSEM, in terms of lesion detectability, using a 3D version of the nonprewhitening matched filter numerical observer. In FORE+NEC-OSEM, only a multiplicative weight was applied (NEC-scaling) that accounts for the effects of both the quantitative corrections and FORE itself. For the fully 3D reconstruction, the generalized NEC-transformation was used (NECG-OSEM3D), with both multiplicative (NEC-scaling) and additive (NEC-shifting) factors to account for the effects of the corrections. In addition to NEC-OSEM, FORE+AW-OSEM (attenuation weighted) and ANW-OSEM3D (attenuation and normalization weighted) were also tested. We used simulated data of 3D whole-body PET exams with 1 cm diameter inserted lesions to perform the study. From the results we conclude: for the existence of an optimum postsmoothing filter with FWHM of 5.5 mm; for an overall better performance of both ANW-OSEM3D and FORE+NEC-OSEM over FORE+AW-OSEM. The comparison between NECG-OSEM3D and the other algorithms depends very much on the number of iterations. The NPWMF numerical observer seems not to be the best figure-of-merit to determine the optimum number of iterations the NPWMF.
Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2013
ABSTRACT Myocardial perfusion-gated-SPECT (MP-gated-SPECT) imaging often shows radiotracer uptake... more ABSTRACT Myocardial perfusion-gated-SPECT (MP-gated-SPECT) imaging often shows radiotracer uptake in abdominal organs. This accumulation interferes frequently with qualitative and quantitative assessment of the infero-septal region of myocardium. The objective of this study is to evaluate the effect of ingestion of different fat content on the reduction of extra-myocardial uptake and to improve MP-gated-SPECT image quality. In this study, 150 patients (65 ± 18 years) who were referred for MP-gated-SPECT underwent a 1-day-protocol including imaging after stress (physical or pharmacological) and resting conditions. All patients gave written informed consent. Patients were subdivided into five groups: GI, GII, GIII, GIV and GV. In the first four groups, patients ate two chocolate bars with different fat content. Patients in GV – control group (CG) – had just water. Uptake indices (UI) of myocardium (M)/liver(L) and M/stomach–proximal bowel(S) revealed lower UI of M/S at rest in all groups. Both stress and rest studies using different food intake indicate that patients who ate chocolate with different fat content showed better UI of M/L than the CG. The UI of M/L and M/S of groups obtained under physical stress are clearly superior to that of groups obtained under pharmacological stress. These differences are only significant in patients who ate high-fat chocolate or drank water. The analysis of all stress studies together (GI, GII, GIII and GIV) in comparison with CG shows higher mean ranks of UI of M/L for those who ate high-fat chocolate. After pharmacological stress, the mean ranks of UI of M/L were higher for patients who ate high- and low-fat chocolate. In conclusion, eating food with fat content after radiotracer injection increases, respectively, the UI of M/L after stress and rest in MP-gated-SPECT studies. It is, therefore, recommended that patients eat a chocolate bar after radiotracer injection and before image acquisition.
Compressed sensing (CS) is a new approach in medical imaging which allows a sparse image to be re... more Compressed sensing (CS) is a new approach in medical imaging which allows a sparse image to be reconstructed from undersampled data. Total variation (TV) based minimization algorithms are the one CS technique that has achieved great success due to its virtue of preserving edges while reducing image noise. The purpose of this work is to implement and evaluate the performance of a TV minimization filter able to increase the signal difference to noise ratio (SDNR) of digital breast tomosynthesis (DBT) images. Assuming a Poisson noise model, the authors present a practical methodology, based on Rudin, Osher, and Fatemi model, which directly applies a TV minimization filter to real phantom and clinical DBT images. Different moments of filter application (before and after image reconstruction) and the suitable Lagrange multiplier (λ) to be used in filter equation are studied. Also, the relationship between background standard deviation (σB) of unfiltered images and optimal λ values is det...
In this work we use the NEC transformation method in the OSEM reconstruction technique as a proce... more In this work we use the NEC transformation method in the OSEM reconstruction technique as a procedure to partially restore the Poisson characteristics of 3D whole-body PET precorrected data. We compare the use of FORE+NEC-OSEM with a fully 3D implementation of NEC-OSEM, in terms of lesion detectability, using a 3D version of the nonprewhitening matched filter numerical observer. In FORE+NEC-OSEM, only a multiplicative weight was applied (NEC-scaling) that accounts for the effects of both the quantitative corrections and FORE itself. For the fully 3D reconstruction, the generalized NEC-transformation was used (NECG-OSEM3D), with both multiplicative (NEC-scaling) and additive (NEC-shifting) factors to account for the effects of the corrections. In addition to NEC-OSEM, FORE+AW-OSEM (attenuation weighted) and ANW-OSEM3D (attenuation and normalization weighted) were also tested. We used simulated data of 3D whole-body PET exams with 1 cm diameter inserted lesions to perform the study. From the results we conclude: for the existence of an optimum postsmoothing filter with FWHM of 5.5 mm; for an overall better performance of both ANW-OSEM3D and FORE+NEC-OSEM over FORE+AW-OSEM. The comparison between NECG-OSEM3D and the other algorithms depends very much on the number of iterations. The NPWMF numerical observer seems not to be the best figure-of-merit to determine the optimum number of iterations the NPWMF.
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Papers by Pedro Almeida