scholarly journals Evaluation of Image Quality Improvements When Adding Patient Outline Constraints into a Generalized Scatter PET Reconstruction Algorithm

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Hongyan Sun ◽  
Stephen Pistorius
Keyword(s):  
Expectation Maximization ◽  
Reconstruction Algorithm ◽  
Geometrical Shape ◽  
Quality Improvements ◽  
Positron Emission ◽  
Cold Source ◽  
Quantitative Accuracy ◽  
Relative Standard ◽  
Maximum Likelihood Expectation Maximization ◽  
Pet Reconstruction

Scattered coincidences degrade image contrast and compromise quantitative accuracy in positron emission tomography (PET). A number of approaches to estimating and correcting scattered coincidences have been proposed, but most of them are based on estimating and subtracting a scatter sinogram from the measured data. We have previously shown that both true and scattered coincidences can be treated similarly by using Compton scattering kinematics to define a locus of scattering which may in turn be used to reconstruct the activity distribution using a generalized scatter maximum-likelihood expectation maximization (GS-MLEM) algorithm. The annihilation position can be further confined by taking advantage of the patient outline (or a geometrical shape that encompasses the patient outline). The proposed method was tested on a phantom generated using GATE. The results have shown that for scatter fractions of 10–60% this algorithm improves the contrast recovery coefficients (CRC) by 4 to 28.6% for a source and 5.1 to 40% for a cold source while the relative standard deviation (RSD) was reduced. Including scattered photons directly into the reconstruction eliminates the need for (often empirical) scatter corrections, and further improvements in the contrast and noise properties of the reconstructed images can be made by including the patient outline in the reconstruction algorithm as a constraint.

scholarly journals Evaluation of the Feasibility and Quantitative Accuracy of a Generalized Scatter 2D PET Reconstruction Method

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Hongyan Sun ◽  
Stephen Pistorius
Keyword(s):  
Expectation Maximization ◽  
Reconstruction Algorithm ◽  
Reconstruction Method ◽  
Diagnostic Quality ◽  
Reconstruction Methods ◽  
Positron Emission ◽  
Quantitative Accuracy ◽  
Maximum Likelihood Expectation Maximization ◽  
Pet Reconstruction ◽  
Limiting Case

Scatter degrades the contrast and quantitative accuracy of positron emission tomography (PET) images, and most methods for estimating and correcting scattered coincidences in PET subtract scattered events from the measured data. Compton scattering kinematics can be used to map out the locus of possible scattering locations. These curved lines (2D) or surfaces (3D), which connect the coincidence detectors, encompass the surface (2D) or volume (3D) where the decay occurs. In the limiting case where the scattering angle approaches zero, the scattered coincidence approaches the true coincidence. Therefore, both true and scattered coincidences can be considered similarly in a generalized scatter maximum-likelihood expectation-maximization reconstruction algorithm. The proposed method was tested using list-mode data obtained from a GATE simulation of a Jaszczak-type phantom. For scatter fractions from 10% to 60%, this approach reduces noise and improves the contrast recovery coefficients by 0.5–3.0% compared with reconstructions using true coincidences and by 3.0–24.5% with conventional reconstruction methods. The results demonstrate that this algorithm is capable of producing images entirely from scattered photons, eliminates the need for scatter corrections, increases image contrast, and reduces noise. This could be used to improve diagnostic quality and/or to reduce patient dose and radiopharmaceutical cost.

scholarly journals Influence of X ray computed tomography (CT) exposure and reconstruction parameters on positron emission tomography (PET) quantitation.

2020 ◽  
Author(s):  
Ivan Ho Shon ◽  
Christopher Reece ◽  
Thomas Hennessy ◽  
Megan Horsfield ◽  
Bruce McBride
Keyword(s):  
Low Dose ◽  
Reconstruction Algorithm ◽  
Lung Tumour ◽  
Beam Hardening ◽  
Low Dose Ct ◽  
Ct Dose ◽  
Positron Emission ◽  
Significant Difference ◽  
Pet Reconstruction ◽  
The Impact

Abstract Background: The CT of PET CT provides diagnostic information, anatomic localisation and attenuation correction (AC). When only AC is required very lose dose CT is desirable. CT iterative reconstruction (IR) improves image quality with lower exposures however there is little data on very low dose IR CT for AC of PET. This work assesses the impact of CT exposure and reconstruction algorithm on PET voxel values.Method: An anthropomorphic torso phantom was filled with physiologically typical [18]F concentrations in heart, liver and background compartments. A 17mm diameter right lung “tumour” filled with [18]F was included (surrounding lung contained no 18[F]). PET was acquired followed by 24 CT acquisitions with varying CT exposures (15 - 50mAs, 80 – 120kVp, pitch 0.671 or 0.828). Each CT was reconstructed twice using filtered back projection (FBP) or IR and these used for AC of PET. The reference PET reconstruction (RR) used CT acquired at 50mAs, 120kVp, pitch 0.828, IR, all others were test PET reconstructions (TR). Regions of interest (ROIs) were drawn in liver, soft tissue and over “tumour” on each TR and compared with the RR. Voxel values in each TR were compared to the RR using a paired t-test and by calculating which and what proportion of voxels in each TR differed by a quantitatively significant difference (QSD) from the RR.Results: TRs reconstructed using lower dose CTs underestimated mean and maximum ROI activity relative to the RR; greater with IR than FBP. Once CT dose index (CTDI) increased to 1 mGy, differences were less than QSD. On voxel analysis all TRs were significantly different to the RR (p <0.0001). TRs reconstructed at the lowest CT exposure with IR had 6% of voxels that differed by greater than QSD. Differences were reduced with increasing CTDI and FBP reconstruction. Voxels which exceeded the QSD were spatially localised to regions of high activity, interfaces between different attenuation and areas of CT beam hardening.Conclusions: Very low dose CT exposures are feasible for accurate PET AC. Scanner and reconstruction specific validation should be employed prior very low dose CT AC for PET.

scholarly journals Influence of X-ray computed tomography (CT) exposure and reconstruction parameters on positron emission tomography (PET) quantitation

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Ivan Ho Shon ◽  
Christopher Reece ◽  
Thomas Hennessy ◽  
Megan Horsfield ◽  
Bruce McBride
Keyword(s):  
Low Dose ◽  
Reconstruction Algorithm ◽  
Lung Tumour ◽  
Beam Hardening ◽  
Low Dose Ct ◽  
Ct Dose ◽  
Positron Emission ◽  
Significant Difference ◽  
Pet Reconstruction ◽  
The Impact

Abstract Background The CT of PET CT provides diagnostic information, anatomic localisation and attenuation correction (AC). When only AC is required, very lose dose CT is desirable. CT iterative reconstruction (IR) improves image quality with lower exposures however there is little data on very low dose IR CT for AC of PET. This work assesses the impact of CT exposure and reconstruction algorithm on PET voxel values. Method An anthropomorphic torso phantom was filled with physiologically typical [18]F concentrations in heart, liver and background compartments. A 17-mm-diameter right lung “tumour” filled with [18]F was included (surrounding lung contained no 18[F]). PET was acquired followed by 24 CT acquisitions with varying CT exposures (15–50 mAs, 80–120 kVp, pitch 0.671 or 0.828). Each CT was reconstructed twice using filtered back projection (FBP) or IR and these used for AC of PET. The reference PET reconstruction (RR) used CT acquired at 50 mAs, 120 kVp, pitch 0.828, IR, all others were test PET reconstructions (TR). Regions of interest (ROIs) were drawn in the liver, soft tissue and over “tumour” on each TR and compared with the RR. Voxel values in each TR were compared to the RR using a paired t test and by calculating which and what proportion of voxels in each TR differed by a quantitatively significant difference (QSD) from the RR. Results TRs reconstructed using lower dose CTs underestimated mean and maximum ROI activity relative to the RR; greater with IR than FBP. Once CT dose index (CTDI) increased to 1 mGy, differences were less than QSD. On voxel analysis, all TRs were significantly different to the RR (p < 0.0001). TRs reconstructed at the lowest CT exposure with IR had 6% of voxels that differed by greater than QSD. Differences were reduced with increasing CTDI and FBP reconstruction. Voxels which exceeded the QSD were spatially localised to regions of high activity, interfaces between different attenuation and areas of CT beam hardening. Conclusions Very low dose CT exposures are feasible for accurate PET AC. Scanner- and reconstruction-specific validation should be employed prior very low dose CT AC for PET.

scholarly journals Influence of X Ray Computed Tomography (CT) Exposure and Reconstruction Parameters on Positron Emission Tomography (PET) Quantitation

2020 ◽  
Author(s):  
Ivan Ho Shon ◽  
Christopher Reece ◽  
Thomas Hennessy ◽  
Megan Horsfield ◽  
Bruce McBride
Keyword(s):  
Low Dose ◽  
Reconstruction Algorithm ◽  
Beam Hardening ◽  
Low Dose Ct ◽  
Ct Dose ◽  
Positron Emission ◽  
Significant Difference ◽  
Pet Reconstruction ◽  
The Right ◽  
The Impact

Abstract Background:The CT of PET CT provides diagnostic information, anatomic localisation and attenuation correction (AC). When only ACis required very lose dose CT is desirable.CT Iterative reconstruction (IR) improves image quality with lower exposures however there is little data on very low dose IR CT for AC of PET. This work aims to assess the impact of CT exposure and reconstruction algorithm on PET voxel values.Method: An anthropomorphic torso phantom was filled with physiologically typical [18]F concentrations in heart, liver and background compartments. A 17mm diameter “tumour” was included in the right lung. PET was acquired followed by 24 CT acquisitions with varying CT exposures (15-50mAs, 80 – 120kVp, pitch 0.671 - 0.828). Each CT was reconstructed twice using filtered back projection (FBP) or IR and these used for AC of PET. Regions of interest (ROIs) were drawn in liver, soft tissue and over “tumour” on each test reconstruction (TR) and compared with the reference reconstruction (RR), (50mAs, 120kVp, pitch 0.828, IR). Comparison of voxel values in each TR compared to the RR was undertaken using a paired t-test and by calculating which and what proportion of voxels in each TR differed by a quantitatively significant difference (QSD) from the corresponding RR voxel.Results: TRs reconstructed using lower dose CTs underestimated mean and maximum ROI activity relative to the RR; greater with IR than FBP. Once CT dose index (CTDI)increased to 1 mGythe differences were less than QSD. On voxel analysis all TRs were significantly different to the RR (p <0.0001). TRs reconstructed at the lowest CT exposure with IR had 6% of voxels that differed by greater than the QSD. Differences were reduced with increasing CTDI and FBP reconstruction. Voxels which exceeded the QSD were spatially localised to regions of high activity, at interfaces between different attenuation and in areas of CT beam hardening.Conclusions: Very low dose CT exposures are feasible for accurate PET AC. Scanner specific validation should be employed prior very low dose CT AC for PET reconstruction.

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