Karin Knesaurek

A new iterative reconstruction technique for attenuation correction in high-resolution positron emission tomography

A new iterative reconstruction technique (NIRT) for positron emission computed tomography (PET), which uses transmission data for nonuniform attenuation correction, is described. Utilizing the general inverse problem theory, a cost functional which includes a noise term was derived. The cost functional was minimized using a weighted-least-square maximum a posteriori conjugate gradient (CG) method. The procedure involves a change in the Hessian of the cost function by adding an additional term. Two phantoms were used in a real data acquisition. The first was a cylinder phantom filled with uniformly distributed activity of 74 MBq of fluorine-18. Two different inserts were placed in the phantom. The second was a Hoffman brain phantom filled with uniformly distributed activity of 7.4 MBq of18F. Resulting reconstructed images were used to test and compare a new iterative reconstruction technique with a standard filtered backprojection (FBP) method. The results confirmed that NIRT, based on the conjugate gradient method, converges rapidly and provides good reconstructed images. In comparison with standard results obtained by the FBP method, the images reconstructed by NIRT showed better noise properties. The noise was measured as rms% noise and was less, by a factor of 1.75, in images reconstructed by NIRT than in the same images reconstructed by FBP. The distance between the Hoffman brain slice reconstructed by FBP and the perfect PET Hoffman brain slice created from the MRI image was 0.526, while the same distance for the Hoffman brain slice reconstructed by NIRT was 0.328. The NIRT method suppressed the propagation of the noise without visible loss of resolution in the reconstructed PET images.

Two new experimental methods of calculating scatter fraction as a function of depth in scattering media: a comparison study.

Two new experimental methods of calculating scatter fraction (SF), as a function of depth, are presented and used in a comparison study. These methods are based on the assumptions that the total point spread function (psft) consists of geometrical (psfg) and scattering (psfs) components, and that the psft and its components are radially symmetric functions. Both methods assume that psfg is a two-dimensional (2-D) Gaussian function. The first proposed method is based on the serial model of the psft. According to the serial model, psfs is also a 2-D Gaussian function. However, the second method is based on the assumption that the psfs is a monoexponential function. Thus the main difference between these two experimental methods is the way in which the psfs is treated. Published data obtained by Monte Carlo simulations compared to the new experimental results shows that for depths less than 5 cm, both new methods yield smaller values for scatter fraction than Monte Carlo simulation or the subtraction method. However, for depths from 5 to 20 cm, the results of these two new methods were very close to the values obtained by both the Monte Carlo simulation and the subtraction method. These two methods have allowed assessment of the scatter fraction with higher accuracy and reliability and reporting data concludes that the new methods are less error sensitive than the subtraction method.

Comparison of correction techniques for simultaneous 201Tl/99mTc myocardial perfusion SPECT imaging: a dog study

We compared two correction methods for simultaneous 201Tl/99mTc dual-isotope single-photon emission computed tomography (SPECT). Both approaches use the information from the third energy window placed between the photopeak windows of the 201Tl and 99mTc. The first approach, described by Moore et al, corrects only for the contribution of the 99mTc to the 201Tl primary 70 keV window. We developed the three-window transformation dual isotope correction method, which is a simultaneous cross-talk correction. The two correction methods were compared in a simultaneous 201Tl/99mTc sestamibi cardiac dog study. Three separate acquisitions were performed in this dog study: two single-isotope and one dual-isotope acquisition. The 201Tl single-isotope images were used as references. The total number of counts, and the contrast between the left ventricular cavity (LVC) and the myocardium, were used in 70 keV short axis slices as parameters for evaluating the results of the dual-isotope correction methods. Three consecutive short-axis slices were used to calculate averaged contrast and the averaged total number of counts. The total number of the counts was 667000+/-500 and 414500+/-400 counts for the dual isotope (201Tl+/-99mTc) and single-isotope (201Tl-only) 70 keV images, respectively. The corrected dual-isotope images had 514700+/-700 and 368000+/-600 counts for Moores correction and our approach, respectively. Moores method improved contrast in the dual isotope 70 keV image to 0.14+/-0.03 from 0.11+/-0.02, which was the value in the 70 keV non-corrected dual-isotope image. Our method improved the same contrast to 0.22+/-0.03. The contrast in the 201Tl single-isotope 70 keV image was 0.28+/-0.02. Both methods improved the 70 keV dual-isotope images. However, our approach provided slightly better images than Moores correction when compared with 201Tl-only 70 keV images.

Phantom study to determine optimal PET reconstruction parameters for PET/MR imaging of 90Y microspheres following radioembolization

Yttrium-90 (90Y) radioembolization involves the intra-arterial delivery of radioactive microspheres for treating liver tumors. Although primarily a β − emitter, 90Y occasionally emits positrons via internal pair production. There is growing interest in positron emission tomography (PET) imaging of these microspheres following radioembolization to localize and quantify their distribution. Due to the low abundance of positron emission (0.0032%), the PET images are highly sensitive to the parameters of iterative reconstruction algorithms used in clinical PET imaging. In this study, we aim to determine the optimal 90Y PET reconstruction parameters for PET/MRI that provide maximal activity recovery while maintaining a moderate noise level. We imaged an ACR phantom filled with 90Y chloride solution on two Siemens Biograph mMR scanners with a total activity of 1.00 GBq–7.43 GBq. Images were reconstructed with varying iteration number, post-reconstruction filter size, and scatter correction method. In addition, we evaluated the effects of incorporating point spread function (PSF) compensation as well as reducing the scan time and imaging off the central axis of the scanner in order to simulate realistic patient acquisition protocols as closely as possible. Recovery coefficients (RCs) for hot cylinders 8–25 mm in diameter reached near convergence with limited noise at 3 iterations, 21 subsets, 5 mm FWHM Gaussian post-reconstruction filter, use of PSF compensation, and absolute scatter correction across all scans. RCs increased by as much as 17% and noise decreased by as much as 29% when scan time duration was 30 min compared to only 15 min. Images acquired with the phantom placed 7–10 cm off the central axis of the scanner exhibited slightly reduced RCs, especially for the lowest activity scan. Although optimal reconstruction parameters with current reconstruction software were determined in this study, these parameters failed to achieve perfect count recovery, suggesting further investigation of 90Y PET imaging is required.

Optimization of yttrium-90 PET for simultaneous PET/MR imaging: A phantom study

PURPOSE Positron emission tomography (PET) imaging of yttrium-90 in the liver post radioembolization has been shown useful for personalized dosimetry calculations and evaluation of extrahepatic deposition. The purpose of this study was to quantify the benefits of several MR-based data correction approaches offered by using a combined PET/MR system to improve Y-90 PET imaging. In particular, the feasibility of motion and partial volume corrections were investigated in a controlled phantom study. METHODS The ACR phantom was filled with an initial concentration of 8 GBq of Y-90 solution resulting in a contrast of 10:1 between the hot cylinders and the background. Y-90 PET motion correction through motion estimates from MR navigators was evaluated by using a custom-built motion stage that simulated realistic amplitudes of respiration-induced liver motion. Finally, the feasibility of an MR-based partial volume correction method was evaluated using a wavelet decomposition approach. RESULTS Motion resulted in a large (∼40%) loss of contrast recovery for the 8 mm cylinder in the phantom, but was corrected for after MR-based motion correction was applied. Partial volume correction improved contrast recovery by 13% for the 8 mm cylinder. CONCLUSIONS MR-based data correction improves Y-90 PET imaging on simultaneous PET/MR systems. Assessment of these methods must be studied further in the clinical setting.

Comparison of standardized uptake value ratio calculations in amyloid positron emission tomography brain imaging

Amyloid positron emission tomography (PET) imaging with florbetapir 18F (18F-AV-45) allows in vivo assessment of cerebral amyloid load and can be used in the evaluation of progression of Alzheimers disease (AD) and other dementias associated with b-amyloid. However, cortical amyloid deposition can occur in healthy cases, as well as in patients with AD and quantification of cortical amyloid burden can improve the 18F-AV-45 PET imaging evaluations. The quantification is mostly performed by cortical-to-cerebellum standardized uptake value ratio (SUVr). The aim of our study was to compare two methods for SUVr calculations in amyloid florbetapir 18F PET brain imaging. In amyloid florbetapir 18F PET brain imaging study, we imaged 42 cases with the mean age of 72.6 ± 9.9 (mean ± standard deviation). They were imaged on different PET/computed tomography systems with 369.0 ± 34.2 kBq of 18F florbetapir. Data were reconstructed using the vendors reconstruction software. Corresponding magnetic resonance imaging (MRI) data were retrieved, and matched PET and MRI data were transferred to a common platform. Two methods were used for the calculation of the ratio of cortical-to-cerebellar signal (SUVr). One method was based on the MIM Software Inc., Version 6.4 software and only uses PET data. The second approach used the PMOD Neuro tool (version 3.5). This approach utilizes PET and corresponding MRI data (preferably T1-weighted) for better brain segmentation. For all the 42 cases, the average SUVr values for MIM and PMOD applications were 1.24 ± 0.26 and 1.22 ± 0.25, respectively, with a mean difference of 0.02 ± 0.15. The repeatability coefficient was 0.15 (12.3% of the mean). The Spearmans rank correlation coefficient was very high, r = 0.96. For amyloid-negative cases, the average SUVr values were lower than all group SUVr average values, 0.96 ± 0.07 and 1.00 ± 0.09, for MIM and PMOD applications, respectively. A mean difference was 0.04 ± 0.12, the repeatability coefficient was 0.12 (12.9% of the mean) and the Spearmans rank correlation coefficient was modest, r = 0.55. For amyloid-positive patients, the average SUVr values were higher than the same all grouP values, 1.34 ± 0.16 and 1.35 ± 0.20, respectively, with a mean difference of 0.01 ± 0.16. The repeatability coefficient was 0.16 (11.9% of the mean). The Spearmans rank correlation coefficient was high, r = 0.93. Our results indicated that the SUVr values derived using MIM and PMOD Neuro are effectively interchangeable and well correlated. However, PET template-based quantification (MIM approach) is clinically friendlier and easier to use. MRI template-based quantification (PMOD Neuro) better delineates different regions of the brain, can be used with any tracer, and therefore is more suitable for research.

Quantitative comparison of pre-therapy 99mTc-macroaggregated albumin SPECT/CT and post-therapy PET/MR studies of patients who have received intra-arterial radioembolization therapy with 90Y microspheres

OBJECTIVE The aim of our study was to compare yttrium -90 (90Y) dosimetry obtained from pre-therapy 99mTc-macroaggregated albumin (MAA) SPECT/CT versus post-therapy PET/MRI imaging among patients with primary or metastatic hepatic tumors. MATERIALS AND METHODS Prior to 90Y radioembolization (RE), 32 patients underwent a scan using MAA mimicking 90Y distribution. After RE with 90Y microspheres, the patients were imaged on a PET/MRI system. Reconstructed images were transferred to a common platform and used to calculate 90Y dosimetry. The Passing-Bablok regression scatter diagram and the Bland and Altman method were used to analyze the difference between dosimetry values. RESULTS For MAA and PET/MRI modalities, the mean liver doses for all 32 subjects were 43.0 ± 20.9 Gy and 46.5 ± 22.7 Gy, respectively, with a mean difference of 3.4 ± 6.2 Gy. The repeatibility coefficient was 12.1 (27.0% of the mean). The Spearman rank correlation coefficient was high (ρ = 0.92). Although, there was a substantial difference in the maximum doses to the liver between the modalities, the mean liver doses were relatively close, with a difference of 24.0% or less. CONCLUSIONS The two main contributors to the difference between dosimetry calculations using MAA versus 90Y PET/MRI can be attributed to the changes in catheter positioning as well as the liver ROIs used for the calculations. In spite of these differences, our results demonstrate that the dosimetry values obtained from pre-therapy MAA SPECT/CT scans and PET/MRI post-therapy 90Y studies were not significantly different.

TAU IMAGING WITH [ 18 F]T807/AV-1451 IN ATHLETES WITH POST-CONCUSSIVE COMPLAINT AND CONTROLS

P4-232 TAU IMAGING WITH [F]T807/AV-1451 IN ATHLETES WITH POST-CONCUSSIVE COMPLAINTAND CONTROLS Samuel Gandy,DaraDickstein, Mariel Pullman, Jennifer Short, Lale Kostakoglu, Karin Knesaurek, Barry Jordan, Wayne Gordon, Kristen Dams-O’Connor, Cheuk Tang, Edmund Wong, Steven DeKosky, James Stone, George Farmer, Elaine R. Peskind,Mary Sano, Patrick R. Hof, James J. Peters VA Medical Center, Bronx, NY, USA; Uniformes Services University of Health Science, Bethsda, MD, USA; Icahn School of Medicine at Mount Sinai, New York, NY, USA; Mount Sinai, New York, NY, USA; Burke Rehabilitation Hospital, White Plains, NY, USA; Burke Rehabilitation Hospital/Burke Med Res Inst, White Plains, NY, USA; University of Florida, Gainesville, FL, USA; University of Virginia, Charlottesville, VA, USA; Cortice Biosciences, New York, NY, USA; Veterans Affairs Puget Sound Health Care System, Seattle, WA, USA. Contact e-mail: dara.dickstein.ctr@usuhs.edu Figure 1. Brain regions showing significant correlation between PCC functional connectivity and the decline of IQ, (A) aMCI group; (B) mild AD group. Visual inspection reveals the differential correlation pattern between aMCI group and mild AD group. The maps are the results of correlation analysis with corrected p<0.001 and cluster size>(A) 31 voxels; (B) 75 voxels, respectively. Red and blue denotes positive and negative functional connectivity. The color bar indicated the z-values. For the details of the involved regions, see Table 1. PCC, Posterior cingulate cortex. Background:Chronic post-concussive syndromes are a major source of morbidity and mortality and can develop into neurodegenerative disorders such as chronic traumatic encephalopathy (CTE). Methods:Methods of assessment and prediction of outcome are major areas of research focus, in particular molecular neuroimaging with positron emission tomography (PET) using ligands for neuropathological lesions such as plaques and tangles. CTE is characterized pathologically by the presence of neurofibrillary tau deposits. In living persons, advances in diagnosis have been made through positron emission tomography (PET) using tracers binding to aggregated tau. Here we examined [F]T807 uptake in athletes with mild traumatic brain injury resulting from multiple concussions. Methods:College and professional athletes were included if they reported >1 concussion and cognitive affective or behavioral complaints. LOC > than an hour was exclusionary. Controls without head injury, psychiatric or neurological conditions were matched to age and gender (all males, 24 athletes age 52 6 9.589; 4 controls, age 48 6 5.629). Consented participants were evaluated as part of a research study. All subjects underwent PET for tau ([F]T807/AV-1451) and amyloid ([F]florbetapir/AV45), MRI and neuropsychological and clinical assessment. Results: We report here on 24 athletes and 4 controls. There were minimal differences on cognition between athletes and controls and significant differences in behavioral and affective symptoms. All subjects were negative for [F]florbetapir. Eight of 24 (33%) athletes had abnormal [F]T807 ligand retention and none of the controls did. While the amount of ligand retention varied in athletes, the pattern resembles postmortem CTE, with tau distribution in the sulci. Conclusions:Our study of in vivo imaging of tau deposition in the brains of retired athletes provides insight into the phenomenology and pathogenesis, of CTE. Tauopathy imagingmay provide useful diagnostic or prognostic screening information. This research was supported by a grant from the Alzheimer’s Disease Drug Foundation.