3,642 research outputs found
A Semi-parametric Technique for the Quantitative Analysis of Dynamic Contrast-enhanced MR Images Based on Bayesian P-splines
Dynamic Contrast-enhanced Magnetic Resonance Imaging (DCE-MRI) is an
important tool for detecting subtle kinetic changes in cancerous tissue.
Quantitative analysis of DCE-MRI typically involves the convolution of an
arterial input function (AIF) with a nonlinear pharmacokinetic model of the
contrast agent concentration. Parameters of the kinetic model are biologically
meaningful, but the optimization of the non-linear model has significant
computational issues. In practice, convergence of the optimization algorithm is
not guaranteed and the accuracy of the model fitting may be compromised. To
overcome this problems, this paper proposes a semi-parametric penalized spline
smoothing approach, with which the AIF is convolved with a set of B-splines to
produce a design matrix using locally adaptive smoothing parameters based on
Bayesian penalized spline models (P-splines). It has been shown that kinetic
parameter estimation can be obtained from the resulting deconvolved response
function, which also includes the onset of contrast enhancement. Detailed
validation of the method, both with simulated and in vivo data, is provided
Combination GLP-1 and Insulin Treatment Fails to Alter Myocardial Fuel Selection Versus Insulin Alone in Type 2 Diabetes
Context
Glucagon-like peptide-1 (GLP-1) and the clinically available GLP-1 agonists have been shown to exert effects on the heart. It is unclear whether these effects occur at clinically used doses in vivo in humans, possibly contributing to CVD risk reduction.
Objective
To determine whether liraglutide at clinical dosing augments myocardial glucose uptake alone or in combination with insulin compared to insulin alone in metformin-treated Type 2 diabetes mellitus.
Design
Comparison of myocardial fuel utilization after 3 months of treatment with insulin detemir, liraglutide, or combination detemir+liraglutide.
Setting
Academic hospital
Participants
Type 2 diabetes treated with metformin plus oral agents or basal insulin.
Interventions
Insulin detemir, liraglutide, or combination added to background metformin
Main Outcome Measures
Myocardial blood flow, fuel selection and rates of fuel utilization evaluated using positron emission tomography, powered to demonstrate large effects.
Results
We observed greater myocardial blood flow in the insulin-treated groups (median[25th, 75th percentile]: detemir 0.64[0.50, 0.69], liraglutide 0.52[0.46, 0.58] and detemir+liraglutide 0.75[0.55, 0.77] mL/g/min, p=0.035 comparing 3 groups and p=0.01 comparing detemir groups to liraglutide alone). There were no evident differences between groups in myocardial glucose uptake (detemir 0.040[0.013, 0.049], liraglutide 0.055[0.019, 0.105], detemir+liraglutide 0.037[0.009, 0.046] µmol/g/min, p=0.68 comparing 3 groups). Similarly there were no treatment group differences in measures of myocardial fatty acid uptake or handling, and no differences in total oxidation rate.
Conclusions
These observations argue against large effects of GLP-1 agonists on myocardial fuel metabolism as mediators of beneficial treatment effects on myocardial function and ischemia protection
Optimized acquisition time and image sampling for dynamic SPECT of Tl-201
Author name used in this publication: Dagan FengAuthor name used in this publication: Pak-Kong LunVersion of RecordPublishe
Estimation of input function and kinetic parameters using simulated annealing : application in a flow model
Author name used in this publication: Dagan FengCentre for Multimedia Signal Processing, Department of Electronic and Information Engineering2002-2003 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Characterization of 3D PET systems for accurate quantification of myocardial blood flow
Three-dimensional (3D) mode imaging is the current standard for positron
emission tomography-computed tomography (PET-CT) systems. Dynamic imaging for
quantification of myocardial blood flow (MBF) with short-lived tracers, such as Rb-82-
chloride (Rb-82), requires accuracy to be maintained over a wide range of isotope
activities and scanner count-rates. We propose new performance standard
measurements to characterize the dynamic range of PET systems for accurate
quantitative imaging. Methods: 1100-3000 MBq of Rb-82 or N-13-ammonia was injected
into the heart wall insert of an anthropomorphic torso phantom. A decaying isotope scan
was performed over 5 half-lives on 9 different 3D PET-CT systems and 1 3D/twodimensional
(2D) PET-only system. Dynamic images (28x15s) were reconstructed using
iterative algorithms with all corrections enabled. Dynamic range was defined as the
maximum activity in the myocardial wall with <10% bias, from which corresponding
dead-time, count-rates and/or injected activity limits were established for each scanner.
Scatter correction residual bias was estimated as the maximum cavity blood-tomyocardium
activity ratio. Image quality was assessed via the coefficient of variation
measuring non-uniformity of the left ventricle (LV) myocardium activity distribution.
Results: Maximum recommended injected activity/body-weight, peak dead-time
correction factor, count-rates and residual scatter bias for accurate cardiac MBF imaging
were: 3-14 MBq/kg, 1.5-4.0, 22-64 Mcps singles and 4-14 Mcps prompt coincidence
count-rates, and 2-10% on the investigated scanners. Non-uniformity of the myocardial
activity distribution varied from 3-16%. Conclusion: Accurate dynamic imaging is
possible on the 10 3D-PET systems if the maximum injected MBq/kg values are
respected to limit peak dead-time losses during the bolus first-pass transit
Cardiac PET/CT with Rb-82: optimization of image acquisition and reconstruction parameters.
Our aim was to characterize the influence of time-of-flight (TOF) and point spread function (PSF) recovery corrections, as well as ordered subset expectation maximization (OSEM) reconstruction parameters, in (82)Rb PET/CT quantification of myocardial blood flow (MBF) and myocardial flow reserve (MFR). Rest and stress list-mode dynamic (82)Rb PET acquisition data from 10 patients without myocardial flow defects and 10 patients with myocardial blood flow defects were reconstructed retrospectively. OSEM reconstructions were performed with Gaussian filters of 4, 6, and 8 mm, different iterations, and subset numbers (2 × 24; 2 × 16; 3 × 16; 4 × 16). Rest and stress global, regional, and segmental MBF and MFR were computed from time activity curves with FlowQuant(©) software. Left ventricular segmentation using the 17-segment American Heart Association model was obtained.
Whole left ventricle (LV) MBF at rest and stress were 0.97 ± 0.30 and 2.30 ± 1.00 mL/min/g, respectively, and MFR was 2.40 ± 1.13. Concordance was excellent and all reconstruction parameters had no significant impact on MBF, except for the exclusion of TOF which led to significantly decreased concordance in rest and stress MBF in patients with or without perfusion defects on a coronary artery basis and in MFR in patients with perfusion defects.
Changes in reconstruction parameters in perfusion (82)Rb PET/CT studies influence quantitative MBF analysis. The inclusion of TOF information in the tomographic reconstructions had significant impact in MBF quantification
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Improving PET-Based Physiological Quantification Through Methods of Wavelet Denoising
The goal of this study was to evaluate methods of multidimensional wavelet denoising on restoring the fidelity of biological signals hidden within dynamic positron emission tomography (PET) images. A reduction of noise within pixels, between adjacent regions, and time-serial frames was achieved via redundant multiscale representations. In analyzing dynamic PET data of healthy volunteers, a multiscale method improved the estimate-to-error ratio of flows fivefold without loss of detail. This technique also maintained accuracy of flow estimates in comparison with the "gold standard," using dynamic PET with O15-water. In addition, in studies of coronary disease patients, flow patterns were preserved and infarcted regions were well differentiated from normal regions. The results show that a wavelet-based noise-suppression method produced reliable approximations of salient underlying signals and led to an accurate quantification of myocardial perfusion. The described protocol can be generalized to other temporal biomedical imaging modalities including functional magnetic resonance imaging and ultrasound
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