Go Akamatsu

Improvement in PET/CT Image Quality with a Combination of Point-Spread Function and Time-of-Flight in Relation to Reconstruction Parameters

The aim of this study was to investigate the effects of the point-spread function (PSF) and time-of-flight (TOF) on improving 18F-FDG PET/CT images in relation to reconstruction parameters and noise-equivalent counts (NEC). Methods: This study consisted of a phantom study and a retrospective analysis of 39 consecutive patients who underwent clinical 18F-FDG PET/CT. The body phantom of the National Electrical Manufacturers Association and International Electrotechnical Commission with a 10-mm-diameter sphere was filled with an 18F-FDG solution with a 4:1 radioactivity ratio compared with the background. The PET data were reconstructed with the baseline ordered-subsets expectation maximization (OSEM) algorithm, with the OSEM+PSF model, with the OSEM+TOF model, and with the OSEM+PSF+TOF model. We evaluated image quality by visual assessment, the signal-to-noise ratio of the 10-mm sphere (SNR10 mm), the contrast of the 10-mm sphere, and the coefficient of variance in the phantom study and then determined the optimal reconstruction parameters. We also examined the effects of PSF and TOF on the quality of clinical images using the signal-to-noise ratio in the liver (SNRliver) in relation to the NEC in the liver (NECliver). Results: In the phantom study, the SNR10 mm was the highest for the OSEM+PSF+TOF model, and the highest value was obtained at iteration 2 for algorithms with the TOF and at iteration 3 for those without the TOF. In terms of a postsmoothing filter full width at half maximum (FWHM), the high SNR10 mm was obtained with no filtering or was smaller than 2 mm for algorithms with PSF and was 4–6 mm for those without PSF. The balance between the contrast recovery and noise is different for algorithms with either PSF or TOF. A combination of PSF and TOF improved SNR10 mm, contrast, and coefficient of variance, especially with a small-FWHM gaussian filter. In the clinical study, the SNRliver of the low-NECliver group in the OSEM+PSF+TOF model was compared with that of the high-NECliver group in conventional OSEM. The PSF+TOF improved the SNRliver by about 24.9% ± 9.81%. Conclusion: A combination of PSF and TOF clearly improves image quality, whereas optimization of the reconstruction parameters is necessary to obtain the best performance for PSF or TOF. Furthermore, this combination has the potential to provide good image quality with either lower activity or shorter acquisition time, thus improving patient comfort and reducing the radiation burden.

Influences of point-spread function and time-of-flight reconstructions on standardized uptake value of lymph node metastases in FDG-PET

PURPOSE The purpose of this study was to investigate the effects of point-spread function (PSF) and time-of-flight (TOF) on the standardized uptake value (SUV) of lymph node metastasis in FDG-PET/CT. MATERIALS AND METHODS This study evaluated 41 lymph node metastases in 15 patients who had undergone (18)F-FDG PET/CT. The lesion diameters were 2.5 cm or less. The mean short-axis diameter of the lymph nodes was 10.5 ± 3.7 mm (range 4.6-22.8mm). The PET data were reconstructed with baseline OSEM algorithm, with OSEM+PSF, with OSEM+TOF and with OSEM+PSF+TOF. A semi-quantitative analysis was performed using the maximum and mean SUV of lymph node metastases (SUVmax and SUVmean) and mean SUV of normal lung tissue (SUVlung). We also evaluated image quality using the signal-to-noise ratio in the liver (SNRliver). RESULTS Both PSF and TOF increased the SUV of lymph node metastases. The combination of PSF and TOF increased the SUVmax by 43.3% and the SUVmean by 31.6% compared with conventional OSEM. By contrast, the SUVlung was not influenced by PSF and TOF. TOF significantly improved the SNRliver. CONCLUSION PSF and TOF both increased the SUV of lymph node metastases. Although PSF and TOF are considered to improve small-lesion detectability, it is important to be aware that PSF and TOF influence the accuracy of quantitative measurements.

Benefits of point-spread function and time of flight for PET/CT image quality in relation to the body mass index and injected dose.

&NA; The PET image quality of overweight patients and patients who receive low injected doses deteriorates because of increases in statistical noise. The purpose of this study was to investigate the benefits of the point-spread function (PSF) and time-of-flight (TOF) for PET/CT image quality in such patients. Methods The PET images were reconstructed using the baseline ordered-subsets expectation-maximization algorithm (OSEM), OSEM + PSF, OSEM + TOF, and OSEM + PSF + TOF. In the phantom study, we used a National Electrical Manufacturers Association body phantom with different radioactivity concentrations and analyzed image quality using the coefficient of variance in the background (CVphantom). In the clinical study, we retrospectively studied 39 patients who underwent clinical 18F-FDG PET/CT. The patients were classified into groups based on body mass index and injected dose. Image quality was evaluated using the CV in the liver (CVliver). Results In the phantom study, PSF and TOF improved the CVphantom, especially in low-activity models. Among all of the reconstructions, the best CVphantom was obtained with OSEM + PSF + TOF. In the clinical study, the CVliver of the low-dose group with OSEM + PSF + TOF was comparable to that of the high-dose group with conventional OSEM. Conclusions Point-spread function and TOF improved PET/CT image quality for overweight patients who received a lower injected dose. Therefore, the use of PSF and TOF is suggested to maintain the image quality of such patients without extending scanning times. It is greatly beneficial to obtain sufficient image quality for larger patients, especially in delivery institutions where the injection dose cannot be easily increased.

Influence of Statistical Fluctuation on Reproducibility and Accuracy of SUVmax and SUVpeak: A Phantom Study

Standardized uptake values (SUVs) have been widely used in the diagnosis of malignant tumors and in clinical trials of tumor therapies as semiquantitative metrics of tumor 18F-FDG uptake. However, SUVs for small lesions are liable to errors due to partial-volume effect and statistical noise. The purpose of this study was to evaluate the reproducibility and accuracy of maximum and peak SUV (SUVmax and SUVpeak, respectively) of small lesions in phantom experiments. Methods: We used a body phantom with 6 spheres in a quarter warm background. The PET data were acquired for 1,800 s in list-mode, from which data were extracted to generate 15 PET images for each of the 60-, 90-, 120-, 150-, and 180-s scanning times. The SUVmax and SUVpeak of the hot spheres in the 1,800-s scan were used as a reference (SUVref,max and SUVref,peak). Coefficients of variation for both SUVmax and SUVpeak in hot spheres (CVmax and CVpeak) were calculated to evaluate the variability of the SUVs. On the other hand, percentage differences between SUVmax and SUVref,max and between SUVpeak and SUVref,peak were calculated for evaluation of the accuracy of SUV. We additionally examined the coefficients of variation of background activity and the percentage background variability as parameters for the physical assessment of image quality. Results: Visibility of a 10-mm-diameter hot sphere was considerably different among scan frames. The CVmax and CVpeak increased as the sphere size became smaller and as the acquisition time became shorter. SUVmax was generally overestimated as the scan time shortened and the sphere size increased. The SUVmax and SUVpeak of a 37-mm-diameter sphere for 60-s scans had average positive biases of 28.3% and 4.4%, compared with the reference. Conclusion: SUVmax was variable and overestimated as the scan time decreased and the sphere size increased. In contrast, SUVpeak was a more robust and accurate metric than SUVmax. The measurements of SUVpeak (or SUVpeak normalized to lean body mass) in addition to SUVmax are desirable for reproducible and accurate quantification in clinical situations.

Automated PET-only quantification of amyloid deposition with adaptive template and empirically pre-defined ROI

Amyloid PET is useful for early and/or differential diagnosis of Alzheimers disease (AD). Quantification of amyloid deposition using PET has been employed to improve diagnosis and to monitor AD therapy, particularly in research. Although MRI is often used for segmentation of gray matter and for spatial normalization into standard Montreal Neurological Institute (MNI) space where region-of-interest (ROI) template is defined, 3D MRI is not always available in clinical practice. The purpose of this study was to examine the feasibility of PET-only amyloid quantification with an adaptive template and a pre-defined standard ROI template that has been empirically generated from typical cases. A total of 68 subjects who underwent brain (11)C-PiB PET were examined. The (11)C-PiB images were non-linearly spatially normalized to the standard MNI T1 atlas using the same transformation parameters of MRI-based normalization. The automatic-anatomical-labeling-ROI (AAL-ROI) template was applied to the PET images. All voxel values were normalized by the mean value of cerebellar cortex to generate the SUVR-scaled images. Eleven typical positive images and eight typical negative images were normalized and averaged, respectively, and were used as the positive and negative template. Positive and negative masks which consist of voxels with SUVR  ⩾1.7 were extracted from both templates. Empirical PiB-prone ROI (EPP-ROI) was generated by subtracting the negative mask from the positive mask. The (11)C-PiB image of each subject was non-rigidly normalized to the positive and negative template, respectively, and the one with higher cross-correlation was adopted. The EPP-ROI was then inversely transformed to individual PET images. We evaluated differences of SUVR between standard MRI-based method and PET-only method. We additionally evaluated whether the PET-only method would correctly categorize (11)C-PiB scans as positive or negative. Significant correlation was observed between the SUVRs obtained with AAL-ROI and those with EPP-ROI when MRI-based normalization was used, the latter providing higher SUVR. When EPP-ROI was used, MRI-based method and PET-only method provided almost identical SUVR. All (11)C-PiB scans were correctly categorized into positive and negative using a cutoff value of 1.7 as compared to visual interpretation. The (11)C-PiB SUVR were 2.30  ±  0.24 and 1.25  ±  0.11 for the positive and negative images. PET-only amyloid quantification method with adaptive templates and EPP-ROI can provide accurate, robust and simple amyloid quantification without MRI.

Exploratory human PET study of the effectiveness of 11C-ketoprofen methyl ester, a potential biomarker of neuroinflammatory processes in Alzheimer's disease

INTRODUCTION Neuroinflammatory processes play an important role in the pathogenesis of Alzheimers disease (AD). As a biomarker of neuroinflammatory processes, we designed (11)C-labeled ketoprofen methyl ester ([(11)C]KTP-Me) to increase the blood-brain barrier permeability of ketoprofen (KTP), a selective cyclooxygenase-1 (COX-1) inhibitor. Animal studies indicated that [(11)C]KTP-Me enters the brain and accumulates in activated microglia of inflammatory lesions. In a first-in-human study, we reported that [(11)C]KTP-Me is a safe positron emission tomography (PET) tracer and enters the brain; the radioactivity is washed out from normal cerebral tissue. Here we explored the efficacy of [(11)C]KTP-Me as a diagnostic biomarker of neuroinflammatory processes in AD. METHODS [(11)C]KTP-Me was synthesized by rapid C-[(11)C]methylation of [(11)C]CH3I and the corresponding arylacetate precursor. Nine subjects (four healthy subjects, two Pittsburgh compound-B (PiB)-positive patients with mild cognitive impairment (MCI), and three PiB-positive AD patients) underwent a dynamic brain PET scan for 70min after injection. We evaluated differences in cortical retention and washout rate in the brain between healthy subjects and MCI/AD patients. RESULTS A brain distribution pattern reflecting blood flow in the early-phase image was seen in both healthy subjects and MCI/AD patients. Cortical activity gradually cleared in all groups. However, we observed no obvious difference in the washout rate between healthy subjects and MCI/AD patients or between MCI and AD patients. CONCLUSIONS [(11)C]KTP-Me cannot be useful as a potential diagnostic biomarker for MCI/AD. Further improvements in binding affinity and specificity, etc., are needed to be a diagnostic biomarker of neuroinflammation in AD. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE [(11)C]KTP-Me is a new tracer that targets COX-1. [(11)C]KTP-Me is expected to be a diagnostic biomarker of neuroinflammation in AD in the future. The effectiveness was limited in a small number of AD patients. Therefore, further studies are needed to clarify the usefulness of [(11)C]KTP-Me.

Impact of Time-of-Flight PET/CT with a Large Axial Field of View for Reducing Whole-Body Acquisition Time

The aim of this study was to evaluate the imaging performance of 39- and 52-ring time-of-flight (TOF) PET/CT scanners. We also assessed the potential of reducing the scanning time using a 52-ring TOF PET/CT scanner. Methods: PET/CT scanners with 39- and 52-ring lutetium oxyorthosilicate detectors were evaluated. The axial fields of view were 16.2 and 21.6 cm, respectively. We used a National Electrical Manufacturers Association International Electrotechnical Commission body phantom filled with an 18F solution containing background activity of 5.31 and 2.65 kBq/mL for the studies. The sphere-to-background ratio was 4:1. The PET data were acquired for 10 min in 3-dimensional list mode and then reconstructed with both ordered-subsets reconstruction maximization and ordered-subsets reconstruction maximization plus point-spread function plus time-of-flight algorithms. PET images with different acquisition times were reconstructed (from 1 to 10 min). The image quality was physically assessed using the sensitivity, noise-equivalent counting rate, coefficient of variation of background activity, and relative recovery coefficient. Results: The total system sensitivities of the 39- and 52-ring scanners were 5.6 and 9.3 kcps/MBq, respectively. Compared with the 39-ring scanner, the noise-equivalent counting rate of the 52-ring scanner was 60% higher for both the high-activity and the low-activity models. The recovery coefficient was consistent, irrespective of the number of detector rings. The coefficient of variation of the 52-ring scanner using a 3-min acquisition time was equivalent to that of the 39-ring scanner using a 4-min acquisition time. Conclusion: The image quality of the 52-ring scanner is superior to that of the 39-ring scanner. The acquisition time per bed position of the 52-ring system can be reduced by about 25% without compromising image quality. In addition, the number of bed positions required is 25% lower for the 52-ring system. Finally, the examination time required for a whole-body PET scan is considered to be reduced by about 40% if the 52-ring scanner is used.

standardization of dual time point (18F) 2-Deoxy-2-fluoro-D-glucose-positron emission tomography performed with different positron emission tomography scanners using partial volume correction

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Whole-body biodistribution and the influence of body activity on brain kinetic analysis of the 11 C-PiB PET scan

Dynamic 11C-PiB PET imaging with kinetic analysis has been performed for accurate quantification of amyloid binding in patients with Alzheimer’s disease (AD). In this study, we measured the whole-body biodistribution of 11C-PiB in nine subjects. We then evaluated the effect of body activity on quantitative accuracy of brain 11C-PiB three-dimensional (3D) dynamic PET. Based on clinical biodistribution data, we conducted phantom experiments to estimate the effect of body activity on quantification of the brain 3D dynamic 11C-PiB PET data and the error introduced by body activity using six different PET camera models. One of the PET cameras was used to acquire 11C-PiB brain 3D dynamic PET data on a patient with AD. We calculated the distribution volume ratio (DVR) in two kinetic methods using both the original human time-activity-curve (TAC) data and the TAC corrected for the error caused by body activity. In the early phase, both healthy subjects and patients with AD showed a biodistribution of 11C-PiB that reflected regional blood flow. In the simulated early phase of the phantom experiments, activity outside the field of view led to a maximum 6.0% overestimation of brain activity in the vertex region. Conversely, the effect of body activity on the DVR estimate was small (≤1.2%), probably because the tested kinetic methods did not rely heavily on early phase data. These results indicate that the effect of body activity on brain 11C-PiB PET quantification is generally small and that it depends on the method of kinetic analysis, the region of interest, and the PET camera model used.

Technical Considerations on Scanning and Image Analysis for Amyloid PET in Dementia

Brain imaging techniques, such as computed tomography (CT), magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and positron emission tomography (PET), can provide essential and objective information for the early and differential diagnosis of dementia. Amyloid PET is especially useful to evaluate the amyloid-β pathological process as a biomarker of Alzheimers disease. This article reviews critical points about technical considerations on the scanning and image analysis methods for amyloid PET. Each amyloid PET agent has its own proper administration instructions and recommended uptake time, scan duration, and the method of image display and interpretation. In addition, we have introduced general scanning information, including subject positioning, reconstruction parameters, and quantitative and statistical image analysis. We believe that this article could make amyloid PET a more reliable tool in clinical study and practice.