Three-dimensional Ordered Subset Expectation Maximization Research Articles

Feasibility of noise-reduction reconstruction technology based on non-local-mean principle in SiPM-PET/CT

Quantitative values of positron emission tomography (PET) images using non-local-mean in a silicon photomultiplier (SiPM)-PET/computed tomography (CT) system with phantom and clinical images.The evaluation was conducted on a National Electrical Manufacturers Association body phantom with micro-spheres (4, 5, 6, 8, 10, 13 mm) and clinical images using the SiPM-PET/CT system.The signal-to-background ratio of the phantom was set to 4, and all PET image data was obtained and reconstructed using three-dimensional ordered subset expectation maximization, time-of-flight, point-spread function, and a 4-mm Gaussian filter (GF) and clear adaptive low-noise method (CaLM) in mild, standard, and strong intensities.The evaluation included the standardized uptake value (SUV), percent contrast (QH), coefficient of variation of the background area (CVbackground) clinical imaging for SUV of lung nodules, liver signal-to-noise ratio (SNR), and visual evaluation.SUVmax for 8-mm sphere in phantom images at 2 min for GF and CaLM (mild, standard, strong) were 2.11, 2.32, 2.02, and 1.72; the QH, 8 mm was 27.33 %, 27.47 %, 21.81 %, and 16.09 %; and CVbackground was 12.78, 11.35, 7.86, and 4.71, respectively.CaLM demonstrated higher SUVmax in clinical images than GF for all lung nodule sizes. The average SUVmax for nodules with a diameter of ≤ 1 cm were 5.9 ± 2.4, 9.9 ± 4.9, 9.9 ± 5.0, and 9.9 ± 5.0 for GF and CaLM-mild, standard, and strong intensities, respectively.Liver SNRs were higher for CaLM (mild, standard, strong) compared to GF, with increasing CaLM intensity causing higher liver SNR. CaLM-mild and standard demonstrated suitability for diagnosis in visual evaluation.

Evaluation of standardized uptake value on 131I-6β-iodomethyl-19-norcholesterol scintigraphy for diagnosis of primary aldosteronism and correspondence with adrenal venous sampling.

Adrenal venous sampling (AVS) is a reliable method for lateralization of adrenal hormone secretion, which is important for discriminating between aldosterone-producing adenoma and bilateral adrenal hyperplasia, both of which cause primary aldosteronism (PA). The aim of this study was to evaluate the diagnostic accuracy of the maximum and mean standardized uptake values (SUVmax and SUVmean, respectively) of 131I-6β-iodomethyl-19-norcholesterol (NP-59) single-photon emission computed tomography (SPECT) for PA and its correspondence with AVS. Adrenal NP-59 scintigraphy was performed in 14 patients with suspected PA, and AVS was also performed in 7 of them. SUVmax and SUVmean of the adrenal lesions on the dominant side and their ratios to the values on the non-dominant side (SUVRmax and SUVRmean, respectively) were calculated on SPECT images using ordered-subset conjugate gradient minimization (OSCGM) and three-dimensional ordered-subset expectation maximization (3D-OSEM) reconstruction algorithms. SUVmax and SUVmean on NP-59 SPECT images were significantly higher for aldosterone-producing adenoma than for bilateral adrenal hyperplasia or non-functioning adenoma and slightly superior to SUVRmax and SUVRmean (P = 0.0475 and P = 0.0447 vs. P = 0.124 and P = 0.132, respectively, with OSCGM). The respective areas under the receiver-operating characteristic curve for SUV and SUVR were 0.933 and 0.725 with OSCGM and 0.844 and 0.750 with 3D-OSEM, while SUVmax and SUVRmax had exactly the same diagnostic accuracy as SUVmean and SUVRmean. SUV and SUVR were associated with the diagnostic features on AVS and consistent with lateralization by AVS in most patients. In this study, SUV on NP-59 SPECT helped in the diagnosis of PA and was consistent with the results of AVS in nearly all cases.

Beads phantom for evaluating heterogeneity of SUV on 18F-FDG PET images.

This study aimed to develop a dedicated phantom using acrylic beads for texture analysis and to represent heterogeneous 18F-fluorodeoxyglucose (FDG) distributions in various acquisition periods. Images of acrylic spherical beads with or without diameters of 5- and 10-mm representing heterogeneous and homogeneous 18F-FDG distribution in phantoms, respectively, were collected for 20min in list mode. Phantom data were reconstructed using three-dimensional ordered subset expectation maximization with attenuation and scatter corrections, and the time-of-flight algorithm. The beads phantom images were acquired twice to evaluate the robustness of texture features. Thirty-one texture features were extracted, and the robustness of texture feature values was evaluated by calculating the percentage of coefficient of variation (%COV) and intraclass coefficient of correlation (ICC). Cross-correlation coefficients among texture feature values were clustered to classify the characteristics of these features. Heterogeneous 18F-FDG distribution was represented by the beads phantom images. The agreements of %COV between two measurements were acceptable (ICC ≥ 0.71). All texture features were classified into four groups. Among 31 texture features, 24 exhibited significant different values between phantoms with and without beads in 1-, 2-, 3-, 4-, 5-, 20-min image acquisitions. Whereas, the homogeneous and heterogeneous 18F-FDG distribution could not be discriminated by seven texture features: low gray-level run emphasis, high gray-level run emphasis, short-run low gray-level emphasis, low gray-level zone emphasis, high gray-level zone emphasis, short-zone low gray-level emphasis, and coarseness. We have developed the acrylic beads phantom for texture analysis that could represent heterogeneous 18F-FDG distributions in various acquisition periods. Most texture features could discriminate homogeneous and heterogeneous 18F-FDG distributions in the beads phantom images.

The usefulness of SwiftScan technology for bone scintigraphy using a novel anthropomorphic phantom

The aim of this study was to demonstrate the usefulness of SwiftScan with a low-energy high-resolution and sensitivity (LEHRS) collimator for bone scintigraphy using a novel bone phantom simulating the human body. SwiftScan planar image of lateral view was acquired in clinical condition; thereafter, each planar image of different blend ratio (0–80%) of Crality 2D processing were created. SwiftScan planar images with reduced acquisition time by 25–75% were created by Poisson’s resampling processing. SwiftScan single photon emission computed tomography (SPECT) was acquired with step-and-shoot and continuous mode, and SPECT images were reconstructed using a three-dimensional ordered subset expectation maximization incorporating attenuation, scatter and spatial resolution corrections. SwiftScan planar image showed a high contrast to noise ratio (CNR) and low percent of the coefficient of variance (%CV) compared with conventional planar image. The CNR of the tumor parts in SwiftScan SPECT was higher than that of the conventional SPECT image of step and shoot acquisition, while the %CV showed the lowest value in all systems. In conclusion, SwiftScan planar and SPECT images were able to reduce the image noise compared with planar and SPECT image with a low-energy high-resolution collimator, so that SwiftScan planar and SPECT images could be obtained a high CNR. Furthermore, the SwiftScan planar image was able to reduce the acquisition time by 25% when the blend ratio of Clarity 2D processing set to more than 40%.

Accuracy of metabolic volume and total glycolysis among six threshold-based target segmentation algorithms.

This study aimed to evaluate the accuracy of six threshold-based segmentation methods with different target-to-background ratios (TBR), images with different voxel sizes and image noise, in measuring metabolic volume (MV) and total glycolysis (TG). A standard body phantom consisting of six spheres (inner diameters of 37, 28, 22, 17, 13, and 10mm) was filled with 18F-FDG solution. The background radioactivity level was 2.65kBq/mL, and the TBRs were 4 and 8. PET data were acquired for 30min with list mode. PET data for 30 and 3min were reconstructed with a three-dimensional ordered subset expectation maximization algorithm plus time-of-flight information with images with 2 and 4mm isotropic voxels. The six methods examined were absolute standardized uptake value (SUV) of 2.5 (SUV2.5), 41%, 50%, adaptive 41%, and adaptive 50% thresholds of maximum SUV (Th41, Th50, ThA41, and ThA50, respectively); and the contrast-oriented algorithm (ThCOA). Segmented MV and TG were compared with the actual inner volume and expressed as percentages (%MVseg and %TGseg, respectively). In addition, the segmented MV was converted to the diameter, and the differences of it from the reference diameter were compared among six methods. The ThCOA method yielded the most accurate measurements of %MVseg and %TGseg; the difference between %MVseg or %TGseg and its reference were smaller than 10% in 30-min and 15% in 3-min images, but the segmented contour was almost the same as the reference diameter. Measurements with Th50 and ThCOA were highly accurate for both %MVseg and %TGseg in the large spheres, and the adaptive threshold methods, including ThA41, ThA50, and ThCOA, were also highly accurate in the small spheres. The voxel sizes affected the accuracy of %MVseg and %TGseg with a TBR of 4 in any threshold-based methods. Of the six threshold-based segmentation methods studied, ThCOA was the most accurate method for evaluating MV and TG and had only minor dependence on TBRs and sphere size. The small voxel sizes improved the variation of the accuracy in low TBR.

Fluctuation of quantitative values on acquisition time and the reconstruction conditions in 99mTc-SPECT.

This study aims to carry out a quantitative analysis with high reproducibility using single-photon emission computed tomography/computed tomography (SPECT/CT); we investigated the optimum parameters for the acquisition and the reconstruction. SPECT images were acquired with varying time per view using SPECT phantom (JS-10) and the body phantom of National Electrical Manufacturers Association and International Electrotechnical Commission (Body-phantom), respectively. For the image reconstruction condition, we changed the product of subset and iteration (SI product) and the Gaussian filter using a three-dimensional ordered subset expectation maximization. A combination of no scattering correction and no attenuation correction (SC-/AC-) and a combination of scattering correction and attenuation correction by CT images (SC+/AC+) were performed. The dose linearity, the recovery coefficient, the scatter ratio, and the coefficient of variation were evaluated using JS-10. Using Body-phantom, contrast-to-noise ratios of the hot spheres (13, 17 mm) were calculated. Moreover, the change in the maximum standardized uptake value (SUVmax) and the average SUV (SUVmean) were evaluated for each sphere. From the evaluation results using the JS-10, dose linearity, recovery coefficient, scatter ratio, and coefficient of variation were all good when time per view was 50-150 s, the Gaussian filter was 8-12 mm, and the SI product was 150. From the evaluation results using Body-phantom, comparing the Gaussian filter with 8 mm and 12 mm, the contrast-to-noise ratio was better for 12 mm and the error rate to the change of the scan-time was up to 3.7%. However, SUVmax and SUVmean using 8 mm were closer to the design value of the phantom. It is necessary that Quantitative SPECT be acquired at 50 s or more per view per detection, reconstructed using a three-dimensional ordered subset expectation maximization with SC+/AC+, the SI product is 150 times, and the Gaussian Filter is 8-12 mm. This suggested that the quantitative analysis would be carried out with good reproducibility.

Bayesian penalized-likelihood reconstruction algorithm suppresses edge artifacts in PET reconstruction based on point-spread-function

PurposeThe Bayesian penalized-likelihood reconstruction algorithm (BPL), Q.Clear, uses relative difference penalty as a regularization function to control image noise and the degree of edge-preservation in PET images. The present study aimed to determine the effects of suppression on edge artifacts due to point-spread-function (PSF) correction using a Q.Clear. MethodsSpheres of a cylindrical phantom contained a background of 5.3 kBq/mL of [18F]FDG and sphere-to-background ratios (SBR) of 16, 8, 4 and 2. The background also contained water and spheres containing 21.2 kBq/mL of [18F]FDG as non-background. All data were acquired using a Discovery PET/CT 710 and were reconstructed using three-dimensional ordered-subset expectation maximization with time-of-flight (TOF) and PSF correction (3D-OSEM), and Q.Clear with TOF (BPL). We investigated β-values of 200–800 using BPL. The PET images were analyzed using visual assessment and profile curves, edge variability and contrast recovery coefficients were measured. ResultsThe 38- and 27-mm spheres were surrounded by higher radioactivity concentration when reconstructed with 3D-OSEM as opposed to BPL, which suppressed edge artifacts. Images of 10-mm spheres had sharper overshoot at high SBR and non-background when reconstructed with BPL. Although contrast recovery coefficients of 10-mm spheres in BPL decreased as a function of increasing β, higher penalty parameter decreased the overshoot. ConclusionsBPL is a feasible method for the suppression of edge artifacts of PSF correction, although this depends on SBR and sphere size. Overshoot associated with BPL caused overestimation in small spheres at high SBR. Higher penalty parameter in BPL can suppress overshoot more effectively.

Does applying resolution recovery to normal databases confer an advantage over conventional 3D-stereotactic surface projection techniques?

We evaluated a novel normal database (NDB) generated using single photon emission computed tomography (SPECT) data obtained from healthy brains by using a SPECT/CT system, analyzed using a resolution recovery (RR) technique applied to the three-dimensional stereotactic surface projection (3D-SSP) technique. We used a three-dimensional ordered subset expectation maximization method (3D-OSEM) with applied scatter correction (SC), attenuation correction, and RR to reconstruct the data. We verified the accuracy of the novel NDB's values (Z, extent, and error scores), and compared the novel NDB to the 3D-SSP technique by using simulated misery perfusion-related patient data from a conventional NDB. In addition, Z, extent, and error scores at the precuneus, cuneus, and posterior cingulate were compared under different reconstruction conditions by using the patient data. In the simulation, Z scores decreased when using the novel NDB corrected using computed tomography-based attenuation correction (CTAC), SC, and RR. The extent scores of the posterior cingulate increased using the novel NDB, relative to the other NDBs. The error score with the novel NDB without RR decreased by 15% compared to that of the conventional NDB. Z scores generated from patient data decreased in the novel NDB with RR. The extent scores tended to decrease in the novel NDB with RR. The extent scores in the novel NDB with RR improved at the posterior cingulate, compared to the scores with the other NDBs. However, applying RR to the novel NDB conferred no advantage because the cut-off of the current Z score must be reconsidered when using the additive RR technique.

Pre-clinical Positron Emission Tomography Reconstruction Algorithm Effect on Cu-64 ATSM Lesion Hypoxia.

Objective:Application of distinct positron emission tomography (PET) scan reconstruction algorithms can lead to statistically significant differences in measuring lesion functional properties. We looked at the influence of two-dimensional filtered back projection (2D FBP), two-dimensional ordered subset expectation maximization (2D OSEM), three-dimensional ordered subset expectation maximization (3D OSEM) without 3D maximum a posteriori and with (3D OSEM MAP) on lesion hypoxia tracer uptake using a pre-clinical PET scanner.Methods:Reconstructed images of a rodent tumor model bearing P22 carcinosarcoma injected with hypoxia tracer Copper-64-Diacetyl-bis (N4-methylthiosemicarbazone) (i.e. Cu-64 ATSM) were analyzed at 10 minute intervals till 60 minute post injection. Lesion maximum standardized uptake values (SUVmax) and SUVmax/background SUVmean (T/B) were recorded and investigated after application of multiple algorithm and reconstruction parameters to assess their influence on Cu-64 ATSM measurements and associated trends over time.Results:SUVmaxSUVmax or T/B between 2D FBP, exhibited convergence for OSEM reconstructions while ANOVA results showed a significant difference in SUVmax or T/B between 2D FBP, 2D OSEM, 3D OSEM and 3D OSEM MAP reconstructions across all time frames. SUVmax and T/B were greatest in magnitude for 2D OSEM followed by 3D OSEM MAP, 3D OSEM and then 2D FBP at all time frames respectively. Similarly SUVmax and T/B standard deviations (SD) were lowest for 2D OSEM in comparison with other algorithms.Conclusion:Significantly higher magnitude lesion SUVmax and T/B combined with lower SD were observed using 2D OSEM reconstruction in comparison with 2D FBP, 3D OSEM and 3D OSEM MAP algorithms at all time frames. Results are SUVmax or T/B between 2D FBP, consistent with other published studies however more specimens are required for full validation.

3D-OSEM and FP-CIT SPECT quantification

Dopamine transporter imaging with single-photon emission computed tomography (SPECT) is a valuable tool for both clinical routine and research studies. Recently, it was found that the image quality could be improved by introduction of the three-dimensional ordered subset expectation maximization (3D-OSEM) reconstruction algorithm, which provides resolution recovery. The aim of this study was to systematically evaluate the potential benefits of 3D-OSEM in comparison with 2D-OSEM under critical imaging conditions, for example, scans with a high radius of rotation. Monte Carlo simulation scans of a digital brain phantom with various disease states and different radii of rotation ranging from 13 to 30 cm were reconstructed with both 2D-OSEM and 3D-OSEM algorithms. Specific striatal binding and putamen-to-caudate ratios were determined and compared with true values in the phantom. The percentage recovery of true striatal binding was similar between both reconstruction algorithms at the minimum rotational radius; however, at the maximum rotational radius, it decreased from 53 to 43% for 3D-OSEM and from 52 to 26% for 2D-OSEM. 3D-OSEM matched the true putamen-to-caudate ratios more closely than did 2D-OSEM in scans with high SPECT rotation radii. 3D-OSEM offers a promising image quality gain. It outperforms 2D-OSEM, particularly in studies with limited resolutions (such as scans acquired with a high radius of rotation) but does not improve the accuracy of the putamen-to-caudate ratios. Whether the benefits of better recovery in studies with higher radii of rotation could potentially increase the diagnostic power of dopamine transporter SPECT in patients with borderline striatal radiotracer binding, however, needs to be further examined.

The usefulness of fully three-dimensional OSEM algorithm on lymph node metastases from lung cancer with 18F-FDG PET/CT

This work assessed the usefulness of fully three-dimensional ordered subset expectation maximization (3D-OSEM) algorithm for lymph node (LN) metastases from lung cancer. 3D-OSEM images were evaluated by comparing them with those reconstructed by conventional algorithms, such as conventional OSEM algorithm (2D-OSEM) for 2D acquisition and Fourier rebinning plus conventional OSEM algorithm (FORE + OSEM) for 3D acquisition. In a phantom study, the contrast ratio, the image noise and the signal-to-noise ratio (SNR) were calculated, and the detectability and the image quality of these images were visually evaluated. In a clinical study, 14 patients suffering from lung cancer with LN metastases were evaluated. The image quality and the malignancy, and the detectability were visually evaluated. The contrast ratio was significantly improved using 3D-OSEM as compared with FORE + OSEM, and it was similar to 2D-OSEM. The image noise and SNR in 3D-OSEM images were significantly improved compared with those by other algorithms (p < 0.001). In the visual assessment, the image quality was significantly improved in 3D-OSEM images compared with those by 2D-OSEM and FORE + OSEM (p < 0.001, p = 0.001, respectively). In the clinical study, the image quality and the detectability of LN metastases were improved in 3D-OSEM images compared with those by FORE + OSEM (p < 0.001, p = 0.006, respectively), and image quality and detectability were similar to those of 2D-OSEM images. 3D-OSEM algorithm successfully improved the diagnostic accuracy of LN metastases in 3D-PET tests.

Localization of temporal epilepsy foci by subtraction ictal perfusion single photon emission computed tomography is enhanced when using 3D-OSEM iterative reconstruction

Subtraction ictal single photon emission computed tomography (SPECT) images, provided by filtered back-projection (FBP), may exhibit a confusing high level of noise. This study was aimed at assessing an optimized three-dimensional ordered subset expectation maximization (3D-OSEM) iterative reconstruction in this setting. On phantom images, parameters of 3D-OSEM reconstruction were selected as those providing the higher signal/noise ratio but a high enough spatial resolution, equivalent to that of conventional FBP reconstruction (full width at half-maximum = 11 mm). Thereafter, subtraction ictal ethylene cysteine dimer-SPECT coregistered to MRI and reconstructed with either FBP or 3D-OSEM were compared in 21 patients with well-characterized temporal epilepsy foci (subsequent successful surgical treatment). On subtraction images, the use of the selected 3D-OSEM reconstruction (five iterations, 16 subsets and a 9 mm Gauss filter) instead of FBP was associated with: (i) marked reductions in background activity (0.05 ± 0.09 vs. 0.25 ± 0.18 cps, P < 0.001) and in the size of temporal foci (10 ± 7 vs. 14 ± 11 cm, P = 0.01) and (ii) a trend toward higher accuracy in identifying the involved temporal lobes (86 vs. 76%). Localization of temporal epilepsy foci by subtraction ictal SPECT is likely to be enhanced by using 3D-OSEM rather than FBP reconstruction because of marked reductions in background activity and in the size of detected foci.

Detection of Visual Activation in the Rat Brain Using 2-deoxy-2-[18F]fluoro-d-glucose and Statistical Parametric Mapping (SPM)

This study was designed to assess changes in brain glucose metabolism in rats after visual stimulation. We sought to determine whether visual activation in the rat brain could be detected using a small-animal positron emission tomography (PET) scanner and 2-deoxy-2-[(18)F]fluoro-D: -glucose (FDG). Eleven rats were divided into two groups: (a) five animals exposed to ambient light and (b) six animals stimulated by stroboscopic light (10 Hz) with one eye covered. Rats were injected with FDG and, after 45 min of visual stimulation, were sacrificed and scanned for 90 min in a dedicated PET tomograph. Images were reconstructed by a three-dimensional ordered subset expectation maximization algorithm (1.8 mm full width at half maximum). A region-of-interest (ROI) analysis was performed on 14 brain structures drawn on coronal sections. Statistical parametric mapping (SPM) adapted for small animals was also carried out. Additionally, the brains of three rats were sliced into 20-microm sections for autoradiography. Analysis of ROI data revealed significant differences between groups in the right superior colliculus, right thalamus, and brainstem (p < or = 0.05). SPM detected the same areas as the ROI approach. Autoradiographs confirmed the existence of hyperactivation in the left superior colliculus and auditory cortex. To our knowledge, this is the first report that uses FDG-PET and SPM analysis to show changes in rat brain glucose metabolism after a visual stimulus.

First in Vivo SPECT Imaging of Mouse Femorotibial Cartilage Using 99mTc-NTP 15-5

This study aimed to report the first single-photon emission computed tomographic (SPECT) imaging of articular cartilage in mice using 99mTc-NTP 15-5 radiotracer. Mice intravenously injected with 99mTc-NTP 15-5 were submitted to (1) dynamic planar imaging, (2) static planar imaging, (3) 1 mm pinhole SPECT acquisition, and (4) dissection. Tomographic reconstruction of SPECT data was performed with a three-dimensional ordered subset expectation maximization algorithm, and slices were reconstructed in three axes. 99mTc-NTP 15-5 rapidly accumulated in the joint, with a peak of radioactivity being reached from 5 minutes postinjection and maintained for at least 90 minutes. Given that bone and muscle did not show any accumulation of the tracer, highly contrasted joint imaging was obtained from 15 minutes postinjection. When 1 mm pinhole SPECT acquisition was focused on the knee, the medial and lateral compartments of both the femoral condyle and tibial plateau were highly delineated, allowing a separate quantitation of tracer accumulation within each component of the femorotibial joint. A good correlation was found between tracer uptake determined by region of interest analysis of both planar and SPECT scans and dissection. This new approach to imaging of cartilage in mice provides joint functionality assessment in vivo, giving a unique opportunity to achieve a greater understanding of cartilage physiology in health and disease.