فهرست مطالب mohammadreza ay

This study proposes various designs of partial-ring geometry total-body positron emission tomography (PET) scanners which maintain an extended axial field of view (AFOV) while remaining cost-effective, without sacrificing image quality. The total-body uEXPLORER PET scanner was simulated using the GATE Monte Carlo code.  Partial-ring PET configurations were simulated, reducing the number of detectors by 25% in both the transaxial and axial directions. The sensitivity, noise equivalent count rate (NECR), and image quality of the partial-ring configurations were compared to those of the full-ring configuration. The system sensitivity of partial-ring designs was 0.61 and 0.77 times that of the full-ring detector PET for detector reduction in the axial and transaxial directions, respectively. Notably, despite the higher sensitivity, the 10 mm sphere could not be detected in the transaxial reduction mode. When considering all spheres except the 10 mm one, the mean relative error of contrast recovery (CR) for the same time duration was 2% for detector reduction in the axial direction, whereas it increased to 9% for reduction in the transaxial direction. The results show that reducing the number of detectors in total-body PET scanners can significantly lower manufacturing costs associated with long AFOV PET systems. Although the reduced detector configuration resulted in lower sensitivity, the image quality of the NEMA phantom was found to be superior in the axial reduction mode compared to the transaxial reduction mode. Additionally, the image quality exhibited only a slight difference from that of the full-ring scanner.

32-time scan duration reduction of 18F-Fluorodeoxyglucose )18F-FDG( Positron Emission Tomography (PET) images through the generation of standard scan duration images using a multi-slice cycle-consistent Generative Adversarial Network (cycle-GAN) was studied. Also, the effect of the image augmentation methods on the performance of the cycle-GAN model was evaluated.

Four subsets of standard and 32-time short scan duration PET image pairs, each contacting image data of 10 patients were used to train and test (80 percent for training and 20 percent for testing) a multi-slice cycle-GAN separately. Another patient’s image data was used as the validation dataset for different training subsets. When training the cycle-GAN model for each subset, two approaches were followed: with and without image augmentation. Common image quality metrics of Peak Signal-to-Noise Ratio )PSNR (, Structural Similarity Index Measure )SSIM(, and Normalized Root Mean Squared Error )NRMSE( were used to assess the generation performance of the cycle-GAN model. Paired sample t-test statistical testing with a confidence interval of 0.95 was used to determine whether the differences between approaches were statistically significant or not.

For subsets 1-3, both training approaches improved the image quality of the short scan duration inputs (p < 0.001) while for subset 4 only the training approach with image augmentation was capable of improving the image quality. However, the training approach with image augmentation offered better results than the approach without image augmentation (p < 0.001).

Employing the training approach with image augmentation, the cycle-GAN model was capable of improving the image quality of 1/32nd short scan duration images through the generation of synthetic standard scan duration images. In the case of the training approach without image augmentation, except for subset 4, the model trained on all subsets 1-3 was capable of improving the image quality. Image augmentation does indeed improve the performance of the cycle-GAN model, especially in the case of insufficient available training datasets.

This study evaluates scan time reduction using time-of-flight (TOF) PET, when quantitative parameters including volumetric measures are considered.

32 patients were included in the study. The reconstruction parameters for TOF were 2 iterations, 18 and 24 subsets, and for non-TOF was 3 iterations and 18 subsets. A post smoothing filter with FWHM of 5.4 mm and 6.4 mm were used for TOF and 6.4 mm for non-TOF. TOF reconstruction was performed with 2, 2.5 and 3 min/bed position, and 3 min/bed position scan time was applied in non-TOF. Quantitative parameters such as coefficient of variation (COV), signal-to-noise ratio (SNR), lesion-to-background ratio (LBR), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were utilized. Standard uptake value (SUV) was also measured. Different segmentation thresholds were studied.

Improvement in SNR for TOF relative to non-TOF was observed when utilizing 18 subsets, 5.4 mm filter size with 3 min scan time/bed position (P-value<0.0001), and for 18 subsets, 6.4 mm filter size when 2.5- and 3-min scan time/bed positions was applied (P-value≤0.02). Scan time reduction did not illustrate significant variation for the SUVs and lesion size. In all TOF protocols for both TLG and MTV, the measured values decreased with increasing segmentation thresholds, as expected, with significantly more impact for higher thresholds (70%, 75%). Meanwhile, higher values were observed for higher post smoothing filter in each specified threshold. With increasing of the threshold, ΔTLG was increased with more impact for higher post smoothing filter. ΔMTV were -10.10±11.09 (-1.35±8.59) and 0.68±17.51 (12.42±18.90) in 2 min/bed position with 5.4 (6.4 mm post smoothing filter) for threshold of 45% and 75% respectively.

Scan time reduction from 3 to 2 min can be obtained with TOF in comparison with non-TOF, especially when higher segmentation threshold values with higher subset number (24) and 6.4 mm filters are utilized.

 The quality of positron emission tomography/computed tomography (PET/CT) images plays an important role in tumor detection. This imaging method often yields poor-quality images of overweight patients due to the high level of noise, originating from scattering and photon attenuation.

 The point spread function (PSF) is mostly used to enhance the spatial resolution and signal-to-noise ratio (SNR); however, it is known to increase the edge artifacts. The time-of-flight (TOF) principle can reduce edge artifacts in PSF modeling and improve lesion detection, especially in the thorax. The present study aimed to assess these two new techniques by applying different reconstruction parameters.

 An in-house phantom with an inner diameter of 35 cm was used for the simulation of overweight patients. Lesion-to-background ratios (LBRs) of 2: 1 and 8: 1, as well as background activity concentrations of 3 and 5 kBq/cc, were considered in this study. The list-mode data were reconstructed with various reconstruction protocols, numbers of subsets, and filter sizes. Quantitative analyses, including the coefficient of variation (COV), SNR, and recovery coefficient (RC), were also carried out. Moreover, box-and-whisker plots were performed.

 At LBR of 2: 1, by changing the protocol from ordered subset expectation maximization (OSEM) to OSEM + PSF + TOF, the median value of SNR for 13-mm lesions (37 mm) increased by 39.25% and 53.45% (42.22% and 56.21%), at background activity concentrations of 3 and 5 kBq/cc respectively. However, at LBR of 8: 1, the corresponding values were 33.22% and 48.94% (40.22% and 52.15%) at background activity concentrations of 3 and 5 kBq/cc respectively.

 The TOF protocols were strongly recommended for both background activity concentrations at LBR of 2: 1 and for the low background activity concentration at LBR of 8: 1, especially when using smaller filter sizes. Moreover, subset numbers of 18 and 24 were appropriate for all protocols. However, a smaller subset number was suitable when a low background activity concentration and a smaller filter size were applied, especially at a lower LBR.

The present study aims to assess the impact of various image reconstruction methods in 18F-FDG PET/CT imaging on the quantification performance of the proposed technique for joint compensation of respiratory motion and partial volume effects (PVEs) in patients with non-small cell lung cancer. 

An image-based deconvolution technique was proposed, incorporating wavelet-based denoising within the Lucy-Richardson algorithm to jointly compensate for PVEs and respiratory motion. The method was evaluated using data from 15 patients with 60 non-small cell lung cancer. In these patients, the lesions were classified by size, location and Signal-to-Background Ratios (SBR). In each study, PET images were reconstructed using four different

OSEM with time- of-flight (TOF) information, OSEM with point spread function modelling (PSF), OSEM with both TOF and PSF (TOFPSF), and OSEM without PSF or TOF (OSEM). The Contrast to Noise Ratio (CNR), Coefficient of Variation (COV) and Standardized Uptake Values (SUV) were measured within the lesions and compared to images that were not processed using the joint-compensation technique. Furthermore, variabilities arising due to the choice of the reconstruction methods were assessed.

Processing the images using the proposed technique yielded significantly higher CNR and SUV, particularly in small spheres, for all the reconstruction methods and all the SBRs (P<0.05). Overall, the incorporation of wavelet-based denoising within the Lucy Richardson algorithm improved COV and CNR in all the cases (P<0.05.( In the patient data, the median values of the relative difference (%) of CNR for the compensated images in comparison to the uncompensated images were 40.9%, 41.2%, 45.3% and 40.8% for OSEM, PSF, TOF, and TOFPSF, respectively, in the small lesions (equivalent diameter <15 mm), 31.0%, 25.9%, 34.1% and 28.2% in the average-sized lesions (equivalent diameter<30 mm), 35.7%, 33.7%, 37.8% and 33.2% in the lesions in the lower lung lobes, 33.5%, 31.0%, 35.7% and 30.6% in the lesions in the upper lung lobes, 39.7%, 37.9%, 45.1% and 39.0% in the low-SBR lesions and 28.8%, 27.8%, 34.8% and 25.7% in the high-SBR lesions. Changes in motion amplitude, target size and SBRs in the patient data resulted in significant inter-method differences in the images reconstructed using different methods. Specifically, in a small target size, quantitative accuracy was highly dependent on the choice of the reconstruction method.

Our results showed that joint compensation, and incorporation of wavelet-based denoising, yielded improved quantification from PET images. Quantitative accuracy is greatly affected by SBR, lesion size, breathing motion amplitude, as well as the choice of the reconstruction protocols. Overall, the choice of reconstruction algorithm combined with compensation method needs to be determined carefully.

Positron Emission tomography (PET) as a nuclear medicine imaging modality is increasingly used in clinical practice to diagnose disease and cancer. To achieve a high quality PET image for diagnostic purposes, a standard dose of radioactive tracer must be injected into the patient's body, which increases the risk of radiation damage. However, reducing the tracer dose leads to increase in noise and decrease in the signal-to-noise ratio and the quality of the PET. This paper aims to evaluate the performance of Gaussian filter, Bilateral filter, Non-Local Mean and Wavelet Transform filters in improving the quality of low-dose PET images. First, these filters were optimized separately for two dose levels, and then the optimal filters were applied to 40 PET brain images with a 5% and 10% dose levels. Finally, the performance of these filters was evaluated and compared using PSNR, RMSE criteria in the whole brain and RMSE and Bias criteria in different areas of the brain (e.g, thalamus, cerebellum, putamen, etc.).

This study aimed to investigate the impact of image preprocessing steps, including Gray Level Discretization (GLD) and different Interpolation Algorithms (IA) on 18F-Fluorodeoxyglucose (18F-FDG) radiomics features in Non-Small Cell Lung Cancer (NSCLC).

One hundred and seventy-two radiomics features from the first-, second-, and higher-order statistic features were calculated from a set of Positron Emission Tomography/Computed Tomography (PET/CT) images of 20 non-small cell lung cancer delineated tumors with volumes ranging from 10 to 418 cm3 regarding five intensity discretization schemes with the number of gray levels of 16, 32, 64, 128, and 256, and four Interpolation algorithms, including nearest neighbor, tricubic convolution and tricubic spline interpolation, and trilinear were used. Segmentation was based on 3D region growing-based. The Intraclass Correlation Coefficient (ICC), Overall Concordance Correlation Coefficient (OCCC), and Coefficient Of Variations (COV) were calculated to demonstrate the features' variability and select robust features. ICC and OCCC < 0.5 presented weak reliability, ICC and OCCC between 0.5 and 0.75 illustrated appropriate reliability, values within 0.75 and 0.9 showed satisfying reliability, and values higher than 0.90 indicate exceptional reliability. Besides, features with less than 10% COV have been selected as robust features.

All morphology family (except four features), statistic, and Intensity volume histogram families were not affected by GLD and IA. And the rest of them, 10 and 61 features showed COV ≤ 5% against GLD and IA, respectively. Ten and 80 features showed excellent reliability (ICC values greater than 0.90) against GLD and IA. Eight and 60 features showed OCCC≥0.90 against GLD and IA, respectively. Based on our results Inverse difference normalized and Inverse difference moment normalized from Grey Level Co-occurrence Matrix (GLCM) were the most robust features against GLD and Skewness from intensity histogram family and Inverse difference normalized and Inverse difference moment normalized from GLCM were the most robust features against IA.

Preprocessing can substantially impact the 18F-FDG PET image radiomic features in NSCLC. The impact of gray level discretization on radiomics features is significant and more than Interpolation algorithms.

This study introduces a novel polyvinyl chloride (PVC)/tungsten composites with characterization of their shielding properties by employing different techniques. The PVC/tungsten composites were produced by employing various weight fractions of tungsten micro-particles including 0, 20, and 40 % wt via melt blending method. In the next step, the linear attenuation coefficients of prepared composite samples were experimentally measured at 662 keV γ-ray, and then were compared to the data estimated using MCNP simulation code and XCOM software. Also the shielding properties of samples were evaluated experimentally with an X-ray tube at 40 kVp. Recorded results showed that by increasing the weight percentage of the tungsten micro-particles, the coefficient of linear attenuation and also the absorbed dose values were increased dramatically. Samples containing 20, and 40% wt of tungsten micro-particles reached to 89.60 and 92.26 %of dose absorption, respectively. Interestingly the proposed composition were approximately 2.3 lighter than the commercial shields. The linear attenuation coefficient of the composite shields has been calculated to be 0.20 cm-1, which was comparable with commercial Pb-based shields. Tungsten micro-particles addition to PVC matrix can increase the absorbed dose value. Plasticized PVC has suitable flexibility and low stiffness value, therefore it can be a good alternative for commercial aprons and other Pb-based shields in low energy voltages.

Using an itra-operative gamma probe after injection of radiotracer during surgery helps the surgeon to identify the sentinel lymph node of regional metastasis through the detection of radiation. This work reports the design and specification of an integrated gamma probe (GammaPen), developed by our company.

GammaPen is a compact and fully integrated gamma probe. The detector module consists of a thallium-activated Cesium Iodide (CsI (Tl)) scintillator, and a Silicon Photo Multiplier (SiPM), shielded using Tungsten housing. Probe sensitivity, spatial resolution and angular resolution in air and water, and side and back shielding effectiveness were measured to evaluate the performance of the probe based on NEMA NU3 standard.

The sensitivity of the probe in the air/water at distances of 10, 30, and 50 mm is 18784/176800, 3500/3050, and 1575/1104 cps/MBq. The spatial and angular resolutions in the air/scattering medium are 40/47 mm and 77/87 degrees at a 30 mm distance from the probe. The detector shielding effectiveness and leakage sensitivity are 99.91% and 0.09%, respectively.

The results and surgeon experience in the operating room showed that GammaPen can be effectively used for sentinel lymph node localization.

This review paper aimed to examine radiation safety issues related to relatives as well as caregivers of patients with thyroid diseases treated with radioiodine (I-131). During I-131 therapy for thyroid disorders such as hyperthyroidism, patients receiving I-131 doses (200-800 MBq) emit radioactive radiations which pose a prospective risk to other people. Critical groups are patients’ visitors and families, especially children. Following the updated international guidelines, the doses received by members of the public as a proportion of the therapy of a patient have been decreased. The public annual dose limits are 1 mSv, although higher doses are permitted for adults in the patient’s family, provided that the maximum 5 mSv is not surpassed for 5 years. Without compliance with the current recommendations, extended hospitalizations for patients are essential. Family members should therefore limit close interactions with an individual for some duration following thyroid therapy with I-131.

Relative to classical methods in computed tomography, iterative reconstruction techniques enable significantly improved image qualities and/or lowered patient doses. However, the computational speed is a major concern for these iterative techniques. In the present study, we present a method for fast system matrix calculation based on the line integral model (LIM) to speed up the computations without compromising the image quality. In addition, we develop a hybrid  line–area integral model (AIM) that highlights the advantages of both LIM and AIMs.

The contributing detectors for a given pixel and a given projection view, and the length of corresponding intersection lines with pixels, are calculated using our proposed algorithm. For the hybrid method, the respective narrow‑angle fan beam was modeled by multiple equally spaced lines. The computed system matrix was evaluated in the context of reconstruction using the simultaneous algebraic reconstruction technique (SART) as well as maximum likelihood expectation maximization (MLEM).

The proposed LIM offers a considerable reduction in calculation times compared to the standard Siddon algorithm: 2.9 times faster. Differences in root mean square error and peak signal‑to‑noise ratio were not significant between the proposed LIM and the Siddon algorithm for both SART and MLEM reconstruction methods (P > 0.05). Meanwhile, the proposed hybrid method resulted in significantly improved image qualities relative to LIM and the Siddon algorithm (P < 0.05), though computations were 4.9 times more intensive than the proposed LIM.

We have proposed two fast algorithms to calculate the system matrix. The first is based on LIM and was faster than the Siddon algorithm, with matched image quality, whereas the second method is a hybrid LIM–AIM that achieves significantly improved images though with its computational requirements.

The accuracy of positron emission tomography with computed tomography (PET/CT), positron emission mammography (PEM), and breast specific-gamma imaging (BSGI) in diagnosing breast cancer has never been systematically assessed, the present systematic review was aimed to address this issue. 

PubMed, Scopus and EMBASE were searched for studies dealt with the detection of breast cancer by PET/CT, PEM or BSGI. Histopathologic examination and/or at least six months imaging follow-up were used as a golden reference. To calculate diagnostic test parameters: sensitivity, specificity, summary receiver operating characteristic curves (SROC) and to test for heterogeneity, true positive (TP), true negative (TN), false positive (FP) and false negative (FN) were extracted.

Thirty one studies were included in the analysis. On per-patient basis, the pooled sensitivities after corrected for threshold effect for 18F-FDG PET/CT, PEM, and 99mTc-MIBI BSGI were 0.89 (95% CI: 0.78- 0.95), 0.73 (95% CI: 0.41 - 0.92), and 0.80 (95% CI: 0.72 - 0.86) respectively. The pooled specificities for detection of breast cancer using FDG PET/CT, PEM, and 99mTc-MIBI BSGI were 0.93 (95 % CI, 0.86 - 0.96), 0.91 (95 % CI, 0.77- 96), and 0.78 (95 % CI, 0.64 - 0.88), respectively. AUC of FDG PET/CT, PEM, and BSGI were 0.9549, 0.8852 and 0.8573, respectively.

This meta-analysis indicated that PET/CT showed better diagnostic accuracy than PEM, and BSGI on per-patient basis. On per-lesion analysis, PEM with the highest AUC, DOR and Q* was better than PET/CT, and BSGI for detecting breast cancer.

MAMMI is a dedicated PET based on high resolution detectors placed close to the breast. In this study, we presented a GATE model for the simulation of MAMMI scanner and model its performance of the MAMMI based on an adaptation of the NU 4-2008 NEMA standard.  A detailed of geometry MAMMI system that uses scintillation crystals coupled to position sensitive photomultipliers. The detector ring consists of 12 LYSO detector modules with a scanner aperture of 186 mm. We validated the model against experimental measurement, including spatial resolution, sensitivity, counting rates, noise equivalent count rate (NECR) and scattering pattern. Overall results showed reasonable agreement between simulation and experimental data. For a breast phantom with a capillary source, the SF reaches 50.9 and NECR is 45 kcps with an activity of 11 MBq, 18F in quad rings. The spatial resolution at the axial FOV of quad rings (2.1 mm axial, 1.8 mm radial, and 1.7 tangential) is slightly better than that measured at the axial center of dual rings (2.1 mm axial, 1.8 mm tangential and radial). The MAMMI-PET has excellent spatial resolution and high sensitivity for primary breast cancer lesions. The results show performance improvement, especially in the absolute sensitivity, because of the more rings introduced in the MAMMI PET. The performance of the scanner and the validation results are considered to be reasonable enough to support its use in breast cancer imaging.

Positron Emission Tomography (PET) imaging is a nuclear medicine imaging technique based on the recording of two photons as coincidence created by positron annihilation.

PET coincidence events include true and unwanted coincidences (random, scattered, multiple coincidences). We modeled the Discovery 690 (D-690) PET scanner using the GATE simulation tool and estimated the effect of the diameter of the scattering medium out of the Axial Field of View (AFOV) on the random coincidence rates.

The validation results indicated that the average difference between simulated and measured data for sensitivity and scatter fraction tests are 5% and 3%, respectively. Moreover, the results revealed that the increasing diameter of the scattering medium out of the AFOV has a direct effect on the random coincidence rates within the Field of View (FOV).

The study concluded that the presence of a scattering medium near the FOV increases the rate of random coincidences.

Integration of single photon emission computed tomography (SPECT) and computed tomography (CT) scanners into SPECT/CT hybrid systems permit detection of coronary artery disease in myocardial perfusion imaging (MPI). Misregistration between CT and emission data can produce some errors in uptake value of SPECT images. The aim of this study was evaluate the influence of attenuation correction (AC) versus non-attenuation correction (NC) images and the effect of misregistration on all segments of SPECT images for quantitative and qualitative analysis. 99 patients (45 males, 54 females) underwent stress/rest myocardial perfusion imaging (MPI) using 99mTc-MIBI were used in this study. We also utilized cardiac insert and lung insert in cylinder phantom. Phantom studies were performed with and without defect. The misregistration of all patient data was measured and variation in misregistration of our population was recorded. The effect of attenuation correction (AC) and non-attenuation correction (NC) images were also evaluated in both phantom and patient data. The CT images were shifted by ±1, ±2, ±3 pixels along X-, Y- and Z-axis (Left/right, dorsal/ventral, cephalic/caudal) for both phantom and patient studies. Differences between misalignment data and misregistration correction images were also measured. Results displayed with 20 segments polar map analysis and illustration in standard orientations for cardiac tomographic images. In the patient population data, 1.5% were perfectly registered, 17% and 73% misaligned under 1 pixel and more than 1 pixel, respectively. AC of SPECT images showed increased uptake value in normal phantom and false positives findings were disappeared versus to NC images. In patient data, statistically significant variation were shown for the most segments before and after AC (P-value<=0.004) and also between AC of SPECT image and misregistration correction images (P-value<=0.048). Along X-axis, in 3 pixel shift in right direction, the percent of relative difference in lateral wall were 11.94% for mid anterolateral. Along Y-axis, the Ventral shift caused -15.9% changes in basal inferolateral and along Z-axis -8.59 % changes in apical anterolateral were also observed in caudal direction when 3 pixel shifts were used. This study showed that CT-based attenuation correction of cardiac images in hybrid SPECT/CT is important to improve image quality. Misalignment in caudal, cephalad, ventral and right direction introduced significant variation even in 1 pixel shift. It is important to apply misregistration correction even in small misalignment routinely in clinical myocardial perfusion imaging.

The position estimation in gamma detection system will have constant misplacements which can be corrected in the calibration procedure. In the pixelated crystal uniformly irradiation of detector will produce irregular shape due to position estimation errors. This image is called flood field image and is used to calibrate the position estimation. In this work we present a novel approach to automatically calibrate pixelated crystal array position estimation. In the flood image of a pixelated crystal array the local peaks represent the estimation of position for the gamma photons that interacted in a single crystal pixel. First, the method detects 2-D peak locations automatically in the case of blurred pixel responses in the presence of noise and disturbance of the image. The algorithm consists of a filtering step for smoothing the image followed by two rounds of local peak detection. After localizing image peaks, the correction routine will map the image locations to the crystal pixels using the thin-plate spline interpolation method. The algorithm is tested for two flood images obtained from developed detector with different irregularity levels. By configuring constant parameters according to the detector configuration the method detected all crystal pixels in the image and map them correctly. The method further has been tested for10 identical blocks and the result showed automatic peak detection routine for all the blocks. An automatic peak detection is presented to work instead of time consuming manual calibration routines. The method shows robust performance in the presence of image noise.

  There has been a curiosity about the spheroid geometry for PET scanners developments since several years ago, therefore in this study, we are aiming to evaluate the performance of this geometry and compare its performance with cylindrical geometry using Monte Carlo simulation. We simulated a spheroid geometry with a radius of 199 mm, patient bore with of radius of 175 mm, which is compatible with brain size. In second design, cylindrical geometry was simulated with transaxial FOV and ring radius of 175 mm as well. Photon detection efficiency (PDE), NEMA line source sensitivity, spatial resolution and Derenzo phantom image quality were analyzed. We obtained PDE about 21.7% versus 23.8% in 250-750 keV and 19.5% versus 21.3% in 410-613 keV for point source in center of FOV for spheroid and cylindrical PET respectively. The results of NEMA sensitivity measurements indicate 3.29 kcps/MBq versus 3.64 kcps/MBq for spheroid and cylindrical designs. The spatial resolution (FWHM) calculations using MLEM reconstruction algorithm show around 1.6 mm for transvers and axial resolution for point source placed in center of FOV for both scanners. Also we found for spheroid and cylindrical designs 4.8 and 2.7 mm versus 4 and 3.6 mm as transvers and axial mean resolution for off-center point sources. Performance evaluation study indicates that the spheroid geometry delivers better axial resolution whereas cylindrical design can still provide higher sensitivity and transvers spatial resolution than the spheroid geometry PET with same scanner bore size.

Spatial resolution and accurate quantification in animal SPECT plays a critical role in preclinical imaging. Appropriate Projections filtering can help to address the issue of resolution compensation and recovery coefficients. The main aim of current study was to explore a new version of MLEM algorithm with pre-reconstruction Fourier transform filtering to improve the Recovery Coefficient RC by filtering the projections. A complete set of measurements was performed using HiReSPECT system. Different phantom studies were performed using point sources, NEMA NU 4 and dedicated hot rod phantom. All data was reconstructed using the developed Maximum-Likelihood Expectation-Maximization (MLEM) algorithm with and without resolution recovery information and also with our presented pre-reconstruction Fourier transform filter. Image quality was assessed by different parameters such as Coefficient Of Variation (COV), Recovery Coefficient (RC) and FWHM. FWHM in tangential direction was improved 0.6 and 0.2 for our presented algorithm against MLEM without and with CDRF, respectively. Fourier filtering image led to improvement of image quality where hot rods with 1.6 and 1.8 mm in diameter could be recognized clearly in our presented algorithm in dedicated hot rod phantom. Our presented algorithm resulted in rapid convergence and growth of RC in lower iteration. The purpose of the current study was to introduce new pre-reconstruction filter. The results of this investigation showed that the inclusion of our proposed filter can lead to better image quality and quantification in lower iteration. These data suggest that current filter can provide higher RC in lower iteration.

Substantive amount of work has been done in modeling and analyzing the scintillation camera system processes including positioning and image formation. The goal of this work is to develop a framework for analyzing performance of nonlinear positioning methods upon construction of a mathematical model of the system. In this study, the photodetector array counts are assumed to follow a multinomial distribution.
We studied effects of several parameters on system performance, including photomultiplier tube (PMT) non-uniform response, gains, shape, size and positioning methods. This was done by constructing linearity and resolution maps, feeding the system a uniform grid of point sources showing the distorted output along with associated blurring intensity. The spatial resolution and linearity parameters are used to evaluate the performance of simulated scintillation camera.
The study findings revealed that the square PMT is the best option due to better fitting and quality especially near the edge of the detector and also ability to cover the rectangular crystal area with minimum numbers of PMTs. Also, the resolution resulted from CSE is 5% and 20% better than center of mass and modified center of mass respectively.
We showed that the rectangular gamma camera accompanied by an array of square PMTs can introduce the optimum performance regarding linearity and resolution if the nonlinear method, called CSE, is used as positioning method. Further evaluation is needed to evaluate the performance of the proposed gamma camera in practice.

This study aims to investigate the influence of background activity variation on image quantification in differently reconstructed PET/CT images.
Measurements were performed on a Discovery-690 PET/CT scanner using a custom-built NEMA-like phantom. A background activity level of 5.3 and 2.6 kBq/ml 18F-FDG were applied. Images were reconstructed employing four different reconstruction algorithms: HD (OSEM with no PSF or TOF), PSF only, TOF only, and TOFPSF, with Gaussian filters of 3 and 6.4 mm in FWHM. SUVmax and SUVpeak were obtained and used as cut-off thresholding; Metabolic Tumor Volume (MTV) and Total Lesion Glycolysis (TLG) were measured. The volume recovery coefficients (VRCs), the relative percent error (ΔMTV), and Dice similarity coefficient were assessed with respect to true values.
SUVmax and SUVpeak decreased and MTV increased as function of increasing the background dose. The most differences occur in smaller volumes with 3-mm filter; Non-TOF and Non-PSF reconstruction methods were more sensitive to increasing the background activity in the smaller and larger volumes, respectively. The TLG values were affected in the small lesions (decrease up to 12%). In a range of target volumes, differences between the mean ΔMTV in the high and low background dose varied from -11.8% to 7.2% using SUVmax and from 2.1% to 7.6% using SUVpeak inter reconstruction methods.
The effect of the background activity variation on SUV-based quantification in small lesion was more noticeable than large lesion. The HD and TOFPSF algorithms had the lowest and the highest sensitivity to background activity, respectively.

MapCHECK2 is a two-dimensional diode arrays planar dosimetry verification system. Dosimetric results are evaluated with gamma index. This study aims to provide comprehensive information on the impact of various factors on the gamma index values of MapCHECK2, which is mostly used for IMRT dose verification.
Seven fields were planned for 6 and 18 MV photons. The azimuthal angle is defined as any rotation of collimators or the MapCHECK2 around the central axis, which was varied from 5 to -5°. The gantry angle was changed from -8 to 8°. Isodose sampling resolution was studied in the range of 0.5 to 4 mm. The effects of additional buildup on gamma index in three cases were also assessed. Gamma test acceptance criteria were 3 /3 mm.
The change of azimuthal angle in 5° interval reduced gamma index value by about 9%. The results of putting buildups of various thicknesses on the MapCHECK2 surface showed that gamma index was generally improved inthickerbuildup,especiallyfor18MV.Changingthesamplingresolutionfrom4to2mmresultedinan increase in gamma index by about 3.7%. The deviation of the gantry in 8° intervals in either directions changed the gamma index only by about 1.6% for 6 MV and 2.1% for 18 MV.
Among the studied parameters, the azimuthal angle is one of the most effective factors on gamma index value. The gantry angle deviation and sampling resolution are less effective on gamma index value reduction.

Metallic artifacts due to pacemaker/ implantable cardioverter defibrillator (ICD) leads in CT images can produce artifactual uptake in cardiac SPECT/CT images. The aim of this study was to determine the influence of the metallic artifacts due to pacemaker and ICD leads on myocardial SPECT/CT imaging.
The study included 9 patients who underwent myocardial perfusion imaging (MPI). A cardiac phantom with an inserted solid defect was used. The SPECT images were corrected for attenuation using both artifactual CT and CT corrected using metal artifact reduction (MAR). VOI-based analysis was performed in artifactual regions.
In phantom studies, mean-of-relative-difference in white-region, between artifact-free attenuation-map without/with MAR were changed from 9.2 and 2.1 to 3.7 and 1.2 for ICD and pacemaker lead, respectively. However, these values for typical patient were 9.7±7.0 and 3.8±2.4 for ICD and pacemaker leads respectively, in white-region. MAR effectively reduces the artifacts in white-regions while this reduction is not significant in black-regions.
Following application of MAR, visual and quantification analyses revealed that while quality of CT images were significantly improved, the improvements in the SPECT/CT images were not as pronounced or significant. Therefore cardiac SPECT images corrected for attenuation using CT in the presence of metallic-leads can be interpreted without correction for metal artefacts.

The most important advantage of positron emission tomography/computed tomography (PET/CT) imaging is its capability of quantitative analysis. The aim of the current study was to choose the proper standardized uptake value (SUV) threshold, when the time-of-flight (TOF) and point spread function (PSF) were used for respiratory artifact reduction in the liver dome in a new-generation PET/CT scanner.
The current study was conducted using a National Electrical Manufacturers Association International Electrotechnical Commission body phantom, with activity ratios of 2:1 and 4:1. A total of 27 patients, with respiratory artifacts in the thorax region, were analyzed. PET images were retrospectively reconstructed using either a high definition (HD) PSF (i.e., a routine protocol) algorithm or HD㴡繌 (PSF䳡; i.e., to reduce the respiratory artifact) algorithms, with various reconstruction parameters. The SUVmax and SUVmean, at different thresholds (i.e., at 45%, 50%, and 75%), were also assessed.
Although in comparison to the routine protocol a higher SUV was observed when using the PSF䳡 method, this approach was used to reduce the respiratory artifact. The appropriate threshold for SUV was strongly related to the lesion size, reconstruction parameters, and activity ratio. The mean of the relative difference between PSF䳡 algorithm and routine protocol for SUVmax varied from 10.58±14.99% up to 35.49±32.60% (which was dependent on reconstruction parameters).
In comparison with other types of SUVs, the SUVmax value illustrated its significant overestimation, especially at the 4:1 activity ratio. The poor agreement between SUVmax and SUV50% was also observed. When the TOF and PSF are utilized to reduce respiratory artifacts, the SUV50% can be an accurate semi-quantitative parameter for PET/CT images, for all lesion sizes. For smaller lesions, however, a smaller filter size was required to observe an accurate SUV.

Various iterative reconstruction algorithms in nuclear medicine have been introduced in the last three decades. For each new imaging system, it is wise to select appropriate image reconstruction algorithms and evaluate their performance. In this study, three approaches of image reconstruction were developed for a novel desktop open-gantry SPECT system, PERSPECT, to assess their performance in terms of the quality of the resultant reconstructed images.
In the present work, a proposed image reconstruction algorithm for the PERSPECT, referred to as quasi-simultaneous multiplicative algebraic reconstruction technique (qSMART), together with two popular image reconstruction methods, maximum-likelihood expectation-maximization (MLEM) and ordered-subsets EM (OSEM), were implemented and compared. Analytic and Monte Carlo simulations were applied for data acquisition of various phantoms including a micro-Derenzo phantom. All acquired data were reconstructed by the three algorithms using different number of iterations (1-40). A thorough set of figures-of-merit was utilized to quantitatively compare the generated images.
OSEM depicted reconstructed images of higher (or matching) quality in comparison to qSMART. MLEM also reached nearly similar quality as OSEM but at higher number of iterations. The graph of data discrepancy revealed that the ranking of the three approaches in terms of convergence speed is as qSMART, OSEM, and MLEM. Furthermore, bias-versus-noise curves indicated that optimal bias-noise results were achieved using OSEM.
The results showed that although qSMART can be applied for image reconstruction if being halted in the early iterations (up to 5), the best achievable quality of images is obtained using the OSEM.