Background: Respiratory movement and the motion range of the diaphragm can affect the quality and quantity of prostate images. Objective: This study aimed to investigate the magnitude of respiratory-induced errors to determine Dominant Intra-prostatic Lesions (DILs) in positron emission tomography (PET) images. Material and Methods: In this simulation study, we employed the 4D NURBSbased cardiac-torso (4D-NCAT) phantom with a realistic breathing model to simulate the respiratory cycles of a patient to assess the displacement, volume, maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), signal to noise ratio (SNR), and the contrast of DILs in frames within the respiratory cycle. Results: Respiration in a diaphragm motion resulted in the maximum superiorinferior displacement of 3. 9 and 6. 1 mm, and the diaphragm motion amplitudes of 20 and 35 mm. In a no-motion image, the volume measurement of DILs had the smallest percentage of errors. Compared with the no-motion method, the percentages of errors in the average method in 20 and 35 mm-diaphragm motion were 25% and 105%, respectively. The motion effect was significantly reduced in terms of the values of SUV max and SUVmean in comparison with the values of SUVmax and SUVmean in no-motion images. The contrast values in respiratory cycle frames were at a range of 3. 3-19. 2 mm and 6. 5-46 for diaphragm movements’,amplitudes of 20 and 35 mm. Conclusion: The respiratory movement errors in quantification and delineation of DILs were highly dependent on the range of motion, while the average method was not suitable to precisely delineate DILs in PET/CT in the dose-painting technique.

Objective(s): To investigate the impact of respiratory motion on localization, and quantification of lung lesions for the Gross Tumor Volume utilizing a fully automated Auto3Dreg program and dynamic NURBS-based cardiac-torso digitized phantom (NCAT).Methods: Respiratory motion may result in more than 30% underestimation of the SUV values of lung, liver and kidney tumor lesions. The motion correction technique adopted in this study was an image-based motion correction approach using, a voxelintensity- based and a multi-resolution multi-optimization (MRMO) algorithm. The NCAT phantom was used to generate CT attenuation maps and activity distribution volumes for the lung regions. All the generated frames were co-registered to a reference frame using a time efficient scheme. Quantitative assessment including Region of Interest (ROI), image fidelity and image correlation techniques, as well as semi-quantitative line profile analysis and qualitatively overlaying non-motion and motion corrected image frames were performed.Results: The largest motion was observed in the Z-direction. The greatest translation was for the frame 3, end inspiration, and the smallest for the frame 5 which was closet frame to the reference frame at 67% expiration. Visual assessment of the lesion sizes, 20-60mm at 3 different locations, apex, mid and base of lung showed noticeable improvement for all the foci and their locations. The maximum improvements for the image fidelity were from 0.395 to 0.930 within the lesion volume of interest. The greatest improvement in activity concentration underestimation was 7.7% below the true activity for the 20 mm lesion in comparison to 34.4% below, prior to correction. The discrepancies in activity underestimation were reduced with increasing the lesion sizes. Overlaying activity distribution on the attenuation map showed improved localization of the PET metabolic information to the anatomical CT images.Conclusion: The respiratory motion correction for the lung lesions has led to an improvement in the lesion size, localization and activity quantification with a potential application in reducing the size of the PET GTV for radiotherapy treatment planning applications and hence improving the accuracy of the regime in treatment of lung cancer.

Introduction: Scattered photons are one of the main causes of degrading the contrast of lesions and resolution in SPECT imaging of the heart that result in error in quantification. The usual technique for the rejection of scattered photons is through energy windowing. However, because of limited energy resolution of current scintillation cameras it is impossible to avoid scatter photons from detection. Modeling of Compton scattering through finding suitable functions was proposed in this study. These functions were used for scatter correction through deconvolution in next step. Materials and Methods: Monte Carlo simulation was used for creating projections of three different activity sources: a line source passed through left ventricle, a point source placed in left ventricle and finally real activity distribution of Tc-99m in torso organs. All of these sources were placed in a digital attenuation phantom which modeled a real patient body. Images of primary and scattered photons were acquired separately. Convolution and 2D deconvolution in Fourier domain was applied for estimating the primary projections through total ones. Results: In the first step, scatter and total images were modeled as convolution of a modified exponential function with primary image. The best exponent value was determined for each of 64 views (0.115 to 0.150 according to heart to detector distance). In the next step, these functions were used for scatter correction through deconvolution. Sum of the square differences between the primary and scatter corrected images were decreased considerably, myocardium to cavity contrast increased for all of 64 views (34% ±10%). Good agreement between the real primary and scatter corrected images were also found. Discussion and Conclusion: These results indicate that deconvolution technique for the scatter compensation can significantly reduce the degrading roles of scattering in quantitative SPECT imaging.

Introduction: It is a common protocol to use 201Tl for the rest and 99mTc for the stress cardiac SPECT imaging. Theoretically, both types of imaging may be performed simultaneously using different energy windows for each radionuclide. However, a potential limitation is the cross-contamination of scattered photons from 99mTc and collimator X-rays into the 201Tl energy window. We used a middle energy window method to correct this cross-contamination.Material and Methods: Using NCAT, a typical software torso phantom was generated. An extremely thin line source of 99mTc activity was placed inside the cardiac region of the phantom and no activity in the other parts. The SimSET Monte Carlo simulator was used to image the phantom in different energy windows. To find the relationship between projections in different energy windows, deconvolution theory was used. We investigated the ability of the suggested functions in three steps: Monte Carlo simulation, phantom experiment and clinical study. In the last step, SPECT images of eleven patients who had angiographic data were acquired in different energy windows. All of these images were compared by determining the contrast between a defect or left ventricle cavity and the myocardium.Results: We found a new 2D kernel which had an exponential pattern with a much higher center. This function was used for modeling 99mTc down scatter distribution from the middle window image. X-ray distribution in the 201Tl window was also modeled as the 99mTc photo peak image convolved by a Gaussian function. Significant improvements in the contrasts of the simultaneous dual 201Tl images were found in each step before and after reconstruction. In comparison with other similar methods, better results were acquired using our suggested functions.Conclusion: Our results showed contrast improvement in thallium images after correction, however, many other parameters should be evaluated for clinical approaches. There are many advantages in simultaneous dual isotope imaging. It halves imaging time and reduces patient waiting time and discomfort. Identical rest/stress registration of images also facilitates physicists’ motion or attenuation corrections and physicians’ image interpretation.

Introduction: Myocardial perfusion SPECT by 99mTc-Sestamibi and 99mTc-Tetrofosmin radiopharmaceuticals usually presents a false significant increase in the radiotracer uptake in the inferior myocardium due to the uptake in organs such as liver, bowel, stomach and biliary system. The present study evaluated a suitable Slit angle for differentiating extra-cardiac activities by Slit Slat collimation.Methods: The Siemens E.CAM gamma camera equipped with a Low Energy High Resolution (LEHR) collimator was simulated with the Simulating Medical Imaging Nuclear Detectors (SIMIND) Monte Carlo program. Following the verification of the simulation, a Slit Slat collimator was simulated for SPECT imaging of a NURBS-based Cardiac Torso (NCAT) phantom with different Slit angels ranged from 0 to 30 degrees. The reconstructed images were qualitatively assessed with blinded observer method by three nuclear medicine specialists.Results: The improved differentiation of the bowel activity from the cardiac was obtained by a Slit-Slat collimator with the Slit angle of 7 degree. While for gastric activity differentiation an angle of 15 degree for the Slit was useful.Conclusion: The results showed that Slit Slat collimation with 7 and 15 Slit angle provide a suitable differentiation of the bowel and gastric activities from the cardia, respectively.

Introduction: An efficient method of tomographic imaging in nuclear medicine is positron emission tomography (PET). Compared to SPECT, PET has the advantages of higher levels of sensitivity, spatial resolution and more accurate quantification. However, high noise levels in the image limit its diagnostic utility. Noise removal in nuclear medicine is traditionally based on Fourier decomposition of images. This method is based on frequency components, irrespective of the spatial location of the noise or signal. The wavelet transform presents a solution by providing information on the frequency content while retaining spatial information. This alleviates the shortcoming of the Fourier transform and thus, wavelet transform has been extensively used for noise reduction, edge detection and compression.Materials and Methods: In this research, we used the SimSET software to simulate PET images of the NCAT phantom. The images were acquired using 250 million counts in a 128×128 matrix. For the reference image, we acquired an image with high counts (6 billion). Then, we reconstructed these images using our own software developed in MATLAB. After image reconstruction, a 250 million counts image (noisy image) and a reference image were normalized and then root-mean-square error (RMSE) was used to compare the images. Next, we wrote and applied de-noising programs. These programs were based on using 54 different wavelets and 4 methods. De-noised images were compared with the reference image using RMSE.Results: Our results indicate that the Stationary Wavelet Transform and Global Thresholding are more efficient at noise reduction compared to the other methods that we investigated.Discussion: The wavelet transform is a useful method for de-noising of simulated PET images. Noise reduction using this transform and loss of high-frequency information are simultaneous with each other. It seems that we should attend to the mutual agreement between noise reduction and the visual quality of the image.

Introduction: Poor sensitivity and poor signal to noise ratio because of low injected thallium dose and presence of scattered photons are the main problems in using thallium in scintigraphic imaging of the heart. Scattered photons are the main cause of degrading the contrast and resolution in SPECT imaging that result in error in quantification. Thallium decay is very complicated and photons are emitted in a wide range of energies of 68-82 keV. It seems possible to achieve better primary to scattered radiation ratio and better image sensitivity simultaneously if the energy window setting is carefully selected.Methods: This investigation was performed in three steps: Monte Carlo simulation, phantom experiment and clinical study. In simulation step, the new 4D digital NCAT phantom was used to simulate the distribution of activity 201Tl) in patient torso organs. The same phantom was used to simulate the attenuation coefficient of different organs of the typical patient's body. Two small defects on different parts of left ventricle also were generated for further quantitative and qualitative analysis. The simulations were performed using the SimSET simulator to generate images of such patient. The emissions arising from TI-201 decay were simulated in four steps using the energies and relative abundances. Energy spectra for primary and scatter photons were calculated. Changing the center and width of energy windows, optimum energy window characteristics were determined. In next step jaszczak phantom was prepared and used for SPECT imaging in different energy windows. In last step SPECT images of 7 patients who had angiographic data were acquired in different energy windows. All of these images were compared qualitatively by four nuclear medicine physicians independently.Results: The optimum energy window was determined as a wider asymmetric window (77keV~30%) that its center is not placed on photo-peak of energy spectrum. This window increased the primary counts rate and PTSR considerably as compared with the conventional symmetric energy window (67keV~~ -%). In a comparison which performed between clinical images acquired in suggested 77-30% window with conventional 67-20% window, a considerable increase was found in myocardial to defect contrast (1.541±0.368)and myocardial to cavity contrast (1.171±0.099). A negligible increase was also found in total counts of images using this window.Conclusion: We found that conventional symmetric energy window (67keV±10%) couldn't be a suitable choice for thallium heart imaging; furthermore three energy windows, 73keV-30%, 75keV-30% and 77keV-30%, were determined as optimum window options. For further analysis the images from such windows were compared in each three steps of this investigation. In all steps conventional symmetric energy window (67keV-20%) was introduced as the worst case and the asymmetric 77keV-30% was determined as the most suitable.

In this paper, the polymerization process of polydicyclopentadiene (PDCPD) obtained by using dicyclopentadiene (DCPD) and the 2nd generation Grubbs’,catalyst is optimized. The curing reaction kinetics was studied by differential scanning calorimetry (DSC), and the solidification reaction process was obtained. The effects of different ratios of monomer to catalyst on the product performance were investigated. In addition, the current common modification methods of PDCPD have been summarized and improved. The results showed that with the increase of the ratio of monomer to the catalyst, the tensile strength, tensile modulus, bending strength and bending modulus of PDCPD all showed a downward trend, and the impact strength showed an upward trend. When nDCPD: NCAT =10000: 1, the comprehensive mechanical properties of PDCPD reached the best. The bending modulus, tensile strength and impact strength of PDCPD achieved 2100 MPa, 52. 4 MPa and 30 kJ/m2, respectively. The glass transition temperature (Tg) of PDCPD also showed a decreasing trend with the increase of the ratio of monomer to the catalyst, at this ratio, the Tg of the polymer reached 147. 6°, C. The catalyst concentration had a large effect on the product performance.