Objective(s): The spatial resolution of emission tomographic IMAGING systems can lead to a significant underestimation in the apparent radioactivity concentration in objects of size comparable to the resolution volume of the system. The aim of this study was to investigate the impact of the partial volume effect (PVE) on clinical IMAGING in PET and SPECT with current state-of-the-art instrumentation and the implications that this has for RADIONUCLIDE dosimetry estimates. Methods: Using the IEC Image Quality Phantom we have measured the underestimation in observed uptake in objects of various sizes for both PET and SPECT IMAGING conditions. Both single pixel measures (i. e., SUVmax) and region of interest mean values were examined over a range of object sizes. We have further examined the impact of the PVE on dosimetry estimates in OLINDA in 177Lu SPECT IMAGING based on a subject with multiple somatostatin receptor positive paragangliomas in the head and neck. Results: In PET, single pixel estimates of uptake are affected for objects less than approximately 18 mm in minor axis with existing systems. In SPECT IMAGING with medium energy collimators (e. g., for 177Lu IMAGING), however, the underestimates are far greater, where single pixel estimates in objects less than 2-3×the resolution volume are significantly impacted. In SPECT, region of interest mean values are underestimated in objects less than 10 cm in diameter. In the clinical case example, the dosimetry measured with SPECT ranged from more than 60% underestimate in the largest lesion (28×22 mm in maximal cross-section,10. 2 cc volume) to >99% underestimate in the smallest lesion (4×5 mm,0. 06 cc). Conclusion: The partial volume effect remains a significant factor when estimating RADIONUCLIDE uptake in vivo, especially in small volumes. Accurate estimates of absorbed dose from RADIONUCLIDE therapy will be particularly challenging until robust solutions to correct for the PVE are found.

Introduction: Low-pass filters eliminate noise, and accordingly improve the quality of filtered back-projection (FBP) in the reconstruction of single photon emission computed tomography (SPECT) images. This study aimed at selection of an optimum low-pass filter for FBP reconstruction of SPECT images of small structures. Material and Methods: Spheres A, B, and C (16 mm, 12 mm, and 11 mm in diameter, respectively) attached to capillary stems were filled with technetium-99m solution (activity concentration 300 kBq/mL). They were then mounted inside a Jaszczak Phantom forming a V-shaped structure. The phantom was then filled with distilled water. Two-dimensional (2D) projections were acquired on 128 ×128 pixels using a Siemens E-Cam dual-head gamma camera. The Parzen, Shepp-Logan, Low Pass Cosine filters (cut-off frequencies: 0. 2-0. 9), and Butterworth filter (order: 1-9; cut-off frequencies: 0. 3-0. 9) were employed during FBP reconstruction. The line command of ImageJ software was used to draw the point spread functions of acquired 2D transaxial central slices and for the measurement of their full-width at half-maximum (FWHM). Results: The FWHM of 2D central image slices of spheres A, B, and C reconstructed using a Butterworth filter measured 20, 20, and 10 pixels, respectively. In comparison, the reconstructed images using the Parzen, Low Pass Cosine, and Shepp-Logan filters measured to 27, 25 and, 22 pixels for sphere A, 24, 22, 20 pixels for B, and 22, 20, 18 pixels for C, respectively. Conclusion: The low-pass filters successfully suppressed noise during the FBP reconstruction of SPECT images of small structures. Accordingly, the Butterworth is a suitable choice.

Background: This study aims to investigate voxel-level dose calculation methods and improve its calculation efficiency in nuclear medicine that can consider animal-specific heterogeneous tissue compositions and radiopharmaceutical biodistributions simultaneously. Materials and Methods: The voxelized mouse phantom was constructed from real mouse CT images and simulated using the Monte Carlo GEANT4 code. According to the dynamic PET images of real mouse, the real distribution of radiopharmaceutical activity was set in the Monte Carlo simulation. The sampling method to improve the calculation efficiency was proposed. Two voxel-level dose calculation methods were implemented in this study. The average absorbed dose in vital target organs and the tumor was calculated by the proposed voxel-level dose calculation methods and the traditional MIRD method respectively. The results of the average absorbed dose calculated by the two methods were compared. Based on the voxel-level dose calculation method, the three-dimensional dose distribution in organs and the tumor was obtained and evaluated. Results: The relative difference of average absorbed dose between the two voxel-level dose calculation methods was mostly less than 10%. The sampling method proposed to improve calculation efficiency for the voxel-level dose calculation can decrease the calculation time by ~34% with less deviation. Conclusion: The results confirmed that the voxel-level dose calculation methods proposed in this study allow for more accurate and efficient assessment of the internal radiation dose.

Statement of problem: Condylar hyperplasia of the mandible is a self limiting abnormality which can cause facial asymmetry, temporomandibular joint (TMJ) dysfunction and esthetic problems. Treatment planning is based on the results of isotope scanning, clinical findings and patient age. Single photon emission tomography (SPECT) is considered to be a sensitive method in the calculation of condylar uptake differences.Purpose: The aim of this study was to determine the growth activity occurring in the mandibular condyles, and to devise an index of side-to-side differences in condylar activity in different individuals. Material and Methods: 38 patients, with an age range of 13 to 34 years, undergoing skeletal scintigraphy for a variety of conditions, were chosen for this study. 25 mci TC- 99 was injected to all subjects in order to assess the difference between right (Rt) and left (Lt) condylar uptake percentage and to calculate the Lt to Rt condylar uptake ratio. The normal index was determined.Results: The maximum amount of difference between the uptake of Rt and Lt condyles was 6.2 percent (Lt side and Rt side were 53.1 % and 46.9 %, respectively) in the male patients and 5.7 percent in the female patients (Lt side and Rt side were 52.85 % and 47.15 %, respectively). The condylar activity difference and ratio of Lt to Rt condylar uptakes did not show a significant difference between the male and female groups.Conclusion: The difference between the growth activity of RT and LT normal TMJs was less than 6.2 percent.

Introduction: In Peptide Receptor RADIONUCLIDE Therapy (PRRT), the administration of RADIONUCLIDE such as Lu-177 label with a pharmaceutical agent useful to destroy the lesion. The amount of Lu-177 radioactivity administered to the patients is still not standardize and generally not more than 7. 4 GBq per session due to the patient’ s safety issues. The first cycle of Lu-177 is an excellent technique to estimate RADIONUCLIDE uptake for organs at risk. This study aims to simplify five SPECT-CT scanning points into less scanning points to estimate absorbed dose to the organ at risk. Methods: Ten patients who have neuroendocrine tumors enrolled in 177Lu-Dotatate therapy dosimetry. The serial SPECT-CT done after 2, 4, 24, 48 and 72 hours to acquired time disintegration for organ at risk. Partik’ s categorical grading criteria is relevantly used in this study to convert the numeric value of Lin’ s concordance coefficient into an ordinal scale. Results: Our current result demonstrated an excellent agreement between three and five scanning with LSA exponential fit method. These excellent results presented for kidney, liver and spleen. However, the bladder shows poor results due to the urinary system. Conclusion: Three data point of SPECT-CT images is the best option to estimate absorbed dose to the lesion and organ at risk for 177Lu-Dotatate dosimetry technique.