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: The limited resolution of the imaging system causes PARTIAL VOLUME EFFECTs (PVEs). These results in spreading of image counts to the neighboring pixels. This phenomenon is called spill-out EFFECT. This study aimed at quantifying PVEs using ImageJ.Methods: Technetium-99m solution of concentration of 74 kBq/ml was filled into spheres A, B and C of diameters: 26 mm, 20 mm and 16 mm respectively. The spheres were imaged mounted inside a Jaszczak phantom filled with activity free water using a Siemens E-Cam dual head gamma camera. Images were quantified using ImageJ following a two-step method. Step 1: Drawing of region of interest 1 (ROI 1) closely on the boundary of the planar image to extract images counts before PVEs correction. Step 2: Drawing region of interest 2 (ROI 2) to extract true sphere image counts. ROI 2 extends from the boundary of ROI 1 by the FWHM of the imaging system.Results: The study revealed that PVEs are aggravated by decrease in sphere size. Underestimation of image counts on the 64×64 pixels matrix was found to be: 9.7%; 15% and 26% in the order of decreasing sphere size. However, an improvement in the spatial resolution decreased PVEs (128×128 pixels: 6.7%; 12.0% and 22.5%; 256×256 pixels: 6.5%; 9% and 19.3%; 256×256 pixels: 6.1%; 8.0% and 18.7% in the order of decreasing sphere size).Conclusion: ImageJ successfully quantified PVEs attributed to the spill-out EFFECT in planar imaging.

Objective(s): The PARTIAL VOLUME EFFECT (PVE) of single-photon emission computed tomography (SPECT) on corpus striatum imaging is caused by the underestimation of specific binding ratio (SBR). A large ROI (region of interest) set using the Southampton method is independent of PVE for SBR. The present study aimed to determine the optimal ROI size with contrast and SBR for striatum images and validate the Southampton method using a three-dimensional mathematical cylinder (3D-MAC) phantom.Methods: We used ROIs sizes of 27, 36, 44, 51, 61, 68, and 76 mm for targets with diameters 40, 20, and 10 mm on reference and processed images reconstructed using the 3D-MAC phantom. Contrast values and SBR were compared with the theoretical values to obtain the optimal ROI size.Results: The contrast values in the ROI with diameters of 51 (target: 40 mm in diameter) and 44 (target: 20 mm in diameter) mm matched the theoretical values. However, this value did not correspond with the 10-mm-diameter target. The SBR matched the theoretical value with an ROI of >44 mm in the 20-mm-diameter target; but, it was under- and overestimated under any other conditions.Conclusion: These results suggested that an ROI should be 4-2 folds larger than the target size without PVE, and that the Southampton method was remarkably accurate.

Objective(s): Somatostatin receptor scintigraphy (SRS) using 111 In-pentetreotide has no established quantification method. The purpose of this study was to develop a new quantitative method to correct the PARTIAL VOLUME EFFECT (PVE) for individual energy peaks in 111 In-pentetreotide single-photon emission computed tomography (SPECT). Methods: Phantom experiments were performed to construct a new quantitative method. In the phantom experiments, a NEMA IEC body phantom was used. Acquisition was performed using two energy peaks (171 keV and 245 keV) on the SPECT/CT system. The VOLUME of interest was set at each hot sphere and lung insert in the SPECT images of each energy peak, and the recovery coefficient (RC) was calculated to understand the PVE. A new quantitative index, the indium uptake index (IUI), was calculated using the RC to correct the PVE. The quantitative accuracy of the IUI in the hot sphere was confirmed. Case studies were performed to clarify the quantitative accuracy. In a case study, the relationship between the IUI and the Krenning score, which is used as a visual assessment, was evaluated for each lesion. Results: The obtained RCs showed that the energy peak at 171 keV was faster in recovering the EFFECT of PVE than that at 245 keV. The IUI in the 17-mm-diameter hot sphere was overestimated by 4. 8% and 8. 3% at 171 keV and 245 keV, respectively, compared to the actual IUIs. The relationship between IUI and Krenning score was rs=0. 773 (p<0. 005) at sum, rs=0. 739 (p<0. 005) at 171 keV, and rs=0. 773 (p<0. 005) at 245 keV. Conclusion: We have developed a new quantification method for 111 In-pentetreotide SPECT/CT using RC-based PVE correction for an individual energy peak of 171 keV. The quantitative accuracy of this method was high even for accumulations of less than 20 mm, and it showed a good relationship with the Krenning score,therefore, the clinical usefulness of IUI was demonstrated.

This paper reports a study on the EFFECT of the heat flux, cooling water flow rate, fill ratio and extra VOLUME on the overall performance of a PARTIALly vacuumed thermosyphon. A rig was made from a 1 m copper tube with an inner and outer diameter of 17.5 and 19 mm. The heights of the evaporator, the adiabatic section and the condenser are 40, 20 and 40 cm, respectively. The temperatures at different places on the thermosyphon and on the inlet/outlet of the cooling water were measured. It was observed that change in heat flux, fill ratio and employing different extra VOLUMEs, has a significant EFFECT on its performance. On the other hand, with changes in the cooling water flow rate the performance of the thermosyphon was altered regarding the trapped air movement. In order to illustrate the EFFECT of the existence of air in deactivating the thermosyphon, the pipe was cooled down by disconnecting the evaporator power input. It was seen that the thermosyphon loses its performance as the trapped gas occupies the whole condenser. The whole study shows that due to the existence of the trapped air, the heat loads can have significant EFFECTs on the thermosyphon performance.

Introduction: Radical radiation therapy of head and neck cancers may injure the salivary glands and reduce their function. Single-photon emission computed tomography (SPECT) images maybe used to evaluate function post-therapy. However, accurate quantification is hindered by the PARTIAL VOLUME EFFECTs (PVEs). The present study involved the introduction of a PVEs quantification technique aimed at improved quantification of the salivary glands function. Material and Methods: The parotid and submandibular salivary glands were mimicked with hollow spheres. The left parotid (LP), right parotid (RP), left submandibular (LSM), and right submandibular (RSM) salivary glands had diameters; 16, 14, 11, and 12 mm, respectively. Technetium-99m solution (activity concentration; 300 kBq/mL) filled the salivary glands prior to implanting into a hollow head and neck phantom later filled with the technetium-99m solution (activity concentration; 1440 Bq/mL). A SPECT image was acquired on 128 × 128 matrix size over 30 min and reconstructed using filtered back projection algorithm (Butterworth filter with a cut-off frequency of 0. 9 cycles per pixel and an order of 9). Reconstructed images were quantified using ImageJ software. Results: The image counts extracted from the LP, RP, RMS, and LMS salivary glands SPECT images were 672 019, 494 842, 398 091, and 262 908, respectively after the quantification of PVEs, compared to 486 320, 347 534, 272 940, and 175 307 before the quantification of PVEs. The respective quantitative errors were 27%, 29%, 31%, and 33%. Conclusion: Quantification of PVEs allows recovery of image counts spread outside the image pixels leading to improved quantification.