Low Energy High Resolution Research Articles

Evaluation of Improved Imaging Properties with Tungsten-Based Parallel-Hole Collimators: A Monte Carlo Study

Abstract Objectives The purpose of a parallel-hole collimator in a scintillation camera system is to transmit only those photons that have an emission angle close to the direction of the hole. This makes it possible to receive spatial information about the origin of the emission, that is, radioactivity decay. The dimension, shape, and intrahole thickness determine the spatial resolution and, by a tradeoff, sensitivity. The composition of the collimator material also plays an important role in determining a proper collimator. In this study, we compared tungsten alloys as a potential collimator material replacement for the conventional lead antimony material used in most of the current camera systems. Materials and Methods Monte Carlo simulations of a commercial scintillation camera system with low energy high resolution (LEHR), medium-energy (ME), and high-energy (HE) collimators of lead, tungsten, and tungsten-based alloy were simulated for different I-131, Lu-177, I-123, and Tc-99m sources, and a Deluxe rod phantom using the SIMIND Monte Carlo code. Planar images were analyzed regarding spatial resolution, image contrast in a cold source case, and system sensitivity for each collimator configuration. The hole dimensions for the three collimators were those specified in the vendor's datasheet. Results Using Pb, W, and tungsten alloy (Wolfmet) as collimator materials, the full width at half maximum (FWHM) measures for total counts (T) for LEHR with Tc-99m source (6.9, 6.8, and 6.8 mm), for ME with Lu-177 source (11.7, 11.5, and 11.6 mm), and for HE with I-131 (6.2, 13.1, and 13.1 mm) were obtained, and the system sensitivities were calculated as 89.9, 86.1, and 89.8 cpsT/MBq with Tc-99m source; 42.7, 17.4, and 20.9 cpsT/MBq with Lu-177 source; and 40.1, 69.7, and 77.4 cpsT/MBq with I-131 source. The collimators of tungsten and tungsten alloy (97.0% W, 1.5% Fe, 1.5% Ni) provided better spatial resolution and improved image contrast when compared with conventional lead-based collimators. This was due to lower septal penetration. Conclusion The results suggest that development of a new set of ME and HE tungsten and tungsten alloy collimators could improve imaging of I-131, Lu-177, and I-123.

Ring Artifact on SPECT Image due to Arbitrary Position of PMT Malfunction

To obtain high-quality images using SPECT (Single Photon Computed Emission Tomography) imaging, quality control (QC) is required. QC is periodically conducted on SPECT based on standard protocol. Ring artifact are one of the factors in determining optimal image quality. Uniformity is a parameter that determines the ring artifact on SPECT image, which can be appeared as full-ring or half-ring. Those artifacts were generated since one or more PMT (photomultiplier tubes) were malfunctioning. A copper sheet with size of 2 × 2 cm2 and 1 mm thick, attached to LEHR (Low Energy High Resolution) collimator in coordinates (x,y) depending on COR (Center of Rotation) of the gamma camera, was used to generate ring artifact during image acquisition using radioisotope 99

IMPROVING THE QUANTIFICATION ACCURACY OF Tc-99m MIBI DUAL-PHASE PARATHYROID SPECT/CT: A MONTE CARLO SIMULATION STUDY

Objective: Quantitative parathyroid SPECT imaging is a technique used to assess Primary hyperparathyroidism that may have potential in the identification and differentiation of parathyroid lesions as well as the estimation of disease severity. Studying the effect of data acquisition parameters on the quantification error is important for maximizing the accuracy of this diagnostic technique. In this study we examine the effects of different data acquisition parameters, namely the type of collimator, scatter correction status and reconstruction iteration number on the quantification accuracy using computer simulation. Methods: The SIMIND Monte Carlo Simulation and CASToR iterative reconstruction program was used to simulate a commercially available SPECT camera (Siemens Symbia Intevo Gamma Camera) with a crystal size of 29.55cm and 128x128 matrix size. A digital cylindrical phantom filled with water was constructed. A 0.36 cm radius spherical adenoma filled with a uniform 1MBq radioactivity is placed within the phantom. Low-Energy High Resolution (LEHR) and Low Energy Ultra High Resolution (LEUHR) collimator models are tested. Along with the presence of Scatter correction and differing iteration numbers (x16, x32). An image FOV based calibration method was used to gather quantitative information and checked against the input radioactivity. Results: The presence of scatter correction caused a 15-20% relative improvement in quantification accuracy. The optimal number of iterations produced a 10% relative improvement. Overall, accuracies as good as 7% in estimated activity concentration could be observed. Conclusion: The optimization of parameters can provide a significant improvement in quantification accuracy.

Impact of Attenuation Correction, Collimator, and Iterative Reconstruction Protocols on 67Ga SPECT/CT Quantification

Purpose: The main goal of this study was to determine the optimal collimator in the absence of medium energy collimators along with the impact of Attenuation Correction (AC) and different iterative reconstruction protocols on the quantitative evaluation of Gallium-67 (67Ga) SPECT/CT imaging.
 Materials and Methods: A GE Discovery 670 dual-head SPECT/CT scanner and a NEMA phantom filled with 67Ga solution were used to scan the patients. The projections were acquired with both Low Energy High Resolution (LEHR) and High Energy General Purpose (HEGP) collimators, and CT images were acquired to evaluate the effect of attenuation correction. SPECT data were reconstructed using the ordered subset expectation maximization (OSEM) method with various combinations of iterations and subsets. The performance was quantified, and a clinical study validated the phantom study.
 Results: Acquired images by the HEGP collimator yielded higher Contrast Recovery (CR) and Contrast to Noise Ratio (CNR) in images with AC than those without non-AC (41.6% and 74.2%, respectively). The CNR in all spheres after AC was increased by 80.4% (82.1%) for the HEGP collimator against the LEHR collimator. Also, an increase in iterations × subsets from 16 to 48 led to the Coefficient of Variation (COV) increasing by 17.2%, 16.67%, 15.50%, 14.4%, 14.2%, and 14.1% for 10 mm to 37 mm sphere diameter, respectively.
 Conclusion: CT-based AC and HEGP collimators can yield improved 67Ga SPECT quantification compared to Non-AC and LEHR collimators. The choice of the optimal collimator with the reconstruction protocol led to changes in the image quality and quantitative accuracy, emphasizing the need to carefully select the appropriate combination of data acquisition factors.

Impact of Wolfmet Tungsten Alloys as Parallel-Hole Collimator Material on Single-Photon Emission Computed Tomography Image Quality and Functional Parameters: A Simulating Medical Imaging Nuclear Detectors Monte Carlo Study.

Objectives Collimators have a significant role in image quality and detectability in single-photon emission computed tomography (SPECT) imaging. Using an appropriate alloy that effectively absorbs scattered photons, without induced secondary x-rays, and with proper rigidity and weight may provide an effective approach to the image improvement that conventionally collimators made of lead (Pb). Materials and Methods A Siemens E.CAM SPECT imaging system equipped with low-energy high-resolution (LEHR) collimator was simulated by the Simulating Medical Imaging Nuclear Detectors Monte Carlo program. Experimental and simulated data were compared based on a 2-mm 99m Tc point source in an acrylic cylindrical Deluxe phantom (Data Spectrum, Inc). Seven types of tungsten (W) alloys (Wolfmet), with W content from 90 to 97% by weight, were then used as collimator materials of the simulated system. Camera parameters, such as energy- and spatial resolution, image contrast, and collimator-related parameters, such as fraction of septal penetration, scatter-to-primary ratios, and percentage of induced secondary x-rays, due to interactions in the collimator, were evaluated. Results Acceptable conformity was found for the simulated and experiment systems in terms of energy spectra, 10.113 and 10.140%, full width at half-maximum (FWHM) of the point spread function (PSF) curves, 8.78 and 9.06 mm, sensitivity, 78.46 and 78.34 cps/MBq, and contrast in images of 19.1 mm cold spheres in the Deluxe phantom, 79.17 and 78.97%, respectively. Results on the parameters of the simulated system with LEHR collimator made from the alloys showed that the alloy consisting of 90% W, 6% nickel, and 4% copper provided an FWHM of 8.76 mm, resulting in a 0.2% improvement in spatial resolution. Furthermore, all the Wolfmet collimators showed a 48% reduction in the amount of X-rays production compared to the Pb. Conclusion A Wolfmet LEHR collimator, made by a combination of W (90%), Ni (6%), and Cu (6%) provides a better image quality and detectability compared to the Pb.

Monte Carlo simulation of SPECT characterization for 223 Ra post-injection scintigraphy.

223 Ra is a promising α-emitting radionuclide for prostate cancer metastasis palliative treatment. Post-injection scintigraphy is of major importance to verify the concentration of the radiopharmaceutical in the targeted sites. Given the low activity administered to patients, the choice of acquisition parameters, including the collimator type, the energy window's width and the photopeak energy to be used, is primordial for the image quality. The purpose of our work was to select the SPECT configuration suitable for 223 Ra post-injection scintigraphy. We conducted simulation studies with a Symbia T6 Siemens SPECT-CT, available in our department. 223 Ra photons energy spectra were assessed for low energy high resolution (LEHR), medium energy (ME) and high energy (HE) collimators. Then, depending on the energy window, we calculated the scatter fraction, the sensitivity and the spatial resolution. Scatter fraction was low for all collimators; however, the contribution of photons that scattered more than twice under the low energy photopeaks was important in the case of LEHR. Sensitivity's best values were obtained in the case of the LEHR collimator; nevertheless, the spatial resolution was very low for this collimator. The latter was best for ME and HE collimators. A combination between a good sensitivity, a high spatial resolution and a low scatter fraction has been determined in the case of the ME collimator, followed by HE collimator as an alternative. To increase the image acquisition statistics with ME collimator, we recommend to use simultaneous energy windows: 20% centered at 82 keV, 20% centered at 154 keV and 20% centered at 270 keV.

Performance evaluation of a novel multi-pinhole collimator on triple-NaI-detector SPECT/CT for dedicated myocardial imaging

BackgroundIn this study we evaluated the imaging capabilities of a novel Multi-pinhole collimator (MPH-Cardiac) specially designed for nuclear cardiology imaging on a Triple-NaI-detector based SPECT/CT system.Methods99mTc point source measurements covering the field of view (FOV) were used to determine tomographic sensitivity (TSpointsource) and spatial resolution. Organ-size tomographic sensitivity (TSorgan) was measured with a left ventricle (LV) phantom filled with typical myocardial activity of a patient scan. Reconstructed image uniformity was measured with a 140 mm diameter uniform cylinder phantom. Using the LV phantom once filled with 99mTc and after with 123I, Contrast-to-noise ratio (CNR) was measured on the reconstructed images by ROI analysis on the myocardium activity and on the LV cavity. Furthermore, a polar map analysis was performed determining Spill-Over-Ratio in water (SORwater) and image noise. The results were compared with that of a dual-head parallel-hole low energy high resolution (LEHR) collimator system. A patient with suspected coronary artery disease (CAD) was scanned on the LEHR system using local protocol of 16 min total acquisition time, followed by a 4-min MPH-Cardiac scan.ResultsPeak TSpointsource was found to be 1013 cps/MBq in the axial center of the FOV while it was decreasing toward the radial edges. TSorgan in the CFOV was found to be 134 cps/MBq and 700 cps/MBq for the LEHR and MPH-Cardiac, respectively. Average spatial resolution throughout the FOV was 4.38 mm FWHM for the MPH-Cardiac collimator. Reconstructed image uniformity values were found to be 0.292% versus 0.214% for the LEHR and MPH-Cardiac measurements, respectively. CNR was found to be higher in case of MPH-Cardiac than for LEHR in case of 99mTc (15.5 vs. 11.7) as well as for 123I (13.5 vs. 8.3). SORwater values were found to be 28.83% and 21.1% for the 99mTc measurements, and 31.44% and 24.33% for the 123I measurements for LEHR and MPH-Cardiac, respectively. Pixel noise of the 99mTc polar maps resulted in values of 0.38% and 0.24% and of the 123I polar maps 0.62% and 0.21% for LEHR and MPH-Cardiac, respectively. Visually interpreting the patient scan images, MPH-Cardiac resulted in better image contrast compared to the LEHR technique with four times shorter scan duration.ConclusionsThe significant image quality improvement achieved with dedicated MPH-Cardiac collimator on triple head SPECT/CT system paves the way for short acquisition and low-dose cardiovascular SPECT applications.

Comparison of Taiwanese and European Calibration Factors for Heart-to-Mediastinum Ratio in Multicenter 123I-mIBG Phantom Studies.

Background: Cross-calibration of 123I-labeled meta-iodobenzylguanidine (mIBG) myocardial-derived indices is essential to extrapolate findings from several clinical centers. Here, we conducted a phantom study to generate conversion coefficients for the calibration of heart-to-mediastinum ratios and compare them between Taiwan and Europe. Methods: We used an acrylic phantom dedicated to 123I-mIBG planar imaging to calculate the conversion coefficients of 136 phantom images derived from 36 Taiwanese institutions. A European phantom image database including 191 images from 27 institutions was used. Conversion coefficients were categorized into five collimator types: low-energy (LE) high-resolution (LEHR), LE general-purpose (LEGP), extended LEGP (ELEGP), medium-energy (ME) GP (MEGP), and ME low-penetration (MELP) collimators. Results: The conversion coefficients were 0.53 ± 0.039, 0.59 ± 0.032, 0.79 ± 0.032, 0.96 ± 0.038, and 0.99 ± 0.050 for LEHR, LEGP, ELEGP, MEGP, and MELP collimators, respectively. The Taiwanese and European conversion coefficients for the LEHR, LEGP, and MELP collimators did not significantly differ. The coefficient of variation was slightly higher for the Taiwanese than the European conversion coefficients (3.7%-7.5% vs. 2.3%-5.6%). Conclusions: We calculated conversion coefficients for various types of collimators used in Taiwan using a 123I-mIBG phantom. In general, the Taiwanese and European conversion coefficients were comparable. These findings further corroborated and highlighted the need for 123I-mIBG standardization using the phantom-determined conversion coefficients.

Three-photon absorption platinum (II) complexes based on DNA and L-lysine recognition for photodynamic antimicrobial therapy

New agents for treating bacterial infections and promoting wound healing are urgently needed in facing the crisis of multidrug-resistant bacteria. The multi-photon AIE complex has good tissue penetration, low energy loss and high resolution, hence, multi-photon AIE complexes have great potential in the treatment of bacterial infections. In this work, platinum (II) complex FLPt1 exhibits better three-photon AIE performance (1450 nm) than FLPt2 in DMSO/H2O system. There are variety of intermolecular forces in FLPt1 and FLPt2 through terminal substituent regulation, leading to the difference in three-photon AIE performance. Furthermore, FLPt1/FLPt2 can induce mitochondrial collapse, and effectively responds to L-lysine and DNA by electrostatic bonding. FLPt1/FLPt2 aggregates around bacteria and destroys bacterial walls containing L-lysine. FLPt1/FLPt2 enters the bacteria and damages the DNA, leading to the bacteria death. From the above all, this work enriches existing antibacterial arsenals and facilitates the development of more promising antibacterial agents with platinum complexes in the future.

Monte Carlo approach to comparison of parallel-hole collimators of clinical scintillation camera system for imaging astatine-211 (At-211)

Astatine-211 (At-211) is a promising alpha particle emitter for targeted radionuclide therapy. Since its daughter isotope (polonium-211(Po-211)) emits characteristic X-rays of about 80 keV, the distribution of At-211 in the body can be imaged by detecting the X-rays with a scintillation camera. However, the isotopes also emit high-energy gamma photons that are collimated with difficulty for a parallel-hole collimator of a clinical scintillation camera system, and thus the selection of a collimator is important. In this study, we compared the performances of low-energy high-resolution (LEHR), low-energy all-purpose (LEAP), medium-energy (ME), and high-energy (HE) parallel-hole collimators for At-211 using Monte Carlo simulation. We simulated a clinical scintillation camera system with the collimators using the Geant4 toolkit. The energy spectra, sensitivities, and spatial resolutions for the point source of At-211 were evaluated. Moreover, we simulated imaging of six sphere sources of At-211 in a 1-cm-thick cylindrical phantom filled with At-211 solution to evaluate image contrast. All of the results in this study are simulation data. The spatial resolution with LEHR was 7.6 mm full width at half maximum (FWHM) and the highest between collimators, while the sensitivity with LEAP was 85 cps/MBq and the highest. The image contrast acquired with the ME collimator was superior to those with the other collimators. We concluded that the LEHR, LEAP, and ME collimators had their advantages, so an optimum collimator should be selected depending on the purpose of imaging of At-211, although there was no advantage in using the HE collimator for the imaging of At-211.

Accuracy of 123I Na Thyroid Imaging in calculating thyroid volume.

Introduction: Hyperthyroidism is often managed with radioactive iodine therapy. The dose of 131Iadministered to the patient is determined based on the calculated size of the thyroid gland in gram and 24 hour iodine uptake. Ultrasonography is a validated modality for determination of thyroid volume. Though necessary for assessing degree of 123I uptake, nuclear scintigraphy also allows for the capability of estimating thyroid volume. Here we compare volume measurements calculated based on ultrasonography and nuclear scintigraphy in a cohort of hyperthyroid patients. Methods: This prospective study designed to evaluate 110 consecutive hyperthyroidism patients who were undergoing thyroid ultrasound and 123I scintigraphy. Scintigraphy was performed after oral administration of approximately 11 MBq 123Isodium, and uptakes at 2 and 24 hours were measured. At 24 hours, the patients underwent thyroid scan with a nuclear medicine camera with LEHR (low energy high resolution) collimator next to the patient's chin. Thyroid measurements were calculated via the formula for determining a prolate ellipsoid. The formula was modified for RAIU as it is a planar image. Volumes calculated with these two modalities were subsequently analyzed and compared by linear regression. All patients had undergone ultrasonography with an average three months from nuclear scan. All of our patient 131I dosages were based on the thyroid measurements obtained by thyroid scintigraphy. Results: We included 110 patients (95 females, 15 males) with age range 20-95 years and average age 56 +/- 17.4 years old. Diagnoses included 66 patients with nodular goiter, and 44 patients with Graves' Disease. There was a linear relationship between measurement of thyroid gland weight by two modalities which can be explained in the following formula: log US(g) = 0.841 + 0.649*log NM(g). Conclusion: We have validated that this method has helped obtain more accurate measurements of the thyroid gland by thyroid scintigraphy. Additionally, we have derived conversion factors that convert the estimated thyroid volume calculated from thyroid scintigraphy to the expected ultrasound value.

Critical Appraisal of Radionuclide Calibrators and Gamma Cameras Prior to Lutetium-177 Internal Dosimetry at Two South African Hospitals.

Introduction The functionality of radionuclide dose calibrator and nuclear medicine imaging systems hasa direct effect on the accuracy and preciseness of internal dosimetry evaluations. Our study, therefore, aimed to critically appraise the radionuclide calibrators and gamma cameras prior to Lutetium-177 ( 177 Lu) internal dosimetry in a developing country. Materials and Methods Two radionuclide calibrators' and three gamma cameras at two South African hospitals were critically appraised in preparation for internal dosimetry of 177 Lu. The radionuclide calibrators' accuracy, linearity, and sample volume abilities were appraised. For the three gamma cameras, the uniformity, energy resolution, center of rotation, and collimator sensitivity were appraised. These appraisals were performed between the years 2014 and 2019. Results The radionuclide calibrators' constancy, accuracy, linearity, and sample volume were within ± 5%. We also integrated a 177 Lu calibration factor into one radionuclide calibrator's library. The three gamma cameras' uniformity was within 2 to 5%, energy resolution within 11%, center of rotation within 2 mm, and the sensitivity recorded for all low energy high resolution collimator. Conclusion Our radionuclide calibrators passed the critical appraisal and may be confidently used for assaying 177 Lu. All three cameras also passed critical appraisal and may be used to assess organ absorbed dose.

Investigation of Different Components of Parallel-Hole Collimator Response to Different Radioisotope Energies Used in Nuclear Medicine Imaging.

The quality of images obtained from the nuclear medicine imaging systems depends on different factors. One of the most important of these factors is the geometrical and physical characteristics of collimator used for imaging with a given radioisotope. The aim of this study is to investigate the contribution of different components of collimator response for determining the most suitable parallel-hole collimator for the different radioisotope energies used in nuclear medicine imaging. In this study, the SIMIND Monte Carlo simulation program is used to determine the contribution of geometrical, penetrating and scattered response components of four hexagonal parallel-hole collimators including low-energy high-resolution (LEHR), low-energy general-purpose (LEGP), medium-energy general-purpose (MEGP), and high-energy general-purpose (HEGP) collimators, for 12 different energies used in nuclear medicine imaging. According to the simulation results, the use of both the LEHR and LEGP collimators leads to a geometrical component above 60% for energies between 69 and 171 keV. On the other hand, for energies between 185 and 245 keV, the MEGP collimator and for energy of 364 keV, the HEGP collimator gives the geometrical components above 70% and 60%, respectively, while for energy of 511 keV, the geometrical response of all four collimators is below 20%. The results of this study show that for two low-energy single-photopeak radioisotopes, Tc-99m and I-123, the LEHR and LEGP collimators, and for high-energy single-photopeak radioisotope, I-131, the HEGP collimator are most suitable collimators. For dual-photopeak In-111 radioisotope and triple-photopeak Ga-67 radioisotope, the MEGP and HEGP collimators and for triple-photopeak Tl-201 radioisotopes, the LEHR and LEGP collimators are proposed as most suitable collimators.

Comparison of Low-Energy and Medium-Energy Collimators for Thyroid Scintigraphy with123I

CE credit: For CE credit, you can access the test for this article, as well as additional JNMT CE tests, online at https://www.snmmilearningcenter.org Complete the test online no later than March 2025. Your online test will be scored immediately. You may make 3 attempts to pass the test and must answer 75% of the questions correctly to receive Continuing Education Hour (CEH) credit. Credit amounts can be found in the SNMMI Learning Center Activity. SNMMI members will have their CEH credit added to their VOICE transcript automatically; nonmembers will be able to print out a CE certificate upon successfully completing the test. The online test is free to SNMMI members; nonmembers must pay $15.00 by credit card when logging onto the website to take the test.123I thyroid scintigraphy can be performed with either a low-energy or a medium-energy (ME) collimator. The high-energy photon emissions from 123I cause septal penetration with scattered photons, which deteriorate image quality. The aim of this study was to evaluate the impact of collimator choice on 123I thyroid scintigraphy in clinical practice. Methods: Forty-seven patients who underwent thyroid planar scintigraphy with both a low-energy, high-resolution (LEHR) collimator and a ME collimator were prospectively recruited using the same imaging protocol. Image quality, collimator sensitivity, and estimation of thyroid size were assessed between LEHR and ME collimators and were compared with thyroid ultrasonography as the gold standard. Results: Images acquired with the ME collimator demonstrated reduced scattered background noise, improved thyroid-to-background contrast, and increased sensitivity in the thyroid gland compared with images acquired by the LEHR collimator. Manual measurement of the thyroid length is more accurate using the ME collimator. Automatic estimation of the thyroid area using the same thyroid threshold is larger in ME collimator images than in LEHR collimator images. Conclusion: Compared with the LEHR collimator, the ME collimator generates cleaner 123I thyroid scintigraphy images with less background noise and has higher collimator sensitivity for thyroid imaging. Different thyroid thresholds should be used to estimate the thyroid area and volume between low and ME collimators.

Evaluation of Iodine-123 and Iodine-131 SPECT activity quantification: a Monte Carlo study

PurposeThe quantitative accuracy of Nuclear Medicine images, acquired for both planar and SPECT studies, is influenced by the isotope-collimator combination as well as image corrections incorporated in the iterative reconstruction process. These factors can be investigated and optimised using Monte Carlo simulations. This study aimed to evaluate SPECT quantification accuracy for 123I with both the low-energy high resolution (LEHR) and medium-energy (ME) collimators and 131I with the high-energy (HE) collimator.MethodsSimulated SPECT projection images were reconstructed using the OS-EM iterative algorithm, which was optimised for the number of updates, with appropriate corrections for scatter, attenuation and collimator detector response (CDR), including septal scatter and penetration compensation. An appropriate calibration factor (CF) was determined from four different source geometries (activity-filled: water-filled cylindrical phantom, sphere in water-filled (cold) cylindrical phantom, sphere in air and point-like source), investigated with different volume of interest (VOI) diameters. Recovery curves were constructed from recovery coefficients to correct for partial volume effects (PVEs). The quantitative method was evaluated for spheres in voxel-based digital cylindrical and patient phantoms.ResultsThe optimal number of OS-EM updates was 60 for all isotope-collimator combinations. The CFpoint with a VOI diameter equal to the physical size plus a 3.0-cm margin was selected, for all isotope-collimator geometries. The spheres’ quantification errors in the voxel-based digital cylindrical and patient phantoms were less than 3.2% and 5.4%, respectively, for all isotope-collimator combinations.ConclusionThe study showed that quantification errors of less than 6.0% could be attained, for all isotope-collimator combinations, if corrections for; scatter, attenuation, CDR (including septal scatter and penetration) and PVEs are performed. 123I LEHR and 123I ME quantification accuracies compared well when appropriate corrections for septal scatter and penetration were applied. This can be useful in departments that perform 123I studies and may not have access to ME collimators.

Comparison of low energy and medium energy collimators in the quantitative assessment of 123I-MIBG cardiac sympathetic innervation imaging

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): University Clinic Hospital of Valencia Aim The assessment of cardiac sympathetic innervation by 123I-metayodobenzylguanidine (123I-MIBG) has proved useful in patients with heart failure and neurodegenerative disorders. The standard quantification of global cardiac uptake is to obtain the heart to mediastinum (HM) ratio in planar images, while SPECT images provide better evaluation of regional extent of denervated areas. Although low energy (LE) collimator has been widely used in these patients, septal penetration of high-energy photons of 123I could affect image quality and quantification accuracy. We have compared in the same patients the effect of collimator type on image quality and quantitative assessment of HM ratio. Methods In a group of 14 patients (11 men, 57-77 y/o, 66.4 ± 5.6) submitted for cardiac sympathetic study, we obtained successive planar anterior chest images 4h after the IV administration of 10 mCi of 123I-MIBG with a low-energy-high-resolution (LEHR) and a medium-energy (ME) collimators. Images were obtained with the same gammacamera Brightview Philips for 10 min on 256x256 matrix, with 159 Kev photopeak and unchanged patient position. For quantification of HM ratio, we use in each patient the same manual heart ROI and rectangular upper mediastinum ROI in the two acquired images to obtain the corresponding HM ratio. Results The image quality was better in all the patients with ME collimator acquisition than with LEHR collimator acquisition, and the HM ratio showed higher values with ME: 1.65-2.61 (mean 2.15 ± 0.28) than with LEHR: 1.27-1.85 (mean: 1.51 ± 0.18) with a mean difference of 0.64 ± 0.15 (0.38-0.88) between ME and LEHR and a mean ratio LEHR/ME of 0.70 ± 0.04 (0.64-0.79). In 9 patients with HM ratio ≤ 1.60 obtained from LEHR collimator acquisition, the mean difference with HM ratio obtained with ME collimator was 0.61 ± 0.12 and mean ratio LEHR/ME was 0.69 ± 0.03 and in 5 patients with HM ratio(LEHR) >1.60, mean difference with HM ratio(ME) was 0.69 ± 0.19 and mean ratio LEHR/ME was 0.71 ± 0.02. Conclusion Use of a ME collimator provides better image quality than LEHR collimator in planar images and higher values of HM ratio, providing a more accurate quantification of cardiac uptake in the patients submitted for evaluation of cardiac sympathetic innervation by 123I-MIBG, and could also improve the evaluation of regional impairment and extent of denervated areas by SPECT.

Highly Sensitive Capacitive Flexible Pressure Sensor Based on a High-Permittivity MXene Nanocomposite and 3D Network Electrode for Wearable Electronics.

With the fast development of consumer electronic and artificial intelligence equipment, flexible pressure sensors (FPSs) have become a momentous component in the application of wearable electronic, electronic skin, and human-machine interfacing. The capacitive FPS possesses the merits of low energy consumption, high resolution, and fast dynamic response, so it is ideal for mobile and wearable electronics. However, capacitive FPS is vulnerable to electromagnetic interference and parasitic capacitance due to its low sensitivity. Microstructure or porous dielectric materials have been applied to improve the sensitivity of the capacitive FPS, but the high sensitivity is just limited to a narrow region. In this work, we propose a different strategy that incorporates a high-permittivity MXene nanocomposite dielectric with a 3D network electrode (3DNE) to improve the sensing performance of the capacitive FPS. Thanks to the high permittivity of the dielectric layer and hierarchical deformation of the electrode, the fabricated capacitive FPS exhibits a high sensitivity of 10.2 kPa-1 in the low pressure range (0-8.6 kPa) and still maintains a relatively high sensitivity of 3.65 kPa-1 with a near-linear response in a wide pressure range (8.6-100 kPa). In addition, the capacitive FPS can withstand over 20,000 times pressure loads without significant signal damping. Furthermore, the working mechanism of the capacitive FPS is illustrated by the finite element analysis (FEA) method and theoretical calculation. The application potential of the sensor in wearable electronics was demonstrated by human pulse wave monitoring and pressure mapping tests with a 4 × 6 sensor microarray.

Monte Carlo simulation of the acquisition conditions for 177Lu molecular imaging of hepatic tumors.

To examine the impact of acquisition time on Lutetium-177 (177Lu) single-photon emission computed tomography (SPECT) images using Monte Carlo simulation. A gamma camera simulation based on the Monte Carlo method was performed to produce SPECT images. The phantom was modeled on a NEMA IEC BODY phantom including six spheres as tumors. After the administration of 7.4GBq of 177Lu, radioactivity concentrations of the tumor/liver at 6, 24, and 72h after administration were set to 1.85/0.201, 2.12/0.156, and 1.95/0.117MBq/mL, respectively. In addition, the radioactivity concentrations of the tumor at 72h after administration varied by 1/2, 1/4, and 1/8 when comparison was made. Acquisition times examined were 1.2, 1.5, 2, 3, 6, and 12min. To assess the impact of collimators, SPECT data acquired at 72h after the administration using six collimators of low-energy high-resolution (LEHR), extended low-energy general-purpose (ELEGP), medium-energy, and general-purpose (MEGP-1, MEGP-2, and MEGP-3) and high-energy general-purpose (HEGP) were examined. After prefiltering using a Butterworth filter, projection images were reconstructed using ordered subset expectation maximization. The detected photons were classified into direct rays, scattered rays, penetrating rays, and characteristic X-rays from lead. The image quality was evaluated through visual assessment, and physical assessment of contrast recovery coefficient (CRC) and contrast-to-noise ratio (CNR). In this study, the CNR threshold for detectability was assumed to be 5.0. To compare collimators, the highest sensitivity was observed with ELEGP, followed by LEHR and MEGP-1. The highest ratio of direct ray was also observed in ELEGP followed by MEGP-1. In comparison of the radioactivity concentration ratios of tumor/liver, CRC and CNR were significantly decreased with smaller radioactivity concentration ratios. This effect was greater with larger spheres. According to the visual assessment, the acquisition time of 6, 6, and 3min or longer was required using ELEGP collimator at 6, 24, and 72h after administration, respectively. Physical assessment based on CNR and CRC also suggested that 6, 6, and 3min or longer acquisition time was necessary at 6, 24, and 72h after administration. 177Lu-SPECT images generated via the Monte Carlo simulation suggested that the recommended acquisition time was 6min or longer at 6 and 24h and 3min or longer at 72h after administration.

Energy window optimization for Bremsstrahlung Y90 SPECT-CT imaging : a phantom study

Introduction: In Yttrium-90 SPECT imaging, the energy window and collimator used during acquisition can have a major effect on image quality. In this work, we used a new and independent method to verify the prevoius results suggest different energy ranges, but all centered at 130 keV. Materials and method: We used Siemens Symbia SPECT-CT system fitted with High Energy General Purpose (HEGP), Medium Energy General Purpose (MEGP) and Low Energy High Resolution (LEHR) to acquire data from NEMA IEC PET Body Phantom with its 6 different spheres of 3.7, 2.8, 2.2, 1.7, 1.3, 1.0 cm diameter. Results:HEGP collimator is the most suitable for acquisitions of 90Y bremsstrahlung radiation from the point of view of the correct volume reproduction. For the bigger sphere’s study, the optimum ISO-counting curves is related to the energy range centred in 130 keV.Conclusion: The results obtained are consistent with previous studies. The Iso Counting Curves method can help to improve image quality.

A novel cooperative compensation method to compensate for return stroke of stick-slip piezoelectric actuators

With the development of micro-electromechanical systems, high precision actuators with high resolution, fast speed, large load capacity are increasingly required. Thanks to the characteristics of flexible structure, fast step speed, low energy consumption, high resolution and unlimited stroke range, stick-slip actuators have been drawing worldwide attention. Traditionally, stick-slip actuators are driven by sawtooth waveform signals with a slow increase and a fast decrease. Therefore, there is an unavoidable return stroke when fast decrease of the driving signal appears, which reduces driving speed and efficiency. In this paper, a novel cooperative compensation method (CCM) to compensate for return stroke of stick-slip actuators is proposed. It uses two signals of specific initial time gap (ITG) to reduce the return stroke to improve speed. A modified two-layer stick-slip piezoelectric actuator based on a triangular compliant driving mechanism is built. Experimental results show that the CCM can effectively increase step size of the actuator, especially driven under low frequencies. When signal is at 10 Hz, the step size of the actuator With CCM is over 29 times of that with traditional single-PSA-driving method (TSM). The maximum step size with CCM is 4.448 µm at 250 Hz, which is more than 40% of TSM.