Gamma Camera Research Articles

High-Flow Nasal Aerosol Therapy; Regional Aerosol Deposition and Airway Responsiveness.

Introduction: In normal subjects, during tidal breathing, aerosols deposit by settling in small airways. With obstructive lung disease (OLD), collapse of airways during expiration causes turbulence and increased deposition in central airways. High-flow nasal cannula (HFNC) therapy, washing out dead space, may affect deposition mechanisms and drug delivery. This study compared aerosol deposition and airway responsiveness in OLD after traditional and HFNC nebulization therapy. Methods: Twelve subjects with moderate to severe OLD participated in a two-day study. Spirometry was measured pre- and post-aerosol inhalation. On Day 1 (D1) subjects tidally inhaled radiolabeled albuterol (99mTc DTPA) by mouth via AeroTech II, (Biodex. Shirley, NY). Day 2 (D2) inhalation was via HFNC using i-AIRE (InspiRx, Inc. Somerset, NJ). The HFNC system (60 L/m) was infused by syringe pump at 50 mL/h. D2 lung deposition was monitored in real time by gamma camera to match D1. Pre and post heart rate, O2 sat, and nasopharyngeal deposition (NP) were measured. Mechanistic contributions were modeled using multiple linear regression (MLR) of deposition rate (DR µg/m) as a function of breathing frequency, airway geometry (FEV1), and parenchymal integrity (DLCO). Results: Albuterol lung depositions were matched (p = 0.13) with D1 central/peripheral (sC/P) ratios 1.99 ± 0.98. Following HFNC, peripheral deposition increased (31% ± 33%, sC/P = 1.51 ± 0.43, p = 0.01). D2/D1% change FVC increased by 16.1 ± 16.7% (p = 0.003). NP deposition averaged 333% of lung. Heart rate and O2 sat were unaffected (p = 0.31, p = 0.63 respectively). DR analysis was markedly different between D1 (R2 = 0.82) and D2 (R2 = 0.12). Conclusion: In subjects with OLD, HFNC nebulization at 60 L/min was well tolerated and increased peripheral drug delivery. Spirometry significantly improved. Systemic effects were undetected indicating limited nasal absorption. MLR demonstrated that different mechanisms of deposition govern traditional vs HFNC aerosol delivery. Breath-enhanced nebulization via HFNC may provide controllable and effective aerosol therapy in OLD.

Thyroid scintigraphy of healthy cats using small-field-of-view gamma cameras

IntroductionSmall-field-of-view (SFOV) gamma cameras can offer higher sensitivities than conventional gamma cameras. However, there are currently no reports on the efficacy and safety of thyroid scintigraphy using SFOV gamma cameras in veterinary medicine. Therefore, we aimed to evaluate the efficacy and radiation safety of an SFOV gamma camera for feline thyroid scintigraphy.Materials and methodsThree veterinary staff members (operator, staff 1, and staff 2) performed thyroid scintigraphy on 10 healthy cats in this study. The operator administered either 2 or 4 mCi of technetium-99m pertechnetate (99mTcO−4) through the cephalic vein. At 20, 40, and 60 min after injection, thyroid images were obtained using a SFOV gamma camera under various acquisition conditions (100,000, 150,000, and 200,000 counts and 30 and 60 s). Thyroid scintigraphy images were analyzed by calculating the thyroid-to-salivary ratios (TSR) and thyroid-to-background ratios (TBR). Surface and ambient radiation were measured hourly from immediately after injection to 6 h. The cumulative occupational radiation doses were measured during the procedure.ResultsThe TSR and TBR median values aligned with the previously reported normal range obtained using a large-field-of-view gamma camera. There were no notable differences in TSR and TBR between the two doses of 99mTcO−4, nor across acquisition conditions and timelines. The 4-mCi group consistently emitted more ambient (p < 0.05) and surface (p < 0.05) radiation than did the 2-mCi group. Staff 1 consistently received higher cumulative radiation doses than did staff 2 and the operator (p < 0.05).ConclusionThe SFOV gamma camera demonstrated adequate image quality for thyroid scintigraphy in healthy cats even with relatively low doses and short acquisition conditions. Radiation exposure during the procedure posed minimal safety concerns. Therefore, the SFOV gamma camera could be a valuable tool for evaluating thyroid glands in cats.

Development of a method to use standard hospital gamma cameras as triage whole body monitors in UK emergencies

This paper outlines the process by which a medical gamma camera can be utilised to support assessment of internal radionuclides for the public. While hospital based gamma cameras are able to detect photopeaks, they are often limited to an energy range of 40-540 keV. However, radionuclides with photopeak energies above 540 keV can still be detected as the partial collection of photon energy increases the count rate at lower energies. By combining extensive mathematical modelling with empirical calibration of multiple gamma cameras it is possible to develop a linear correlation between the efficiency of counting point sources and the overall counting efficiency for the camera. Once established, a simple protocol can be used to characterise any gamma camera, using optimal system settings, and hence generate a system efficiency with sufficient accuracy to allow the camera to be used in a triage process to committed effective doses of 2 mSv.&#xD.

Usefulness and limitations of various detector systems for estimation of 131I thyroid activity following an RN event

Following a radiological or nuclear (RN) event, rapid measurement of131I in members of the public is of utmost importance, and much equipment is needed for a high throughput. In this study, three gamma cameras (GCs), two thyroid uptake meters (TUMs) and one whole-body counter (WBC) were calibrated for activity measurements of131I in the thyroid. Minimum detectable activity was derived for the GCs, the TUMs and the WBC giving that a committed effective dose (CED) in the interval 2.0-85μSv, 13-700μSv and 0.52-6.4μSv, and thyroid absorbed doses in the interval 0.075-2.1 mGy, 0.48-17 mGy, and 0.020-0.15 mGy, respectively, can be assessed for children, adolescents, and adults. These numbers are based on 10 min measurement, performed at 1, 3 and 7 d after intake, and the CED includes intake by ingestion and inhalation of aerosols Type F, with an activity median aerodynamic diameter of 1μm. For a fractional signal loss of 63% due to dead time, a CED up to 2.0, 84 and 3.6 Sv and thyroid absorbed dose up to 47 Gy, 2000 Gy and 88 Gy for the three systems, respectively, can be assessed for children and intake by ingestion as a worst-case scenario in terms of CED, measured 7 d after intake. This study demonstrates the potential and limitations of using equipment readily available at larger hospitals for estimation of131I content in thyroid, which could increase the measurement capability following an RN event.

A Monte Carlo study comparing dead-time losses of a gamma camera between tungsten functional paper and lead sheet for dosimetry in targeted radionuclide therapy with Lu-177.

Dead-time loss is reported to be non-negligible for some patients with a high tumor burden in Lu-177 radionuclide therapy, even if the administered activity is 7.4GBq. Hence, we proposed a simple method to shorten the apparent dead time and reduce dead-time loss using a thin lead sheet in previous work. The collimator surface of the gamma camera was covered with a lead sheet in our proposed method. While allowing the detection of 208-keV gamma photons of Lu-177 that penetrate the sheet, photons with energies lower than 208keV, which cause dead-time loss, were shielded. In this study, we evaluated the usefulness of tungsten functional paper (TFP) for the proposed method using Monte Carlo simulation. The count rates in imaging of Lu-177 administered to patients were simulated with the International Commission on Radiological Protection (ICRP) 110 phantom using the GATE Monte Carlo simulation toolkit. The simulated gamma cameras with a 0.5-mm lead sheet, 1.2-mm TFP, or no filter were positioned closely on the anterior and posterior sides of the phantom. The apparent dead times and dead-time losses at 24h after administration were calculated for an energy window of 208keV ± 10%. Moreover, the dead-time losses at 24-120h were analytically assessed using activity excretion data of Lu-177-DOTATATE. The dead-time loss without a filter was 5% even 120h after administration in patients with a high tumor burden and slow excretion, while those with a lead sheet and TFP were 0.22 and 0.58 times less than those with no filter, respectively. The count rates with the TFP were 1.3 times higher than those with the lead sheet, and the TFP could maintain primary count rates at 91-94% of those without a filter. Although the apparent dead time and dead-time loss with the lead sheet were shorter and less than those with TFP, those with TFP were superior to those without a filter. The advantage of TFP over the lead sheet is that the decrease in primary count rates was less.

Myocardial Perfusion Scintigraphy in Diagnosic of Coronary Heart Disease

<i>Introduction: </i>Atherosclerosis plays a key role in the etiopathogenesis of cardiovascular diseases. Atherosclerosis is a generalized chronic inflammatory disease of the vascular wall, which results in anatomical and histological changes that, together with functional changes, lead to endothelial dysfunction, narrowing of the arterial lumen, and insufficient blood supply to the tissues. The shift in the incidence of cardiovascular diseases to younger age groups is alarming. The presence of microvascular changes in the myocardium is significant. The high incidence of cardiovascular diseases, especially ischemic heart disease, requires early diagnosis and modern treatment. <i>Aim: </i>The aim of the paper is to analyse and point out early diagnosis of coronary heart disease using nuclear medicine methods. <i>Set of examined patients and methodology: </i>Using nuclear medicine methods, we try to detect these changes in time and thus prevent the occurrence of acute coronary events. In nuclear cardiology, instead of a large-area scintillation detector, a new type of cardio-gamma camera "Discovery CZT 530c" based on the principle of semiconductor detectors began to be used. The abbreviation CZT stands for semiconductor composition (Cadmium-Zinc-Tellur). The set of respondents consisted of 4270 people examined in the years 2014-2016 by myocardial perfusion scintigraphy. There were 950 diabetic patients in the analysed group of the 4270 examined. <i>Results:</i> In the analysed group of 4270 respondents, 61% had negative findings and 39% had positive findings in terms of the presence of ischemic heart disease. In the group of diabetic patients, there was a negative finding in 28% of respondents and a positive finding in 72% of the respondents in the sense of positive ischemic heart disease. Using myocardial perfusion scintigraphy in the diagnosis of functional changes, we confirmed a great benefit in detecting early changes in coronary heart disease, including in the diagnosis of microvascular angina. <i>Conclusion:</i> Nuclear medicine methods are of great benefit for the diagnosis of small vessel disease, diabetic cardiomyopathy and cardiac autonomic neuropathy in patients with diabetes mellitus. The new type of cardio gamma camera "Discovery CZT 530c" allows more accurate assessment of myocardial perfusion abnormalities and at the same time the reduction of the radiopharmaceutical dose reduces the patient's radiation load by 50%.

Multislit gamma camera for external beam radiotherapy assistance: Experimental proof of concept

The orthogonal computed tomography (OrthoCT) concept, based on orthogonal ray imaging, is a low-dose imaging technique currently under investigation to potentially aid in external-beam radiation therapy treatments. This technique involves detecting radiation scattered within the patient and emitted at approximately 90° from the direction of the incoming beam. This scattered radiation can be collected by a 1D-detector system with a multisliced collimator positioned perpendicular to the incident beam axis. Such a system holds promise for on-board imaging with the patient positioned and prepared for treatment, as well as for real-time treatment monitoring. In this study, a multi-slice OrthoCT detector prototype was developed and tested under in-beam irradiation. The system utilizes gadolinium orthosilicate scintillator crystals coupled to photomultiplier tubes and a collimator made of lead slices. Experimental measurements were conducted using a heterogeneous phantom made of acrylic with an air cavity inside. The phantom was irradiated with a TrueBeam linac operating at 6 MV in the flattening-filter-free mode. The findings of this study indicate that this innovative imaging technique is capable of providing morphological images of the phantom. This accomplishment is achieved without the need to rotate the X-ray source around the object to be irradiated, demonstrating the feasibility of such a system.

Enhancing bone scan image quality: an improved self-supervised denoising approach.

Bone scans play an important role in skeletal lesion assessment, but gamma cameras exhibit challenges with low sensitivity and high noise levels. Deep learning (DL) has emerged as a promising solution to enhance image quality without increasing radiation exposure or scan time. However, existing self-supervised denoising methods, such as Noise2Noise (N2N), may introduce deviations from the clinical standard in bone scans. This study proposes an improved self-supervised denoising technique to minimize discrepancies between DL-based denoising and full scan images. 
Retrospective analysis of 351 whole-body bone scan data sets was conducted. In this study, we used N2N and Noise2FullCount (N2F) denoising models, along with an interpolated version of N2N (iN2N). Denoising networks were separately trained for each reduced scan time from 5 to 50%, and also trained for mixed training datasets, which include all shortened scans. We performed quantitative analysis and clinical evaluation by nuclear medicine experts.
The denoising networks effectively generated images resembling full scans, with N2F revealing distinctive patterns for different scan times, N2N producing smooth textures with slight blurring, and iN2N closely mirroring full scan patterns. Quantitative analysis showed that denoising improved with longer input times and mixed count training outperformed fixed count training. Traditional denoising methods lagged behind DL-based denoising. N2N demonstrated limitations in long-scan images. Clinical evaluation favored N2N and iN2N in resolution, noise, blurriness, and findings, showcasing their potential for enhanced diagnostic performance in quarter-time scans.
The improved self-supervised denoising technique presented in this study offers a viable solution to enhance bone scan image quality, minimizing deviations from clinical standards. The method's effectiveness was demonstrated quantitatively and clinically, showing promise for quarter-time scans without compromising diagnostic performance. This approach holds potential for improving bone scan interpretations, aiding in more accurate clinical diagnoses.

Optimization of the Pixel Design for Large Gamma Cameras Based on Silicon Photomultipliers.

Most single-photon emission computed tomography (SPECT) scanners employ a gamma camera with a large scintillator crystal and 50-100 large photomultiplier tubes (PMTs). In the past, we proposed that the weight, size and cost of a scanner could be reduced by replacing the PMTs with large-area silicon photomultiplier (SiPM) pixels in which commercial SiPMs are summed to reduce the number of readout channels. We studied the feasibility of that solution with a small homemade camera, but the question on how it could be implemented in a large camera remained open. In this work, we try to answer this question by performing Geant4 simulations of a full-body SPECT camera. We studied how the pixel size, shape and noise could affect its energy and spatial resolution. Our results suggest that it would be possible to obtain an intrinsic spatial resolution of a few mm FWHM and an energy resolution at 140 keV close to 10%, even if using pixels more than 20 times larger than standard commercial SiPMs of 6 × 6 mm2. We have also found that if SiPMs are distributed following a honeycomb structure, the spatial resolution is significantly better than if using square pixels distributed in a square grid.

Comparison of Thyroid Uptake Values Measured from 131I Scintigraphy and Uptake Probe in Hyperthyroid Patients

Objective: Thyroid uptake test plays an important role in diagnosis, treatment planning and radioiodine dose determination in patients with hyperthyroidism. The aim of this study was to compare the % uptake values calculated with gamma camera and uptake probe after diagnostic 131I application in hyperthyroid patients. Materials and Methods: In this study, % uptake values were measured using a thyroid uptake probe and gamma camera in 32 patients who underwent thyroid radioiodine uptake measurement in our Nuclear Medicine center. Thyroid uptake measurements were prepared in the neck phantom with 0.74–0.925 MBq activity of 131I radionuclide. After counting the phantom with 131I separately in the uptake probe and gamma camera, 131I sample was orally administered to the patient. % uptake values were calculated by the uptake probe measurements and drawing regions of interest (ROI) from scintigraphic images at 2 and 24 h. Results: The 2-h mean % uptake values in the probe and gamma camera were calculated as 30.5 ± 20.4 and 27.1 ± 18.6, respectively. The 24-h mean % uptake values in the thyroid probe and gamma camera were calculated as 57.6 ± 21.9 and 55.3 ± 21.5, respectively. Linear regression analyses for the 2- and 24-h % uptake values calculated with the probe and gamma camera were found as R2 = 0.8412 and R2 = 0.7313, respectively. Conclusion: The 2- and 24-h % uptake values with the probe and gamma camera were found to be consistent with each other, indicating that they can be safely used interchangeably in patients with hyperthyroidism.

Optimizing the spatial resolution and gamma discrimination of SiPM-based Anger cameras

SiPM Anger cameras have been designed for use as 2-dimensional thermal neutron detectors for scientific applications such as at single crystal diffraction instruments. These cameras utilize a neutron sensitive scintillator and an array of SiPM photosensors, separated by a light spreading glass. While this optics package is very effective at detecting and positioning neutrons, it is also sensitive to gamma rays, which are a source of unwanted noise. In this work, we underwent a search of scintillator and spreader glass thicknesses to determine the optimal combination for maximizing spatial resolution. Both experimental results and GEANT4 simulations are presented. To address the issue of gamma ray detection, we have also designed and presented a multi-layer scintillator that reduces the amount of scintillation light produced via gamma-ray energy deposition, allowing for easier pulse-height discrimination. A sample of this geometry has been produced that results in a factor of 2 improvement over an equivalent thickness monolithic scintillator.

Nuclear Imaging Modalities in the Diagnosis and Management of Thyroid Cancer.

In this review we have brought forward various nuclear imaging modalities used in the diagnosis, staging, and management of thyroid cancer. Thyroid cancer is the most common endocrine malignancy, accounting for approximately 3% of all new cancer diagnoses. Nuclear imaging plays an important role in the evaluation of thyroid cancer, and the use of radioiodine imaging, FDG imaging, and somatostatin receptor imaging are all valuable tools in the management of this disease. Radioiodine imaging involves the use of Iodine-123 [I-123] or Iodine-131 [I-131] to evaluate thyroid function and detect thyroid cancer. I-123 is a gamma-emitting isotope that is used in thyroid imaging to evaluate thyroid function and detect thyroid nodules. I-131 is a beta-emitting isotope that is used for the treatment of thyroid cancer. Radioiodine imaging is used to detect the presence of thyroid nodules and evaluate thyroid function. FDG imaging is a PET imaging modality that is used to evaluate the metabolic activity of thyroid cancer cells. FDG is a glucose analogue that is taken up by cells that are metabolically active, such as cancer cells. FDG PET/CT can detect primary thyroid cancer and metastatic disease, including lymph nodes and distant metastases. FDG PET/CT is also used to monitor treatment response and detect the recurrence of thyroid cancer. Somatostatin receptor imaging involves the use of radiolabeled somatostatin analogues to detect neuroendocrine tumors, including thyroid cancer. Radiolabeled somatostatin analogues, such as Indium-111 octreotide or Gallium-68 DOTATATE, are administered to the patient, and a gamma camera is used to detect areas of uptake. Somatostatin receptor imaging is highly sensitive and specific for the detection of metastatic thyroid cancer. A comprehensive search of relevant literature was done using online databases of PubMed, Embase, and Cochrane Library using the keywords "thyroid cancer," "nuclear imaging," "radioiodine imaging," "FDG PET/CT," and "somatostatin receptor imaging" to identify relevant studies to be included in this review. Nuclear imaging plays an important role in the diagnosis, staging, and management of thyroid cancer. The use of radioiodine imaging, thyroglobulin imaging, FDG imaging, and somatostatin receptor imaging are all valuable tools in the evaluation of thyroid cancer. With further research and development, nuclear imaging techniques have the potential to improve the diagnosis and management of thyroid cancer and other endocrine malignancies.

Subdiaphragmatic activity-related artifacts in myocardial perfusion scintigraphy.

Myocardial perfusion imaging (MPI) with single photon emission computed tomography is an established non-invasive technique for assessing myocardial ischemia. This method involves the intravenous administration of a radiopharmaceutical that accumulates in the heart muscle proportional to regional blood flow. However, image quality and diagnostic accuracy can be compromised by various technical and patient-related factors, including high non-specific radiopharmaceutical uptake in abdominal organs such as the stomach, intestines, liver, and gall-bladder, leading to subdiaphragmatic artifacts. These artifacts are particularly problematic for evaluating inferior wall perfusion and often necessitate repeated imaging, which decreases gamma camera availability and prolongs imaging times. Despite numerous investigated techniques to reduce interfering gastrointestinal activity, results have been inconsistent, and current MPI guidelines provide scant information on effective procedures to mitigate this issue. Based on our experience, some possible approaches to reducing artifacts include choosing stress testing with an exercise stress test, when possible, late imaging, fluid intake, and consuming carbonated water immediately before imaging.

Effects of lead shielding on gamma radiation scatter energy spectrum during equine bone scintigraphy.

The main aim of this pilot study was to determine how the energy spectrum of scatter radiation emitted from horses after injection of the radiopharmaceutical 99mTechnetium-methyl diphosphonate (99mTc-MDP), changed behind lead shielding of varying thicknesses (0.25 mm, 0.35 mm, and 0.5 mm Pb thickness), and if beam hardening occurred. The effect lead shielding has on the emitted gamma radiation energy spectrum has not been documented. In particular, the presence of beam hardening effects behind lead shielding was investigated, to determine whether or not it could discourage the use of lead shields during bone scintigraphy in horses. Horses were injected intravenously with 99mTc-MDP, and energy spectra emitted from horses without lead shielding were recorded initially to determine the emitted scatter spectrum. Thereafter, different combinations of lead shields of the various thicknesses listed above, draped over the horse and on simulated personnel, were recorded. The energy spectra were obtained at different anatomical locations of five horses on five consecutive days with a pulse height (multichannel) analyser two and a half hours post-injection. Energy spectra recorded from horses without lead shielding showed polychromatic energy spectra that encompassed a large portion of predominantly lower scatter energies (averaging around the 88-94 keV peaks). Higher 99mTc- MDP peaks averaging at 139-143 keV (useful for gamma camera acquisition) were consistently seen in all recordings but made up a very small part of the emitted spectra. With the application of lead shielding, peaks of 83-86 keV, which coincided with K-edges of lead, occurred. No significant beam hardening effects behind lead shields of varying thicknesses were observed. Thus, the wearing of lead shields during bone scintigraphy of horses is encouraged.

Nanopix-v1: A compact miniaturized coded-aperture gamma imager

This article explores the complex challenges associated with detecting and identifying radioactive hotspots in the nuclear industry using gamma cameras. Gamma cameras facilitate the localization of radioactive hotspots by overlaying a visualization of radioactivity onto a visible image. In the nuclear industry, gamma rays are observed in an energy range spanning from 59.5 keV (Am-241) to 1.3 MeV (Co-60).The motivation for this exploration stems from a specific challenge: characterizing hot-cells inaccessible to human operators. At the ORANO La Hague radioactive waste reprocessing plant, access to these restricted regions is possible through apertures with diameters ranging from 8 to 10 cm. In collaboration, the Nanopix-v1, characterized by its compact form as a coded mask gamma imaging system, with dimensions of 8 × 5.1 × 4.3 cm³ and a mass of 268 g, was developed through the synergistic efforts of CEA List and X-ray Imaging Europe (XIE) in partnership with ORANO.This article conducts a detailed examination of the laboratory and in situ performance of the Nanopix-v1, carried out within the challenging operational environment of the La Hague radioactive waste reprocessing plant. The focal point of the article is a comprehensive exploration of the technological components supporting the Nanopix-v1, along with an explanation of the coded mask imaging localization methodologies that underpinned the rigorous evaluation process. The performance of the gamma camera is evaluated through a series of carefully conducted trials, aimed at evaluating the angular resolution and minimum measurement time, including laboratory conditions, experimentation within a metrological Cs-137 irradiator, and practical implementation at the ORANO La Hague site.

Preoperative and Intraoperative Identification of Sentinel Lymph Nodes in Melanoma Surgery.

According to the American Joint Commission on Cancer (AJCC) 8th edition guidelines, SLN biopsy is recommended for primary melanomas with a Breslow thickness of at least 1 mm. Additionally, the National Comprehensive Cancer Network (NCCN) recommends that a SLN biopsy may be considered for melanoma patients with T1b lesions, which are 0.8-1 mm thick or less than 0.8 mm thick with ulceration. It can also be considered for T1a lesions that are less than 0.8 mm thick but have other adverse features, such as a high mitotic rate, lymphovascular invasion, or a positive deep margin. To reduce the false negative rate of melanoma SLN biopsy, we have introduced the intraoperative use of Sentinella, a gamma camera, to enhance the identification rate of SLNs beyond that of the traditional gamma hand-held probe. At the Center for Melanoma Research and Treatment at the California Pacific Medical Center, a multidisciplinary approach has been established to treat melanoma patients when the diagnosis of primary melanoma is made with a referral to our melanoma center. This comprehensive approach at the melanoma tumor board, including the efforts of pathologists, radiologists, dermatologists, surgical, medical and radiation oncologists, results in a consensus to deliver personalized and high-quality care for our melanoma patients. This multidisciplinary program for the management of melanoma can be duplicated for other types of cancer. This article consists of current knowledge to document the published methods of identification of sentinel lymph nodes. In addition, we have included new data as developed in our melanoma center as newly published materials in this article to demonstrate the utility of these methods in melanoma sentinel lymph node surgery. Informed consent has been waived by our IRB regarding the acquisition of clinical data as presented in this study.

3D-localization of single point-like gamma sources with a coded aperture camera

Objective. 3D-localization of gamma sources has the potential to improve the outcome of radio-guided surgery. The goal of this paper is to analyze the localization accuracy for point-like sources with a single coded aperture camera. Approach. We both simulated and measured a point-like 241 Am source at 17 positions distributed within the field of view of an experimental gamma camera. The setup includes a 0.11mm thick Tungsten sheet with a MURA mask of rank 31 and pinholes of 0.08mm in diameter and a detector based on the photon counting readout circuit Timepix3. Two methods, namely an iterative search including either a symmetric Gaussian fitting or an exponentially modified Gaussian fitting (EMG) and a center of mass method were compared to estimate the 3D source position. Main results. Considering the decreasing axial resolution with source-to-mask distance, the EMG improved the results by a factor of 4 compared to the Gaussian fitting based on the simulated data. Overall, we obtained a mean localization error of 0.77mm on the simulated and 2.64mm on the experimental data in the imaging range of 20−100mm . Significance. This paper shows that despite the low axial resolution, point-like sources in the nearfield can be localized as well as with more sophisticated imaging devices such as stereo cameras. The influence of the source size and the photon count on the imaging and localization accuracy remains an important issue for further research.

Development of a single photon emission microscope system with ∼200 μm spatial resolution

With a low-energy pinhole gamma camera, spatial resolution is primarily determined by the intrinsic spatial resolution of the imaging detector, the pinhole diameter, and the magnification ratio of the collimator. However, the pinhole diameter has traditionally been limited to around 1 mm due to manufacturing difficulties with tungsten. To overcome this limitation and enhance the spatial resolution of the pinhole gamma camera, we fabricated a pinhole with a diameter of 0.1 mm. This pinhole was then combined with a YAP(Ce) imaging detector to create an ultrahigh-resolution pinhole gamma camera. The imaging detector consisted of a 38 mm × 38 mm × 1 mm thick YAP(Ce) plate, optically coupled to a 2-inch square flat panel photomultiplier tube (FP-PMT) with a 1 mm thick light guide. The intrinsic spatial resolution of the YAP(Ce) imaging detector was approximately 1.4 mm FWHM for 60 keV gamma photons. The YAP(Ce) imaging detector was encased in a tungsten shield, and the 0.1 mm diameter pinhole collimator was positioned 100 mm from the imaging detector surface. With a magnification ratio of 10 at 10 mm from the pinhole center, the spatial resolution improved to approximately 0.2 mm (200 μm) at 10 mm from the pinhole center using the developed pinhole gamma camera. The system sensitivity was approximately 0.001%. High-resolution transmission images of various subjects were obtained. The developed ultrahigh-resolution pinhole gamma camera was named the “single-photon emission microscope.” This device will be valuable for applications requiring ultrahigh resolution in single-photon gamma or X-ray imaging.

Position-Sensitive Silicon Photomultiplier Arrays with Large-Area and Sub-Millimeter Resolution.

Silicon photomultipliers (SiPMs) are solid-state single-photon-sensitive detectors that show excellent performance in a wide range of applications. In FBK (Trento, Italy), we developed a position-sensitive SiPM technology, called "linearly graded" (LG-SiPM), which is based on an avalanche-current weighted-partitioning approach. It shows position reconstruction resolution below 250 μm on an 8 × 8 mm2 device area with four readout channels and minimal distortions. A recent development in terms of LG-SIPM is a larger chip version (10 × 10 mm2) based on FBK NUV-HD technology (near-ultraviolet sensitive), with a peak photon detection efficiency at 420 nm. Such a large-area detector with position sensitivity is very interesting in applications like MR-compatible PET, high-energy physics experiments, and readout of time-projection chambers, gamma and beta cameras, or scintillating fibers, with a reduced number of channels. These SiPMs were characterized in terms of noise, photon detection efficiency, and position resolution. We also developed tiles of 2 × 2 and 3 × 3 LG-SiPMs, reaching very large sensitive areas of 20 × 20 mm2 and 30 × 30 mm2. We implemented a "smart-channel" configuration, which allowed us to have just six output channels for the 2 × 2 elements and eight channels for the 3 × 3 element tiles, preserving a position resolution below 0.5 mm. These kinds of detectors provide a great advantage in compact and low-power applications by maintaining position sensitivity over large areas with a small number of channels.

Aerosol Delivery Efficiency With High-Flow Nasal Cannula Therapy in Neonatal, Pediatric, and Adult Nasal Upper-Airway and Lung Models.

High-flow nasal cannula (HFNC) systems employ different methods to provide aerosol to patients. This study compared delivery efficiency, particle size, and regional deposition of aerosolized bronchodilators during HFNC in neonatal, pediatric, and adult upper-airway and lung models between a proximal aerosol adapter and distal aerosol circuit chamber. A filter was connected to the upper airway to a spontaneously breathing lung model. Albuterol was nebulized using the aerosol adapter and circuit at different clinical flow settings. The aerosol mass deposited in the upper airway and lung was quantified. Particle size was measured with a laser diffractometer. Regional deposition was assessed with a gamma camera at each nebulizer location and patient model with minimum flow settings. Inhaled lung doses ranged from 0.2-0.8% for neonates, 0.2-2.2% for the small child, and 0.5-5.2% for the adult models. Neonatal inhaled lung doses were not different between the aerosol circuit and adapter, but the aerosol circuit showed marginally greater lung doses in the pediatric and adult patient models. Impacted aerosols and condensation in the non-heated HFNC and aerosol delivery components contributed to the dispersion of coarse liquid droplets, high deposition (11-44%), and occlusion of the supine neonatal upper airway. In contrast, the upright pediatric and adult upper-airway models had minimal deposition (0.3-7.0%) and high fugitive losses (∼24%) from liquid droplets leaking out of the nose. The high impactive losses in the aerosol adapter (56%) were better contained than in the aerosol circuit, resulting in less cannula sputter (5% vs 22%), fewer fugitive losses (18% vs 24%), and smaller inhaled aerosols (5 µm vs 13 µm). The inhaled lung dose was low (1-5%) during HFNC. Approaches that streamline aerosol delivery are needed to provide safe and effective therapy to patients receiving aerosolized medications with this HFNC system.