A custom Python-based Monte Carlo Simulation Tool (PMST) has been developed to assist in the development of portable gamma cameras or the generation of simulated gamma image datasets, e.g. for deep learning. The simulation tool has been validated by comparison between theoretical and experimental results. PMST includes common attenuation interactions such as the photoelectric effect and Compton and Rayleigh scattering and fluorescence and non-radiative secondary effects. It allows users to simulate and visualise a gamma imaging system with multiple absorbers, flexible geometry, and different materials.

Cadmium zinc telluride (CdZnTe) detectors are known to suffer from polarization effects under high photon flux due to poor hole transport in the crystal material. This has led to the development of a high-flux capable CdZnTe material (HF-CdZnTe). Detectors with the HF-CdZnTe material have shown promising results at mitigating the onset of the polarization phenomenon, likely linked to improved crystal quality and hole carrier transport. Better hole transport will have an impact on charge collection, particularly in pixelated detector designs and thick sensors (>1 mm). In this paper, the presence of charge sharing and the magnitude of charge loss were calculated for a 2 mm thick pixelated HF-CdZnTe detector with 250 μm pixel pitch and 25 μm pixel gaps, bonded to the STFC HEXITEC ASIC. Results are compared with a CdTe detector as a reference point and supported with simulations from a Monte-Carlo detector model. Charge sharing events showed minimal charge loss in the HF-CdZnTe, resulting in a spectral resolution of 1.63 ± 0.08 keV Full Width at Half Maximum (FWHM) for bipixel charge sharing events at 59.5 keV. Depth of interaction effects were shown to influence charge loss in shared events. The performance is discussed in relation to the improved hole transport of HF-CdZnTe and comparison with simulated results provided evidence of a uniform electric field.

Background Cardiogenic shock (CS) is defined as hypotension despite adequate filling status with signs of organ hypoperfusion resulting from a primary cardiac disorder. It complicates 8% of acute myocardial infarctions and, despite the widespread availability of primary percutaneous coronary intervention, continues to have a high short term mortality of 35-50%. Traditional mechanical circulatory support (MCS) can improve cardiac output (CO) however these devices have significant adverse event profiles related to their position within the circulation. PALVAD is an extra circulatory left ventricular assist device, designed to be implanted percutaneously. It provides cardiac support whilst sitting outside the circulatory system in the space between the pericardium and left ventricular (LV) free wall. The dual balloon system connects to a currently external pumping system via a driveline. The actuator (ACT) balloon augments CO through ECG gated LV systolic compression and the positioning balloon sits against the pericardial surface dissipating this force across a large area. Due to its position outside the circulation the device avoids risks with traditional MCS such as clot generation or bleeding (if anticoagulation required), haemolysis and the risk of intravascular infection leading to endocarditis. Furthermore, by avoiding the need for surgical implantation PAL-VAD avoids the risk of general anaesthetic in critically ill patients with the potential to enable more widespread timely initiation of MCS targeting improved outcomes in CS. Purpose Assess device efficacy in a low CO state in a non-recovery porcine model. Understand device interactions with the left ventricle and pericardium in a cadaveric model. Methodology Non-recovery porcine model experiments were conducted in ten 40k-60g pigs at a large animal catheterisation facility. In 3 animals a closed chest coronary occlusion reperfusion technique was adopted. In 7 animals an Esmolol infusion was titrated to create a low output state. A Millar catheter was placed in the LV for simultaneous pressure and volume measurements and a Transonic flow probe was placed around the internal carotid for flow measurements. The device was inserted successfully percutaneously and operated for alternating periods of 5 minutes on and 1 minute off. For the cadaveric experiment, the device was inserted into a Thiel embalmed saline or contrast perfused cadaver following which detailed CT and MRI imaging was undertaken with the device in varying configurations. CT images were reconstructed three dimensionally and analysed using NX computer aided design (CAD) software. Results PAL-VAD had a significant impact across all target parameters with a mean increase of 44% ± 14.5 in CO, 43% ± 16.2 in stroke volume, 25% ± 14.7 in pressure and a 30% ± 18.5 in flow. There was no macroscopic evidence of epicardial or pericardial damage. Cadaveric imaging informed optimal positioning of the device in relation to the LV free wall and a 48% reduction in LV volume was seen when the ACT balloon was inflated. Conclusions PALVAD performance during a low CO state in non-recovery porcine experiments is promising. Further recovery experiments, including histology assessment, are planned to evaluate safety and efficacy with longer term use to guide optimisation prior to a first-in-man trial. Conflict of Interest Nil

OBJECTIVETo examine the imaging capability of a novel small field of view hybrid gamma camera (HGC) using 125I seeds prior to surgical use.METHODSThe imaging performance of the camera system was assessed quantitatively and qualitatively at different source depths, source to collimator distances (SCD), activity levels, acquisition times and source separations, utilising bespoke phantoms.RESULTSThe system sensitivity and spatial resolution of the HGC for 125I were 0.41 cps/MBq (at SCD 48 mm) and 1.53 ± 0.23 mm (at SCD 10 mm) respectively. The camera was able to detect the 125I seed at a SCD of 63 mm (with no scattering material in place) in images recorded within a 1-min acquisition time. The detection of the seeds beneath scattering material (simulating deep-seated tumours) was limited to depths of less than 20 mm beneath the skin surface with a SCD of 63 mm and seed activity of 2.43 MBq. Subjective assessments of the hybrid images acquired showed the capability of the HGC for localising the 125I seeds.CONCLUSIONThis preliminary ex vivo study demonstrates that the HGC is capable of detecting 125I seeds and could be a useful tool in radioactive seed localisation with the added benefit of providing hybrid optical γ images for guiding breast conserving surgery.ADVANCES IN KNOWLEDGEThe SFOV HGC could provide high resolution fused optical-gamma images of 125I radioactive seeds indicating the potential use in intraoperative surgical procedure such as RSL.

The development of compact low profile gamma-ray detectors has allowed the production of small field of view, hand held imaging devices for use at the patient bedside and in operating theatres. The combination of an optical and a gamma camera, in a co-aligned configuration, offers high spatial resolution multi-modal imaging giving a superimposed scintigraphic and optical image. This innovative introduction of hybrid imaging offers new possibilities for assisting surgeons in localising the site of uptake in procedures such as sentinel node detection. Recent improvements to the camera system along with results of phantom and clinical imaging are reported.

INTRODUCTION:Hybrid imaging has proven to be a major innovation in nuclear medicine, allowing the fusion of functional information with anatomical detail. In the past, the use of hybrid imaging such as PET-CT, PET-MRI and SPECT-CT has been of great clinical benefit; however, these scanners are relatively large and bulky. We have developed and investigated the clinical application of a compact small field of view hybrid gamma camera (HGC) that is suitable for small-organ imaging at the patient bedside. PATIENTS AND METHODS:The HGC - consisting of a CsI(Tl) scintillation crystal coupled to an electron-multiplying charge-coupled device and an optical camera - was used in this study. Eligible patients attending the nuclear medicine clinic at Queen's Medical Centre, Nottingham University Hospitals NHS Trust, Nottingham, UK, were invited to take part in this study. Following the standard injection of either a Tc-labelled or I-labelled radiopharmaceutical, images of the patient were acquired using the HGC and presented in a fused optical-gamma display. RESULTS:There were 24 patients enrolled in the study (age range between 30 and 83 years, mean: 58.6 years), images of 18 of whom were successfully acquired. These included patients who were undergoing bone, thyroid, lacrimal drainage, DaTscan and lymphatic imaging. In general, the small field of view system was well suited to small-organ imaging. The uptake could be clearly seen in relation to the patient surface anatomy and showed particular promise for lymphatic, thyroid and lacrimal drainage studies. CONCLUSION:This pilot study has demonstrated the first clinical results of hybrid optical-gamma imaging in patients. The use of this system has raised new possibilities for small-organ imaging, in which the localization of radiopharmaceutical uptake can be presented in an anatomical context using optical imaging. The compact nature of the hybrid system offers the potential for bedside investigations and intraoperative use.

A prototype anthropomorphic head and neck phantom has been designed to simulate the adult head and neck anatomy including some internal organs and tissues of interest, such as thyroid gland and sentinel lymph nodes (SLNs). The design of the head and neck phantom includes an inner jig holding the simulated SLNs and thyroid gland. The thyroid gland structure was manufactured using three-dimensional (3D) printing taking into consideration the morphology and shape of a healthy adult thyroid gland.

OBJECTIVE:The hybrid gamma camera (HGC) has been developed to enhance the localization of radiopharmaceutical uptake in targeted tissues during surgical procedures such as sentinel lymph node (SLN) biopsy. To assess the capability of the HGC, a lymph node contrast (LNC) phantom was constructed to simulate medical scenarios of varying radioactivity concentrations and SLN size. METHODS:The phantom was constructed using two clear acrylic glass plates. The SLNs were simulated by circular wells of diameters ranging from 10 to 2.5 mm (16 wells in total) in 1 plate. The second plate contains four larger rectangular wells to simulate tissue background activity surrounding the SLNs. The activity used to simulate each SLN ranged between 4 and 0.025 MBq. The activity concentration ratio between the background and the activity injected in the SLNs was 1 : 10. The LNC phantom was placed at different depths of scattering material ranging between 5 and 40 mm. The collimator-to-source distance was 120 mm. Image acquisition times ranged from 60 to 240 s. RESULTS:Contrast-to-noise ratio analysis and full-width-at-half-maximum (FWHM) measurements of the simulated SLNs were carried out for the images obtained. Over the range of activities used, the HGC detected between 87.5 and 100% of the SLNs through 20 mm of scattering material and 75-93.75% of the SLNs through 40 mm of scattering material. The FWHM of the detected SLNs ranged between 11.93 and 14.70 mm. CONCLUSION:The HGC is capable of detecting low accumulation of activity in small SLNs, indicating its usefulness as an intraoperative imaging system during surgical SLN procedures. ADVANCES IN KNOWLEDGE:This study investigates the capability of a novel small-field-of-view (SFOV) HGC to detect low activity uptake in small SLNs. The phantom and procedure described are inexpensive and could be easily replicated and applied to any SFOV camera, to provide a comparison between systems with clinically relevant results.

Although early gamma scanners were around in the middle part of the last century, the concept of the gamma camera was invented by Hal Anger in 1952 whilst working at the Donner Laboratory in the University of California in Berkeley, USA. e early prototype consisted of a pinhole collimator and a sodium iodide at intensifying screen placed in front of a photographic plate. e device demonstrated the ability to produce a clinically relevant image, by showing the gamma ray distribution emitted from the patient on the at crystal. e sensitivity of the camera was low and a long exposure time and relatively high amounts of radioactivity were required to produce images. A few years later, Anger improved the prototype design by replacing the gamma ray detector with 4 in. diameter scintillator coupled to an array of seven photomultiplier tubes (PMTs). He also developed 'Anger arithmetic' to determine the position of the scintillation event that occurred in the crystal by comparing the photons collected in individual PMTs.

531 Objectives Hybrid imaging has proven to be a major innovation in medical diagnosis. In nuclear medicine hybrid imaging allows the fusion of functional information with anatomical detail, however clinical studies have mainly been been carried out with large whole body scanning instruments. We have developed and characterised a compact small field of view hybrid camera of weight approximately 1kg. The camera consists of a CsI(Tl) columnar scintillator coupled to an electron multiplying CCD. A pinhole collimator coupled with a mirror and optical camera assembly provides alignment of optical images within the same FOV as the gamma camera. Methods Eligible patients attending the nuclear medicine clinic at Queen’s Medical Centre, Nottingham University Hospitals NHS Trust, Nottingham were invited to take part according to ethical approval by the UK National Research Ethics Committee (REC Ref No. 12/EM/0201). In addition to routine imaging following the standard injection of the radiopharmaceutical, hybrid planar images of the patient were acquired and presented in a fused optical-gamma display. Results Patients undergoing routine imaging procedures with Tc-99m and I-123 were investigated. These included DatSCAN, bone, thyroid, lachrimal drainage and lymphatic imaging. Initial investigations of high resolution imaging using a 0.6mm crystal and 0.5mm pin hole resulted in long acquisition times of over 5 minutes. Increasing the thickness of the scintillator to 1.5mm and the diameter of the pin hole to 1mm improved the sensitivity, allowing images to be recorded within 5 minutes. Localisation of DatSCAN uptake in the striatum of patients was not visualised using the thinner crystal and 0.5mm pin hole configuration, however the small field of view system was well suited to small organ imaging. Especially good results were achieved for lymphatic, thyroid and lacrimal drainage studies, where the uptake could be clearly seen in relation to the patient surface anatomy. Conclusions This clinical pilot study has demonstrated the first results of clinical hybrid optical-gamma imaging in a range of patients. Use of the system has raised new possibilities for small organ imaging, where the localisation of radiopharmaceutical uptake can be presented in an anatomical context using optical imaging. The compact nature of the hybrid system offers the potential for bedside investigations and further evaluation of the hybrid camera for intraoperative imaging in a surgical theatre setting is underway.

For intraoperative medical imaging, the development of small field of view (SFOV) hybrid gamma cameras is an expanding area of research. The performance characteristics of a new innovation combining both gamma and optical imaging in a co-aligned configuration, the Hybrid Gamma Camera (HGC) have been evaluated and compared. In this study the HGC was fitted with either 1500 μm thick columnar CsI:TI or 1500 μm thick pixelated GOS scintillators. The columnar CsI:TI scintillator has an intrinsic spatial resolution of 230 μm compared to 1090 μm for the pixelated GOS scintillator. The sensitivity at 140.5 keV of the CsI:TI was 40 %, however, for the GOS it was 54 %. The intrinsic spatial uniformity was comparable for both CsI:TI and GOS scintillators. There was a significant difference between the CsI:TI and GOS scintillators for count rate capability which was lower when using a GOS scintillator.

We designed and demonstrated an InAs avalanche photodiode (APD) for X-ray detection, combining narrow band gap semiconductor materials and avalanche gain from APDs. The InAs APD (cooled by liquid nitrogen) was tested with a 55Fe X-ray source. Full width at half maximum (FWHM) from the spectra decreases rapidly with reverse bias, rising again for higher voltages, resulting in a minimum FWHM value of 401 eV at 5.9 keV. This minimum value was achieved at 10 V reverse bias, which corresponds to an avalanche gain of 11. The dependence of FWHM on reverse bias observed is explained by the competition between various factors, such as leakage current, capacitance and avalanche gain from the APD, as well as measurement system noise. The minimum FWHM achieved is largely dominated by the measurement system noise and APD leakage current.

Objective To develop a method for the assessment of small field of view (SFOV) gamma cameras using a novel phantom designed to simulate the localization of sentinel nodes in the presence of a high-activity injection site.Materials and methods The phantom consisted of a cube-shaped acrylic glass support frame. Sixteen acrylic glass plates and nine bars were stacked within the frame to allow a variable configuration of the simulated node depth and node-to-injection site separation. Syringes filled with Tc-99m were used to simulate activity at the injection site and node. Scintigraphic imaging was carried out and the images were assessed subjectively and quantitatively through calculation of the contrast-to-noise ratio. The detection performance of an SFOV gamma camera was then compared with that of a large field of view gamma camera.Results The detectability studies showed that the SFOV gamma camera could detect low activity in nodes by visual examination of images and with contrast-to-noise ratios ranging from 3 to 62. In particular, the phantom showed the limits of node detection using an SFOV gamma camera over activity ratios less than 1 : 100 and at depths below 45mm with 25mm of node-to-injection site separation. Visual subjective assessment of images acquired under the same conditions showed that the SFOV gamma camera was superior to a large field of view camera for the detection of nodes at a node-to-injection site separation of 25 mm.Conclusion A low-cost phantom has been designed and fabricated that provides a versatile method for the assessment of SFOV gamma cameras intended for sentinel node imaging. Copyright (C) 2015 Wolters Kluwer Health, Inc. All rights reserved.

L.K. Jambi1a, J.E. Lees1, S.L. Bugby1, B.S. Bhatia1,2, M.S. Alqahtani1, W.R. McKnight1, A.H. Ng3 and A.C. Perkins3 a Contact: Lj97@le.ac.uk 1 Space Research Centre, University of Leicester, Leicester, LE1 7RH, UK 2 Clinical Imaging Group, Sandwell and West Birmingham Hospital NHS Trust, West Bromwich B71 4HJ, UK 3 Radiological and Imaging Sciences, Medical Physics and Clinical Engineering, School of Medicine, Queen's Medical Centre, Nottingham, NG7 2UH, UK