A Multimodality Hybrid Gamma-Optical Camera for Intraoperative Imaging

The development of low profile gamma-ray detectors has encouraged the production of small field of view (SFOV) hand-held imaging devices for use at the patient bedside and in operating theatres. Early development of these SFOV cameras was focussed on a single modality-gamma ray imaging. Recently, a hybrid system-gamma plus optical imaging-has been developed. This combination of optical and gamma cameras enables high spatial resolution multi-modal imaging, giving a superimposed scintigraphic and optical image. Hybrid imaging offers new possibilities for assisting clinicians and surgeons in localising the site of uptake in procedures such as sentinel node detection. The hybrid camera concept can be extended to a multimodal detector design which can offer stereoscopic images, depth estimation of gamma-emitting sources, and simultaneous gamma and fluorescence imaging. Recent improvements to the hybrid camera have been used to produce dual-modality images in both laboratory simulations and in the clinic. Hybrid imaging of a patient who underwent thyroid scintigraphy is reported. In addition, we present data which shows that the hybrid camera concept can be extended to estimate the position and depth of radionuclide distribution within an object and also report the first combined gamma and Near-Infrared (NIR) fluorescence images.Peer-reviewedPublisher Versio

A comparison of CsI:Tl and GOS in a scintillator-CCD detector for nuclear medicine imaging

A number of portable gamma cameras for medical imaging use scintillator-CCD based detectors. This paper compares the performance of a scintillator-CCD based portable gamma camera with either a columnar CsI:Tl or a pixelated GOS scintillator installed. The CsI:Tl scintillator has a sensitivity of 40% at 140.5 keV compared to 54% with the GOS scintillator. The intrinsic spatial resolution of the pixelated GOS detector was 1.09 mm, over 4 times poorer than for CsI:Tl. Count rate capability was also found to be significantly lower when the GOS scintillator was used. The uniformity was comparable for both scintillators

Characterisation of a high resolution small field of view portable gamma camera

A handheld, high-resolution small field of view (SFOV) pinhole gamma camera has been characterised using a new set of protocols adapted from standards previously developed for large field of view (LFOV) systems. Parameters investigated include intrinsic and extrinsic spatial resolution, spatial linearity, uniformity, sensitivity, count rate capability and energy resolution. Camera characteristics are compared to some clinical LFOV gamma cameras and also to other SFOV cameras in development

A scheme for assessing the performance characteristics of small field-of-view gamma cameras.

Existing protocols for assessing the performance characteristics of large field-of-view (LFOV) gamma cameras can be inappropriate and require modification for use with small field-of-view (SFOV) gamma camera systems. This communication proposes a generic scheme suitable for evaluating the performance characteristics of SFOV gamma cameras, based on modifications to the standard procedures of NEMA NU1-2007. Key differences in methodology between tests for LFOV and SFOV gamma cameras are highlighted along with the rationale for these changes. It is envisaged that this scheme will provide more appropriate methods for equipment characterisation, ensuring quality and consistency for all SFOV cameras

Lymphoscintigraphic imaging study for quantitative evaluation of a small field of view (SFOV) gamma camera

The Hybrid Compact Gamma Camera (HCGC) is a portable optical-gamma hybrid imager designed for intraoperative medical imaging, particularly for sentinel lymph node biopsy procedures. To investigate the capability of the HCGC in lymphatic system imaging, two lymphoscintigraphic phantoms have been designed and constructed. These phantoms allowed quantitative assessment and evaluation of the HCGC for lymphatic vessel (LV) and sentinel lymph node (SLN) detection. Fused optical and gamma images showed good alignment of the two modalities allowing localisation of activity within the LV and the SLN. At an imaging distance of 10 cm, the spatial resolution of the HCGC during the detection process of the simulated LV was not degraded at a separation of more than 1.5 cm (variation <5%) from the injection site (IS). Even in the presence of the IS the targeted LV was detectable with an acquisition time of less than 2 minutes. The HCGC could detect SLNs containing different radioactivity concentrations (ranging between 1:20 to 1:100 SLN to IS activity ratios) and under various scattering thicknesses (ranging between 5 mm to 30 mm) with high contrast-to-noise ratio (CNR) values (ranging between 11.6 and 110.8). The HCGC can detect the simulated SLNs at various IS to SLN distances, different IS to SLN activity ratios and through varied scattering medium thicknesses. The HCGC provided an accurate physical localisation of radiopharmaceutical uptake in the simulated SLN. These characteristics of the HCGC reflect its suitability for utilisation in lymphatic vessel drainage imaging and SLN imaging in patients in different critical clinical situations such as interventional and surgical procedures

Investigation of an SFOV hybrid gamma camera for thyroid imaging

The Hybrid Compact Gamma Camera (HCGC) is a small field of view (SFOV) portable hybrid gamma-optical camera intended for small organ imaging at the patient bedside. In this study, a thyroid phantom was used to determine the suitability of the HCGC for clinical thyroid imaging through comparison with large field of view (LFOV) system performance. A direct comparison with LFOV contrast performance showed that the lower sensitivity of the HCGC had a detrimental effect on image quality. Despite this, the contrast of HCGC images exceeded those of the LFOV cameras for some image features particularly when a high-resolution pinhole collimator was used. A clinical simulation showed that thyroid morphology was visible in a 5 min integrated image acquisition with an expected dependency on the activity within the thyroid. The first clinical use of the HCGC for imaging thyroid uptake of ¹²³I is also presented. Measurements indicate that the HCGC has promising utility in thyroid imaging, particularly as its small size allows it to be brought into closer proximity with a patient. Future development of the energy response of the HCGC is expected to further improve image detectability

Quantitative investigation of a novel small field of view hybrid gamma camera (HGC) capability for sentinel lymph node detection.

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

Evaluation of XRI-UNO CdTe detector for nuclear medical imaging

Over the last two decades advances in semiconductor detector technology have reached the point where they are sufficiently sensitive to become an alternative to scintillators for high energy gamma ray detection for application in fields such as medical imaging. This paper assessed the Cadmium-Telluride (CdTe) XRI-UNO semiconductor detector produced by X-RAY Imatek for photon energies of interest in nuclear imaging. The XRI-UNO detector was found to have an intrinsic spatial resolution of <0.5mm and a high incident count rate capability up to at least 1680cps. The system spatial resolution, uniformity and sensitivity characteristics are also reported