Sarah L. Bugby

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.

A small field of view camera for hybrid gamma and optical imaging

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.

A hybrid camera for locating sources of gamma radiation in the environment

We present a new concept for a portable environmental imaging system, the Compact Hybrid Gamma Camera (CHGC). This combines an optical and a gamma-photon camera in a co-aligned configuration that offers high spatial resolution multi-modality imaging for superposition of gamma ray and optical images. We report on its potential use for surveying, monitoring and clean-up of radioactive sources in the environment.

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 (123)I 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.

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.

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.

Assessment of the performance of small field of view gamma cameras for sentinel node imaging.

ObjectiveTo 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 methodsThe 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 99mTc 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. ResultsThe 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 45 mm with 25 mm 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. ConclusionA 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.

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.

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.