Aik H. Ng

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.

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.

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 novel compact small field of view hybrid gamma camera: first clinical results

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 99mTc-labelled or 123I-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 novel small field of view hybrid gamma camera for scintigraphic imaging (Conference Presentation)

A novel small field of view Hybrid Gamma Camera (HGC) has been developed to facilitate the process of localizing radiopharmaceutical uptake during surgical procedures. The HGC is a scintillator-based detector consisting of an electron multiplying charge-coupled device coupled to a columnar scintillator (CsI[Tl]). This enables fusion scintigraphic and optical images offering new possibilities for assisting clinicians and surgeons in localising the site of uptake in a number of surgical procedures. This technology also offers bedside imaging for small organs in procedures such as thyroid scintigraphy. In this study, prototype anthropomorphic phantoms have been used to study the capability of the HGC. Images were acquired using a range of bespoke anthropomorphic phantoms. The gamma and hybrid optical images were acquired for the simulated sentinel lymph nodes and thyroid gland. The gamma images produced varied in terms of spatial resolution and detectability, however utilizing pinhole collimators of difference diameters (0.5 and 1.0mm) imaging was enhanced meeting the needs of small field gamma imaging. The hybrid images obtained demonstrated that the HGC is ideally suited for small organ imaging demonstrating good potential in clinical procedures, such as thyroid scintigraphy, when using acquisition times similar to those for conventional gamma imaging. Moreover, clinical scintigraphic images, from patients attending the nuclear medicine clinic, were acquired using the HGC and compared to images from a standard gamma camera. The results of our first clinical feasibility study using the HGC will be presented.

Comparison of columnar and pixelated scintillators for small field of view hybrid gamma camera imaging

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.