L. Menard

POCI: a compact high resolution /spl gamma/ camera for intra-operative surgical use

The development of a hand-held /spl gamma/ imaging probe for inside body localization of small tumors is of first interest for radio-guided operative cancer surgery. In that context, we have developed a sub-millimeter spatial resolution, small field of view, /spl gamma/ per-operative compact imager (POCI). It consists of a head module composed of a high resolution tungsten collimator and a YAP:Ce crystal plate, optically coupled to an intensified position sensitive diode (HSD). We report here the essential imaging performance characteristics of the POCI camera (spatial resolution, position linearity, efficiency and energy response). These were obtained by studying the influence of the collimator and the crystal design to evaluate the optimal configuration. The present version of POCI has a 24 mm diameter usable field of view and an intrinsic spatial resolution of 0.9 mm to 1.2 mm FWHM at 120 keV. These good detection performance characteristics combined with the small size of the camera make the device well suited to provide intra-operative monitoring in several medical procedures, such as thyroid and breast tumor removal.

The Usefulness of a Preoperative Compact Imager, a Hand-Held γ-Camera for Breast Cancer Sentinel Node Biopsy: Final Results of a Prospective Double-Blind, Clinical Study

The aim of this study was to compare the effectiveness of a hand-held preoperative compact imager (POCI) camera with conventional lymphoscintigraphy using a γ-camera for sentinel lymph node (SLN) detection in breast cancer. Methods: The main objective was to demonstrate the noninferiority of the POCI relative to conventional lymphoscintigraphy and to compare the number of SLNs detected by the 2 imaging devices. Our study, a clinical prospective, double-blind, noninferiority study, planned to include 200 patients with early breast cancer and started in January 2006. A standard SLN protocol (4 periareolar injections of 37 MBq of 99mTc-nanocolloids, 2 h before lymphoscintigraphy) was performed preoperatively using a conventional γ-camera and then the POCI camera. Scans were obtained by 2 different nuclear medicine physicians unaware of each others results. The day after, in the operating room, the surgeon, after receiving the previous results, used the counting probe for surgical SLN biopsy. The number and localization of axillary SLNs obtained by lymphoscintigraphy and the POCI and the duration of the whole procedure were determined. Results: Among the 162 patients included, 138 were evaluable. The POCI detected more SLNs than did lymphoscintigraphy in 50 patients (36%), the same number of in 54 patients (39%), and fewer SLNs in 34 patients (25%), representing 84 (61%) discordant pairs. The noninferiority of preoperative compact imaging of axillary SLNs numbers was found to be statistically significant (95% confidence interval, 30%–52%, P = 0.025) using the McNemar test. The duration of acquisition was shorter using the POCI (<10 min in 84% [n = 117] of patients; mean, 7.5 ± 3.3 min) than lymphoscintigraphy (13% [n = 18] of patients; mean, 15.7 ± 3.4 min), with P < 0.001 using the McNemar test for paired proportions. Conclusion: Preoperative compact imaging using a hand-held camera was able to predict the number and localization of breast cancer SLNs and was not inferior to conventional lymphoscintigraphy in this study. Further studies will determine whether preoperative compact imaging could replace lymphoscintigraphy, especially in surgical centers without an on-site nuclear medicine department.

Performance characterization and first clinical evaluation of a intra-operative compact gamma imager

The growing interest of cancer surgeons for intra-operative probes has led to the development of several prototypes of high resolution mini gamma cameras. The aim of this paper is to present a global characterization of the one the authors developed and the corresponding first evaluation in a clinical context. The current prototype of POCI (peroperative compact imager) is a 24 mm diameter intensified position sensitive diode. In order to face the various clinical situations, two sets of collimator/scintillator imaging head have been developed either for high spatial resolution or high efficiency purposes, Both of them have been first optimized for /sup 99m/Tc labeled tumor detection. Intrinsic performances are the following: the spatial resolution ranges from 1 mm up to 1.9 mm (without significant distortion) and the corresponding efficiency ranges from 6.10/sup -h/ up to 2.10/sup -4/. Phantom studies illustrating these results are proposed. First clinical evaluation of POCI concerned sentinel lymph node imaging which is included in melanoma and breast cancer staging protocols. Preliminary results already show that performances of POCI are compatible with intra-operative imaging purposes and suggest how such mini-cameras can improve the success rate of tumor removal surgeries.

An Intraoperative Beta Probe Dedicated to Glioma Surgery: Design and Feasibility Study

Surgery is considered as the primary therapeutic procedure for gliomas and several recent clinical studies have shown that total tumor resection is directly associated with longer survival when compared to subtotal resection. In order to refine the resection in the boundaries of gliomas, we are developing an intraoperative probe specifically dedicated to the localization of residual tumor labeled with positron emitters. The probe is designed to be compact and electrically safe in order to be directly coupled to the excision tool leading to simultaneous detection and removal of tumor tissues. It is built with clear and plastic scintillating fibers held in a closed packed annular arrangement ensheathing the excision tool. The annihilation gamma ray background is eliminated by a real-time subtraction method. Validation of the technical choice and optimization of the probe geometry were performed by preliminary measurements and Monte Carlo simulations based on the MCNP-4C code and an anthropomorphic brain phantom. The theoretical probe sensitivity was found to be 82 cps/muCi/ml with a gamma ray rejection efficiency of 99.6%. The expected minimum radiotracer detectable concentration for tumors labeled with 18 F-FET was 0.10 muCi/ml. When compared to the 0.29 muCi/ml average concentration in the bulk of the tumor, this result demonstrate the potential ability of the probe to define more accurately the extent of brain tumor resection

Optical phantoms with variable properties and geometries for diffuse and fluorescence optical spectroscopy

Abstract. Growing interest in optical instruments for biomedical applications has increased the use of optically calibrated phantoms. Often associated with tissue modeling, phantoms allow the characterization of optical devices for clinical purposes. Fluorescent gel phantoms have been developed, mimicking optical properties of healthy and tumorous brain tissues. Specific geometries of dedicated molds offer multiple-layer phantoms with variable thicknesses and monolayer phantoms with cylindrical inclusions at various depths and diameters. Organic chromophores are added to allow fluorescence spectroscopy. These phantoms are designed to be used with 405 nm as the excitation wavelength. This wavelength is then adapted to excite large endogenous molecules. The benefits of these phantoms in understanding fluorescence tissue analysis are then demonstrated. In particular, detectability aspects as a function of geometrical and optical parameters are presented and discussed.

Physical Performance of an Intraoperative Beta Probe Dedicated to Glioma Radioguided Surgery

The precise delineation and excision of brain tumor extent allows to improve survival outcome and quality of life of surgically treated patients. In order to refine the resection of gliomas, we are developing a novel intraoperative probe specifically dedicated to the localization of residual tumor after the bulk has been excised. The probe, built around clear and plastic scintillating fibers, was designed to detect positrons emitted from radiolabeled brain tissue in order to discriminate more specifically neoplastic from normal tissues. The probe was also built to be directly coupled to the excision tool leading to simultaneous detection and removal of tumor. We report here performances of the first radio-isotopic configuration of the intraoperative probe which consists of a detection head composed of eight detection elements held around the excision tool in a closed packed annular arrangement. This head is coupled to an optic fiber bundle that exports the scintillating light to a multi-channel photomultiplier tube. The gamma ray background generated by the annihilation of beta+ in tissues is eliminated by a real-time subtraction method. The detector exhibits a beta sensitivity of 139 cps/kBq and a gamma ray rejection efficiency of 99.5%. The ability of the probe to detect residual lesions was evaluated with a realistic brain phantom representing the surgical cavity and the boundaries of the tumor. We showed that lesions as small as 5 mm in diameter can be detected for tumor to normal tissue uptake ratios of fluorinated tracers greater than 3.5. This ratio is achieved with radiopharmaceuticals like 18F-FET or 18F-choline. These promising results suggest that the features of our system are compatible with in situ localization of residual radiolabeled tumors.

RITM: a mini /spl gamma/ camera for pre and per-operative radio guided cancer surgery evaluation for bone tumor localization in theater blocks

The authors have developed a multi-functional portable /spl gamma/-radio-imager (RITM) based on a position sensitive photo-multiplier tube (PSPMT) in order to evaluate the potential of such a mini /spl gamma/-camera concept in radio-pharmacology and nuclear medicine. The authors report here an evaluation of their RITM device for bone surgery. It concerns localization of the Osteoid Osteoma (benign bone tumor) performed in the theater block before skin incision and during the surgical lesion extraction. In the over 13 cases the authors studied, the diagnosis furnished by RITM was always confirmed by post-operation anatomopathological analysis. This shows how RITM can be used as an additional indicator to monitor the operation. Following RITM experience, the authors are developing a new small field of view /spl gamma/-per-operative compact imager (POCI) with submillimeter spatial resolution performance. It consists of a high resolution collimator and a YAP:Ce crystal assembly coupled to an intensified position sensitive diode (IPSD). This hand-held imaging probe is first dedicated to intra-operative monitoring for thyroid tumor and neuroblastoma removal. Characteristics of the POCI device and preliminary results are briefly presented.

Asymptotic expansion of the expected spectral measure of Wigner matrices

We compute an asymptotic expansion with precision 1/n of the moments of the expected empirical spectral measure of Wigner matrices of size n with independent centered entries. We interpret this expansion as the moments of the addition of the semicircle law and 1/n times an explicit signed measured with null total mass. This signed measure depends only on the second and fourth moments of the entries.

Spectra of large diluted but bushy random graphs

We compute an asymptotic expansion in

Design of a new BaF/sub 2/ PET module concept and preliminary evaluation results

1/c