L. Pinot

An original emission tomograph for in vivo brain imaging of small animals

The principle of a new tomograph (TOHR) dedicated for small volume analysis with very high resolution is presented. The authors use uncorrelated multi-photon (X- or gamma rays) radioisotopes and a large solid angle focusing collimator to produce tomographic images without a reconstruction algorithm. With this device, detection efficiency and resolution are independent and submillimeter resolution can be achieved. A feasibility study shows that collimators made with a stack of chemically etched plates can achieve the predicted performances of TOHR. The authors discuss its potential in rat brain tomography by simulating a realistic neuropharmacological experiment using a 1.4 mm resolution prototype of the TOHR under development.

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.

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

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.

The Tumor Resection Camera (TReCam), a multipixel imaging probe for radio-guided surgery

Using the POCI camera, we recently demonstrated the clinical impact of per-operative imaging techniques thanks to a successful clinical trial. Taking advantage of both the POCI experience and the availability of new pixelated detectors, we are developing a new hand held gamma camera TReCam (tumor resection camera). The first prototype offers a 49 × 49 mm2 field of view. It combines a 15 mm thick parallel hole collimator (with an efficiency of 5.10-4 and a spatial resolution of 7.5 mm at 50 mm), a 5 mm thick LaBr3:Ce crystal optically coupled to a Hamamatsu H9500 flat panel multianode photomultiplier tube (MAPMT). The read-out of the MAPMT is ensured thanks to a new specific integrated circuit called HARDROC2 (hadronic Rpc detector readout chip). This chip was initially designed for the digital hadronic calorimeter (DHCAL) of the linear collider. The TReCam presents an intrinsic spatial resolution of 0.65 mm (FWHM) and an energetic resolution of 17.4% at 122 keV. The new read-out by the HARDROC2 chip is currently being implemented and using this new device energetic resolution is expected to be better.

TOHR: prototype design and characterization of an original small animal tomograph

The authors have proposed an original method for high resolution in vivo tomography adapted to small animal models studies: TOHR (French acronym for High Resolution Tomograph). They have designed and developed a large solid angle, high resolution and high efficiency focusing collimator which provides a focal point used to scan the animal and finally perform the image. High resolution was improved by using nuclides having a two-photon decay (X- or gamma rays). The authors have built a prototype of a tomograph with a 2/spl pi/ collimator (10 over the 20 sides of an icosahedron). The different parts of the detector (collimator, detector, acquisition) are described. An optimization of the collimator structure and an iso-focusing method of the different modules of the collimator are discussed. Performances of the detector (energy, timing and spatial resolution) are presented using point sources and hot spot phantoms and are compared to numerical simulation results.

RITM and POCI: pre and per-operative mini /spl gamma/ cameras evaluation for bone tumor localization in theater blocks

We 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 miniature /spl gamma/ camera concept in radio-pharmacology and nuclear medicine. We report here an evaluation of our RITM device for cancer surgery. It concerns localization of the osteoid osteoma (bone benign tumor) performed in theater block before skin incision and during the surgical lesion extraction. Over 13 cases we studied, the diagnosis furnished by RITM was always confirmed by postoperation anatomo-pathological analysis. This shows how RITM can be used as an additional indicator to monitor the operation. Following this first experience, we are developing a new small field of view /spl gamma/ per operative compact imager (POCI) performing a sub-millimeter spatial resolution. 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 and neuroblastoma tumor removal. Characteristics of the POCI device and preliminary results are presented.

PIXSIC: A Pixellated Beta-Microprobe for Kinetic Measurements of Radiotracers on Awake and Freely Moving Small Animals

We present a design study of PIXSIC, a new β+ radiosensitive microprobe implantable in rodent brain dedicated to in vivo and autonomous measurements of local time activity curves of beta radiotracers in a small (a few mm3) volume of brain tissue. This project follows the initial β microprobe previously developed at IMNC, which has been validated in several neurobiological experiments. This first prototype has been extensively used on anesthetized animals, but presents some critical limits for utilization on awake and freely moving animals. Consequently, we propose to develop a wireless setup that can be worn by an animal without constraints upon its movements. To that aim, we have chosen a Silicon-based detector, highly β sensitive, which allows for the development of a compact pixellated probe (typically 600 × 200 × 1000 μm3), read out with miniaturized wireless electronics. Using Monte-Carlo simulations, we show that high resistive Silicon pixels are appropriate for this purpose, assuming that the pixel dimensions are adapted to our specific signals. More precisely, a tradeoff has to be found between the sensitivity to β+ particles and to the 511 keV j background resulting from annihilations of β+ with electrons. We demonstrate that pixels with maximized surface and minimized thickness can lead to an optimization of their β+ sensitivity with a relative transparency to the annihilation background.

A new multimodality system for quantitative in vivo studies in small animals: combination of nuclear magnetic resonance and the radiosensitive /spl beta/-MicroProbe

Elucidating complex physiological mechanisms in small animal in vivo requires the development of new investigatory techniques including imaging with multiple modalities. Combining exploratory techniques has the tremendous advantage to record simultaneously complementary parameters on the same animal. In this field, an exciting challenge remains in the combination of nuclear magnetic resonance (NMR) and positron emission tomography (PET) since small animals studies are limited by strict technical constraints in vivo. Coupling NMR with a radiosensitive /spl beta/-microprobe offers therefore an interesting technical alternative. To assess the feasibility of this new dual-modality system, we designed theoretical and experimental approaches to test the ability of the /spl beta/-Microprobe to quantify radioactivity concentration in an intense magnetic field. In an initial step, simulations were carried out using Geant4. First, we evaluated the influence of a magnetic field on the probe field of view. Then, the detection sensitivity and energy response of the probe were quantified. In a second step, experiments were run within a 7-T magnet to confirm our simulations results. We showed that using the probe in magnetic fields leads to a slight attenuation in sensitivity and an increase of the scintillation light yield. These data showed the feasibility of combining NMR to the /spl beta/-microprobe.