Roland Mastrippolito

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.

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

We describe a new positron emission tomography (PET) detection module using BaF/sub 2/ crystals. We use the separation between the fast (0.6 ns, 220 nm) and the slow (630 ns, 310 nm) scintillation component of the barium fluoride through an ultraviolet glass filter to code the interaction localization. The timing is done on the fast component and the spectroscopy on the slow component. The photoelectric yield of BaF/sub 2/ crystals (10 /spl times/ 10 /spl times/ 30, 8 /spl times/ 8 /spl times/ 30, and 6 /spl times/ 6 /spl times/ 30 mm/sup 3/) coupled to 1-in-diameter photomultiplier tubes has been measured to quantify the light losses due to this geometry. As a reference, we present simulations and measurements of the efficiency of these crystals for detection of 511-keV gammas in coincidence and a measurement of the time resolution of the system.

Advantage of using compact gamma cameras for sentinel node radio-guided surgery: Monte Carlo simulation and first clinical evaluation of an intra-operative imager

Summary form only received as follows: The main application of radio-guided surgery concerns sentinel node detection for breast and melanoma cancer staging. In that context, when used as complementary tools of gamma probes, compact cameras are very attractive to provide more efficient node localization. The authors report on Monte Carlo simulations designed to compare performances of a standard commercially available counter to those of the POCl compact gamma camera they developed. A 3-D phantom patient with 8 mm diameter node embedded in a scattering medium (including background activity from the injection site) were generated for various node-to-tumor distances and activity ratios. Other parameters considered included detector energy resolution and acquisition time. Detection performances were compared in terms of contrast and statistical fluctuations. Simulations demonstrate that compact cameras have significant advantages over counters when sentinel node is placed close to the injection site. For a 1/100 activity ratio, the minimum node-to-tumor distance required to identify the node is 11.5 and 1 cm for the probe and the camera respectively. In order to evaluate experimentally the interest of intra-operative imaging, eight patients included in sentinel node protocol have been also investigated with POCl. Clinical results show the reliability of the camera which ensures localization of sentinel node in all patients.

Imaging performances of the large area intra-operative camera POCI

Summary form only received as follows: Intra-operative gamma imagers developed for small tumor localizations are of first interest for radio guided operative cancer surgery. In this context, the authors previously developed and evaluated a compact high resolution gamma imager POCI (Per Operative Compact Imager). This evaluation prototype has a 24 mm diameter field of view. The successful clinical evaluation of this device in theater block (sentinel node protocol for melanoma and breast cancers staging) led the authors to start the development a second prototype. Essentially, this device offers a larger sensitive area by coupling a 60 mm diameter head module (which associates crystal plate and a high resolution collimator) to a 40 mm diameter intensified position sensitive diode (IPSD). It has been designed in order to improve compactness and exploration efficiency during surgery. Measurements of basic detection parameters such as detection efficiency, spatial resolution, position linearity are reported. Characterization with phantoms are also presented and discussed.

Improvement of continuous position sensitive diode performances and associated electronics

In contrast to position segmented detectors, continuous Position Sensitive Detectors (whose localisation is based on current division) remain of interest when count rate is not critical. That is the case with several imaging applications in nuclear medicine and biology. Continuous PSDs offer large detection areas (up to 60/spl times/60 mm/sup 2/) and a spatial resolution inversely proportional to the energy deposited. Therefore, when coupled to an image intensifier tube, their spatial performances are suited to g medical diagnosis. After a brief presentation of the /spl gamma/ compact camera developed and dedicated to localised the sentinel lymph-node; we recall briefly the principle of the 3 kinds of PSD. Then, we describe a simulation model developed using CAO AWB/Cadence which taking into account both detector and readout electronics. In our application, a duo lateral photodiode filtered with a trapezoidal spectroscopy amplifier achieves the best compromise between linearity and spatial resolution. Because a signal deficit appears when PSD is coupled to a classical charge preamplifier, an impedance adaptation which improves detection performances is presented.