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Register a new userA liquid Xenon Positron Emission Tomograph for small animal imaging : first experimental results of a prototype cell
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M.L. Gallin-Martel
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A detector using liquid Xenon (LXe) in the scintillation mode is studied for Positron Emission Tomography (PET) of small animals. Its specific design aims at taking full advantage of the Liquid Xenon scintillation properties. This paper reports on energy, time and spatial resolution capabilities of the first LXe prototype module equipped with a Position Sensitive Photo- Multiplier tube (PSPMT) operating in the VUV range (178 nm) and at 165 K. The experimental results show that such a LXe PET configuration might be a promising solution insensitive to any parallax effect.
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A detector using liquid Xenon in the scintillation mode is studied for Positron Emission Tomography (PET). The specific design aims at taking full advantage of the liquid Xenon properties. It does feature a promising insensitive to any parallax effect. This work reports on the performances of the first LXe prototype module, equipped with a position sensitive PMT operating in the VUV range (178 nm).
PET is a functional imaging technique based on detection of annihilation photons following beta decay producing positrons. In this paper, we present the concept of a new PET system for preclinical applications consisting of a ring of twelve time projection chambers filled with liquid xenon viewed by avalanche photodiodes. Simultaneous measurement of ionization charge and scintillation light leads to a significant improvement to spatial resolution, image quality, and sensitivity. Simulated performance shows that an energy resolution of <10% (FWHM) and a sensitivity of 15% are achievable. First tests with a prototype TPC indicate position resolution <1 mm (FWHM).
First imaging results in liquid xenon of a Liquid Hole Multiplier (LHM) coupled to a Quad-Silicon Photomultiplier (SiPM) array are presented. Ionization electrons deposited in the noble liquid by 5.5 MeV alpha particles, are collected into the holes of a Thick Gas Electron Multiplier (THGEM) electrode having a xenon gas bubble trapped underneath. They drift through the liquid-gas interface, inducing electroluminescence within the bubble. The resulting photons are detected with a Hamamatsu VUV4 quad-SiPM array - providing the deposited energy with a charge-only RMS resolution of 6.6%. The image reconstruction resolution was estimated to be ~200 um (RMS).
188Re is a beta- (Emax = 2.12 MeV) and gamma (155 keV) emitter. Since its chemistry is similar to that of the largely employed tracer, 99mTc, molecules of hyaluronic acid (HA) have been labelled with 188Re to produce a target specific radiopharmaceutical. The radiolabeled compound, i.v. injected in healthy mice, is able to accumulate into the liver after a few minutes. To study the effect of metabolic radiotherapy in mice, we have built a small gamma camera based on a matrix of YAP:Ce crystals, with 0.6x0.6x10 mm**3 pixels, read out by a R2486 Hamamatsu PSPMT. A high-sensitivity 20 mm thick lead parallel-hole collimator, with hole diameter 1.5 mm and septa of 0.18 mm, is placed in front of the YAP matrix. Preliminary results obtained with various phantoms containing a solution of 188Re and with C57 black mice injected with the 188Re-HA solution are presented. To increase the space resolution and to obtain two orthogonal projections simultaneously we are building in parallel two new cameras to be positioned at 90 degrees. They use a CsI(Tl) matrix with 1x1x5 mm**3 pixels read out by H8500 Hamamatsu Flat panel PMT.
Positron emission tomography, like many other tomographic imaging modalities, relies on an image reconstruction step to produce cross-sectional images from projection data. Detection and localization of the back-to-back annihilation photons produced by positron-electron annihilation defines the trajectories of these photons, which when combined with tomographic reconstruction algorithms, permits recovery of the distribution of positron-emitting radionuclides. Here we produce cross-sectional images directly from the detected coincident annihilation photons, without using a reconstruction algorithm. Ultra-fast radiation detectors with a resolving time averaging 32 picoseconds measured the difference in arrival time of pairs of annihilation photons, localizing the annihilation site to 4.8 mm. This is sufficient to directly generate an image without reconstruction and without the geometric and sampling constraints that normally present for tomographic imaging systems.
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