A Network-Enabled PET Detector Module Based on TDCs on FPGA (#3215)
E. Venialgo1, N. Lusardi2, F. Garzetti2, A. Geraci2, E. Charbon1, 3
1 Delft University of Technology, Faculty Electrical Engineering, Mathematics and Computer Science, Delft, Netherlands
Recently, we have demonstrated that state-of-the-art CRT is achievable with time-to-digital converters (TDCs) implemented on an FPGA in combination with low output capacitance SiPMs, such as SensL J-series devices. The fast terminal of these SiPMs allows a direct connection to an off-the-shelf comparator that interfaces the TDC on an FPGA with the SiPMs. Subsequently, a drastic simplification of a PET detector module instrumentation chain is achieved without CRT degradation. Since the FPGA can allocate several TDCs and the comparator has a small footprint, no ASIC is required in order to integrate many channels onto a SiPM array.
In this paper we present a PET detector module based on TDCs implemented on an FPGA that does not require any ASICs. We demonstrate that gamma-photon energy, position, and timemark estimation can be performed utilizing this technology. The module comprises an 8x8 array of 6 mm pitch J-series SiPMs from SensL connected to a custom front-end board. The SiPM array is coupled to a pixelated LYSO scintillator with the same pitch and 15 mm thickness.
Keywords: time-to-digital converter, Field-programmable gate array, Positron emission tomography
Investigation of a Readout Circuit Design that Reduces Effective Capacitance of Large Area SiPMs (#3892)
J. W. Cates1, C. S. Levin1
1 Stanford University, Radiology, Stanford, California, United States of America
This work presents a novel front-end readout circuit for large area silicon photomultipliers (SiPMs) that improves achievable signal-to-noise ratio (SNR) for timing measurement by reducing the effective device capacitance. The major component of the proposed readout is a unity-gain, bootstrap amplifier that exploits the Miller effect to maintain the same AC voltage on two sides of the SiPM, resulting in reduced effective terminal capacitance between the nodes of the device. This technique potentially improves the single photon time resolution (SPTR) of analog SiPMs, which is affected by a sensor’s achievable SNR, dictated by both noise and capacitive shaping of signals from many microcells connected in parallel. The technique could also be exploited to overcome degradations in multiplexed SiPM-based detectors due to capacitive shaping and addition of uncorrelated noise when many SiPMs are connected in parallel to a single output. Simulations were performed to determine the influence of characteristics such as bandwidth of the unity gain amplifier and operation amplifiers used to process signals from the cathode. A test board was designed to measure improvement in SNR seen in the single photon response shape (measured as standard deviation in baseline noise over the slope of the signal’s rising edge). With the prototype test board, a factor of 2.09 improvement in SNR was observed (with the bootstrap amplifier powered on versus no supplied voltage) from the single photon response shape of a Hamamatsu S13360 SiPM, as predicted by the simulation model. The simulation model also indicates that a 3.7-fold improvement in SNR is also possible with optimization of the readout circuit.
Keywords: SiPM Readout, SPTR, Bootstrap
Particle-processing detectors for charged-particle emission tomography (#4364)
H. H. Barrett2, 1, Y. Ding3, L. Caucci2, N. Henscheid4
1 University of Arizona, College of Optical Sciences, Tucson, Arizona, United States of America
Emission Computed Tomography (ECT) is three-dimensional imaging of molecules or cells that have been labeled so that they emit light, high-energy photons or charged particles without significant alteration of their biological function. The familiar forms of ECT are SPECT (Single-Photon Emission Computed Tomography) and PET (Positron Emission Tomography), in which molecules labeled with radionuclides are imaged. In both cases a detector outside the patient’s body records highly penetrating gamma rays. In this presentation, we discuss ECT with less-penetrating radiation, specifically visible or infrared photons in OpECT (Optical Emission Computed Tomography), beta particles in BET (Beta Emission Tomography) and alpha particles in αET (AlphET). BET and αET are forms of CPET (Charged-Particle Emission Tomography).
CPET and OpET can be performed endoscopically, in rodent window chambers, or on the skin for superficial lesions. None of these configurations permits rotation of the detector with respect to the object, so only limited-angle tomography is possible, but accurate reconstructions can be obtained if we measure the radiance in the detector plane. Radiance on a plane is a function of two spatial coordinates, two direction cosines and the energy of a photon or particle. We will show that the null functions of a CPET or OpET system are very small in magnitude if these five attributes are estimated for each detection event.
The object for ECT is a physiological random process, a random function of spatial position and time. All statistical properties of a random process are contained in its characteristic functional. If multiple tracers are used and can be distinguished by their energy attributes, we have a unique tool for studying interacting physiological processes. If one of those processes is a therapeutic drug and one reflects tumor growth, we can use the joint characteristic functional to estimate the response of the tumor to the drug.
Keywords: charged-particle tomography, optical computed tomography, chemotherapy, characteristic functionals
LA-iQID: A novel high-resolution CCD-based gamma camera for lymphatic imaging (#4197)
L. Han1, B. W. Miller1, L. R. Furenlid1, 2
1 University of Arizona, College of Optical Science, Tucson, United States of America
iQID is an intensified quantum imaging detector developed at the Center for Gamma-Ray Imaging, University of Arizona. With columnar scintillator, image intensifier, relay lens and CCD sensor, iQID features ultra-high resolution, versatility, portability and photon-counting capability. Originally developed for preclinical imaging, iQID cameras have been successfully used in small-animal scintigraphy, SPECT imaging, and particle imaging. As the first translation of iQID technology to clinical applications, this paper demonstrates novel design and development of a large-area iQID (LAIQID) camera with ~1 mm resolution performance and FOV of 188 mm x 188 mm for dedicated point-of-care lymphatic imaging.
Keywords: Gamma camera, iQID, High resolution, Lymphatic imaging, Scintigraphy, LEUHR collimator, CCD based
A high rate silicon detector and front-end electronics prototype for single ion discrimination in particle therapy (#3293)
F. Fausti1, 2, G. Mazza2, A. Attili2, N. Cartiglia2, M. Donetti4, M. Ferrero2, S. Giordanengo2, O. H. Alì2, 3, M. Mandurrino2, L. Manganaro2, 3, V. Monaco2, 3, R. Sacchi2, 3, V. Sola2, 3, A. Staiano2, A. Vignati2, R. Cirio2, 3
1 Politecnico di Torino, Dipartimento di Elettronica e Telecomunicazioni, Torino, Italy
On the behalf of the MoVeIT collaboration (Modelling and Verification for Ion beam Treatment planning)
The medical physics group of the Turin section of the National Institute of Nuclear Physics, in the framework of the MoVeIT collaboration, is working at the development of a new prototype of silicon strips detector for particle therapy applications. This device, based on 50 µm thin silicon sensors with internal gain, aims to detect the each beam particle and count their number up to 108 cm2/s fluxes, with a pileup probability < 1%. A similar approach would lead to a drastic step forward, compared to the classical and widely used monitoring system based on ionization chambers. The better sensitivity, the higher dynamic range and the fact that the particle counting is independent on the beam energy, pressure and temperature, make this silicon detector suitable for the on-line dose monitoring in particle therapy applications.
The prototype detector will cover a 3X3 cm2 area. Currently two sets of strip sensors with different geometry and custom design, have been produced and are currently under characterization. The classic orthogonal strip orientation is used for beam profile measures. For what concerns the front-end electronics, the design of two different options is ongoing: one based on a transimpedance preamplifier, with a resistive feedback and a second one including a charge sensitive amplifier followed by a two stages discriminator. The challenging tasks for the design is the expected 3fC-130fC wide input charge range (due to the Landau fluctuation spreading and different beam energies), and the 200 MHz repetition rate.
To effectively design these components, a preliminary investigation of the sensor response to the expected stimuli is crucial. For this reason, before the production of the above mentioned dedicated strip sensors, an extensive work has been done and is still ongoing. Dedicated beam test have been performed at the CNAO hadrontherapy center in Pavia, Italy using 1.2 mm2 area and 50 µm thickness silicon pads with gain
Keywords: Particle therapy; Silicon detectors; High rate front-end electronics.
A novel water-equivalent electronic portal imaging device for radiotherapy with improved detective quantum efficiency: Proof of concept (#2415)
S. J. Blake1, 2, Z. Cheng1, 2, S. Atakaramians3, S. R. Meikle4, M. Lu5, P. Vial1, 6, Z. Kuncic1
1 The University of Sydney, Institute of Medical Physics, School of Physics, Sydney, New South Wales, Australia
Interest in using commercial electronic portal imaging devices (EPIDs) as dosimeters in radiotherapy has grown in recent years. However, their widespread clinical implementation for dosimetry has been limited due to their non water-equivalent dose response. We have developed a novel solution to this problem using an array of water-equivalent plastic scintillating fibers with the photodetector of a commercial EPID, and have previously demonstrated its suitability for dosimetry. The aim of this work was to quantify our prototype’s imaging performance in terms of its modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) relative to a standard EPID. Based on results from a previous Monte Carlo (MC) modeling study, we hypothesized that the prototype’s DQE would exceed that of a standard EPID. The prototype array detector comprised 300 x 300 plastic scintillating fibers, each measuring 30 x 0.5 x 0.5 mm3 and composed of a polystyrene core, polymethyl methacrylate cladding and extra-mural absorber (EMA) to prevent optical cross-talk. A standard EPID was modified into a water-equivalent configuration by removing components above the photodetector and placing the prototype array directly on the imaging panel. The MTF and NPS were measured in both standard and water-equivalent configurations and the DQE was then calculated from these metrics. Measurements were also used to empirically validate optical transport parameters in our MC model. Results demonstrated that the water-equivalent EPID exhibited lower spatial resolution, but also less noise relative to the standard EPID, resulting in an overall DQE(0) of 3%, approximately double that of the standard EPID. Comparison against MC-calculated results suggests that the EMA is an imperfect absorber and core/cladding boundaries are not perfectly smooth. Simulations also demonstrated that significant gains in performance may be realized by further optimizing the prototype design.
Keywords: EPID, Portal imaging, Image quality, DQE, Monte Carlo