DAQs | PET & SPECT

We are pleased to provide downloads, or links, for a number of papers relating to the use of Vertilon's PhotoniQ DAQs in Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT). Many of these papers precede the rise of Silicon Photomultipliers (SiPMs) in the PET market and refer solely to conventional vacuum photomultiplier tubes. Vertilon's PhotoniQ DAQs may also be used with SiPMs and SiPM arrays.

Construction and Testing of a Positron Emission Tomography Demonstrator

T. Zedda, Tampere University of Technology, 5 June 2013

In this thesis we present the Avantomography demonstrator, which is being implemented and tested at Tampere University of Technology (Tampere, Finland). We also describe the first tests performed with it and the obtained results. The final aim of this master thesis is the energy calibration of the scintillating crystals and the electronic chain for data acquisition. This new small Positron Emission Tomography (PET) demonstrator follows the recent innovations presented by the AX-PET group , at CERN. This is the first functioning version of a prototype of a light and compact PET scanner. The novel geometry, used to build the Avantomography demonstrator, is based on scintillating crystals and wavelength shifting (WLS) plastic strips, allowing high resolution and high sensitivity at the same time. The device consists in two small and compact modules, with two different adjustable parts inside. Each detector module is built up from long scintillator bars placed in the trans-axial plane and orthogonal WLS strip arrays. Preliminary tests with a standard positron emitter source has been performed in order to test the acquisition chain and to calibrate the demonstrator. First test has been performed measuring the intrinsic radioactivity of the scintillating crystals. For a complete calibration of one crystal, a test with a linear positron emitter source has been performed at the Tampere University Hospital (Tampere, Finland). From these measurements the spectra of different energy peaks are acquired and plotted. Using a dedicate MATLAB code, different Gaussian fits are calculated to find the position of each peak. With these values a 3-parameters fitting curve has been evaluated in order to obtain the non linear curve for the energy calibration. Furthermore a first evaluation of the energy resolution has been calculated starting from the acquired data. With its compact and light geometry, high resolution and high sensitivity this detector has a promising layout as a preclinical PET scanner.

Optimization of the Angle between Detector Modules in a Dual-Head Cardiac SPECT

Su Jung An, Hyun-Il Kim, Chae Young Lee, Woo Jin Jo, Yong Hyun Chung

In recent years, dedicated cardiac single photon emission computed tomography (SPECT) systems have been undergoing a profound change in design with multiple detectors and various angles between the modules to improve the sensitivity and the resolution by reducing the distance between the heart and the detector. The performance of a dual-head cardiac SPECT for small-animal imaging was characterized as a function of the angle between two detector heads by using GATE simulations, and simulation data were validated with experimental results. Each detector head consists of 50x50x6mm^3 NaI(Tl) optically coupled to a Hamamatsu H8500 position sensitive photomultiplier (PSPMT) and a low-energy high-resolution parallel-hole collimator (LEHR, septal thickness: 0.2 mm, diameter: 1.9 mm). The distance between the collimator surface and the center of rotation was set as 20, 20, 20, 25, or 31.5 mm for 70°, 80°, 90°, 100°, or 110°, respectively, based on a 40-mm field of view (FOV). A point source and a rat cardiac phantom of Tc-99m in scattering media were simulated. Projection data were acquired for 180 angular views in steps of 2° and were reconstructed by using a filtered back-projection algorithm. Results demonstrated that the angle between the detector heads did not make a big difference in the image quality when scattering media were not presented, but the dual heads in the 80° geometry provided the best spatial resolution in the cardiac phantom study. The peak-to-valley ratio between the myocardial wall and the cavity was measured as 1.87, 11.01, 3.28, 3.40, or 2.46 for 70°, 80°, 90°, 100°, or 110°, respectively. Experiments were performed with a dual-head SPECT in the 80° geometry, and the results agreed well with these from the simulations. In this study, the impact of the angle between dual detector heads on the imaging performance was evaluated, and the optimal angle was derived for a dedicated cardiac SPECT.

Characterization of MRI-Compatible PET Detector Modules by Optical Excitation of the Scintillator Material

B. Játékos, Z. Kolozsi, E. Lörincz, F. Ujhelyi, A. Barócsi, G. Erdei

In the field of biomedical imaging there is a strong interest in combining modalities of positron emission tomography (PET) and magnetic resonance imaging (MRI). An MRI-compatible PET detector module has to be insensitive to the magnetic field that is why it needs to incorporate avalanche photodiodes (APDs) or silicon photomultipliers (SiPMs). We propose a new purely optical characterization method for these devices where no nuclear source is needed. In our method we use LED sources for both the direct illumination of silicon sensors and fluorescent excitation of the scintillator material. With this method we can measure the response characteristic and uniformity of pixels in sensor arrays as well as the optical cross-talk between neighboring pixels. In the same experimental setup we can also emulate the pulse response of the detector module (i.e. light-spread over the sensor array from a point source in the scintillator material). We present the detailed construction of the experimental setup and analyze the benefits and drawbacks of this method compared to the nuclear measurements. The viability of the idea is proven through the characterization of a SiPM array and a block detector module based on it.

Gamma Camera with a Two-Layer Diverging-Slat Collimator for Radioisotope Monitoring

Hyun-Il Kim, Cheol-Ha Baek, Su Jung An, Sung-Woo Kwak, Yong Hyun Chung

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 698, 11 January 2013

The purpose of this study was to develop and evaluate a gamma camera with a newly designed diverging collimator for monitoring radiation fields in nuclear medicine. Simulations using the Geant4 Application for Tomographic Emission (GATE) were performed to model the gamma camera system designed to monitor Tc-99m radioactive isotopes usually used in nuclear medicine. A gamma camera consists of a diverging collimator, a CsI(Na) scintillation crystal with dimensions of 50.0 mm by 50.0 mm by 6.0 mm and Hamamatsu H8500 PSPMT. The diverging collimator is composed of two layers of diverging slats stacked directly above each other, and the front layer is rotated by 90 degrees with respect to the back layer. The point source at different positions was simulated, and the optimal slat thickness and slat height were determined by evaluating the spatial resolution and sensitivity. The slat thickness is 1.0 mm, the slat height is 40.0 mm and the angle of slats ranges from 0 to 22.5 degrees. The front and back layers are composed of 40 and 18 slats, respectively, to achieve equal spatial resolution in the x and y directions. The diverging collimator improves the uniformity of the spatial resolution and sensitivity across the field of view and the count rate better than the pinhole collimator. Experimental measurements were performed, and the results agreed well with simulations in terms of spatial resolution and sensitivity. The results demonstrated that the two-layer diverging-slat collimator is suitable for large area monitoring of the radiation fields.

Real-time Scintillation Array Dosimetry for Radiotherapy: The Advantages of Photomultiplier Detectors

P. Z. Y. Liu, N. Suchowerska, P. Abolfathi, D. R. McKenzie

Medical Physics, Volume 39, Issue 4, Radiation Imaging Physics, 8 March 2012

In this paper, a photomultiplier tube (PMT) array dosimetry system has been developed and tested for the real-time readout of multiple scintillation signals from fiber optic dosimeters. It provides array dosimetry with the advantages in sensitivity provided by a PMT, but without the need for a separate PMT for each detector element. The PMT array system consisted of a multianode PMT, a multichannel data acquisition system, housing and optic fiber connections suitable for clinical use. The reproducibility, channel uniformity, channel crosstalk, acquisition speed, and sensitivity of the PMT array were quantified using a constant light source. Its performance was compared to other readout systems used in scintillation dosimetry. An in vivo HDR brachytherapy treatment was used as an example of a clinical application of the dosimetry system to the measurement of dose at multiple sites in the rectum. The PMT array system was also tested in the pulsed beam of a linear accelerator to test its response speed and its application with two separate methods of Cerenkov background removal. The PMT array dosimetry system was highly reproducible with a measurement uncertainty of 0.13% for a 10 s acquisition period. Optical crosstalk between neighboring channels was accounted for by omitting every second channel. A mathematical procedure was used to account for the crosstalk in next-neighbor channels. The speed and sensitivity of the PMT array system were found be superior to CCD cameras, allowing for measurement of more rapid changes in dose rate. This was further demonstrated by measuring the dose delivered by individual photon pulses of a linear accelerator beam. The PMT array system has advantages over CCD camera-based systems for the readout of scintillation light. It provided a more sensitive, more accurate, and faster response to meet the demands of future developments in treatment delivery.

A Feasibility Study on the Use of Arrays of Discrete SiPMs for MR Compatible LYSO Readout using Monte Carlo Simulation

P. Aguiara, A. Iglesias, B. Couce, C. Lois

Journal of Instrumentation, Volume 7, June 2012

This paper shows a feasibility study on the use of discrete SiPMs to read out monolithic scintillator-based detectors for use in molecular imaging applications. Monte Carlo simulations are carried out in order to evaluate the basic performance of 8 x 8 arrays of discrete SiPMs with different PDE values and compare it to conventional 64 channel multi-anode PMT (MA-PMT) readout. A detailed optical transport model was incorporated into the Monte Carlo simulation and a detector module based on a monolithic scintillator crystal of 50 x 50 x 4 mm^3 coupled to a MA-PMT was built for experimental validation. The effect of the SiPM dynamic range was also investigated by including a model of the saturation effects into the optical transport simulation. The results show that a detector module based on an array of 8 x 8 discrete SiPM devices (3 x 3 mm^2 and PDE > 32%) is feasible as a replacement of a 64 channel MA-PMT in order to read out large monolithic crystals for MR-compatible gamma cameras.

Characterization of Low Energy Lu Background on Continuous LYSO Blocks

C. Lois, P. Aguiar, B. Couce, A. Iglesias

Nuclear Science Symposium Conference Record (NSS/MIC), 2010

The presence of the naturally occurring isotope 176Lu gives rise to background count rates in LSO/LYSO crystals to be used in PET and SPECT systems. The aim of this work is to measure 176Lu background count rates and its spatial distributions in a continuous LYSO block. Our results show that the low energy component of 176Lu background is related to partial energy deposition mainly produced near the crystal edge showing a hot-perimeter artifact. Furthermore, 176Lu background rate is observed to be 10 times lower for a 100-180 keV than for a 411-611 keV energy window. Our findings indicate that when using monolithic LYSO crystal blocks, 176Lu background is not expected to significantly deteriorate the performance of single photon detection systems.

Design of a Small Animal PET Imaging System with 1 Microliter Volume Resolution

Ned C. Rouze, Matthias Schmand, Stefan Siegel, Gary D. Hutchins

IEEE Transactions on Nuclear Science, Vol. 51, No. 3, June 2004

The design of a new scanner for use in small animal PET imaging is described. The goal is to achieve 1mm FWHM resolution in each of three orthogonal directions throughout a volume suitable for whole body mouse imaging, roughly 40 mm diameter x 80 mm long. Simultaneously, the design should achieve a sensitivity of greater than 5% of all decays from a point source located at the center of the scanner. The scanner uses 12, plane detector banks mounted in a 160 mm diameter ring on a rotating gantry. Each detector bank consists of a 48 x 108 array of 20 mm long LSO scintillator crystals with an array pitch of 0.87 mm. Each bank uses two Hamamatsu H8500 large-area, multi-anode photomultiplier tubes for fluorescence detection. The detector banks are divided into two sets with the respective lines of response offset by one quarter of the array pitch to give increased sampling density.

Optimization and Performance Evaluation of the MicroPET II Scanner for in vivo Small-Animal Imaging

Yongfeng Yang, Yuan-Chuan Tai, Stefan Siegel, Danny F Newport, Bing Bai, Quanzheng Li, Richard M Leahy, Simon R Cherry

Physics of Medicine and Biology, 49 (2004) 2527–2545

MicroPET II is a newly developed PET (positron emission tomography) scanner designed for high-resolution imaging of small animals. It consists of 17 640 LSO crystals each measuring 0.975 x 0.975 x 12.5 mm3, which are arranged in 42 contiguous rings, with 420 crystals per ring. The scanner has an axial field of view (FOV) of 4.9 cm and a transaxial FOV of 8.5 cm. The purpose of this study was to carefully evaluate the performance of the system and to optimize settings for in vivo mouse and rat imaging studies. The volumetric image resolution was found to depend strongly on the reconstruction algorithm employed and averaged 1.1mm (1.4 µl) across the central 3cm of the transaxial FOV when using a statistical reconstruction algorithm with accurate system modelling. The sensitivity, scatter fraction and noise-equivalent count (NEC) rate for mouse- and rat-sized phantoms were measured for different energy and timing windows. Mouse imaging was optimized with a wide open energy window (150 to 750 keV) and a 10 ns timing window, leading to a sensitivity of 3.3% at the centre of the FOV and a peak NEC rate of 235,000 cps for a total activity of 80 MBq (2.2 mCi) in the phantom. Rat imaging, due to the higher scatter fraction, and the activity that lies outside of the field of view, achieved a maximum NEC rate of 24,600 cps for a total activity of 80 MBq (2.2 mCi) in the phantom, with an energy window of 250 to 750 keV and a 6 ns timing window. The sensitivity at the centre of the FOV for these settings is 2.1%. This work demonstrates that different scanner settings are necessary to optimize the NEC count rate for different-sized animals and different injected doses. Finally, phantom and in vivo animal studies are presented to demonstrate the capabilities of microPET II for small-animal imaging studies.

Novel Design of a Parallax Free Compton Enhanced PET Scanner

A. Braem, M. Chamizo, E. Chesi, N. Colonna, F. Cusanno, R. De Leo, F. Garibaldi, C. Joram, S. Marrone, S. Mathot, E. Nappi, F. Schoenahl, J. Seguinot, P. Weilhammer, H. Zaidi

Nuclear Instruments and Methods in Physics Research A 525 (2004) 268–274

Molecular imaging by PET is a powerful tool in modern clinical practice for cancer diagnosis. Nevertheless, improvements are needed with respect to the spatial resolution and sensitivity of the technique for its application to specific human organs (breast, prostate, brain, etc.), and to small animals. Presently, commercial PET scanners do not detect the depth of interaction of photons in scintillators, which results in a not negligible parallax error. Described here is a novel concept of PET scanner design that provides full three-dimensional (3D) gamma reconstruction with high spatial resolution over the total detector volume, free of parallax errors. It uses matrices of long scintillators read at both ends by hybrid photon detectors. This so-called 3D axial concept also enhances the gamma detection efficiency since it allows one to reconstruct a significant fraction of Compton scattered events. This paper describes the concept, a possible design and the expected performance of this new PET device. Also reported is first characterization measurements of 10 cm long YAP:Ce scintillation crystals.

PET & SPECT

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