The AX-PET demonstrator—Design, construction and characterization Beltrame, P.; Bolle, E.; Braem, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2011, Volume:
654, Issue:
1
Journal Article
Peer reviewed
Axial PET is a novel geometrical concept for Positron Emission Tomography (PET), based on layers of long scintillating crystals axially aligned with the bore axis. The axial coordinate is obtained ...from arrays of wavelength shifting (WLS) plastic strips placed orthogonally to the crystals. This article describes the design, construction and performance evaluation of a demonstrator set-up which consists of two identical detector modules, used in coincidence. Each module comprises 48 LYSO crystals of 100
mm length and 156 WLS strips. Crystals and strips are readout by Geiger-mode Avalanche Photo Diodes (G-APDs). The signals from the two modules are processed by fully analog front-end electronics and recorded in coincidence by a VME-based data acquisition system. Measurements with point-like
22Na sources, with the modules used both individually and in coincidence mode, allowed for a complete performance evaluation up to the focal plane reconstruction of point sources. The results obtained are in good agreement with expectations and proved the set-up to be ready for the next evaluation phase with PET phantoms filled with radiotracers.
The measurements presented in this paper are related to the development of a PET camera based on a 3-D axial geometry with excellent 3-D spatial, timing and energy resolution. The detector modules ...consist of matrices of long axially oriented scintillation crystal bars, which are individually coupled to photodetectors. The axial coordinate is derived from wavelength shifting (WLS) plastic strips orthogonally interleaved between the crystal bars and readout by G-APD arrays. We report on results from measurements with two LYSO crystal bars, read with PMTs, and two WLS strips readout with G-APD devices from Hamamatsu (called MPPC). The WLS strips are positioned orthogonally underneath the LYSO bars. Yields of about 80 photoelectrons from the WLS strips for an energy deposition in the LYSO crystals equivalent to the absorption of 511
keV photons are observed. The axial coordinate in the LYSO bars is reconstructed with a precision of about 1.9
mm (FWHM) using a digital reconstruction method. The resolution of an analog coordinate reconstruction method, which uses the pulse height measurement from the WLS strips is 2.8
mm (FWHM). This resolution is still compromised by the availability of only two WLS strips and will improve with a full stack of LYSO crystals interleaved with WLS strip arrays, which is presently under development for a PET demonstrator set-up.
AX-PET is a novel PET detector based on axially oriented crystals and orthogonal wavelength shifter (WLS) strips, both individually read out by silicon photo-multipliers. Its design decouples ...sensitivity and spatial resolution, by reducing the parallax error due to the layered arrangement of the crystals. Additionally the granularity of AX-PET enhances the capability to track photons within the detector yielding a large fraction of inter-crystal scatter events. These events, if properly processed, can be included in the reconstruction stage further increasing the sensitivity. Its unique features require dedicated Monte-Carlo simulations, enabling the development of the device, interpreting data and allowing the development of reconstruction codes. At the same time the non-conventional design of AX-PET poses several challenges to the simulation and modeling tasks, mostly related to the light transport and distribution within the crystals and WLS strips, as well as the electronics readout. In this work we present a hybrid simulation tool based on an analytical model and a Monte-Carlo based description of the AX-PET demonstrator. It was extensively validated against experimental data, providing excellent agreement.
AX-PET stands for a new geometrical concept for a high resolution and high sensitivity PET scanner, based on an axial arrangement of long scintillating crystals in the tomograph, for a parallax free ...PET detector. Two identical AX-PET modules – consisting of matrices of LYSO crystals interleaved with WLS strips – have been built. They form the AX-PET Demonstrator, which has been extensively characterized and successfully used for the reconstruction of images of several phantoms. In this paper we report on the current status of the project, with emphasis on the most relevant results achieved both in terms of detector characterization and image reconstruction. We also discuss the recent preliminary results obtained with the digital SiPM from Philips (dSiPM), which are currently being tested as a possible alternative photodetector for AX-PET. With their very good intrinsic time resolution, dSiPM could add Time of Flight capability to the AX-PET concept.
AX-PET: A novel PET concept with G-APD readout Bolle, E.; Casella, C.; Chesi, E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2012, Volume:
695
Journal Article
Peer reviewed
Open access
The AX-PET collaboration has developed a novel concept for high resolution PET imaging to overcome some of the performance limitations of classical PET cameras, in particular the compromise between ...spatial resolution and sensitivity introduced by the parallax error.
The detector consists of an arrangement of long LYSO scintillating crystals axially oriented around the field of view together with arrays of wave length shifter strips orthogonal to the crystals. This matrix allows a precise 3D measurement of the photon interaction point. This is valid both for photoelectric absorption at 511keV and for Compton scattering down to deposited energies of about 100keV. Crystals and WLS strips are individually read out using Geiger-mode Avalanche Photo Diodes (G-APDs). The sensitivity of such a detector can be adjusted by changing the number of layers and the resolution is defined by the crystal and strip dimensions.
Two AX-PET modules were built and fully characterized in dedicated test set-ups at CERN, with point-like 22Na sources. Their performance in terms of energy (Renergy≈11.8% (FWMH) at 511keV) and spatial resolution was assessed (σaxial≈0.65mm), both individually and for the two modules in coincidence.
Test campaigns at ETH Zurich and at the company AAA allowed the tomographic reconstructions of more complex phantoms validating the 3D reconstruction algorithms.
The concept of the AX-PET modules will be presented together with some characterization results. We describe a count rate model which allows to optimize the planing of the tomographic scans.
We describe a novel method to extract the axial coordinate from a matrix of long axially oriented crystals, which is based on wavelength shifting (WLS) plastic strips. The method allows building ...compact 3-D axial gamma detector modules for PET scanners with excellent 3-D spatial, timing and energy resolution while keeping the number of readout channels reasonably low. A voxel resolution of about 10
mm
3 is expected. We assess the performance of the method in two independent ways, using classical PMTs and G-APDs to read out the LYSO (LSO) scintillation crystals and the WLS strips. We observe yields in excess of 35 photoelectrons from the strips for a 511
keV gamma and reconstruct the axial coordinate with a precision of about 2.5
mm (FWHM).
AX-PET: A novel PET detector concept with full 3D reconstruction Braem, A.; Joram, C.; Séguinot, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2009, Volume:
610, Issue:
1
Journal Article
Peer reviewed
We describe the concept and first experimental tests of a novel 3D axial Positron Emission Tomography (PET) geometry. It allows for a new way of measuring the interaction point in the detector with ...very high precision. It is based on a matrix of long Lutetium-Yttrium OxyorthoSilicate (LYSO) crystals oriented in the axial direction, each coupled to one Geiger Mode Avalanche Photodiode (G-APD) array. To derive the axial coordinate, Wave Length Shifter (WLS) strips are mounted orthogonally and interleaved between the crystals. The light from the WLS strips is read by custom-made G-APDs. The weighted mean of the signals in the WLS strips has proven to give very precise axial resolution. The achievable resolution along the three axes is mainly driven by the dimensions of the LYSO crystals and WLS strips. This concept is inherently free of parallax errors. Furthermore, it will allow identification of Compton interactions in the detector and for reconstruction of a fraction of them, which is expected to enhance image quality and sensitivity. We present the results of proof-of-principle tests and qualification measurements of the various components prepared to build a larger scale demonstrator consisting of two matrices of
8
×
6
LYSO crystals and 312 WLS strips.
The design and construction of a PET camera module with high sensitivity, full 3-D spatial reconstruction and very good energy resolution is presented. The basic principle consists of an axial ...arrangement of long scintillation crystals around the Field Of View (FOV), providing a measurement of the transverse coordinates of the interacting 511
keV gamma ray. On top of each layer of crystals, an array of Wave-Length Shifter (WLS) strips, which collect the light leaving the crystals sideways, is positioned orthogonal to the crystal direction. The signals in the WLS strips allow a precise measurement of the
z (axial) co-ordinate of the 511
keV γ-ray gamma impact. The construction of two modules used for demonstration of the concept is described. First preliminary results on spatial and energy resolution from one full module will be shown.
Standard Positron Emission Tomography (PET) cameras need to reach a compromise between spatial resolution and sensitivity. To overcome this limitation we developed a novel concept of PET. Our AX-PET ...demonstrator is made of LYSO crystals aligned along the
z coordinate (patient's axis) and WLS strips orthogonally placed with respect to the crystals. This concept offers full 3D localization of the photon interaction inside the camera. Thus the spatial resolution and the sensitivity can be simultaneously improved and the reconstruction of Compton interactions inside the detector is also possible. Moreover, by means of G-APDs for reading out the photons, both from LYSO and WLS, the detector is insensitive to magnetic fields and it is then suitable to be used in a combined PET/MRI apparatus. A complete Monte Carlo simulation and dedicated reconstruction software have been developed. The two final modules, each composed of 48 crystals and 156 WLS strips, have been built and fully characterized in a dedicated test set-up. The results, obtained with a
22Na point source (0.25
mm diameter), of the single module performances and a first estimation of the performances with the two module system are reported.
High-resolution electro-magnetic calorimetry with noble liquids Schinzel, D.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/1998, Volume:
419, Issue:
2-3
Journal Article
Peer reviewed
Open access
Electromagnetic calorimeters with noble liquids and their limits in resolution are discussed. The origins of “initial” current measurement in calorimetry are retraced and the performance and first ...results of the NA48 calorimeter (quasi-homogeneous calorimeter with longitudinal electrode structure) are presented. Results of the prototype calorimeters of KEDR (quasi-homogeneous calorimeter with transverse electrode structure) and of ATLAS (sampling calorimeter with longitudinal electrode structure), are summarized.
PDF