Crystal Clear Collaboration Research Articles

Structural, mechanical and light yield characterisation of heat treated LYSO:Ce single crystals for medical imaging applications

Five single crystals of cerium-doped lutetium yttrium oxyorthosilicate (LYSO:Ce) grown by the Czochralski method were submitted to structural characterisation by X-ray (XRD) and neutron (ND) diffraction, scanning (SEM) and transmission (TEM) electron microscopy and energy dispersive microanalysis (EDS). The Ultimate Tensile Strength (UTS), the Young Modulus (YM) and the Light Yield (LY) of the samples were also measured in order to correlate the mechanical and the optical behaviour of the crystals with the characteristics of their microstructure. Two of the samples analysed were also heat treated at 300°C for 10h to evidence possible variations induced by the temperature in the optical and mechanical response of the crystals. Results showed that the mean compositional variations evidenced by the structural analyses do not affect the mechanical and optical behaviour of the samples. On the contrary, the thermal treatment could induce the formation of coherent spherical particles (size 10 to 15nm), not uniformly distributed inside the sample, that strongly reduce the UTS and YM values, but it does not affect the optical response of the crystal. This latter result was attributed to the low value of the heating temperature (300°C) that is not sufficiently high to induce annealing of the oxygen vacancies traps that are responsible of the deterioration of the scintillation properties of the LYSO:Ce crystals.This study was carried out in the framework of the Crystal Clear Collaboration (CCC).

157: ClearPEM-Sonic: a multimodal PET-ultrasound mammography system

The ClearPEM-Sonic is a multimodal system dedicated to mammography, capable of providing co-registered metabolic, anatomical and structural information through combination of positron emission tomography with ultrasound elastographic imaging. The project is aimed to improve early stage detection of breast cancer through the high-resolution and high-sensitivity metabolic information provided by PEM, and the high-resolution anatomic information from US. Further improvements in the specificity of the system is provided by the ability to rule out non-cancerous findings from PEM, taking advantage of elastography imaging information. The ClearPEM-Sonic has been developed by the Crystal Clear Collaboration and is currently installed at Hopital Nord, Marseille, in the frame of CERIMED, the European Centre for Research in Medical Imaging. The detector is based on LYSO:Ce crystals, each of 2x2x20 mm3, grouped in 192 matrices of 8x4 crys- tals. BaSO4 is used as coating material and reflector. Read out is performed individually on both 2x2 mm2 faces of each crystal, using avalanche photodiodes (APDs). The detector performance has been thoroughly tested during the commissioning phase, confirming a spatial resolution of 1.5 mm, and a DOI precision of 2 mm. The co-registration software developed has proved to accurately superimpose images coming from the different modalities with a precision better than 2 mm. The clinical trial (phase 1) is being carried out on 20 patients with a known breast lesion who have been injected with FDG for a whole-body PET/CT as part of their diagnostic process. Results are compared to conventional imaging and MRI, with biopsy as a golden standard, to validate the use of ClearPEM-Sonic as a clinical imaging instrument for early detection of breast cancer.

ClearPEM, un TEP dédié au sein

Conventional breast imaging (mammography, ultrasound, MRI) relies on the analysis of anatomical characteristics. Whole-body positron emission tomography (PET) allows for the acquisition of a metabolic image, yet is limited by its poor spatial resolution. The Crystal Clear Collaboration developed a PET dedicated for breast imaging, the ClearPEM, in order to offer a high-resolution nuclear imaging technique. The patient is installed in the prone position on the exam bed, with two detector plates rotating around to breast to acquire a 3-dimensional image. Two prototypes were built and installed in hospitals. We summarize the technical solutions necessary for the development of this system and present a summary of its performances as well as an outlook on preclinical and clinical tests.

Development of an Anthropomorphic Breast Phantom for Combined PET, B-Mode Ultrasound and Elastographic Imaging

Combining the advantages of different imaging modalities leads to improved clinical results. For example, ultrasound provides good real-time structural information without any radiation and PET provides sensitive functional information. For the ongoing ClearPEM-Sonic project combining ultrasound and PET for breast imaging, we developed a dual-modality PET/Ultrasound (US) phantom. The phantom reproduces the acoustic and elastic properties of human breast tissue and allows labeling the different tissues in the phantom with different concentrations of FDG. The phantom was imaged with a whole-body PET/CT and with the Supersonic Imagine Aixplorer system. This system allows both B-mode US and shear wave elastographic imaging. US elastography is a new imaging method for displaying the tissue elasticity distribution. It was shown to be useful in breast imaging. We also tested the phantom with static elastography. A 6D magnetic positioning system allows fusing the images obtained with the two modalities. ClearPEM-Sonic is a project of the Crystal Clear Collaboration and the European Centre for Research on Medical Imaging (CERIMED).

Characterization of avalanche photodiode arrays for the ClearPEM and ClearPEM-Sonic scanners

The ClearPEM scanner is a high-resolution Positron Emission Mammography prototype, developed by the Portuguese PET Consortium in the framework of the Crystal Clear Collaboration at the European Organization for Nuclear Research (CERN). The scanner is based on a novel readout scheme which uses fine-pitch scintillator crystals, avalanche photodiodes, low-noise high-gain integrated electronics and a fast reconfigurable digital data acquisition system. The scanner uses two planar detector heads each composed of 96 detector modules. The detector module is composed of a matrix of 32 identical 2 × 2 × 20 mm3 LYSO:Ce scintillator crystals, coupled at both ends to Hamamatsu S8550 APD arrays for Depth-of-Interaction (DOI) measurements. More recently, a new scanner named ClearPEM-Sonic which combines the ClearPEM technology with an Ultrasound apparatus, is being produced. A set of 984 APD arrays used in both scanner assemblies followed a quality control protocol and a characterization procedure. This paper describes the methods used in these measurements and the results obtained with the full APD production batch.

Simulation results of a veto counter for the ClearPEM

The Crystal Clear Collaboration (CCC) has built a prototype of a novel positron emission tomograph dedicated to functional breast imaging, the ClearPEM. The ClearPEM uses the common radio pharmaceutical FDG for imaging cancer. As FDG is a rather non-specific radio tracer, it accumulates not only in cancer cells but in all cells with a high energy consumption, such as the heart and liver. This fact poses a problem especially in breast imaging, where the vicinity of the heart and other organs to the breast leads to a high background noise level in the scanner. In this work, a veto counter to reduce the background is described. Different configurations and their effectiveness were studied using the GATE simulation package.

Design Considerations of Phoswich Detectors for High Resolution Positron Emission Tomography

A way to improve the spatial resolution in positron emission tomography (PET) is to determine the depth-of-interaction (DOI) in the detector. A way to achieve this is to use the phoswich approach, a detector with two or more layers of different scintillators. The layer identification is done by using differences in scintillation decay time and pulse shape discrimination techniques. The advantages of the concept have been demonstrated in the HRRT high resolution PET system using a LSO/LYSO combination giving a high spatial resolution uniformity of around 2.5 mm within a larger part of the imaged volume. A phoswich combination that lately has received attention is LuAP/LSO or LuYAP/LSO. The suggestions come from the crystal clear collaboration and there is a patent application for its use in PET. This particular combination of phoswich may, however, have a complication since both LuAP and LuYAP emit in the excitation band of LSO, thus making the functionality more complex. In the present paper we have looked into this and suggested different ways to overcome potential drawbacks.

Depth of interaction resolution of LuAP and LYSO crystals

The Crystal Clear Collaboration (CCC) has built a prototype of a novel positron emission tomograph dedicated to functional breast imaging, the ClearPEM. One aim of the ClearPEM is to be able to depict small tumours with a diameter of 2–3 mm in the breast and axilla region. To achieve such a spatial resolution one needs to know the position of the photon interaction in the crystal—the depth of interaction (DOI) with a precision of a least 2 mm. The main component of the detector are 20 mm long LYSO crystals read out at both ends with avalanche photo diodes (APD). The method to determine the DOI in the ClearPEM is via light sharing between the two end faces of the crystal. In this work 20 mm long LuAP and LYSO crystals were used to study the spatial resolution of the DOI in the crystal. The influence of the surface state (polished and unpolished) and wrapping on the DOI resolution and the light yield were also investigated.

Performance and quality control of Clear-PEM detector modules

Clear-PEM is a dedicated PET scanner for breast and axilla cancer diagnosis, under development within the framework of the Crystal Clear Collaboration at CERN, aiming at the detection of tumors down to 2 mm in diameter. The camera consists of two planar detector heads with active dimensions 16.0×14.5 cm 2. Each head has 96 Clear-PEM detector modules consisting of 32 LYSO:Ce pixels with dimensions 2×2×20 mm 3 packed in a 4×8 BaSO 4 reflector matrix compressed between two Hamamatsu S8550 APD arrays in a double-readout configuration for Depth-of-Interaction (DoI) determination. The modules are individually measured and characterized before being grouped into Supermodules (comprised of 24 modules). Measured properties include photo-peak position, relative gain dispersion, energy resolution, cross-talk and DoI resolution. Optical inspection of matrices was also performed with the aid of a microscope, to search for pixel misalignments and matrix defects. Modules’ performance was thoroughly evaluated with a 511 keV collimated beam to exactly determine DoI resolution. In addition, a fast quality control (QC) procedure using flood irradiations from a 137Cs source was applied systematically. The overall performance of the 24 detector modules complies with the design goals of the Clear-PEM detector, showing energy resolution around 15%, DoI resolution of about 2 mm and gain dispersion among pixels of 15%.

Characterization and quality control of avalanche photodiode arrays for the Clear-PEM detector modules

Clear-PEM is a Positron Emission Mammography (PEM) prototype being developed in the framework of the Crystal Clear Collaboration at CERN. This device is a dedicated PET camera for mammography, based on LYSO:Ce scintillator crystals, Avalanche PhotoDiodes (APD) and a fast, low-noise electronics readout system, designed to examine both the breast and the axillary lymph node areas, and aiming at the detection of tumors down to 2 mm in diameter. The prototype has two planar detector heads, each composed of 96 detector modules. The Clear-PEM detector module is composed of a matrix of 32 identical 2×2×20 mm 3 LYSO:Ce crystals read at both ends by Hamamatsu S8550 APD arrays (4×8) for Depth-of-Interaction (DoI) capability. The APD arrays were characterized by the measurement of gain and dark current as a function of bias voltage, under controlled temperature conditions. Two independent setups were used. The full set of 398 APD arrays followed a well-defined quality control (QC) protocol, aiming at the rejection of arrays not complying within defined specifications. From a total of 398 arrays, only 2 (0.5%) were rejected, reassuring the trust in these detectors for prototype assembly and future developments.

Clear-PEM system counting rates: a Monte Carlo study

Positron Emission Mammography (PEM) with 18F-Fluorodeoxyglucose (18F-FDG) is a functional imaging technique for breast cancer detection. The development of dedicated imaging systems with high sensitivity and spatial resolution are crucial for early breast cancer diagnosis and an efficient therapy. Clear-PEM is a dual planar scanner designed for high-resolution breast cancer imaging under development by the Portuguese PET Mammography consortium within the Crystal Clear Collaboration. It brings together a favorable combination of high-density scintillator crystals coupled to compact photodetectors, arranged in a double readout scheme capable of providing depth-of-interaction information.A Monte Carlo study of the Clear-PEM system counting rates is presented in this paper. Hypothetical breast exam scenarios were simulated to estimate the single event rates, true and random coincidence rates. A realistic description of the patient and detector geometry, radiation environment, physics and instrumentation factors was adopted in this work. Special attention was given to the 18F-FDG accumulation in the patient torso organs which, for the Clear-PEM scanner, represent significant activity outside the field-of-view (FOV) contributing to an increase of singles, randoms and scattered coincidences affecting the overall system performance. The potential benefits of patient shielding to minimize the influence of the out-of-field background was explored. The influence of LYSO:Ce crystal intrinsic natural activity due to the presence of the 176Lu isotope on the counting rate performance of the proposed scanner, was also investigated.

Long-term stability of the Clear-PEM detector modules

Experimental evaluation of the imaging system Clear-PEM for positron emission mammography, under development within the framework of the crystal clear collaboration at CERN, is presented in terms of its long-term stability. The detector modules and experimental setup are described. Time evolution results of signal yield, energy resolution, depth-of-interaction and inter-channel crosstalk for a reference detector module are reported.

Raytest ClearPET™, a new generation small animal PET scanner

The ClearPET is a high-performance small animal PET scanner that has been developed by the Crystal Clear Collaboration (CCC) and is now commercially available to customers worldwide through the Raytest group. Its high sensitivity and spatial resolution are achieved, thanks to a patented phoswich configuration made of two types of scintillating crystals: L(Y)SO and LuYAP:Ce, thus providing depth of interaction information. The ClearPET presents a modular design and it allows for 360° rotation of the detector modules around the field of view (FOV). The ClearPET also presents the unique feature of having an adjustable FOV diameter, thus being suitable for small and medium size animal PET studies. This paper shows the performances of the commercial ClearPET in terms of its spatial resolution, sensitivity and quality of phantoms and preclinical images obtained. It also describes the updated situation of the first commercial unit sold to the Animage platform in Lyon.

Image reconstruction for the ClearPET™ Neuro

ClearPET™ is a family of small-animal PET scanners which are currently under development within the Crystal Clear Collaboration (CERN). All scanners are based on the same detector block design using individual LSO and LuYAP crystals in phoswich configuration, coupled to multi-anode photomultiplier tubes. One of the scanners, the ClearPET™ Neuro is designed for applications in neuroscience. Four detector blocks with 64 2×2×10 mm LSO and LuYAP crystals, arranged in line, build a module. Twenty modules are arranged in a ring with a ring diameter of 13.8 cm and an axial size of 11.2 cm. An insensitive region at the border of the detector heads results in gaps between the detectors axially and tangentially. The detectors are rotating by 360° in step and shoot mode during data acquisition. Every second module is shifted axially to compensate partly for the gaps between the detector blocks in a module. This unconventional scanner geometry requires dedicated image reconstruction procedures. Data acquisition acquires single events that are stored with a time mark in a dedicated list mode format. Coincidences are associated off line by software. After sorting the data into 3D sinograms, image reconstruction is performed using the Ordered Subset Maximum A Posteriori One-Step Late (OSMAPOSL) iterative algorithm implemented in the Software for Tomographic Image Reconstruction (STIR) library. Due to the non-conventional scanner design, careful estimation of the sensitivity matrix is needed to obtain artifact-free images from the ClearPET™ Neuro.

A PET imaging system dedicated to mammography

The imaging system Clear-PEM for positron emission mammography, under development within the framework of the Crystal Clear Collaboration at CERN, is presented. The detector is based on pixelized LYSO crystals optically coupled to avalanche photodiodes (APD) and readout by a fast low-noise electronic system. A dedicated digital trigger and data acquisition system is used for on-line selection of coincidence events with high efficiency, large bandwidth and negligible dead-time. The detector module performance was characterized in detail.

The data acquisition system of ClearPET neuro - a small animal PET scanner

The Crystal Clear Collaboration has developed a modular system for a small animal PET scanner (ClearPET). The modularity allows the assembly of scanners of different sizes and characteristics in order to satisfy the specific needs of the individual member institutions. The system performs depth of interaction detection by using a phoswich arrangement combining LSO and LuYAP scintillators which are coupled to Multichannel Photomultipliers (PMTs). For each PMT a free running 40 MHz ADC digitizes the signal and the complete scintillation pulse is sampled by an FPGA and sent with 20 MB/s to a PC for preprocessing. The pulse provides information about the gamma energy and the scintillator material which identifies the interaction layer. Furthermore, the exact pulse starting time is obtained from the sampled data. This is important as no hardware coincidence detection is implemented. All single events are recorded and coincidences are identified by software. The system in Ju/spl uml/lich (ClearPET Neuro) is equipped with 10240 crystals on 80 PMTs. The paper will present an overview of the data acquisition system.

Development of an optimized LSO/LuYAP phoswich detector head for the Lausanne ClearPET demonstrator

This paper describes the LSO/LuYAP phoswich detector head developed for the ClearPET small animal PET scanner demonstrator that is under construction in Lausanne within the Crystal Clear Collaboration. The detector head consists of a dual layer of 8/spl times/8 LSO and LuYAP crystal arrays coupled to a multi-anode photomultiplier tube (Hamamatsu R7600-M64). Equalistion of the LSO/LuYAP light collection is obtained through partial attenuation of the LSO scintillation light using a thin aluminum deposit of 20-35 nm on LSO and appropriate temperature regulation of the phoswich head between 30/spl deg/C to 60/spl deg/C. At 511keV, typical FWHM energy resolutions of the pixels of a phoswich head amounts to (28/spl plusmn/2)% for LSO and (25/spl plusmn/2)% for LuYAP. The LSO versus LuYAP crystal identification efficiency is better than 98%. Six detector modules have been mounted on a rotating gantry. Axial and tangential spatial resolutions were measured up to 4 cm from the scanner axis and compared to Monte Carlo simulations using GATE. FWHM spatial resolution ranges from 1.3 mm on axis to 2.6 mm at 4 cm from the axis.

Design and evaluation of the clear-PEM scanner for positron emission mammography

The design and evaluation of the imaging system Clear-PEM for positron emission mammography, under development by the PEM Consortium within the framework of the Crystal Clear Collaboration at CERN, is presented. The proposed apparatus is based on fast, segmented, high atomic number radiation sensors with depth-of-interaction measurement capabilities, and state-of-the-art data acquisition techniques. The camera consists of two compact and planar detector heads with dimensions 16.5/spl times/14.5 cm/sup 2/ for breast and axilla imaging. Low-noise integrated electronics provide signal amplification and analog multiplexing based on a new data-driven architecture. The coincidence trigger and data acquisition architecture makes extensive use of pipeline processing structures and multi-event memories for high efficiency up to a data acquisition rate of one million events/s. Experimental validation of the detection techniques, namely the basic properties of the radiation sensors and the ability to measure the depth-of-interaction of the incoming photons, are presented. System performance in terms of detection sensitivity, count-rates and reconstructed image spatial resolution were also evaluated by means of a detailed Monte Carlo simulation and an iterative image reconstruction algorithm.

Clear-PEM: A dedicated pet camera for improved breast cancer detection

Positron emission mammography (PEM) can offer a non-invasive method for the diagnosis of breast cancer. Metabolic images from PEM using 18F-fluoro-deoxy-glucose, contain unique information not available from conventional morphologic imaging techniques like X-ray radiography. In this work, the concept of Clear-PEM, the system presently developed in the frame of the Crystal Clear Collaboration at CERN, is described. Clear-PEM will be a dedicated scanner, offering better perspectives in terms of position resolution and detection sensitivity.

Comparison of LuAP and LuYAP crystal properties from statistically significant batches produced with two different growth methods

Abstract Measurements of the light yield, decay time and transmission were carried out on LuAP:Ce and mixed LuYAP:Ce crystals, which are new scintillation materials considered for Positron Emission Tomography (PET) and are used in the ClearPET™ [Auffray et al., Nucl. Sci. Methods A 527 (2004) 171 [15] ], the small animal PET scanner developed by the Crystal Clear Collaboration at CERN [CR & D for the study of new fast and radiation hard scintillators for calorimetry at LHC, Crystal Clear Collaboration, project RD 18, CERN/DRDC/P27/91–15 [16] ]. The purpose was to compare the properties of these two crystal types and to evaluate LuAP and LuYAP crystals produced by one of the authors (A. Petrosyan) from the Institute for Physical Research (IPR), Armenia in comparison to the crystals commercially available from Photonics Materials Ltd. (PML), Glasgow, UK as well as from the Bogoroditsk Techno Chemical Plant (BTCP) in Russia. The influence of the Ce-concentration on the crystal properties was studied for crystals from IPR. The non-proportionality of the light output and the energy resolution at different energies for the best four crystals was compared to a LYSO crystal.