1. Acquisition time6 min1 min 12 s Collimator height25 mm (Anger)12 mm (HiSens) Detector1 layer, 1 pixel / hole3 layers, 1 pixel / hole3 layers, 4 pixels / hole Geometry 2D image (sum X-Y reconstructed object) Study context Objectives Depth of Interaction (DOI) accuracy Parameters of HiSens Simulation ConclusionProspects Investigation of a Gamma Camera Architecture based on CdZnTe / CdTe Semiconductors: HiSens architecture Lucie GUERIN, Loïck VERGER, Véronique Rebuffel, Guillaume MONTEMONT LETI-CEA-MINATEC Recherche Technologique, 17 rue des Martyrs, 38054 Grenoble cedex 9, France. Corresponding author: loick.verger@cea.fr, Tel +33 (0)4 38 78 59 72, Fax +33 (0)4 38 78 51 64 HiSens Architecture In both planar and tomographic acquisition mode, HiSens architecture allows to ensure a spatial resolution similar to Anger Camera’s one while improving the system sensitivity by a factor 5. HiSens is a versatile architecture (electronic processing of the DOI information):  adaptable on any existing system,  usable for all NM modalities (thyroid, bone, cardiac, scintimammography)  that can be associated with other collimators as CardiArc or Spectrum Dynamics Experimental validation of HiSens architecture with a small field of view CdZnTe based gamma camera (“Minigami” camera), Results in planar acquisition mode Results in tomographic acquisition mode Good detection efficiency High count rate R e < 3 % at 140 keV Pixel < 1mm (XY) Depth of interaction (Z)  high sensitivity  high intrinsic spatial resolution  good scatter rejection - Limitation of energy resolution (R e ) by NaI(Tl) scintillator - Tradeoff between. Spatial resolution (R s ): limitation by collimator and by scintillator. Sensitivity (S): limitation by collimator Collimator (parallel-hole) Planar or tomographic Image Image processing Photomultiplicator Optical light guide Electronic NaI(Tl) Scintillator Source Image processing Dedicated collimator Pixellated monolithic CdZnTe detector Dedicated electronic Source Planar or tomographic Image Combine CdZnTe performances with a new collimation architecture in order to improve the tradeoff between spatial resolution and sensitivity: method of reconstruction  Investigation of HiSens TM (High Sensitivity) architecture with dedicated method of reconstruction  Simulation  Simulation of the system and evaluation of performances in planar and tomographic acquisition mode Z X CdZnTe detector (1 layer) Anger Collimator cathode anodes scheme not on correct scale use the DOI information and pixellated detector HiSens Architecture  representative scheme of the different angular apertures collimator associated with 5 mm thick CdZnTe detector including 1 layer or n layers (for instance three equally-probable-thickness layers)  use the depth of interaction information: CdZnTe detector is virtually composed of several layers and every layer is associated with a different angular aperture of the parallel square hole collimator and provides different information on source location Anger Architecture  estimation of Depth of Interaction (DOI) accuracy  include DOI information into an iterative reconstruction (in planar and tomographic acquisition mode)  CdZnTe detector 6.4 x 6.4 x 5 mm 3, with 4 x 4 pixels, 1.4 x 1.4 mm² size, 1.6 mm pitch and 5 mm thick Anode rise time (channel) distance between cathode and depht of interaction (mm) FWHM Submillimetric accuracy of DOI with CdZnTe  Discreteness of object and detector  Iterative algorithm to solve the linear equation system [p] = [R].[f] with: -each element f i in [f] is an object voxel value to be reconstructed -each element p k in [p] is a projection measurement on the detector -R ki in [R] is a coefficient expressing the contribution of pixel f i to projection p k Principle: Integration of DOI information into a reconstruction process Discrete object [f] f1f1 f2f2 f3f3 f5f5 f7f7 f4f4 f8f8 f9f9 f 10 f 11 f 12 f6f6 Discrete detector [p] p 11 p 21 p 31 p 41 p 51 p 12 p 22 p 32 p 42 p 52 p 13 p 23 p 33 p 43 p 53 p 14 p 24 p 34 p 44 p 54 p 15 p 25 p 35 p 45 p 55 Co l limator layer block one layer of detector R ki  The matrix [R] is evaluated by SINDBAD * tool, allowing to consider accurate system geometry, object self-attenuation and septal penetration  Iterative algorithms are used both in: -planar reconstruction (with acquisition of several layers detector at one direction) -tomographic reconstruction (with acquisition of several views angles and several layers detector)  OSEM Iterative algorithm is used within an ordered subsets framework (detector layer blocks) and with regularization (MRP-OSEM) Reconstruction method based on iterative algorithm 57 Co source of 10 MBq 100 mm 5 mm 25 or 12 mm Thyroid source in planar acquisition mode Dimension: 59 x 71 x 18 mm 3 Cold inserts diameter 6, 11 and 13 mm Hot inserts diameter 11 mm Collimator (Pb) - septal thickness : 0.2 mm - hole size : 1.5 mm - septal height : 25 mm (Anger) or 12 mm (HiSens) CdZnTe Detector - 1 layer or 3 equally-probable-thickness layers - 1 pixel (1.5 mm size) or 4 pixels (0.75 mm size) per collimator hole Geometry Reconstructed volume  OSEM and MRP-OSEM reconstructions with subsets equal to detector layers and stopped after 20 iterations  Dimension of reconstructed 3D object : 81 x 81 x 81 mm 3 with object voxel: 1.5 x 1.5 x 1.5 mm 3  Resulting images represented in planar acquisition mode by: sum X-Y reconstructed object (the sum along the Z axis of the reconstructed 3D object), and in tomographic acquisition mode by: Z-Y reconstructed object X-Y object Reconstructed object 3D sum along Z axis sum X-Y reconstructed object (image 2D) X Y Z-Y object X Y Z X Y Z HiSens Collimator CdZnTe detector (several layers & pixels per collimator hole) cathode anodes HiSens Collimator CdZnTe detector (several layers) cathode anodes cathode anodes cathode anodes cathode anodes Gain 5 on sensitivity 3D phantom in tomographic acquisition mode Dimension: 70 mm diameter and 64.5 mm height Cold spheres: 3 of 15 mm and 1 of 20 mm diameter Z X Y Acquisition time6 min1 min 12 s Collimator height25 mm (Anger)12 mm (HiSens) Detector1 layer, 1 pixel / hole3 layers, 1 pixel / hole3 layers, 4 pixels / hole Geometry 2D image (Z-Y reconstructed object) cathode anodes cathode anodes cathode anodes Experimental investigation with a test bench Thyroid source 57 Co Parallel-square-hole collimator XY table CdZnTe detector and specific electronic Image processing “Minigami” camera Optimization of HiSens architecture (quantification, robustness, optimized parameter set) by using Gate simulation tool, Further developments including HiSens principles into other collimation architectures. Principles of HiSens architecture Needs to study HiSens architecture Current limitation of Anger camera New  -ray CdZnTe detector performances at CEA-LETI * CEA-LETI simulation tool activity 0 activity 1 activity 2 Y X Gain 5 on sensitivity We have considered a 5 mm-thick CdZnTe detector composed of three equally-probable-thickness layers, and a configuration of 4 pixels per collimator hole (0.75 mm pitch). We have simulated a “HiSens” collimator with a hole height reduction allowing to have a gain of 5 in term of system sensitivity in comparison to the standard Anger gamma camera. For the considered phantoms, in both planar and tomographic acquisition mode, HiSens architecture allows to ensure a spatial resolution similar to Anger Camera’s one while improving the system sensitivity by a factor 5. or DOI accuracy Dedicated Reconstruction Method test bench Collimator localization (hole of 0.6 mm) 57 Co point source (with leaded protection) Detector 16 ASICs pre-amplificators 16 amplificators FWHM Counts 253 Anode pulse height (channel) Anode rise time (channel) DOI accuracy