High spatial resolution time of flight PET detectors for brain imaging (#2106)
M. Kapusta1, R. Mintzer1, L. Byars1, C. Catana2, M. Schmand1
1 Siemens Medical Solutions USA, Inc., Molecular Imaging, Rockford, Tennessee, United States of America
In this work we evaluate PET detector prototypes which combine and surpass the high-resolution research tomograph (HRRT) and BrainPET detector capabilities. Our goal is to assess the feasibility of constructing higher performance PET systems to address the needs of the neuroscience community. Three different geometries of detectors were investigated. One of the detector modules consists of a 10×10 array of 1.6×1.6×15 mm3 LSO crystals read out by a 4×4 element array of silicon photomultipliers. Such a configuration of the detector does not allow depth-of-interaction determination, but provides excellent spatial resolution and average coincidence timing resolution of 237 ps FWHM. Two other configurations with depth-of-interaction capability were constructed. The simplest realization consists of 5×5 air coupled LSO crystals, 3.2×3.2×10 mm3 in size, arranged in two stacked layers. The crystals of the top and bottom layers were selected to differ by their light outputs and decay times. The second is a triple layer detector built with a bottom layer of 4×4 elements, 4×4×10 mm3 in size, a middle layer of 6×6 elements, 2×2×10 mm3 in size, and a top layer of 5×5 elements, of 2×2×10 mm3 in size. The triple layer detector had 3M ESR foil in between the pixels to enhance pixel separation. To understand how the pixelation influenced our timing results a single continuous LSO block 16×16×20 mm3 in size was also tested.
Keywords: high resolution PET detectors, scintillation detectors, timing resolution, depth of interaction
System Calibration for FASTSPECT III: An Ultra-High Resolution CCD-Based Pinhole SPECT System (#4198)
L. Han1, L. Caucci2, B. W. Miller1, H. H. Barrett1, 2, J. M. Woolfenden2, L. R. Furenlid1, 2
1 University of Arizona, College of Optical Sciences, Tucson, United States of America
FastSPECT III is a recently developed ultra-high-resolution small-animal SPECT imaging system. With 20 CCD-based intensified quantum-imaging cameras (iQID) and 250-micron diameter platinum pinhole apertures, this stationary SPECT system offers ~250 microns isotropic linear resolution. This paper presents a novel system calibration method for FASTSPECT III and other high-resolution CCD/CMOS-based stationary pinhole SPECT systems. The performance of the new system calibration method was evaluated using multi-bed-position MLEM reconstruction and helically scanned objects. Originally designed for high-resolution rodent brain imaging to study neurological pathologies, FastSPECT III now offers whole-body mouse imaging capability with ultra-high spatial resolution.
Keywords: High resolution SPECT, FASTSPECT III, System Calibration, Stationary, CCD based, Preclinical imaging, Pinhole, Geometry Characterization, Multi-bed-position reconstruction
Experimental Validation of a Preclinical SPECT/MR Insert (#3533)
M. Carminati1, 2, M. Occhipinti1, 2, F. M. Baratelli1, G. L. Montagnani1, 2, K. Nagy3, Z. Nyitrai3, A. Nagy3, M. Czeller3, A. Kuehne4, T. Niedorf4, D. Mathe5, S. Belloli6, S. Valtorta6, R. M. Moresco6, A. Falini7, L. Ottobrini8, C. Fiorini1, 2
1 Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria, Milano, Italy
The experimental characterization of a SiPM-based 10-module SPECT gamma imager suitable for insertion and operation inside unmodified MR scanners for simultaneous (and potentially multi-tracer) preclinical imaging is presented. The design challenges, here fulfilled, such as compactness while granting proper cooling, mutual compatibility and resilience to high (3-7T) magnetic fields inside the bore, suitable energetic (better than 14% at 140 keV) and spatial resolution (1 mm) are discussed. Design rules for materials and layout of the detection module are highlighted. The carefully optimized detection module – 5 x 5 cm2 CsI(Tl) scintillator coupled to arrays of SiPM conditioned by a 36-channel ASIC – and the digital daisy chain infrastructure are the basis for the realization of a larger (20-module ring) clinical insert. Moreover, planar image reconstruction based on advanced statistical approaches such as maximum likelihood and iteratively estimated light response function is reported. Simultaneous SPECT and MR imaging on animals at San Raffaele Hospital (Milano, Italy) with the full instrument is presented.
Keywords: multimodal imaging, magnetic field compatibility, SPECT/MRI, Anger camera, SiPM
Performance Characteristics for a Low Cost, Dual Sided, Position Sensitive Sparse Sensor (DS-PS3) PET Detector with Depth of Interaction Positioning (#2169)
R. S. Miyaoka1, W. C. J. Hunter1, D. Q. DeWitt1, L. Pierce1
1 Univesrity of Washington, Department of Radiology, Seattle, United States of America
Objectives: The performance characteristics of a dual-sided, position sensitive sparse sensor (DS-PS3) array, PET detector module is investigated. The DS-PS3 detector provides depth of interaction (DOI) positioning while requiring less than one half the number of sensors associated with a tightly packed array and single-sided, non-DOI readout. The overall goal of this work is to develop low cost, high spatial resolution PET detector modules for organ specific imaging systems (e.g., brain or breast).
Methods: The performance of a 15x15 LYSO crystal array readout by two 16 (i.e., 4x4) sensor PS3 arrays, one positioned on the entrance surface of the crystal array and one on the exiting surface was investigated. The crystal array was comprised of 1.93x1.93x20 mm^3 discrete, optically isolated LYSO crystals. Each PS3 assembly consists of a sparse arrangement of silicon photomultiplier (SiPM) dies coupled to a custom light guide and reflective mask. The SIPM dies used had 3x3 mm^2 active areas. Crystal of interaction decoding was assessed using a flood source. Energy resolution and depth of interaction positioning performance was assessed using a coincidence setup and side illumination.
Results: Experimental results indicate excellent three-dimensional crystal decoding performance is achieved using a DS-PS3 detector design. The average peak to valley ratio for a flood crystal map was >4. Binning the flood data into three dimensional maps led to improved crystal decoding and energy resolution. The average energy resolution for the crystal array was ~16%. The average depth of interaction positioning resolution was ~3.5 mm FWHM.
Conclusions: The DS-PS3 methodology has been shown to be a cost-effective method to fabricate high spatial resolution PET detectors for organ specific imaging systems. Even with dual-sided readout, number for the SiPM elements is reduced by at least a factor of 50% versus conventional SiPM arrays.
Keywords: PET detector, Depth of interaction, low cost
Performance Evaluation and MR-Compatibility of MADPET4: A Small Animal PET Insert for 7T MRI (#2083)
N. Omidvari1, J. Cabello1, G. Topping1, F. R. Schneider1, 2, S. Paul3, S. I. Ziegler1, 4
1 Klinikum rechts der Isar (TUM), Nuklearmedizin, Munich, Germany
The design of an MR-compatible PET insert is challenging, since the performance characteristics of the PET and MRI systems must be similar to the ones obtained with them as independent systems. MADPET4 is a high resolution small animal PET insert for a 7T MRI scanner. The system aims for a spatial resolution below 1 mm at the center and below 2.5 mm at 80% of its 88 mm transaxial field of view (FOV). The unique geometrical design of the system allows for high count rate capability with depth of interaction correction. The complete system is composed of 2640 LYSO crystals with cross section area size of 1.5x1.5 mm2, arranged in a dual layer conﬁguration with lengths of 6 mm and 14 mm in inner and outer layers. They are one-to-one coupled to 1.2x1.2 mm2 non-magnetic, high gain KETEK SiPMs, which eliminates the need for high frequency preamplifier components inside the MRI scanner. The system consists of 8 rings covering 19.7 mm in the axial direction. All crystals are transaxially facing the center of the FOV in each ring. PETsys SiPM readout system, which is equipped with time-over-threshold (ToT) ASICs, is used for data acquisition and bias voltage regulation of the SiPMs. An OS-EM image reconstruction algorithm is implemented using a Monte-Carlo system matrix (SM) and polar voxels. This allows exploiting 264 cylindrical symmetries of the system, which significantly reduces the simulation time and SM ﬁle size. First tomographic images were successfully acquired using the NEMA NU4 image quality phantom and a mouse size high resolution hot-rod phantom. 1.2 mm rods were fully recovered and 1 mm rods were separable close to the center. Furthermore, simultaneous PET/MR images were acquired using the FLASH, RARE, and EPI sequences with small loss in both modalities. The system is currently being calibrated for energy nonlinearity correction and timing alignment. The operating point of the SiPMs as well as acquisition parameters are studied for optimal image quality.
Keywords: PET, PET/MRI, SiPM, Small Animal PET
Development of a simultaneous PET/Ultrasound imaging system with near real-time reconstruction capability for point-of-care applications (#3547)
J. Jiang1, K. Li2, S. Komarov1, J. A. O'Sullivan2, Y. - C. Tai1
1 Washington University in St. Louis, Department of Radiology, St. Louis, Missouri, United States of America
In this project, we propose to investigate the feasibility of a novel technology that will bring both PET and ultrasound imaging to the patient bedside to support point-of-care（PoC） molecular imaging applications. The system will comprise of a panel detector placed behind the patient and a maneuverable probe that consists of a PET detector and an ultrasound transducer which can measure targets’ depth with resolution as high as ~ tens of um. The probe can be moved around a region-of-interest in the patients’ body to collect both PET coincidence events and ultrasound signals. The location of the maneuverable probe relative to the back panel detectors is tracked in real-time as coincidence events are recorded. These events are used for list-mode image reconstruction in near real-time to provide visual feedback to the operator who can interactively control the probe to collect additional counts from the most critical locations and/or angles in order to dynamically optimize the image quality. To prove the concept, we developed a prototype that consists of a single channel SiPM(SensL FB30035) coupled to a 3.0×3.0×20.0 mm3 LSO crystal as the back detector. The maneuverable probe consists of an ultrasound transducer and a PMT(Hamamatsu H8500) coupled to 48×48 LSO crystals of 1.0×1.0×10.0 mm3 each. A robotic arm allows us to position the probe at arbitrary locations. Coincidence timing resolution of 470 ps FWHM has been achieved. We have implemented a GPU-based fully 3D list-mode Time-Of-Flight image reconstruction algorithm that can model the dynamically changing geometry of this PoC system . In this study, we report preliminary results from both actual experiments using this prototype and simulations using GATE. Detector modules with larger sensitive volume will be fabricated and tested to perform more imaging studies in order to explore the capability of this class of system.
Keywords: PET imaging, Ultrasound imaging, Point of Care, Robotic arm, GPU reconstruction