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From MRC-SPECT-I to MRC-SPECT-II: Towards High-Performance MR-Compatible SPECT Imaging of Small Lab Animals (#4339)
L. - J. Meng1, 2, E. M. Zannoni2, X. Lai3, M. D. Wilson4
1 University of Illinois at Urbana-Champaign, Nuclear, Plasma and Radiological Engineering, Urbana, Illinois, United States of America
In this presentation, we will discuss the series of research effort that we have carried out at the University of Illinois in developing MR-compatible SPECT systems for small animal brain imaging studies.
The first half of the presentation, we discuss the technical details around the MRC-SPECT-I system, including the small-pixel semiconductor detector technology developed from scratch for this application, the design of the MR-compatible collimation apertures, the techniques for correcting the MR-induced distortion in SPECT images, low-profile and low-penetration RF-coils, and preliminary imaging studies of phantoms and mouse with neural stems cells carrying radiotracers that demonstrates the high-resolution simultaneous SPECT-MR imaging capability of the MRC-SPECT-I system.
Following the introduction to the MRC-SPECT-I system development project, we will continue to discuss the new MRC-SPECT-II project. This system is designed to offer a dramatically improved sensitivity over the MRC-SPECT-I system. To achieve this goal, we have introduced a radical design concept, called inverted compound eye (ICE) camera inspired by the natural compound eyes often found on small invertebrates. During our recent feasibility studies, we have demonstrated that the ICE-camera design allows for a dramatically improved sensitivity with an ultra-compact detection system. Additionally, the MRC-SPECT-II system will be built around a custom-designed small pixel CZT detector that is read out with the HEXITEC ASIC developed by the Rutherford Appleton Lab, STFC, UK, which offers an excellent energy resolution. In this presentation, we will discuss the detailed design consolations, our recent progress in developing the MRC-SPECT-II detection systems and preliminary experimental results.
Keywords: MR-compatible SPECT, brain imaging, small animal
Comparison of Designs for Dedicated Brain SPECT Systems (#4323)
M. A. King1, T. Fromme1, A. Könik1, J. C. Goding1, N. Zeraatkar1, B. Auer1, K. S. Kalluri1, S. Banerjee1, X. Li2, M. Kupinski2, G. Zubal3, L. R. Furenlid2
1 University of Massachusetts Medical Scgool, Department of Radiology, Worcester, Massachusetts, United States of America
Novel designs for multi-modular multi-pinhole brain-dedicated SPECT imaging systems using scintillator-based detectors are presented along with a review of the constraints imposed in developing these designs. The designs varied in terms of the shape of the aperture plate about the head from being a truncated spherical shape which keeps the apertures close to the head, to a cylinder plate which approximates that achieved by circular rotation of camera heads. Variation was also considered in the number, shape and layout of the detectors. Irradiation of any location on the detectors by more than one aperture (multiplexing) was allowed to occur only when selected by activation of a shuttering mechanism. Besides the potential for increasing sensitivity through multiplexing the shuttering of apertures was also envisioned to be used to increase angular sampling with large detectors. The systems were constrained to perform stationary imaging without truncation for a 21 cm diameter volume of interest (VOI) encompassing the head. Comparison is made of design features, and estimated spatial resolution and sensitivity.
Acknowledgment: This research was supported by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health under Award Number R01 EB022521. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Keywords: SPECT, Brain Imaging
Optimized Image Acquisition for Dopamine Transporter Imaging with Ultra-high Resolution Clinical Pinhole SPECT (#4326)
Y. Chen1, 2, B. Vastenhouw2, 3, C. Wu1, 2, M. C. Goorden1, F. J. Beekman1, 2
1 Delft University of Technology, Section Radiation, Detection & Medical Imaging, Delft, Netherlands
SPECT can be used to image Dopamine Transporter (DaT) density in the human striatum for diagnosis of e.g. Parkinson disease. However, traditional SPECT provides limited resolution and sensitivity, which sacrifices visual and quantitative assessment accuracy and requires doses of DaT tracer that can inhibit longitudinal studies. We proposed a full ring focusing multi-pinhle SPECT system with stationary detectors (G-SPECT-I, [Beekman et al., EJNMMI, p S209, 2015]), which demonstrated excellent resolution-sensitivity tradeoff, resulting in a reconstructed resolution down to 3 mm. G-SPECT-I achieves data completeness in the scan region of interest by shifting the bed with an automated stage and combining projections from all bed positions into reconstruction using the scanning focus method (SFM, [Vastenhouw et al., J Nucl Med, pp 487-493, 2007]). This paper aims to develop dedicated SFM parameters for performing a DaTscan with maximized effective sensitivity and ensured data completeness. To this end, the longitudinal scanning length was miniminzed to a level such that quantitative accuracy was minimally affected compared to full brain sampling. Next, optimized transaxial sampling with a decreasing number of bed stops were determined based on a hull completeness model to further maximize scan speed while ensuring trans-axial data completeness. Our results show that one axial bed position was sufficient to have a quantitative error < 2% in relevent trans-axial slices (along 36 mm length). For such a focused striatum scan with single bed stop in axial direction, the maximum error was 2.08%, 1.20% and 0.91% when 4, 6 and 8 trans-axial positions were used respectively. Thus, DaTscan with a limited number (e.g. 4) of bed positions is still quantitatively accurate. The estimated overhead of bed-moving is only a few seconds, which is a small fraction of commonly used acquisition times. This would enable protocols for extremely fast dynamic brain SPECT and motion correction.
Keywords: DaTscan, pinhole SPECT, sampling, data completeness, brain imaging
Challenges and opportunities for simultaneous brain SPECT/MRI (#4332)
B. F. Hutton1, D. Salvado1, K. Erlandsson1
1 University College London, Institute of Nuclear Medicine, London, United Kingdom of Great Britain and Northern Ireland
There are specific challenges in designing a SPECT system for simultaneous SPECT/MRI. The objective of this paper is to discuss these challenges, to explore what opportunities are offered and to suggest potential clinical applications for such a system. The specific technical challenge is to design a clinical system with comparable performance to conventional SPECT that is small enough to fit within an MRI gantry. Simultaneous acquisition provides similar advantage to PET/MRI with potential for correction of partial volume effects and motion. The stationary design is well suited for kinetic studies. Potential clinical applications include use in stroke, movement disorders, epilepsy and tumor imaging.
Keywords: Single photon emission computed tomography, SPECT, SPECT/MRI
Implementation of monolithic crystals in stand-alone brain PET, and PET-MR insert, developments (#4319)
A. J. González1, A. González-Montoro1, R. Marti1, F. Sánchez1, J. M. Benlloch1
1 Institute for Instrumentation in Molecular Imaging, i3M, Valencia, Spain
With spatial resolutions of about 1 mm it will be possible to answer specific questions relating to brain function in small brain regions. In contrast to current whole body PET technology, brain dedicated PET systems can achieve this goal. There is a variety of applications for both stand-alone PET or combined with MR. There are several designs worldwide for both brain PET and brain PET-MR, some even commercially available. All use crystal arrays as the scintillation base material. In this work we aim at showing the advantages of using monolithic crystals for the design of brain PET imagers.
We have developed two brain dedicated PET systems, one MR compatible within the EU grant MindView, and another also through EU funding for Alzheimer investigations, so-called CareMiBrain. Both PET systems use arrays of 12×12 SiPMs per block. Also both scanners use monolithic LYSO crystals with 50 mm × 50 mm side, but 20 mm in the brain PET insert and 15 mm for the stand-alone PET. The PET insert has 330 mm in diameter (20 blocks per ring), whereas the stand-alone PET has 260 mm (16 blocks per ring). Both systems cover 150 mm in the axial axis. To improve the detector block performance, a retroreflector layer has been added to the entrance crystal face. This makes it possible to bounce back the scintillation light to the emission source, preserving the light distribution.
At the detector level, we will show the possibility to use the whole scintillation volume (without edge restrictions) during the calibration and reconstruction processes. We found average spatial resolution (measured FWHM) nearing 1.5 mm, with a DOI resolution in the 3.5 mm range, and a uniform energy resolution below 13%. Concerning reconstructed images, the PET insert showed the system capability to resolve 1.6 mm rods in a mini Derenzo phantom using several reconstruction algorithms, including FBP. Images from the stand-alone PET are still under analysis.
Keywords: Depth of interaction, brain PET dedicated, PET-MR, Monolithic scintillators
Initial Results of a High Resolution PET System with MR Compatible DOI-TOF PET Detectors (#4318)
J. S. Lee1, G. B. Ko1, H. Park1, J. - W. Son1, M. S. Lee1, S. Lee1, J. Y. Won1, K. Y. Kim1
1 Seoul National University College of Medicine, Nuclear Medicine, Seoul, Republic of Korea
Objectives: Ultra-high magnetic field MRI system provides in-depth information about the structure, metabolism, and functions of the human brain. The ultimate goal of a project that we are working on is the development of a high-end dedicated brain PET insert that we will combine with ultra-high field (7T) MRI system. In this workshop, we will present the initial results of the PET experiments with the first prototype system produced from this project.
Methods: In the developed high-resolution PET system, Fourteen DOI-TOF PET detector modules were arranged in a ring shape with a 25.4-cm distance between the front surfaces of the opposite detector modules. The detector module supports four (2 × 2) detector blocks. Each PET detector block consists of a 13 × 13 array of 1.86 × 1.86 × 8 mm3 (upper layer) and a 14 × 14 array of 1.86 × 1.86 × 12 mm3 (lower layer) LSO crystals. The lower layer is coupled on the 2 × 2 array of 4 × 4 TSV MPPC sensors. PET data were acquired using a PET DAQ system that includes FPGA-based time-to-digital converters and real-time coincidence modules.
Results: Radial, tangential, and axial spatial resolutions at the center of the field-of-view were 1.42, 1.65, and 1.43 mm, respectively (OSEM reconstruction of a 22Na point source in air). The absolute peak sensitivities measured with an energy window of 220–750, 350–650, and 400–600 keV were 1.55%, 1.13%, and 1.01%, respectively. Based on the phantom imaging studies, the prototype system resolved hot rods up to 1.6 mm. The benefits from the developed PET scanner were also demonstrated in the Hoffman brain phantom images: The detail structures (e.g. the gyri in the occipital cortex) in the Hoffman brain phantom were better demonstrated by the developed PET system with less interpolation and edge artifacts than Siemens mCT scanner.
Conclusions: The prototype PET system developed in this study has shown promising initial results.
Keywords: Brain, PET, MRI, TOF, DOI
Design and initial results of an RF-penetrable TOF PET insert dedicated for brain PET/MRI (#4337)
C. - M. Chang1, 2, B. J. Lee2, 3, I. Sacco2, Q. Dong2, C. S. Levin4
1 Stanford University, Applied Physics, Stanford, California, United States of America
Combined PET/MRI allows physicians to acquire multi-parametric (anatomical, functional and molecular) information about a patient’s diseases in one imaging session. A PET insert dedicated to brain PET/MRI offers several advantages compared to the commercial integrated whole-body PET/MRI systems, including 2-3 times higher sensitivity, better spatial resolution, and significantly lower price. We are developing an RF-penetrable TOF PET insert dedicated for brain PET/MRI. The trans-axial field-of-view (FoV) of the scanner is 28 cm, and the axial FoV is 16 cm. The PET ring consists of 16 detector modules. Within each detector module, 6 sub-modules are arranged in the axial direction of the scanner. Each sub-module consists of an array of 8 x 16 LYSO crystals, each 3.2 mm x 3.2 mm x 20 mm, coupled one-to-one to an array of 8 x 16 SiPMs. Four PETA6 ASICs are placed on the sub-module to read out the signals from the SiPMs. Energy resolution at 511 keV and coincidence timing resolution (CRT) achieved in preliminary coincidence measurements acquired with two 4 x 4 LYSO crystal arrays are 12.3 ± 0.3% and 285 ± 14.0 ps FWHM, respectively. The sub-modules, with minimized trace length between the SiPMs and the PETA6 ASICs and active liquid cooling, are currently under production aiming for a system CRT goal of 250 ps FWHM. The 250 ps FWHM CRT goal will provide an image SNR gain of 2 from TOF, which will help to further enhance visualization and quantification of brain images. In this presentation, we will present the design and initial results of this new RF-penetrable TOF PET insert.
Keywords: time-of-flight, TOF, Brain, Insert, PET/MRI, positron emission tomography, MRI
A trimodality (PET/MR/EEG) scanner for brain imaging (#3222)
A. Del Guerra1
1 University of Pisa, Department of Physics E.Fermi, PISA, Italy
TRIMAGE Coordinator - On behalf of TRIMAGE collaboration
TRIMAGE is an interdisciplinary FP7- funded European, 11 partner collaboration aimed at developing a PET/MR/EEG brain scanner for early diagnosis of schizophrenia (www.trimage.eu). The project started 1 December 2013 and will close 30 November 2018. The total EU funding is 6 M€.
The brain activity measured with the highly sensitive temporal information from EEG (ms time scale), with fMRI (second to minute time scale), combined with the highly sensitive molecular information provided by PET (minute to ten of minutes time scale) converges into a new imaging tool for diagnosis, monitoring and follow-up of mental disorders.The TRIMAGE scanner has been designed and built with the aim of producing a cost-effective, brain dedicated device.
The experimental results reached so far in the construction and characterization of the scanner and the clinical results obtained in the pilot study for the search of imaging biomarkers for early diagnosis of schizophrenia will be presented.
Keywords: Brain Pet, Trimodal scanner, MR, EEG, Biomarkers for schizophrenia