M6B2  High Resolution and Preclinical Systems II

Saturday, Nov. 7  10:30-12:30  Pacific Salon 1&2

Session Chair:  Jae Sung Lee, Seoul National University, South Korea; Steven Meikle, University of Sydney, Australia

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(10:30) M6B2-1, Fast Motion Tracking of Radioactive Markers for Motion Correction of Awake and Unrestrained Rat Brain PET

A. Miranda, S. Staelens, S. Stroobants, J. Verhaeghe

Molecular Imaging Center Antwerp, Antwerp, Belgium
In motion correction for small animal PET, the motion of the subject must be tracked during the PET scan. Most of the recent motion correction implementations in small animal PET rely on external devices for the tracking of the subject, e.g. optical stereo cameras. In this work we propose to track the motion of the subject using the PET scanner itself by tracking the position of radioactive point sources attached to the head of the animal. Point sources made out of ceramic molecular sieves with a diameter of ~1 mm and an activity of 200 kBq were used in the current experiments. For the tracking we developed an image-based approach that used the brackprojected images of the LORs in small time frames of 32 ms. Two validation experiments were performed: a microDerenzo phantom experiment and a 20 minutes awake [18F]FDG rat brain scan. The small point sources were well tolerated by the rat and the tracking was successful in 99.6% and 99.9% of the time frames for the microDerenzo and rat scans respectively. The motion information was then used for motion correction and proved sufficient to recover the 3, 2.5 and 2 mm hot rods in the microDerenzo phantom albeit with some resolution loss compared to motion free reconstructions (FWHM of 3.6 mm versus 2.9 mm for the 3 mm rods). In addition, typical [18F]FDG rat brain uptake patterns were found after motion correction in several regions of the brain, with an average error of only 4% in comparison with a scan under anesthesia. The use of radioactive point sources therefore shows great promise for brain PET scanning in small animals as it alleviates the need for an external motion tracking system.

(10:45) M6B2-2, Synthetic Compound Eye Gamma Camera for SPECT Imaging: Systems Within Systems

L.-J. Meng, X.-C. Lai, G. Gao

Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, USA
One of the biggest limitation in pinhole SPECT system design is that one has to make a painful compromise between imaging resolution and photon detection efficiency. Although an ultrahigh spatial resolution (say <500 µm or even <250 µm for small animal imaging) could be readily achievable with the use of small pinholes and high magnification ratios, the practical application of this capability is limited by the typically low sensitivity. In order to alleviate this intrinsic bottle-neck, we have recently explored the use of the inverted compound eye (ICE) gamma camera design for ultrahigh resolution SPECT imaging. An ICE gamma camera is a collection of a large number of independent micro-camera-elements closely packed in a dense array (e.g. 10-20 independent camera-elements per cm2), and each of the micro-camera-elements covers a narrow view angular through the object (shown in Fig. 1). A SPECT system constructed with the ICE-camera modules has the potential of offering a dramatically improved tradeoff between sensitivity and spatial resolution. In this work, we further extend the ICE camera concept to a more generic concept called synthetic inverted compound-eye (S-ICE) camera, which consists of a mixture of different types of micro-camera-elements with different angular coverages, resolutions, sensitivities, and are distributed with different density across the S-ICE camera module. With this design, one could retain the intrinsic benefit of the ICE cameras, namely the ultrahigh sensitivity, and have a much more flexible imaging performances to suit different imaging applications. The synthetic compound eye camera design essentially allows one to construct a compact imaging system that consisting SPECT systems within SPECT systems, all with different imaging performances and characteristics.

(11:00) M6B2-3, A SiPM-Based Detection Module for SPECT/MRI Systems

P. Busca1,2, C. Fiorini1,2, M. Occhipinti1,2, P. Trigilio1,2, K. Nagy3, T. Bukki3, M. Czeller3, Z. Nyitrai3, C. Piemonte4, A. Ferri4, A. Gola4, J. Rieger5

1Politecnico di Milano., Milano, Italy
2INFN - Sezione di Milano, Milano, Italy
3Mediso Medical Imaging Systems, Budapest, Hungary
4Fondazione Bruno Kessler, Trento, Italy
5MRI.TOOLS GmbH, Berlin, Germany
In the present work, we show the development of a SiliconPhoto Multiplier (SiPM)-based detection module for SPECT/MRI systems. The module is designed for preclinical SPECT systems for mouse and rat brains imaging. The SPECT ring will be composed by ten independent gamma-ray detection modules and will fit 7 and 9.4 T MRIs with 20 cm bore diameter for multi-modality applications. The same module is also compatible for future clinical SPECT systems. This work is part of the INSERT project (INtegrated SPECT/MRI for Enhanced Stratification in Radiochemo Therapy). The single gamma-ray detection module is designed on the well-established Anger architecture, with a continuous 5 cm × 5 cm CsI:Tl scintillator read by an array of SiPMs (RGB-HD with 25 µm SPAD cells). The electrical signals from SiPMs are conveyed to a 36-channel ASIC in 0.35 µm CMOS technology and digitized by an external data acquisition system. An operative temperature between 0 and 5C is mandatory to reduce the dark count rate of the SiPM array and to enhance the final performance of the detector in terms of energy and spatial resolution. An MRI-compatible heat sink is realized with a plastic material (Coolpolymer D5506) with a glycol-water mixture as cooling fluid. Gamma-ray measurements with a SiPM array (RGB with 40 µm cell) have provided an energy resolution better than 15% at 122 keV and an intrinsic spatial resolution below 1.35 mm. Improvements with the new RGB-HD technology are expected and will be reported. Preliminary compatibility tests were performed with a 7 Tesla whole body MRI system (MAGNETOM by Siemens). The static magnetic field and the RF did not produce any relevant erroneous behaviour on the acquisition. The switching gradients induced voltage drops on the power supply line that are currently under investigation. On the MRI side, gradient echo image were registered while the module was working and no relevant noise was observed in the images.

(11:15) M6B2-4, Design Optimization and Performances of an Intraoperative Positron Imaging Probe for Radioguided Cancer Surgery

S. Spadola1, C. Esnault1, L. Pinot1, M.-A. Verdier1, B. Aissaoui1, B. Janvier1, Y. Charon1, M.-A. Duval1, N. Dinu2, L. Ménard1

1IMNC - UMR 8165, CNRS IN2P3, University Paris-Sud, Université Paris Diderot, Orsay, France
2LAL - UMR 8607, CNRS IN2P3, Orsay, France
Image guided surgery is actually a tool of interest to improve the accuracy of tumor resection. Availability of specific tumor radiotracers labeled with positron emitters allows the development of intra-operative beta probes. Detection of beta particles, thanks to their shot range, offers a more sensible and accurate tumor localization compared to gamma rays detection. In that context, we are currently developing a positron imaging probe, using SiPM photosensor array, to perform real time tumor localization and control of surgical cavity after tumor resection. To obtain high sensitivity detection of beta emitters in narrow surgical cavity, we designed a detector head of extreme compactness, based on a single organic scintillator and passive rejection of the gamma ray background noise. The probe design, including scintillator material and thickness, light spreading window and optical coating, was optimized for beta sensitivity, spatial performances and gamma rejection efficiency with Montecarlo simulations and measurements. Different reconstruction algorithms was also studied. We show that a imaging probe composed by a 0.1 mm thick p-terphenyl organic scintillator coupled to a 64-channel SiPM array with 3x3 mm2 elements through a 2 mm light guide offers good gamma ray background rejection performances while maintaining high positron sensitivity and a submillimetric intrinsic resolution and bias over its usable field of view. These performances can be improved thanks to neural network reconstruction methods which significantly reduce the bias on the detector edges and the computational time. Based on this optimization study we are currently developing a fully operational probe with miniaturized electronic readouts. These results and preliminary results on realistic phantoms will be presented at the conference.

(11:30) M6B2-5, X-Ray Microradiography and Microtomography of Ex-Vivo Murine Organs with Photon Counting Detectors

J. Dudak1,2, J. Zemlicka1, F. Krejci1, J. Karch1,2, J. Jakubek1, M. Patzelt3,4, P. Zach3,4, J. Mrzilkova3,4

1Institute of Experimental and Applied Physics Czech Technical University in Prague, Prague, Czech Republic
2Faculty of Biomedical Engineering Czech Technical University in Prague, Prague, Czech Republic
3First Faculty of Medicine, Charles University in Prague, Prague, Czech Republic
4Third Faculty of Medicine Charles University in Prague, Prague, Czech Republic
X-ray microradiography and microtomography became a popular tool for different applications in biomedical research. The spatial resolution achievable using state-of-the art laboratory-scale devices starts to be comparable to conventional methods as like histology. Although very high spatial resolution imaging of soft biological tissue using X-rays is still difficult task as soft tissue exerts very low intrinsic contrast for X-rays. Usually, it requires complicated procedures to increase the contrast of a particular soft tissue structure. Since hybrid semiconductor detectors work in dark-current-free quantum-counting mode it integrates photons without any noise and therefore its dynamic range is virtually unlimited. Extremely high dynamic range enables to obtain reasonable contrast even in weakly attenuating materials such as different types of biological tissue. In this contribution we demonstrate the performance of Timepix detector technology for imaging ex-vivo murine organs in native and ethanol preserved form. High resolution and high contrast radiographies and tomographies acquired using a compact small animal micro-CT scanner equipped with Timepix Quad (512 by 512 pixels, area 2.8 by 2.8 cm2) as well as results obtained using recently developed large area Timepix detector WidePIX10×5 (2560 by 1280 pixels, area 14.3 by 7.15 cm2) are presented.

(11:45) M6B2-6, Animal Imaging and Performance Analysis of the BNL/Penn PET-MRI System for Rodents

T. Cao1, M. Budassi1, J. Fried2, S. Stoll3, M. L. Purschke3, M. Werner4, E. Blankemeyer4, S. Pickup4, R. Zhou4, J. S. Karp4, D. J. Schlyer5, C. L. Woody3, P. Vaska1,5

1Biomedical Engineering, Stony Brook University, Stony Brook NY, USA
2Instrumentation Division, Brookhaven National Lab, Upton NY, USA
3Physics Department, Brookhaven National Lab, Upton NY, USA
4Radiology Department, University of Pennsylvania, Philadelphia PA, USA
5EBNN, Brookhaven National Lab, Upton NY, USA
Here we report new results from the BNL/Penn whole body rodent imaging system which is capable of concurrent PET and MRI imaging within a Varian 9.4 T MRI. A new ambient air cooling system has been implemented which has stabilized the system performance. Cross-modality interference has been evaluated, including MRI B0 map with PET on and off and effects on PET count rates and energy, time, and spatial resolution. Initial PET-MRI rat images of brain and heart demonstrate the potential of the system for preclinical research. We have also improved the quantification accuracy of the system by applying better corrections for detector efficiency and attenuation and scatter.

(12:00) M6B2-7, First Simultaneous Images and Characterization of a Small Animal PET Insert for PET/MR Imaging

G. Stortz1, M. S. Khan2, J. D. Thiessen3, X. Zhang4, E. Shams5, A. L. Goertzen6,7, G. Schellenberg7, C. J. Thompson8, F. Retiere9, P. Kozlowski10, V. Sossi1

1Physics & Astronomy, University of British Columbia, Vancouver, BC, Canada
2Electrical & Computer Engineering, University of Manitoba, Winnipeg, MB, Canada
3Imaging Program, Lawson Health Research Institute, London, ON, Canada
4Biomedical Engineering, University of California, Davis, Davis, CA, USA
5Biomedical Engineering Graduate Program, University of Manitoba, Winnipeg, MB, Canada
6Radiology, University of Manitoba, Winnipeg, MB, Canada
7Physics & Astronomy, University of Manitoba, Winnipeg, MB, Canada
8Montreal Neurological Institute, McGill University, Montreal, QB, Canada
9Detector Development Group, TRIUMF, Vancouver, BC, Canada
10Radiology, University of British Columbia, Vancouver, BC, Canada
We have built a first prototype of a novel small animal MR compatible PET insert, designed to fit in a 114 mm diameter gradient coil used in Bruker 7T MRI systems. The insert consists of a ring of 16 detector blocks, each having 22×10 6 mm long LYSO crystals in the bottom layer and 21×9 4 mm long LYSO crystals in the top layer, arranged in the dual layer offset configuration with a pitch of 1.27 mm. Crystal arrays are read out with MR compatible silicon photomultipliers, and identified with Anger logic. The ring has a 65.8 mm diameter, providing a useful field of view of 28 mm axially and ~50 mm in diameter. The OpenPET data acquisition system digitizes signals from the detectors and sends Singles mode data to a PC via QuickUSB 2.0 interface. Coincidences are currently sorted in software, further sorted into sinograms, and reconstructed into images using filtered back projection 3D reprojection as implemented in STIR 3.0. We present here the first images of a NEMA NU4 image quality phantom, as well as 18F-FDG images of mice imaged simultaneously with a Bruker 7T MRI. In addition, we characterize spatial resolution, sensitivity, and noise equivalent count rate (NECR). Images appear artifact free and high resolution. The radial full width at half maximum of the point spread function ranged from 1.2 to 1.9 mm. No intermodality interference is detected. The peak sensitivity at the center of the field of view is 1.3%. The NECR currently has a peak value of ~1.0 kcps at ~0.8 MBq for the NU4 mouse count rate phantom. The count rate performance is currently limited by the firmware version used on the OpenPET system, which has a large data packet size (140 bytes/event) and a poor timing resolution (~80 ns) due to the manner in which the triggering is implemented. Future OpenPET firmware upgrades will address these limitations. We will soon implement PSF-modeling MLEM reconstruction software, which will result in superior image quality compared to filtered back projection.

(12:15) M6B2-8, A Protoype Gamma Tomosynthesis System for Molecular Breast Imaging

D. Gilland1, B. Welch2, S. J. Lee3, B. Kross3, A. Weisenberger3

1Biomedical Engineering, University of Florida, Gainesville, FL, U.S.A.
2Dilon Technologies, Inc., Newport News, VA, U.S.A.
3Thomas Jefferson National Accelerator Facility, Newport News, VA, U.S.A.
The purpose of this work was to develop an improved gamma camera for molecular breast imaging (MBI) that allows tomographic imaging and improved signal-to-noise over conventional planar methods. While MBI has shown the ability to complement mammography for women with dense breasts, more wide spread use requires a reduction in radiation dose to the patient while maintaining satisfactory image quality. We have developed a novel gamma camera for MBI that utilizes limited angle tomography, similar to x-ray tomosynthesis, to generate images with depth information and improved signal-to-noise. A unique feature of the gamma tomosynthesis system is a variable-angle, slant hole (VASH) collimator. This collimator allows the camera to remain flush against the compression paddle during the tomographic acquisition, which achieves high spatial resolution and simplified detector motion. We have previously demonstrated in simulation studies the signal-to-noise advantages of this system. In this work, we constructed a VASH collimator from a stack of tungsten sheets, each sheet containing a matrix of holes created by photo-etching. With the holes of the sheets aligned, a parallel-hole collimator is created; shearing the sheets (like a deck of cards) creates a variable angle, slant hole collimator. The shearing is precisely controlled by a motorized mechanism. The collimator was mounted on a commercial MBI camera and projection data were acquired of a set of capillary tube line sources over a 50 degree range of angles. The projection data were reconstructed using the iterative MLEM method. The reconstructed images demonstrated the ability of the system to resolve in the depth dimension, and spatial resolution matched expected values. We conclude that the proposed gamma tomosynthesis system has the potential to provide improved signal-to-noise over conventional MBI methods and allow a reduction in the administered radioactivity and patient dose.