Image quality with the mini-EXPLORER long axial field-of-view PET scanner (#2397)
E. Berg1, X. Zhang1, B. Patel1, M. Spriet2, J. Qi1, S. R. Cherry1
1 University of California, Davis, Biomedical Engineering, Davis, California, United States of America
Image quality was evaluated with the mini-EXPLORER long axial FOV scanner with respect to its large maximum acceptance angle (46 degrees). Reconstructed spatial resolution, image SNR, and contrast recovery (CRC) were measured with imaging phantoms, and lesion detection was evaluated in a canine cancer imaging study. Images were reconstructed using an OSEM algorithm that includes an accurate resolution model, normalization, and attenuation factors. Spatial resolution was measured using a Na-22 point source reconstructed in a warm background, and was 3 mm FWHM in all directions at the center of the FOV. Axial spatial resolution improved by 0.5 mm with a reduced acceptance angle of 14 degrees. CRC was evaluated using three sphere diameters (10, 15, and 20 mm) inside a 10 cm diameter cylinder with a 5:1 sphere-to-background contrast. CRC values were 46 +/- 1%, 63 +/- 1%, and 69 +/- 1% for 10 mm, 15 mm, and 20 mm spheres, respectively. Reducing the maximum acceptance angle to 14 degrees provided ~3% higher CRC, but with ~2-fold increase in standard deviation. Image SNR was measured with a 10 cm diameter uniform cylinder at two activity concentrations: 13 kBq/cc and 2.2 kBq/cc. SNR at the center of the FOV was ~ 1.7-fold higher than at ¼ axial FOV for both activity concentrations. Further, the relationship between noise equivalent count rate (NECR, measured from sinograms) and SNR was in reasonable agreement with the widely-used square root correlation. Lastly, excellent image quality was obtained in a canine whole-body FDG study, where the high sensitivity allowed detection of several small lesions throughout the patient. Lesion SNR was ~1.8-fold higher with the 46 degree acceptance angle vs. 14 degrees. These results demonstrate image noise reduction enabled by increased sensitivity with a wide acceptance angle, with minor trade-offs such as small degradation in axial spatial resolution and slightly lower CRC compared to a conventional, smaller acceptance angle.
Keywords: Total-body PET, Image quality, Lesion detection, Long axial field-of-view
Concrete realization of the whole gamma imaging concept (#3670)
E. Yoshida1, H. Tashima1, Y. Okumura2, M. Suga2, N. Kawachi3, K. Kamada4, K. Parodi5, T. Yamaya1, 2
1 National Institutes for Quantum and Radiological Science and Technology (QST), National Institute of Radiological Sciences (NIRS), Chiba, Japan
PET is recognized as a successful method to pursue cancer diagnosis and molecular imaging. However, in order to meet emerging demands for widened imaging applications and super high-sensitivity imaging, we need to break through the principle of PET itself. In this paper, therefore, we propose a new concept of whole gamma imaging (WGI), which is a novel combination of PET and Compton imaging. An additional detector ring, which is used as the scatterer, is inserted in a conventional PET ring so that single gamma rays can be detected by the Compton imaging method. Therefore, in addition to Compton imaging (single-gamma mode), missing pairs of annihilation photons in PET, at least one of which is undetected, can be used for imaging (PET mode). Further large sensitivity gain can be expected for triple gamma emitters such as 44Sc, that emits a pair of 511 keV photons and a 1157 keV gamma ray almost at the same time (triple-gamma mode). In principle, only a single decay would be enough to localize the source position: (1) the coincidence detection of a pair of 511keV photons locates the source position along a line-of-response (LOR), and (2) the source position is identified as one of two intersection points of the LOR with a Compton cone after measuring the 1157 keV gamma ray. Using GEANT4, we simulated an “insert geometry”, in which a scatter ring (24 x 24 array of 1 x 1 x 6 mm3 GAGG crystals, 20 cm diameter and 5 cm long,) was inserted into a PET ring (16 x 16 x 4-DOI array of 2.9 x 2.9 x 7.5 mm3 GSOZ crystals, 66 cm diameter and 22 cm long). In the single-gamma mode, spatial resolution for the 511keV source obtained by 3D OSEM was 6.2 mm FWHM (center)-3.0 mm FWHM (8 cm off-center). In the triple-gamma mode, the position distribution of a 22Na point source projected on a line-of-response was 7.3 mm FWHM at the 5 cm off-center position without applying any image reconstruction. From the simulation results, we were able to develop the first prototype of the WGI system.
Keywords: PET, Compton camera, triple gamma
Comparative Performance Analysis of Scintillation and Semiconductor Imaging Systems: Progression Toward a High Resolution Preclinical Semiconductor-Based PET Modality (#3239)
A. Groll1, L. - J. Meng1, 2
1 University of Illinois at Urbana-Champaign, Nuclear, Plasma, and Radiological Engineering, Urbana, Illinois, United States of America
The current state of the art for commercial preclinical PET instrumentation yields a spatial resolution performance between 1-2 mm. For applications focused on small animal neurodegenerative disease, it is critical that the current 1 mm spatial resolution barrier be overcome. Given the well understood properties of scintillator materials, some have naturally progressed toward a pixelated silicon photomultiplier (SiPM) monolithic detector architecture. Our efforts differ, we focus on developing a prototype semiconductor benchtop PET system utilizing a modified detector readout scheme.
We have implemented a hybrid pixel-waveform readout in a CdTe coincidence system which uniquely combines information from the detector cathode and anode. From the cathode, we are able to derive (a) depth of interaction, (b) initial interaction time of each event, and (c) the total energy deposited without concern for charge loss on the pixelated anode. The anode only provides the X-Y position of each event. Using this method, we have successfully shown the sub-500 μm spatial resolution achievable with the system.
This work aims to contextualize the potential performance of a preclinical semiconductor system against the current scintillator state of the art to determine the limitations, benefits, and feasibility of developing a system for high resolution PET imaging for neurodegenerative disease.
Keywords: PET, Preclinical, CdTe, Scintillation
Direct Phloem Transport Measurement (#3687)
S. Komarov1, K. Li1, Y. - C. Tai1
1 Washington University in St. Louis, Radiology, St.Louis, Missouri, United States of America
In this work we estimated the transport speed of photosynthates in the wild type maize. The transport was measured by tracing radioactive carbon (11CO2) uptake in plant. In order to apply pulse chasing techniques, only the tip of one selected leaf was labeled with short (4 min) labeling time.
Three related studies were done: 1) “developmental” study of the same plant within approximately one week period (2 subjects); 2) “comparison” study between 7 different plants at the same age; and 3) “morphological” study where different leaves of the same plant were labeled (1 subject).
Although an estimated transport speed (assumable phloem transport) was in large variety (from 1 to 30 mm/min) for different roots and different plants, the histogram of all measured velocities has two distinct peaks: sharp peak for 3±1 mm/min (43%) ;and broad peak for 13±4mm/min (34% of all measurements).
Also in this paper we discuss the usage of Positron Emission Tomography (PET) and beta/Cherenkov Luminescence imaging (CLI) for plant studies.
Also the results of similar measurements for phloem transport in tomatoes and common beans will be presented.
Keywords: PET, phloem transport, dynamic PET studies
Free running mouse brain PET imaging using point source motion tracking (#3393)
A. Miranda1, J. Vleugels3, G. De Bruyne3, S. Stroobants2, 1, S. Staelens1, J. Verhaeghe1
1 University of Antwerp, Molecular Imaging Center Antwerp, Antwerp, Belgium
Scanning of small awake rodents for brain positron emission tomography (PET) is of interest to avoid the use of anesthesia and its influence in the animal brain. In this work we further refine the radioactive point source motion tracking, previously used in awake rat brain PET, to perform head motion tracking of free running mouse during PET imaging. The point source motion data is then used for motion correction of the PET data. An awake mouse experiment was performed using four point sources pasted on the mouse head to track its motion. To avoid spill over from a point source close to the brain, a foam spacer was build and the point source was pasted on top of it to increase the distance to the brain. In addition a cylindrical holder was built to limit the motion of the mouse inside the PET field of view. The mouse was injected with 18.5 MBq of [18F]FDG and scanned awake during 20 min. Afterwards a 20 min under anesthesia motion-free scan was performed for comparison. During the awake scan the mouse moved constantly through the cylindrical holder and it could be tracked 75% of the time. The motion tracking standard deviation was 0.1 mm. The awake mouse brain motion corrected reconstructions showed good resemblance with the motion-free reconstructions (0.97 image correlation coefficient) and regions such as cerebellum, cortex and hippocampus could be identified. The proposed method is minimally invasive, well tolerated by the mouse and allows accurate motion tracking without the use of additional hardware.
Keywords: Mouse brain, motion correction
Silhouette-Based Markerless Motion Estimation of Awake Rodents in PET (#3888)
A. Z. Kyme1, 2, P. Strenge3, F. Lee4, S. R. Meikle5, 2
1 University of Sydney, School of AMME, Faculty of Engineering & IT, Sydney, NSW, Australia
The ability to image the brain of a freely moving rodent using motion-compensated PET presents many exciting possibilities for exploring the links between brain function and behavior. A key requirement of this approach is obtaining accurate estimates of animal pose throughout a scan. Markerless optical approaches for pose estimation have several potential advantages over marker-based methods: improved accuracy and increased range of detectable motion; no ‘decoupling’ of marker and head motion; and no acclimatization of the animals to attached markers.
Our aims in this work were (i) to describe and validate a calibrated multi-camera setup for capturing image streams of a freely moving rat; (ii) to describe techniques for extracting silhouettes from these image streams; and (iii) to demonstrate how silhouettes can be used in conjunction with an a priori rat model to extract pose estimates in close agreement with ground-truth measurements.
Random-walk and K-means clustering approaches were very adaptable to uneven lighting and generally provided excellent silhouette segmentations. In obtaining a high quality rat model, shape-from-silhouette (140 views) and laser scanning both resulted in useful models; laser scanning provided sub-millimeter resolution with very few artifacts and was the method of choice. In our experimental validation, the 3D-2D (model-silhouette) optimization clearly converged to close alignment of the measured and estimated silhouettes. The average discrepancy between estimated and ground-truth poses was 0.94 mm ± 0.51 mm, suggesting that the method is suitably accurate for the application.
This investigation focused on rigid motion of the whole body as a proof-of-principle of the technique. Future work will focus on testing the approach for head-only data, where the rigid-body assumption is very reasonable, and also use of a non-rigid rodent body model to apply the method to a freely moving animal during PET imaging.
Keywords: Markerless motion estimation, Motion tracking, Optimization, Awake animal PET, Segmentation