This session will include presentations on new PET and SPECT scanner configurations and methods
The PennPET Explorer Scanner for Total Body Applications (#3172)
J. S. Karp1, M. J. Geagan1, G. Muehllehner1, M. E. Werner1, T. McDermott1, J. P. Schmall1, V. Viswanath1, A. E. Perkins2, C. - H. Tung2
1 University of Pennsylvania, Department of Radiology, Philadelphia, Pennsylvania, United States of America
A high-performance TOF PET scanner is being developed with a very large axial FOV as part of the Explorer consortium. The primary goal is to develop a research instrument intended for the exploration of new clinical applications as well as to further the understanding of the bio-distribution of tracers. We describe the development and preliminary performance of U of Penn’s prototype scanner, which is being constructed initially with 3 rings for an axial FOV of 70 cm to test the design, with potential expansion to 140 cm with 6 rings or 210 cm with 9 rings. Each ring is based on the Philips tile detector; an array of 8*8 LYSO scintillation crystals, each of which is 3.9*3.9*19 mm3, coupled in a 1-to-1 configuration to the PDPC dSiPM sensor. Individual tiles are assembled onto a detector module in 7 rows axially and 4 columns in the transverse direction. These are constructed in a ring of 18 modules with a transverse diameter of 76.4 cm and an axial extent of 22.9 cm per ring. Compared to the commercial implementation, the ring has a modified cooling design using chilled water to maintain a temperature on the tiles below 20˚C. Our research system also differs from the commercial system in writing singles event data from each ring, which will be synchronized to ensure that singles events can be combined from any combination of rings and sorted off-line into coincidence pairs. The intrinsic spatial, energy, and timing resolution values will meet or exceed those of the single-ring Philips Vereos scanner; respectively 4.0 mm, 11%, and 320 ps, with stable performance at high activity levels. We have performed GATE simulations for the 3-ring scanner with 70 cm AFOV and predict a NEMA sensitivity of 90.5 kcps/MBq and NECR peak of greater than 4.6 Mcps at 60 kBq/cc.
Keywords: PET scanner, Large axial field-of-view, Time-of-flight
Mono-static CW Doppler radar for quantifying respiratory motion during PET/CT scans (#1693)
A. Ghahremani1, M. Roknsharifi1, J. Hamill1
1 Siemens Medical Solutions, Molecular Imaging, Knoxville, Tennessee, United States of America
Respiration-correlated waveforms (amplitude as a function of time) are the basis for motion-compensated PET reconstruction and also for gated or triggered CT scans. These are typically based on hardware attached to the patient’s chest or abdomen, and are related to skin motions of a few mm. Pfanner et al. have demonstrated that waveforms can instead be based on internal organ motions in the range 1 to 3 cm. CW Doppler radar was used at frequencies that penetrate deep into the body. Those authors placed bi-static radar with several antennas near the back of a supine patient. An advantage was the ease of setup. A disadvantage was the radar’s sensitivity to noise due to motions of the CT scanner, the patient bed, and technologists’ movement near the patient during setup. The use of several antennas in direct contact with the patient was also detrimental. In this work, these disadvantages were overcome. First, only one antenna and a circulator were used, the mono-static approach. The antenna was designed to have higher directivity of radiation into the patient with reduced side-lobe radiation. The design included antenna loading by a human body. A frequency near 875 MHZ was selected with consideration of this loading. The antenna was embedded in the foam pad of a PET/CT system. The circulator isolated transmitted and received signals. Second, the antennas’ placement was optimized to reduce sensitivity to motions near the bed. EM field measurements indicated that the radar was a short-range device according to FCC specifications. Human volunteers were placed over the antenna in a PET/CT system that performed the normal motions of a PET/CT scan. The waveforms correlated strongly with waveforms based on an infrared camera and a marker placed on the chest (Varian RPM). This radar is suitable for motion compensation in clinical PET/CT, is safe, and requires essentially no operator setup.
Keywords: PET/CT, respiration, radar
A prototype flat-panel virtual-pinhole PET insert system for improving lesion detectability (#3696)
J. Jiang1, K. Li2, Q. Wang1, D. Tomov1, 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
High resolution detector inserts with virtual pinhole (VP) PET geometry have been demonstrated effective in improving regional spatial resolution and sensitivity of existing clinical and pre-clinical PET scanners. A second-generation VP PET insert in a flat panel shape that aims to enhance the image resolution and system sensitivity of a whole-body PET/CT scanner for an arbitrary organ-of-interest has been developed. This study validates the functionality of the system and evaluates its potential improvement in tumor detectability. The flat-panel insert is consisted of 4×8 high-resolution detectors, each containing a 4-by-4 SiPM array and 16×16 LYSO crystals of 1.0×1.0×3.0 mm3 each. A robotic system is used to place the flat-panel at arbitrary locations. A procedure to register the PET scanner coordinate system into the robot controller as the base has been developed. New firmware and software were developed to support the additional detector signals without compromising the scanner functions. We evaluated the positioning accuracy of the robot by (1) mounting a Na-22 point-source to the flat-panel and stepping the source across known scanner lines-of-response (LOR); (2) comparing centroids of the coincidence count profiles to their theoretical values. Results shows that an accuracy better than 0.5-mm in all 3-directions can be achieved. List-mode MLEM image reconstruction running on multi-GPU computer is used to jointly reconstruct the Scanner-Scanner (SS) and Insert-Scanner (IS) coincidence events acquired from arbitrary insert locations. We performed Monte Carlo simulation and real experiments under clinically used setup. Monte Carlo results show expected improvement in the resolution and detectability of small lesions. Experimental results validated the overall functionality of the system and work flow and also indicate the requirement for developing a more precise and robust robot positioning method. Additional imaging studies will be conducted and presented.
Keywords: Virtual pinhole PET, Flat-panel insert, Tumor detectability, Robotic arm, GPU reconstruction
Phantom Evaluation of a Multi-Pinhole Cardiac SPECT Camera for 3D Molecular Breast Imaging (#3927)
M. P. Tornai1, F. A. McDougal1
1 Duke University Medical Center, Radiology & Medical Physics, Durham, North Carolina, United States of America
A tomographic clinical cardiac SPECT system consisting of 19 static CZT-based pinhole gamma cameras is evaluated for dedicated, pendant 3D molecular breast imaging (MBI). A Styrofoam embedded array of 3mL point sources on 2.5cm pitch was stepped in front of the 4.7mm diameter pinholes in order to characterize the reconstructed spatial resolution variations and linearity of the spherically symmetric FOV. Next, a series of anthropomorphic phantom measurements using 0.4 and 0.9mm diameter lesions was performed; lesion-to-background ratios ranged from [20:1] to [3:1] to simulate various biological uptake, and were acquired from 30-300sec; three breasts were 470-1700mL in volume. Basic SNR and contrast was measured with increasing levels of anthropomorphic background: (1) breast only containing lesions; (2) breasts and lesions on a torso containing cardiac background; (3) breasts and lesions with cardiac, hepatic and torso backgrounds. All data was reconstructed using MLEM with various iterations on the commercial workstation. Results of the mean linearity were 1.85±2.70mm variation from known locations, while the spatial resolution was 7.9±4.6mm FWHM for 7 planes throughout the FOV. The large lesion could be easily seen in all breast sizes down to 2min acquisition time at [13:1], indicating that either faster scans or lower injected doses could be utilized for this uptake. While visualization varied for both lesion sizes, uptake ratios, acquisition times and breast sizes, this high sensitivity SPECT system could be used for dynamic 3D MBI for lesions diagnostics or therapeutic monitoring, especially with appropriate ROI-drawing changes to the visualization software.
Keywords: molecular breast imaging, SPECT, CZT, pinhole
Real-time gain control of PET detectors using emission spectrum from “dirty” isotopes (#3945)
F. Jansen2, M. Fries3, T. Deller2, M. Khalighi1
1 GE Healthcare, ASL West, Menlo Park, California, United States of America
Accurate gain control of PET detectors ensures the accuracy of energy information; as energy resolution of detectors gets better, and energy windows become tighter to eliminate more scatter from the data, small shifts in peak position can affect the accuracy of scatter scaling and degrade quantitative accuracy. It has previously been shown that it is possible to use intrinsic radiation of Lu-177 in LSO and related scintillators to provide some information about the gain of detectors; in this paper we describe a method that utilizes information from the entire spectrum (intrinsics, photopeak, other emissions) to create a real-time gain control method that maintains gain of PET detectors stable to < 0.5% in the presence of significant transient thermal gradients that may be present in PET detectors in hybrid PET/MR scanners. We describe the methods used to combine information about multiple peaks, and how this algorithm is implemented in a way that permits real-time processing (running in an FPGA with a total computation cycle time of just 220 ns per event). To confirm the photopeak position of Y-90 (with a photofraction of just 0.0032%), we estimate the bremsstrahlung and subtract it from the observed singles spectrum; for the case where high scatter makes peak determination challenging, we use a centered line source and electronic collimation (allowing only unscattered events into the spectrum). At the conference, we will show results of operation of this algorithm with a range of dirty positron emitters - in particular, response time and accuracy.
Keywords: Control Systems, Gain Control, Positron Emission Tomography
Development of the helmet-neck PET prototype: comparison with the helmet-chin PET (#1605)
H. Tashima1, E. Yoshida1, Y. Iwao1, H. Wakizaka1, T. Maeda1, Y. Takado1, C. Seki1, M. Higuchi1, T. Suhara1, T. Yamashita2, T. Yamaya1
1 National Institutes for Quantum and Radiological Science and Technology, National Institute of Radiological Sciences, Chiba, Chiba, Japan
We are developing the helmet PET in which detectors are arranged on a hemisphere with an add-on detector for high sensitivity brain imaging. We have developed the helmet-chin PET prototype having the add-on detector at the chin position to improve the sensitivity. However, the add-on detector at the chin position gave an oppressive feeling to the patient, and the moving part of the add-on detector was not convenient for the patient setup. On the other hand, our previous simulation has shown that the add-on detector covering the neck position has an equivalent effect for improving the sensitivity and imaging quality. In this study, therefore, we developed a helmet-neck PET prototype, which has the add-on detector at the neck position, by remodeling our first helmet-chin PET prototype. The prototype has 54 4-layer depth-of-interaction detectors each of which consists of 16x16x4 array of 2.8×2.8×7.5 mm3 Zr-doped GSO scintillators and a 64-ch position sensitivity photomultiplier tube. We measured sensitivity with a hemispherical pool phantom for the brain region, and we found that the add-on detector at the neck position was more effective for improving the sensitivity for the region than that at the chin position. This was because the arrangement of the detector at the chin position requires a larger margin for designing the gantry, in which the detector position becomes farther away than in the case of the neck position. We conducted a healthy volunteer study using the helmet-neck PET prototype. The result showed that the helmet-neck PET has promising performance for high sensitivity brain imaging and improved convenience for patient studies.
Keywords: Positron emission tomography, brain PET, helmet PET, Alzheimer’s disease, dementia diagnosis