Engineering and Performance (NEMA and Animal) of a Lower-Cost Higher-Resolution Animal PET/CT Scanner Using Photomultiplier-Quadrant-Sharing Detectors

Wong, Wai-Hoi; Li, Hongdi; Baghaei, H.; Zhang, Yuxuan; Ramirez, Rocio; Liu, Shitao; Wang, Chao; An, Shaohui

doi:10.2967/jnumed.112.103507

Cited by 27 publications

(31 citation statements)

References 21 publications

(21 reference statements)

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“…To evaluate the spatial resolution, the NEMA standard mandates the use of point source scans which are reconstructed using filtered backprojection. However, basically all modern PET scanners instead use an iterative maximum likelihood expectation maximization (MLEM) algorithm for reconstruction [5,6,7,8,9,10,4,11,12,13,14,15], so a scanner's spatial resolution using filtered backprojection is not necessarily indicative of its spatial resolution for applications. While the mandated filtered backprojection is intended to benchmark the detector performance alone, we will demonstrate in the following that it disadvantages certain scanner geometries.…”

Section: Spatial Resolutionmentioning

confidence: 99%

Comments on the NEMA NU 4-2008 Standard on Performance Measurement of Small Animal Positron Emission Tomographs

2020

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The National Electrical Manufacturers Association's (NEMA) NU 4-2008 standard specifies methodology for evaluating the performance of small-animal PET scanners. The standard's goal is to enable comparison of different PET scanners over a wide range of technologies and geometries used. In this work, we discuss if the NEMA standard meets these goals and we point out potential flaws and improvements to the standard.For the evaluation of spatial resolution, the NEMA standard mandates the use of filtered backprojection reconstruction. This reconstruction method can introduce star-like artifacts for detectors with an anisotropic spatial resolution, usually caused by parallax error. These artifacts can then cause a strong dependence of the resulting spatial resolution on the size of the projection window in image space, whose size is not fully specified in the NEMA standard. If the PET ring has detectors which are perpendicular to a Cartesian axis, then the resolution along this axis will typically improve with larger projection windows.We show that the standard's equations for the estimation of the random rate for PET systems with intrinsic radioactivity are circular and not satisfiable. However, a modified version can still be used to determine an approximation of the random rates under the assumption of negligible random rates for small activities and a constant scatter fraction. We compare the resulting estimated random rates to random rates obtained using a delayed coincidence window and two methods based on the singles rates. While these methods give similar esimates, the estimation method based on the NEMA equations overestimates the random rates.In the NEMA standard's protocol for the evaluation of the sensitivity, the standard specifies to axially step a point source through the scanner and to take a different scan for each source position. Later, in the data analysis section, the standard does not specify clearly how he different scans have to be incorporated into the analysis, which can lead to unclear interpretations of publicizeded results.The standard's definition of the recovery coefficients in the image quality phantom includes the maximum activity in a region of interest, which causes a positive correlation of noise and recovery coefficients. This leads to an unintended trade-off between desired uniformity, which is negatively correlated with variance (i.e. noise), and recovery.With this work, we want to start a discussion on possible improvements in a next version of the NEMA NU-4 standard.

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Section: Spatial Resolutionmentioning

confidence: 99%

Comments on the NEMA NU 4-2008 Standard on Performance Measurement of Small Animal Positron Emission Tomographs

2020

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“…Currently, the spatial resolution of most dedicated small-animal PET scanners is only 1–2 mm (1–4). Mice are the most frequently used animals for animal model studies of human diseases.…”

Section: Introductionmentioning

confidence: 99%

A Prototype High-Resolution Small-Animal PET Scanner Dedicated to Mouse Brain Imaging

et al. 2016

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A prototype small-animal PET scanner was developed based on depth-encoding detectors using dual-ended readout of very small scintillator elements to produce high and uniform spatial resolution suitable for imaging the mouse brain. Methods The scanner consists of 16 tapered dual-ended readout detectors arranged in a ring of diameter 61 mm. The axial field of view is 7 mm and the transaxial field of view is 30 mm. The scintillator arrays consist of 14×14 lutetium oxyorthosilicate (LSO) elements, with a crystal size of 0.43×0.43 mm2 at the front end and 0.80×0.43 mm2 at the back end, and the crystal elements are 13 mm long. The arrays are read out by 8×8 mm2 and a 13×8 mm2 position-sensitive avalanche photodiodes (PSAPDs) placed at opposite ends of the array. Standard nuclear instrumentation module (NIM) electronics and a custom designed multiplexer are used for signal processing. Results The detector performance was measured and all except the very edge crystals could be clearly resolved. The average detector intrinsic spatial resolution in the axial direction was 0.61 mm. A depth of interaction resolution of 1.7 mm was achieved. The sensitivity of the scanner at center of the field of view was 1.02% for a lower energy threshold of 150 keV and 0.68% for a lower energy threshold of 250 keV. The spatial resolution within a field of view that can accommodate the entire mouse brain was ~0.6 mm using a 3D Maximum Likelihood-Expectation Maximization (ML-EM) reconstruction algorithm. Images of a micro hot-rod phantom showed that rods with diameter down to 0.5 mm could be resolved. First in vivo studies were obtained using 18F-fluoride and confirmed that 0.6 mm resolution can be achieved in the mouse head in vivo. Brain imaging studies with 18F-fluorodeoxyglucose were also acquired. Conclusion A prototype PET scanner achieving a spatial resolution approaching the physical limits for a small-bore PET scanner set by positron range and acolinearity was developed. Future plans are to add more detector rings to extend the axial field of view of the scanner and increase sensitivity.

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“…The PET and CT images of a mini mouse from the MuPET/CT system [7] are tested in this study. The CT images are the stitching results from three bed positions, and the PET images are from one bed position.…”

Section: Methodsmentioning

confidence: 99%

Automatic self-alignment and registration for PET/CT reconstruction by a cross-correlation maximization method

Zhang

Baghaei

et al. 2013

2013 IEEE Nuclear Science Symposium and Medical Imaging Conference (2013 NSS/MIC)

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Abstract-The images obtained from a PET/CT system need to be registered and fused together to provide the doctor a better view of the tumor's anatomical locations. Ideally, the PET and CT are aligned in the manufacturing/setup stages. However, patient loading, bed deflection and subject movement can cause misalignment in fusion registration. The misalignment also introduces scattering and attenuation correction errors to the PET images resulting in quantitative errors and artifacts. In this study, we propose an automatic self-alignment method for PET/CT fusion registration by deriving the PET and CT alignment-transformation matrix from the real object/patient data based on cross-correlation maximization principle. The new method can reduce the requirement for the mechanical precision between the PET and CT; eliminate the use of specially designed calibration phantoms; the patient-table deflection effect is already included in the self-alignment process thus will be corrected automatically. An iterative procedure based on 2D cross-correlation maximization on the three projections is developed. Several modification techniques for the projections are studied to improve the accuracy and convergence of the iterations. Real mouse images from the MuPET/CT system are tested and good alignment results are achieved.

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Engineering and Performance (NEMA and Animal) of a Lower-Cost Higher-Resolution Animal PET/CT Scanner Using Photomultiplier-Quadrant-Sharing Detectors

Cited by 27 publications

References 21 publications

Comments on the NEMA NU 4-2008 Standard on Performance Measurement of Small Animal Positron Emission Tomographs

Comments on the NEMA NU 4-2008 Standard on Performance Measurement of Small Animal Positron Emission Tomographs

A Prototype High-Resolution Small-Animal PET Scanner Dedicated to Mouse Brain Imaging

Automatic self-alignment and registration for PET/CT reconstruction by a cross-correlation maximization method

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