Evaluation of a High-Sensitivity Organ-Targeted PET Camera

Abstract

The aim of this study is to evaluate the performance of the Radialis organ-targeted positron emission tomography (PET) Camera with standardized tests and through assessment of clinical-imaging results. Sensitivity, count-rate performance, and spatial resolution were evaluated according to the National Electrical Manufacturers Association (NEMA) NU-4 standards, with necessary modifications to accommodate the planar detector design. The detectability of small objects was shown with micro hotspot phantom images. The clinical performance of the camera was also demonstrated through breast cancer images acquired with varying injected doses of 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (18F-FDG) and qualitatively compared with sample digital full-field mammography, magnetic resonance imaging (MRI), and whole-body (WB) PET images. Micro hotspot phantom sources were visualized down to 1.35 mm-diameter rods. Spatial resolution was calculated to be 2.3 ± 0.1 mm for the in-plane resolution and 6.8 ± 0.1 mm for the cross-plane resolution using maximum likelihood expectation maximization (MLEM) reconstruction. The system peak noise equivalent count rate was 17.8 kcps at a 18F-FDG concentration of 10.5 kBq/mL. System scatter fraction was 24%. The overall efficiency at the peak noise equivalent count rate was 5400 cps/MBq. The maximum axial sensitivity achieved was 3.5%, with an average system sensitivity of 2.4%. Selected results from clinical trials demonstrate capability of imaging lesions at the chest wall and identifying false-negative X-ray findings and false-positive MRI findings, even at up to a 10-fold dose reduction in comparison with standard 18F-FDG doses (i.e., at 37 MBq or 1 mCi). The evaluation of the organ-targeted Radialis PET Camera indicates that it is a promising technology for high-image-quality, low-dose PET imaging. High-efficiency radiotracer detection also opens an opportunity to reduce administered doses of radiopharmaceuticals and, therefore, patient exposure to radiation.

Image quality evaluation for a clinical organ-targeted PET camera

“…Images show the same breast in: (A) FFDM in the CC plane with extensive distortion; (B) 3-D Radialis PET image in the CC plane 1 hour after 178 MBq 18 F-FDG injection; (C) 3-D Radialis PET image in the CC plane where multiple distinct regions of contrast uptake are still evident 4 hours after 18 F-FDG injection. Mean lesion SUV corrected for lean body mass (SUV mean, LBM ) is 1.8, with SUV max, LBM equal to 3.4.; (D) image of a 3-D volume of different foci generated from Radialis PET in the CC view based upon tissue metabolism across all image slices ( 12 ).…”

“…The device employs two planar detector heads mounted on a movable gantry ( Figure 1 ). Each detector head contains 12 four-side tileable (mosaic) sensor modules that are arranged against each other in a 3x4 array ( 12 ) to assemble a seamless, uniform sensing area measuring ~230 mm × ~173 mm ( Figure 2 ). The detector heads are enclosed in a thin housing which permits the active imaging area to be just 4 mm from the housing edge.…”

“…The adjustable gantry permits positioning of the detectors proximal to the organ of interest. Detailed information on the Radialis PET technology can be found in reference ( 12 ).…”

“…The number of iterations was selected to optimize visualization of small objects while maintaining acceptable flood field uniformity. Default clinical reconstruction parameters are applied to all images unless otherwise specified, including median root prior (MRP) filter ( 18 ), attenuation and scatter correction, and solid angle allowance filter ( 12 ). Reconstructed images are saved in DICOM format with 24 axial image slices in the XY plane.…”

“…Indeed, the NEMA NU-4 requirement of back-projection image reconstruction does not represent the methods used in current real-world, clinical applications. Therefore, the described tests have potential flaws in accurately representing the system performance metrics during typical use ( 12 , 14 ). In addition, since NEMA NU-4 standard tests were developed for preclinical imaging, they do not account for unique aspects of clinical organ-targeted PET [e.g., relatively large field-of-view (FOV)] and detector architectures, including planar detectors and modular, adjustable gantry.…”