Mini EXPLORER II: a prototype high-sensitivity PET/CT scanner for companion animal whole body and human brain scanning

Yang Lv, Xinyu Lv, Weiping Liu, Martin S Judenhofer, Allison Zwingenberger, Erik Wisner, Eric Berg, Sarah McKenney, Edwin Leung, Benjamin A Spencer, Simon R Cherry, Ramsey D Badawi, Yang Lv, Xinyu Lv, Weiping Liu, Martin S Judenhofer, Allison Zwingenberger, Erik Wisner, Eric Berg, Sarah McKenney, Edwin Leung, Benjamin A Spencer, Simon R Cherry, Ramsey D Badawi

Abstract

As part of the EXPLORER total-body positron emission tomography (PET) project, we have designed and built a high-resolution, high-sensitivity PET/CT scanner, which is expected to have excellent performance for companion animal whole body and human brain imaging. The PET component has a ring diameter of 52 cm and an axial field of view of 48.3 cm. The detector modules are composed of arrays of lutetium (yttrium) oxyorthosilicate (LYSO) crystals of dimensions 2.76 × 2.76 × 18.1 mm3 coupled to silicon photomultipliers (SiPMs) for read-out. The CT component is a 24 detector row CT scanner with a 50 kW x-ray tube. PET system time-of-flight resolution was measured to be 409 ± 39 ps and average system energy resolution was 11.7% ± 1.5% at 511 keV. The NEMA NU2-2012 system sensitivity was found to be 52-54 kcps MBq-1. Spatial resolution was 2.6 mm at 10 mm from the center of the FOV and 2.0 mm rods were clearly resolved on a mini-Derenzo phantom. Peak noise-equivalent count (NEC) rate, using the NEMA NU 2-2012 phantom, was measured to be 314 kcps at 9.2 kBq cc-1. The CT scanner passed the technical components of the American College of Radiology (ACR) accreditation tests. We have also performed scans of a Hoffman brain phantom and we show images from the first canine patient imaged on this device.

Figures

Figure 1.
Figure 1.
Scanner design. Top left: gantry as installed at UC Davis. Top right: gantry in factory with cover off, and PET and CT scanners separated. Bottom left: single PET detector module. Bottom right: diagram of the signal readout.
Figure 2.
Figure 2.
Left: diagram showing human subject positioning for brain imaging. Center: volunteer positioned for CT scanning. Right: volunteer positioned for PET scanning.
Figure 3.
Figure 3.
Anesthetized canine patient on the scanner bed.
Figure 4.
Figure 4.
Flood map from a single detector block. Irradiation was provided by a 68Ge line source with approximately 1 mCi of activity placed at the center of the transaxial FOV.
Figure 5.
Figure 5.
Count rate response for a single detector module exhibiting dead-time behavior close to the mean response. Left: for clinically relevant singles rates (Poon et al 2012). Right: over the entire experimental range. The r2 for the linear fit was >0.9999. The characteristic dead-time for the single exponential fit was 99 nanoseconds.
Figure 6.
Figure 6.
NEMA sensitivity and event rate results. Left: NU-2–2012 sensitivity; corrections for the branching ratio of 18F were not applied. Center: event rates and scatter fractions from NU2–2012 test. Right: event rates and scatter fractions from NU4–2008 test.
Figure 7.
Figure 7.
Module 2 of the ACR phantom with an ROI over the signal and background of the phantom. Both ROIs were placed at a fixed radius. This method was repeated for all four acquisitions. The measurements are shown in table 5.
Figure 8.
Figure 8.
15 cm × 50 cm uniform cylinder scan. Top: axial and coronal PET images. Bottom left: orthogonal transaxial normalized pixel intensity profiles. Bottom right: axial central normalized pixel intensity profile (blue) and pixel coefficient of variance (red) demonstrating the level of axial uniformity.
Figure 9.
Figure 9.
PET images of the mini-Derenzo phantom. Left: photograph showing rod diameters. Right: reconstruction with the rotating projector (3 iterations and 20 subsets). The reconstructed pixel size is 0.6 mm × 0.6 mm.
Figure 10.
Figure 10.
PET images (left and center) and CT images (right) of a Hoffman brain phantom. The pixel size of the PET image is 1.2 mm × 1.2 mm. Reconstruction was performed with 10 iterations and 20 subsets.
Figure 11.
Figure 11.
CT (upper row) and PET (lower row) images of the first canine patient. (a) head (arrow indicates normal grey matter uptake); (b) thorax (arrow indicates normal myocardial uptake); (c) proximal pelvic limbs (arrows indicate unexpected bilateral uptake in the gracilis muscles); (d) representative PET/CT overlay image.
Figure 12.
Figure 12.
Zoomed image of the left antebrachial region from the first canine patient. (a) CT image (arrow indicates moderate diffuse iodinated contrast enhancement); (b) PET image (arrow indicates mild FDG uptake); (c) PET/CT overlay image.

Source: PubMed

Sponsoren und Mitarbeiter

Krankheiten

Drogeninterventionen

3
Abonnieren