VECTor: A Preclinical Imaging System for Simultaneous Submillimeter SPECT and PET

Abstract

Today, PET and SPECT tracers cannot be imaged simultaneously at high resolutions but require 2 separate imaging systems. This paper introduces a Versatile Emission Computed Tomography system (VECTor) for radionuclides that enables simultaneous submillimeter imaging of single-photon and positron-emitting radiolabeled molecules. Methods: g-photons produced both by electron-positron annihilation and by single-photon emitters are projected onto the same detectors by means of a novel cylindric high-energy collimator containing 162 narrow pinholes that are grouped in clusters. This collimator is placed in an existing SPECT system (U-SPECT-II) with 3 large-field-of-view g-detectors. From the acquired projections, PET and SPECT images are obtained using statistical image reconstruction that corrects for energy-dependent system blurring. Results: For PET tracers, the tomographic resolution obtained with a Jaszczak hot rod phantom was less than 0.8 mm, and 0.5-mm resolution images of SPECT tracers were acquired simultaneously. SPECT images were barely degraded by the simultaneous presence of a PET tracer, even when the activity concentration of the PET tracer exceeded that of the SPECT tracer by up to a factor of 2.5. Furthermore, we simultaneously acquired fully registered 3-and 4-dimensional multiple functional images from living mice that, in the past, could be obtained only sequentially. Conclusion: High-resolution complementary information about tissue function contained in SPECT and PET tracer distributions can now be obtained simultaneously using a fully integrated imaging device. These combined unique capabilities pave the way for new perspectives in imaging the biologic systems of rodents.

Performance Assessment of a Preclinical PET Scanner with Pinhole Collimation by Comparison to a Coincidence-Based Small-Animal PET Scanner

“…VECTor is a simultaneous SPECT-PET system containing 3 stationary flat-panel NaI(Tl) detectors, 9.5 mm thick (1,3). It is a 511-keV-prepared U-SPECT-II (7) combined with dedicated reconstruction software and shielding.…”

“…These ROIs had equal area and positioning, but the effective slice thickness (after averaging 3 slices) was 0.054 mm. Standardized uptake values (SUVs, units of g/cm 3 ), equal to the ROI mean activity concentration divided by the injected activity per unit body weight, were calculated. Contrasts between striatum and cortex and striatum and septal nucleus were found as the difference in SUV divided by the SUV in the striatum.…”

“…This work directly compares the PET capabilities of the VECTor small-animal scanner (MILabs B.V.) (1,3) with the microPET Focus120 (Concorde Microsystems Inc.) (4,5). Although VECTor can perform less than 0.5-mm SPECT imaging and less than 0.75-mm PET imaging simultaneously (1), we considered the PET mode only.…”

NEMA NU4-2008 Performance Evaluation of Albira: A Two-Ring Small-Animal PET System Using Continuous LYSO Crystals

“…There is also a number of commercial tri-modal, pre-clinical PET/SPECT/CT platforms including: Gamma Medica Triumph [2,3], Siemens Inveon [4 -6], MILabs VECTor [7] and Bruker Albira [8 -12]. Table 1 summarises the basic information about PET systems within those three platforms.…”

Utilizing High-Energy γ-Photons for High-Resolution 213Bi SPECT in Mice

“…Imaging of the highenergy (440 keV) photons is severely compromised for most small-animal SPECT systems, because of the penetration of pinhole edges and the collimator wall. Recently, however, a new dedicated small-animal SPECT system based on use of many clustered pinholes has been developed that enables imaging over an energy range from 25 to 600 keV (10). This system has shown to be able to, for example, image SPECT and PET tracers simultaneously at 0.5-and 0.75-mm resolution, respectively (11).…”