Quarter-Millimeter-Resolution Molecular Mouse Imaging with U-SPECT⁺

Abstract

Limited spatial resolution of preclinical positron emission tomography (PET) and single-photon emission computed tomography (SPECT) has slowed down applications of molecular imaging in small animals. Here we present the latest-generation U-SPECT system (U-SPECT⁺, MILabs, Utrecht, the Netherlands) enabling radionuclide imaging of mice with quarter-millimeter resolution. The system was equipped with the newest high-resolution collimator with 0.25 mm diameter circular pinholes. It was calibrated with technetium-99 m point source measurements from which the system matrix was calculated. Images were reconstructed using pixel-based ordered subset expectation maximization (OSEM). Various phantoms and mouse SPECT scans were acquired. The reconstructed spatial resolution (the smallest visible capillary diameter in a hot-rod resolution phantom) was 0.25 mm. Knee joint images show tiny structures such as the femur epicondyle sulcus, as well as a clear separation between cortical and trabecular bone structures. In addition, time-activity curves of the lumbar spine illustrated that tracer dynamics in tiny tissue amounts could be measured. U-SPECT⁺ allows discrimination between molecular concentrations in adjacent volumes of as small as 0.015 μL, which is significantly better than can be imaged by any existing SPECT or PET system. This increase in the level of detail makes it more and more attractive to replace ex vivo methods and allows monitoring biological processes in tiny parts of organs in vivo.

Ultra-High-Sensitivity Submillimeter Mouse SPECT

“…The new collimator was mounted in the U-SPECT 1 (MILabs) series of scanners (7). This system uses three 595 • 472 mm NaI (Tl) stationary detectors, a set of replaceable focusing multipinhole collimators, and a user interface that aids both total-body SPECT and 3D focused imaging (8).…”

Preclinical molecular imaging: development of instrumentation for translational research with small laboratory animals

“…In the latter approach, detectors, collimators and image reconstruction tools are developed and built to be used specifically in preclinical environments, with targets ranging from mice to adult rats. (15,16,29,30) …”

Performance Evaluation of Fifth-generation Ultra-high-resolution Spect System With Two Stationary Detectors and Multi-pinhole Imaging

“…In this study, a novel fifth-generation U-SPECT system (U-SPECT5/CT E-Class; MILabs, Utrecht, The Netherlands), in the following referred to as "2DT-Scanner" was investigated with focus on its SPECT performance. The scanner construction is similar to the previous generation micro-SPECT system (U-SPECT + ; MILabs) [7] and consists of stationary detectors with an exchangeable multi-pinhole collimator. A XYZ-stage moving the scanned object in a spiral stepmode through the field of view (FOV) enables whole body and focused scans [6,8,9].…”

“…Moreover, this allows the region of interest to be measured very precisely, which helps with focused imaging [5][6][7][8][9][10]. In contrast to conventional systems operating three detectors, the novel fifth-generation U-SPECT system tested in this study uses a two-detector set-up without the bottom detector.…”