This paper introduces a pioneering approach for developing high-resolution perovskite CsPbBr3 detectors capable of single-photon γ-ray imaging, essential for advancing nuclear medicine, particularly SPECT. The research addresses limitations in current technologies (e.g., NaI(Tl), CdZnTe) regarding energy resolution, detection sensitivity, spatial resolution, and cost. By employing a chemical-mechanical surface processing method, the team eliminated charge transport losses at the surface, achieving exceptional performance uniformity, near-unity charge collection efficiency, and long-term device stability. This led to record energy resolutions of 2.5% at 141 keV (for 99mTc) and 1.0% at 662 keV (for 137Cs). Single-photon imaging with 99mTc γ-ray sources demonstrated high sensitivity of 0.13%~0.21% cps/Bq. Furthermore, Derenzo phantom imaging distinctly delineated individual column sources spaced 7 mm apart, indicative of an impressive spatial resolution of 3.2 mm. These findings lay critical groundwork for integrating cost-effective yet superior-performing perovskite detectors into clinical nuclear medicine γ-ray imaging systems.
Single Photon γ-ray Imaging with Perovskite Semiconductors for Nuclear Medicine
Introduction: Advancing Nuclear Medicine Imaging: Single-Photon Emission Computed Tomography (SPECT) requires significant improvements in energy resolution (ER), detection sensitivity, and spatial resolution for precision medicine.
Current Limitations: Conventional NaI(Tl) scintillator cameras offer 9.8% ER at 141 keV and ~5 mm spatial resolution, while CdZnTe (CZT) semiconductor detectors improve ER to 5.5% at 141 keV and spatial resolution to 2.8 mm but are high-cost due to crystal growth issues and poor hole transport.
Perovskite Promise: CsPbBr3 perovskite semiconductors offer spectral performance and cost advantages, with previous work achieving 1.4% ER at 662 keV in hole-only sensing detectors. However, their use in single-photon γ-ray imaging for SPECT remained unexplored.
Problem Statement: Achieving high ER in perovskites is hindered by non-uniformity caused by charge transport variance and charge losses at the perovskite/electrode interface, preventing near-unity charge collection efficiency (CCE).
Novel Perovskite γ-ray Camera Concept: The paper presents a proof-of-concept camera designed for single-photon γ-ray imaging, featuring a tungsten collimator, a pixelated CsPbBr3 detector (4x4 pixels), and a multichannel signal readout system.
Surface Optimization (Results): A chemical-mechanical polishing method using dimethyl sulfoxide (DMSO) as an etching agent was developed. This reduced surface roughness from ~15.8 nm to ~5.5 nm, eliminated scratches, and decreased surface trap density, significantly improving CCE uniformity and device stability.
Record Energy Resolution (Results): The optimized pixelated CsPbBr3 detectors achieved record overall ERs:
2.8% at 122 keV (57Co)
2.5% at 141 keV (99mTc), superior to current CZT systems (5.5%).
1.0% at 662 keV (137Cs), outperforming previous perovskite records and comparable to state-of-the-art pixelated CZT detectors.
Best single-pixel ERs were 2.2% at 141 keV and 0.87% at 662 keV.
High Sensitivity (Results): Single-photon γ-ray imaging with 99mTc radionuclide sources showed a remarkable detection sensitivity of 0.13%–0.21% cps/Bq using single parallel hole and line collimators.
Impressive Spatial Resolution (Results): Derenzo phantom imaging clearly delineated individual 99mTc column sources (0.7 mm diameter, 7 mm spacing), demonstrating a system spatial resolution of 3.2–3.8 mm.
Operational Stability (Results): Detectors showed excellent long-term stability with no shift in peak position or count rate over 11 hours of continuous operation under bias. Aged detectors maintained performance after 33 days. Active cooling reduced leakage currents to 0.3–2 nA, ensuring high electrical stability.
Mechanism of Performance (Results): Pixelated detectors leverage the "small pixel effect," primarily reflecting hole drift-induced charges and minimizing electron trapping, which helps to reduce low-energy tailing. A digital readout system with depth-correction algorithms further improved ER from 1.9% to 0.91% at 662 keV by rejecting near-pixel events.
Crystal Growth and Quality (Methods/Results): High-quality, large-volume CsPbBr3 single crystals (30 mm diameter) were grown using an improved Bridgman melt method, exhibiting ~80% optical transmittance, long photoluminescence lifetimes (76 ns rapid, 276 ns slower), and low shallow trap densities (~2.1 × 10^14 cm^-3).
Conclusion (Discussion): These findings confirm the suitability of perovskite semiconductors as a practical, low-cost technology for high-resolution nuclear medicine γ-ray imaging, paving the way for advanced metabolic functional imaging applications.