Online program Overview Session: MIC-07

Abstract

Online brachytherapy delivery verification requires two complementary capabilities: anatomical verification of the applicator prior to irradiation and dynamic tracking of the radioactive source during dose delivery. This study experimentally evaluated the feasibility of a dual-mode C-arm CT/SPECT imaging concept using a single commercially available X-ray flat-panel detector. The core paradigm repurposes a standard X-ray detector into a shared hardware platform: an uncollimated mode for structural visualization, and a collimator-attached mode for radioactive source tracking. The experimental setup utilized a DRTECH EXT1616R digital detector. In the uncollimated X-ray mode, projection images of a PMMA–agar phantom containing a two-ovoid applicator were acquired at 90 kV and 10 mAs during rotational acquisition. The acquired projections successfully distinguished the applicator, air cavities, and phantom tissue surrogate layers. For the SPECT mode, a parallel-hole tungsten collimator was attached to the identical detector. Projection frames of a 58.12 GBq Co-60 source were acquired continuously at 1 frame/s during rotation. Following image intensity enhancement, the Co-60 source profile yielded full width at half maximum values of 3.80 mm and 2.91 mm in the x and y directions, respectively. Furthermore, to demonstrate the ultimate clinical utility of this dual-mode concept, a high-quality reference CT image of a patient-specific 3D-printed pelvic phantom was overlaid with the reconstructed SPECT source distribution, successfully illustrating CT/SPECT fusion feasibility. These findings robustly support the experimental viability of utilizing a commercial X-ray detector for both anatomical assessment and frame-based source delivery verification.

Abstract

This study explores nuclear medicine imaging toward visualization of both radiotracer distribution and microscopic chemical environment using ¹¹¹In cascade gamma-ray correlation. PAC coefficients of ¹¹¹In-labeled agents were quantitatively evaluated under different pH conditions to assess local chemical-environment sensitivity. Cell experiments using ¹¹¹In-labeled molecular probes were performed to examine applicability to biological samples. In vivo DPECI visualized ¹¹¹In-labeled agent biodistribution in mice, showing liver and tumor signals consistent with ex vivo organ biodistribution. These results provide a basis for future multimodal imaging that integrates PAC-derived microscopic chemical information with DPECI-based spatial visualization.

Abstract

In presurgical epilepsy evaluation, noninvasive localization remains challenging in patients with negative or suspicious magnetic resonance imaging findings or inconsistent multimodal results. Positron emission tomography provides metabolic information, while electroencephalography records abnormal electrical activity. However, conventional fixed PET systems usually require supine and constrained positioning, limiting simultaneous monitoring during seizure-related states, task conditions, or near-natural behaviors. To address this limitation, we integrated scalp electroencephalography with an ultra-light wearable motion-following brain PET system to evaluate the feasibility of simultaneous metabolic-electrophysiological imaging in epilepsy subjects. Compatibility was first assessed using an electroencephalography-equipped brain phantom. Phantom images acquired with and without electroencephalography electrodes showed comparable structures, and electroencephalography waveforms remained interpretable with and without PET operation. Initial human evaluation was then performed in an epilepsy patient. Wearable brain PET imaging and simultaneous wearable PET/EEG acquisition were successfully completed. During prolonged acquisition, the subject fell asleep, causing detector displacement and motion artifacts in reconstructed PET images. These results demonstrate the technical feasibility of simultaneous wearable metabolic-electrophysiological brain imaging and highlight the need for improved fixation, motion tracking, and motion correction in future natural-state neuroimaging studies.

Abstract

PETcoil Gen II is a second-generation RF-penetrable time-of-flight (TOF) positron emission tomography (PET) brain insert designed for simultaneous PET/MRI. We evaluated initial imaging performance using a 3D Hoffman brain phantom and present the first clinical ¹⁸F-FDG brain PET images acquired with the system. Randoms correction was performed using delayed-window (DW) estimates. A computed tomography (CT)-based attenuation (μ) map was generated and extrapolated to 511 keV using piecewise linear interpolation, while scatter fractions were estimated via OpenSSS. In the Hoffman phantom and research subject scan, full corrections improved signal-to-background ratio from 3.48 to 4.50 and from 2.69 to 3.20, respectively, with improved visualization of cortical and subcortical structures. These results indicate that the correction methods are functioning and demonstrate the ability of the PETcoil Gen II to produce high-quality images.

Abstract

This study aims to develop a 9.4 T MRI-compatible small-animal PET insert with sub-millimeter spatial resolution and system-level magnetic compatibility. The PET insert consists of 84 dual-ended readout detector arrays arranged in 7 axial rings, with 12 detector modules per ring. Each detector array contains a 28 × 28 LYSO crystal matrix with a crystal size of 0.75 × 0.75 × 20 mm³. Compact front-end amplification electronics, row-column multiplexed readout, non-magnetic mechanical support, and inner/outer carbon-fiber tubes were integrated to meet the spatial and electromagnetic compatibility requirements of a 9.4 T MRI scanner. Point-source imaging was performed to evaluate spatial resolution. A prototype PET insert was developed and integrated. ²²Na point-source images reconstructed using OSEM with 5 iterations demonstrated sub-millimeter spatial resolution, indicating high-resolution imaging capability for 9.4 T small-animal PET/MRI applications.