Magnetic shieldless ultra-low-field MRI with an optically pumped magnetometer.

Among magnetic resonance imaging (MRI) techniques, ultra-low field (ULF) MRI has the potential to significantly lower the cost of implementation and maintenance, as well as the size of the scanning system. Due to the small amplitude of the signals produced by ULR-MRI, extremely sensitive magnetic sensors are required. Optically pumped magnetometers (OPMs) have been proposed for use in ULF-MRI as ultra-sensitive magnetic sensors capable of detecting very small signals. However, the cost of a ferromagnetic magnetic shield is often not affordable for many applications. By increasing the Larmor frequency, the influence of low-frequency magnetic noise can be mitigated, allowing OPM to be operated without the use of a magnetic shield chamber. This lowers the cost of the magnetic shield and further raises the signal strength, resulting in benefits such as non-prepolarization. We present a method for implementing the ULF-MRI using low-cost OPMs in this study. The Larmor frequency was adjusted to 300 kHz, and three-dimensional (3D) images of a phantom were acquired with a digital resolution of 3 × 3 × 3 mm3 using a static magnetic field of 7.05 mT without using a magnetic shield room or a prepolarization coil. Additionally, we corrected the frequency response to acquired images to consider the narrow bandwidth, and the SNR of 3D imaging was 18. The experimental results, we believe, establish a new guideline for higher-performance, lower-cost ULF-MRI that does not require expensive magnetic shielding.

Performance evaluation of a high-resolution brain PET scanner using four-layer MPPC DOI detectors.

A high-resolution positron emission tomography (PET) scanner, dedicated to brain studies, was developed and its performance was evaluated. A four-layer depth of interaction detector was designed containing five detector units axially lined up per layer board. Each of the detector units consists of a finely segmented (1.2 mm) LYSO scintillator array and an 8 × 8 array of multi-pixel photon counters. Each detector layer has independent front-end and signal processing circuits, and the four detector layers are assembled as a detector module. The new scanner was designed to form a detector ring of 430 mm diameter with 32 detector modules and 168 detector rings with a 1.2 mm pitch. The total crystal number is 655 360. The transaxial and axial field of views (FOVs) are 330 mm in diameter and 201.6 mm, respectively, which are sufficient to measure a whole human brain. The single-event data generated at each detector module were transferred to the data acquisition servers through optical fiber cables. The single-event data from all detector modules were merged and processed to create coincidence event data in on-the-fly software in the data acquisition servers. For image reconstruction, the high-resolution mode (HR-mode) used a 1.2 mm2 crystal segment size and the high-speed mode (HS-mode) used a 4.8 mm2 size by collecting 16 crystal segments of 1.2 mm each to reduce the computational cost. The performance of the brain PET scanner was evaluated. For the intrinsic spatial resolution of the detector module, coincidence response functions of the detector module pair, which faced each other at various angles, were measured by scanning a 0.25 mm diameter 22Na point source. The intrinsic resolutions were obtained with 1.08 mm full width at half-maximum (FWHM) and 1.25 mm FWHM on average at 0 and 22.5 degrees in the first layer pair, respectively. The system spatial resolutions were less than 1.0 mm FWHM throughout the whole FOV, using a list-mode dynamic RAMLA (LM-DRAMA). The system sensitivity was 21.4 cps kBq-1 as measured using an 18F line source aligned with the center of the transaxial FOV. High count rate capability was evaluated using a cylindrical phantom (20 cm diameter × 70 cm length), resulting in 249 kcps in true and 27.9 kcps at 11.9 kBq ml-1 at the peak count in a noise equivalent count rate (NECR_2R). Single-event data acquisition and on-the-fly software coincidence detection performed well, exceeding 25 Mcps and 2.3 Mcps for single and coincidence count rates, respectively. Using phantom studies, we also demonstrated its imaging capabilities by means of a 3D Hoffman brain phantom and an ultra-micro hot-spot phantom. The images obtained were of acceptable quality for high-resolution determination. As clinical and pre-clinical studies, we imaged brains of a human and of small animals.

Highly durable carbon-supported Pt catalysts prepared by hydrosilane-assisted nanoparticle deposition and surface functionalization.

Hydrosilane enabled the formation of Pt nanoparticles and the silane functionalization of a carbon support material in one pot. The metal/Si-modified carbon composites are highly durable during catalytic methane oxidation.

Effect of nitrate on nodule and root growth of soybean (Glycine max (L.) Merr.).

The application of combined nitrogen, especially nitrate, to soybean plants is known to strongly inhibit nodule formation, growth and nitrogen fixation. In the present study, we measured the effects of supplying 5 mM nitrate on the growth of nodules, primary root, and lateral roots under light at 28 °C or dark at 18 °C conditions. Photographs of the nodulated roots were periodically taken by a digital camera at 1-h intervals, and the size of the nodules was measured with newly developed computer software. Nodule growth was depressed approximately 7 h after the addition of nitrate under light conditions. The nodule growth rate under dark conditions was almost half that under light conditions, and nodule growth was further suppressed by the addition of 5 mM nitrate. Similar results were observed for the extending growth rate of the primary root as those for nodule growth supplied with 5 mM nitrate under light/dark conditions. In contrast, the growth of lateral roots was promoted by the addition of 5 mM nitrate. The 2D-PAGE profiles of nodule protein showed similar patterns between the 0 and 5 mM nitrate treatments, which suggested that metabolic integrity may be maintained with the 5 mM nitrate treatment. Further studies are required to confirm whether light or temperature condition may give the primary effect on the growth of nodules and roots.