M. J. Chen

Characterization of tumors using high-Tc superconducting quantum interference device-detected nuclear magnetic resonance and imaging

The characterization of cancerous livers in rats using nuclear magnetic resonance and magnetic resonance imaging (NMR/MRI) based on high-Tc superconducting quantum interference devices (SQUIDs) is presented. The T1−1 were observed to be 6.5±0.5 s−1 for controlled livers and 2.85±0.2 s−1 for cancerous livers, which indicate that the T1 can be used to distinguish the cancerous tissues from controlled liver tissues. The intensity ratio for tap water, cancerous tissue, and controlled tissue, respectively, is 1:1.15:0.56 at TBp=1 s. The SQUID-detected NMR/MRI exhibits potential applications in research and clinics.

High-Tc SQUID gradiometer system for magnetocardiography in an unshielded environment

We have designed a magnetocardiography (MCG) system that is capable of measuring magnetocardiograms in an unshielded environment. In order to carry out such a measurement, one has to contend with various ambient noise sources. These include power line and RF interference, microphonics pickup, fluctuations in the earth’s magnetic field, and electrostatic pickup. Earlier solutions devised to overcome these problems have entailed the use of a second-order gradiometer inside a deep mine or inside a magnetically shielded enclosure [1]. Apart from the above problems which are common to both low-Tc and high-Tc SQUIDs, high-Tc SQUIDs exhibit additional 1/f noise [2]. This noise is the result of hopping of flux vortices that are trapped in the body of the field cooled high-Tc SQUID, and can only be eliminated by zero-field cooling the SQUID.

Temperature and concentration-dependent relaxation of ferrofluids characterized with a high-Tc SQUID-based nuclear magnetic resonance spectrometer

We investigated the relaxation of protons in magnetic fluids using a high-Tc SQUID magnetometer. It was found that the longitudinal relaxation rate, 1/T1, is slower than the transverse relaxation rate, 1/T2, for ferrofluids in the same field. This is due to the fact that the 1/T1 process involves returning the magnetization to the z-direction, which automatically involves the loss of magnetization in the x-y plane governed by the 1/T2 process. Additionally, 1/T1 and 1/T2 at high temperatures are slower than the corresponding relaxation rates at low temperatures, which is due to the enhanced Brownian motion of nanoparticles at high temperatures.

High quality step-edge substrates for high-Tc superconducting devices

Despite the significant progress in fabrication methods of step edge, the lack of reproducibility still hinders their use in more complicated systems. To pursue the high reproducibility and quality of step edge for high-Tc superconducting devices, we have developed the technique to fabricate high quality step-edge substrates with arbitrary step angles. We used two steps to improve the step ramp quality substantially. The surface microscopy of step substrates shows high uniformity with respect to any step angle. There are no needles, waves, trenches, cascades, or other flaws on these surfaces. Serial Josephson junctions and superconducting quantum interference device arrays were fabricated onto step-edge substrates. The step-edge devices exhibit excellent results.

Superconducting-quantum-interference-device array magnetometers with directly coupled pickup loop and serial flux dams

In this work, we studied the engineering of high-transition-temperature superconductor Josephson junctions and superconducting quantum interference device (SQUID) by using step-edge or the bicrystal grain-boundary technologies. Serial Josephson junctions and bare SQUID array reveal high quality device characteristics. A high-Tc SQUID magnetometer exhibiting magnetic field sensitivity of 33fT∕Hz1∕2 in the white regime and 80fT∕Hz1∕2 at 1Hz was demonstrated by incorporating the flux dams and serial SQUID into the pickup loop of magnetometer. Furthermore, we demonstrate the opening of the flux dams by applying an external magnetic field to induce a current higher than the critical current of the serial flux dams. We show that the serial flux dams effectively suppress the low frequency 1∕f-like noises.

Enhancing the tumor discrimination using antibody-activated magnetic nanoparticles in ultra-low magnetic fields

In this paper, we report an enhanced liver tumor discrimination for rats using antibody-activated magnetic nanoparticles (MNs) and ultra-low-field magnetic resonance imaging ex vivo. It was found that the intensity ratio between the magnetic resonance image of tumor and normal liver tissues is 2–3 absence of antibody-activated MNs in rats. The intensity ratio rises to ∼100 when antibody-activated MNs are expressed in liver tumors through vein injection. Enhancing tumor discrimination using antibody-activated MNs is demonstrated using T1-weighted contrast imaging in ultra-low magnetic fields.

Effect of the grooved SrTiO3 bicrystal line on the YBa2Cu3O7 grain boundary

Abstract Using atomic force microscope (AFM), we have investigated the correlation between the characteristics of grooved SrTiO3 (STO) bicrystal line and the grain-boundary (GB) microstructure of the YBa2Cu3Oy (YBCO) film. When the underlying groove becomes deeper and steeper, the density of growth spirals along the boundary line increases and the meandering configuration of GB gradually disappears. From the measured signals of the dc-SQUIDs patterned on the films, we also conclude that the homogeneity of the GB is improved.

Magnetic Resonance Imaging of Hyperpolarized

Nuclear magnetic resonance and imaging (NMR/MRI) of optically pumped (OP) hyperpolarized 3He were studied by using a high-Tc SQUID magnetometer device in microtesla magnetic fields. The OP cell was filled with a few milligrams of Rb metal, 0.0798 bar N2 gas and 0.705 bar 3He gas. The 3He cell had been hyperpolarized at an optical pumping system for 5 ~ 6 hours first; then it was moved to the SQUID-detected nuclear magnetic resonance and imaging system to measure. An appropriate B1 pulse level and time duration generated a 5° low flip angle of polarization. The free induction decay NMR signals were measured. The spin-lattice relaxation time (T1) of 3He was 4.7 hours. We improved the line width of NMR spectrum to 0.8 Hz by compensating the inhomogeneous gradient field of environment. The filtered back projection image of hyperpolarized 3He could show a clear image in one shot. The SQUID-detected NMR/MRI would be a great interest for biological imaging.

^{3}{\hbox {He}}

In this work, a study of hepatocellular carcinoma and normal livers in rats using nuclear magnetic resonance (NMR) based on superconducting quantum interference devices (SQUIDs) was presented. The time domain free induction decay signals, Sy(t), of cancerous liver tissue and control liver tissue of rats were measured to study the respective longitudinal relaxation rate T1-1 . The NMR data were fitted to [1-exp(-TBp/T1)] to derive the longitudinal relaxation times T1 for cancerous liver tissue and control liver tissue. It is found that T1, cancer of cancerous liver tissues is 2.3 times higher than T1, control of control liver tissues. Statistically the data suggest that T1, cancer/T1, control can be used to discriminate cancerous liver tissue from control tissue. Furthermore, differentiating cancerous tissues from control tissues was demonstrated using magnetic fluid phantoms as phantoms for cancerous and control tissues. The SQUID-detected NMR/MRI exhibits potential applications in clinical research.

Detected With a High-

A scanning magnetocardiography (MCG) system constructed from SQUID sensors offers potential to basic or clinical research in biomagnetism. In this work, we study a first order scanning electronic high-Tc (HTS) SQUID MCG system for biomagnetic signals. The scanning MCG system was equipped with an x–y translation bed powered by step motors. Using noise cancellation and μ-metal shielding, we reduced the noise level substantially. The established scanning HTS MCG system was used to study the magnetophysiology of hypercholesterolaemic (HC) rabbits. The MCG data of HC rabbits were analysed. The MCG contour map of HC rabbits provides experimental models for the interpretation of human cardiac patterns.