• Measurement and visualization of magnetic properties of biological and physical sample
• Limit sensitivity of NMR tomography and spectroscopy using the SQUID magnetometric systems

Result 1: Measurement and visualization of magnetic properties of biological and physical sample

Project: VEGA 2/5043/26 in cooperation with Department of Medical Informatics and Bioengineering, Uppsala University, Sweden

Investigators: I. Frollo, P. Andris, V. Juráš, Z. Majdišová, J. Weis

A new original technique of measuring and mapping thin planar layers has been developed and tested using imaging methods based on magnetic resonance. The achieved sensitivity was at level of units of microtesla, resolution of image was 100 micrometers on samples with magnetic layer within 10 nanometers.

It is measurement of magnetic susceptibility of thin biological and physical layers of ferromagnetic or paramagnetic samples. The technique is based on projection of magnetic domains into homogeneous phantom and subsequent application of NMR imaging method based on the gradient echo sequence.

The technique was tested using electrical generators of weak magnetic field. Experiments were performed successfully on biological samples using magnetic liquids, on printed images and on documents with hidden magnetic characters eg on banknotes. The technique was applied also for measurement and imaging magnetic fields of RF coils and arbitrarily for measurement of inhomogeneities of magnetic fields. The novel technique is forward for use in biological and medical sciences and for nanotechnologies (imaging thin layers) and in microelectronics as well.

In the figure above an optical image of botanical sample (leaf) and of physical samples (circular sections made of cellulose) can be found, with different concentrations of water solution of magnetic liquid – nanoparticles of magnetit Fe₃O₄ (adulterating 1:2:4:8:16:32). In the figure below NMR image of a sample projected into homogeneous phantom can be found, sampling 512x512, resolution 100 μm.

Publications:

• FROLLO, Ivan - ANDRIS, Peter – JURÁŠ, Vladimír – MAJDIŠOVÁ, Zuzana.: Magnetic field distribution measurement of thin-layers using magnetic resonance imaging sequences. In: XVIII IMEKO World Congress. Metrology for a Sustainable Development. Proceedings. Brazil, Sept. 17 – 22, 2006. pp. 1-4.
• WEIS, Ján - ANDRIS, Peter - FROLLO, Ivan – AHLSTRÖM, Hakan: A simple method for mapping the B1 field distribution of linear RF coils. MAGMA - Magnetic Resonance Materials in Physics, Biology and Medicine, 18, 2005, 283-287.

Result 2: Limit sensitivity of NMR tomography and spectroscopy using the SQUID magnetometric systems

Project: VEGA 2/4091/04

Investigators: V. Zrubec, J. Maňka

A theoretical analysis of properties of high-frequency magnetic field receivers with SQUID magnetometers for NMR systems with low magnetic field (Low-Field-NMR - RF band) has been performed. Derived relations for the equivalent spectral sensitivity of the magnetic induction cover the influence of the active elements noise, the influence of losses due to resistances of the antenna circuit and measured sample, and the influence of their noise temperatures. The achievable parameters have been compared with the parameters of low-noise semiconductor amplifiers. On a set of examples the connection of the actual parameters with the sensitivity of the receiver and the achievable signal-to-noise ratio on the receiving channel output intended for the frequency band of 2.2 × 10⁶ Hz (B_o ~ 0.05 T) has been shown. The computed values of the equivalent spectral sensitivity are in the range of (10^-19 - 10^-17) T Hz^-1/2. The analysis showed when the use of SQUID magnetometers is efficient. Their advantages can manifest especially in NMR spectroscopy of small-volume solid state samples with the low RF losses.

Publication:

• ZRUBEC, V. – MAŇKA, J.: Sensitivity of superconducting quantum RF magnetic field receivers for NMR spectroscopy and tomography. Physica C, 435, 2006, 132-135.