Compensation System for Biomagnetic Measurements with Optically Pumped Magnetometers inside a Magnetically Shielded Room.

Magnetography with superconducting quantum interference device (SQUID) sensor arrays is a well-established technique for measuring subtle magnetic fields generated by physiological phenomena in the human body. Unfortunately, the SQUID-based systems have some limitations related to the need to cool them down with liquid helium. The room-temperature alternatives for SQUIDs are optically pumped magnetometers (OPM) operating in spin exchange relaxation-free (SERF) regime, which require a very low ambient magnetic field.

Automatic detection of ultrasonic Doppler signal episodes resulting from fetal breathing movements.

A method for automatic detection of fetal breathing movements has been proposed, based on the time-frequency structure of the corresponding continuous wave ultrasonic Doppler signals. The method uses spectral analysis of the envelope of the directional Doppler signal and cross-correlation analysis of both directional envelopes. Detection rule comprises the following criteria: presence of the peak in the envelope spectrum and of the adequate signal level in the frequency range corresponding to the fetal breathing rhythm, the peak value and the position limits of the peak of the cross-correlation coefficient of the both directional envelopes.

Measurements of the neutron dose near a 15 Mv medical linear accelerator.

In this work, simplified recombination methods for routine estimation of dose equivalent in mixed (gamma and neutrons) radiation field outside the irradiation field of linear medical accelerators is considered. The author's earlier reported method of H(10) measurements, involving determination of the recombination index of radiation quality, Q(4) by tissue-equivalent recombination chamber was combined with the new method for determination of the photon to neutron dose ratio D(X)/D(n) from the ratio of ion collection efficiencies measured in the investigated radiation field and in two reference fields of gamma and neutron radiations. The method is suitable when the neutron contribution to the total absorbed dose, D(n)/D, is >3%.

The discrimination of stenosed carotid bifurcation models with smooth and irregular plaque surface. Part II. The multivariate statistical analysis of ultrasonic Doppler velocity data.

According to the conclusion of the first part of the paper the Doppler spectral indices were analyzed in a detailed manner to provide a means to differentiate bifurcation models with different irregularities. Autoregressive (AR) models using the Akaike FPE criterion were fitted to the curves of the spectral broadening index, turbulence intensity index and coefficient of symmetry. These curves were also submitted to the data reduction significant point extraction algorithm.