Abstract
Several papers on the applications of the nuclear magnetic resonance (NMR) technique-for the biological measurements have been published since the first proposal of the NMR blood flowmeter by Bowman. However, the problems arising inherently from the non-invasive measurements of the specified area in the body were not discussed in these papers. The authors proposed previously the magnetic focusing technique as one of the new approaches and discussed some problems related to this technique.
In this paper, some basic problems of the applications of NMR for the non-invasive measurements are discussed and the fundamental properties affecting the measuring sensitivity attained by the magnetic focusing technique is analyzed. The problems treated and the obtained results are as follows :
1) The relations among parameters such as relaxation times and radio frequency magnetic field which influence the measuring sensitivity are experimentally analyzed.
2) The distributions of RF magnetic field inside or outside the transmitter coil are theoretically calculated. Approximate values of relaxation time of 1-2 sec. and 0.1-1 sec. are experimentally obtained respectively with the various body fluids and tissues of the dog and the human. Philosophy of choosing the appropriate parameters are discussed based on these results by taking the saturation factor in Bloch's equation and the measuring sensitivity into account.
3) Application for the tumor detection is discussed and the differences of 20% and 200% in relaxation time between normal and cancer cases are experimentally obtained respectively with the tissues from the stomach and the breast. Further, it has been found that the relation between hematocrit of blood and its relaxation time was linear.
4) The deterioration of signal output by body tissues is examined by a model experiment. According to this experiment, it is shown that the deterioration of S/N ratio was equal to approximately 30%, at f = 60 MHz.
5) From above results, in the case of applying our proposed magnetic focusing technique, the resolution or the minimally detectable volume of water in the typical organs by S/N of unity at resonance frequency of 60 MHz should be about 0.3 ml.
