It has been about thirty years, since ultrasonics have been applied to diagnostic methods in medicine. Through this time, the ultrasonic diagnostic methods have been instrumental in developing a new field in medical science, and applications thereof to clinical work now involve almost all the organs of the human body. The reasons of such developments are that the ultrasonic diagnostics have the following merits : First, ultrasonic methods offer full effect in the diagnostics of soft tissue maladies which are not easily examined by other methods. Second, ultrasonic methods are free from harmful aftereffects when it is applied to clinical examination. Third, ultrasonic methods involve no operative examinations and impose practically no physiological burden on the patient.
This paper presents current aspects of the diagnostical applications of ultrasonic methods to the following medical fields together with the corresponding techniques : To neurology through the midline echo-method and the ultrasonotomography ; to the cardiology through the synchronized ultrasono-cardiotomography, ultrasonotomo-kymography and ultrasono-cardiotomography of multi-information system; to the obstetrics and gynecology, in particular, the diagnosis of fetus through the Doppler method and the ultrasonotomography; etc.
This paper also describes the current topics of the apparatuses developed for the ultrasonic diagnostics.

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General view of the mechanical transducers to measure the surface vibration of human body has been outlined and the problems involved in the measurement techniques with the various types of transducer have also been discussed. As the quantities measured with the mechanical transducer should always be well-defined, the need for a suitable type of standard mechanical transducer for the surface vibrations of human body, and for the establishment of the calibration method has been pointed out. The reciprocity technique has been proposed as the most preferable calibration method of mechanical transducers for human body.

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The impedance of blood is influenced by various factors, such as temperature, applied voltage and flow rate. It has been reported that the impedance of the flowing blood differs from that of the blood in a stationary state. The most important reason for this phenomenon is the orientation of red cells. In this paper the effect of red cell orientation is discussed. The impedance of blood has been discussed both theoretically and experimentally by many investigators. In most of these investigations, red cells are considered to be of spherical shape. However, red cells are actually circular biconcave disks. In this paper, the shape of red cells is simulated as a rotational ellipsoid, because the impedance of blood can easily be derived theoretically by this assumption. The theoretical results of the relationship between impedances and hematocrit values are in good agreement with the results of experiments. The effect of red cell orientation on the impedance of blood can also be discussed from the theoretical results. The effect of red cell orientation on the impedance of blood is also discussed experimentally. Red cells are orientated by the application of electric field and by the shearing rate of flow. The change of the resistance of blood due to the orientation of red cells is very large and is dependent on the hematocrit values, the shapes of red cells and the degree of oriented red cells. The results of our theoretical calculations agree well with the results of experiments. The effect of red cell orientation is useful for the electrical measurement of hematocrit values and the shape of red cells and so on. However, this effect sometimes influences the measurement error of electromedical instruments, such as electromagnetic flowmeters and impedance plethysmographs.

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Since it is very desirable to measure the blood flow transcutaneously in clinical practices a sinusoidal electromagnetic flowmeter is applied for this purpose. The magnetic field is applied towards the blood vessel from the skin surface, and a couple of electrodes are placed on the skin surface close to the vessel to detect induced emf. The induced emf between these electrodes is proportional to the blood flow rate in the vessel under the skin.
Although the relationship between the induced emf and the blood flow rate is. theoretically highly complicated, a simple relationship is obtained under some reasonable assumptions. The results may be useful for further progress relating to the availability of the electromagnetic induction for our purpose.
There are many problems involved in the accomplishment of this type of transcutaneous flow detection. The most important problem is the electrostatic coupling and the leakage resistance coupling between exciting and detecting cables. Since the magnetic field of this. flow transducer must be so strong as to require very high exciting voltage, the coupling voltages are very high compared with the emf induced by the blood flow. In order to minimize the effect of these coupling voltages on the flow signal, the following two techniques have been very useful. One is complete electrostatic shielding of both exciting and detecting circuits. The other is to balance out these coupling voltages using well known Wagner ground method. The electromagnetic coupling between exciting and detecting circuits is also quite important, because this coupling voltage is quite high compared with flow signal and is not stable. For the reduction of this transformer component, a negative feedback method is used and the transformer component is easily reduced to 10% of the voltage without negative feedback.
A specially designed flow transducer is used for experimental measurements of flow rate on both models and human cubital arteries. The results of model experiments are in good agreement with the theoretical results. The flow patterns of the human cubital arteries are obtained successfully by this new approach, and further clinical applications of this method to transcutaneous flow detection seems to be promising.

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By applying the time shared pulse drive on the square-wave electromagnetic multiplex flow system, a new catheter-tip flow sensor has been developed. Due to this pulse drive, the tiny sensor receives much less rms power compared to a single flow model of a continuous 1A magnet drive, which is related to reciprocal numbers of the multiplex channels. Since the sensitivity of this tiny sensor is dependent upon the peak current value of the square pulse, its sensitivity is quite equal to that expected of the single flow model.
The finished dimensions of this new sensor are 2. 5 to 4 mm in outer diameter and 5 to 10 mm in length; it is mounted at the tip of the heart catheter. The surface temperature never exceeds 41°C even when it is used for over 30 minutes. The conversion ratio between the flow velocity and the flow induced emf voltage is measured by 0.5 micro V/cm/s, which may make it the most sensitive among this kind of sensors previously published.
When flow tracings by this new sensor were compared with the simultaneously recorded tracings using ordinary extra-vascular probes at the same vascular location, the results indicated close coincidence in their wave forms and in the flow rate.

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