Ephraim H. Frei

The safety of ultrasound in fetal monitoring

Abstract Since ultrasonic (Doppler) fetal monitoring systems are technically feasible, it is most important to establish whether repeated prolonged irradiations are safe to both the mother and the fetus. The safety of ultrasonic exposures was investigated in this study with particular regard to structural changes, congenital malformation, and chromosomal aberration. Intensity levels of 164, 272, 490, 1,050 mW. per square centimeter have been used at a frequency of 2.28 megahertz (MHz), for 5 or 60 minutes, either singly or for 5 consecutive exposures. At an intensity of 1,050 mW. per square centimeter, tissue damage was recorded proportional to the duration of exposure. Macroscopic and microscopic examinations including chromosomal analysis showed these tissue effects to be identical with those found in overheating. It has been found that an intensity level of 490 mW. per square centimeter did not cause critical tissue temperature rise. There were no pathologic findings on the macroscopic and microscopic examinations in the mothers, fetuses, and neonates, and no congenital malformations were recorded. Moreover, there were no pathologic findings in neonates of the third generation produced by brother-sister cross-mating from the fetuses which had been irradiated. All of the exposed mothers were able to conceive again, producing healthy offspring. Chromosome squash preparations were done from irradiated fetuses, revealing an equal incidence of chromosome aberrations as compared with that of the control group.

A Method for Resolving Multiple Responses in a Parallel Search File

It is possible to build memories in which the contents of all registers are tested simultaneously, and in which there is a single indication of the presence or absence of any number of positive responses to the test criterion. A method is described for separately identifying the members of a set of responses by presenting sequences of tests which generate an identification number for each member. The testing algorithm is easily mechanized, and the number of tests required per item is approximately proportional to the logarithm of the number of file registers. The method also may be used to search for items with contents falling within arbitrary numerical ranges.

Selective Cerebral Catheterization

This paper describes a new method for selective cerebral catheterization based on the Pod catheter [6], [7], guided and propelled by means of external magnetic fields. The principles of the Pod catheter, and the necessary equipment are described, and conclusions are drawn from experiments with a glass model. The middle cerebral artery was catheterized selectively, and cytotoxic material was injected into it to treat a malignant tumor of the brain hemisphere.

A Review of Medical Applications of Magnet Attraction and Detection

A review of selected medical applications involving detection and attraction of magnetic materials.

Subminiature Apparatus for Radio-Telemetering of EEG Data

The use of radio-telemetering has several advantages for the recording of EEG data from unrestrained subjects. By use of transistor techniques, miniaturization of the apparatus carried by the subject is made possible. Design considerations for a transistorized high input impedance, low-noise, single-sided amplifier for the EEG frequency and dynamic range are evaluated. Common-collector configuration and an unconventional input circuit of the first stage, and careful choice of transistors and their operating points, enable one to obtain satisfactory noise performance in the actual amplifier. A differential-input amplifier, based on features utilized in the design of a single-sided type, was developed. Rejection of in-phase signals (better than 3000 to 1 at 50 cps), an input impedance of 300 kilohms, and low noise referred to the input (3?v peak-to-peak at 20 kilohms of interelectrode resistance), determine the main features for EEG amplification purposes. A VHF FM one-stage oscillator, working at 30 Mc, provides transmission of signals up to a distance of 10 m. EEG records taken from subjects free in behavior, and even during convulsions, show no artifacts.

Model of a pvdf piezoelectric transducer for use in biomedical studies

Abstract A model is developed for a piezoelectric palpation device, consisting of EC array of PVDF sensors which are pressed with a uniform stress against a soft biological tissue containing embedded hardened regions. The elastic and piezoelectric equations were solved for the cases of both cylindrical and spherical inclusions. Computer calculations were made for the piezoelectric voltage response and the voltages appeared to be well within the range of possible experimental measurement. A simple analysis of the response curves permits the calculation of the ratio of depth to diameter of the hardened regions, suggesting that the device may have significant biomedical utility.