Noise in ultrasonic imaging

The feasibility of noise measurement in medical ultrasonic imaging has been studied and a theoretical evaluation of stochastic noise influence upon the perceived image has been undertaken. The influence of noise on a perceived image has been calculated by considering the light intensity perception characteristic of the human eye and it has been found taht the additive noise in the video signal pushes the small signals in the image towards the invisible (black) region. Impulse noise measurements of amplitude and time jitter have been set up using a standard water/CCl4 interface and pulse amplitude analysis to take into account the random nature of noise by distribution measurements.

Effects of patient positioning and of thickness variations on radiotherapy

Correct patient positioning is essential for good aiming in radiotherapy. This can be achieved using back and side pointers, but sometimes these devices are not being used in order to simplify and make the positioning faster. The effects of such a simplification have been studied and measured. The results of this experimental study show that in thicker patients (over 24 cm) the use of back and side pointers is of great importance, because the variation of the patient thickness and angulation can significantly influence the aiming angles and dose percentages.

Estimation of fetal weighty by ultrasonic abdominometry

The fetal abdomen was measured with an ultrasonic contact scanner in order to correlate abdomenal circumference and birth weight. A sample of 134 measurements was used to calculate a standard graph, which was then tested against a subsequent 280 measurements, giving a mean estimation error of 105 Gm. Head-to-abdomen circumference ratio measurements were used to assess the type of growth retardation.

The energy response of LiF, film and a chemical dosemeter to high energy photons and electrons

The physical responses of LiF, film and a chemical dosemeter in high energy photon and electron beams has been studied. It is shown that the response for film and the chemical dosemeter does not change significantly up to 42 MeV, while for LiF it decreases by about 10%. Analysis of calculations and measurements showed that this decrease could not be explained by existing theories.

Study of the Double-Layer by A.C. Polarography

Possible effects of the structure of the double-layer on the a.c. polarographic phenomena observed have been considered. Results obtained in the reduction of zinc and uranium, at potentials more negative than the e.c.m., and of copper at potentials more positive than the e.c.m., were explicable in terms of double-layer influences. A.C. polarograms sometimes showed changes in double-layer structure much more clearly than double-layer measurements per se, suggesting the utility of a.c. polarography specifically in double-layer studies.

Alternating current polarography of organic compounds. V. Quantitative treatment of the adsorption process

Equations are derived to express the adsorption equilibrium subsisting at an adsorbent surface in the presence of two adsorbable species. These equations are applied to the case of the reduction of organic compounds at the dropping mercury electrode. It is well known that adsorption at the electrode can produce irreversibility in the D.C. step, and a qualitative explanation is provided. The same treatment is used to explain the shape of the A.C. calibration curves.

Alternating current polarography of organic compounds

In previous papers of this series (Breyer, Bauer, and Hacobian 1954 ; Breyer and Bauer 1956) it was shown that the A.C. polarographic behaviour of organic com- pounds can be explained by postulating adsorption of the substances at the electrode. Empirical and theoretical expressions for the dependence of the alternating current on the bulk concentration of depolarizer were qualitatively correlated. In the present paper, the theoretical treatment is developed further, permitting the evaluation of the adsorption coefficients of the oxidized and reduced forms at the electrode surface.

The influence of the supporting electrolyte on tensammetric waves

The influence of the supporting electrolyte on the height and frequency dependence of tensammetric waves is examined. Anions generally affect the positive tensammetric waves whereas cations have little effect on either positive or negative waves. A tentative explanation of the underlying phenomena is given and the possible mechanism discussed.

Alternating current polarography of organic compounds. III. Chloranilic acid

The behaviour of chloranilic acid at the dropping mercury electrode has been techniques of ordinary and of alternating current polarography. A new type of tensammetric wave has been encountered, which is probably an outcome either of multilayer adsorption and/or of a change in state of the adsorbed film. At the same time, a new tensammetric phenomenon, the exchange of one species of surface-active molecules against another, has been observed. Alternating current polarography can be used for estimating chloranilic acid at concentrations as low as 10-7M, whereas conventional polarography does not permit analysis at concentrations below 10-5M.

Theory of alternating current polarography. II. Significance of the Heyrovsky-Ilkovic equation and its relation to the production of A.C.Polarogrphic waves

The significance of the Heyrovsky-Ilkovic equation is discussed and the relationship between reversibility of the electrochemical reaction and polarographic reversibility critically examined. It is shown that even reversible electrochemical processes might yield D.C. polarograms of the irreversible type. The relationship between different types of electrode reactions and the production of A.C. polarographic waves is elucidated.

Theory of alternating current polarography. III. Frequency of alternating field and reaction rate

The equation of the A.C. polarographic current for processes where the frequency of the alternating field is comparable with the rate of the electrode reaction is derived. Relative values of equilibrium rate constants of some first order electrode reactions are evaluated experimentally.

Alternating current polarography of Organic compounds. IV. Perinaphthenone

The behaviour of perinaphthenone at the dropping mercury electrode has been investigated by the combined techniques of conventional (D.C.) and alternating current (A.C.) polarography. Two D.C. steps were observed, but an A.C. polarographic wave was found only at the potential of the more positive D.C. step. Two tensammetric waves were also seen, one of which appears to be the outcome of multilayer adsorption or of a change in state of the adsorbed film.

Alternating current polarography of organic compounds

The alternating current polarography of quinone and hydroquinone has been investigated. The calibration curves follow an equation of the type of the Langmuir isotherm. The method can be used for quantitative analysis, the accuracy being greatest at low temperatures and in a concentration rang between 10-5 and 10-4M.

Alternating current polarography of organic compounds. I. General introduction and theory

The theoretical principles governing the alternating current polarography of organic compounds are presented. The role of adsorption, and the relationship between the A.C. and D.C. criteria of polarographic reversibility are discussed.

Theory of alternating current polarography. I. Equation of the reversible AC polarographic wave

An equation for the A.C. polarographic current is derived from considerations of concentration changes produced at the dropping mercury electrode in virtue of the superposition of a small sinusoidal alternating voltage onto the direct potential, for the case of reversibly reduced inorganic ions. The equation predicts the magnitude of the A.C. polarographic current at any point on the polarogram.