Patent No. 4270545 Apparatus for examining biological bodies with electromagnetic fields

 

Patent No. 4270545  Apparatus for examining biological bodies with electromagnetic fields (Rodler, Jun 2, 1981)

Abstract

The primary field generated by a transmitting loop or coil energized with a AC current induces secondary currents within the body which in turn generate a secondary field. The secondary field is picked up by a pick-up loop or coil. A compensation coil is energized so that no voltage is induced in the pick-up coil when a reference body having the same resistivity is substituted for the body in which measurement are to be carried out. To compensate for body movements, the primary field can have a lower and a high freqency component. Since the high frequency components penetrate the body only to a predetermined depth (or not at all) the difference between the picked-up high or low frequencies signals is substantially independent of the distance between the object being measured and the measuring apparatus. Sectional views of larger areas of the body are generated by scanning sequentially with a plurality of transmitters spaced from each other and energized with phase-shifted currents and display of the corresponding picked-up signals on a cathode ray tube.

 

Notes:

 

BACKGROUND OF THE INVENTION

The present invention relates to apparatus for examining, measuring and recording physiologic processes in biological bodies or parts of bodies by use of electromagnetic fields. Specifically, the body or parts of the body are exposed to electromagnetic alternating fields generated by a transmitting device and the resulting magnetic phenomena in the body are measured at its surface.

Measuring apparatus for the examination of physiological processes in biological objects was already proposed in German Auslegeschrift No. 2,255,757. In this publication, apparatus was disclosed in which the processes were to be identified and measured by measurement of the electromagnetic as well as the electrical component of the primary field. However, the measurement of these two components cannot yield adequate results, since in order to do so both of the field strengths must relate to the same enclosed space. If they do not relate to the same space they cannot be put into a mathematical relationship to each other, as is required if the impedance of the space is to be calculated.

Further, in known apparatus the distance between the object to be measured and the measuring system may affect the measuring results to a greater extent than do the physiological processes in the body. Movement of the body also distorts the result and can mask the changes resulting from physiological causes. It must also be considered that physiological processes internal to the body cause changes in the order of 1/1000 of the effective resistance of the body, thereby having only little influence on the primary field. The primary field does not vary greatly as a function of the impedance of the body, since the resistance to radiation of the proposed arrangement is relatively low ohmic.

SUMMARY OF THE INVENTION

It is an object of the present invention to furnish apparatus which allows physiological processes whose effect lies under 1/100th or even 1/1000th of the body's impedance to be determined.

The present invention relates to apparatus for measuring physiological processes in a biological body. It comprises transmitting means for generating a primary electromagnetic field adapted to induce currents in the body, said current creating a secondary field. Pick-up means are provided which are coupled to said secondary field for furnishing measurement signals indicative of the value of a predetermined characteristic of said secondary field but substantially independent of said primary field. The pick-up means comprises display means for furnishing a display of the measurement signals.

In a preferred embodiment of the present invention the pick-up means comprises at least one pick-up element arranged in said primary and secondary fields in such a manner that measurement signals furnished thereby are substantially independent of said primary field.

In a further preferred embodiment, said pick-up means comprises a pick-up element for furnishing pick-up signals having a first component resulting from said primary and a second component resulting from said secondary electromagnetic field, a compensation element arranged relative to said pick-up element and said transmitting means so that it furnishes compensation signals adapted to cancel said first component of said pick-up signals, and circuit means connected to said pick-up element and said compensation element for furnishing said measurement signals in response to said pick-up signals and said compensation signals.

In a preferred embodiment of the invention said primary electromagnetic field has a reference phase angle and said pick-up means comprises a pick-up coil furnishing pick-up signals and having an electromagnetic axis. Means are provided for adjusting the angle between said reference phase angle and said electromagnetic axis until two equally large primary field components canceling each other are created in said pick-up coil, whereby said pick-up signals vary as a function of said secondary field only.

In all embodiments of the present invention, the effects of the primary, that is of the exciting field, are suppressed or compensated for and do not appear in the displayed measurement results. Only the effects of the secondary field, that is the field generated by the secondary currents induced in the object by the primary electromagnetic field are considered. The latter have a much closer relationship to the impedances within the body and can be modulated by the physiological processes to an extent that can be measured. In one embodiment, regulating means are provided which are adjusted by compensating fully for the primary electromagnetic field in a homogenous comparison body and transferring the full compensation to the body to be measured, whereby differences between the compensation values and the picked-up values constitute the desired measurement signals. Rhythmic physiological processes as, for example, circulatory changes, breathing and flow processes may be monitored. In a preferred embodiment of the invention, the transmitting means comprises a plurality of transmitting elements, and energizing means for energizing each of said transmitting elements at a frequency different from the other transmitting elements. By thus generating a primary field with different frequencies, frequency-dependent physiological processes are monitored. This is particularly useful for measuring processes within the interior of the biological body, since the induced secondary current and thereby also the secondary field have a direct relationship with the resistivity .rho.. Since (.rho.) is a pure material constant, this unit includes all physiological processes.

Both the magnitude of the secondary field and the direction of the secondary field vector can be determined in a further embodiment of the present invention wherein the pick-up means comprises a first and second pick-up element arranged at 90.degree. to each other, the pick-up elements having an electromagnetic axis. In this embodiment the pick-up means further comprises means for rotating said pick-up elements in such a manner as to rotate said electromagnetic axis thereof relative to the reference angle of said primary electromagnetic field until said measurement signal is substantially independent of the latter. Measurement means are provided which are interconnected between said first and second pick-up element and said display means, for furnishing amplitude and phase angle signals in response to signals furnished by said first and second pick-up elements.

In another embodiment three or more transmitting elements are arranged along the circumference of a circle, with the axes positioned radially or axially, while the exciting currents delivered by the oscillator are phase-shifted in the transmitting elements in accordance with the angular distribution of the latter, so that a rotating field results. The pick-up elements comprise one or more crossed spool arrangements, whose axes are arranged at an angle to the primary field for compensation thereof, the pick-up elements being connected to measuring and evaluating devices for determining the phase and amplitude. Since a rotating field, as is well known, flows through the object with differing field directions and different angles, the picked up secondary field can be indentified in correspondence to its phase position with the biological happenings which lie in the direction of the current thereby new criteria for the evaluation has been developed.

In accordance with the present invention, the phase position of the transmitting elements is mutually adjustable, so that measurements can be carried out in preferred directions. The superimposed phase position is herein utilized as a criterion of the direction, this phase position also being automatically controllable by a corresponding device.

In accordance with the invention, the object to be measured is positioned between the transmitting element and the pick-up element.

Since an abundance of information is hidden in the so-derived measuring voltages, it is practical to store the latter and, from the relationship among a plurality of components and measuring values derived from different angles, compute the desired values and display the same in topographical representation.

Thus in accordance with the present invention for topographic evaluation and storage, XY position pick-offs are arranged on the movable pick-up elements, the picked-up measured values of the latter controlling the graphic plotting device and computer device with respect to position. Storage devices are provided for storage of the measuring signal and the position signal.

By suitable programming of the computer, it is possible to generate a display of circulatory processes, since blood has the characteristic of changing resistivity with increasing velocity. Observation of the circulatory processes is thus made possible without interference and above all over longer time periods. Many metabolic processes which are otherwise only derivable by means of isotope methods, that is with a radiation load, may also be registered in accordance with this method, since many metabolic processes coexist with electro-biological and electro-chemical processes which result in resistance changes. A particular advantage is that these observations are derivable in a real time process. Further, parts of the body which are meant for transplanting can be examined in this way for their functional efficiency. By means of an XY position pick-off, yielding position signals signifying the position relative to the body to be measured, the distance between the body and the pick-up member can be taken into account by the computer device.

In order to eliminate the distance and movement effects between the pick-up element and the biological body and to be able to conduct topographic depth sensing, in accordance with the present invention, the primary field is formed with two frequencies, and in particular one low measuring frequency, and a frequency very high relative to the low frequency for elimination of surface effects, a part of the pick-up element being selectively tuned to this higher frequency and a part to the lower frequency and the measuring values generated in the pick-up elements being fed to a computer for separating the surface effects from the depth effects.

(a) Since changes in distance between the measuring apparatus and the body being scanned will, within certain limits, affect the high and low frequency fields to the same extent, compensation for distance variations can be achieved by comparing corresponding components of the high and low frequency fields and deriving the desired measurement signals from the difference therebetween.

(b) This difference is modulated by biological processes within the body only starting at a depth of penetration exceeding the depth of penetration of the higher frequency field.

(c) A topographic recording can thus be generated by scanning the body from different angles with a movable measuring device.

For forming the difference the computer device comprises an analog subtraction device in which the difference value is created by application of both measuring values with opposite phase and polarity. However, for arithmetic evaluation and storage it is practical to digitalize the measuring signals and to process the same by means of digital computers.

The construction of the arrangement is determined both by the part of the body to be measured and by the frequencies used. When higher frequencies are used (e.g., the transmitting elements are formed as a loop, in which a pick-up loop is centrally located. Between pick-up and transmitting loop at least one compensation element, also in the form of a loop, is provided.

In accordance with the present invention, the pick-up elements may also be constructed as spools, the compensation element being a spool coupled to, and surrounding the pick-up winding and excited by the primary current through phase shift elements and amplitude control elements. The primary control circuit preferably consists of a plurality of spools, which are coupled by ferrite cores which form a hollow body inside of which the pick-up element as well as the compensation device and the exciting spools are placed, the whole arrangement being surrounded by shielding.

This arrangement can, for example for recordings of the skull or measuring of the whole body, completely surround the latter and at the same time shield it from the outside so that external fields have little effect. For these measuring arrangements often not the absolute value but only the relative changes in the measured value by pulsation or other biological processes is of interest and the measured value is normalized by suppression of the carrier. In this embodiment, the primary carrier signal and the picked-up signal are applied to a product detector for deriving the amplitude, and a phase detector for deriving the phase angle of the desired measurement signal.

Functionally, the effect of the biological processes on the secondary field is to be considered a modulation. Thus, for complete supression of the carrier frequency, as happens with total compensation, only the sidebands remain. The product detector, which can also be constructed as a ring demodulator, allows sideband demodulation under simultaneous application of a new carrier portion from the primary field. An automatic control is supplied so that the control of the compensation need not be carried out by hand. For this purpose the measuring voltage is derived in accordance with the present invention via an amplifier from the pick-up element and this voltage, through an amplitude detector, controls an electronic amplitude control device and through a phase detector an electronic phase control device, the two control devices controlling the compensation devices. The measured amplitude value and the measured phase value are derived from the amplitude detector and the phase detector respectively, for recording. In accordance with the present invention the outputs of the demodulation device, the phase detector and the XY position take-off are provided with analog-digital converters, all three digital results being applied to storage and computer devices, means for graphic and pictorial display of the measuring results being connected thereto.

In accordance with the present invention, compensation for the primary field takes place only after demodulation of the measuring signal as well as of a compensation voltage which varies as a function of the primary field, by forming the difference of the demodulated signals. In this form of compensation, the amplifiers and the demodulation devices are included in the compensation. This measuring arrangement has the advantage that it requires only amplitude control. When measurements are to be conducted in real time processes, it is of advantage that the pick-up elements do not scan the field by means of actual movement, but that in accordance with the invention, a plurality of pick-up elements with compensation devices are mounted in a common transmitting element, the former being sequentially connected to the recording device by means of electronic switches.

For calibration of the apparatus, an amplitude modulation adjustable in degree of modulation and a phase modulation adjustable in degree of modulation are applied to the primary field for a short time, each with approximately the same order of magnitude as the biological happening. The absolute magnitudes of the resistance values as well as the phase shifts can then be derived by comparison with the calibrating modulation. Specificially, the degree of modulation is changed until the artifically superimposed modulation and the modulation resulting from the physiological happening are equally large. The amplitude of the artifical modulation then corresponds to the amplitude of the biological change. For this form of calibration not only the absolute values, but also percent changes and data in percent or in per thousand may be furnished.

The amplitude of the modulation values can however also be printed out or furnished in numerical values, the biological modulation being compared by means of a comparator with a step type calibration modulation. In this case the modulation value can be directly converted into a numerical value by means of an analog-digital converter and can be displayed or printed out.

The measuring of impedances has assumed a continually growing importance in medicine since such impedance measurements are more reliable than other presently known measurements in various fields, such as, for example, early detection of a number of different kinds of cancers.

New investigations have also shown that the life capacity of transplants can be estimated by means of impedance measurements.