Guide to Medical Electronics and Applications: Introduction

This guide is concerned with describing the application of technological methods to medical diagnosis and therapy. It is instructive to review its development through recorded history. It is apparent that the fastest advances in the application of technology to medicine have occurred in the 20th Century and with an increasing pace. The following paragraphs touch on some events in this chain. We should recall that systematic technological assistance has only recently been widely applied to medicine through engineering. An understanding of the pathology which technology often helps to identify has largely been developed hand in hand with its application. In these paragraphs, we identify a number of the technologically based systems which are described more fully in the succeeding sections: their descriptions here are necessarily rather terse.

Medicine arose as a Scientific discipline in ancient times. Bernal (1957) notes that by the time of the establishment of the Greek civilization, physicians were a notable professional group whose activities were essential to the affluent, partly as a result of their unhealthy lifestyle.

They had by the 3rd Century BC distinguished between sensory and motor nervous functions. In the same era the Hippocratic Oath, or the code of conduct for physicians was written: it remains today as an ethical basis for much of medical practice.

Spectacles are first described in mid 14th Century Italy. Whilst optical glass had been used for a long period, the quality of glass used by the ancients was too flawed to be of use for eyesight correction. The continuing development of spectacle lenses led by about 1600 to the development of the first telescopes. By the Renaissance period in the early 15th Century, medicine was becoming more formalized. Anatomical knowledge progressively improved, and although the topics of pathology and physiology were recognized, they had advanced little from the time of Galen in Second Century Greece. Modern scientific medicine based on biological science has largely developed since the mid 19th Century work by Pasteur and others. Bernal (1957) notes that they provided the theories which led to an understanding of epidemiology and to rational descriptions of nervous function.

The practical development of a thermometer suitable for measurement of body temperature dates back to 1625. Whilst internal sounds from the body have been observed by physicians since the time of the Romans, the stethoscope dates back to the 19th Century, in a form reasonably similar to the present.

Whilst crafted artificial replacements for severed limbs have been in use for many centuries, the development of both implanted prosthesis and functional artificial limbs is recent.

The measurement of the electrical signals carried by our nervous system (known as Biopotentials) dates from the early years of the 20th Century with the first measurements of the Electrocardiograph. By the 1940s paper chart recordings of the detected waveforms could be made. The same era saw the development of the use of Electrosurgery, which employs resistive heating either to make delicate incisions or to cauterize a wound. By the 1960s, electrical stimulation of the heart was employed, firstly in the defibrillator either to restart or resynchronize a failing heart, and secondly in miniaturized pacemakers which could be used in the long term to bypass physical damage to parts of the heart. Electricity has also been applied, perhaps more controversially, since the 1940s in Electroconvulsive Therapy (ECT) to attempt to mitigate the effects of a number of psychiatric conditions.

Apart from sensing signals generated by the body, clinical medicine has been greatly advanced by the use of imaging techniques. These afford the possibility of viewing structures of the body which are otherwise inaccessible. They may either operate on a scale which is characterized by the transfer of chemicals or on a structural level, perhaps to examine the fracture of a bone.

X-rays have been applied to diagnosis since soon after their discovery by Rontgen in 1895.

The source of diagnostic radiation was the Cathode Ray Tube (CRT) which produced penetrating photons which could be viewed on a photographic emulsion. The early days of the 20th Century saw the first use of ionizing radiation in Radiotherapy for the treatment of cancerous conditions. A failure to appreciate the full extent of its dangers led to the premature deaths of many of its early proponents. Early medical images were recorded using the ancestors of the familiar X ray films. However, since the 1970s, acquisition of radiographic data using electronic means has become progressively more commonplace. The newer technique affords the possibility of processing the image to 'improve' aspects of it, or enable its registration with other images taken at another time to view the progress of a condition.

A major technique for the visualization of anatomical structures and the metabolism has been the use of radionuclides introduced into the body. The technology, known as Nuclear Medicine, has been used since about 1948 when radioactive iodine was first used to help examine the thyroid. The resolution available from nuclear medicine has progressively increased with increasing miniaturization of the photomultiplier tubes used in its detectors and improvements to collimators.

Computerized Tomography (CT) has developed from its initial application as a medical diagnostic technique in 1972. It had an earlier history when many aspects of the technique were demonstrated although without medical application. The use of computerized tomography has been one of the signal events in the development of medical imaging, enabling views of internal structures of a quality hitherto impossible. The technique has been refined somewhat from its inception in terms of degree: the time to obtain an image has significantly been accelerated and thereby provided commensurate reductions in patient radiation dose. Processing of the images obtained has also moved forward dramatically enabling three dimensional images to be obtained and presented with an illusion of perspective.

Much of the work in image processing in general owes its origins to fields outside of medicine. The mathematics developed for image analysis of astronomical data has been applied to contribute to a number of aspects of medical image processing. In order to be of reasonably general use, images should ideally provide representations of the systems which they examine in terms which are accessible to a non-specialist. The early projection X ray images are characterized by information accumulated from the summation of absorption of radiation along the paths of all rays. The resulting image does not represent the morphology of a single plane or structure but instead is a complex picture of all the contributing layers. This requires a high degree of skill to interpret. Image processing may help in ways such as clarifying the data of interest, removing movement artifacts and providing machine recognition of certain structures. These functions enable the extension of the application of medical imaging to the quantification of problems such as the stroke volume of the heart so that its operation may be properly assessed whilst minimizing the use of invasive techniques.

Another technique which has been applied to medicine in the recent past and with increasing success is ultrasonic diagnosis. This arose from two fields. The first was the application of sonar in the Second World War to submarine location. Also developed during the War was Radar: this relies on very a similar mathematical basis to obtain images by what is essentially the reflection of a portion of the energy from a source back to a detector. The development of signal processing for radar has been one of the major early inputs into the development of medical ultrasonic diagnosis systems. A significant difference in difficulty of analysis of their respective signals is due to the much greater non-uniformity of the medium through which ultrasound is passed. Ultrasound diagnostic systems are now in widespread use, particularly in applications such as gynecology in which the hazards due to ionizing radiation present an unacceptable risk for their routine use. Gynecological screening by ultrasound is undertaken now routinely in many countries: although doubts about its absolute safety have been expressed, no causative links to ailments have yet been established.

Ultrasound also provides a suitable mechanism for use with Doppler techniques, again borrowed substantially from radar, to measure the velocities of blood or structures. Doppler ultrasonic examinations provide a safe non-invasive means for the measurement of cardiovascular function which previously required the use of much more hazardous techniques including catheterization.

Since the early 1980s there has been a rapid introduction of the medical application of Nuclear Magnetic Resonance (NMR). The physical phenomenon was first described in 1946, and was able to determine the concentrations of certain chemicals in samples. In the application in medicine it is able to provide three dimensional discrimination of the positions of concentrations of the nuclei of atoms which have characteristic spins: in particular the location of hydrogen nuclei may be recognized. The information obtained by NMR is called Magnetic Resonance Imaging, or MRI, in its medical application. The images provide an excellent resolution and discrimination between many corporeal structures. They are obtained without known deleterious effects in most cases, although the equipment required to obtain MRI images costs significantly more than that required for other image acquisition mechanisms, known as modalities.

The development of electronics, and particularly that of computers has made possible many of the technologies which we shall examine.

Firstly, computers are the central elements involved in processing signals in many cases, and particularly those obtained from images. The special nature of the processing required to obtain the image improvements required and the consequential flexibility in their application mean that the complexity of the algorithms for processing would be excessive unless software was used for managing the process. Medical image processing frequently requires that different views may need to be synthesized in the examination of a condition relating to each particular patient. The exact form of the views may be difficult to predict, so computers provide the ideal platform for their analysis.

Secondly the increasing use of computers in medical applications has led to an ever increasing capability to retain medical data. This may be used to facilitate health care planning and to provide for a reliable storage of patient related data which may be readily recovered. They also provide the ability to communicate data using standardized mechanisms which we may expect will increasingly allow data to be acquired in one location and viewed at another.

Finally computers have potential for providing us with systems which mimic the diagnostic processes employed by physicians. Pilot systems which can provide some diagnostic assistance have been tried for a number of years in certain areas both within and outside medicine.

They are particularly prevalent in manufacturing industry where they may be employed to assist in the design process and to control the flow of goods through factories. Clearly such systems are limited in their scope by the complexity of their programming. We should also not forget that humans undertake certain tasks particularly well, such as pattern recognition of faces as a result of possibly innate training.

We should end this overview of the application of technology to medicine by considering two things.

1. When we contemplate applying a technological solution to a problem, will it benefit the patient? The benefit may either be direct in terms of an immediate improvement in the patient's condition, or one which facilitates action as a result of time saving. A computer may, in some circumstances, undertake a task either much more quickly, or more reliably than a human. On the other hand, there are many cases when the computer's instructions have not been formulated in a manner which enable it to handle the task at all.

2. Will the application provide a global benefit, or is it likely to result in some other detrimental effect? In cases where technology is used without considering all its effects, it frequently transpires that the task could have been undertaken more simply. Much more seriously, the problem may be reflected by placing excessive reliance on a technological solution in an inappropriate manner. We must be particularly confident when we hand a safety critical task to a machine that we retain a sufficient view and knowledge of the problem in order to take appropriate action should unforeseen circumstances arise. In other words we should not always be excessively comforted by the reliability of the apparatus to lull us into a false sense of security.