Roentgen diagnosis and therapy

Front matter

NLM OS2311ee 4

NATIONAL LIBRARY OF MEDICINE

SURGEON GENERAL’S OFFICE

Preface

Tuts book is a revision and enlargement of the author’s Manual of X-ray Technic. Its object is to furnish to the student and practitioner a concise account of the essentials for the practice of roentgenology. The author’s experience as a teacher, both of graduate and undergraduate students, has led him to believe that there is need in this country for such a book. The aim throughout has been to furnish a practical guide, and for that reason theoretical considerations have been for the most part omitted. A special effort has been made to present the facts so simply and in such order that the beginner will find it easy to acquire a knowledge of the essentials of roentgen technic, diagnosis and therapy.

The student of roentgenology must recognize the fact that he is dealing first with an art and that he can hope for success only by perfecting himself in the technic of that art. Good technical work is the very foundation of success in the practice of roentgenology. In addition to this, however, he must realize that this is a special branch of medical science whose data must be interpreted in the light of a broad general knowledge of medicine. He cannot place too great emphasis upon the importance of correlating all the information received through his roentgenological examination with the history, clinical course, and physical signs. This vi PREFACE necessitates not only broad medical training and experience but also a disposition on his part to codperate to the fullest possible extent with his medical colleagues.

Although we have drawn freely upon the general literature of the subject, for the sake of simplicity specific references are given only when further reading is considered essential to a complete understanding of the matter under discussion.

I wish to acknowledge with grateful thanks the assistance of Dr. Fred O. Coe in the preparation of the chapters on Technic and of my _ colleague, Dr. Thomas A. Groover, who has written the section on

Therapy.

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Contents

V. APPARATUS AND Equipment. Hicu TENSION TRANSFORMERS eM AUWAMRWOR. oo oo ceeds eee eee 85

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XI. Tue Cuest, Diseases or tHE Lunes, Heart AND GREAT VESSELS,

Chapter I Electricity And Magnetism

NATURE AND PROPERTIES.—The nature of electricity is known only by its effects. The word is derived from the Greek elektron, meaning amber, in which substance Thales, about 600 B. C. first noticed some of the phenomena of electricity. The word “electrics” was first applied by Dr. Gilbert about the year 1600 A. D. to certain substances like amber, sealing wax, ete., which become electrified by friction.

Electricity may be either static or dynamic.

Static electricity is electricity at rest; it is produced by some form of friction or “‘influence’’ machine.

Dynamic electricity may be faradic or galvanic.

Faradic electricity, named from Michael Faraday, is a derived (induced) form of electricity, in which there are rapid alternations of direction.

Galvanic electricity is that produced by the galvanic cell, which, in its simplest form, consists of a jar of dilute sulphuric acid in which are dipped a plate of zine and one of copper (Fig. 1).

According to the theory of Arrhenius the affinity of the zine for the acid radical SO, starts a chemical reac- 1 tion which results in the determination of positive ions toward the copper and of negative ions, called electrons, toward the zinc. In consequence of this ionic movement an electrical current is produced from the zine to the copper through the liquid, and outside of the cell from the copper to the zine through a connecting wire. LHlectric generators serve the same ultimate purpose as the galvanie cell, that is, to separatenegative from positive ions and to cause them to travel in opposite directions. The idea of the electrical constitution of theatom is now accepted.

The atom is made up of positive and negative particles which may exist by themselves. The negative particles have received various names, among which are cathode rays, corpuscles, beta rays, electric ions and electrons.

DIRECT CURRENT.—Galvanic cells, storage batteries, static machines and direct current dynamos produce a current whose flow is in only one direction. Such a current is called a direct current, even though it may be intermittent or pulsating.

Fia. 1.—The galvanic cell.

ELECTRICITY AND MAGNETISM 3

ALTERNATING CURRENT.—When the current flows for a short time in one direction and then for an equal length of time in the opposite direction, it is called alternating. There is a rise from zero to a maximum and then a fall again to zero when the current immediately flows in the opposite direction and again reaches zero, when the cycle is complete. A current which has 60 such cycles or 120 alternations per second is called a 60 cycle current. Practically the only source of alternating currents are a—c. dynamos.

DEFINITIONS OF ELECTRICAL TERMS.—The ohm is the unit of electrical resistance and is represented by the resistance of a column of mercury 106.3 em. long and 14.4521 gm. in mass at 0° C.

The ampere is the unit of current strength and is that current which deposits silver at the rate of 0.001118 gm. per second. One milliampere equals 1/1000 ampere.

The volt is the unit of electrical pressure or electromotive force; it is that electromotive force which applied toone ohm produces one ampere. A _ kilovolt equals 1000 amperes.

The coulomb is the unit of quantity, being the quantity of electricity conveyed by one ampere in one second.

The watt is the unit of power. One ampere with a pressure of one volt produces one watt. One kilowatt equals 1000 watts.

These terms are analogous to certain hydraulic terms. The voltage or electromotive force corresponds to the head or pressure of water. Electrical resistance, the unit of which is the ohm, is analogous to the frictional resistance to the flow of water in a pipe. The current strength, whose unit is the ampere, is represented by the rate of flow of the water through the pipe. The quantity of electricity per second (coulomb) corresponds to the amount of water delivered per second. In other words, if an electromotive force of one volt is working against a resistance of one ohm it produces a current of one ampere; which, flowing for one second, produces a coulomb of electricity.

OHM’S LAW.—Current strength in amperes is equal to the electromotive force in volts divided by the resistance in ohms. If C represents the current strength, E the electromotive force and R the resistance, then

It is evident from this that the current strength varies directly as the electromotive force and inversely as the resistance.

KINDS OF ELECTRIFICATION.—Electrification may be manifested by repulsion as well as by attraction, and is of two kinds, opposite in character, called positive and negative. Bodies similarly electrified repel each other and those oppositely electrified attract each other.

CONDUCTION.—Electrification by conduction is the process of charging a body by putting it in contact with an electrified body. The charge thus produced is of the same kind as that of the communicating body.

INDUCTION.—This is the process of electrifying a body by bringing it near to, but not in contact with, an electrified body. The charge thus produced is of the

ELECTRICITY AND MAGNETISM 5 opposite kind to that of the communicating body. A current of electricity in one of two wires placed near each other produces no effect in the second wire so long as the current flows steadily, but whenever the current is increased or decreased in strength a current is “‘induced” in the second wire. This current in the second wire depends upon the presence of a “field of force”’ which surrounds every electrically charged body. At the instant when the primary current begins or increases in strength a weak current in the opposite direction is generated in the secondary wire; at the instant when the primary current stops or decreases in strength a

strong current in the same direction is generated in the secondary.

MAGNETISM.—Magnetism is the property by virtue of which a body attracts iron or steel, and which causes the iron or steel when suspended to take a position pointing approximately north and south.

A magnet may be a natural one, as lodestone, or an artificial one. Artificial magnets are either permanent or temporary.

The ends of a magnet are called the poles. The end which points to the north when the magnet is freely suspended is the north, marked, or + pole; while that which points to the south is the south, unmarked, or — pole.

MAGNETIC FIELD.—When a bar magnet is placed beneath a sheet of paper on which are some iron filings, the filings will arrange themselves in lines radiating from each pole of the magnet as shown in Figure 2. The area surrounding any magnetic body is called a magnetic field; it is the space through which the magnetic force acts. The lines of force are supposed to flow from the north to the south pole outside of the magnet and in the opposite direction inside, making a complete circuit. ELECTROMAGNETISM.—It can be shown experimentally that an electric current has magnetic prop-

Fic. 2.—Action of bar magnet on iron filings.

erties; it will deflect the magnetic needle and will cause iron filings to arrange themselves as they do when placed in the field of a magnet.

A coil of wire through which a current is passing is called a solenoid and has all the properties of a magnet (Fig. 3). An electromagnet is a bar of iron magnetized by an electric current passing through a coil of wire surrounding it (Fig. 4).

The strength of an electromagnet is directly proportional to the strength of the current passing through the wire surrounding it, and to the number of turns of the wire. Since electric currents may be made very strong and since we may use as many turns of wire as desired, it becomes possible to make electromagnets of enormous strength.

ELECTRICITY AND MAGNETISM 7

Just as a current may be induced in one of two wires lying near each other by increasing or decreasing the strength of the current in the other wire, in the same ad

Fia. 3.—Solenoid. Fia. 4.—Electromagnet,

_ manner a current may be induced in a coil of wire surrounding an electromagnet but insulated from it. Upon this fact depends the action of induction coils, transformers, and motor generators, all of which are used in a-ray work.

Chapter II The Roentgen Ray. History And Properties

HISTORY.—The first vacuum tubes were made by Geissler about the year 1858. The passage of an electric current through these tubes, which were of low vacuum, caused a faint glow, varying in intensity with the degree of vacuum. Hittorf discovered about 1860 that the stream of discharge in a Geissler tube could be deflected by a magnet. It was in 1879 that Sir William Crookes, experimenting with tubes of very high vacuum, discovered the cathode rays. The glow which is present in the tubes of low vacuum has disappeared in these high-vacuum tubes and is replaced by a greenish fluorescence of the walls of the tube. To this form of ‘radiant energy’’ Crookes gave the name cathode rays.

The study of the discharge in high-vacuum tubes was continued by many investigators, prominent among whom were Professor Hertz and his assistant Professor Lenard. In 1894 Lenard proved that the rays produced in high-vacuum tubes caused phenomena outside of the tube. Experimenting with a tube having a sheet of aluminum in the end opposite to the cathode he observed that radiation passed through the aluminum and caused fluorescence in such substances as platinobarium cyanide. The next year, 1895, Professor William Conrad Roentgen at Wiirzburg, was experimenting with a high-vacuum tube covered with black paper 8

THE ROENTGEN RAY 9 impervious to ordinary light. He noticed that a nearby paper covered with platinobarium cyanide fluoresced brilliantly while the tube was in action. Roentgen realized that this phenomenon must be caused by some hitherto unrecognized force, differing essentially from the cathode rays. Continuing his experiments Roentgen found that he could obtain shadow pictures on photographic plates of metallic objects in a box which was impervious to light, and also of the bones of the hand. He soon made his discovery public and it was only a short time until the use of the rays became general for diagnosis, and not long until valuable therapeutic effects also were observed.

ELECTRONS.—It is now known that the so-called cathode rays are streams of electrified particles which are shot off from the cathode when a high voltage current is passed through a tube of high vacuum. They are simply electrons which have been freed from their atoms and set in motion. They have the following properties: (1) They travel at very high speed, which varies somewhat with the voltage applied to the tube but which is approximately 60,000 miles a second; (2) they travel in straight lines; (3) they have a constant and fixed negative electric charge which they never lose; (4) they have a definite mass which they never lose; (5) they can be deflected from their course by a magnet or by an electric field; (6) they cause fluorescence of certain substances, notably the glass of the vacuum tube in which they are formed.

RELATION OF ELECTRONS TO ROENTGEN RAYS.—In a perfect vacuum no current can pass.

Electrons must be present in the tube to carry the current across the vacuum. In “gas”’ tubes electrons are furnished by the breaking down of the atoms of the gas, and in Coolidge tubes by liberating them from the metal of the cathode by heating the latter. The mere presence of electrons in the tube is not sufficient, however, to produce X-rays. It is necessary that they be put in rapid motion. This is accomplished by the force of the high tension current applied to the tube.

Whenever electrons travelling at high speed in a vacuum tube are suddenly stopped, roentgen rays or X-rays are produced. The two latter terms are synonymous. The sudden stopping of motion is accomplished in modern roentgen tubes by placing a metal target in such a position that the stream of electrons will strike upon it. The roentgen rays are produced at the point of impact and are of an entirely different nature from the cathode rays which produce them. Roentgen rays are analogous to light rays and have the following properties: (1) They are not deflected by a magnet; (2) they are invisible, but cause fluorescence and phosphorescence of certain substances; (3) they affect photographic emulsions like ordinary light; (4) they travel in straight lines, that is, they cannot be reflected or refracted, if we except the slight reflection that takes place when the roentgen ray is passed through crystals; (5) they pass through all known substances with varying degrees of intensity; (6) they cause gases to become conductors of electricity, or in other words they cause the ionization of gases; (7) they have marked effects on living tissue.

THE ROENTGEN RAY 11

Wave-length of the Roentgen Ray.—It is now known that roentgen rays are identical in their nature with light except that the wave-lengths of the former are much shorter than those of the latter. The roentgen rays, in fact, occupy a place in a continuous spectrum of electro-magnetic waves, at one end of which are the Hertzian waves, which vary in wave-length from a few millimeters to 25,000 meters, and at the other end the gamma rays of radium which are the shortest waves known. The spectrum is continuous from the Hertzian waves through the infra-red rays, the visible light rays, the ultra-violet rays, and the roentgen rays, to the gamma rays of radium. The roentgen-ray beam, however, is not made up of rays which are all of the same wave-length, some are much shorter than others. The passage of the rays through any substance is directly proportional to the shortness of the wave-length, that is, the shorter the wave-length the more readily they pass through matter. Short wave-lengths are produced only by applying high voltage to the roentgen-ray tube. The higher the voltage, the shorter the wave-length and consequently the greater the penetration of the ray. In passing through matter three things happen to the roentgen beam—some are scattered, some are absorbed and some pass through. Some of the waves are scattered as light is scattered in passing through fog. This scattering renders the shadows made on the photographie plate less distinct than they would be otherwise. The Potter-Bucky diaphragm which will be described in another chapter has been devised to eliminate the evil results of scattering upon the roentgen picture and the screen image. Some of the waves are absorbed in their passage through matter, the degree of absorption being directly proportional to the density of the material. The remainder of the beam that is neither scattered nor absorbed passes straight through.

The factors necessary for the production of roentgen rays are (1) Some means of obtaining a supply of electrons in a suitable vacuum; (2) a current applied to the roentgen tube of sufficiently high voltage to give the electrons high speed; (3) some means _ of suddenly stopping the stream of electrons.

The apparatus essential for the accomplishment of these results consists of suitable vacuum tubes and of apparatus for the production of electric currents of high voltage.

Chapter III

Tuer earliest forms of vacuum tubes were the Geissler tubes. These are of low vacuum and transmit electric currents more readily than air. During such passage the tube lights up with a soft

luminous glow. As the tube is _ still further exhausted the current passes with difficulty and the increasing luminous glow is replaced by a greenish fluorescence of the walls of the tube.

When it reaches this degree of vacuum it isknownasa Crookes tube and in it are produced the cathode rays.

The first roentgen-ray tubes were somewhat conical in shape, es the cathode, which was a flat disc, being placed in the small end (Fig. 5). The cathode rays were thus thrown upon the opposite end of the tube, the anode being ring-shaped so as not to obstruct the passage of the rays.

A great advance was made when Herbert Jackson devised a tube with a metallic target fixed within it, at or near the focus point of the cathode stream (Fig. 6). This ‘“‘focus”’ tube has undergone many modifications, the most important of which was the addition of an accessory anode and of a device to regulate the vacuum. 13

A late model roentgen tube is one in which the air has been exhausted by means of mercury pumps to about one-millionth of an atmosphere. The essential parts of the tube are the cathode, the anti-cathode or target, the accessory anode, and some device to regulate the vacuum (Fig. 7).

The cathode of a focus tube is made of aluminum, because this metal does not suffer disintegration with

Fic. 6.—Jackson’s focus tube.

consequent discoloration of the walls of the tube. The concave form of the cathode causes the cathode rays to be focused upon a point on the target, or anti-cathode, called the focus spot.

In modern tubes the target is an anode of the tube, but it is not necessarily so. Since a high degree of heat is generated at the focus spot the target must be made of a metal which has a high melting point. If the metal is heated to such a degree that it melts the face of the target, the area about the focus spot soon becomes a deep crater; and if the heat is still higher, the metal vaporizes and is deposited upon the walls of the tube. Either of these occurrences interferes with the efficiency of the tube. Formerly platinum, which has a melting point of 1750° C., was generally used; but even platinum is not infusible and often melts under the intense heat generated. Iridium and osmium have been used to some extent but tungsten, with a fusing point of 3300° C., has now replaced all other metals. The tungsten disc is set in a solid block of copper which is a good con-

Fig. 7—Modern type of roentgen-ray or focus tube. 1, cathode; 2, target; 3, accessory anode; 4, vacuum regulator; 5, adjustable wire; 6, X-ray hemisphere.

ductor of heat and as an additional precaution against fusing, the target is placed at a point just beyond the mathematical focus of the electronic stream. Water-cooled tubes are also used successfully. In such tubes water flows through the hollow anti-cathode and comes into direct contact with the target. Another means of cooling the target is by the use of a metal radiator attached to the anti-cathode, outside of the tube. The radiator type of Coolidge tube, to be described later, makes use of this method. The amount of heat generated at the focus point on the target also depends somewhat upon the size of the focus point.

In a “fine-focus”’ tube, that is, one in which the cathode stream is focused on a very small area, fusing takes place with the application of less energy than is the case with a tube of medium or broad focus. In the latter cases the heat is spread over a larger area.

The accessory anode is made of aluminum. It is connected to the anti-cathode by a wire outside of the tube. Tubes furnished with an accessory anode do not seem to increase in resistance so rapidly as do those of older models.

REGULATING THE VACUUM IN THE ROENT- GEN TUBE.—The tendency of the roentgen tube to increase in resistance, that is, to become higher in vacuum, making it increasingly difficult for the current to pass through it, has caused the introduction of many contrivances for lowering the vacuum when it has become too high. One of these was the osmo-regulator of Villard, now obsolete. It consisted of a platinum pin sealed into the tube with one end projecting outside. Heating the projecting end with a flame caused the platinum to become porous and to absorb hydrogen, thus lowering the vacuum of the tube. The same principle was made use of in the palladium tube in which palladium was used instead of platinum.

Baking a tube in an oven at 200° to 300° F. for several hours will also lower the vacuum.

In 1896 Queen’s self-regulating tube came into use (Fig. 8). This tube had a relatively large accessory bulb B in which was sealed a smaller bulb 6, the latter containing some chemical such as potassium chlorate. The smaller bulb connected directly with the main bulb.

When the vacuum in the main bulb was too high the current could no longer pass directly through the tube but sparked across the path of less resistance from the cathode C to the end of the adjustable wire W, causing the potassium chlorate in the small bulb to become heated. The vapor given off into the tube from the potassium chlorate lowered the vacuum in the main

Fig. 8.—Queen’s self-regulating tube.

bulb until the current could pass directly through, when the sparking from the cathode to the adjustable wire ceased.

The regulating device most largely used at present is one in which the accessory tube connects directly with the main bulb (Fig. 7). Asbestos is the substance ordinarily used instead of thie chemical of the old Queen’s tube. When the current sparks across from the cathode to the adjustable wire, air is forced out of the interstices of the asbestos and the vacuum consequently iowered. Instead of using the adjustable wire on the tube the regulating device may be connected by a third wire to an adjustable spark-gap on the coil or transformer. This is the most convenient method since it enables the operator to regulate the vacuum from a distance.

When new tubes are ordered it is necessary to specify whether they are to be used with a coil or a transformer, since tubes pumped for use with a coil are of too high vacuum for use with a transformer.

When a new tube is received it is usually found to be of relatively low vacuum, but after being used a few times it reaches its point of maximum usefulness. The vacuum then seems to remain about stationary for some time and then gradually increases until it reaches a point where it must be lowered every time it is used. Finally the vacuum becomes so high that it can no longer be lowered sufficiently to allow the current to pass.

Directions for Regulating the Vacuum.—lIf the current cannot pass through the tube on account of the high vacuum it sparks across between the positive and negative terminals of the coil or transformer. An adjustable spark-gap is provided so that the operator may measure the length of the spark. The length of spark that a tube will “back up” is a measure of the resistance of that tube.

If the tube is too high to allow the current to pass when the latter is at its full strength, the end of the adjustable wire should be placed at a distance of about two inches from the cathode (never touching it) and the weakest current possible allowed to spark across to the regulator. The wire is then moved to a distance of five or six inches from the cathode and the current turned on to its full strength. This process is repeated until the tube lights up properly and there is no sparking at the parallel spark-gap. The same method is followed when the adjustable regulating spark-gap on the apparatus is used instead of the adjustable wire on the tube. Great care must be exercised in this matter of lowering the vacuum of a tube for it is exceedingly easy to lower it to such an extent as to render it valueless until it is repumped. If a strong current is used for regulating, it will cause a thick yellow spark to jump across and probably destroy the vacuum.

To increase the vacuum of a tube a weak current may be run through it in a reverse direction for several times. If this is done every day for considerable time the tube becomes higher. A tube will also increase in resistance by constant use. The best and quickest way, however, to increase the vacuum of a tube which is soft is to send it back to the manufacturer to be repumped.

A roentgen tube is said to be soft when the vacuum is low, and hard when it is high. The penetrative power of the roentgen rays increases with the degree of vacuum and with the strength of the current.

When working well the tube shows a well-marked hemisphere of greenish fluorescence in front of the target, while the part of the tube behind the target is dark.

THE COOLIDGE TUBE (Fig. 9).—This tube was invented by Dr. W. D. Coolidge, of Schenectady, N. Y., and constitutes a remarkable advance in roentgen apparatus. It differs fundamentally from the older type of tubes. In the latter the stream of electrons is produced by the bombardment of the cathode with positive ions which are produced by the passage of the electric current through the gas contained in the tube. The Coolidge tube is pumped to a much higher degree of vacuum than the gas tubes, so high in fact that no current will pass through it unless the cathode is heated. The electrons constituting the cathode stream are thrown out by the heated cathode instead of being pro-

Fig. 9.—The Coolidge tube.

duced by bombardment of the cathode with positive ions. In order to secure a pure electron discharge from the heated cathode it is, of course, necessary to completely exhaust the tube itself and also to entirely free the electrodes from gas. It was known that the rate of emission of electrons from a hot cathode in very high vacuum increases as the temperature of the cathode rises.

The Coolidge tube differs from the ordinary tube in the following particulars:

(1) The vacuum is as high as it is possible to make it.

(2) The cathode consists of a cylindrical tube of molybdenum, 6.3 mm. inside diameter. This is supported on two molybdenum wires which are sealed into the end of the glass tube. This molybdenum ring acts as a focusing device. Inside of the ring is a closely wound spiral of very fine tungsten filament mounted so as to be concentric with the ring. The spiral is welded to two wires which pass out at the negative end of the tube. Through these two wires passes a low voltage current which serves to heat the tungsten filament, the degree to which it is heated being controlled by an adjustable rheostat. The source of the current for heating the filament may be a small storage battery, or the 110 V. alternating current reduced to the proper voltage by a suitable transformer. When only the direct current is available a small motor generator is necessary in addition to the transformer. Whether a storage battery or transformer is used it must be insulated from the ground, since it is connected with the high potential current.

(3) The target, instead of being a platinum- or tungsten-faced copper block, is a solid block of tungsten. The target functions as anode, and there is no accessory anode.

Radiator Type of Coolidge Tube (Fig. 10).—The ordinary form of Coolidge tube, described above, requires a unidirectional current, since the target must always be the positive and the cathode the negative terminal of the tube. If the alternating current were applied to the tube without rendering it unidirectional (rectification) the target would be the negative end of the tube during every other alternation. While the target is thus acting as the cathode, electrons are formed upon it and are shot off to form roentgen rays in other parts of the tube, greatly interfering with its efficiency. A rectifying apparatus operated by a motor must therefore be used to render the current unidirectional when the ordinary form of Coolidge tube is used. It will be remembered,