A manual of x-ray technic

Preface

This short manual on the technic of X-ray examination has been prepared with a view to the needs of the medical service of the United States Army. The small number of medical officers in the service necessitates frequent change of station, so that it often becomes necessary for one to familiarize himself in a comparatively short time with the essentials of radiologic technic. With this in mind it has been the author's aim to limit this work to the absolute essentials, a knowledge of which will enable the operator to do satisfactory work in X-ray diagnosis.

The book may also be found useful by that increasingly large number of physicians and surgeons in private practice who find it necessary or expedient to do their own X-ray work for diagnosis. Resort to a specialist in radiology is earnestly reconmiended -^-^ whenever such services can be obtained, but in the ^ smaller cities and towns this is often impossible. It I is believed that mastery of the facts contained in this ^ manual will enable those so situated to do satisfactory ^ radiography.

^ In the preparation of this book many of the larger ^ text-books and many monographs have been freely ^ drawn upon. It has not been deemed necessary, howv^ iii iv PREFACE

ever, to give an extensive bibliography, for the publications in the entire field of radiology, from the time of the discovery of the X-ray up to the present, are covered in that excellent work, " Die Rontgen- Literatur," by Prof. Dr. Hermann Gocht.

Only a few reproductions of radiograms are published as illustrations to the text because it is believed that ability to interpret radiograms can be gained only by experience with the originals.

Every X-ray operator is urged to make himself thoroughly familiar with the details of construction of the particular apparatus with which he is working. He is then in position to keep it constantly at its point of maximum efficiency. With his apparatus in good condition he can then gradually master the small details so essential to good X-ray work, and with practice in examining radiograms he will finally acquire ability to properly interpret them and so to arrive at correct diagnoses.

A. C. Christie.

Washington, D. C, October, 1913.

Contents

CHAPTEB PAGE

I. Electricity and Magnetism 1

II. The X-ray. History and Properties 10

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, etc., which become electrified by friction. The phenomena of electricity are supposed to be due to some stress or strain in the ether.

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 galvanic or faradic.

Faradic electricity is a derived (induced) form of electricity, so named from Michael Faraday, 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 zinc and one of copper (Fig. 1).

According to the theory of Arrhenius the affinity of the zinc for the acid radical SO4 starts a chemical

Fig. 1. — The galvanic cell.

reaction which results in the determination of positive ions toward the copper and of negative ions toward the zinc. In consequence of this ionic movement an electrical current is produced from the zinc to the copper through the liquid, and outside of the cell from the copper to the zinc through a connecting wire.

Polarization of a galvanic cell takes place by the collection of bubbles of hydrogen gas on the copper plate and interferes with or stops the action of the cell. Various devices have been used to prevent this.

Types of Cells. — There are many different types of cells, but only two will be described here.

The Daniell cell consists of a zinc plate immersed in dilute sulphuric acid contained in a porous vessel, outside of which is a perforated copper plate surrounded by a solution of copper sulphate. The hydrogen is taken up by the sulphate before it reaches the copper plate. This cell is very constant because polarization is entirely prevented.

The potassium bichromate cell consists of zinc and carbon plates immersed in a solution of potassium bichromate in dilute sulphuric acid. The action of the sulphuric acid on the bichromate liberates chromic acid, which oxidizes the hydrogen to form water and thus prevents polarization.

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 cm. 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.

The volt is the unit of electrical pressure or electro-motive force; it is that electro-motive force which applied to one ohm produces one ampere.

The coulomh 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.

These terms are analogous to certain hydraulic terms. The voltage or electro-motive 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 electro-motive 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 electro-motive force in volts divided by the resistance of ohms.

C=^OTE=CxRorR = ~

Methods of Grouping Galvanic Cells. — Cells may be grouped in series or in parallel. They are grouped in series (Fig. 2) when the positive pole of one is connected to the negative of the next, and so on. The grouping is in parallel or multiple arc (Fig. 3)

Fig. 2. — Cells grouped in series.

when all of the positive poles are connected together on one side and all of the negatives on the other.

By connecting cells in series a relatively high voltage may be obtained. The E. M. F. is made to

Fig. 3. — Cells grouped in parallel.

equal the E. M. F. of each cell multiplied by the number of cells. With n cells grouped in this manner we have the following adaptation of Ohm's law:

R being the external and r the internal resistance. From this it is evident that when the external resistance is great, grouping cells in series will give a greater current than parallel grouping.

By connecting cells in parallel the E. M. F. remains that of only one cell, while the resistance becomes that of one cell divided by the number of cells. The amperage is thus increased and becomes the amperage of one cell multiplied by the number of cells. The formula for Ohm's law now becomes n

This method of grouping would therefore give the best results when the external resistance is small.

Kinds of Electrification. — Electrification may be manifested by repulsion as well as by attraction, and is of two kinds, opposite in character. The electrification developed by rubbing glass with silk is called positive, and that developed by rubbing sealing wax with flannel is called 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 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 Fig. 4. 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.

Fio. 4. — Action of bar magnet on iron filings.

Electro-magnetism. — It can be shown experimentally that an electric current has magnetic properties ; 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. 5) . An electro-magnet is a bar of iron magnetized by an electric current passing through a coil of wire surrounding it (Fig. 6).

The strength of an electro-magnet 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 electro-magnets of enormous strength.

Fig. 6. — Electro-magnet.

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

Chapter II

The X-ray. History and Properties.

History. — The first vacuum tubes were made by G^issler 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 of 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 cathode rays caused phenomena outside of the tube, for experimenting with a tube having a sheet of aluminum in the end opposite to the cathode he observed that the radiation which passed through the aluminum could cause fluorescence in such substances

THE X-RAY. HISTORY AND PROPERTIES 11

as platino-barium cyanide. The next year, 1895, Prof. William Conrad Rontgen, at Wiirzburg, was experimenting with a high vacuum tube covered with black paper impervious to ordinary light. He noticed that a near-by paper covered with platinobarium cyanide fluoresced brilliantly while the tube was in action. Rontgen realized that this phenomenon must be caused by some hitherto unrecognized force, differing essentially from the cathode rays. Continuing his experiments Rontgen 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 were also observed.

The Cathode Rays. — These rays are formed at the cathode of high vacuum tubes and are believed to be streams of electrified molecules shot off from the cathode. They have the following properties: (1) they can be deflected by a magnet; (2) they cause fluorescence and phosphorescence of certain substances; (3) they affect photographic plates like ordinary light; (4) they have no known effect on the bodily tissues.

The Relation of the Cathode Rays to X-rays. — The X-ray is formed at the point of impact of the cathode ray upon any solid object.

X-rays themselves are believed to be due to some disturbance in the ether and to be true rays. They 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 aff*ect photographic plates like ordinary light ; { 4 ) they travel in straight lines, — cannot be reflected or refracted; (5) they will pass through all known substances with varying degrees of intensity; (6) they cause the air to become a conductor and consequently cause the discharge of electrically charged bodies; (7) they have marked efl'ects on the bodily tissues.

CHAPTER III. Apparatus for the Production of X-rays

The apparatus necessary for the production of Xrays consists of suitable vacuum tubes, and of some form of installation for the production of suitable currents (static machine, induction coil, or transformer).

VACUUM TUBES.

The eai-liest 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 greater difficulty and the luminous glow is replaced by a greenish fluorescence of the walls of the tube. When it reaches this degree of vacuum it is known as a Crookes tube and in it are produced the cathode rays. These in turn give rise to the X-ray wherever they strike any solid object.

The first X-ray tubes were somewhat conical in shape, the cathode, which was a flat disc, being placed in the small end (Fig. 7). 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.

IS

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. 8) . This " focus " tube has undergone many modifications, among which the most important were the addition of an accessory anode, and of a device to regulate the vacuum.

A late model X-ray tube is one in which the air

Fia. 7. — Early type of X-ray tube.

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. 9 ) .

The cathode of a focus tube is made of aluminum, because this metal does not suiFer disintegration with consequent discoloration of the walls of the tube. The concave form of the cathode causes the cathode rays to be focussed upon a point on the target, or anti-cathode, as it is called.

Fig. 8. — Jackson's foous tube.

As tubes are now constructed, the target is always an anode of the tube, but it is not necessarily so. The target is usually made of platinum, because the intense

Fig. 9. — Modern type of X-ray or focus tube. 1, cathode; 2, target; 3, accessory anode; 4, vacuum regulator; 5, adjustable wire; 6, X-ray hemisphere.

heat generated at the point of impact of the cathode stream requires a metal whose fusing point is very high. Even platinum is not entirely infusible and often melts under the intense heat generated. Iridium and osmium have been used to some extent, and tubes are now being made with tungsten targets. The latter bids fair to entirely replace platinum for this purpose. The target is usually surrounded by a heavy block of some metal, such as copper, which is a good conductor of heat. As an additional precaution against fusing, the target is often placed at a point just beyond the mathematical focus of the tube. Water-cooled tubes, in which a colunm of water is sealed in a tube surrounding the anti-cathode, or allowed to flow through it, are also used to prevent fusing of the target. If certain defects, such as the danger of breakage, could be overcome in these tubes they would be ideal for Xray work. The target is placed obliquely to the axis of all X-ray tubes so that the greater part of the Xrays are thrown out at one side.

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 increase in resistance so rapidly as do those of older models.

Regulatestg the Vacuum in the Focus Tube. — The tendency of the X-ray tube to increase in resistance, 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 osmoregulator of Villard. 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.

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

Fio. 10. — Queen's self-regulating tube.

In 1896 Queen's self -regulating tube came into use (Fig. 10) . This tube had a relatively large accessory bulb B in which was sealed a smaller bulb h, 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 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. 9). Asbestos is the substance usually used instead of the chemical of the old Queen 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 lowered. 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. — ^If 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 " backup " 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 re-pumped. 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.

An X-ray tube is said to be soft when the vacuum is low and hard when it is high. The penetrative power of the 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.

Secondary Rays or Sagnac Rays. — These are rays given off when the X-ray strikes an object, as parts of the apparatus or tissues of the body. They pass in all directions and may blur the radiogram; they may even pass through the plate in the wrong direction.

Indirect Rays. — These are rays formed at the extremities of the arc and are useless for radiography.

The useful rays are those which come off at right angles from the target. The use of a diaphragm with a circular aperture eliminates most of the indirect rays, and also much of the secondary radiation.

Means of Determining the Intensity or Penetrative Power of the X-rays. — ( 1 ) Appearance of the Tube: In a tube of low vacuum the greenish fluorescence is soft and somewhat yellowish and the tube is not so distinctly divided into hemispheres. There is also a bluish color just in front of the cathode, and if the vacuum is very low a blue line may be seen extending from the cathode to the target. In the tube of high vacuum the fluorescence is of a bright green color and the tube is divided into two distinct hemispheres. (2) Fluoroscopy ■' Using the fluoroscope and some object such as a skeleton hand as an indicator. It is very dangerous for the operator to use his own hand because of the liability to X-ray dermatitis and its sequels. (3) The Spark Gap: The length of the spark that a tube " backs up " varies with the strength of the current as well as with the resistance of the tube, but if taken in conjunction with the reading of the milliamperemeter it is a good indication of the penetrative power. (4) The milliammeter: The reading of the milliammeter also varies with the strength of current and resistance of tube. It must be remembered that a high reading does not necessarily mean a tube of high penetration. Indeed it more often means just the opposite. The lower the tube the greater the amount of current that can pass through and consequently the higher the reading of the milliammeter. But if the tube gives a spark of four and a half to six inches in length, and at the same time the milliammeter has a high reading, then the degree of penetration is great. (5) The radiochromometer of Benoist: The construction of this instrument is based upon the fact that different metals vary in their penetrability to the X-ray. A silver disk 0.11 mm. in thickness placed in the centre of the device is used as the standard of comparison. Round this centre are placed layers of aluminum of varying thickness. The diaphragm is rotated until the tint of the sector corresponds to that of the centre, when it is read off, as No. 1, 2, 3, 4, etc., Benoist.

For radiographic work the length of the spark gap and the reading of the milliammeter taken together probably afford the most practical and best method of determining the degree of penetration.

Care of the X-ray Tube. — It is necessary to take certain precautions in using focus tubes in order to keep them at the point of maximum usefulness for the longest possible time. In cold weather the tube should be warmed before use. When hot it should not be allowed to cool off too suddenly. The lead wires ought not to come in contact with the tube when in action, since a spark may jump across to the glass and cause puncture. Keep tubes perfectly clean; a small particle of dust may attract the current and cause puncture. New tubes are likely to be rather unstable in vacuum and should be used cautiously with weak currents, and with very short exposures with strong currents, until they become seasoned. Avoid overheating the tube by too long or too frequent use. The place of greatest heating is around the cathode, and it is here that the greatest number of punctures occur.

Means of Determining the Positive and Negative Terminals. — In order to connect the Xray tube properly it is necessary to know which is the positive and which the negative terminal of the apparatus from which the current is being taken. This may be determined in the following ways: (1) On the induction coil or transformer the left hand side is usually the positive pole; (2) if both poles are immersed in water, bubbles arise from the negative; (3) the negative pole ionizes a solution of potassium iodide, turning the solution red around this pole by liberating free iodine; (4) the spark at the negative pole is thick and white, while that at the positive is thin and wiry; (5) when the tube is properly connected, the anode to the positive terminal and the cathode to the negative, the tube lights up in the normal manner with well-marked hemispheres, while if the current is passing through in the opposite direction rings of light are seen extending around the tube in many different directions.

Chapter IV

Apparatus for Exciting the X-ray Tube, static machine and induction coil.

The apparatus used to excite X-ray tubes may be a static machine, an induction coil, or a high potential transformer.

The static machine is now httle used for X-ray work, its use being confined to radiotherapy. It gives a very uniform discharge at exceedingly high voltage, but the amperage is so low as to necessitate unduly long exposures for radiographic work.

the INDUCTION COIL.

An induction coil consists of a core of soft iron .wire upon which is wound a primary coil of coarse wire. Upon the primary coil, carefully insulated from it, is wound the secondary coil. The latter is made up of very many turns of fine wire, while the primary consists of relatively few turns of coarse wire. A current is passed thi'ough the primary winding and magnetizes the iron core, thus setting up a strong magnetic field through and around the secondary winding. The current in the primary is made to vary rapidly in strength by means of some form of interrupter, thus producing rapid changes in the intensity of the magnetic field. This reacts upon the windings of the secondary and induces an electro-motive force in each turn of the wire. At each make of the current in the primary coil a weak current flowing in the opposite direction is set up in the secondary ; while at each break in the current there is induced in the secondary a strong current flowing in the same direction. This break current is the one used to excite the X-ray tube. If the make current is allowed to pass into the tube " inverse rays " are produced and the efficiency of the ray is greatly reduced.