US2387704A - X-ray radiography of inclusions - Google Patents

Description

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Oct. 23, 1945. D, McLAcx-iLAN` JR 2,387,704

X-RAY RADIOGRAPHY OF INCLUSIONS Original Filed Plarch 23, 1943 6 Sheets-Sheet l Oct. 23, 1945. D. MCLACHLAN, .1R

X-RAY RADIOGRAPHY OF NCLUSIONS Original Filed March 23, 1943 6 Sheets-Sheet 2 ,4 7 70k/wry Oct. .22, 1945.

E'OSS REFERENCE D. MCLACHLAN, .1R

X-RAY RADIOGRAPHY OF INGLUSIONS Original Filed March 23, 1943 6 Sheets-Sheet 3 Hmm/UNER.

iwmwzm Oct. 23, 1945. D` MCLACHLAN, JR

X-RAY RADIOGRAPHY OF INCLUSIONS original Filed March 23, 1943 6 sheets-sheet 4 VMMQM Ju immuun..

l-lu lll Oct. 23, 1945. D. MCLACHLAN, JR

heets-Sheet 5 ATTORNEZ Oct. 23, 1945. D. McLAcHLAN, JR 2,387,704

x-RAY RADIOGRAPHY 0F INcLUsIoNs Original Filed March 23, 1943 6 Sheets-Sheet 6 [5v/Wd@ M I Patented Oct. 23, 1945 X-RAY RADIOGRAPHY or INCLUsIoNs Dan McLachlan, Jr., Old Greenwich, Conn., as-

signor to American Cyanamid Company, New York, N. Y., a corporation of Maine Original application March 23, 1943, Serial No. 480,151. Divided and this application February 18, 1944, Serial No. 522,885

1 Claim. (Cl. Z50-*108) .within and on the surface of commercialand medical objects'subjected to X-ray'examinaton. I.

However, the'embedding technique herein de- 'scribed-and the use of the immersion technique nof--this inventionehave Ygreatly.extended the-use n fulness of X-ray examination in the eld of medical radiography.

' The specific problem solved by the method and technique of this invention involves a means and method for increasing the relative contrast of the images produced on a roentgenogram by the various particles and bodies being radiographed.

It is a particular object of this invention to reveal the details of bodies and inclusions within a particular body containing such inclusions so as to render the same readily perceptible.

In the drawings, forming a part of this disclosure:

Fig. 1 is a roentgenogram of a hand X-rayed in the usual manner, showing that the X-rays are attenuated more by the bones than by the iieshy` part of the hand;

Fig. 2 is a roentgenogram of a hand X-rayed While immersed in water, showing only the bones in the fully immersed lingers, the X-rays being equally attenuated by the pure water and by the ileshy part of the iingers in this region;

Fig. 3 is a roentgenogram of a hand X-rayed in the usual manner, showing only two particles of glass as clearly discernibly in the iiesh of the hand, one above the second joint of the thumb and one to the right of the second joint of the index finger; a

Fig. 4 is a roentgenogram of the same hand shown in Fig. 3 but immersed in water and shows four particles of glass indicated by the fogging within the circles as clearly discernible in the iiesh of thehand;

Fig. 5 is a diagrammatical illustration of the effect of using various immersion techniques showing the leveling eiect of Water immersion as contrasted to ordinary air radiography; and

Fig. 6 is a roentgenogram of a hand X-rayed in air but having the second or middle finger embedded in a paste of greater opacity more nearly matching the esh of the hand.

Although this invention is not to be deemed limited by any theory as to its operation, a somewhat lengthy discussion of the theoretical considerations involved herein is believed necessary to the further understanding of its modus operandi.

Since all radiographs are shadow-graphs which are taken with the object between the source of radiation and the lm, a discussion of the transmission of X-rays through matter underlies any attempt to explain the use of the products and processes involved herein. The fundamental law of attenuation of transmitted light, known as Lamberts law of optics forms the basis of any explanation of absorption and transmission of X-rays through matter. Lamberts law states I =Inc"t where I is the intensity of the transmitted radiation Io is the intensity of the radiation incident upon the object Y t is the thickness of the object and p. is the linear absorption coefficient of the material forming the object The linear absorption coe'icient ,u for any substance depends upon the state of the substance, i. e., whether it be a solid, a liquid or a gas. Thus, the intensity of an X-ray beam is not decreased as much by traversing one centimeter of water vapor or steam as it is by passing through one centimeter of water. Among other factors determining the value of the linear absorption coe'- cient /i are principally the mean atomic number of the material in question, the specic gravity of that material and the wave length of the radiation employed.

A more useful relationship is that obtained by dividing the linear absorption coeilicient 1L by the density p to obtain the mass absorption coecient which is the same regardless of the state of the substance (i. e., liquid or vapor) and expresses the fraction of the intensity lost per unit of mass having unit cross-section. This ratio gives the absorption of a substance in any state for a given X-ray wavelength; its value, however, decreases rapidly with decreasing atomic weight and decreasing wave length. It measures the ability of a substance to absorb energy from an X-ray beam.

This energy absorption or the factors preventing an X-ray beam from going directly through an object without attenuating the beam consists of two portions,

bis

where is the mass photo absorption coeihoient and is the mass scattering coeicient. However, the

mass scattering ooeicient is usually so small that it can be omitted without introducing an. error and for practical purposes and may be used interchangeably.

For certain wave lengths, however, discontinuie.

ties occur in the mass photo absorption coeflicient, particularly in the vicinity of the critical absorption Wave lengths at which the charaoter.v

istic spectral lines known as the K, L, M, N, etc., series of the various elements are produced.v At Such Wave lengths, the value of v is less above each critical wave length than it is below, and between these discontinuities the value of increases with increasing wave length approximately in accordance with the equation:

where C is a constant depending upon the atomic number of the absorbing element and changes abruptly at the critical wave lengths, Z is the atomic number of the element and JOO is a function of the Wave length A, fOr) taking values such as im, A3, etc., depending upon the wave length of the X-radiation and on the elements X-rayed.

The following table gives the mass photo absorption coefficients and hence approximate Values for tlie mass absorption coefficients of any great importance in the nal calculations. ,20

of some common substances as a function of the wave length of the X-radiation.l i

TABLE I Mass absorption coelcn'ents of some chosen l substances Mass photo Specific Substance Chemical composition absorption Weight coefficient Water 1. 0 H20 2. 500i3 Aibumeu C H 7%, N 10%, o 24%, 1. 7813 1, Fei (human). 0. 9 o 75.0%,H12.0%. o 11.8%.. 1.1351.3 Muscle W 72%, E 20%, F 7.6%, Sa 2.57

1 Bloed 1.06 W E 19.1%, sa 0.9%... 2. 61 'lransudate 1.008 W 96.8%, E 2.4%, As 0.9%.- 2. 72 Exudate l. 02 W 93.3%, E 5.9%. As 0.8%.. 2. 09 Pus.... 1.06 w 90.6%, E 7.8%, F 0.8%, 2.07

The mass absorption coefficients of some of the more common elements found in organic compounds are given below in Table II at 30 kv., the .mean efective wave length being approximately .es f

In Table I where the chemical composition is not indicated by the atomic symbol representing the element present, the following notation eX- plains the composition: W=water, E.=protein, F=fat, Sa=salts, As=asl1, Ch=chloresterin.

Table Ia is a supplementary table giving the mass absorption coeicients of additional substances.

' TABLE Ia Spe- Mass photo Substance cil'lc Chemical composition absorption weight coeicient siriew" (eerineci- 1.1 w 02.0%, E 34.7%, F and 2. :i7

ing tissue). related substances 1.9%,

. inorganic Sa 0.5%. Fat tissue 0.92 W 11.7%, E 21%, F 86%, 1.6i

` As 0.2%. Liver 1.06 w 70%, E 20%, F 3%, As 2.01

1 Spleen 1.05 Wl78%, E 16%, F 5%, As 2. 61 Lung W 80.1%, E 10%, F 2.7%, 2. 09

As 1.2 Thyroid gleam... 1. 0s w 82%, E 16% 2. 70 Mamma o l d 0.96 lV 45%, E 9.7%, F 44.8%, 1.93

atropliied). As 0.5%. Placenta 1.06 W 0.85%, As 0.9%, 2.75

Nerves 1.03 w 70%, E' 7%, oir and 3.12

Lipoide 13.5%, As 1.5% l Bone cortex 1.9 W 26%, E 24.5%, F 23%, 15.24

As 17.2% N cartilage 1.11 W 72%, E 20 3%, As 1.7%. 2. 70 Hair 1. a C 50.5%, H 6 4%, N 17.1%, 2. 89

o 20.7%, s 5%, As 0.3%. Finger nail C 51%, H 6.8%, N 16.9%, 2. 57

o 21 ,s 3%, As 1%. Rectal odeno- 1.06 W 76%, E 22.9 As 1.1% 2.67

carcinoma. l Chemical glass- Ca 2.6 S102 77%, KzO 7 7%, NazO 15.05 ware. 5%, CaO 10 3% l Sand stone 2.3-2.9 10.25 Iron 7.86 Fe 107. 7 Kidney 1.00 W 83.5%, E 15.7%, As 2. 6 0.8%.

TABLE II The mass absorption coeficients of some of the more common elements i Mass absorption u Chcinicalelernciit Symbol i coemeleut ,at

i 1:.03 A. Oxygen 0 .90 Hydrogen. H .433 Carbon C .4.61 Nitrogen N .010

From'this table-itis possible tocalculate the vmass absorption coefficient of water, noting however, .that 'when a-material is `composed of :more :than 'onefelemenu each .element contributes its share of thetotal absorption in :proportion tolthe :concentration C1, C2,1etc.,.of the elementspresent in accordance with the `following fequation:

auch@creen e.

is the .mass Aabsorption coeicent of the element of which C1 is the fraction of that element present,vetc., and where p is the density of the material or compound made up of the fractions C1, C2, C3, etc. Y

Thus, for example, the mass absorption coefficientiof water for X-.radiationproduced at a p- .tential-.of .30 kv. and .hence having a mean reffective wave length of .63.. is obtained by substituting inEquation 4 -the mass absorptioncoefflcient .of .hydrogenat this wave length, namely, .435, and of oxygen, namely .90, and noting that wateris-.composed .of 11 hydrogenand89 .oxygenand hasa density .of unity:

value 285 for 'the value of 'for water checks almost 'exactly with the Imass absorption coeicient vof water obtained from Table I, 70C) being takenlas the -function )x5/2 or 'A4,'X3/2, letc., 4most appropriate for the Awave llength of :63 and making some small allowance for the relative 'importance at 4such comparatively short wave 'lengths of the absorption due to the mass scattering coefficient lof the elements Vpresent.

The mass absorption coeicients of some common compounds have Vbeen calculated -from the values ,given in Table II and are included in the following table:

TABLE III -Mass absorption coeicients of some organic compounds Percent Percent'Perceut Percent Den- Compound C N sity u .63

Formlc acid 69.6 4.35 26. 2 0.0 1.22 .943 Urea 26.' 7 6. 66 20. 0 46. 7 l. 33 86 Water 89. 0 ll. 0 0. 0 0. 0 l. 0 85 Methyl alcohol--. 50. 0 l2. 5 37. 5 0. 0 0. 79 54 Ethyl a1c0ho1. 34. 8 13.0 52. 2 0. 0 0.80 49 -Propyl alcohol... 26. 7 13. 3 60. 0 6. 0 0. 80 46 Butyl alcoho1 21.6 13. 5 64. 8 0. 0 0.81 45 Cyclohexane N 0.0 A14.3 85.7 0.0 0.66 .31 N uj (A petroleum fraction) 87 4 l Parain (A petroleum precipitate) .89 42 A summary of the above statistical facts discloses briey, .that X-rays are attenuated as they pass through matter by interaction with the materials or tissues through which they pass. In each case the amount of attenuation depends Vupon the kind of .material and the thickness of the tissue through which it passes. Thus, a ray passing through one or two centimeters of bone is greatly -attenuated -because of-fthe relatively lhigh density of the elements Ca Q'and "P -inthe bone while Ya ray-passing through lO centimeters of iniiated vlung tissue is only slightly attenuated.

RewritingEquation 1 as follows:

shows clearly that the ,intensity fof 'transnutted radiationdepends onthe .value of the product of (1) the mass absorption coeflicient, (2) the den sityand (3) the thickness of the `material and hence the Visibility of an image produced on ia lm is aiTected by a predominance of anyone of these 3 factors orby a combination of all three.

The fundamental problem of roentgenography is to choose such technical procedures as to produce roentgenograms that have a minimum fof observable unsharpness and an image havin-g a predetermined'optimum of density and contrast. -Hence for an object to cast an image which can be distinguished from the background of a phosue or material whose base is theparticular small area of the film, and extending vfrom this area towards the focal spot of the X-ray tube.

Usually, a .distinct image can be obtained .by the use of reasonable care provided there `is a difference of at least 2% between the .intensity striking Athe film at the image and that striking the immediately surrounding areas and also .provided the applied kilovoltage isso .adjusted that about 82% of the X-rays are vabsorbed ingoing through the object. Thesecond requirement for a distinct image is fullled upon adjusting the kilovoltage in accordance with the instructions given in various radiographic manuals depending upon the thickness of the body being observed.

In the case of the radiography of a piece of metal containing a blow-hole, the bubble will be visible only if its diameter exceeds about 2% of the thickness of the metal block. From an inspection of the values given in Table rI it is to be noted that if mass absorption coefficients .Were the only factors involved, fat tissue, bone, and various other body substances would be visible against .a background of muscle. But, in accordance with Formula 5 other factors enter. and, moreover most of the individual tissues and organs of the human body are se small in thickness compared to the effective thickness of the subject and are so often so interpositioned and intertwined that they do not produce a distinct image. In addition, various other factors contribute to the obliteration or unsharpness of the image, such as variations in the outside shape of the object, or variation in the thickness of the object.

Various auxiliary roentgenographic devices have been devised to improve the results obtained by the conventional methods where the objects are radiographed in air in order to produce an image having a minimum of observable unsharpness and a predetermined optimum average density and contrast. Among such devices may be mentioned the Potter-Bucky diaphragm to reduce fogging of the film due to scattering, the use of a cone to reduce scattering of X-rays in air, the choosing of exposure factors such as X-ray tube voltage, exposure time, and the like.

'I'he present invention utilizes a technique embodying the immersion or embedding of the body to be radiographed in liquids or pastes of selected opacities, particularly of opacities equaling those of the external part or of the continuous phase of the heterogeneous object being radiographed in order to obtain improved photographic results.

In order to explain the process of this invention more clearly, a number of actual roentgenograms are reproduced herein. Fig. 1 illustrates the results obtained from the usual practice of radiographing the hand surrounded by air. This figure shows clearly the outline of the ilesh at the iinger tips. It is to be noted that the flesh also shows up with varying degrees of blackness because of its different thickness in various parts of the hand. 'I'he immersion technique of this invention was utilized in obtaining Fig. v2 by radiographing the hand while the latter was immersed in water. 'Ihis ngure shows the esh as practically eliminated from the resulting roentgenogram.

This result can be explained on the basis of mass absorption and Lamberts Formula 1.` Reference to Y Table I shows the value of the .inass absorption coeicient ofA water to be approximateiyias'oc fm while thath'pf muscle, linger nails and"'similar tissue is about 2.50. Since these valuesqarje almost the same,

little kor no contrast is-'produced in the lm due to the contours of the'esh'and hence only thel bone structure is prominent.` Since the water didf not cover a part of the handylespecially at the" wrist, in Fig. 2, the outline of the ilesh is still persimilar small objects embedded in the flesh, as v may be seeny by comparing the roentgenograms of Figs. 3 and 4. Fig. 3 shows an X-ray photograph takenv by the ordinary methods in air. This gure shows only two glass particles to be visible, one above the second joint of the thumb and one to the right of the second joint of the index iinger. Fig, 4 shows the same hand, subjected to the same exposure conditions but X- rayed under water. Fig. 4 shows four glass particles to be visible, as indicated by the fogging within the circles. Of the two additional glass fragments, one is located at the base and to the right of the little finger and the other at the base and to the left of the foreiinger. Neither of these fragments are visible in the X-ray picture of Fig. 3. In this photograph of a clinical case, four pieces of glass were actually extracted from a patients hand, only two of which would normally have been disclosed by the use of the ordinary roentgenographic technique in air.

Thus, by eliminating the effect of thicknessdifferences by the immersion technique herein described the improved roentgenographic immersion technique of this invention shows the presence of several small glass fragments very clearly. The greater visibility of the images produced by the glass inclusions in an immersed specimen depends on the fact that slight photographic density diierences are seen most clearly when they occur against a uniform background. The graphical representation of this density leveling effect is clearly understood by referring to Fig. 5 where the upper half of the diagram shows the incident X-ray beams which are attenuated in intensity in accordance with the projected representations shown in the lower half of the diagram. In A the drawing depicts a nger radiographed in air, in B the linger is radiographed while immersed in water, while in C an opaque liquid such as a 7% solution of barium chloride in water is used as the immersion liquid. The image of the foreign body falling on the iield of uniform density in B shows diagrammatically that the contrast eiected by the contiguous uniform densities on the iilm in B in the neighborhoodof the foreign body facilitates thev discovery of the body as compared to the unsharpness and non-uniformity of the contiguous densities in A and C in thel neighborhood ofthe foreign body.

faces may be resorted to. Thus, in Fig. 6 two pastes of different opacities havek been packed about the fingers of a hand. The third nger is embedded in a paste having an opacity equal to that of water. Such a paste is obtained by mixing 100 parts of petrolatum with 50 parts of v beeswax andY adding 2% of barium sulfate.

The paste shown `around the second or mid. dle finger of Fig. 6 has an opacity equivalent to that of a 7% solution of barium chloride in water. 'Sucha paste is obtained by starting with,

a radiolucent paste such aS that obtained from mixing 100 parts of petrolatum with 50 parts of beeswax and blending in measured quantities of very nely divided or ground barium sulfate, zinc oxide, or the like. Thus the addition of .885 gram of iinely ground zinc oxide to about grams of the radiolucent paste gives a paste having an opacity equal to that of water. Further additions of zinc oxide give a paste of still rgreater opacity.

Among various other commercially available powders which are non-toxic and capable of being added to a paste-like mixture of parts of petrolatum and 50 parts of beeswax to produce an X-ray paste having an opacity approximately that of human iiesh are the following;

Grams oi substance small Ypieces of v.bone em-Y Y This case is a division of U. S. Serial No. Astable radiolucent paste comprising 100 parts 480,151, led March 23, 1943, by the applicant. of petrolatum and 50 parts of beeswax together It is to be understood that the examples and with suicient amounts of radiopaque substances processes above described are merely illustrative to give a paste having a mass absorption coefand not limitative embodiments of the invention 5 cient for X-rays of predetermined wave-length the scope of which is encompassed Within the equivalent to that of flash for X-rays of the appended claim and equivalents thereof. same wave-length.

I claim: DAN MCLACHLAN, JR.

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