Methods

Coronary ArteriographyDevices for the Improvement of the Cineradiographic System*

WILLIAM MCLAUGHLIN, E.E.,t MARTIAL A. DEMANY, M .D .,I}AALY TAMBE, M.D.t andIIENRY A. ZIMMERMAN, M.D ., F . .A .C .C . +

Cleveland, Ohio

I N RECENT years, major advances in the diag-nosis of cardiovascular disease have been

made possible by the use of cineangiographyrand cinearteriography, especially coronary cine-arteriography . 2 The attractiveness of apply-ing the tine method to angiocardiography haslong been evident, but its limitations were tooserious to encourage widespread applicationuntil the last decade .'

In all conventional cineroentgen studies, theproblem of obtaining adequate light withoutexposing the patient to excessive radiation hasbeen a major one . The development of imageintensification has made it possible to performcinefluorographic studies at doses of radiationsignificantly below those previously required .°The quality of the image obtained is obviouslyof paramount importance to the accuracy of theexamination . For this reason, the cineradio-graphic system used in these procedures hasbecome a cornerstone of every modern cardio-vascular laboratory .

A brief review of a cineradiographic systemcan be accomplished by listing its significantelements in their normal operational sequence .The list includes :

A. Size of the x-ray source and its intensityB . Collimation of the x-ray beam to the subjectC. Patient-supporting deviceD. Device creating a suitable x-ray image of the

area under investigationE. Device converting the x-ray image into a visi-

ble image suitable for fluoroscopic observa-tion or for recording on film or on othermeans, such as magnetic tape

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549

F. Fluoroscopic optical assemblyG . Recording mechanismH . Diagnostic viewing device

Improvements in the performance of any oneelement of such a system will better the relativevalue of the final information submitted for in-vestigation .This paper discusses the improvement of a

cineradiographic system by the use of severaldevices (Fig. 1) affecting (1) the intensity of thex-ray source ; (2) the automatic control of itsintensity ; (3) the collimation of the x-ray beamand (4) the optics of the recording system(See Appendix) .

INTENSITY OF X-RAY SOURCE

It is a basic principle of radiography that thesize and intensity of the x-ray source are offundamental importance in determining thesharpness of the detail in the x-ray image . Thesource should be as small as feasible and itsintensity as great as possible . In practice thesefactors are in direct opposition . A reductionin the size of the source requires a decrease inthe maximal permissible intensity if the x-raytube is not to be destroyed . However, there is away to obtain the optimal combination of sizeand intensity .

If the x-ray tube is operated at a constantpotential, the maximal Useful radiation may beobtained from a source of a given size . Thepotential of the "normal" cineradiographic sys-tem varies as a series of half sine waves (Fig . 2A) .In contrast, the grid system operates from a con-

*

the Department of Advanced Development, Picker X-Ray Corporation f and the Cardiovascular Labora-tory, St. Vincent Charity Hospital, I Cleveland, Ohio .

Address for reprints : Henry A. Zimmerman, M.n ., 250 Hanna Building, Cleveland, Ohio 44115 .

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stant source of potential, and radiation is emittedin a series of square-wave pulses (Fig. 2B) . Fora given rate of energy input to the x-ray tube,the grid system emits more usable radiation be-cause the tube is not energized during the timeintervals between the square-topped pulses .The dotted segments of the sine waves betweenthe grid pulses (Fig . 2B) represent input of powerto the x-ray target . This power produces heatin the tube but contributes little to the final x-rayimage . The radiation emitted during theseperiods by the normal cineradiographic systemwill not penetrate the patient but will be ab-sorbed by the tissues and produce heat .

In the grid system, a special x-ray tube andcontrol system is used to turn the radiation onand off by switching the current through thex-ray tube . This switching can be extremelyrapid . In the system we used the switchingtime is of the order of 30 to 40 msec . Such aspeed facilitates cineradiography at high framerates and also lends itself well to fast automaticcontrol of image brightness .

AUTOMATIC CONTROL OF INTENSITY

The automatic control of radiation can beaccomplished by varying for each frame theperiod of exposure to radiation . A method com-monly used to achieve this goal is diagrammedin Figure 3A . Control elements in the lowvoltage range of the x-ray power source, auto-matically delay the time at which power isturned on, so that the total power delivered issufficient to maintain an average level of imageintensity . Power does not flow during the dot-ted portion of the sine waves, only during thesolid line portion . This type of switching con-trol is intrinsically slow, partly because it re-quires that the control guess where the turn-onpoint should be on the basis of the past frames orpulses . When a pulse is started, it must con-tinue until the sine wave returns to zero . Thus,there is no turn-off capability .

In contrast, the grid system (Fig . 3B) auto-matically determines where the individualpulses should be started and stopped on the basisthat enough energy has been delivered for thatparticular pulse of fluoroscopy or for that par-ticular frame of film. In essence, the film isphotoelectrically timed frame by frame to in-sure constant density through varying patientopacity. Rapid automatic control is inherentto the grid switching system . The cinecamerasignals the grid switch when a frame of film is inplace ready for exposure . This signal startsthe pulse of radiation . When enough energy

VOLUME 21, APRIL 1968

Coronary Arteriography

551

has been delivered for the proper exposure ofthat frame of film, the photoelectric timingcircuitry signals the grid switch to turn off .During fluoroscopy, the pulses are initiated by aseparate source and automatic brightness con-trol is maintained by the photoelectric systemcontrolling pulse width .

COLLIMATION

When a beam of x-radiation is directed at asubject, the formation of an x-ray profile of the

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552

McLaughlin et al .

subject in space has the greatest sharpness ofdetail if the size of the source is small and if thevolume of matter irradiated is kept to a mini-mum. The ideal source would be of theoreticpoint size . The real size is the projected viewof the electron-bombarded area on the x-raytarget .

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Fin. 4 . A, conventional sectrnzgula shutter system relativelyremote from the focal spot. Penumbra is present .B, double variable diameter iris diaphragming system used toreduce penumbra .

FIG . 5 . A and B, diagrams showing recording and pro-jection with conventional camera equipment . C and D,diagrams showing recording and projections with vari-able focal length lens . Ratio of size of image to size offilm grain pattern has been increased .

The effective size is that of the bombardedarea plus the area of the target that can be seenby the observer through the collimating system .The area of the target outside the focal spot ormain source of radiation is a lower intensitysource of radiation of sufficient size to blur theimage formed by the radiation from the focalspot .

In Figure 4A, the round dot centrally locatedin the x-ray tube housing represents the focalspot or main source of radiation . The darkenedarea above and to each side of the center repre-sents the sources of radiation outside the focalspot . The radiation coming from this areaoutside the focal spot produces a penumbraaround the main field, as outlined by the shut-ters . In addition to the penumbra, there is agenerally blurred radiation image superim-posed over the entire field of the main image .This blurred image amounts to a general foggingof the principal image and appreciably reducesits diagnostic value .

Because the input-end of an image intensifieris round, it seemed reasonable to believe that around field collimating system would be ap-propriate . Such a system is shown in Figure4B . Two round diaphragms of variable diam-eter are used, one of them close to the x-ray tubeto cut off the radiation coming from the targetareas outside the focal spot . This system effec-tively improves the contrast of the x-ray imageby removing the overlying blurred image.Contrast is further sharpened by using a portionof the field as small as is compatible with theexamination . This is conveniently accom-plished by means of a switch controlling thediameter of the field . Thus, an x-ray image ofbetter quality is presented to the input-end ofthe image intensifier .

RECORDING SYSTEM OPTICS

In the system we used the recording mecha-nisnt is a relatively standard 35 mm . cameraoperating at 60 frames per second . This formatand frame rate are routine . The Shellburstfilm is processed in x-ray developer .

The uppermost diagram of Figure 5 shows animage of given size being recorded of film by acamera . The dots represent the normal grainstructure of the film emulsion . With a highrecording speed emulsion such as Shellburst,*this grain pattern is relatively coarse and forms

* Shellburst fhn has been selected for the time beingbecause it seems to render better visibility of fine detailin this particular system . It is recognized that otherfilms are available having higher recording speed, butthe visibility of small vessels seems to be materiallyreduced .

THE AMERICAN JOURNAL OF CARDIOLOGY

a mottled overlay on the fine structure of theimage being studied, thus causing a certaindegree of optical confusion .When the developed film is projected (Fig .

5B), the image of the grain pattern has a cer-tain coarseness depending on the size of theprojected image . The higher the degree ofprojection magnification, the coarser the grainpattern . Fine details may be made morereadily visible by optically magnifying the imagebefore it is recorded on the film .

In Figure 5C, the same object as in Figure 5Agives a larger image on the film after some altera-tions in optical equipment of the camera . Asmaller portion of the object is photographed

B

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Coronary Arteriography 553

because of the limitations imposed by the filmformat, which remains unaltered . During pro-jection of this image (Fig. 5D) the apparent sizeof the film grain has been reduced because thisnew image does not require the same degree ofprojection magnification as the image obtainedwith the normal recording system. Thus, onemay see finer details without excessively magni-fying the grain pattern of the film .

To achieve this result, the camera has beenfitted with a lens of variable focal length whichcan be adjusted at will by the operator to coverall of the available field at the minimal imagesize . At maximal magnification, the centralthird of this field will fill the entire film frame

Fro. 6 . Right coronary artery of a 34 year old whiteman (left anterior oblique projection) . A, frame fromcoronary cinearteriogram taken with a typical 6-inch imageamplifier and normal magnification. The main trunk istotally obstructed ; five small collateral vessels arevisible . B, frame showing the same area as in A, taken with6-inch image amplifier b u t with an optical change prooidingmagnification of the recorded image by 2 . Examination ofthe main trunk shows its diameter to be twice thatmeasured in A . A greater number of small collateralvessels can be seen with only a very small increase inapparent graininess of the image . C, frame shaming thesame area as in A but with a normal photographic enlargementby means of projecting printing . The vessels demonstratedin A can also be seen, but the marked increase in graini-ness of the image makes the examination difficult for theeye .Frame B reveals the presence of a larger number of

small vessels (right lower section of frame) than C be-cause of the higher resolution and contrast . Frame Cillustrates the objection to magnifying the grain size ofthe original film .

554

A wide variety of field diameters and magnifica-tions can be selected by the operator to suit therequirements of the examination .

Figure 6 illustrates the change in size and theamount of finer details in the coronary circula-tion obtained with such an improved cineradio-graphic system .

All the elements composing the cincradio-graphic system have not been treated in thispaper. It is recognized that there are otherareas for improvement that must be investigatedas time and technology permit .

SUMMARY

The various elements through which an imageis transmitted for final diagnostic viewing arehighlighted, with emphasis on the followingpoints :

1 . The level of radiation must be such thatsufficient statistical data are present in the x-rayimage . This is accomplished by grid switchingin the x-ray tube working on a constant po-tential power source .

2 . The signal-to-noise ratio in the x-rayimage is kept high by means of a good collimat-ing system and by using as small a focal spot aspossible .

3 . The x-ray image is converted to a highquality light-iutage by choosing a high gain,high solution image amplifier .

4 . Resolution is optimized by use of a varia-ble focal length system that records an imagemagnified to a degree in keeping with the de-sired field of view . This makes visible fine ves-sel detail that otherwise would be lost in thegrain structure of the filet . The present imagequality at the image amplifier output phosphoris such that optical magnification beyond threetimes produces little or no increase in fine vesselvisibility because of the grain structure andscintillation pattern of the image amplifier . Tosome extent the scintillation pattern can be re-duced by increasing radiation to the patient .As indicated in the Appendix, we believe that areasonable optimum has been selected for thecurrently available components .

The work presented here deals with only a fewof the steps by which a cineradiographic systemcan be improved. We recognize that there areother areas for improvement which will be in-vestigated in the future.

REFERENCES1 . CAMPBELL, J. A . and KLATTE, E. C . Current status

of cinefluoroscopy in cardiac diagnosis . Progr .Cardiovas . Dir., 2 : 20, 1959 .

McLaughlin et al .

2 . Solves, F. M ., JR . and SHIREY, E. K. Cinecoronaryarteriography . Mod. Concepts Cardiovas . Dis ., 31 :735, 1962 .

3 . ABRAMS, H . C . An approach to biplance cine-angiocardiography. L Background and objective.Radiology, 72 : 735, 1959 .

4 . MORGAN, R. M. Screen intensification : A reviewof past and present research with an analysis offuture development . Am. J. Roentgenol ., 75 : 69,1956 .

5 . GI . .ASSER, 0 . Medical Physics, Vol. 2, pp . 879, 963 .Chicago, 1960. Year Book Publishers .

6 . CLARK, G. L . Applied x-ray, ed . 3, p . 134. NewYork, 1940 . McCraw Hill .

7 . JENKINS, F. A . and WHITE, Il. E. Fundamentals ofOptics, ed . 2, p . 155. New York, 1950. Mc-Graw Hill .

8 . NEBLETTE, C. B. Photography : Its Principle andPractice, ed . 4, pp. 149, 209 . Lancaster, Pa ., 1946 .Lancaster Press .

9 . HARDER, A. The Ilford Manual of Photography,ed. 5, p. 213 . Ilford, Essex, England, 1960 .Ilford Ltd .

10. Kodak Reference Handbook (Publication H-I), ed .

The Half Value Layer : At 120 kv., about 4 .1 mm .of aluminum .

Radiation Measurements: Stated as input to patientincluding backscatter .

Image Intensifier: Six-inch Phillips with about 5000gain at 50 lines/in .

Type of X-Ray Tube : Machlett Labs. HDDX50with 0 .5 to 1 .5 mm. focal spots . The 0.5 mm .spot is used for fluoroscopy with normal anoderotation . The 1 .5 mm. spot is used for eine-radiography with triple speed anode rotation.

X-ray Technic : 80 to 120 kv . approximately coilstant potential . Selection is made on basis oftechnician's estimate . Cine is done at 300 ma.Brightness control is by means of automaticallyvarying pulse time .

Give Film : 35 mm. Kodak Linagraph Shellburst .Processor: Picker X-Ray Corp . continuous roll film

processor. Picker "Pix" liquid concentrate de-veloper and "pix" fixer concentrate both di-luted to fill 3 .5 gallon tanks using 1 gallon ofconcentrate .

Development: 4.5 minutes at 80 ° F .

THE AMERICAN JOURNAL OF CARDIOLOGY

4. Rochester, N. Y., 1966 . Eastman Kodak .

APPENDIX

Technical Physical Data

PhantomCm. ofWater

Kv. toX-ray Tube

Roentgens/Min.

Fluoroscopy

Roentgens/Min .

Cinrradiog-raphy

7 70 0 .60 3 .57 100 0 .657 120 0.6514 70 4 .00 10 .014 100 1 .55 9 .814 120 1 .45 9 .821 100 9 .40 23 .221 120 6 .20 21 .8