CA1048166A

CA1048166A - Nuclear imaging system

Info

Publication number: CA1048166A
Application number: CA288,544A
Authority: CA
Inventors: Sergio Colombo; Vitaliano Carugati; Gianni Ferramola; Sergio Ferrari
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1970-10-16
Filing date: 1977-10-12
Publication date: 1979-02-06
Also published as: CA949231A; US3735132A

Abstract

ABSTRACT
A nuclear imaging device comprising a plurality of scanning heads spaced apart in a predetermined configuration with the aid of a support member that permits the individual scanning heads to scan in parallel, anti-parallel, and tomographic modes. The support member which is driven in both X and Y
directions in mechanically connected with the stylus of a graphical X-Y plottervia a backlash linkage. Displays are provide wherein the color of the ink dot on printed paper or the intensity of the light projected on photographic film are related to the nuclear particle count in a preselectable manner.

Description

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This application is a division of our Canadian Patent Application Serial No. 184,589 filed October 30, 1973 which, in turn, is a division of our Canadian Patent Application Serial No. 124,957 filed October 12, 1971 (now Canadian Patent 949,231 issued June 11, 1974).
~ is invention relates to nuclear imaging devices and more particu-larly to a means for recording data obtained from simultaneous scans by a plurality of scanning heads.
In obtaining an image of a radioactive source it is frequently con-venient to use a plurality of scanning heads, for example, a pair of scanning heads, in which the scanning heads may be arranged for parallel scanning, anti-parallel scanning or tomographic scanning. In the situation where a human patient is being treated with radio pharmaceuticals and a radiograph of the chest is to be obtained, the scanning heads may be arranged to effect a parallel scan in which one scanning head scans the upper portion of the chest while the other scanning head scans the lower portion of the chest, thereby providing radiographs of the entire chest in half the time. Alter-: natively, it may be desirable to compare images obtained from scanning the chest fro~ a ~rontal view and also from a rear view, in this case the scanning heads would be arranged in anti-parallel configuration in which one scanning head is positioned above the patient and the other scanning head is positioned beneath the patient. It may also be desirable to provide a tomographic dis-play which is accomplished by positioning the two scanning heads side by side and at an angle to each other to provide two views of a common source of radiation such that the two views are oriented at an angle to each other. In these three situations it is desirable that the two scanning heads be rigidly mounted relative to each other to insure a correspondence between the imaging points on the two radiographs provided by the two scanning heads, but since the plurality of scanning heads are to be supported in a fixed configuration by a rigid member, provision must also be made for varying the orientation of these scanning heads to provide the different modes of scanning, and further-~` :
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more, the scanning heads must be connectecl to writing heads which provide theradiographs.
An attempt to solve the foregoing problem was made by D.E. Kuhl as shown in "Progress in Medical Radioisotope Scanning", pages 186 and 187, published by the United States Atomic Energy Commission, and in "Clinieal Scintillation Scarming", edited by L.M. Freeman and P.M. Johnson, page 34, published by Harper & Row. Kuhl's scanning apparatus comprises a large com-plex mechanism which is cumbersome for a small hospital installation.
A further problem arises in the interpretation of the radiographs.
Radiographs are generally read visually and the interpretations made from the radiograph are based on the capability of an observer for reading these radiographs. In particular the observer must be able to distinguish between radiations of higher and lower intensities. While X-Y plots in color have been utilized, the relationship between the selection of color or gray scale is preset and cannot be varied to suit the particular situation or the part-icular observer.
An additional problem commonly known as "scalloping" is found in X-Y plots produced by imaging systems which are responsive to the counting of - nuclear particles, such as gamma ray photons, emitted by the source of radia-tion. In such imaging systems the count of the quanta of radiation are scaled sueh that a point is provided on the radiograph for a specified number of eounts. As the seanning head is moved along during a scarming operation, the count is aeeumulated so that at the end of some small region of the radiograph, an image point or mark is printed upon the X-Y plot. At the end of a seanning line when the direction of the scanning head is reversed it becomes apparent that two image points will be printed on the X-Y plot cor-responding to the same X displacement, these two points having different values in the X dimension. This is the so-ealled sealloping effeet, and it is desirable to provide an imaging system which precludes this sealloping.
The apparatus disclosed provides for an imaging system in which a plurality of transducers or scanning heads are mounted on a positioning means comprising a rigid transport beam, a rigid frame rotatably mounted thereon, and a plurality of arms slidably and rotatably attached to the frame. Mov-ing means are provided for moving the positioning means in an X direction in which the main beam is displaced along its axis and in a Y direction in which the transport beam is displaced in a direction perpendicular to its axis. The transport beam also mechanically moves a writing head which pro-vides a colored image on an X-Y plot, and is further connected to two photo-heads for providing two radiographs on photographic film, one radiograph corresponding to each of the scanning heads, or alternatively, to a combina-tion of the data of two scanning heads. The direct mechanical connection provides for the correlation of data obtained from the scanning with position on the radiograph. A backlash device interconnects the printing head with the main beam such that upon a reversal in the scanning direction by the transport beam there is a momentary lag in motion of the writing head to permit the positioning means to move a short distance for accumulating a count of nuclear particles before a mark is imprinted on the X-Y plot. There is also disclosed means for varying the responsivity of the color coding in a colored radiograph as well as the responsivity of the gray code in a photographic radiograph as a function of the counter of the quanta of radiant energy impinging upon the scanning heads.
In addition, the disclosed apparatus has a film lock preventing accidental exposure of a photographic radiograph and a means for indicating when a writing head has been set for too high a writing rate.
Thus, in accordance with one aspect of the invention, there is provided a radiographic imaging system comprising: a detector system of radiation providing successive electrical pulses in response to radiation incident thereupon; means coupled to said detector system and reponsive to said electrical pulses for computing an output signal having a value ~ -3-~' ' , ' ' ' ' ' .

representing the number of said electrical pulses occurring during a pre-determined interval; said computing means including means for accumulating amounts of quanta of said radiation occurring during said predetermined interval and providing data signals representing said accum~lated amounts, . means for storing said data signals and rneans coupled to said storing means for combining said data signals to provide said output signal; a display having a longitudinal color medium having color bands extending longitudinal-`. ly thereof; means for movably supporting said color medium to permit the ; positioning of individual ones of said color bands; and means coupled bet~een said computing means and said supporting means to alter the positions ; of said bands of color in accordance with the rnagnitude of said output sig-nal.
According to another aspect of the invention there is provided a radiographic imaging system comprising: means for scanning a region of space permeated Witll radiant energy, said scanning means providing electrical pulses corresponding to incidences of said radiant energy; means connected ~ to said scanning means a~d responsive to a sequence of said electrical :: pulses during a predetermined interval for converting said sequence of electrical pulses into a signal having a magnitude representing the amount of said radiant energy; said converting means including means for accumulat-: ing amounts of quanta of said radiant energy occurring during said predeter-: mined interval, means for storing said amounts and means for combining individual ones of said amounts of quanta of said radiant energy to provide ` said signal having a magnitude representing the amount of said radiant .j energy; a display having means coupled to said scanning means for stimulating a media of said display in response to signals of said converting means, said media stimulating means comprising a source of light directing rays : of light toward said media; an apertured member having apertures of differing dimensions, said member being positioned relative to said source to permit 3a--;

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a perimeter of one of said apertures to enclose the rays of light emitted by said source, and means for moving said member to selectively position one of said apertures about said rays of light.
In accordance with another aspect of the invention there is pro-vided a radiographic imaging system comprising: means for sensing quanta of radiant energy, said sensing means providing successive signals in response to the sensing of successive quanta of radiant energy; means for moving said sensing means through a region of space permeated with said radiant energy; means coupled to said sensing means for counting sequences of said signals thereof during a predetermined interval of time; means for storing counts of said counting means, and means coupled to said storing means for combining counts of said counting means; means coupled to said combining means for converting digital counts thereof to output signals having amplitudes proportional to the counts of said combining means; and means coupled to said converting means for displaying marks representing a magnitude of said digital counts of said combining means.
According to a further broad aspect of the invention there is provided a radiographic imaging system comprising: radiation detection means for providing elec~rical signals, sequential ones of said electrical 2Q signals representing the presence of radiation in response to radiation incident upon said detection means from a radiant subject; means for impart-ing a relative motion between said detection means and said radiant subject;
means coupled to said detecting means for accumulating amounts of said electrical signals; means coupled to said accumulating means for storing said accumulated amounts; means coupled to said storing means for combining said accumulated amounts to provide an image point signal; a display; and timing means coupled to said moving means and to said storing means for activating said moving means and said storing means at predetermined rate, said image poin~ signal representing data of an image presented on said ~, ~'L ~
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display in response to said incident radiation.
The aforementioned objects and other features of the invention are explained in the following description taken in connection with the accom-panying drawings wherein:
Figure 1 is a pictorial representation, partially cut away to show the drive mechanism, of the imaging system of the invention;
Figures 2A, 2B and 2C show various configurations for arranging the scanning heads of the imaging system of the invention;
Figure 3 is a block diagram showing the operation of the imaging system;
Figures 4 and 4A are a bloek diagram and a timing diagram of a pulse height selector;
Figure 5 is a bloek diagram of digital data processing equipment;
Figure 6 is a block diagram of ehannel selection cireuitry;
Figure 7 is an isometric view of a writing head;
Figure 8 is an isometric view of the drive mechanism which imparts a scanning motion to the scanning heads;
Figures 9 and 10 are isometric and diagrammatic views of an anti-scalloping feature of the invention;
Figure 11 is an isometric view, partially in section, of a photo-- head and its transport mechanism;
. Figure 12 is a block diagram of a drive circuit for a writing head;
Figure 13 is a block diagram of a drive cireuit for a photohead;
Figure 14 is an isometrie view of film eassettes showing a novel loek; and Figure 15 is a sehematie diagram of a eontrol eireuit for scanning motors of the imaging system.
FGr the sake of completeness and ease of understanding the present invention, the present diselosure ineludes all the material of the afore-~ ~L
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l66 mentioned parent application Serial No. 124,957. It will be understood, of course, that some features disclosed herein are only specifically claimed in the aforementioned parent application. Furthermore, other features are claimed in another divisional application, Serial No. 178,846 filed August 15, 1973, and in the aforementioned divisional application Serial No. 184,589.
Referring now to Figure 1 there is shown an imaging system 20 in accordance with the invention comprising a pair of scanning heads 22A and 22B which are pivotally mounted by pivots 24A and 24B to a corresponding pair of rachet arms 26A and 26B which are slidably mounted within a C-frame 28. The C-frame is pivotedly mounted by pivot 30 to a transport beam 32 which is .;, `:~

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-3d-supported within a carriage 3L~, partially shown in Figure 1, for transla-tional motion in a direction parallel to the axis of the carrier beam 32, hereinafter referred to as the X direction, and in a direction perpendicular to the transport beam 32, hereinaEter referred to as the Y direction. The carriage 34 is mounted within a housing 36 in a manner to be described with reference to Figure 8. The transport beam 32 enters the housing 36 via cur-tain 37. Writing heads 38A and 38B are affixed to the opposite end of the carrier beam 32 by means of a backlash linkage 40 which permits printing of a radiographic display upon a paper copy 42 while precluding the presence of lO the well known scalloping effect. In addition, two photographic copies of radiographs are formed by means of a pair of push rods 44 and 46 connected to the carrier beam 32 by means shown in Figure 8 for driving a correspond-ing pair of photoheads 50 and 52 over film plates 54 and 56. The film plate 54 and 56 are contained within light-tight boxes or cassettes 58 and 60 positioned within a housing 62. The cassettes 58 and 60 are secured in a novel manner by locks 64 which prevent accidental exposure of the film plates 54 and 56. The housing 62 and the housing 36 are supported by means of a frame 66 which facilitates location of the imaging system within a room such as the room of a hospital. The housing 36 has a hinged section 67 to 20 expose electronic equipment (not shown) located therein.
Referring now to Figures 2A, 2B and 2C there are shown three meth-ods by which a patient 68 may be examined to produce a radiographic image.
A source of radiation is provided by a radio pharmaceutical which may be ingested by the patient 68 and which then migrates through the body of the patient 68 to accumulate in the organ of the body which is to be observed.
In Figures 2A and 2B the C-frame 28 has been rotated about pivot 30 with the aid of crank 70 (seen in Figure l) to a hori~ontal position and tightened by knob 71A of Figure 1. The two scanning heads 22A and 22B have been rotated to parallel positions in Figure 2A by means of the pivots 24A and 24B as 30 seen in Figure l and tightened by knobs 71B and 71C. The scanning heads 22A
and 22B have been spaced apart a predetermined distance by means of the ratchet arms 26A and 26B which are driven respectively by ratchetcranks 72A
_ 1~ _ :~4~ 6 and 72B of Figure l. With the arrangement of Figure 2Atwo separate radio-graphic images can be provided as by use of film plate 54 and film plate 56 of Figure l which taken together provide a complete image of the chest of the patient 68 which has absorbed the radio pharmaceutical. In this manner a radiographic image can be obtained in half the time normally required, thereby permitting a hospital to process an increased number of patients with a single imaging system.
In Figure 2B the scanning heads 22A and 22B are arranged by means as described with reference to Figure 2A in a manner permitting a tomograph-ic radiographic display in which the rays of radiation emanating from anorgan 74 such as a thyroid gland are observed from two directions as is indicated by the angular orientation of the two scanning heads 22A and 22B
relative to each other. In the situation of Figure 22B as in the case of Figure 2A the C-frame 28 has been orientated in a horizontal position by means of the crank 70 and the ratchetarms 26A and 26B have been positioned by means of ratchet drive gears 72A and 72B to provide the desired position of the scanning heads 22A and 22B relative to each other.
In Figure 2C the C-frame has been positioned in a vertical position and the scanning heads 22A and 22B have been pivoted about pivots 24A and 24B to face each other in an antiparallel orientation such that the rays of radiation emanating from the head of the patient 68 in a vertical direction are intercepted by the scanning rays 22A while the rays of radiation emanat-ing in the opposite direction are intercepted by scanning head 22B. In this way radiographic images of information obtained from the right side as well as the left side of the patient 68 can be obtained.
Referring now to Figure 3 there is shown a block diagram of the imaging system 20.Two sources of data are provided by the scanning heads 22A and 22B of Figure l, and the data is pro-cessed respectively by channel l and channel 2 as shown in Figure 3. The scanning heads such as scanning head 22A has the well known form comprising a collimator 90, a scintillator 92 and a photomultiplier 94 which is separated from the scintillator by a glass plate 96. The photomultiplier 94 comprises a photocathode 98 and an ;

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anode 100 which are maintained at a difference of potential of typically1000 volts by means of voltage source 102~ A glass envelope 104 encloses the scintillator 92 as well as the photomultiplier 94 and is further sur-rounded by a lead shield 106 for capturing stray rays of radiation. Thus, the scanning head 22A is responsive to X-radiation, gamma radiation and radiation of nuclear particles.
A quanta of radiation, such as a gamma ray emitted from the organ 74 in the patient 68 of Figure 2B, passing through the collimator 90 and impinging on the scintillator 92 causes optical photons to be emitted from the scintillator 92. The optical photons are intercepted by the photocath-ode 98 thereby emitting photoelec-trons which are accelerated across the dif-ference of potential to the anode 100 which results in an electrical signal to which amplifier 108 is responsive.
The amplifier 108 provides a pulse signal corresponding to each quanta of radiant energy received by the scanning head 22A. Some of these quanta of energy are due to background radiation and are of a lower energy content than the quanta of energy, such as a gamma ray photon, emitted from the organ 74 of Figure 2B. Accordingly, a pulse height selector 110, fre-quently referred to as a window, is utilized to pass those pulse signals from amplifier 108 having an amplitude indicating the presence of a quantum of energy emitted directly from the organ 74. The pulse height selector 110 is preset for the anticipated level of radiation associated with the radio pharmaceutical administered to the patient 68 by means of a plug-in module, hereinafter referred to as an isotope plug 112, positioned on the housing 36 in Figure 1 and described in further detail with reference to Figure 4.
The pulse signals provided by pulse height selector 110 are of unif`orm amplitude suitable for processing by digital equipment such as the data processor 114 which will be described in further detail with reference to Figure 5. The data processor 114 weighs the data provided by the succes-sive signal pulses from the pulse height selector 110 and provides an out-put signal waveform which is suitable for operating the writing heads 38A-B
and the photoheads 50 and 52. Channel 2 comprises scanning head 22B (not _ 6 --8~66 shown in Figure 3) and an amplifier and data processor corresponding to the amplifier 108 and data processor 114 of channel 1. A selection and a com-bination of the data of channel 1 and channel 2 are provided by a channel selector 116 which is described in further detail with reference to Figure 6. For example, by means of the channel selector 116 the sum or the dif-ference of the data of channel 1 and channel 2 may be provided to the writ-ing heads 38A-B, or as a further example, the data of channel 1 may be pro-vided to operate the photohead 50 while the data of channel 2 is provided to operate the photohead 52 to provide simultaneously on film plate 51l and film plate 56 of Figure 1 radiographs corresponding to the radiation inci-dent upon the scanning heads 22A and 22B. The writing heads 38A-B provide either a black and white display or alternatively a multicolor display, while the photoheads 50 and 52 provide a photographic image of varyine gray scale in response to the radiation incident upon the scanning heads 22A and 22B. The responsi~ity of the color selec-tion in the case of the writing heads 38A-B and the gray scale in the case of the photoheads 50 and 52 to the data provided by the channel selector 116 may be varied in a novel man-ner by means of a predetermined functional relationship which is preset by data enhancement circuits 118A-D in the form of plug-in modules on the hous-ing 36 as will be described with reference to Figure 7. As shown in Figure3, the data enhancement circuits 118A-D connect respectively with writing head drivers 120A and 120B and with photohead drivers 122A and 122B, de-scribed respectively in Figures 12 and 13, to provide radiographs in which the data is more readily interpreted.
Referring now to Figures l~ and 4A there are shown respectively a block diagram of the pulse height selector 110 and a timing diagram useful in explaining its operation. The pulse height selector 110 is responsive to signals from the amplifier 108, such signals being shown illustratively in Figure 4A by pulses 128 and 130. The two pulses 128 and 130 are shown with their rise times exaggerated for purposes of illustration. The intersection of pulse 128 with line 132 and the intersection of pulse 130 with line 133 are at the minimum window voltage or threshold (shown as Vth in the figure) :. . , ,' ' ''. ' ' , : ' . . ' :

which is regarded as an acceptable input signal. Thus, pulses provided by amplifier 108 having a peak value which is less than this threshold value are presumed to occur in response to an excessively low value of radiation incident upon the scanning head 22A such as might occur from Compton scat-tering in the vicinity of the organ 74 of Figure 2B. The intersection of pulse 130 and the line 134 is at a maximum value of window voltage, V ax~
of an acceptable input signal. Thus, as exemplified by pulse 130, the pulse 130 would be an unacceptable input signal in that it exceeds this maximum voltage and is presumed to be produced in response to an excessively high value of radiation incident upon the scanning head 22A of Figure 3 such as might be caused by an extra terrestrial g~mma ra~. The pulse 128 of Figure 4A represents an acceptable pulse in that its peak amplitude is greater than the threshold voltage yet less than the maximum voltage.
; The pulse height selector 110 comprises a pair of comparators 136 and 138 which compare signals from amplifier 108 with respectively the threshold window voltage and the maximum window voltage, and provide output pulse signals (not shown) having leading and trailing edges respectively occurring when an input pulse such as pulse 130 crosses the threshold and the maximum window voltage values. Reference voltages representing the 20 threshold window voltage and the maximum window voltage are provided respec-tively along lines 140 and 142.
The comparators 136 and 138 drive respectively monostable or "one shot" multivibrators 144 and 146 to provide pulses 148 and 150. The leading edges of pulses 148 and 150 correspond respectively to the time instants - when the pulse 130 crosses the threshold window voltage and the maximum window voltage. The pulse 148 has a duration of sufficient length such that the trailing edge of pulse 148 occurs approximately at the midpoint of pulse 150.
Multivibrator 152 is a monostable or "one shot" multivibrator 30 which is triggered by the trailing edge of pulse 148 to produce an output pulse 154 and is inhibited by pulse 150 such that when pulse 150 is applied to the multivibrator 152 the output pulse 154 does not appear. ~1hen the pulse 150 is present, it is applied to the multivibra-tor 152 prior to the , - 8 ~

occurrence of the trailing edge of pulse 148 and is, therefore, effective to inhibit the multivibrator 152. Thus, when an input signal pulse such as pulse 128 is present an output pulse 154 is produced, however, when an input signal such as pulse 130 is present the multivibrator 152 is inhibited so that the pulse 154 is not produced. Also, in the event that an input signal --of peak value less than the threshold window voltage is present, then none of the pulses 148, 150 and 154 is produced. In this way the pulse height selector 110 selects those input signal pulses having peak voltage values falling within the range of values bounded by the threshold and maximum window voltages, and provides output pulses 154 of uniform amplitude and duration corresponding to each one of the input pulse signals having an ac-ceptable voltage value.
The reference voltages applied along lines 140 and 142 are ob-tained via switch 156 from resistors 158A, 158B, 160A and 160B which form a pair of voltage divider circuits, or alternatively, from potentiometers 162 and 164. The voltage divider circuit of resistors 158A and 158B, the volt-age divider circuit of resistors 160A and 160B, and the potentiometers 162 and 164 are energized from voltage source 166 so that either the voltage divider circuits or the potentiometers may be utilized to provide the ref-erence voltages along lines 140 and 142. The switch 156 is mounted on the housing 36 of Figure 1. A novel plug-in module hereinafter referred to as an isotope plug, 168 comprises the resistors 158A, 158B, 160A and 160B, and is conveniently mo~mted on the housing 36 of Figure 1 for operation of the imaging system 20 with the appropriate values of window voltages for the pulse height selector 110.
Referring now to Figure 5 there is shown a block dia,gram of the data processor 114 which comprises a counter 178, a storage unit 180, a digital-to-analog converter 182 and a clock 184. Counter 1~8 is a digital counter responsive to successive pulses such as the pulse 154 from the pulse height selector 110 for counting these pulses and providing a digital number indicating such count. The storage unit 180 has the well known form of a group of flip-flops in parallel connection with ~ach of the output bits of _ 9 _ the counter 178. A strobe pulse provided by clock 184 along line 186 ini-tiates the transfer o~ the digital number from the counter 178 to the stor-age unit 180. Immediately after the strobe pulse on line 186, a reset pulse is provided by clock 184 along line 188 to reset the counter 178 to zero.
The digital number in the storage unit 180 is continuously applied to the digital-to-analog converter 182 which provides an output voltage having a magnitude proportional to the digital number stored in the storage unit 180.
The analog output of the dlgital-to-analog converter 182 corresponding to successive changes in the digital number stored in the storage unit 180 is shown illustratively by the voltage waveform 190. The pulse repetition frequency of both the s-trobe pulse on line 186 and the reset pulse on line 188 provided by clock 184 is set by the scanning speed control knob 192 con-nected to the clock 184 and located on the housing 36 of Figure 1. The scanning speed control knob 192 is also connected to the motor circuit of Figure 15.
In operation, therefore, the data processor 114 is responsive to ; a sequence of individual pulses 154 from the pulse height selector 110 to ; provide an analog voltage output, such as the voltage waveform 190, in which the voltage amplitude corresponds to the number of pulses 154 occurring within the interval between successive reset pulses on line 188. According-ly3 the data processor 114 functions as an integrator in which the voltage waveform 190 is updated periodically at the frequency of the strobe and re-set pulses on lines 186 and 188. As will become apparent in the description with reference to F:igures 8 and 15, the speed at which the scanning head 22A
is moved for scanning is proportional to the ~requency of the ClOck 184, or equivalently the frequency of the strobe and the reset pulses on lines 186 and 188, due to the fact that the motor circuit of Figure 15 and the clock v 184 are both connec-ted to the scanning speed control knob 192. Thus, the count accumulated in an interval between successive reset pulses on line 188 may equally well be regarded as the count accumulated over an interval of scanning in the X direction, such interval being, for example, four milli-meters.

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Referring now to Figure 6 there is shown a schematic diagram of the channel selector 116 which accepts input signals from channel l and channel 2 and independently switches the signals by means of switches 202, 204, 206 and 208 to writing head drivers 120A and 120B and photohead drivers 122A and 122B of Figure 3. The input signal from channel 1 on line 210 is provided by the data processor 114 of Figure 3, and a corresponding signal from channel 2 on line 212 is pro~ided by the data processor of channel 2.
A summing amplifier 214 and a difference amplifier 216 provide the sum and difference of the signals on lines 210 and 212 such that the sum signal appears on line 218 at the output of summing amplifier 214 and the differ-ence signal appears on line 220 at the output of the difference amplifier 216. The lines 218 and 220 connect with the four switches 202, 204, 206 and 208 so that the sum and difference signals may also be individually switched to the writing head drivers 120A and 120B and also to the photo-head drivers 122A and 122B. The four switches 202, 204, 206 and 208 are conveniently mounted on the housing 36 to facilitate the selection of the appropriate data to be displayed on the paper copy 42 and the film plate 54 and 56 of Figure 1.
Referring now to Figure 7 there is sho~m an interior view of the writing head 38A. ~riting head 38B has the same form as writing head 38A
and is not showm in Figure 7. A mark or imprint is made upon the paper copy 42, seen also in Figure 1, by means of a tapered rod, preferably of steel, hereinafter referred to as a tapper 230. The tapper 230 is affixed at its upper end to magnetic material not showm in the drawing which is enclosed by a solenoid 232 so that upon energization of the solenoid with an electric current provided by the writing head driver 120A of Figure 12 along wires 234, the tapper 230 is drawm dowmwards toward the paper copy 42. A spring 236 affixed concentrically to the tapper 230 and also mounted to the under-: side of the solenoid 232 withdraws the tapper 230 from the paper copy 42 upon deenergization of the solenoid 232. The solenoid 232 and the tapper 230 are supported by a bracket 238 which in turn connects with a frame mem-. ber 239 of the backlash linkage 40 which is seen also in Figures 8 and 9.

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To provide a black and white radiograph~ the paper copy 42 com-prises preferably a pressure sensitive paper which when struck by the tapper 230 produces a black mark at the point of impact. The shape of the mark depends on the shape of the tip of the tapper 230 so that a dot or an elon-gated mark ma.y be provided by an appropriate selection o~ the tip of the tapper 230.
To provide a multicolor radiograph, a multicolored ink ribbon 240 is wound around two spools 242A and 242B, positioned on plate 244 and rotated in a well known manner by a small motor (not shown) and is guided by struts 246, 247 and 248 across the -tip of the tapper 230. Upon energization of the solenoid 232, the tapper strikes against a portion of the ribbon 240 and thereby imparts a mark of colored ink to the paper copy 42, the color of the ink depending on the strip, such as a strip 250 containing blue ink, struck by the tapper 230. The struts 246, 247 and 248 are mounted to the plate 244 which is pivotally mounted about the frame member 239 by means of fingers 252 extending from the plate 244. A potentiometer 253 is mounted to the frame member 239 such that its shaft, not shown, connects with a finger 252 with the shaft axis coincident to the pivot axis of the finger 252. The potentiometer 253 provides an electrical signal, to be described with refer-ence to Figure 12, which is responsive to the angle of pivot, or accordingly the color of the mark imprinted on the paper copy 42. The struts 246 and 247 have surfaces which are lower, respecti.vely, outwardly and inwardly along the centers of their axes to provide a uniform spacing of the ribbon 240 relative to the tapper 230 independently of the pivoting of plate 244. Pivoting of the plate 244 is provided by a sector gear 254 affixed to the top of the plate 250, and a worm gear 255 meshing with the sector gear 251, and driven by a stepping motor 256. In response to electrical signals energizing the stepping motor 256, as will be described with reference to Figure 12, the stepping motor 256 i:mparts a rotation to the worm gear 255 to pivot the plate 244 for positioning the ribbon 240 beneath the tapper 230.
Referring now to Figure 8 there is shown an isometric view of the ; carriage 34 and push rods 44 and 46 partially seen in Figure 1. The carriage .. : . . .. ' ,, .

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34 comprises fron-t plate 260, back plate 262, and four connecting struts 264A-D. The transport beam 32 passes through an aperture 266 in the front plate 260 and an aperture 268 in the back plate 262. The carriage 34 is mountea on rails 270 and 272 for motion in the Y direction by means of rol-lers 274 having a flat surface and contacting rail 270 and by means of rol-lers 276 having a concave surface and making contact with rail 272. The concavity of the rollers 276 aids in positioning the carriage 311 upon the - rails 270 and 272. The push rods 44 and 46 are mechanically connected to the transport beam 32 by means of a rigid member referred to as hanger 278 which is rigidly affixed to the transport beam 32. The push rods 44 and 46 are also slidably mounted within a bracket 280 rigidly affixed to the back plate 262 for guiding the push rods 44 and 46 through curtains 282 for posi-tioning the photoheads 50 and 52 seen in Figure 1. The curtains 282 prevent ; the entry of light into the cassettes 58 and 60 of Figure 1 as~he carriage 34 moves back and forth during the scanning operation.
The carriage 34 is positioned in the X direction by means of a - worm drive 284 which comprises worm gear 286, traveler 288 affixed to the ~.
front plate 260 and a chain drive 290 through which the worm gear 206 is driven by motor 292. Upon energi~ation of the motor 292, as will be de-" 20 scribed with reference to Figure 13, the carriage 34 is displaced along the .~ X direction, the amount of displacement depending upon the amount of rotation of the worm gear 286.
The transport beam 32 is supported by the carriage 34 with the aid : of rollers 294 mounted on both the front plate 260 and the back plate 262 around the apertures 266 and 268 in contact with each of the four sides of - the transport beam 32. The rollers 294 permit movement of the transport beam 32 in the Y direction while the transport beam 32 is displaced in the X di-rection by movement of the carriage 34 in response to the worm drive 284.
; The transport beam 32 is displaced in the Y direction by means of " .
a worm drive 296 which comprises a worm gear 298, a traveler 300 rigidly af-fixed to the transport beam 32 and a chain drive 302 through which the worm gear 298 is driven by motor 30L~. In response to an exertation of motor 304 ''' , ' , . . ~:

as will be described with reference to Figure 15 the -transport beam 32 is moved back and forth in the Y direction independently of its displacement in the X direction. In this way the transport beam 32 receives both X and Y
displacements independently of each other to effect a scanning motion of the scanning heads 22A and 22B as well as a scanning motion of the backlash linkage 40, writing heads 38A and38B and the push rods 44 and 46, all of which are seen in Figure 1. It is noted that the scanning motion of the writing heads 38A and 38B is identical to that of the scanning heads 22A and 22B with the exception of the slight displacement of the scanning heads 38A
and 38B afforded by the backlash linkage 40 for elimination of scalloping as will be described with reference to Figures 9 and 10. The use of a single mechanical connection, namely the transport beam 32 provides a precise cor-relation between the position of the writing heads 38A and 38B and the posi-tion of the scanning heads 22A and 22B.
~ Referring now to Figures 9 and ~0 there are shown respectively a cutaway view of the backlash linkage 40 and a diagrammatic view of a radio-graph explaining the scalloping mechanism. The backlash linkage 40 comprises an outer shell 306 and frame member 239 to which is affixed the writing heads 38A and 38B, the outer shell 306 being closed off by a cover plate 308. The outer shell 306 encloses an end of the transport beam 32 and is in mechani-cal contact therewith by means of roller assemblies 310 each of which has a pair of rollers which ride along a track 314 on the transport beam 32. The ; transport beam 32 is hollow to permit the carrying of electric wires within the transport beam for making connection between the scanning heads 22A and 22B and the writing heads 38A and 38B of Figure 1, and accordingly, the outer shell 306 encloses only the end portion of the transport beam 32 to permit electrical wires to make entry into the interior of the transport beam as by means of connector 316.
The amount of backlash provided by the backlash linkage 40 is equal to the spacing between the cover 308 and a striker plate 318 mounted directly to the end of the transport beam 32. A drag rod 320 is affixed to the outer shell 306 and, as is shown in Figure 8, the drag rod 320 extends ~ - 14 -:,-~ . . . .
.

along the beam 32 and passes through a fitting 322 affixed to the back plate 262 of the carriage 34. The fitting 322 makes frictional contact with the drag rod 320 to supply the drag force. Upon a reversal in the direction of travel of the transport beam 32, as for example, when the transport beam 32 has been moving in a direction towards the backlash linkage 40 and then reverses direction, the striker plate 318 moves away from the cover plate 308 until a spacing between the striker p:Late 318 and the cover plate 308 is equal to the amount of scalloping to be negated, for example, six milli-meters. At this point the roller assemblies 310 reach the end of the respec-tive tracks 314 and are contacted by the back side of the striker plate 318 whereupon the roller assemblies 310 and the outer shell 306 proceeds to move along with the transport beam 32 in the direction of the scanning heads 22A
and 22B. As a second example, the transport beam 32 again reverses direc-- tion to move towards the writing heads 38A and 38B in which case there is again an interval of time when the outer shell 306 is momentarily stationary as the transport beam 32 advances toward the writing head 38A and 38B. The outer shell 306 remains stationary until the striker plate 318 moves the distance of six millimeters whereupon it strikes the cover plate 308 at which time the outer shell 306 commences to move along in unison with the transport beam 32. The effect of the six millimeter backlash distance in counteracting a scalloping effect will become apparent in the description of the scalloping as will now be described with reference to Figure 10.
Referring now to Figure 10 there is shown a diagra~matic represen-tation of a simplified view of the imaging system 20 which is shown compris-ing a scanning head 22A, the backlash linkage 40 and a writing head 38A with a tapper 230, the scanning head 22A being shown mechanically connected to the backlash linkage 40 by means of a rigid connection representing the transport beam 32. For simplicity the C-frame 28 and the ratchet arm 26A of Figure 1 have been deleted. The imaging system 20 is shown forming an image on the paper copy 42 in response to a test pattern 33ll painted by way of example with radioactive paint on a film 336 which is posi-tioned beneath the scanning head 22A. As the scanning head 22A moves in both the X and Y direc-- 15 _ .

l66 tions, the tapper 230 provides a series of image marks 338 which correspond to the paint marks 340 of the test pattern 334. The arrows 342A and 342B
trace the direction of movement of the scanning heads 22A and the tapper 230.
Assuming, for the moment, that the backlaah linkage 40 has been disabled, it is observed that while the paint marks 340 of the test pattern 334 are ar-ranged in regular rows and columns, the series of image marks 338 are also arranged in regular rows; however, the columns of the series of image marks 338 have an irregular shape corresponding to the well known scalloping ef-fect. By way of example, the displacement of the image marks 338 from their true columnar positions is presumed to be six millimeters. The backlash linkage 40 is now presumed to be ad~usted to provide six millimeters of back-lash distance whereupon the scalloping effect disappears.
The scalloping effect may be explained as follows. Recalling the description of the data processor 114 with reference -to Figure 5, the data provided along line 210 seen also in Fig~re 3 is updated at the repetition frequency of the reset pulse on line 188 from clock 184. Or, equivalently, the data on line 210 is undated once during each four millimeter scanning interval in the X direction. Now, with reference to Figure 10, is readily appreciated that each of the image marks 338 may be delayed from its corres . 20 ponding paint mark 340 by a distance of up to six millimeters. Thus, when the transport beam 32 reverses direction the first image mark 338 to be placed in the new row is offset by six millimeters, and simila~ly the re-maining image points 338 in that row are offset by the six millimeter dis-tance. The scalloping effect is cured with the aid of the backlash linkage ~O since on a reversal of direction of motion of the transport beam 32 the writing head 38A remains stationary until the scarming head 22A and the transport beam 32 have advanced six millimeters in the X direction whereupon the tapper 230 imprints an image mark 338 in the correct columnar position.
Referring now to Figure 11 there is shown a detailed isometric 30 view of the photohead 50 and a carriage 350 with portions of the figure shownin section. Photohead 52 is identical to photohead 50 and is, there-fore, not shown in the figure. The photohead 50 is suspended from the carriage 350 by - 16 _ .

6~
means of a bracket 352 affixed to a transport plate 354 which forms a part of the carriage 350. The carriage 350 further comprises a pair of support rods 356 and 358, by which the transport pla-te 354 is slidably supported in the X direction, a roller assembly 360 and a roller assembly 362 affixed to the ends of the support rods 356 and 358. Roller assemblies 360 and 362 comprise respectively concave surfaced rollers 364 and flat surfaced rollers 366 for supporting the carriage 350 on rails 368 and 370 to provide motion in the Y direction. The concave surfaces of the rollers 364 serve to posi-tion the carriage 350 on the rails 368 and 370.
The photohead 50 comprises an electronic flash lamp 372 which flashes in response to an electric signal from the photohead driver 122A
transmitted along electrical conductors 374. A lens 376 supported in spaced relationship to the flash lamp 372 by support 378 -~ocuses light from the flash lamp 372 upon film plate 54 within the cassette 58. An aperture plate 380 having a plurality of apertures, such as aperture 381, of differing shapes is positioned between the flash lamp 372 and the lens 376 to provide a desired shape to the spot of light impinging upon the film plate 54. An aperture is selected as follows. A motor 382 positioned within the support 378 rotates the aperture plate 380 about shaft 384 via a step down gear train 386 to position the desired aperture in front of the flash lamp 372. A
plurality of microswitches 388 positioned on top of support 378 have arms 390 which engage cams 392 for actuation of an individual one o~ the micro-switches 388 corresponding to a desired aperture for deenergizing the motor ; 382 when the desired aperture is in position.
The carriage 350 is positioned in the X direction by means of push rod 44, seen also in Figures 1 and 8, which engages the carriage 350 by means of a backlash linkage 394, the backlash linkage 394 being provided to coun-teract the scalloping effect described earlier with reference to Figures 9 and 10. The backlash linkage 394 comprises a striker 396 slidably mounted within the transport plate 354 and affixed to the push rod 44 which is slid-ably extended through end portions 398A and 398B of the transport plate 354.
A small amount of friction is provided between the transport plate 354 and .

the support rod 356, as for example, by means of a spring assembly 400, indi-cated diagrammatically, which exerts a slight pressure upon the support rod 356. In operation, the push rod 44, in response to motion of the hanger 278, the transport beam 32 and the carriage 34 of Figure 8, moves the carriage 350 in both the X and the Y direction in precise synchronism with the motion : of the writing heads 38A and 38B of Figure 1. Upon reversal of motion in the X direction by push rod 44, the transport plate 354 remains stationary momentarily until the striker 396 has advanced a distance sufficient to : counteract the scalloping effect, as was explained with reference to Figures 10 9 and 10, whereupon the striker 396 strikes the transport plate 354 for re-sumption of motion of the transport plate 354. To facilitate movement of - the carriage 350 in the X direction, the push rod 44 passes through the rol-ler assemb~y 360, seen also in Figure 8, and slidably contacts the roller assembly 360 for urging it in the X direction.
Referring now to Figure 12 there is shown a block diagram of the writing head driver 120A and the data enhancement circuit 118A which is ~ interconnected with the writing head driver 120A. The writing head driver - 120A accepts a signal from the channel selector 116 as shown in Figures 3 and 6, the input signal having an amplitude proportional to the number of 20 photons counted in a predetermined interval as described earlier with refer~
ence to the description of the data processor 114 of Figure 5. The input signal is applied via a variable gain amplifier 410 and switch 412 to a variable frequency pulse generator 414 which is responsive to the amplitude of the signal provided by the variable gain amplifier 410. The pulse gener-ator 414 provides a sequence of electrical pulses for energizing the solenoid 232 of the writing head 38A, the sequence of electrical pulses occurring at a pulse repetition frequency linearly related to the amplitude of the signal provided by the variable gain amplifier 410. Thus, the solenoid 232 drives the tapper 230 of the writing head 38A with a repetition frequency, or tap-30 ping rate, linearl~ related to the amplitude of the signal from the channelselector 116. This linear relationship is dependent on the scaling factor of the variable gain amplifier 410 as is set by a knob 416 labeled "density ,.~
., .

control" connecting with the variable gain amplifier 410 and located on the housing 36 of Figure 1. The density control knob 416 is utilized to estab-lish the spacing between contiguous marks on the paper copy 42 of Figure 10.
In an alternative mode of operation the switch 412 is operated to connect the pulse genera-tor 414 to a voltage source 418 which provides a constant input voltage to the pulse generator 414 so that the marks on the paper copy 42 of F~gure lO are unifor~y spaced; this mode of operation is frequently useful when data is presented in color on the papar copy 42.
An additional feature is provided by means of a comparator 420 and a lamp 421 which indicates when the tapping rate provided by the solenoid 232 becomes excessively high. The comparator 420 compares the output volt-age of the variable gain amplifier 410 to a reference voltage on line 422 provided by a suitable source of voltage (not shown). When the output volt-age of the variable gain amplifier 410 is greater than the reference voltage on line 422, thus indicating that the pulse repetition frequency of the pulse train provided by the pulse generator 414 exceeds the frequenc~ response of the solenoid 232 and the tapper 230. The comparator 420 provides an output voltage which energizes the lamp 421, located on the housing 36, thereby providing an indication of the excessive tapper repetition frequency.
The stepping motor 256 which positions the ribbon 240 described earlier with reference to Figure 7, is energized from the sienal provided by the chalmel selector 116 via the color data enhancement circuit 118A and a color drive circuit 423 which comprises a pair of comparators 424 and 426, a pair of gates 428 and 430, and a feedback loop comprising the potentiometer 253 described with reference to Figure 7 and a difference amplifier 432.
The input signal is modified by the data enhancement circuit 118A to provide an enhanced signal on line 434 in a manner to be described. The stepping motors 256 is energized in the following manner: to provide both clockwise and counterclockwise rotation. A pulse generator 436 provides pulses to the windings of the stepping motor 256. The stepping motor 256 has a pair of windings, indicated diagrammatically, for producing either clockwise or counterclockwise rotation, the clockwise winding 438 and the counterclock-_ 19 --wise winding 440 being shown diagrammatically. The clockwise winding 438 is energized with pulses from the pulse generator 436 via the gate 428; and the counterclockwise winding 440 is energized with pulses from the pulse genera-tor 436 by the gate 430. As described earlier with reference to Figure 7, the voltage provided by the potentiometer 253 represents the position of the plate 250 and ribbon 240 as well as the color of the ink being u-tilized by the tapper 230. The desired color is represented by the value of the volt-age of the enhanced signal on line 434. The difference amplifier 432 pro-vides a signal representing the difference of these two voltages. When the signal provided by the difference amplifier 432 is greater than a reference 446 supplied by a suitable voltage source (not shown) and applied to the com-parator 424, the comparator 424 provides a signal which enables the gate 428 thereby passing pulses from the pulse generator 436 to energize the clock-wise winding 438. When the signals provided by the difference amplifier 432 has a value of voltage lower than the voltage of a reference 446 applied to the comparator 426, the comparator 426 provides a signal which enables the gate 430 thereby permitting pulses from the pulse generator 436 to energize the counterclockwise winding 440. And7 when the value of the voltage of the signals provided by the difference amplifier 432 is less than the voltage of the reference 442 and greater than the voltage of the reference 446 then neither gate 428 or gate 430 is enabled and the stepping motor 256 is de-energized and is not rotating. Thus, the stepping motor 256 is able to pro-vide the desired colors as requested by the enhanced signal on line 434 to provide a colored radiograph on the paper copy 42 of Figure 1.
The data enhancement circuit 118A and the data enhancement circuit 118B, seen in Figure 3, operate in the same fashion, and therefore, the data enhancement circuit 118B is not shown in Figure 12. The data enhancement circuit 118A increases the responsivity of the color drive circuit 423 to a preselected range of colors while decreasing the responsivity of the color 30 drive circuit 423 to other preselected colors. This is in contradistinction to the signal provided by the channel selector 116 which induces a uniform responsivity of the color drive circuit 423 to the various colors. The vari-., .... ~

iation and responsivity occurs by virtue of the enhanced signal on line 434.
For example, in the absence of the data enhancement circuit 118A there is a linear relationship between the color selected and the amplitude of the sig-nal provided by the channel selector 116. Again, by way of example, it may be desirable to emphasize those areas of a radiograph corresponding to high intensity radiation which might be represented by warm colors such as red, orange and yellow. In this case, the voltage of the enhanced signal on line 434 would be of a relatively low value even when the voltage of the signal provided by the channel selector 116 has risen to a moderately high value, but as the voltage provided by the channel selector 116 rises to a higher - value, then, the voltage of the enhanced signal on line 434 would be observed to rise sharply with the result that the colored radiograph provided on the paper copy 42 of Figure 1 would have cooler colors such as green, blue, purple over most of the radiograph with the warmer colors, red, orange and yellow appearing only at those spots corresponding to high intensity radia-tion, thereby emphasizing these spots of high intensity radiation.
The data enhancement circuit 118A comprises a series of comparators of which three are shown in the drawing, the three comparators being desig-nated 448A, 448B, and 448C. Each of these comparators 448A-C are provided with separate reference signals having different values of voltage, three such reference signals being shown in the Figure designated at 450A-C. The comparators 448A-C provide output signals when their input signals on lines designated respectively by 452A-C are greater than the voltages of the res-pective reference signals 450A-C. The output signals of the comparators 448A-C are summed together in a summing circuit 454 to provide the enhanced sig-nal.
The desired enhancement characteristic is provided by a plug-in module hereinafter referred to as a color plug 456 which is located on the housing 36 of Figure 1. The color plug 456 comprises a series of resistors 458A-C which function as a voltage divider of the voltage provided by the channel selector 116, the values of the various voltages obtained on the lines 452A~C depending on the values of the various resistors such as the ~8~6~
resistors 458A-C. Thus, the use of -the color plug Li56 in combination with the comparators 448A-C and the summing circuit 454 provides the desired en-hancement characteristic to the signal of the channel selector 116 thereby providing the desired responsivity of the color drive circuit 423 to the color command represented by the voltage value of the signal o~ the channel selector 116.
Referring now tb Figure 13 there is shown a diagrammatic represen-tation of the photohead driver 122A, seen in Figure 3, which energizes the flash lamp 372 of Figure 11. The circuit of the photohead driver 122B o~
Figure 3 is the same as that of 122A and is, accordingly, not shown in Fig-ure 13. The flash tube 372 is of a well known form comprising an anode 468, a cathode 470 and a grid 472. A pulse generator 474 applies voltage pulses between the terminals of the grid 472 and the cathode 470 to gate the flash tube 372 0~ and OFF. Light rays 476 are emitted when the flash tube 372 is gated on by the pulse generator 474. The intensity of the light rays 476 is dependent on the voltage impressed between the terminals of the anode 468 and the cathode 470 by means of a variable gain amplifier 478. The gain of the amplifier 478 is varied by means of a knob 480 located on the housing 36 of Figure l and connecting with the variable gain amplifier 478.
The photohead driver 122A is responsive to the signal provided by the channel selector 116 via switch 206 as indicated in Figure 6, in that the signal is applied to the variable gain amplifier 478 which acts as a scaling factor to provide a voltage for energizing a flash tube 372 which it linearly related to the amplitude of the voltage provided by the channel selector 116.
The photohead driver 122A is furthermore responsive to the signal from the channel selector 116 in that the signal is applied to a su~ming circuit 482 and thereby combined with a second signal on line 484 to provide an output voltage which is applied to the pulse generator 474. The pulse repetition frequency o~ the pulse generator 47ll is linearly related to the voltage pro-vided by the summing circuit 482 so that an increase in the signal voltage provided by the channel selector 116 results in an increase in the pulse repetition frequency of the pulse generator 474 with a corresponding increase in the rate of flashing of the light rays 476 of the flash tube 372.
The photohead driver 122A is also responsive to the scanning speed - of the transport beam 32 such that with increased scanning speeds the flash-ing repetition frequency of the flash lamp 372 is increased to provide an image density on the film plate 54 of Figure 11 which is invariant with scan-, ning speed. Since the flashing rate of the flash tube 372 is sufficiently great such that the light from the various flashes overlap on the film plate 54, as seen in Figure 11, a varying of the flash rate with the scanning speed ensures an image density which is invariant with scanning speed. Ac-cordingly, a potentiometer 486 energized by a voltage source 488 is operated by the speed control knob 192, described with reference to Figures 5 and 15, and generates the signal on line 484 for the summing circuit 482, thereby providing the desired responsivity of the photohead driver 122A to the scan-ning speed. The variable gain amplifier 478 and the summing circuit 482 constitute the data enhancement circuit 118C seen also in Figure 3 and ensure that light flashes from the flash tube 372 have an intensity and a pulse repetition frequency dependent on the amplitude of the signal provided by the channel selector 116.
Referring now to Figure 14 are shown the locks 64 for the cassettes 58 and 60 of Figure 1. The locks 64 comprises a bolt 496 slidably mounted , . .
, within a guide 498 for engaging channel 500 of the housing 62 seen in Figure 1. Access to the bolt 496 in the form of a handle is provided by a pin 502 extending outwardly from the bolt 496 through a slot 504 in the guide 498.
The bolt 496 is positioned by sliding the pin 502 in the slot 504. A slide .
506 is provided in the cassette 58 and 60 for protecting the film plate such as the film plate 54 of Figure 11 from light when the cassette is extracted from the housing 62. The width of the slide 506 is such that the edge of the slide clears the guide 498 of a cassette such as cassette 58 when the ` slide is removed from the cassette 58. ~Iowever, when the bolt 496 extends ; 30 beyond this end of the guide 498 it catches the edge of the slide 506 there-.':;
~-~ by preventing accidental removal of the slide 506. Since -the lock 64 pro-vides a novel arrangement wherein it secures the cassette 58 to the housing . .

~L0~66 62 of F'igure 1 or, alternatively, releases the cassette 58 from the housing 62 while engaging the slide 506. The front lip 508 of the slide 506 serves as a handle for extracting the cassette 58 from the housing 62.
Referring now to Figure 15 there is shown a schematic diagram of the circuitry for energizing the motor 292 and 304 of Figure 8 which provide respectively movement of the transport beam 32 in the X direction and move-ment of the carriage 34 in the Y direction. The motor 292 is energized from - a source of power 516 (shown symbolically as a battery) supplied via a vari-able gain amplifier 518, a power-on switch 520 and a relay 522. The relay 522 is energized fromasource of power 524 via microswitches 526 and 528 and a set of contacts 530 of the relay 522 itself.
Returning momentarily to Figure 8 the microswitches 526 and 528 are seen located respectively on the front plate 260 and the back pla~e 262 of the carriage 34. The microswitches 526 and 528 are utilized to initiate and to terminate the movements of the transport beam 32 in the X direction.
A pair of scales 532 and 534 are mounted on the transport beam 32. A pair of knobs 536 and 538 are slidably mounted respectively on the scales 532 and ` 534 for setting the extreme points of the scanning movement of the transport beam 32. The knob 536 serves as a cam for actuating the microswitch 526 when the knob 536 passes by the front plate 260. The knob 538 serves as a cam for actuating the microswitch 528 as the knob 538 passes by the back plate 262. Actuation of the microswitches 526 and 528 causes the motor 292 to reverse direction as is shown on Figure 15.
Returning now to Figure 15 the relay 522 is shown deenergized and the motor 292 lS energized via the two sets of relay contacts 540 and 542.
The motor 292 drives the transport beam 32 from the back plate 262 towards ' the front plate 260 in the manner described with reference to Figure 8.
This movement of the transport beam 32 continues until the knob 538 actuates the microswitch 528 on the back plate 262. As shown in Figure 15 actuation ` 30 of the microswitch 528 closes the circuit containing the source of power 524 thereby energizing the relay 522 with the result that the motor 292 is ener-gized through another set of relay contacts 544 and 546 with the result that - 24 _ - , , ~4~
electric current enters the winding (not shown) of the motor 292 in the reverse direction thereby reversing the motor direction of rotation. The motor mayhave by way of example, a permanent magnet stator, and a rotor which is energized through a commutator by an external current such that reversal of this current, as in the case of -the motor 292, results in a reversal of the direction of rotation. Energization of the relay 522 also closes the set of relay contacts 530 providing a second path of energization of the re-lay with power from the source of power 524 via the microswitch 526. The reversed direction of the motor 292 now drives the transport beam 32 of Fig-ure 8 from the front plate 260 towards the back plate 262 so that the knob 538 is no longer engaging the microswitch 528 with the result that the mi-croswitch 528 opens one of the circuits energizing the relay 522. However, the relay 522 remains energized via the microswitch 526. The movement of the transport beam 32 continues until the knob 536 actuates the microswitch 526 on the front plate 260 thereby breaking the circuit for energizing the relay 522. Thus, the relay 522 becomes deenergized and assumes the contact position shown in ~igure 15. Accordingly, the motor 292 reverses direction such that the transport beam 32 is again traveling in a direction from the back plate 262 towards the front plate 260 thereby completing the cycle in 20 the X direction.
The motor 304 is energized by a source of power 556 via the power-on switch 520, two sets o~ relay contacts 558 and 560 of relay 562, and by the parallel combination of microswitches 526 and 528 and the relay 564.
The relay 562 is energized from a source of power 566 via a first circuit including microswitch 568 and a second circuit including microswitch 570 and a set of contacts 572 of the relay 562 itself. It is noted that the motor 304 remains deenergized until such time as either the microswitch 526 or microswitch 520 is actuated. Thus, during a scanning movement of the trans-port beam 32 themotor 304 is deenergized and the carriage 34 does not move 30 in the Y direction. However, at the conclusion of a single scan in the X
direction when the transport beam 32 reverses direction, the microswitch 526 or the microswitch 528 is actuated respectively by the knob 536 or the knob , . :

538 to effect the reversal of direction of the transport beam 32. At the moment of actuation of microswitch 526 or 528 the motor 30~1 is energized and the carriage 34 is displaced in the Y direction in the manner described with reference to Figure 8. Energization of the motor 304 also results in an energization of the relay 564 with the consequent closing of its set of con-tacts 574. The closure of the contacts 574 in circuit with the counter-switch unit 576, seen also in Figure 8, retains the state of energization of the motor 304 even after the microswitches 526 and 528 are no longer actuated by the knobs 536 and 538. Thus, the motor 304 is able to position the car-riage 34 independently of the length of time that the microswitches 526 and 528 are actuated.
The motor 304 is deenergized when the carriage 34 has been dis-placed or indexed by a preset amount, this amount being set by the counter-switch unit 576 which as shown in Figure 8 is located on the end of worm drive 284 and mounted on the housing 36. The counter-switch unit 576 com-prises a rotary member 578 directly connected to the worm gear 286, and a stationary member 580 connected to the housing 36. The counter-switch unit 576 counts the number of rotations of the worm gear 286 and opens its switch when the prescribed count has been reached. The counter-switch unit 576 is 20 of a well known form and may comprise, for example, a rotary member 578 hav-ing a permanent magnet which actuates reed switches (not shown) in the sta-tionary member 580, the reed switches being arranged in a counting circuit.
- Alternatively, the stationary member 580 may comprise a magnetic coil pick-up which energizes a digital counter whenever the pickup coil is energized , ~
by the magnet of the rotary member 578. Upon reaching the desired count the counter-switch unit 576 opens its switch which deenergizes the relay 564 thereby deenergizing the motor 304 so that the carriage 34 remains station-ary at its new position.
When the carriage 34 has reached an extreme position in the Y
30 direction its motion must then be reversed to bring it back. The motor re-versal circuit for the motor 304 is similar to that described earlier with reference to the motor 292. A scale 582, seen in Figure 8, is mounted to ~4~
the rear of the housing 36. Two knobs 584 and 586 are slidably mounted on the scale 582 for setting the extreme points of the indexing motion of the : carriage 34. In one extreme position in the Y direction of the carriage 34, the knob 584 serves as a cam to actuate the microswitch 568; and in the other extreme position of the carriage 34 in the Y direction, the knob 586 serves as a cam to actuate the microswitch 570. When the relay 562 is de-energized, as shown in Figure 15, the motor 304 being energized through the sets of contacts 558 and 560 drives the carriage 34, in the manner as de~
scribed in Figure 8, in a direction towards the knob 584. When the micro-switch 568 reaches the knob 584, the knob 584 acts as a cam which actuates the microswitch 568. The actuation of the microswitch 568 closes the circuit containing the source of power 566 to energize the relay 562. Upon energiz-ation of the relay 562 the motor 304 receives electric current through the sets of contacts 588 and 590 of relay 562, rather than the sets of contacts 558 and 560~ with the result that current is applied in the reverse direc-tion to the motor 304 which then rotates in the reverse direction. Since - the motor 304 is now rotating in the reverse direction, the carriage 34 is now traveling in a direction away from the knob 584 and towards the knob 586. The energization of the relay 562 by the microswitch 568 has also re-..
20 sulted in a closure of the set of contacts 572 which provides a second path of energization of the relay 562 by the microswitch 570. Thereby, upon motion of the carriage 34 away from the knob 584 and the deactivation of the microswitch 568 the relay 562 remains energized. Accordingly, the succes-- sive indexing operation of the carriage 34 are performed with a direction of .` motion on the carriage 34 away from the knob 584. The carriage 34 reaches the other extreme of this motion; the knob 586 activates the microswitch 570 breaking the second circuit of energization of the relay 562. The deenergiz-ation of the relay 562 reverses the direction of current to the motor 304 with the result that the carriage 34 now proceeds to index in the reverse ; 30 direction towards the knob 584 thus completing the cycle.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A radiographic imaging system comprising: a radiation detector system responsive to radiation incident thereupon for providing electrical pulses representative of the value of said radiation, computing means coupled to said detector system for converting said electrical pulses to output signals each of which has a magnitude representing the number of said electrical pulses occurring in a predetermined interval; said computing means including means for storing said pulses and means coupled to said storing means for combining said pulses to provide an output signal; a display including means coupled to said output signal of said computing means for printing marks having colors representing said magnitude of said output signal, said printing means including a color ribbon having bands of color positioned longitudinally thereof, means positioned adjacent said ribbon for urging a portion of one of said bands toward a medium of said display for imparting a colored mark thereto, means responsive to said output signal of said computing means for moving said ribbon in a transverse direction thereof to position one of said bands beneath said urging means, means coupled to said transverse moving means for developing a feedback signal representing the position of said transverse moving means, and means coupled between said computing means and said transverse moving means for forming the difference between said output signal and said feedback signal for energizing said transverse moving means.

2. A radiographic imaging system comprising: a detector system of radiation providing successive electrical pulses in response to radiation incident thereupon; means coupled to said detector system and responsive to said electrical pulses for computing an output signal having a value representing the number of said electrical pulses occurring during a pre-determined interval; said computing means including means for accumulating amounts of quanta of said radiation occurring during said predetermined interval and providing data signals representing said accumulated amounts, means for storing said data signals and means coupled to said storing means for combining said data signals to provide said output signal; a display having a longitudinal color medium having color bands extending longitudinal-ly thereof; means for movably supporting said color medium to permit the positioning of individual ones of said color bands; and means coupled between said computing means and said supporting means to alter the positions of said bands of color in accordance with the magnitude of said output sig-nal.

3. A radiographic imaging system comprising: means for scanning a region of space permeated with radiant energy, said scanning means providing electrical pulses corresponding to incidences of said radiant energy; means connected to said scanning means and responsive to a sequence of said electrical pulses during a predetermined interval for converting said sequence of electrical pulses into a signal having a magnitude representing the amount of said radiant energy; said converting means including means for accumulating amounts of quanta of said radiant energy occurring during said predetermined interval, means for storing said amounts and means for combining individual ones of said amounts of quanta of said radiant energy to provide said signal having a magnitude representing the amount of said radiant energy; a display having means coupled to said scanning means for stimulating a media of said display in response to signals of said converting means, said media stimulating means comprising a source of light directing rays of light toward said media; an apertured member having apertures of differing dimensions, said member being positioned relative to said source to permit a perimeter of one of said apertures to enclose the rays of light emitted by said source, and means for moving said member to selectively position one of said apertures about said rays of light.

4. A system according to claim 3 further comprising a lens positioned between said member and said media for focussing said aperture on said media.

5. A radiographic imaging system comprising: means for sensing quanta of radiant energy, said sensing means providing successive signals in response to the sensing of successive quanta of radiant energy; means for moving said sensing means through a region of space permeated with said radiant energy; means coupled to said sensing means for counting sequences of said signals thereof during a predetermined interval of time; means for storing counts of said counting means, and means coupled to said storing means for combining counts of said counting means; means coupled to said combining means for converting digital counts thereof to output signals having amplitudes proportional to the counts of said combining means; and means coupled to said converting means for displaying marks representing a magnitude of said digital counts of said combining means.

6. A radiographic imaging system comprising: radiation detection means for providing electrical signals, sequential ones of said electrical signals representing the presence of radiation in response to radiation incident upon said detection means from a radiant subject; means for impart-ing a relative motion between said detection means and said radiant subject;
means coupled to said detecting means for accumulating amounts of said electrical signals; means coupled to said accumulating means for storing said accumulated amounts; means coupled to said storing means for combining said accumulated amounts to provide an image point signal; a display; and timing means coupled to said moving means and to said storing means for activating said moving means and said storing means at predetermined rate, said image point signal representing data of an image presented on said display in response to said incident radiation.

7. A radiographic imaging system for providing data of a radiant subject, said system comprising: a detector system providing signals representing the occurrences of rays of radiation incident upon said detector system; means coupled to said detector system for converting said detector signals to signals having a digital format, said converting means including means for accumulating detector signals during a predetermined interval of time; storage means coupled to said converting means for storing data of said detector signals, and means coupled to said storage means for combining values of accumulated detector signals; and means coupled to said storage means for displaying an image of said radiant subject, said image having intensity data of said detector signals representing said occurrences of rays of radiation.

8. A radiographic imaging system for providing data of a radiant subject, said system comprising: detection means positioned to detect quanta of radiant energy radiating from said subject; scanning means for imparting a relative motion between said subject and said detection means, said relative motion continuing during a succession of intervals; data means coupled to said detection means for converting signals of said detection means into digital numbers providing data representing the amount of said quanta detected during a plurality of said successive intervals; said data means including means for storing said digital numbers during successive ones of said intervals; means coupled to said storing means for combining the data of one of said digital numbers with the data of a second of said digital numbers to provide output data at successive instances of time, a display; said combining means being further coupled to said scanning means to provide upon said display data relative to the position o-f said detection means; and means coupled to said combining means for offsetting said data at predetermined points of a scan of said scanning means to provide data upon said display which is free of scalloping effect.