Radiation imaging monitor control improvement

A radiographic imaging system and method is disclosed having improved monitor control for enhancing the flexibility of a monitor so that one monitor can perform optimally under several system operating modes. The monitor automically detects the line rate most suitable for producing an image in the selected mode. Brightness compensation is accomplished as a function of the scan line rate at which the monitor is operating. Aspect ratio of the monitor produced image is also adjusted automatically in accordance with the operating mode selected. The system incorporates monitor brightness adjustment as a function of aspect ratio as well. Where the system incorporates a video tape or disk recorder, a time constant of the monitor is adjusted to optimize the monitor's compatibility with the video data output from the recorder in response to the selection of an operating mode wherein the recorder feeds the monitor with video information.

TECHNICAL FIELD 
This invention relates generally to multimode fluoroscopic/radiographic 
imaging, and more particularly to a viewing monitor control for optimizing 
performance of a single monitor in each of a multiple number of modes of 
operation. 
BACKGROUND ART 
Modern x-ray fluoroscopic/radiographic imaging systems include means for 
operating in a plurality of imaging modes. Such systems, sometimes called 
"x-ray suite", include a radiation source, which directs x-rays through a 
patient onto the input face of an image intensifier tube. The image 
intensifier tube converts a relatively large area of x-rays to a smaller, 
relatively bright visual image corresponding to the x-ray pattern emerging 
from the patient. A television camera views an output image from the image 
intensifier tube and produces a video output comprising an ensemble of 
signals, including video and appropriate sync signals, which collectively 
define the viewed pattern, and is known as a composite video signal. 
The video signal from the television can be directly coupled to a viewing 
monitor which produces a visible image corresponding to that viewed by the 
television camera. Alternately, the video can be directed to various 
display processing components, such as digital acquisition systems and 
video tape or video disk recorders. Such devices store and/or process the 
video signals and playback the video signals to the monitor at a later 
time. 
Such x-ray fluoroscopic/radiographic imaging systems include a "system 
controller" actuable by an operator to determine the mode in which the 
x-ray imaging system will operate. There are several such possible 
operating modes. In fluoroscopy, for example, the video from the camera is 
transmitted directly to the monitor for real time viewing. There are at 
least two types of fluoroscopic imaging, i.e., the standard mode and the 
high resolution mode. The standard mode employs a 525 line per screen 
image, while the high resolution mode employs a 1049 line image. 
In another mode, video from the camera can be directed to a digital 
acquisition system for storage and later playback. In this mode, the 
digital acquisition system (DAS) digitizes the information, which is later 
reconverted to analog form for presentation to the monitor for the 
production of a viewable image. 
In still another mode, video is directed for recording on tape or disc, for 
later playback. Upon playback, the tape or disc is rerun and a video 
output is directed to the monitor which produces the viewable image. 
A problem which has arisen in operation of these multimode systems or 
suites is that the various modes of imaging impose different requirements 
on the viewing monitor for optimal imaging. This multiplicity of monitor 
requirements has necessitated either the provision of multiple monitors in 
such x-ray systems, one preset for each mode requiring different 
performance, or made necessary manual adjustment of a monitor prior to 
each change in imaging mode. 
Parameters of monitor operation which must change for different operating 
modes are the line scan rate of the image, the aspect ratio of the image, 
the brightness of the image, and a time constant or delay imposed by the 
video input circuitry of the monitor on incoming video signals. 
As mentioned above, in fluoroscopy, it is often necessary to change between 
525 line and 1049 line display formats. Brightness adjustment must be made 
as a function of which line rate is selected. In fluoroscopy, a 1:1 aspect 
ratio is desirable. 
Where the digital acquisition system is used as a display source, playing 
back reconverted digital information to the monitor for imaging, the 
aspect ratio of the monitor-produced image must be changed from 1:1 to 
4:3. As in the case of fluoroscopy, either a 525 line or 1049 line display 
can be selected, depending on the degree of resolution desired. Monitor 
brightness must be adjusted for each change in line rate and in aspect 
ratio. 
Where a video tape recorder or video disk recorder is used as a display 
source for the monitor, again, either a 525 line or 1049 line display 
format can be selected, depending on the degree of resolution desired. 
Brightness of the monitor must be adjusted as a function of the line rate. 
The desirable aspect ratio for modes using the video recorders as display 
sources is 1:1, and, if that aspect ratio represents a change, brightness 
must be adjusted accordingly with that variable as well. In addition, 
where a video recorder is used as a display source, a time delay imposed 
by the input circuitry of the monitor should be decreased to facilitate 
the display of a stable image. 
In the past, these various requirements have been satisfied by the 
inclusion, with an x-ray system or suite, of multiple monitors, each being 
preset for operation in accordance with one or another of the various 
combinations of parameters which are called for for each of the operating 
modes. 
For example, one system uses one monitor to display continuous fluoroscopy, 
an additional monitor to display images from a digital acquisition system 
used as a display source, and a third monitor for video recorder output. 
These monitors, sometimes different in size and brand, add to the cost of 
the system, can distract the operator by their complexity, and generally 
complicate the viewability of the diagnostic information. The combination 
of several monitors also can create a perception that a system is not well 
integrated due to a number of "add-ons". 
DISCLOSURE OF THE INVENTION 
It is an object of the present invention to consolidate monitor displays in 
a multimode fluoroscopic/radiographic system. A single monitor with 
associated control circuitry displays all required diagnostic images. 
A diagnostic system constructed in accordance with the invention includes a 
radiation source and a camera for generating video signals representing a 
sensed pattern of radiation. The sensed pattern will typically provide an 
image corresponding to the internal structure of a patient whose condition 
is being diagnosed. 
The system further includes a video recorder or video digitzer that can 
receive video signals from the camera and then present those signals to 
the monitor in a modified format. 
A monitor is adapted to display signals directly from the camera as well as 
video signals that have first been stored by the video recorder or that 
have been digitized by the video digitizer. The monitor includes circuitry 
to generate synchronization signals, to adjust image brightness, to adjust 
the image aspect ratio, and to control the image resolution. 
A system video switcher includes a programmable switch to selectively route 
video signals from an image source to the monitor. The controller video 
switcher with a user console which can be switched to a particular viewing 
mode. The video switcher automatically routes a video signal from a 
selected image source to the monitor and modifies the monitor operation to 
correspond to the selected viewing mode. The user does not have to adjust 
the monitor nor select from a number of monitors which have been 
previously adjusted for a particular viewing mode. The confusing and 
awkward systems of the prior art are obviated. 
The programmable video switcher that routes video signals has a number of 
contacts that are closed by a programmable address decoder preferably 
embodied in an electronically erasable read only memory. This allows the 
control system to be easily reprogrammed. 
Signals from the programmable address decoder also automatically configure 
circuitry interfacing the viewing monitor to adjust monitor operation. 
This circuitry automatically selects the aspect ratio and horizontal time 
constant of the monitor without requiring operator intervention. 
Details of the different user selectable options and the affect a choice of 
those options has on the controller and viewing monitor are presented 
below where a detailed description of a preferred embodiment of the 
invention is described in conjunction with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 illustrates in generallized form a radiation imaging system 
incorporating the present invention. The system of FIG. 1 includes a 
source 10 for producing penetrative radiation, such as x-rays, which are 
propagated along a path 12 toward an input face 14 of an image intensifier 
tube 16. The image tube 16 is sufficiently spaced from the source 10 to 
accommodate the positioning of a patient or subject 18. X-rays from the 
source pass through the patient and the emergent radiation pattern is 
incident upon the input face 14 of the image tube 16. The image tube 16, 
of known variety, produces a visible light image at an output face 20 
corresponding to the pattern of x-rays incident upon its input face 14. 
A television camera 22 is aligned to view the image appearing at the output 
face 20 of the image tube 16. The television camera 22 produces an 
ensemble of video signals which collective define the image viewed by the 
camera at the output face 20 of the image tube 16. 
More specifically, the television camera 22 receives light output from the 
output face 20 of the image tube, and produces a video signal set 
representing the light distribution of the viewed image along with 
appropriate synchronization signals. The video and synchronization signals 
are either transmitted directly to a monitor 24, or are transmitted 
indirectly to the monitor 24 by a video signal processing subsystem 23 
(FIG. 1) that includes a plurality of other display sources. 
The fluoroscopic/radiographic imaging system in which the present invention 
is incorporated includes a console 27 having a keyboard input 29 for 
selecting whether the video signal is transmitted directly to the monitor 
from the camera 22, or is transmitted to one of the plurality of other 
display sources in the video signal processing subsystem 23 for subsequent 
playback on the viewing monitor 24. 
A preferred monitor 24 is a CRT type Model HRD 1240 Sierra monitor 
commercially available from Sierra Scientific of Sunnyvale, Calif., USA, 
and includes provisions for adjustment of several imaging parameters. 
Among the parameters of which adjustment is provided is aspect ratio, 
which is the ratio between the horizontal and vertical deflection, volt 
for volt, of the electron beam which is used to produce the image on the 
face of the CRT. A circuit within the monitor 24 also provides for 
adjusting the brightness and contrast of the image. Additionally included 
in the monitor is a horizontal phase lock loop (PLL) Circuit which 
synchronizes the horizontal deflection voltages with the horizontal sync 
pulses that form part of the composite video signal. An R-C circuit in the 
PLL circuit imposes a particular time response on incoming video 
horizontal information. The R-C circuit helps improve the responsiveness 
of the horizontal PLL to lock to horizontal sync pulses, and avoids 
"tearing" of the monitor image due to improper horizontal synchronization. 
FIG. 2 illustrates components of the video processing subsystem 23 
interposed between the television camera unit 22 and the monitor 24. FIG. 
2 illustrates the video signal from a television camera output transmitted 
to an input A of a multi-input, multi-output video switch unit 28. Coupled 
to other inputs B-D of the video switch unit 28 are outputs of other video 
display sources, such as two outputs of a digital acquisition system 30 
and a video recorder unit 32. Some of the outputs of the switch unit 28 
are coupled to inputs of the auxiliary display sources 30, 32, while one 
of the outputs, extending over a video signal path 34, is coupled to a 
video input terminal of the monitor 24. 
Additionally, output signals from the video switch unit 28 are directed, 
over a two line opto-isolated signal path represented by the dotted line 
designated by reference character 36, to remote control terminals of the 
monitor 24. 
The video switching unit, depending on the x-ray system mode of operation 
selected via the console 27, enables the monitor 24 to display video 
information from the appropriate source of video signals. 
Table 1 (below) lists x-ray image viewing mode choices, and specifies the 
video routing (Video In and Video Out) through the video switcher unit 28 
for each choice. Table 1 also specifies the aspect ratio, line scan rate, 
and time delay requirements of the monitor for each viewing mode of the 
diagnostic system. 
TABLE 1 
______________________________________ 
Video Video Aspect VTR Scan 
Mode In Out Ratio Y/N Rate 
______________________________________ 
Fluoro A .fwdarw. 
3 1:1 N 525 
525 A .fwdarw. 
2 
Fluoro A .fwdarw. 
3 1:1 N 1049 
1049 A .fwdarw. 
2 
DAS A .fwdarw. 
1 
Position 
B .fwdarw. 
3 4:3 N 525 
DAS A .fwdarw. 
1 
Image B .fwdarw. 
3 4:3 N 525 
DAS A .fwdarw. 
1 
HRES C .fwdarw. 
3 4:3 N 1049 
VTR 
Play D .fwdarw. 
3 1:1 Y 525 
______________________________________ 
The video switch unit 28 is "crosspoint" in design, which means it can 
connect any of its inputs to any of its outputs without video termination 
problems. The selection of the video path through the switch unit 28 
(characterized by the ".fwdarw." which connotes "connected to/from") 
depends on which of the modes of operation is selected for the system. The 
console 27 interfaces the video processing subsystem 23 by a 
multiconductor cable multiconductor cable which is interfaced to a 
programmable switch circuit 40 by way of a system signal distribution 
circuit 44. 
Circuitry that interfaces the monitor brightness, deflection, and phase 
lock loop circuits is schematically depicted in FIGS. 3 and 4. In FIG. 3 
the composite video signal input 34 from the switch unit 28 is coupled to 
a sync processor 50 within the monitor that strips the signal of its video 
portion and produces a sequence of horizontal and vertical sync pulses. 
The rate of these pulses indicates whether the video scan rate is 525 or 
1049 lines per image screen. A rate detection circuit 52 (within the 
monitor) generates a D.C. output sensitive to rate, 52a, coupled to a 
comparator 54. When the scan rate is 525 lines the D.C. level of the 
output 52a is higher than when the resolution is 1049 lines. A comparator 
output 54a goes high when the 1049 line scan mode is sensed by the rate 
detection circuit 52. A high output from the comparator gates an analog 
switch 56 closing a switch contact 56a to add a resistor 58 in parallel 
with a second resistor 60. The parallel combination of resistors is 
coupled to a monitor phase lock loop circuit 62 connection A1 to adjust a 
voltage of a voltage controlled oscillator (VCO) that governs the 
horizontal sweep frequency of the monitor. 
The two signal opto-isolated path 36 of FIG. 2 is shown as two conductors 
66, 68 coupled to two opto-isolators 70, 72 in FIG. 4. A high signal on 
the conductor 66 causes the monitor to display video information with a 
1:1 aspect ratio and a low signal at the conductor 66 selects a 4:3 aspect 
ratio. The aspect ratio is adjusted by adding a resistor in parallel to an 
existing monitor resistor to increase the gain of a horizontal deflection 
amplifier in the monitor 24 by a factor of 4/3. 
The conductor 68 carries a signal that indicates whether a time delay is 
imposed. When the input goes low a response time is speeded on video 
signals to configure the monitor for receipt of video signals from the 
recorder 32. This speeded up response time eliminates the known phenomena 
of "flagging" where the image tears at the top of the picture with video 
originating at the video recorder 32. When the recorder 32 is used as the 
video source it is necessary to speed up a time response of the monitor's 
horizontal phase lock loop. This is accomplished by shunting a 
resistor-capacitor circuit to ground. 
The opto-isolator circuits 70, 72 activate gate inputs to analog switches 
80, 56. One output A2 from the switch 80 is coupled to the monitor 
deflection circuit, a second output C3 from the switch 80 is coupled to a 
video preamplifier circuit and adjusts a clamp circuit reference voltage 
to restore monitor brightness independent of aspect ratio choice. An 
output B1 from the switch 56 is coupled to the horizontal phase lock loop 
circuit to alter the signal response of the horizontal sweep generator. 
Thus, a change in aspect ratio affects brightness, as well as aspect ratio 
and a change to the video recorder changes the time delay imposed on video 
signals utilized by the phase lock loop. 
Detailed schematics of the switch unit 28 and programmable switch logic 40 
are presented in FIGS. 5-8. FIG. 5 illustrates an impedance matching input 
channel for the switch inputs A, B, C, D in FIG. 2. Each input channel 
includes a gain of two differential amplifier 105 having two double 
emitter high frequency transistors 102, 104. An output from the collector 
of the transistor 104 is coupled to a buffer amplifier 106 having a signal 
output designated IN A in FIG. 5. Although one input channel for the 
switch 28 is depicted in FIG. 5, it is appreciated that each of the four 
switch inputs A, B, C, and D is coupled to a differential amplifier 
circuit configuration identical to the FIG. 5 circuit. 
FIG. 6 illustrates an array of 16 switch contacts K1-K16 representing relay 
control contacts for coupling one of the signal inputs IN A, IN B, IN C, 
IN D to one of the four channel outputs labelled channel 0-channel 3. The 
array of 16 switch contacts K1-K16 forms a multiplexer 110 to controllably 
direct input signals at inputs A-D to output signals at the four output 
channels, channel 0-channel 3. Each of the four channel outputs 0-3 
includes a buffer amplifier 112 interposed between its associated switch 
contacts and the channel output. 
The status of the relay contacts K1-K16 (FIG. 6) is determined by the 
output status of relay drivers which in turn is determined by the output 
of a 16 line output labelled K1-K16 in FIG. 7. A series of four selector 
circuits 114-117 control the status of these 16 outputs. The selector 
circuit 114 selectively controls energization of relay coil drivers that 
open and close the first four relay contacts K1-K4 associated with channel 
output 0 (FIG. 6). In the illustrated embodiment of the invention, only 
one of the contacts K1-K4 is closed at a given time. The selector circuit 
114 includes four outputs one for each of the contacts K1-K4. Receipt of 
an enable input to the selector circuit 114 asserts one of the four 
outputs based upon the status of two address inputs A0, A1 to the selector 
114. 
The operation of each of the other selector circuits 115-117 is similar. 
Each of these selector circuits is associated with one output channel of 
the switch unit 28 and in particular the selector circuit 115 closes the 
contacts K5-K8 associated with channel 1, the selector circuit 116 closes 
the contacts K9-K12 associated with channel 2, and the selector circuit 
117 closes the contacts K13-K16 associated with channel 3. 
The address and enable inputs to the two selector circuits 114, 115 are 
presented on a 6 bit data bus 120. Data is presented to the data bus 120 
by six data outputs D0-D2, D4-D6 of an electronically erasable read only 
memory unit (EEROM) 122. 
The EEROM unit 122 has a series of 11 address inputs A0-A10 and defines a 6 
bit output presented on the data bus 120. During normal operation, an 
output enable control 124 of the EEROM 122 is rendered active so that the 
EEROM unit 122 presents as its data output the contents of a storage 
location addressed by an address bus 125 having address inputs A0-A10. 
As seen in FIG. 7, a second EEROM unit 126 having a sequence of 6 outputs 
is tied to a second data bus 130 which controls 6 inputs to the selector 
circuits 116, 117. In a completely analogous fashion, whenever an output 
enable control 132 to to the ROM unit 126 is rendered active, the ROM unit 
126 presents data onto the data bus 130 for the selector circuits 116, 
117. The two output enable control inputs 124, 132 to the EEROM units 122, 
126 are coupled together and are active so long as a toggle switch 140 
(FIG. 7) is open. 
The address signals on the address bus 125 are generated at the 
distribution circuit 44 so that depending upon the mode of operation a 
user selects via the console 27, a particular address is presented on the 
address bus causing the two read only memory units 122, 126 to present 
appropriate data for activating the switch contacts K1-K16. In the 
disclosed embodiment of the invention, the EEROM units 122, 126 are 
programmed to couple each input at input A-D (FIG. 2) to only one output 
at output channel 0-3 with the disclosed design, however, any interconnect 
combination is possible. 
The toggle switch 140 (FIG. 7) is closed to reprogram the EEROM units 122, 
126. If the EEROM unit 122 is to be reprogrammed, a write enable input 142 
to the EEROM unit 122 must be rendered active and this is accomplished by 
closing a pushbutton switch 144. When this happens, the ROM unit 122, 
latches the data on the data bus 120 and stores it in a storage location 
dictated by the address bus 125. The data presented on the data bus 120 to 
reprogram the EEROM is controlled by inputs to a bi-directional buffer 150 
which is coupled to user activated programming switches (not shown) that 
are manually set. 
The ROM unit 126 can be reprogrammed by appropriate selection of data to 
the input of a second bi-directional buffer 152 that interfaces the data 
bus 130. The reprogrammability of the ROM units 122, 126 allows the 
various input/output combinations depicted in Table 1 to be changed as the 
diagnostic system of FIG. 1 is reconfigured. 
Circuitry for generating the opto-isolated aspect ratio and time constant 
signals is depicted in FIG. 8. The switch unit 28 includes four aspect 
ratio and time constant decoder circuits, one for each output channel. A 
representative decoder circuit 160 for channel 3 is depicted in FIG. 8. 
Two outputs 160a, 160b from a decoder circuit 160 controllably energize 
two light emitting diodes 162, 164 which turn on and off two transistors 
166, 168 coupled via the conductors 66, 68 to the opto-isolator circuits 
70, 72 of FIG. 4 when the channel 3 output is coupled to the monitor 24. 
The status of the outputs 160a, 160b is controlled by two address inputs 
A.sub.1, A.sub.0 coupled to the EEROM unit 126 of FIG. 7 (data pins 
D.sub.4, D.sub.5) and a switch array 170 coupled to an eight bit data bus 
172. The switch array 170 is organized in four groups of two switch 
contacts to a group. Each group of two switch contacts is associated with 
a particular input channel. The address inputs A.sub.0, A.sub.1 to the 
decoder 160 instruct the decoder which input channel is connected to 
output channel 3. When the channel A (TV camera) input is coupled directly 
to the monitor output of output channel 3 the aspect ratio is 1:1 and no 
time delay adjustment is required (See Table 1). Two switch contacts 170a, 
170b of the switch array 170 are accordingly set to cause the decoder 160 
to turn off the transistors 166, 168 to present high inputs to the 
opto-isolators 70, 72 of FIG. 4. Other appropriate switch settings in the 
array 170 are made to characterize monitor display characteristics when 
video data originates from input channels B-D. 
Details of the FIGS. 3 and 4 monitor adjustment circuitry is depicted in 
FIG. 9. The comparator circuit 54 has one input coupled to an output 52a 
from the rate detector circuit 52 and a second input coupled to a 
reference potential generated by a variable resistor 210. An output from 
the comparator 54 is coupled to a one-shot 212 that is gated by a vertical 
sync pulse from the monitor so that the one-shot 212 acquires the output 
data from the comparator 54 only during the vertical blanking period of 
monitor operation. 
Two output signals 212a, 212b that are the complement of each other from 
the one-shot 212 are coupled to gate inputs that control the status of two 
contacts 56a, 56b of the analog switch 56. The switch contact 56a adds a 
resistor 214 in parallel to a second resistor 216 which controls a voltage 
control output in the phase lock loop circuit. This voltage control output 
determines the frequency of a reference oscillator and particular 
configures this oscillator for either 525 or 1049 lines on the monitor 
display. The circuit connection A1 represents a connection to the voltage 
control input to a phase lock loop integrated circuit SGS Brand Integrated 
Circuit (Part No. 1180P) of the Sierra Scientific monitor. Circuit 
connection C1 is controlled by switch contact 56b which is closed when 
contact 56a is open, and is connected to pin 14 of the PLL circuit. 
A third contact 56c of the analog switch 56 is coupled to the opto-isolator 
72 which determines whether the existing time response of the phase lock 
loop must be modified. When the signal originates from the recording 
device the switch contact 56c is closed and a resistor/capacitor circuit 
connection B1 at pin 11 of the PLL circuit is grounded so that the time 
response of the phase lock loop is shortened. 
The output from the opto-isolation circuit 70 is coupled to a first switch 
contact 80a of the analog switch 80. When the contact 80a closes, an 
adjustable resistance is coupled to a connection A2 in the monitor 
horizontal deflection circuit. The contact closes in response to a low 
input on the conductor 66 indicating an aspect ratio of 4:3 is required. 
This introduces a resistor into a gain control of the horizontal 
deflection circuit to increase the horizontal deflection gain or 
horizontal size. 
A switch contact 80b closes in conjunction with the contact 80a and is 
coupled to a contrast calibration circuit 220 having a relay coil RC1 
which is energized when an aspect ratio of 4:3 is chosen. When the coil 
RC1 is energized a switch contact 224 is coupled to a resistor array 226 
in the contrast calibration circuit 220. Two additional switch contacts 
230, 232 are controlled by a second relay coil RC2 coupled to an analog 
switch contact 80d whose status is controlled by the output 212a from the 
one shot 212. As noted above, this signal 212a controls monitor scan rate, 
so the contact 80d and status of the resistor array 226 is controlled to 
compensate for contrast changes due to monitor scan rate. Additionally, a 
junction C3 in the contrast calibration circuit 220 is coupled to a 
monitor video pre-amplifier to control the gain of a video amplifier 
circuit. 
Two additional monitor junction connections A3, B3 adjust monitor 
brightness. A brightness compensation network 240 includes a third relay 
coil RC3 energized under control of the output 80d from the analog switch 
contact. When energized, the coil RC3 closes a contact 242 to add a 
resistor 244 to the brightness compensation network 240 and thereby 
adjusts a clamp reference signal of the video amplifier section of the 
monitor to increase the brightness when the resolution changes from 525 
lines per screen to 1049 lines per screen. 
Table 2 listed below illustrates the four different status conditions of 
the relay coils RC1, RC2, RC3 depicted in FIG. 9 for different 
combinations of aspect ratio and monitor resolution. 
TABLE 2 
______________________________________ 
Scan Rate 
1049 line 525 line 
______________________________________ 
ASPECT 1:1 RC2 & RC3-ON RC2 & RC3-OFF 
RATIO RC1-OFF RC1-OFF 
4:3 RC2 & RC3-ON RC2 & RC3-OFF 
RC1-ON RC1-ON 
______________________________________ 
One additional analog switch contact 80c controlled by the output 212a from 
the one shot 212 changes a horizontal flyback delay of the monitor. This 
assures the image on the monitor screen is centered for both line formats. 
The particular circuit connects A1-E1, A2 and B2, and A3-C3 are junctions 
the FIG. 9 circuit interfaces the Sierra Scientific monitor. It should be 
appreciated, however, that for other viewing monitors similar control 
circuitry for adjusting the operation of the monitor would be apparent 
from the present disclosure. 
Although the present invention has been described with a degree of 
particularity it is the intent that the invention include all 
modifications and alterations from the disclosed design falling within the 
spirit or scope of the appended claims.