INSTRUMENTATION by Ralph H. Müller
Automatic plotting device for radiation therapy applicable to instrumental analysis
'"puis month we borrow an example of ' fine instrumentation from the field of radiation therapy. Aside from its immediate and important use. the development presents techniques which are directly applicable to problems which the instrumental analyst encounters. Carl Β voir and Associates, 10 East 40th St.,'New York 16. X. Y.. draw our attention to the automatic plotting device for radiation therapy studies. It was designed by />. P. Azary and ('. S. Simons of the Alice Crocker Lloyd Radiation Therapy Center at the University of Michigan Hospital. Some modifications of conventional re corders were made by Minneapolis Honeywell's Industrial Division in con nection with this development. In radiation therapy, the radiologist uses radiations from x-ray machines and radioactive materials. He wants to know how radiation intensity is distributed in the patient in order that the proper amount may be prescribed. One method of getting this information is to make isodose (iso-intensity) curves. These curves are usually made Inallowing radiation to fall on and pene trate a "'phantom'' that has approxi mately the same absorption character istics as human tissue. Water is fre quently used as a convenient phantom material. The intensity of radiation is measured at many points and plotted on crosssection paper, point by point. Lines are then drawn connecting points which have equal intensity, yielding contour lines similar to those on a topograph ical map. This point-by-point proce dure can require several days of tedious measurements and may be inaccurate at some critical points.
that have the same intensity. AVith this plotter an entire set of isodose curves is produced in less than an hour. The information is gathered and the curves plotted by the three main parts of the system: (1) a sensing probe which can be driven vertically and horizontally through the phantom. (2) an Electronic
strip chart potentiometer that automati cally plots isodose curves, and (3) a Brown 40X servo amplifier and motor, and automatic gain control unit that automatically drives the probe along a preselected isodose curve. In portraying the required informa tion, the probe is made to explore the
Figure 1. Schematic of isodose plotting device
Isodose Plotting Device Designed
Azary and Simons have designed and built an isodose plotting device which, gives a continuous plot of all [joints
Figure 2 . Wiring schematic o f portion o f servo amplifier and automatic gain control VOL. 29, NO. 7, JULY
957 ·
51 A
INSTRUMENTATION 2 0 0 : 1 ratio of m a x i m u m to minimum speed.
I F VISCOSITY I S O N E OF YOUR PRODUCT'S D I M E N S I O N S Brookfield 8-speed Viscometer will answer every measurement problem! W h y not invest a three-cent stamp and see what we mean? Our illustrated brochure shows you how the Brookfield 8-speed viscometer and specialized accessories will answer every viscosity measurement problem you m a y have. You'll see how this one, easily operated, portable instrument will provide precise measurement readings directly in centipoises. Even in applications involving extremes in viscosity, temperature or corrosion! Complete information will be yours, too, about the Brookfield Helipath Stand. With it, it's easy to test, study and control highly-plastic materials, gels and semi-gels. It automatically lowers a Brookfield Viscometer equipped with a special bar-type spindle through a helical path providing constant measurement of undisturbed material. Write for full information today. WORLD'S S T A N D A R D FOR VISCOSITY M E A S U R E M E N T
Brookfield ENGINEERING
LABORATORIES
INCORPORATED
S T O U G H T O N 112 , M A S S A C H U S E T T S For further information, circle number 52 A on Readers' Service Card, page 73 A
52 A
·
ANALYTICAL CHEMISTRY
, radiation beam in the phantom systematically. Movement of the probe involves the simultaneous action of two motor drives: the patrolling drive, which causes the probe to be driven horizontally across the radiation beam and is under control of the operator; and the hunting drive, which causes the probe to search vertically for the desired radiation intensity and is under the control of a servo system. The schematic in Figure 1 illustrates the principle. The operator sets the isodose selector switch at the desired radiation intensity. The hunting drive, which uses the servo balancing motor, then moves the probe vertically into the phantom until the output voltage of the probe is equal to that of the isodose selector. At this balanced condition, the vertical motion of the hunting drive should cease. But the patrolling drive moves the probe horizontally across the phantom, at the operator's command. This, of course, changes the radiation intensity on the probe and leaves the system in an unbalanced state. The servo amplifier (hunting drive) then causes the probe to be driven vertically, up or down, until the radiation intensity on the probe again equals the preset value. The chart of the electronic recorder (designed by Honeywell's Industrial Division) is driven by a receiver Selsyn. The transmitter Selsyn is mechanically coupled to the vertical motion of the radiation probe, and, therefore, sends a signal which represents the depth in the phantom at which the analysis is being made. The horizontal motion of the probe is mechanically coupled to a 40-turn Helipot that has a fixed voltage impressed across it. The output voltage from the Helipot thus represents the horizontal position of the probe. Since it is fed into the amplifier of the recorder in order to actuate the pen, the pen takes a position which represents the horizontal position of the probe within the phantom. Thus the path of the probe as it is moved through the phantom along the line of selected radiation intensity is accurately indicated by the ink line of the chart. Servo Amplifier Used The heart of the servo system is the Brown 40X servo amplifier. It was chosen for its high sensitivity, which is required at certain portions of the curves. But at other portions of the curves, the amplifier must handle extremely large input signals from the detecting element. These signals, more than 1 volt in some instances, would normally greatly overload the amplifier and seriously distort the wave form of
SS-1 & S S-ΙΑ SUPERSPEED ANGLE CENTRIFUGE NOW—Sealed
Rotor w i t h Superspeeds
u p to 1 6 , 0 0 0 r p m — 3 2 , 7 0 0 χ G — 4 0 0 m l
Have you asked us about ourNÈWServall "SzentGyorgyi—Blum" Continuous Flow Centrifuge? SS-1 and SS-1A may be adapted.
Figure 3. Instrument range of input signals
"The workhorse of the modern research laboratory" Only SERVALL offers you speeds and capacity in these ranges, together with a rotor and cover that give an airtight seal against escape of rotor contents— maximum safety for personnel when infectious or otherwise hazardous materials are being centrifuged. Eight rotor compartments accommodate 50 ml tubes, or adapters for wide range of smaller tubes. SERVALL-BLUM designed Self-Centering Direct Drive Assembly ensures smooth, trouble-free operation. Variable transformer for remote control. New literature available: Write for Bulletin AC-71S.
DESIGNERS, MANUFACTURERS A N D DISTRIBUTORS O F "SERVALL" LABORATORY INSTRUMENTS
Ivan Sorvall, Inc. NORWALK · CONNECTICUT
For further information, circle number 54 A-1 on Readers' Service Card, page 73 A
Capacity:
12" sq. χ 19"
deep, with 2 shelves . . . range,
adjustable Temperature
room
to 2 0 0 ° C .
$
wide
its signal to the two-phase servo motor. As a result the motor would just barely turn when it should be going at full speed. This difficulty was remedied by adding an automatic gain control (A.G.C.) which allows the amplifier to operate at full sensitivity when the input signals are small, and at reduced sensitivity when they are large. The wiring schematic, Figure 2, il lustrates the relationship of the A.G.C. to the 40X amplifier. The stage in volving the second half of the 12AX7 (V-2 in the 40X amplifier) was discon nected at the three points marked X in the schematic. Then the A.G.C. circuit, which uses a variable-ιημ pen tode, was inserted. The new circuit values were chosen so that the 6BD6 stage has approximately the same gain as the replaced triode stage. Output of the stage is sampled at the existing test jack on the servo amplifier and is fed into a diode (6AL5) which rectifies the a.c. signal. After the rectified voltage is filtered, it is fed as a bias to control the gain of the 6BD6. It is desirable that this gain control action should not begin until the signal voltage reaches a certain value. In order to accomplish this delayed A.G.C, a voltage divider chain across the d.c. supply places a high potential on the cathode of the diode. It was also found that the first half of the 12AX7 introduced some distor tion with large input signals. This was eliminated by the introduction of
M o d e l 5850
375.
See your Laboratory
Write
handles
Supply
for Free
Dealer
or .
Catalog
NATIONAL APPLIANCE CO. 7 6 3 4 S . W . CAPITOL H W Y . Since 7918 . . . Serving Manufacturers
·
PORTLAND 1 9 , OREGON
INDUSTRY - RESEARCH - MEDICINE
of Ovens, Incubators,
Baths and other
Appliances
For further information, circle number 54 A-2 on Readers' Service Card, page 73 A 54 A
·
ANALYTICAL CHEMISTRY
Figure 4 . Complete isodose and recorder
plotter
INSTRUMENTATION
instrument abstracts Applied Physics
Corporation/Pasadena/California
At R i k e r L a b o r a t o r i e s
Cary Model 14 Spectrophotometer leads to discovery of new alkaloid in Rauwolfia series C. Howard Stimmel, Analytical Chemist at Riker Laboratories, says: "With the Cary Model 14 we detected structure in the spectra of crude Reserpine samples which was not revealed with our manual spectrophotometer. Further research led Figure 5.
to the discovery of Canescine, a pre v i o u s l y u n i d e n t i f i e d m e m b e r of t h e Rauwolfia series. Differing only slightly from Reserpine, Canescine has notable therapeutic properties of its own."
Typical isodose plot
self-bias in t h e cathode of this stage. T h e time constants in t h e above cir cuits were chosen t o achieve a rea sonably clean d.c. grid bias, y e t main tain a sufficiently quick response t o large changes in t h e input signal. Sensitivity of t h e 4 0 X amplifier can be adjusted t o produce m o t o r drive from signals much less t h a n 1.2 μν. B u t t h e small fluctuations in probe o u t p u t m a k e it undesirable t o operate t h e amplifier a t a n y greater sensitivity in this application. W i t h t h e addition of t h e A.G.C. circuit t o t h e amplifier, full speed of t h e operation of t h e balancing m o t o r can be obtained with i n p u t signals t h a t range from 60 μν. to a t least 1.5 volts (Figure 3). T h e motor speed is proportional t o t h e i n p u t voltage a t values below 60-μν. Below 100-μν. input, there is no A . G . C . action while above this value, t h e A.G.C. functions excellently as observed both b y oscilloscope exam ination a n d actual performance. T h e complete isodose plotter is shown in Figure 4 with t h e control center on t h e right a n d recorder on t h e left. A typical record is shown in Figure 5. I n this record, vertical a n d horizontal distances on t h e c h a r t rec ord correspond t o t h e same distances in t h e p h a n t o m . I n related techniques—for example, in t h e location of administered I 1 3 1 in t h e thyroid g l a n d — t h e m a p p i n g h a s been achieved b y a mechanical scanner combined with photographic techniques. I n this m e t h o d , t h e scanner carries a Geiger t u b e or scintillator, t h e o u t p u t of which triggers a flash lamp which prints images on photographic film or paper. W i t h proper mechanical syn chronization, a contour m a p results. These a r e techniques which serve t h e u n r e m i t t i n g search for more d a t a a n d their precise delineation.
Investigation of unusual features in crude Reserpine absorption spectra obtained by Riker Laboratories with the Cary Model 14 led to the discovery of the important new alkaloid Canescine (left), a relative of Reserpine (right). Riker chemists particularly appreciate the speed and accuracy of the Model 14, according to Stimmel. He says: "Our reasons for buying the Cary Model 14 were two-fold. One, the automatic scan ning feature enables us to get more spec tra in a given time; and two, we get more information from the spectra because of the instrument's greater inherent accu racy. Our laboratories are using the
Riker Laboratories, an ethical pharmaceutical specialties house with main offices in Los Angeles, California, is primarily engaged in pro ducing hypotensive agents, including alkaloids in pure and mixed form.
Model 14 eight hours per day, five days per week, for both production control and research. Since purchasing the Model 14, we have been able to quadruple our output of spectra." "Before," Stimmel continues, "we were selective as to what we analyzed because of time limitations. Our research depart ment now sends through anything they are even vaguely interested in analyzing. We feel the performance of the Cary Model 14 justifies o u r reading signifi cance into every 'wiggle' of the spectra." Resolving power of the Cary Model 14 is better than 1A in most of the ultra-, violet visible region and better than 3 A in the near-infrared. Stray light is en tirely negligible for most applications — less than 0.001% between 2100A and 1.8 microns, and less than 0 . 1 % at 1860A and 2.6 microns. Wavelength scale of the Model 14 is linear, and accurate to bet ter than 4A throughout most of its range: reproducibility is better than 0.5Â. W h y don't you consider the advantages of the Model 14's greater resolving power and speed? Write to Applied Physics Corporation, 362 W. Colorado Street, Pasadena, Calif., for bulletinAC-27.
For further information, circle number 55 A on Readers' Service Card, page 73 A
VOL. 29, NO. 7 , JULY 1957 ·
55 A
