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October 1969 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
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In his trademark style, electronics-themed storyteller John T. Frye used his
Mac's Service Shop venue to introduce readers to another new development in the
medical electronics field - the "ultrasonoscope." It was the forerunner to modern
sonogram machines. Relatively recent advances in solid state electronics and signal
processing techniques - albeit mostly analog in nature - made design and construction
of compact devices practical and affordable by medical facilities. Unlike today
where many doctor's offices have their own x-ray and sonogram machines, it was still
mostly hospitals that owned them in the late 1960s when this piece was written.
Mac McGregor schools his right-hand-man Barney on the benefits of expanding their
knowledge universe to include some of the newfangled medical devices in order to
help assure future business. I found (and link to) a paper describing one of the
first ultrasonoscopes manufactured by Grumman Engineering.
Mac's Service Shop: Medical Electronics Servicing
John Frye
 Servicing medical electronic equipment can be
a rewarding job for responsible, knowledgeable, well-equipped technicians.
It was a jewel of an October morning - sparkling with dew, flooded with sunshine,
and tinged with just a trace of that too-good-to-last gentle melancholy that always
is a part of true beauty. Barney reluctantly stepped out of the glorious autumn
morning into the service shop, but his eyes widened as he saw Mac, his employer,
seated cross-legged on the service bench reading a loose-leaf brown manual.
"Hey," the youth exclaimed, "I didn't know your rheumatic old legs would fold
up like that. How come you're sitting on the bench?"
"Because Matilda beat me down here this morning and painted both the bench stools,"
Mac growled, nodding to where the bright green stools rested on top of the "intermittent-cooker"
bench. "They didn't really need it. I painted them myself only ten or twelve years
ago."
"When you encounter a determined woman with a paintbrush, you may as well give
in gracefully," Barney advised. "Even I, a bachelor, know that much. What are you
reading?"
 "A service manual on a piece of medical
diagnostic equipment called an 'UltraSonoscope.' Last week I had a phone call from
the manufacturer on the East Coast who said one of these units was being sold to
the local hospital. A couple of doctors in the lab here had suggested we be contacted
to see if we would undertake service of the instrument in case of failure."
"You see it's hardly practical for a manufacturer of medical electronic equipment
to maintain service stations manned by factory-trained personnel in all parts of
the country. Not enough units are sold to warrant that. Neither is it feasible to
send a serviceman out from the factory every time trouble is reported with one of
the units, especially when most of these difficulties are simply 'cockpit troubles'
caused by improper adjustment or operation. A more satisfactory arrangement, according
to the man who called me, is to locate a well-equipped service technician in the
area who is willing to undertake maintenance of the unit."
"Yeah, but can a radio and TV service technician successfully undertake a job
like that?" Barney questioned. "It seems to me be should have both a medical and
electronic background for that kind of work."
"A medical background certainly wouldn't hurt," Mac admitted, "but in this case,
at least, it's not really essential to understanding the operation of the instrument.
Let me tell you what an UltraSonoscope does:
"Essentially it's a precision short-range sonar system using sharply beamed pulses
of ultrasonic sound to probe tissue by observing on a CR tube echoes returned from
interfaces in the tissue. The transducer used to send the pulses into the tissue
also is used to pick up the returning echoes and feed them into an amplifier for
display on the scope tube.
"Since sound waves travel through tissue at a velocity of about 150,000 cm/s,
the horizontal sweep of the scope can be calibrated in terms of the depth of tissue
through which the echo is returned. A precision marker generator and dividers in
the instrument produce a calibrated base-line display marked off in centimeters
and fractions of tissue penetration. If the instrument is adjusted so that the 'main
bang' pip indicating the surface of the body is on a centimeter mark at the left
of the screen, the indicated distance to the right of this mark that an echo pip
appears is a measure of the depth of tissue through which the echo is returning.
"This is with the instrument operating in the 'A-Scan' mode in which the horizontal
axis represents time translated into tissue penetration and the vertical axis represents
intensity of the echo. In the 'B-Scan' mode, the display is effectively turned through
90 degrees so that the former vertical pips come out towards the observer. In other
words, the beam is intensity modulated by the echo signals feeding the receiver.
Now if the location of the initial pulse on the face of the tube can be directly
correlated with the movement of the transducer over the body and if a photograph
of the resulting scanned display be made, the result is a 'tomogram.' a kind of
cross-sectional view of the tissue beneath the scanning transducer.
"In another application, called 'echocardiography,' the transducer is applied
over a beating heart and the dimmed horizontal trace. intensity modulated by echoes
returning from moving tissues of the heart, is swept slowly upwards from the bottom
of the CR tube while a camera photographs the resulting scanned display. Movement
of tissue surfaces toward and away from the transducer - say the surfaces of the
leaves of the mitral valve - cause the echoes returned from this tissue to move
respectively left and right on the base line. When the base line is scanned upwards
at a uniform velocity, this lateral shift in the echo signal traces out a continuous
sawtooth-like display. If an EKG trace is simultaneously displayed on the left side
of the screen, the position of the parts of the mitral valve - or any other moving
parts of the heart, for that matter - can be correlated with any particular portion
of the heartbeat cycle."
"Hold on," Barney interrupted, "Let's see if I'm with you so far, doctor. Apparently
this UltraSonoscope consists essentially of a precision laboratory-type scope, a
marker generator that's probably crystal-controlled, an ultrasonic pulser, and a
specialized vertical amplifier for displaying the echoes. That much would take care
of the A-Scan display. The slow-sweep vertical scan used in B-Scan echocardiography
would require a vertical sweep circuit. And to produce that tomogram you were talking
about there would have to be some device that would cause the movement of the transducer
to produce spot-positioning voltages for the CR tube. How am I doing?"
"Not bad, but of course things are not quite that simple.
For example, the UltraSonoscope has an adjustable Sensitivity Depth Compensation
circuit to compensate automatically for the attenuation of pulse signal echoes as
they are returned from deeper and deeper tissues. This is actually a time-variable
gain control keyed to the horizontal sweep so that the gain of the vertical amplifier
increases as the trace moves to the right, insuring that the strength of the echo
returned will be a function of the interface itself and will not be greatly influenced
by how far this interface lies beneath the surface of the body. There are other
tricky circuits involved in both the basic instrument and the many accessory modules
available for it. Still and all, the circuitry consists of sophisticated applications
of fundamental electronic concepts that should be understood by any good TV service
technician."
"You did, then, agree to take on the maintenance job?"
"Yes, after a little arm twisting. The manufacturer agreed to furnish complete
service data on the instrument plus consultation privileges. In other words, if
something goes wrong with the instrument that cannot be easily and quickly located
from directions - contained in this service manual, I can pick up the telephone
and call the company and talk with their engineer. His experience and familiarity
with the instrument plus my observation of symptoms and carrying out of suggested
tests will, hopefully, get the thing going again in jig time."
"I'm still surprised you let him talk you into it. Surely the comparatively small
amount of loot involved in servicing one instrument wasn't a factor."
"No, but there are other things to consider. In the first place this is an opportunity
for us to expand our knowledge of electronic applications. Secondly, it may open
the door to a great deal more of this kind of specialized service that could become
quite lucrative. We both know medical electronics is just starting to take off,
and this could be an opportunity for us to get in on the ground floor. Finally,
someone must service medical electronic equipment if it is to take the place it
should in the prevention and curing of disease. If we, who can do it, won't, the
widespread application of such equipment will lag far behind its true potential;
and people will suffer and die needlessly as a result."
"You sound as though you're getting ready to plunge into medical electronics
servicing with both feet."
"Far from it! I'm just dipping a cautious toe into the water. Candidly, this
kind of service work is not for every TV technician, and anyone considering it should
do a lot of soul searching before he tries it.
"This kind of servicing requires a truly responsible person. When you are working
on equipment that may mean life or death to an individual, there is no room for
guessing, carelessness, or slipshod techniques. You must be willing to devote extra
time and effort to the job. Not only must you be willing to study the operation
and service manuals thoroughly in advance of any service needed, but you must be
prepared to drop everything and take care of the equipment when it does fail - even
though that means working extra long hours,
"You must be constantly - safety-minded in working on this equipment. This service
manual has several paragraphs on just that subject as applied to the UltraSonoscope
and its use. Every effort has been made to prevent leakage and to insure good grounding
of the instrument and all its attachments, but the maintenance technician must take
every care to see to it that these precautions continue in effect."
"But in spite of all these drawbacks, you are still going to venture into this
kind of service."
"Yes, for the reasons I mentioned and because doing this kind of service may
sharpen our TV service techniques. Working as we do on the same basic kind of equipment
day after day, there is an increasing tendency for us to depend more and more on
well-learned experience and habit and to divorce the higher thought processes from
what we are doing. As lots of guys boast, 'I can service these things in my sleep.'
Servicing unfamiliar equipment will force us to think hard about every symptom we
perceive and every test we make. If the doctors are going to be able to depend on
the UltraSonoscope to diagnose faulty hearts, locate brain tumors or objects in
the eye, determine the size and shape of gall stones, or measure the size of an
unborn infant's head, we are going to have to be on our toes every minute we are
servicing the instrument.
"Hey," Mac broke off, "why are you staring at your shop coat so hard? Something
on it?"
"No, but I was just wondering if maybe we shouldn't trade these green jobs in
for some smart-looking white laboratory smocks more in keeping with our new career,"
Barney said with a grin. "But come on, Grandpa; unkink your legs and crawl down
off that bench while you still can, It makes me hurt just to look at you!"
Mac's Radio Service Shop Episodes on RF Cafe
This series of instructive
technodrama™
stories was the brainchild of none other than John T. Frye, creator of the
Carl and Jerry series that ran in
Popular Electronics for many years. "Mac's Radio Service Shop" began life
in April 1948 in Radio News
magazine (which later became Radio & Television News, then
Electronics
World), and changed its name to simply "Mac's Service Shop" until the final
episode was published in a 1977
Popular Electronics magazine. "Mac" is electronics repair shop owner Mac
McGregor, and Barney Jameson his his eager, if not somewhat naive, technician assistant.
"Lessons" are taught in story format with dialogs between Mac and Barney.
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