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Development of Instrumentet13. ... Nuclear kedicine
****
D. A. Ross, C. C. Harris, M. M. Satterfield, and P. R. B:11**
Oak Ridsstional Laboratory
Oak Ridge, Tennessee
United States of America
Libst.act)
Considerable progress has been realized in the improvement of al.ag-
nostic methods, through collaboration between the cliniciars, the bio-
chenists, and the instrument designers. Improved counting efficier.cy
permits the meas:irement of very low-activity samples of biood, tissues,
etc., so that the radioactive dose given the patient has been stil
further reduced. New radionuclides are entering the diagnostic and re-
search fields. The value of samma-ray spectrometry is now weli established,
doctors and technicians have been taught how to apply it, and the mousure-
measuring a patient's total radionuclide content, and at recoråing the
position, size, and shape of small deposits of activity hidden away in
one or more of his internal organs. The latter procedure, called
"scanning", is now well established in the radiodiagnostic field, and
several types of scanning instruments have been developed, each using,
its own principle of detection.
There are also several ways of recording
the scan.
The most important remaining problem is the correct interpretation
of the radiodiagnostic data, but even in this difficult field new instru-
ments can help the doctor see things that he might otherwise miss.
"Research sponsored by the U. S. Atomic Energy Commission, under con-
tract with Union Carbide Corporation.
**Paper to be presented by Ross. Address for all four authors is:
ORNL - Building 9201-2
Box Y, Oak Ridge, Tennessee
U.S.A.
Development of Instrumentation for Nuclear Medicine
Oak Ridge Natioual laboratory
Oak Ridge, Tonno8800
The people who design instruments for the field of nuclear medioino
have plenty to do. Now diagnostic tests make new demands on the equipment.
Now radionuclides become commercially available, and the characteristics
of their radiation seperate now instrumental problems. There is no scarcity
of developmental projects waiting for attention.
Several general trends are discernible in present-day nuclear medicine.
We find ourselves moving toward:
1) reduced radiation dose to the patient;
2) low-activity counting;
3) shorter scanning times, for "dynamic Atudies";
4) accessory devices to facilitate interpretation.
Let us spend a little time with each.

-
-
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Fewer Ions in the Patient
The only method we have of detecting medically useful gamma radiation
is to let it lonize something. Ion production in the detector, therefore,
18 essential. Ion production in the patient, on the other hand, 18 unde-
sirable, for many patients are afraid of radiation and are easily persuaded..
that the doctor's tests will do them harm. We are continually under pressure,
therefore, to reduce the dose of radiation that the patient is asked to accept.
Hore we are apoaking, of course, of diagnostic tests and research studies;
treatient with radionuclides is another mattor.
The most obvious way to reduce the irradiation of the patient is to cut
down on the quantity of administered material. This lovers the amount of
L
* Toxt of a papor presented at the Sixth Japan Conferanco a Radioisotopes,
Tokyo, November 19, 1966. Work sponsored by the U.S. Atomic Enero Commission,
under contract with Union Carbide Corporation.
.
..
.
X
-2-
ionization in the patient, to be sure, but it f.130 lowers the nurber of
rays available to an exterim I detector, and thus it drives the instrucent
designer fartier into the dirficult field of low-activity counting. To make
matters worse, the doctor often needs to continue his study of a patient for
a proiongea period --- sometimes wecks or even months --- and for both phys-
ical and physiological reasons the radiation avaiiable for measuremont gets
weaker every day. So the doctors are continually complaining to their en-
gineering colleagues, vegging them for increased counting sensitivity. The
designers, on the other hand, are all too likely to retort that the doctor
should be thankful for what he has already been given.
Another way to reduce the radiation dose to the patient is to switch
to an isotope having a faster physical decay, in which case it can't re-
main in the patient for long. The duration of the exposure is not the only
factor, of course, for the kind of radiation emitted is also important.
What one would like to do is to find an emitter that makes fewer ions in
-
the patient and more ions in the detector, but solde times gain on one front
'*
involves loss cn the other. It is clear, at any rate, that the short-lived
nuclides will not be suitable for long-term studies, which may deprive the
doctor of important information. This limits the usefulness of these sub-
2.1
E
stances.
.
---
-
15
A third way to deliver less radiation to the patient is to utilize
-
5
the electron-capture nuclides. It is beyond question that the proper use
of these emitters can substantially reduce the on-site dose, by which we
r
.
*
mean the concentrated dose of radiation delivered to the tissues in the
immediate neighborhood of the decaying atoms. The electron-capture nuclides,
most of which are low-energy emitters, are currently enjoying a surge of
popularity, but they are not an unmixed blessing. Their drawbacks are felt
most severely in scanning and in other situations where good collimation is
3.
important, so we will leave a discussion of their pros and cons until we
01.c to the section on scannine (:jë ).
It is cicar that attempts to safeguard the patient's health are likely
to present the instrument designer with new headaches --- particularly with
the problem of measuring still smaller amounts of radiation with acceptable
accuracy. There are other considerations, not rolated to patient health,
that are driving us toward low-activity counting. allout studies are
occupying the attention of many workers, for there 18 growing interest in
the pathwa: 8 through which the various fallout elements can get into plants,
animals, and man. Typically the fallout levels in foodstuffs are exceeding-
ly low --- perhaps only a few picocuries (uuc) per granú, and it takes a
picocurie 27 seconds, on the average, to give us even one disintegration.
Consequently a food sample must consist of several kilograms If we are to
measure its radioactivity, and the detector must be adapted for large
volumes as well as near-zero activity. This is just the thing to drive the
designer out of his mind.
Often the doctor needs to count the radiation coming out of a whole
patient, rather than from some small region of the body containiag the
spleen, or the thyroid gland, or the kidney, and so on. The whole patient
is simply a special kind of "large-volume sample", and if the subjects of
a doctor's study are like most of us, who have acquired minute body burdens
of fallout but are otherwise normal, they will also average no more than a
few picocuries per gram. Here again we are faced with the problem of large-
volume, low-activity counting. It calls for agonizing effort in the fabri-
cation of the detectors and their low-background shields.
Low-activity counting -
We won't have space here to discuss all the problems involved in low-
level counting, but we might list the more important things that the instru-
I
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.
.
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ment des.rer must try to do:
.
?) minimize wicountiä disini.motions;
2) ridic provision for a lar!eavolume sample;
3) organize an all-out attack on bac crowd.
Under the first of these headings there are four main reasons wiyar
explodini atom can give off a ray that falls to register as a count in the
oxperimenter's scaler. First of all, many of the emitteü rays never reach
the detector at all. Some are absorbed within the patient, of course, but
apart from these the radiation is emitted in all directions, and the detec-
tor usually occupies only a small fraction of the total solid angle ---
.
.
i
commonly no more than a few per cent. The best way to achieve good detector
geometry is to make the substance of ihe detector surround the radioactive
source - as is done, for example, in the familiar well counter. This
policy runs into difficulties, of course, when the radioactive source be-
comes as large as an adult human subject; in this case the cost of surround-
ing him with sodium iodide becomes prohibititive and one has to settle for
less desirable detector materials such as the liquid or plastic scintillators.
..
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Secondly, many of the emitted rays that succeed in reaching the de-
tector go right through it without leaving any telltale ions, in which case
the detector simply doesn't know they are there. We try to overcome this
difficulty by making the detector thick enough to present several half-
layers to the oncoming radiation, for then most of the incident rays will
deposit their energy in the detector, and this energy can then be used to
produce electrical pulses that can be counted. The trouble with the liquid
and plastic scintillators is that their stopping power is not nearly as
guod as that of the much more expensive sodium iodide.
A third source of lost efficiency arises because a ray may enter the
crystal and deposit only part of its energy, some of it being allowed to
*
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escape in the form of a scattereà protca or eectron. There is no need
locuphasize, to a group of industrial desicners, the advantages of good
S
C
r esclution !r. a pulse-height spectrometer, and good resolution will
not be achieved 11 the detector allows portions of the inconing energy to
cscape from the crystal. We give preference, accordingly, to detectors
that permit only negligible escape of the incoming energy, and here again
the liquid and plastic scirtillators are greatly inferior to sodium 10di.de.
A fourth source of inefficiency (a minor one fortunately) arises be-
cause we dust usually use some sort of "window" mechanism in selecting the
electrical pulses that are to be counted in the scaler, this being neces-
sary mainly to keep down the interfering effects of background. The best.
way to use the spectrometer's winde is to adjust its position and opening
in such a way that it accepts most of the pulses in the total-absorption
peak of the spectrum. The difficulty here is that if one makes the window
wide enough to see substantially all of the total-absorption pulses it will
accept too much of the background spectrum. A simple mathematical analysis
shows that the optimum window is one that counts about 85 per cent of all
the primary pulses; if one widens the opening beyond this point the rather
minor improvement in "signal" counts will be more than offset by the rapidly
increasing background "noise."
So much for the difficulties encountered in trying to minimize the
number of uncounted disintegrations. We might do well now to review briefly
some of the problems encountered in whole-body counting, since these counters
illustrate very nicely what can be done, and what can't, in coping with the
two remaining problems: a large-volume sample and a troublesome background.
Whole-body Counters - If we want to measure the radioactive content of
normal people, or of patients to who:n tracer doses of radionuclides have
been administered, we run into trouble right away because the "sample" is
.
6.
80 large that it is impossible to achieve good geometrical efficiency and
Intrinsic detector efficiency at the same time. The result is that some
whole-body counters strive for high geometry while others aim at good spectro-
metry, and we can't have both. The "tank" type of counter, first developed at
Los Alamos Laboratory, almost surrounds the patient with a liquid scintillator,
but it gives poor spectral information. On the other hand, the "human spectro-
meter" type developed at Argoiine Naticnal Laboratory, which uses tho karinelli
chair and a large sodium iodide crystal, provides good spectral resolution but
has to accept a detectar geometry that is down to around 5 porcent. In between
these two extremes are the plastic-scintillator systems that give better spectro-
metry than the tank and better geometry than the sodium iodide, tut aren't really
good at either. Many modifications of the three basic designs have also
evolved, some being aimed at achieving portability, some at reducing cost, sone
at providing more detailed localizing information, and so on.
*
?
Two whole-body counters have been set up in Japan, both exhibiting un-
usual features. The Atomic Energy Research Institute has built one at Tokai
Village (1). It consists of a fairly small, steel room, lined with lead,
in which the subject lies on his back. Just under him are nine plastic
scintillators, each 114 centimeters in diameter by 10 centimeters high,
fixed in position. Above him is a 13 x 10 centimeter sodium iodide crystal,
supported on norizontal tracks and provided with a motor-driven mechanism
so that it can be moved into various positions for the detailed study of
local deposits. A 100-channel memory is used for spectral analysis. The
other Japanese installation is at the National Institute of Radiological
Sciences at Chiba (2). It also uses both plastic and sodium iodide detec-
tors, but in separate steel rooms. Both detector systems are in the "opposed"
configuration - that is symetrically arranged above and below the subject,
who lies on his back. The two sodium iodide detectors measure 20 x 10 centi-
A

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meters; they can be adjusted vertically to charge the spacing and can be
oved in tiie patient's long axis. They can also be collimated as required
for local study. The plastic detectors in the adjoining steel room consist
or ciunt large slabs, each measuring 50 x 50 x 15 centimeters; they are
fixed in position, four above the patient and four below. Thus the detec-
tor geometry is relatively nich (perhaps nearly 2n or 50 per cent), compared
with that of the sodium iodide system.
A world-wide survey of the whole-body counters in operation as of mid-
1962 is available for those interested (3). An additional paper (4) provides
nore detailed numerical data for the syst.ns using sodium iodide detectors.
Background - In whole-body counters the problem of adequately control-
ling the background is unusually difficult, for if the detector is sensitive
enough to measure the exceedingly weak radiations emitted by a normal or
near-normal person, it will also have high sensitivity to background radia-
tion. This will be true whether the detector is of the high-geometry type,
which will have a high background because its volume is so large, or of the
sodium iodide type, which will also have background probleins because the
crystal will be unusually large and will have excellent stopping power.
Moreover, when a low-activity counter is installed in a hospital unit,
special background hazards are likely to be present. X-ray equipment will
be running intermittently, penetrating radiation from teletherapy machines
may be flying about, "hot" patients containing various radionuclides may be
Background is particularly destructive if it is variable, which it will be
in the foregoing instances. It might therefore be instructive to consider
for a moment the design features of a new whole-body counter in which an
unusually painstaking effort has been made to eliminate the hazard of vari-
able background generated in the associated hospital unit.
This is in the low-background facility recently constructed at the
TIL
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Medical Di /ision of the Oak Ridge Institute of Nuclear Studies (5). Here
the patient-counting chamber ("cave") has been buried in a bank of clay
(Fig. 1), with about 4 meters of earth shielding it from the main part of
the hospital, and much more than this between the cave and the teletherapy
units. This provides a very helpful shield, but we found out early that
the earth itself is by no means "cold", for it contains elements o: the
uranium and thorium series, plus potassium-40 and fallout. Care was taken,
therefore, to provide the following additional shielding between the earth
and the detecting system: 1) a concrete wɛ.2.1 with ingredients selected for
low radioactivity:; * 2) a 60-centimeter layer of crushed rock (North Carolina
dunite) containing almost no activity at all; 3) a 3.3-centimeter steel box
similarly close to zero activity. For good measure the box is lined with
six millimeters of cold lead and là millimeters of stainless steel, the
latter providing an air-tight seal to exclude radon gas that might come in
from the concrete. Figure 2 shows a vertical section of the counting room,
with the patient in the counting position. To keep the detection sensitivity
nearly uniform throughout the body, eight crystals, 122 x 10 cm, are used,
arranged in longitudinal rows above and below the patient. The patient lies
on a stretcher enclosed by a thin, plastic box, so that only 8.per cent of
the air inside the steel room has to be ventilated; this greatly reduces
the threat from radon and dust in the ventilating air. As this is written
the detector installation is still incomplete, but preliminary measurements
of the cave background are highly encouraging.
Scanning
Turning now to the scanning instruments, we find that progress in this
"Cola" concrete was a dream that vanished. One can get (for a price)
low-activity substitutes for gravel and sand, but even reasonably cold port-
land cement could not be found.

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lleid zas taken four main directions: 1) toward improvement in te er:161-
cacy and resolution c. the conventional, moving type of detector; 2) tworu
special detectors for use with the low-energy emitters; 3) toward new, stá-
tiorur; detectors aimed at better efficiency and shorter scanning tires; and
:-) toward recording and/or reproducing tricks designed to facilitate the .
cilnical into gretation of the scan pictures.
Conventional detectors -
For a while design efforts were directed mainly toward the development
of honeycomb ("ifocused") collimators that would perform satisfactorily
with the relatively high energies used for brain scanning and other non-
thyroid work. Collinators were provided with thicker lateral shielding
made of tungsten, anå penetration of the radiation through the septa be-
tween the holes of the honeycomb was greatly reduced by using gold as the
absorbing material (6). These devices performed well, but had the drawoack
of high cosü. Recent work has shewn that substantiall; the same performance
can be obtained at about half the cost through the use of a lead colli-
mator of increased length (7). In a long collimator a potentially pene -
trating ray can strike a septum only at a very acute angle, and thus the
septum, in effect, presents increased thickness to the oncoming radiation.
This makes the lead partitions, because they are long, functionally com-
petitive with the shorter gold ones. Figure 3 shows how similar the re-
sponse curves are.
The long collimator has two minor drawbacks. One is that the crystal
must be larger, if the same detection sensitivity is to be achieved, because
the long collimator backs the crystal farther away from the focal point.
The other disadvantage is increased weight: the crystal is heavier, and the
shield will also be heavier if the same lateral protection is to be obtained.
Nevertheless, the 50-percent reduction in cost, as compared with the gold-
-10.
.
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tungsten version, represents an impressive gain. There is a trend, there-
fore, toward larger crystals and long collimators made of lead. Still
larger crystals; to provide better geometry, are contemplated for situations
.
.
V
.
m
.
where high sensitivity is of paramount importance.
-
Low-energy emitters -
These recent arrivals are receiving considerable attention for two
reasons: 1) most of the medically useful ones happen to decay by electron
capture, and the absence of high-speed beta particles reduces the on-site
ionization in the patient's tissues;^ and 2) in view of this radiation's
*
low penetrating power, the walls of a collimator can be much thinner and .
still be effective. This means that a honeycomb collimator can have thin septa;
consequently a source placed at the focus will see more of the crystal, and de-
tection efficiency goes up. For example, in an ordinary collimator designed
for medium energies (300-400 kev), the focal point may see only 45 per cent
of the crystal's front face, whereas in a properly designed, low-energy
collimator (30-80 kev) with the same resolution, 85 per cent could be visible.
The fabrication of a honeycomb with -mm septa is less difficult than one
might think (8). Casting is not likely to be practical, but sheet lead of
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.
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.
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the proper thickness can be wrapped once around one of the tapered, hexa-
-
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-
.-
.
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.-
gonal pins used to make the mold for the medium-energy casting. A suitable
number of the tapering tubes are then fitted together and fastened with
cement. The process is easily done in the laboratory.
..
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.
.
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.
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.
* There will be conversion and Auger electrons, but often they carry
rather low kinetic energy. They should not be treated carelessly, however,
for they are responsible for most of the on-site dose.
-12-
The X-rays and gamma rays emitted by the medically useful members of
the electron-capture group are typically low in energy, often so low that
absorption within the patient 18 severe. This makes their use in quanti-
.
tative tests difficult. Absorption can also bother the detector, for wless
the can that surrounds the crystal 18 wusally thin, it and the wderlying
reflector (A120,) will savagely massacre an incoming stream of 30-kev photons.
We must recognize, then, that neither the crystal nor the collimator of a ...
medium-energy detector can be expected to perform effectively at low energies,
and vice versa; each should be designed for the energy range in which it
will be asked to work.
The low-energy photons Buffer from another drawback that one should
not overlook: they have nasty scattering habits (9). The differential
Klein-Nishina cross-section increases witá decreasing energy, which 18 a-
nother way of saying that low-energy photons make more Compton scatter than
the higher-energy ones do. Moreover, the difference in energy between the
primary and the scattered photon 18 likely to be small when the primary energy
18 low, and this means that Compton-scattered rays are more difficult to
identify and supress by the usual techniques of pulse-height spectrometry.
To make matters still worse, the resolution of a pulse-height spectrometer,
deteriorates as the energy goes down, and thus the operator 18 deprived of
resolving power just when he needs it most. Figure 4 illustrates the three-
pronged offensive mounted by low-energy scatter.
It follows, therefore, that low-energy rays can enter the collimator's
field of vision from off-target sites and be scattered from there up into
the detector in considerable numbers. The scattered rays are then 11kely
to be registered along with the primary' rays that arise in the legitimate
-
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field of vision because the energy loss during the scattering process is
too small to permit the spectrometer to recognize the deflected rays and
throw them out. In short, the low-energy emitters make the problem of
collinator transparency easier, but they make the scattering problem worse.
We feel that energies of around 150 key are about the best for scanning; at
energies lower than this the difficulties begin to multiply. Special window
arrangements (9) can be of some help in dealing with scattered rays having
insufficient energy degradation, but it is better to stay within the energy
range that gives the spectrometer a fighting change to do its selecting job.
Stationary detectors -
These have arisen in competition with the moving detectors, the theory
being that the moving detector looks at only a small portion of the patient
at one time and throws the rest of the radiation away. Furthermore, in a
conventional scan the various parts of the picture are evolved at different
times, and this can introduce distortion if the radionuclide concentrations
are changing rapidly. The stationary detectors accept rays from any part
of the field of vision at any time, although they see a smaller solià angle
of radiation from each point. They can be made fast, at the
expense of fine detail. Stationary detectors of the pinhole type (10) are
bedevilled by a fundamental geometrical distortion thet impairs their use-
fulness unless all parts of the organ being scanned are at approximately
the same distance from the pinhole.
Autofluoroscope - This rather recent development (11, 18) makes use
of the multiple-hole collimator of an earlier device (38); in this case it
consists of 293 parallel, tapered holes in a thick, lead plate. Behind each
hole is a slendor crystal, 92 x 51 mm (Fig. 5, top); thus each crystal seos
only its own small part of the patient. When a scirillation occurs in a
crystal, it causes a momentary spot to appear in the corresponding position
.
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.
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-13-
on a cathode-ray tube, and these flashes are photographed by a time-exposure
camera. In the original model the electronic linkage between the detector
and the scope tube was of the kind used by Anger for his pinhole camera (10)...
Tise more recent, "Digital Autofluoroscope" uses an X-Y coordinate system,
as Illustrated, in simplified form, in Fig. 5, bottom. All crystals in one.
vertical row are connected through light pipes to a single phototube; this
tube therefore defines the "x" coordinate for that row, and it delivers the
appropriate horizontal deflection in the CRO tube. Each of the other verti-
cal rows similarly has its own "x" phototube and "x" deflection. Each bori-
zontal row has its own myn phototube, providing the correct Y component of
the deflection. For 15 rows of 20 tubes each there would be 15 "y" tubes
and 20 "x" tubes, or 35 in all --• a vast improvement over having one photo-
tube for each crystal.
Because each crystal 18 positively identified by a pair of numbers,
this system has obvious advantages: the scan data can be stored in a mag-
netic memory, recorded on tape, relayed to a remote computer for analysis,
and so on. The autofluoroscope, still experimental, shows considerable
promise in situations where quick short-exposure scans have to be made , .•••
for example, in studying rapid changes in nuclide concentration or position
in an organ such as the kidney. The device 18 not yet available commercially.
...
no
-
:
Autofluorograph - Various attempts have been made to utiliso image intensi-
flors in scanning, with and without pinhole collimation; the early instruments are
reviewed in reference (10). A more recort wrsian (12) uses a multiple-hole col-
limating plato covering the sensitive end of an X-ray image Intensifior, the output
image being photographed (mig. 6). The intensilier dooan't so wall at energies
above 150 Kov, and the Instrument has boon tooted mainly with lodine-125 (28 Kov).
Strong claims are made for ito information-gathering potentialities, but it has
not yet been olinioully useful. Current developments, utilising a two-stage
Intensilior and a tolerican link, pranzo. to improve it. .

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-14-
KELLERSHOHN et al. (13, 14) have recently described a novel device for the
reduction of endogenous noise in an image-intensifier tube, and it promises to
clean up the output image to a considerable degree. Basic detector sensitivity
should remain unchanged, but the noise suppressor could permit the use of much
greater light amplification. As of April 1964 a working model was still to
be built.
Syark-chamber detector (13, 14) - This radical device is perhaps the
newest of the detectors, although in a sense it is as old as the Geiger-
Mueller tube. As in the previous three instruments, it collimates the rays
with a multiple-hole, lead plate (Fig. 7). Passing beyond this, a gamma
ray enters a gas chamber through a thin, aluminium sheet; Compton or photo-
electrons here encounter a strong electrostatic field, and an avalanche of
ions results. Given proper voltages, the avalanche remains quite local and
is self-quenching (14), and thus there is a spot where the gas glows momen-
tarily. The little flashes are photographed through the glass plate at the
top of the chamber, and a scan results. Resolution of the visualizing
system is excellent; resolution of the collimator will be determined by hole
length, diameter, etc., as with other multiple-hole collimators. The ex-
perimental spark chamber of early 1964 has rather low sensitivity and has
DO
been tested mainly with iodine-125, but there are a number of contemplated
changes that promise to improve it. We will watch its progress with interest.
Devices to facilitate clinical interpretation
The doctor's impression depends only on what he can see in the scans,
and sometimes the important information is obscured by non-contributory room
or body background --- "noise", in the language of the engineers. Conse-
quently there have been various attempts to achieve "background erase",
"contrast enhancement", and so on. Technically it is easy enough to suppress
counts that come in at low rates, but this always leaves the operator wonder-
ing whether he hasn't thrown away information that might be important. Most
of us think that one should not leave the success or failure of a diagnostic
procedure in the hands of an unintelligent erasing circuit, allowing it to
-15-
destory all information that it doesn't consider clinically significant.
Contrast enhancement -
We need not describe in detail the older expedients that have al.
ready been fully reported. There is the policy of repeating the scan
several times, once without any background erase, followed by several re-
.
peats at increasing threshold levels. This is fine for the doctor but hard
on the patient and technician. A better plan is to record the original
scan on magnetic tape without cutoff (15); the tape is then printed out
through a cutoff circuit, this beinj done several times with different
threshold levels, including zero. Background suppression can be photographic rather
thún electronic (16). Or, photographic contrast can be enhanced by circuitry
that makes the intensity of the light source vary with count rate (17).
Closed-circuit television - In this system (18) a single photo-
recording is made from the patient, care being taken to get as much infor-
mation as possible on the scan. The developeä recording is then viewed
.....
.
by a TV c{umera; the TV receiver, placed nearby, reproduces the scan, but
the doctor studying the TV picture can alter the video gain at will, and
thus bring out weak contrast differences irrespective of the level of black-
ness at which they occur in the original scan. He thus provides himself,
in effect, with an infinite series of scans taken with different levels of
background erase. This is done, however, without destroying any of the
original information, or requiring the patient to be scanned more than
once.
Rescenzer - The TV viewer just mentioned is a valuabie diamnostic
tool, but its cost is a handicap. With tris in mind, the rescanner tries
to use as much as possible of the equipment that the operator already has
on hand. The original rescanner has been described before (19), vut re-
cently new versatility has been added (20).

1
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An optical sensor sweeps back and forth across the original or "primary"
scan, and the resulting electrical signals are converted by a "howler" cir-
cuit into a new and somewhat smoothed series of pulses; these are then re-
corded as a rescan. Howler sensitivity provides contrast, and a biasing
arrangement provides threshold control. A rescan need take only one-tenth
of the original scanning time, and a new re-scan can be made if the dial
settings 'used for the first one turn out unhappily:
: A failure, and the consequent need for a repeat rescan, is caused most often
by a poor choice of threshold, and accordingly we have recently provided
.
the rescanner with a kind of "automatic threshold control."
This is
achieved by surrounding the circular field of vision that gives the "signal"
with an outer belt whose purpose is to give information about the general
level of blackness against which the signal is to be evaluated. Figure 8
shows the structure of the compound sensing head and its photocells. When
the two sensing systems are connected in electrical opposition, what the
rescanner records is not the absolute blackness of either the inner or
the outer field, but the difference between them. Thus it indicates con-
trast only, and if the threshold needs to be different in different parts
of the original scan (as it often does), this is automatically taken care
of. A front-panel switch can reverse the connections of the outer sensor
so that the two signals add, which is sometimes useful for special purposes.
Figure 9 shows the contrast-enhancing properties of the rescanner. In
the original photorecording the cerebellar astrocytoma is barely visible,
whereas in the rescan the tumor stands out quite clearly.
Color scanning - This approach has two purposes: 1) to provide contrast
enhancement, making the high count rates look prominent, and 2) to make the
scan semi-quantitative by assigning a specific color to each of several
bands of count rate. Once the second objective has been attained, the first
-17-
1.
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will follow if an appropriate assignment of colors is made. In an ordinary
SC
scan the density of the dot pattern gives an indication of count rete, but
the eye is rather uncritical in dealing with rates that differ by less than
20 per cent or so. The color coding reinforces - or corrects - a judgement.
that might otherwise be uncertain.
The first attempt at color scanning appears to have been made in Eng-
land by Mallard and Peachey (21), who caused a recording hammer to print
dots at regular intervals, and used short strips of inked ribbon that were
shifted into position under the hammer by a d'Arsonval galvanometer move-
ment driven from a rate-meter circuit. With such a system the only indi-
cation of rate is the color, for the dots are regularly spaced. In a later
L
-
version (22) the hammer is activated from a scaler output in the conventional
..
way, combining dot spacing with color to indicate count rate. Long colored
ribbons, stored on spools, made the device more practical.
These workers
scanned by moving the patient rather than the detector; they consider this
an advantage, while most others think not. They were able to show, at any
rate, that a weak spot of activity, in the presence of background, could
produce an easily visible color change, whereas the spot would be quite,
imperceptible when recorded with black dots alone.
In the U.S., Hine (23) has developed a somewhat similar system. He
starts with a commercial, moving-detector scanner and mounts a battery of
colored typewriter ribbons on its recording arm. The color-selecting
mechanism is servo-driven, taking its instructions from a rate-meter cir-
cuit.
In Japan, Kakehi and his colleagues (24) have incorporated the color
principle into a photo-recording system. In their original model a xenon
discharge tube was excited by pulses from the scaler, and the flashes of
light were reflected from one of seven colored papers, the appropriate one
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being moved into position by a d'Arsonval movement driven by a rate-meter.
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Recording was by color camera. In this early model they were unhappy with
the saw-toothed borders caused by the lag in the rate-meter, and they avoided
this distortion by recording during only one of the two directions of the .
scanning sweep. They were also unhappy with the delay of a week or so be-
tween the actual running of the scan and the return of the developed color
film. In a more recent model (25) they liave eliminated the rate-meter, and
have selected the color to be printed on the basis of the total number of
counts accumulated during a preselected, fixea time interval. (They can
also record on a fixed-count basis, but they consider the other policy pref-
erable.) The elimination of the rate-meter permits them to record in both
scanning directions, thus cutting the scanning time in half. The delay re-
.
3
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.
.
.
.
quired for development of the colored film has been overcome by using color
T4U
printing paper, which can be processed locally within a half an hour after
the scan has been run.
.
The Japanese workers have been refreshingly open-minded in experiment-
ing with their color coding. They have not become obsessed with the color
sequence of the visible spectrum; its basis is physical, whereas the effect
:
.
.
--
one is aiming for is psychosensory. They are also open-minded as to whether
the background should be light or dark, and have purposely designed their
new color scanner so that all kinds of color sequences can be experimented
with.
.
.
-
-
-
Other color-scanning systems have been developed in Japan, but com-
plete descriptions of them have not yet appeared in any language that I can
read, and I do not feel qualified to discuss them. Ozeki and Furukawa will
be describing their system, in English, in an article that is still in press
(26). Other references are given for readers conversant with Japanese (27-35).
Very recentiy Adams and Jaffe (37) have exhibited a color-photorecording
-19-
.:1
*
system in which the source of light is a cathode -ray tube. Colored filters,
moved by rate-meter, are placed between the tube and the recording camera.
The CRO beam is turned on only when a pulse présents itself, so the back-
ground is dark. The color sequence is that of the visible spectrum, and
they place violet at the low-rate end. The results are certainly striking:
A number of color scans, taken with this system, are available for inspection (39).
A full description of the device is to appear shortly in the Journal of Nuclear
Medicine.
It is all too easy for a novice to sit in his armchair and criticize
the efforts of his elders and betters --- easy but risky. Nevertheless I
am inclineů to guess that the best color sequence should be related to
subjective brilliance, with the lowest count rate contrasting only weakly
with the background (whether light or dark) and so on up the line. Yellow
is seen strongly against black but weakly against white; violet is strong
.
:
against white but weak against black. If the background is to be dark,
accordingly, I suspect that maximum count rate should be white, with the
lower rates grading successively through yellow, yellow-green, blue-green,
blue, violet, and finally black. I can agree with Adams and Jaffe in their
choice of violet for the lowest rate, against a dark background,
but I am not convinced that they are sound in using red for their "hottest"
color, since it is not the most brilliant. In fact, red doesn't seem to
fit in happily anywhere, and perhaps it might best be left out. I think
Kakehi and his colleagues are vise in providing for 10 colors, without being
determined to use them all, and in their frankly experimental approach to
the search for the most informative color arrangement.
Kakehi and Uchiyama, during their current visit at ORINS, are collabor-
ating with our group at ORNL to develop a rescanner with colored, photo-
graphic printout. We may guess that color scanning has not yet reached its
full potential.

.
*
.
.
.
.
.
*
-20-
Conclusion
.
*
?
2
!
,
.
.
.
.
The foregoing discussion of the numerous instruments now coming
into use in medical research and diagnosis serves to re-emphasize the value
of collaboration between the physicists and engineers on one hand, and the
doctors on the other. Neither is likely to make adequate progress without
the other, and this is the reason for the "societies of nuclear medicine"
that have sprung up here in Japan and elsewhere, each one embracing the
members of several scientific disciplines. We wish them all success.
-
-
-
-2,1-
References
(1) SUGURI, S., Whole-body Counting, IAEA, Vienna (1952) 219.
(2) ETO, H., WATANABE, H., TANAKA, E., and HIRAMOTO, T., Whole-body
Counting, IAEA, Vienna (1962) 211.
(3) MEHL, H. G., and RUNDO, J., Health Physics 9 (1963) 607.
(4) MEHL, J., Nucleonics 21, #10 (1963) 50.
(5) ROSS, D. A., NURRIS, A. C., Jr., Medical Division Research Report
ORINS-42, off. Tech. Serv.,U.S. Dept. of Commerce; Washington 25
(1962) 48..
(6) FRANCIS, J. E., Jr., HARRIS, C. C., and BELL, P. R., J. nuc. Med. 3,
(1962) 10.
(7) HARRIS, C. C., BELL, P. R., SATTERFIELD, M. M., ROSS, D. A. and JORDAN,
J. C., Paper #SM-51/59 in IAEA Symposium on Medical Radioisotope Scan-
ning, Athens, in press (1964).
(8) HARRIS, C. C., JORDAN, J. C., SATTERFIELD, M. M., GOODRICH, J. K.,
STONE, H. L., and HILL, R. W., J. nue. Med. 5, in press (1964).
(9) ROSS, D. A., HARRIS, C. C., SATTERFIELD, M. M., BELL, P. R., and
JORDAN, J. C., Radioaktive Isotope in Klinik und Forschung, Band 6,
in press, Urban und Schwarzenberg, München und Berlin (1964) 108.
(10) ANGER, H. O., Medical Radioisotope Scanning, IAEA-WHO, Vienna (1959) 59
(11) BENDER, M. A. and BLAU, M., Nucleonics 21, #10 (1963) 52. Also (18) p. 151.
(12) TER-POGOSSIAN, M. M. and EICHLING, J. O., Paper #SM-51/77 in IAEA
Symposiun on Medical Radioisotope Scanning, Athens, in press (1964).
(13) KELLERSOHN, C., LANSIART, A., and DESGREZ, A., (Service hospitalier
Frédéric Joliot, Dépt. de Biologie, Commissariat à l'Energie Atomique)
Paper #SM-51/86 in IAEA Symposium on Medical Radioisotope Scanning,
r
.:
H. Mimi
Id..
Wh
.
eis
-22-
11
(14) LANSIART, A., and LELOUP, J., (Service d'Electronique physique,
Départment d'Electronique, Cornissariat à l'Energie Atomique)
Comptes rendues du Colloque International sur l'Electronique Nucléaire,
Paris (1963).
(15) FACINTYRE, W. J., FRIEDELL, H. L., CRESPO, G. G., and REJALI, A. M., , .
Radiology. 73, (1959) 329.
(16) DEWEY, W. C., HEIDELBERG, J. G., and MOORE, E. B., I. nuc. Med. 3,
(1962) 51.
(117) BENDER, M. A., and BLAU, M., Medical Radioisotope Scanning, IAEA-WHO,
Vierna (1959) 31.
(13) BENDER, M. A. and BLAU, M., Progress in Medical Radioisotope Scanning,
U.S. -AEC report #TID-7673 (1962): TV viewer p. 105; autorluoroscope p. 151.
(19) HARRIS, C. C., BELI., P. R., FRANCIS, J. E., Jr., JORDAN, J. C. and
SATTERFIELD, M. M., Progress in Medical Radioisotope Scanning, U.S.-
AEC report #TID-7673 (1962) 81.
ARKTS, C. C., BELL, P. R., SATTERFIELD, M. M., ROSS, D. A., and
JORDAN, J. C. Paper #SM-51/66 in IAEA Symposium on Medical Radioisotope
Scanning, Athens, in press (1964).
(21) MALLARD, J. R., and PEACHEY, C. J., Brit. J. Radiol. 32 (1959) 652.
(22) MALLARD, J. R., FOWLER, J. F., and SUTTON, M., Brit. J. Radiol. 34
(1961) 562.
(23) HINE, G. J., I. nuc. Med. 4 (1.963) 439.
(24) KAKEHI, H., ARIMIZJ, M., and UCHIYAMA, G., Progress in Medical Radio
isotope. Scanning, U.S. -AEC report #TID-7673 (1962) 111.
(25) KAKEHI, H., ARIMTZU, N., UCHTYAMA, G., GENTA, H. and KUBO, S., IAEA
Symposium on Medical Radioisotope Scanning, Athens, Paper #SM-51/7,
in press (1964).
(20)
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Y
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.
.
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.-
TE
u
.
-
-
-
-
-
-
-
- -
-
-
-
-
. -
-
.
.
-
-23-
(26) OZEKI, M., and FURUKAWA, Y., IAEA Symposium on Medical Radioisotope
Scanning, Athens, Paper #34-51/9, in press (1954.
(27) ATSUDA, T. et al., Wipe Acta Redlc.. 22 (1962) 1297
(23) !ISHIBORI, K. et al., in Proceedings of the 5th Conference on Radio-
isotopes, Japan Atomic Industrial Forum, Inc. (1963) 3-151/153. .
(29) CZEKI, M., Nipp. Acta Rad!01. 22 (1962) 448.
(30) OZEKI, M., in Proceedings of the 5th Conference on Radioléotopes
(contributed to the panel discussion), Japan Atomic Industrial Forum,
Inc. (1963) 1-93/124.
(31) OZEKI, M., FURUKAWA, Y., et al., in Proceedings of "he 5th Conference
on Radioisotopes, Japan Atomic Industrial Forum, Inc. (1963) 3-148/150.
(32) KAKELHI, H., Acta Radiologica Japonica 22 (1962) 415/447.
(33) UCKTIAMA, G., Acta Radiologica Japonica 22 (1962) 929/932.
(34) UCHIYAMA, G., ARIMIZU, N. and KAKEHI, H., Proceedings of the First
Annual Meeting of the Japanese Association of Nuclear Medicine, The
Japan Radioisotope Association, Tokyo (1952) 18-19.
(35) KAKEHI, H., ARIMIZU, N. and UCHIYAMA, G., Genshiryoku Kogyo (Atomic
Pover Industry) 2 (1963) 26/31.
(36) TOR-POGOSSIAN, M., KASTNER, J., and VEST, T. B., Radiology 81 (1963) 984.
(37) ADAMS, R., and JAFFE, H. L., J. nuc. Med. 5 (1964) 346, "T-5".
(38) JOHANSSON, S. A. E. aid SKANSE, B., Acta Radiol. 39 (1953) 317.
(39) Medical news item: J. imer. Med. Assoc. 188 (June 15/64) 26.
w
.
1.
-24
:
Legends
P16. 1 - The Low-background Facility at the Oak Ridge Institute's Medical
Division 18 located underground, to protect the "cave" from vari.
able radiation arising within the hospital. There are 4 metres of
dense clay between the cave and the hospital wall, and many additional
mne tres of earth attenuate the scatter from the tele therapy machines
(not shown). Courtesy of ORINS Medical Division (5).
F18, 2 - Vertical section through the ORINS cave, showing the arrangement
of the patient, the surrounding plastic box, the 8 de tectors, and
the massive shield. The latter consists of a 13-cm steel box,
lined with lead and stainless steel, a 60-cm layer of crushed Olivine
(dunite), and the : "fairly low-activity" concrete wall (5).
Fig. 3 - Showing semi-logarithmic response curves, as per cent of maximum,
for the ORNL gold-tungsten (left) and long-lead (right) collimators.
Counts are taken as small (ca. 5 mm) source was presented in the
focal plane, moving across the long axis of the honeycomb's hexagon.
After Harris. et al. (7), courtesy of IAEA.
Fig. 4 . Illustrating the threefold scattering problem caused by a low-
energy primary ray (100 kev, left) as compared with a medium-
energy ray (500 kev, right). At low energies (a) the scattered
radiation is more abundant, (b) the energies are crowded together,
and (c) the spectrometer's resolution is poor. Abundances are cal-
culated from the Klein-Nishina relationship. From Poss et al. (9),
courtesy of Urban und Schwarzenberg, München.
- Top: The original autofluoroscope of Bender and Blau (11), showing
the multiple-hole collimator, the bank of 293 slender NaI crystals,
and the Anger transfer system (10) that tells the cathode-ray tube
which crystal is flashing. Courtesy of Nucleonics. Bottom: Simpli-
-25-
fied diayrar, showing the mechanism of the new transfer system of
tric dieta? autorluoroscopo, which provides X and Y coördinatos
for each of the 293 crystals, and deflects the CRO beam accordingly-
see text.
FIG. 6 - The nechanism of the "autofluorograps", after Ter-Pogossian et al.
000). A multiple-hole collimates causes selective excitation of
the input screen of an X-ray imasi intensifier, and the output image
is photographed. Courtesy of Radiology
FIC. 7 - The "spark-chamber scanning detector", redrawn from Kellershohn,
Lanslart and Desprez (13). Rays enter through the multiple-hole
collimator and produce localized flashes in the internal ses.
The flashes are photographed by a time-exposure camera that looks
through the glass plate at the top. Courtesy of IAEA.
Tis. 3 - The compound light-sensing unit that provides "automatic thres-
hold control" in the new ORVI rescanner. The circular, inner
field provides the "signal", while the outer belt registers the
ievel of the surrounding "noise", against which the signal is to
be evaluated. Redrawn after Harris et al. (20), courtesy of IAEA.
ris. 9 - Left: primary brain scan, using 14S-HSA at 24 hours, right lateral
view. The cerebellar astrocytoma is poorly contrasted with its
surroundings, and its size is difficult to estimate. Right: the
rescan brings out the tumor strongly. From Harris et al. (20),
courtesy of IAEA.
* Fig. 10 Color scan of a highly abnormal liver, made by Adams and Jaffe (37)
with their new color scanner, which uses a cathode -ray tube as the
the NOT AVAI cathode ray tube /as the
light source. The white dots indicate the costal margins. The

vivid colors, together with the dark background, produce a very
striking picture. We are greatly indebted to Mr. Adams for
permission to reproduce his original slide.
..............
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dense clay between the cave and the hospital wall, and many additional
metres of earth attenuate the scatter from the teletherapy machines
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- LEGAL NOTICE
This report was prepared as an account of Government sponsored work. Neither the United
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A. Makan day warranty or representation, expropied or implied, with respect to the acou-
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of may taformation, apparatus, method or procesi dincloped in this report may not latringo
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B. Asmos muy habilites with respect to the un of, or for damages resulting from the
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As used in the above, pornon noting on behalf of the Coromisslon" includes any om
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insanlardan
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END
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