Object Radiography Contrived to Illustrate Basic Principles1 Enrique Pantoja, Candace Kabler, Ching Po Li,, MD
add variety ny, we imaged
to radiologic teaching and to lower view box monotoordinary objects in circumstances that illustrate-can-
To
catune
might
ciples.
We
be
lenge
amenable
Yet
a better
tried
principles,
word-basic
to make
each
to solution and
object
MD ARRT
the
can
and
image
through
has
result
radiography
pathologic
object
use
it sparingly
the
principles
in question.
always
the
monotony
it is designed
logical
added
play
an
to our
of such sessions.
teaching
with the
pninchal-
teaching
ancillary
in combination Otherwise,
radiologic
interpretation
application
spice
only
and
an
cases
role;
that
technique
we
illustrate
itself
may
add
to
to combat.
INTRODUCTION
U
Entranced
by
how
swiftly
the
expert
seems
to home
in on
the
right
diagnosis,
stu-
are apt to imitate only his or her outward motions and demeanor, oblivious to the toil that alone can entwine swiftness with accuracy. Thus, when confronted with a radiograph, they tend to inspect it briefly and, propping meager findings with intuition, they grope for an instant diagnosis. Admittedly, when simple cases recur, the knee-jerk approach works. However, this leads the student to believe that this approach, being the easiest, is also a trusted road to success in radiology. It is not. dents
Unlike
other
principles
branches
are based
transcend
clinical
of medicine,
radiology
on immutable medicine
and
physical the
is more
laws
human
a science than an art. Its so universal that they
and are
sphere-even
the
animal
world-and
apply to vegetable and inanimate objects as well. Fundamental as they are, these principles are not inborn knowledge. Not only must they be learned, they must be mastered. It is their mastery that consecrates radiology as a science, becoming the foundation
on
This
article
which
radiologic
demonstrates
education
with
should
several
nest.
illustrations
how
mastery
of the
basic
principles may be achieved with object radiography. In Figure 1 (and in Figure 24) , the radiographs call for an explanation, since the “object” in them is actually the human foot. The aim here was to demonstrate that what looks like a clinical ra-
Index
terms:
Physics
RadioGraphics I
From
ter,
the
Dayton,
reprint (cRSNA,
1990; Department OH requests 1990
#{149} Radiography
10:323-340 of Radiological
45435.
From
the
Sciences, 1988
RSNA
Wright annual
State meeting.
University
School
Received
March
of Medicine, 30,
1989;
I 24G acceptedJune
Fred
White 7.
Cen
Address
to E.P.
323
diograph
expert, miliar U
may
baffle
when with
momentarily
the
GENERAL
basic
the
fa-
principles.
PRINCIPLES
Problem
1.-What
diograph scheduled
of a foot (Fig for a morning
ination,
even
he or she is not thoroughly
had
is unusual
taken
about
this
1)? The patient, pyclographic
a laxative
the
night
ra-
exambefore
and had stubbed his toe against the bathroom door at 2:00 AM. By the time this radiograph was taken the next morning, the toe had turned black-and-blue. Solution 1.-If the radiograph puzzles read on. Its meaning will become clear fore the end of the article.
you, be-
1
-
..
*
-
Problem 2.-What is unusual about these two tomatoes madiographed while both were resting on the film (Fig 2), and how can it be
explained? Solution 2.-It takes a trained eye to expect the larger one to be denser and a trained intellect to recognize it as only half a tomato. Principle.-Absorben thickness along the x-ray beam has a major influence on radiographic density, a known fact often over-
looked.
Thus,
in a recent
hibit, authors described denser than a smaller implying a difference
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mammography
cx-
a nodule as being one in the same breast, in their composition!
Volume
10
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2
may
be made
denser
without
making
it heavi-
en than water (though it would become heavier than pure oil). Principles-Photoelectric absorption, dominant in the diagnostic x-ray kibovobtage range, varies with the third power of the atomic number of the absorber. Increasing the average atomic number of a liquid (eg, by adding iodinc)increases its radiation absorption faster than its weight. This radio-
:
graph
also
illustrates
the
effect
of surface
tension:
Note the rounding of the oil-water interface but the absence of such rounding the interface between the other two liquids. A third principle culty in comparing
demonstrated
is the
at
diffi-
nonadjacent radiographic densities. Oil (top) and water (bottom), which are distinctly different in density when imaged side by side, now appear deceptiveby isodense.
r
3.-In
Problem
this
radiograph
of a cylindni-
cal plastic bottle containing water and two other liquids (Fig 3), why is it that the liquid at the bottom is not the densest radiographicabby? Solution
eral piodol
oil
3.-The
(at the top) (an
iodized
other and poppy
two liquids a suspension seed
oil)
are mmof Liin miner-
al oil (in the middle). Lipiodob is heavier and denser than water because of its large iodine content. If only a small amount of Lipiodol is mixed with oil, however, the batter
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SILHOUETTE
SIGN
4.-In
Problem glass cup, is the
AND
Problem
water,
tomato
this
radiograph
and
a tomato
floating
4.-The
Solution
in the
tomato
Solution tail end
is not even radio-
graphic principles justify the assertion. The first is called the silhouette sign. An interface between isodense materi-
is the
326
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with
each
other
radiographically. summation
placing (tomato
a medium replacing
creases
the
RadioGraphics
in
5.-Fingers of the
banana
one, were
effect.
An
Pantoja
second
object
less dense air in this
radiographic
U
is nonre-
The
than case)
density.
et al
in some
of the
me-
itself in-
four,
and
five
underwater
plus when
the radio-
graphed. images
Principles.-These
in contact
defects
differences between the two (Fig 5) call for an explanation.
4),
water?
separate
Princ4’les.-Two
solvable
soft-tissue
and density ends of this banana What is it?
of a (Fig
the cup.
abs
5.-The
fingers
EFFECT
SUMMATION
illustrate
the
silhou-
ette sign. The outermost layer of the banana peel is water equivalent (and disappears when submerged), but the rest contains tiny air pockets that make the banana float and render that part of the peel radiolucent in water. Note the relativity of density
perception:
The
peel
is dense
in air,
but
the
portion underwater appears radiobucent. Note also the summation effect of the other end of the banana and, particularly, of the index finger, where the summation
is to both
water
and
banana.
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10
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2
Problem
the same cup?
6.-The exposure
same egg and cup were factors (Fig 6) Is there .
imaged
twice
air on water
with in the
Solution 6.-The egg shows a summation effect in Figure 6b but not in Figure 6a. If the cup had contained air, the egg would have looked the same in and out of the cup, with a summation
effect
in both.
Therefore,
the
cup
must
have
been
filled with water, the egg being inside the cup in Figure 6a and outside in Figure 6b. Because the shell contains calcium, the silhouette sign does not apply here, but the summation effect still does.
U EFFECT LENGTH Problem Figure
OF ON
TANGENT RESOLUTION
7.-Both cups in 7 contain the same water, two cylindrical
thing: pieces of ice, and a piece of lead. Figure 7a was taken only a couple of minutes before Figure
7b,
sure
factors are the two (Turnpagefor
7a.
March
and
the
were
same
used.
images the
expo-
Why
different? solution.)
7b.
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ice cylinder with ballast
C
B
A
7d.
7c.
7 and Principle.-Figure literature: The length
Solution
diobogic rninant
of interface
resolution
7a and
of the when
the
length
of the tangential contact with (B ), on point (C ) tangents (Fig 7c).
7b
The
resulting
radiograph
(Fig
7a)
along
contrast
a fact
the path
across
the
generally
neglected
of the x-ray interface
beam
is poor.
in the
is a major Depending
ra-
deteron the
the beam, interfaces may be classified as bong (A) , round Figure 7a and 7b demonstrate that, to resolve a poor-con-
trast interface such as that of ice and water, For this demonstration, two ice cylinders float vertically) were placed in a cup with 7d.
demonstrate
interface
the beam must strike a long tangent to it. (one containing a lead ballast in one end to make water and imaged in the position shown in Figure
shows
the
lead
ballast
and
only
that
part
of the
ice
it
above
the water line. The x rays, striking only a round tangent to the cylinders, failed to show the submerged part of the ice. After a couple of minutes, enough ice had melted to release the ballast, and both cylinders floated horizontally side by side. A second exposure (Fig 7b) was made after the cup was rotated so that the beam would strike a bong tangent to the cylinders. Figure 7b cleanly
shows
Problem
considered between
the
ice-water
interface;
8.-Paraffin-mineral
nonresolvabbe them is poor.
the
oil
lead
interfaces
(1 ,2), and, indeed, Can such an interface
piece
is barely
have
long
visible
in the
bottom
of the
cup.
been
the contrastS be resolved ra-
diographically? Solution 8.-Figure 8 shows that it can, provided the interface presents a bong tangent to the beam. A paraffin cylinder floating in a layered mixture of oil and water was imaged with the beam parallel (Fig 8a) and perpendicular (Fig 8b) to the long axis of the cylinder. Although the resulting long
tangent interface was resolved in both oil and water (Fig 8a) (the cylinder appeared as a sphere) , the round tangent interface was resolved only in water (Fig 8b) , and then barely so (four dots mark Principle.-The
can be a major
the
factor
corners length
of the cylinder). of an interface tangent
in interface
resolution
and
to the
beam
radiographic
contrast.
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Problem (Fig 9) cotton
9.-The
linear
is suggestive thread.
Since
the edge
of the apple,
Solution
9.-A
density
in the center
of a piece the
vertical
but
it was
used
was
enough
radiation
why
should
beam
of this
of wire,
was
the cotton used
by a
to darken
appear
to image
apple
caused
the
so dense? apple,
which was suspended with a 3-foot-long fine cotton thread. The thread nearly coincided with the position of the central ray of the x-ray beam. Had it been exactly in the central ray, the thread would have appeared as a white dot instead of a wirelike shadow (note that the part of the thread remote from the x-ray film appears blurred; only its lower end is sharply defined) With the exposure required to image an apple, such .
a thread
would
beam (round fect of tangent
not
tangent) length
be seen . This
if struck perpendicularly is another demonstration
on interface
by the of the
ef-
resolution.
10. U LOGIC PRINCIPLES
Problem
AND
RADIOGRAPHIC ha.
10.-Is
ure 1 0 really grapes?
the radiograph in Fig. of a banana and a bunch of
Problem 11.-What is unusual about this radiograph of a glass cup, two ointment bottles, and one of correction fluid (Fig 1 la)? (Turn pagefor the solution.)
the resemblance of what looks like a banana to the human thorax (the chest wall is denser than the central lungs) . If this were a banana, the center, where it is thicker, should be denser. Note also that the two grapes overlying the banana paradoxicably appear less dense than the others. The radiograph was taken of two halved grapes resting on a banana peel, with a bunch of whole grapes nearby. Solution
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Solution 11.-The film must have been exposed with a horizontal beam (note the air-fluid bevel) . But the latter mdicates
that
deed, 1 ib,
the
image
the image with
the
is upside
was cup
made
and
one
down.
In-
as in Figure ointment
bottle resting upside down on sponges. The other two bottles were glued to a cardboard, which rested on the cup. Princ4,les.-The two principles illustrated in this figure are air-fluid 1eveb and the burning out of a bow-density material with a barge exposure dose.
sponge #{149} #{149}#{149}......#{149}#{149}......#{149}#{149}#{149}#{149}I#{149}#{149}#{149}#{149}
hhb.
Problem
the subject
12.-What in Figure
Pulmonary
consolidation?
Solution
graph
is the matter with 1 2? Aerophagia?
12.-The
is dead.
through
broken its lungs
bird
Killed
a glass
and
now
in this
trying
window,
with
set in rigor
collapsed,
under water. A plastic madiolucent compared ulates air swallowing.
the
bird pellet with
radio-
to fly
its neck mortis was
and imaged
in its beak, water, sirn-
h2.
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Problem 13.-If the only 1 3a) is water, how could for the solution.)
liquid
involved
it have
been
in this
obtained?
image
(Fig
(Turn
page
Hi1 _:c’
Problem
what
14-The confusing,
but
d
radiograph shown careful observation
iion of basic principles will several pertinent observations.
not overlap,
they
all have
itself eggfis significantly than all the others. The e is so weak that where than that of eggfabone.
et between tic feature
March
the outer of chicken
1990
clear
the Where
the same
in Figure 1 4a is someand logical appbicaconfusion. There eggs a, b, c, and
radiographic
are d do
density.
By
denser, while egg e is less dense summation effect of eggs b, c, d, and all four overlap, the density is less Only eggs a andfshow the air pock-
membrane and the shell, a characteniseggs. (Turn pagefor the solution.)
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film
-S
h3b. Solution 13.-Bottle 1 shows an air-fluid level but so do bottles 2 and 4, and these levels give conflicting testimony as to the way the film was exposed. The level in bottle 1 is not as sharp and smooth as the other two. Bottle 3 is overflowing with something that, to judge by its radiolucency, should be air.
Because
than
air,
the
none have
of the bottles been exposed
it must
background
is uniform
be a liquid,
hence
and
water.
are capped, the picture must upside down. The overfibling of bottle 3 demonstrates surface tension. The fallacious level in bottle 1 was not due to an air-fluid interface but to hardened paraffin.
The 1 3b. them
setup
for this
radiograph
is shown
All four bottles contained float in the water tank,
down
against
aluminum scnibed.
the block
Problem
but
Plexiglas
plate
on which
the
15.-Each
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air to make were forced
supports numbers
by the are
in-
14b.
x-ray
14-The weak summation effect of air pockets suggest that eggs b, c, d, and e are empty shells, which they are. But why does a, a whole egg, show the Solution
and
absence
same density as an empty reason that egg e appears than the other shells-a
water (shaded rectangle) (Fig 1 4b) . This is whyf only
one
iion
effect.
in the
image
shell? For the same so much less dense and e are both in ;
the others
are not
a whole egg, is the with a distinct surnrna-
of these
two radiographs (Fig 1 5a) shows a chicken egg and two bird eggs (no empty shells now) . How could these pictunes have been made? (Turn page 334for the solution.)
332
in Figure
enough they
I
denser
Since
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10
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Problem
1 7.-Radiographs
in
Figure 1 7 depict the same pain ofgrapcfruits. In Figure 17a, the two grapefruits have a distinct summation effect. Two components
of the
dermis”
skin-”epi-
and a more
“subcutaneous
nadiolucent
tissue”
(the
ma-
diolucency is due to microscopic air pockets)-and the interface
corresponding
to the
deep fascia are evident. In Figune 1 7b, the background is denser and has a fine granulanity that
is more
that seen summation
h7a.
obvious
in Figure effect
than
1 7a. No or epidermis
of the grapefruit on the left is seen in Figure 1 7b. Recalling Figure 5, one is bound to suspect that the changes in the skin of this grapefruit, those of the banana
like before,
are
due to underwater radiography. That indeed is the case-anothen manifestation of the silhouette sign and somewhat d#{233}j#{224} vu. But the challenge in Figure 1 7b is on
the
right
side.
If that
grapefruit is not in the water, why does it back a summation effect? And if it is, why is the epidermis preserved? (Turn pagefor the solution.)
h7b.
h6a. Problem in Figure
16.-Which 1 6a was
of the four
stationary exposure? (Turn
diognaphic
eggshells
at the time of mapagefor the so-
lution.)
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x-ray
h5b. Solution
fect,
15.-Egg
so it was
a shows
simply
a summation
superimposed
efon
the
chicken egg (E) Egg c, on the other hand, shows no such effect, as if it had been inside the larger egg (F) . Such a feat would have .
been difficult to contrive. unc 1 5b, egg c was simply (shaded rectangle) , which same which
As shown put
in water
produces
the
ten? Density differences egg in a dense medium
are relative. A whole (iodine solution in rectangles]) can be made to
[black an empty
shell
in water.
16.-None;
Solution As seen
glued
But what about eggs b and d, look bike empty shells in wa-
effect. indeed
this case look like
in Fig-
in Figure
together
they 1 6b,
the
as a unit
were
all moving.
eggshells
and were
were
spinning
around the one in the center, which was hanging by a thread along the central x ray. In Figure 16b, only the spinning central shell and its shadow underneath are not blurred by the motion. Principle.-In Figure 1 6a, the three mevolving eggshells were blurred, but the spinning one in the center and the thread that spins
with
it were
not.
Motion
of an
interface
in its own plane and the spinning of an axis on itself are not detrimental to the resolution of their respective images. The old technique of autotomography nested mainly on this
334
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in a Styrofoam sheet. The fruit on the might (A) was squeezed into this hole; the one on the left (H) was allowed to rest on the Stymofoam. To keep this buoyant assembly under water, it was covered with a Plexiglas sheet, which was forced down with bead weights as shown. Prlnciples.-Thc reason for all this was to demonstrate imaging principles that are not always clean in the mind of the student: (a) Only contrasting interfaces struck tangentiabby by the beam can be resolved radiographically, (b) both tangency and contrast
are not only
necessary
sure trast
resolution, critical at the
interface is only
When
a grapefruit,
but
sufficient and point
for instance,
the
(C)
to encon-
of tangency.
is imaged
in
a pole-to-pole direction, skin near the equator skin part of the image.
only a slice of the is responsible for the The grapefruit could therefore be under water and its skin imaged all around, provided there is contrast at the point of tangency (the reason for the Styrofoam sheet).
h7c. Solution 1 7.-The upper part of Figure 1 7c shows the setup for Figure 1 7a; the bottom shows that of Figure 1 7b. In both cases, the separation of the grapefruit on the left from the film accounts for its magnification, and
the sheet of Styrofoam on which one fruit rests explains the granularity seen in the background of both radiographs. For the setup
in Figure
to admit
1 7b,
a grapefruit
Problem
18.-The
a mound
with
keen
hole,
big
a tight
enough
fit, was cut
observer
may
notice
that
ground in Figure 1 8a has a density intermediate of Figure 1 7a and 1 7b. Other pertinent findings 1 8a are
the
greater
ten definition planes,
on
do the two
density
of the
of the epidermis the
other
grapefruits
hand,
fruit
on the are
appear
better
different?
on the
right.
the
back-
between in Figure left
The
and
the
that bet-
“fascial”
defined on the left. (Turn pagefor
Why the
solution.)
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Solution 18.-As image on the left
shown represents
in Figure a polar
1 8b, the section
at the interface urn (air in this
with case)
the surrounding mcdiand at the interface with
of a grapefruit; the one on the right, a slice through the equator. To keep the two 5cc-
the subcutaneous
lions
equidistant
from
the
make
the
more
comparable,
18b) and, therefore, bong enough good resolution with the available But in the polar section, the beam
images
film
and
thereby
the equa-
tonal slice was placed on a plastic support (solid gray rectangle) . Because the polar 5cclion is thicker, its fascial planes present long-
en tangents to the beam than those of the othem section, which is why these planes are betten defined in the image on the left. On the right, however, the epidermis has greaten definition, which brings us to anothen concept: resolution of point tangent yensus ally
round
tangent
strikes
Problem discussed
19.-On so far,
contents Solution
on the
other,
fluid
suspect,
is oil.
Note
imposed
(Fig
and
defect,
are
In the equatorial round
a point tangent, which interfaces, particularly
the least contrast the subcutaneous Principle-As increases with
and with tangent
both
contrast may
the
two
interface
with
a rube, interface resolution the length of the tangent
across
the interface.
compensate
for
and vice versa; ample contrast need for tangent length.
poor
A long
contrast
reduces
the
the
material
medium)
that
upper
is
the other
tomato
that .
One fluid .
appears
on the cup,
is indicated
like
it but
by the fact something of medium. one in Prob-
is not.
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19.
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than the oil in which it is partially imThat it is inside, rather than super-
bern 20 books
U
both with
The
one
indicates
contrast
contrast
correctly, that
objects.
which
that this tomato, too, produces a defect in the positive contrast This setup is quite simple; the
336
(Fig
to allow contrast. strikes
degrades the one
(namely, tissue). both
tangents
19)?
the lower
is positive
an aqueous
could denser mersed.
cup
are tomatoes;
as a filling
lower
only these
tissue.
these
the basis of the principles what can be said about the
cup shown has two nonof different densities, one
objects
(actually
actutwice:
19.-The
floating
the
beam
epidermis
paper
fluids
seen
The
to the
of this
miscible two
interfaces.
a tangent
section,
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cends the cup with two tomatoes shown in Figure 20a, the contrast between each tomato and the surrounding medium, as well as between the two tomatoes where they approach one another, has increased Problem
20.-In
drastically
compared
with
that
seen
in Figure
19. The decreased doxical. appears
contrast between the two fluids has just as drastically. This seems paraThe lower part of the upper tomato so dense that, on the basis of what
was said
before, one is inclined to assume the lower tomato is in the cup. But to explain all the findings. (Turn the solution.)
that only this fails pagefor
U
SIMULATED
CONDITIONS Problem 21.-To with a meniscus
representing plastic bottle ral effusion” Figure
March
PATHOLOGIC simulate
sign,
a pleural
an inflated
effusion
balloon
the lung was inserted inside a (the chest cavity) and a “pleuintroduced between the two. In 2 1 , note the meniscus sign in the up-
1990
position,
lung and somehow
replace the entire cupy
bottle, pleural
tapering
between
as it as-
the elastic
just
as lung
space
when
level layers in the
were air to to fill
expands
to oc-
an effusion
We also put mineral to simulate an abscess
companied shape
effusion
gravity
the chest wall. If this fluid removed without allowing it, the balloon would expand
the
drained. balloon fluid fluid
the
against
is
oil inside the with an air-
and to emphasize the point that out perfectly flat only when ac-
by free bottom
air. But why of the
the peculiar
balloon?
Solution 21.-The peculiar shape was produced by adding a small amount of water to the oil. Since water is heavier, it sinks under the oil, and, being under two forces (gravity and surface tension) , it assumes the oblong shape observed. In the process, it again demonstrates the principle of the silhouette sign. Because the effect of the intervening rubber is negligible,
water
inside
and
balloon blends on contact, and torn of the balloon is invisible.
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Solution
ence
20.-The is applicable
inductive to radiology.
method of sciIt enjoins its
disciples to be exhaustive in gathering facts and to consider all possibilities in explaining those facts. With a little more thoroughness,
we might have tale sign-that
discovered the lower
a subtle but telltomato barely
crosses the fluid interface and yet remains madiolucent when it does. This finding would have suggested another possibility-one that explains all the findings-that both tomatoes are outside the cup. The setup is shown in Figure 20b. The cup contains only oil and water. Behind it is a rectangular vessel contaming the lower tomato immersed in positive contrast material, while the upper one is outside both vessels. Incidentally, in Figure 20a, the polar axis of both tomatoes beam. The batter,
tangent
to the
was lined therefore,
internal
up with strikes
interfaces
toes so that these interfaces are ten than in the setup in Problem that is another matter.
22.
Radiograph
of a banana
in Figure
trates incomplete fractures side of a long bone, where ject to tensile stress. These et disease of bone.
2 2 illus-
on the convex the latter is subare typical of Pag-
the a longer
of the tornadefined 19-but
bet-
23. Radiograph
of an
apple
core
in Figure 23 illustrates radiographic appearance circumferential lesion gut. Note the overhanging edges
338
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and
ulcerated
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10
typical of a in the
mucosa.
Number
2
24.
Problem 22.-The strate trauma to the
madiographs shown second metatarsal
in Figure in a patient
24 demonwith sirnu-
lated neurofibromatosis. There is indeed a subchondnal fractune of the distal end of the left second metatarsal (might madiograph) , the fragment lying free in the joint. Incidentally, the patient also has osteoporosis of the fourth metatarsal, degenerative joint disease bilaterally, and a congenital hypertrophy of the bromatosis). This
case
second
toe
illustrates
(fraudulently
some
attributed
additional
basic
to neurofiprinciples.
One
could consider as a basic principle the fact that having seen one or more abnormalities on a radiograph (three in this case) , one is likely to let down his or hen guard and quit looking. Note that the phalanges of the great toes, and some of the other phalanges too, are rather short for the amount of soft
tissue.
Solution
Why? 22.-The
soft
tissues
and
the
bones
belong
to dif-
fement subjects. The bones are cadaver bones joined with glue (the subchondrab fracture occurred when a previously glued joint was disarticulated) To make the picture, we supcmimposed the bones on a wax model of one of the authoms’ .
feet. Prlnclple.-Depth
tional
perception
radiography.
small amount a hand! Did you
is nonexistent
in conven-
The
elongation of the toe required of additional wax and an extra phalanx-from notice
that?
And
did
you
miss
the
only
a
sesamoids?
The setup for Figure 1 is probably clean by now, but just in case it is not, the toe was imaged while immersed in positive contrast material.
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U CONCLUSIONS The techniques illustrated in this ideal for developing problem-solving in medical
students
at an
early
stage
article
are skills
in their
education, since a knowledge of pathology and other medical subjects is not necessary to understand object radiography. Object madiogmaphs may be used, however, at any bevel of training, residency included. In the latter instance, they may help reinforce principles already learned. The main reason for employing object radiography in teaching is to bring variety to the classroom and thereby help keep monotony at bay.
To
this
be integrated
end,
with
the
those
radiographs
of clinical
should
cases,
since object radiography alone will create a monotony of its own. Small doses of object radiogmaphs that are relevant to the point being discussed and that are added with good timing yield the best results. They give the student
a second
visual
demonstration
of the
point in question and allow the teacher to emphasize it again without seeming to be repetitious. Little expense is involved in implementing this practice, other than the cost of film, since the objects to be madiographed are inexpensive, if not entirely free. Even if they
were
expensive,
Acknowledgments:
U
RadioGraphics
U
Pantoja
et al
are not
in anyway
We thank
Eastman
for photographing the radiographs way and Ken Budzek for the artwork. U 1.
dam-
2.
and
Kodak Mary
Ridg-
REFERENCES Felson B, Felson H. Localization of intrathoracic lesions by means of the postero-antenior roentgenognam: the silhouette sign. Radiology 1950; 55:363-374. Longuet R, PhelanJ, Tanous H, Bushong S. Criteria of the silhouette sign. Radiology 1977;
340
they
aged in the process. What is needed most is a radiologist to plan each demonstration and a skillful technician to execute the plan and produce the images.
122:581-585.
Volume
10
Number
2
add variety ny, we imaged
to radiologic teaching and to lower view box monotoordinary objects in circumstances that illustrate-can-
To
catune
might
ciples.
We
be
lenge
amenable
Yet
a better
tried
principles,
word-basic
to make
each
to solution and
object
MD ARRT
the
can
and
image
through
has
result
radiography
pathologic
object
use
it sparingly
the
principles
in question.
always
the
monotony
it is designed
logical
added
play
an
to our
of such sessions.
teaching
with the
pninchal-
teaching
ancillary
in combination Otherwise,
radiologic
interpretation
application
spice
only
and
an
cases
role;
that
technique
we
illustrate
itself
may
add
to
to combat.
INTRODUCTION
U
Entranced
by
how
swiftly
the
expert
seems
to home
in on
the
right
diagnosis,
stu-
are apt to imitate only his or her outward motions and demeanor, oblivious to the toil that alone can entwine swiftness with accuracy. Thus, when confronted with a radiograph, they tend to inspect it briefly and, propping meager findings with intuition, they grope for an instant diagnosis. Admittedly, when simple cases recur, the knee-jerk approach works. However, this leads the student to believe that this approach, being the easiest, is also a trusted road to success in radiology. It is not. dents
Unlike
other
principles
branches
are based
transcend
clinical
of medicine,
radiology
on immutable medicine
and
physical the
is more
laws
human
a science than an art. Its so universal that they
and are
sphere-even
the
animal
world-and
apply to vegetable and inanimate objects as well. Fundamental as they are, these principles are not inborn knowledge. Not only must they be learned, they must be mastered. It is their mastery that consecrates radiology as a science, becoming the foundation
on
This
article
which
radiologic
demonstrates
education
with
should
several
nest.
illustrations
how
mastery
of the
basic
principles may be achieved with object radiography. In Figure 1 (and in Figure 24) , the radiographs call for an explanation, since the “object” in them is actually the human foot. The aim here was to demonstrate that what looks like a clinical ra-
Index
terms:
Physics
RadioGraphics I
From
ter,
the
Dayton,
reprint (cRSNA,
1990; Department OH requests 1990
#{149} Radiography
10:323-340 of Radiological
45435.
From
the
Sciences, 1988
RSNA
Wright annual
State meeting.
University
School
Received
March
of Medicine, 30,
1989;
I 24G acceptedJune
Fred
White 7.
Cen
Address
to E.P.
323
diograph
expert, miliar U
may
baffle
when with
momentarily
the
GENERAL
basic
the
fa-
principles.
PRINCIPLES
Problem
1.-What
diograph scheduled
of a foot (Fig for a morning
ination,
even
he or she is not thoroughly
had
is unusual
taken
about
this
1)? The patient, pyclographic
a laxative
the
night
ra-
exambefore
and had stubbed his toe against the bathroom door at 2:00 AM. By the time this radiograph was taken the next morning, the toe had turned black-and-blue. Solution 1.-If the radiograph puzzles read on. Its meaning will become clear fore the end of the article.
you, be-
1
-
..
*
-
Problem 2.-What is unusual about these two tomatoes madiographed while both were resting on the film (Fig 2), and how can it be
explained? Solution 2.-It takes a trained eye to expect the larger one to be denser and a trained intellect to recognize it as only half a tomato. Principle.-Absorben thickness along the x-ray beam has a major influence on radiographic density, a known fact often over-
looked.
Thus,
in a recent
hibit, authors described denser than a smaller implying a difference
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mammography
cx-
a nodule as being one in the same breast, in their composition!
Volume
10
Number
2
may
be made
denser
without
making
it heavi-
en than water (though it would become heavier than pure oil). Principles-Photoelectric absorption, dominant in the diagnostic x-ray kibovobtage range, varies with the third power of the atomic number of the absorber. Increasing the average atomic number of a liquid (eg, by adding iodinc)increases its radiation absorption faster than its weight. This radio-
:
graph
also
illustrates
the
effect
of surface
tension:
Note the rounding of the oil-water interface but the absence of such rounding the interface between the other two liquids. A third principle culty in comparing
demonstrated
is the
at
diffi-
nonadjacent radiographic densities. Oil (top) and water (bottom), which are distinctly different in density when imaged side by side, now appear deceptiveby isodense.
r
3.-In
Problem
this
radiograph
of a cylindni-
cal plastic bottle containing water and two other liquids (Fig 3), why is it that the liquid at the bottom is not the densest radiographicabby? Solution
eral piodol
oil
3.-The
(at the top) (an
iodized
other and poppy
two liquids a suspension seed
oil)
are mmof Liin miner-
al oil (in the middle). Lipiodob is heavier and denser than water because of its large iodine content. If only a small amount of Lipiodol is mixed with oil, however, the batter
March
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U
SILHOUETTE
SIGN
4.-In
Problem glass cup, is the
AND
Problem
water,
tomato
this
radiograph
and
a tomato
floating
4.-The
Solution
in the
tomato
Solution tail end
is not even radio-
graphic principles justify the assertion. The first is called the silhouette sign. An interface between isodense materi-
is the
326
U
with
each
other
radiographically. summation
placing (tomato
a medium replacing
creases
the
RadioGraphics
in
5.-Fingers of the
banana
one, were
effect.
An
Pantoja
second
object
less dense air in this
radiographic
U
is nonre-
The
than case)
density.
et al
in some
of the
me-
itself in-
four,
and
five
underwater
plus when
the radio-
graphed. images
Principles.-These
in contact
defects
differences between the two (Fig 5) call for an explanation.
4),
water?
separate
Princ4’les.-Two
solvable
soft-tissue
and density ends of this banana What is it?
of a (Fig
the cup.
abs
5.-The
fingers
EFFECT
SUMMATION
illustrate
the
silhou-
ette sign. The outermost layer of the banana peel is water equivalent (and disappears when submerged), but the rest contains tiny air pockets that make the banana float and render that part of the peel radiolucent in water. Note the relativity of density
perception:
The
peel
is dense
in air,
but
the
portion underwater appears radiobucent. Note also the summation effect of the other end of the banana and, particularly, of the index finger, where the summation
is to both
water
and
banana.
Volume
10
Number
2
Problem
the same cup?
6.-The exposure
same egg and cup were factors (Fig 6) Is there .
imaged
twice
air on water
with in the
Solution 6.-The egg shows a summation effect in Figure 6b but not in Figure 6a. If the cup had contained air, the egg would have looked the same in and out of the cup, with a summation
effect
in both.
Therefore,
the
cup
must
have
been
filled with water, the egg being inside the cup in Figure 6a and outside in Figure 6b. Because the shell contains calcium, the silhouette sign does not apply here, but the summation effect still does.
U EFFECT LENGTH Problem Figure
OF ON
TANGENT RESOLUTION
7.-Both cups in 7 contain the same water, two cylindrical
thing: pieces of ice, and a piece of lead. Figure 7a was taken only a couple of minutes before Figure
7b,
sure
factors are the two (Turnpagefor
7a.
March
and
the
were
same
used.
images the
expo-
Why
different? solution.)
7b.
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ice cylinder with ballast
C
B
A
7d.
7c.
7 and Principle.-Figure literature: The length
Solution
diobogic rninant
of interface
resolution
7a and
of the when
the
length
of the tangential contact with (B ), on point (C ) tangents (Fig 7c).
7b
The
resulting
radiograph
(Fig
7a)
along
contrast
a fact
the path
across
the
generally
neglected
of the x-ray interface
beam
is poor.
in the
is a major Depending
ra-
deteron the
the beam, interfaces may be classified as bong (A) , round Figure 7a and 7b demonstrate that, to resolve a poor-con-
trast interface such as that of ice and water, For this demonstration, two ice cylinders float vertically) were placed in a cup with 7d.
demonstrate
interface
the beam must strike a long tangent to it. (one containing a lead ballast in one end to make water and imaged in the position shown in Figure
shows
the
lead
ballast
and
only
that
part
of the
ice
it
above
the water line. The x rays, striking only a round tangent to the cylinders, failed to show the submerged part of the ice. After a couple of minutes, enough ice had melted to release the ballast, and both cylinders floated horizontally side by side. A second exposure (Fig 7b) was made after the cup was rotated so that the beam would strike a bong tangent to the cylinders. Figure 7b cleanly
shows
Problem
considered between
the
ice-water
interface;
8.-Paraffin-mineral
nonresolvabbe them is poor.
the
oil
lead
interfaces
(1 ,2), and, indeed, Can such an interface
piece
is barely
have
long
visible
in the
bottom
of the
cup.
been
the contrastS be resolved ra-
diographically? Solution 8.-Figure 8 shows that it can, provided the interface presents a bong tangent to the beam. A paraffin cylinder floating in a layered mixture of oil and water was imaged with the beam parallel (Fig 8a) and perpendicular (Fig 8b) to the long axis of the cylinder. Although the resulting long
tangent interface was resolved in both oil and water (Fig 8a) (the cylinder appeared as a sphere) , the round tangent interface was resolved only in water (Fig 8b) , and then barely so (four dots mark Principle.-The
can be a major
the
factor
corners length
of the cylinder). of an interface tangent
in interface
resolution
and
to the
beam
radiographic
contrast.
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Problem (Fig 9) cotton
9.-The
linear
is suggestive thread.
Since
the edge
of the apple,
Solution
9.-A
density
in the center
of a piece the
vertical
but
it was
used
was
enough
radiation
why
should
beam
of this
of wire,
was
the cotton used
by a
to darken
appear
to image
apple
caused
the
so dense? apple,
which was suspended with a 3-foot-long fine cotton thread. The thread nearly coincided with the position of the central ray of the x-ray beam. Had it been exactly in the central ray, the thread would have appeared as a white dot instead of a wirelike shadow (note that the part of the thread remote from the x-ray film appears blurred; only its lower end is sharply defined) With the exposure required to image an apple, such .
a thread
would
beam (round fect of tangent
not
tangent) length
be seen . This
if struck perpendicularly is another demonstration
on interface
by the of the
ef-
resolution.
10. U LOGIC PRINCIPLES
Problem
AND
RADIOGRAPHIC ha.
10.-Is
ure 1 0 really grapes?
the radiograph in Fig. of a banana and a bunch of
Problem 11.-What is unusual about this radiograph of a glass cup, two ointment bottles, and one of correction fluid (Fig 1 la)? (Turn pagefor the solution.)
the resemblance of what looks like a banana to the human thorax (the chest wall is denser than the central lungs) . If this were a banana, the center, where it is thicker, should be denser. Note also that the two grapes overlying the banana paradoxicably appear less dense than the others. The radiograph was taken of two halved grapes resting on a banana peel, with a bunch of whole grapes nearby. Solution
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Solution 11.-The film must have been exposed with a horizontal beam (note the air-fluid bevel) . But the latter mdicates
that
deed, 1 ib,
the
image
the image with
the
is upside
was cup
made
and
one
down.
In-
as in Figure ointment
bottle resting upside down on sponges. The other two bottles were glued to a cardboard, which rested on the cup. Princ4,les.-The two principles illustrated in this figure are air-fluid 1eveb and the burning out of a bow-density material with a barge exposure dose.
sponge #{149} #{149}#{149}......#{149}#{149}......#{149}#{149}#{149}#{149}I#{149}#{149}#{149}#{149}
hhb.
Problem
the subject
12.-What in Figure
Pulmonary
consolidation?
Solution
graph
is the matter with 1 2? Aerophagia?
12.-The
is dead.
through
broken its lungs
bird
Killed
a glass
and
now
in this
trying
window,
with
set in rigor
collapsed,
under water. A plastic madiolucent compared ulates air swallowing.
the
bird pellet with
radio-
to fly
its neck mortis was
and imaged
in its beak, water, sirn-
h2.
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Problem 13.-If the only 1 3a) is water, how could for the solution.)
liquid
involved
it have
been
in this
obtained?
image
(Fig
(Turn
page
Hi1 _:c’
Problem
what
14-The confusing,
but
d
radiograph shown careful observation
iion of basic principles will several pertinent observations.
not overlap,
they
all have
itself eggfis significantly than all the others. The e is so weak that where than that of eggfabone.
et between tic feature
March
the outer of chicken
1990
clear
the Where
the same
in Figure 1 4a is someand logical appbicaconfusion. There eggs a, b, c, and
radiographic
are d do
density.
By
denser, while egg e is less dense summation effect of eggs b, c, d, and all four overlap, the density is less Only eggs a andfshow the air pock-
membrane and the shell, a characteniseggs. (Turn pagefor the solution.)
Pantoja
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film
-S
h3b. Solution 13.-Bottle 1 shows an air-fluid level but so do bottles 2 and 4, and these levels give conflicting testimony as to the way the film was exposed. The level in bottle 1 is not as sharp and smooth as the other two. Bottle 3 is overflowing with something that, to judge by its radiolucency, should be air.
Because
than
air,
the
none have
of the bottles been exposed
it must
background
is uniform
be a liquid,
hence
and
water.
are capped, the picture must upside down. The overfibling of bottle 3 demonstrates surface tension. The fallacious level in bottle 1 was not due to an air-fluid interface but to hardened paraffin.
The 1 3b. them
setup
for this
radiograph
is shown
All four bottles contained float in the water tank,
down
against
aluminum scnibed.
the block
Problem
but
Plexiglas
plate
on which
the
15.-Each
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air to make were forced
supports numbers
by the are
in-
14b.
x-ray
14-The weak summation effect of air pockets suggest that eggs b, c, d, and e are empty shells, which they are. But why does a, a whole egg, show the Solution
and
absence
same density as an empty reason that egg e appears than the other shells-a
water (shaded rectangle) (Fig 1 4b) . This is whyf only
one
iion
effect.
in the
image
shell? For the same so much less dense and e are both in ;
the others
are not
a whole egg, is the with a distinct surnrna-
of these
two radiographs (Fig 1 5a) shows a chicken egg and two bird eggs (no empty shells now) . How could these pictunes have been made? (Turn page 334for the solution.)
332
in Figure
enough they
I
denser
Since
Pantoja
et al
to
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10
Number
2
Problem
1 7.-Radiographs
in
Figure 1 7 depict the same pain ofgrapcfruits. In Figure 17a, the two grapefruits have a distinct summation effect. Two components
of the
dermis”
skin-”epi-
and a more
“subcutaneous
nadiolucent
tissue”
(the
ma-
diolucency is due to microscopic air pockets)-and the interface
corresponding
to the
deep fascia are evident. In Figune 1 7b, the background is denser and has a fine granulanity that
is more
that seen summation
h7a.
obvious
in Figure effect
than
1 7a. No or epidermis
of the grapefruit on the left is seen in Figure 1 7b. Recalling Figure 5, one is bound to suspect that the changes in the skin of this grapefruit, those of the banana
like before,
are
due to underwater radiography. That indeed is the case-anothen manifestation of the silhouette sign and somewhat d#{233}j#{224} vu. But the challenge in Figure 1 7b is on
the
right
side.
If that
grapefruit is not in the water, why does it back a summation effect? And if it is, why is the epidermis preserved? (Turn pagefor the solution.)
h7b.
h6a. Problem in Figure
16.-Which 1 6a was
of the four
stationary exposure? (Turn
diognaphic
eggshells
at the time of mapagefor the so-
lution.)
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x-ray
h5b. Solution
fect,
15.-Egg
so it was
a shows
simply
a summation
superimposed
efon
the
chicken egg (E) Egg c, on the other hand, shows no such effect, as if it had been inside the larger egg (F) . Such a feat would have .
been difficult to contrive. unc 1 5b, egg c was simply (shaded rectangle) , which same which
As shown put
in water
produces
the
ten? Density differences egg in a dense medium
are relative. A whole (iodine solution in rectangles]) can be made to
[black an empty
shell
in water.
16.-None;
Solution As seen
glued
But what about eggs b and d, look bike empty shells in wa-
effect. indeed
this case look like
in Fig-
in Figure
together
they 1 6b,
the
as a unit
were
all moving.
eggshells
and were
were
spinning
around the one in the center, which was hanging by a thread along the central x ray. In Figure 16b, only the spinning central shell and its shadow underneath are not blurred by the motion. Principle.-In Figure 1 6a, the three mevolving eggshells were blurred, but the spinning one in the center and the thread that spins
with
it were
not.
Motion
of an
interface
in its own plane and the spinning of an axis on itself are not detrimental to the resolution of their respective images. The old technique of autotomography nested mainly on this
334
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in a Styrofoam sheet. The fruit on the might (A) was squeezed into this hole; the one on the left (H) was allowed to rest on the Stymofoam. To keep this buoyant assembly under water, it was covered with a Plexiglas sheet, which was forced down with bead weights as shown. Prlnciples.-Thc reason for all this was to demonstrate imaging principles that are not always clean in the mind of the student: (a) Only contrasting interfaces struck tangentiabby by the beam can be resolved radiographically, (b) both tangency and contrast
are not only
necessary
sure trast
resolution, critical at the
interface is only
When
a grapefruit,
but
sufficient and point
for instance,
the
(C)
to encon-
of tangency.
is imaged
in
a pole-to-pole direction, skin near the equator skin part of the image.
only a slice of the is responsible for the The grapefruit could therefore be under water and its skin imaged all around, provided there is contrast at the point of tangency (the reason for the Styrofoam sheet).
h7c. Solution 1 7.-The upper part of Figure 1 7c shows the setup for Figure 1 7a; the bottom shows that of Figure 1 7b. In both cases, the separation of the grapefruit on the left from the film accounts for its magnification, and
the sheet of Styrofoam on which one fruit rests explains the granularity seen in the background of both radiographs. For the setup
in Figure
to admit
1 7b,
a grapefruit
Problem
18.-The
a mound
with
keen
hole,
big
a tight
enough
fit, was cut
observer
may
notice
that
ground in Figure 1 8a has a density intermediate of Figure 1 7a and 1 7b. Other pertinent findings 1 8a are
the
greater
ten definition planes,
on
do the two
density
of the
of the epidermis the
other
grapefruits
hand,
fruit
on the are
appear
better
different?
on the
right.
the
back-
between in Figure left
The
and
the
that bet-
“fascial”
defined on the left. (Turn pagefor
Why the
solution.)
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Solution 18.-As image on the left
shown represents
in Figure a polar
1 8b, the section
at the interface urn (air in this
with case)
the surrounding mcdiand at the interface with
of a grapefruit; the one on the right, a slice through the equator. To keep the two 5cc-
the subcutaneous
lions
equidistant
from
the
make
the
more
comparable,
18b) and, therefore, bong enough good resolution with the available But in the polar section, the beam
images
film
and
thereby
the equa-
tonal slice was placed on a plastic support (solid gray rectangle) . Because the polar 5cclion is thicker, its fascial planes present long-
en tangents to the beam than those of the othem section, which is why these planes are betten defined in the image on the left. On the right, however, the epidermis has greaten definition, which brings us to anothen concept: resolution of point tangent yensus ally
round
tangent
strikes
Problem discussed
19.-On so far,
contents Solution
on the
other,
fluid
suspect,
is oil.
Note
imposed
(Fig
and
defect,
are
In the equatorial round
a point tangent, which interfaces, particularly
the least contrast the subcutaneous Principle-As increases with
and with tangent
both
contrast may
the
two
interface
with
a rube, interface resolution the length of the tangent
across
the interface.
compensate
for
and vice versa; ample contrast need for tangent length.
poor
A long
contrast
reduces
the
the
material
medium)
that
upper
is
the other
tomato
that .
One fluid .
appears
on the cup,
is indicated
like
it but
by the fact something of medium. one in Prob-
is not.
I
19.
RadioGrapbics
of
than the oil in which it is partially imThat it is inside, rather than super-
bern 20 books
U
both with
The
one
indicates
contrast
contrast
correctly, that
objects.
which
that this tomato, too, produces a defect in the positive contrast This setup is quite simple; the
336
(Fig
to allow contrast. strikes
degrades the one
(namely, tissue). both
tangents
19)?
the lower
is positive
an aqueous
could denser mersed.
cup
are tomatoes;
as a filling
lower
only these
tissue.
these
the basis of the principles what can be said about the
cup shown has two nonof different densities, one
objects
(actually
actutwice:
19.-The
floating
the
beam
epidermis
paper
fluids
seen
The
to the
of this
miscible two
interfaces.
a tangent
section,
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Pantoja
et al
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right
cends the cup with two tomatoes shown in Figure 20a, the contrast between each tomato and the surrounding medium, as well as between the two tomatoes where they approach one another, has increased Problem
20.-In
drastically
compared
with
that
seen
in Figure
19. The decreased doxical. appears
contrast between the two fluids has just as drastically. This seems paraThe lower part of the upper tomato so dense that, on the basis of what
was said
before, one is inclined to assume the lower tomato is in the cup. But to explain all the findings. (Turn the solution.)
that only this fails pagefor
U
SIMULATED
CONDITIONS Problem 21.-To with a meniscus
representing plastic bottle ral effusion” Figure
March
PATHOLOGIC simulate
sign,
a pleural
an inflated
effusion
balloon
the lung was inserted inside a (the chest cavity) and a “pleuintroduced between the two. In 2 1 , note the meniscus sign in the up-
1990
position,
lung and somehow
replace the entire cupy
bottle, pleural
tapering
between
as it as-
the elastic
just
as lung
space
when
level layers in the
were air to to fill
expands
to oc-
an effusion
We also put mineral to simulate an abscess
companied shape
effusion
gravity
the chest wall. If this fluid removed without allowing it, the balloon would expand
the
drained. balloon fluid fluid
the
against
is
oil inside the with an air-
and to emphasize the point that out perfectly flat only when ac-
by free bottom
air. But why of the
the peculiar
balloon?
Solution 21.-The peculiar shape was produced by adding a small amount of water to the oil. Since water is heavier, it sinks under the oil, and, being under two forces (gravity and surface tension) , it assumes the oblong shape observed. In the process, it again demonstrates the principle of the silhouette sign. Because the effect of the intervening rubber is negligible,
water
inside
and
balloon blends on contact, and torn of the balloon is invisible.
Pantoja
et al
outside
the
the very
U
bot-
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U
337
Solution
ence
20.-The is applicable
inductive to radiology.
method of sciIt enjoins its
disciples to be exhaustive in gathering facts and to consider all possibilities in explaining those facts. With a little more thoroughness,
we might have tale sign-that
discovered the lower
a subtle but telltomato barely
crosses the fluid interface and yet remains madiolucent when it does. This finding would have suggested another possibility-one that explains all the findings-that both tomatoes are outside the cup. The setup is shown in Figure 20b. The cup contains only oil and water. Behind it is a rectangular vessel contaming the lower tomato immersed in positive contrast material, while the upper one is outside both vessels. Incidentally, in Figure 20a, the polar axis of both tomatoes beam. The batter,
tangent
to the
was lined therefore,
internal
up with strikes
interfaces
toes so that these interfaces are ten than in the setup in Problem that is another matter.
22.
Radiograph
of a banana
in Figure
trates incomplete fractures side of a long bone, where ject to tensile stress. These et disease of bone.
2 2 illus-
on the convex the latter is subare typical of Pag-
the a longer
of the tornadefined 19-but
bet-
23. Radiograph
of an
apple
core
in Figure 23 illustrates radiographic appearance circumferential lesion gut. Note the overhanging edges
338
U
RadioGraphics
U
Pantoja
et al
and
ulcerated
Volume
10
typical of a in the
mucosa.
Number
2
24.
Problem 22.-The strate trauma to the
madiographs shown second metatarsal
in Figure in a patient
24 demonwith sirnu-
lated neurofibromatosis. There is indeed a subchondnal fractune of the distal end of the left second metatarsal (might madiograph) , the fragment lying free in the joint. Incidentally, the patient also has osteoporosis of the fourth metatarsal, degenerative joint disease bilaterally, and a congenital hypertrophy of the bromatosis). This
case
second
toe
illustrates
(fraudulently
some
attributed
additional
basic
to neurofiprinciples.
One
could consider as a basic principle the fact that having seen one or more abnormalities on a radiograph (three in this case) , one is likely to let down his or hen guard and quit looking. Note that the phalanges of the great toes, and some of the other phalanges too, are rather short for the amount of soft
tissue.
Solution
Why? 22.-The
soft
tissues
and
the
bones
belong
to dif-
fement subjects. The bones are cadaver bones joined with glue (the subchondrab fracture occurred when a previously glued joint was disarticulated) To make the picture, we supcmimposed the bones on a wax model of one of the authoms’ .
feet. Prlnclple.-Depth
tional
perception
radiography.
small amount a hand! Did you
is nonexistent
in conven-
The
elongation of the toe required of additional wax and an extra phalanx-from notice
that?
And
did
you
miss
the
only
a
sesamoids?
The setup for Figure 1 is probably clean by now, but just in case it is not, the toe was imaged while immersed in positive contrast material.
March
1990
Pantoja
et al
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Ra4ioGrapbics
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339
U CONCLUSIONS The techniques illustrated in this ideal for developing problem-solving in medical
students
at an
early
stage
article
are skills
in their
education, since a knowledge of pathology and other medical subjects is not necessary to understand object radiography. Object madiogmaphs may be used, however, at any bevel of training, residency included. In the latter instance, they may help reinforce principles already learned. The main reason for employing object radiography in teaching is to bring variety to the classroom and thereby help keep monotony at bay.
To
this
be integrated
end,
with
the
those
radiographs
of clinical
should
cases,
since object radiography alone will create a monotony of its own. Small doses of object radiogmaphs that are relevant to the point being discussed and that are added with good timing yield the best results. They give the student
a second
visual
demonstration
of the
point in question and allow the teacher to emphasize it again without seeming to be repetitious. Little expense is involved in implementing this practice, other than the cost of film, since the objects to be madiographed are inexpensive, if not entirely free. Even if they
were
expensive,
Acknowledgments:
U
RadioGraphics
U
Pantoja
et al
are not
in anyway
We thank
Eastman
for photographing the radiographs way and Ken Budzek for the artwork. U 1.
dam-
2.
and
Kodak Mary
Ridg-
REFERENCES Felson B, Felson H. Localization of intrathoracic lesions by means of the postero-antenior roentgenognam: the silhouette sign. Radiology 1950; 55:363-374. Longuet R, PhelanJ, Tanous H, Bushong S. Criteria of the silhouette sign. Radiology 1977;
340
they
aged in the process. What is needed most is a radiologist to plan each demonstration and a skillful technician to execute the plan and produce the images.
122:581-585.
Volume
10
Number
2
