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Visual Assessment of Regional Myocardial
Perfusion Utilizing Radioactive Xenon
and Scintillation Photography
By P. J. CANNON, M.D., J.
I.
HAFT, M.D.,
AND
P. M. JOHNSON, M.D.
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SUMMARY
A method was devised to visualize the areas of left ventricle supplied by various
coronary arterial branches utilizing scintillation photography and an inert radioactive
gas which distributes instantaneously between coronary blood and perfused myocardial
cells. From 1 to 5 millicuries of 133Xe dissolved in saline solution was injected through a
catheter into the anterior descending or posterior circumflex branch of the left coronary
artery of 15 dogs. Scintillation images produced during arrival and washout of 133Xe
in the various regions of the heart were recorded by an image intensifier scintillation
camera and high speed television monitor and were reproduced on Polaroid film during
replay of the videotape on an oscilloscope. The resulting scintiphotographs defined the
region of the left ventricle supplied by the coronary arterial branch. In nine of the dogs
acute myocardial infarctions were produced by occluding one or the other branch of the
left coronary artery. When 133Xe was injected again into the coronary artery proximal
to the occlusion, that area of the left ventricle t-hat was deprived of nutrient blood flow
was no longer visualized on the gamma-ray scintiphotograph. The results indicate that
regional myocardial perfusion may be dynamically visualized in the intact animal.
Additional Indexing Word
Coronary blood flow
Myocardial infarction
Animal study
Radioisotope
I NVESTIGATION of the effectiveness of
blood flow to various regions of the myocardium has acquired greater therapeutic
significance since the demonstration that revascularization procedures may be of symptomatic value in the treatment of patients with
coronary artery disease.14
Currently available technics to assess the
regional myocardial circulation have intrinsic
limitations, however. Coronary cineangiography affords precise visualization of major
branches of the coronary arteries but does not
provide information concerning the adequacy
of perfusion of myocardial cells.5 6 The limitations of angiography as a sole method of evaluating patients with coronary atherosclerosis
have recently been emphasized in reports: (1)
of patients without angina pectoris in whom
significant narrowing or occlusion of coronary
arteries was documented radiographically,5' 6
and (2) of patients with typical angina pectoris, electrocardiographic signs suggestive of
ischemia, and evidence for increased myocardial lactate production in whom angiographically normal coronary arteries were found.7-10
Technics now employed clinically to measure the rate of myocardial blood flow in
patients with coronary artery disease are also
From the Department of Medicine, College of
Physicians and Surgeons, New York, New York.
Part of this work was presented at the Forty-First
Scientific Sessions of the American Heart Association,
Bal Harbour, Florida, November 24, 1968. Abstract in
Circulation 38 (suppl. VI): VI-92, 1968.
This research was supported by Grants 5RO1-HE10182-03 and HE-05741 from the U. S. Public Health
Service and by a grant from the J. Hartford
Foundation. Dr. Cannon is recipient of Career
Development Award 5K3-15031-05 from the U. S.
Public Health Service.
Address for reprints: Dr. P. J. Cannon, Department
of Medicine, College of Physicians & Surgeons, 630
West 168th Street, New York, New York 10032.
Circulation, Volume XL, September 1969
Inert gas
277
CANNON ET AL.
92478
of limited value because they provide a measurement of blood flow per unit volume or
weight of a large mass of heart muscle and
thus do not indicate regional variations of
myocardial perfusion. It is probable that deficient perfusion of small areas of ventricular
muscle in patients with angina pectoris", 12
may remain undetected by these measurements 1.3-22
The present experiments
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were undertaken
with a twofold purpose: (1) to develop a technic by which the regions of left ventricle supplied by various branches of the left coronary
artery of the dog could be dynamically visualized and (2) to ascertain whether, utilizing this
technic, areas of myocardium where perfusion
is inadequate could be localized in the intact
animal. In the experiments, advantage was
taken of the unique properties of radioactive
xenon and of the recent development of the
gamma-ray scintillation camera.
SDogHeart
jSource of Radioactivity
Camera
Cine
Figure
Schematic illustration of the Ter-Pogossian (Picker)
image intensifier scintillation camera. In the actual
experiments reported, the experimental animal was
anesthetized and lying
its right side with the point
of maximal cardiac impulse 1 cm from the center of
the multichanneled collimator.
on
radiation energy is detectable by external monitoring and is readily collimated owing
to its relatively low energy; the short biologic
half-life of the isotope also reduces radiation
exposure.31 Because of the absence of significant recirculation, 133Xe, as well as 85Kr, has
been widely utilized to measure nutrient blood
flow in a variety of tissues by the SchmidtKety application of the Fick principle.3248
The validity of blood flow measurements calculated from the externally monitored washout of these isotopes has been documented in
heart muscle by several investigators.19-21
gamma
Theoretical Considerations
Properties of '33Xenon
'33Xe is a radioactive isotope of a gaseous
element which is chemically inert and physiologically inactive.23 24 Because of its small
molecular size and lipid solubility, xenon is
highly diffusible. After injection into an artery,
its passage across capillary walls into the
tissue supplied by the artery is rapid and is
not limited by diffusion through pores.25 26
The myocardium to blood partition coefficient
(y) is 0.72.27, 28 Due to its great diffusibility
xenon also readily passes through pulmonary
capillaries into alveoli and is largely eliminated
into respired air in one passage through the
lungs,29 30 a feature which minimized recirculation after arterial injection into a regional
vascular bed.20
The isotope, 133Xe, is produced in a nuclear
reactor by fission of 235uranium. It decays to
stable '33cesium by emission of beta particles
of a maximum energy of 347 kiloelectron volts
(kev) followed by emission of gamma rays of
81 kev and characteristic x-rays of 31 kev; the
physical half-life of 133Xe is 5.3 days. The beta
emission of 133Xe is absorbed in 1-mm tissue
and is unsuitable for external detection. The
Scintillation Camera
The principles of the Ter-Pogossian scintillation camera39' 40 used in the present studies
are schematically illustrated in figure 1.* The
source of radioactivity ('33Xe deposited in dog
myocardium by injection into the left coronary
artery) emits gamma rays which pass through
parallel holes in a 2-inch thick, fine collimator
(2,611 channels, each 1/8 inch wide with septal thickness of 0.003 inch) and interact with
a 9-inch diameter cesium iodide scintillation
crystal where incident photons are converted
*Magnacamera, manufactured by Picker Nuclear,
White Plains, New York.
Circulation, Volume XL, September 1969
279
MYOCARDIAL PERFUSION BY SCINTIPHOTOGRAPHY
light flashes in proportion to their energy
and abundance. The light flashes produced by
the scintillator are detected by the light-sensitive photocathode of an image intensifier tube
applied to the crystal which amplifies and
focuses them to produce a small brighter image
on an output phosphor screen. This screen is
optically coupled to an Orthicon system which
scans the image for additional amplification
and display on a television monitor and videotape. Scintillation images produced in this
fashion during arrival and washout of 133Xe
in myocardium are thus dynamically recorded
on videotape. During replay of the videotape
on an oscilloscope, changes in isotope position
and movement may be viewed and photographed on cine-film, or single or integrated
photographs can be taken with a Polaroid
camera at specific times after injection of the
isotope. Since the position and energy of
gamma-photon interactions in the large crystal
determine the position and brightness of light
flashes on the output phosphor of the image
intensifier tube, the resulting scintiphotographs
reflect the intensity and distribution of radioactivity in the tissue under study.
In preliminary studies the image intensifier
scintillation camera employed in the present
experiments was shown to be highly efficient
for gamma-emitting isotopes with low energies, 35 to 150 keV41; the detection efficiency
of the instrument was poorer above 280 kev.
Within the optimal energy range, higher
energy events are more easily detected by the
camera because they produce a brighter
scintillation which is more easily distinguished
from background. This particular system does
not permit pulse height analysis, a disadvantageous feature at higher energies, but one
which is less important at energies of 35 to 140
kev, where differences between the primary
and scattered photons are often relatively
small. Because the intrinsic tube resolution is
about 2 mm, the effective resolving power of
the system* is determined by the collimator.
to
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*Effective resolution is defined as the minimum
distance at which two line-sources of identical
radioactivity can be distinguished clearly when
separated by a gap containing no radioactivity.
Circulation, Volume XL, September 1969
By utilizing the fine collimator and phantom
the effective resolution was found to
be slightly less than 1 cm over the energy
range 35 to 280 kev.41 The effective resolution
did not decrease significantly when the
collimator was separated from a 133Xe source
by 1 to 4 cm of air or a tissue equivalent.
Because collimation reduces efficiency, approximately a fourfold increase in source
activity was required to produce an image
with the fine collimator which was as bright as
that obtained from the same source with a
700-hole, coarse collimator. Phantom studies
also indicated good spatial linearity and
minimal distortion of concentricity, or variation in field uniformity with the camera. The
effective speed of the system was 30 videotape
frames per second.4'
sources,
Methods
Experimental Technic
Myocardial perfusion patterns were studied in
15 mongrel dogs weighing 16 to 25 kg. Each dog
was anesthetized with pentobarbital (30 mg/kg)
and placed on his right side with the left anterior
part of the chest directly beneath the multiholed
collimator of the scintillation camera. Under
fluoroscopic control a J-tipped, no. 7 cardiac
catheter was passed down the right carotid artery
and positioned in the anterior descending or in
the posterior circumflex branch of the left
coronary artery (fig. 2). A fine (0.1-mm outside
diameter) radiopaque Teflon catheter was then
rapidly threaded through the cardiac catheter into
the branch of the coronary artery (fig. 2) and the
no. 7 catheter was withdrawn into the aorta.
Positioning of the fine catheter was done
fluoroscopically, and coronary angiograms were
made to verify the vascular anatomy. Femoral
arterial blood pressure was recorded with a
Sanborn 236 pressure transducer, and electrocardiograms were monitored with a Model 100
Sanbom ECG machine.
Four millicuries of 133Xe dissolved in 1 to 3 ml
of sterile pyrogen-free saline solutiont was
injected rapidly (2 to 6 sec) into the coronary
artery, and the arrival and washout of isotope in
the heart were viewed with the scintillation
camera. The center of the fine collimator in each
study was positioned 1 cm above the point of
maximal impulse of the cardiac beat. Radioactive
markers were attached to the dog to verify that
tObtained as "Xenisol-133" from Neisler Laboratories, Tuxedo Park, New York.
CANNON ET AL.
280
EXPERIMENTAL TECHNIQUE
the large positioning catheter was removed.
Electrocardiographic changes of early myocardial
infarctions were recorded in the nine dogs after
positioning of the plug. Preliminary experiments
had demonstrated that when ECG changes of
infarction were not observed after positioning the
plug, the coronary artery was not occluded, and
neither the 133Xe perfusion patterns nor the '33Xe
washout rates were altered significantly from
control values. After myocardial infarctions had
been demonstrated by ECG in the nine dogs,
repeat studies of myocardial perfusion were
performed by injecting '33Xe in saline proximal to
the site of occlusion through a side-hole in the
fine catheter (fig. 2).
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Figure 2
Illustration of the anatomy of the canine heart and of
the experimental techniques employed to catheterize
the coronary arteries and to produce experimental myocardial infarctions. For details see text.
there was no change in the relative positions of
animal and collimator in sequential studies.
Orthicon voltage and "beam" settings were
optimized for each dog; the former usually ranged
from 80 to 105, the latter from 145 to 155. The
arrival and washout of '33Xe in dog myocardium
was recorded on videotape at 30 frames/second.
When the tape was replayed on the oscilloscope,
Polaroid pictures integrated for 1-sec intervals
were obtained at specific intervals after the
isotope injection which had been recorded on the
sound track of the videotape in each study. In 13
animals the washout of 133Xe from the myocardium was also monitored with a 2-inch Nal
scintillation crystal coupled to a dual-rate computer and digital printout,* and myocardial
nutrient blood flow was calculated according to
the method described by Herd's'8 and Ross's20
groups.
Experimental Myocardial Infarctions
In nine dogs acute myocardial infarctions
were
produced by a closed chest technic.42 The fine
Teflon catheter positioned in a branch of the left
coronary artery in control studies was withdrawn
and was replaced by another fine catheter with a
Teflon plug on the tip (fig. 2). This plug was
wedged into the anterior descending or posterior
circumflex branch with the large J-shaped cardiac
catheter and occluded the artery; following this
*Models 628-145 and 628-143, Picker Nuclear,
White Plains, New York.
Circulation, Volume XL, September 1969
Results
133Xe dissolved in saline solution was
injected into a branch of the left coronary
artery of the 15 dogs; in each study the arrival
and washout of isotope were recorded contin-
uously on videotape which was subsequently
replayed on an oscilloscope and photographed. Sequential scintiphotographs of 1-sec
duration taken at various times after the
injection into the posterior circumflex branch
of dog J are depicted in figure 3. The
maximal intensity of radioactivity was present in sec 4 after injection, and the washout
of isotope from the left ventricle was sufficiently rapid that isotope was not visually
detected after 45 sec. Myocardial nutrient
blood flow during this study, calculated from
the '33Xe washout curve, was 77 ml/ 100
g/min.
In figure 4 the scintiphotographs obtained
during the 1 sec of peak radioactivity after
injection of 133Xe into the anterior descending
and posterior circumflex branches of dog N
are depicted. Accompanying each photograph
is a schematic representation of the cardiac
silhouette, with the distribution of radioactivity in the myocardium indicated by diagonal
lines. The different shapes and sizes of the
areas of distribution of radioactivity in the left
ventricular myocardium in the two studies are
apparent. Similar radioisotope distribution
patterns were observed in the other 14 dogs;
characteristic and distinct perfusion patterns
were visible after injection of isotope into
either branch of the left coronary artery.
In nine dogs acute myocardial infarctions
MYOCARDIAL PERFUSION BY SCINTIPHOTOGRAPHY
281
DOG N
Catheter in anterior descending branch
Of Lt. coronary
. . . .~ .~ oi
II
.P-
u..,y
m.
Catheter in poster or ct rcumf lex branch
Of Lt. coronary.
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Scntl photograph
@&Area Perfused
Figure 4
Radioisotope perfusion patterns after injection of
133Xe. Anterior myocardial perfusion after injection
into the anterior descending branch of the left coro-
Figure 3
Integrated 1-sec Polaroid views taken at various times
after injection of 133Xe into the posterior circumflex
artery of dog J are shown. The largest radioisotope
image occurred during the second of peak radioactivity
(4 sec after injection); isotope was no longer visible
after 45 sec.
were produced by plug occlusion of one of the
coronary arterial branches after control studies
had been completed. Injection of 3t3BXe in
saline into the artery proximal to the occlusion
was then repeated. The upper portion of
figure 5 demonstrates the area of perfusion
which was detected by the scintillation
camera after injection of 4 millicuries of '33Xe
into the left anterior descending coronary
artery of dog P. Beneath the control study is
the scintiphotograph obtained 20 min after
experimental infarction had been produced.
Circulation, Volume XL, September 1969
nary artery (top) and posterior myocardial perfusion
after injection into the circumflex branch of the left
coronary artery. To the left of each scintiphotograph
appears a schema in which the silhouette of the dog
heart is outlined, along with a tracing of the 133Xe
perfusion pattern.
The scintillation image was considerably
smaller and altered in shape after the
experimental infaretion. The gray area on the
accompanying schema indicates the region
of left ventricular myocardium perfused in
the control study no longer receiving
adequate nutrient blood flow. Three days later
this dog was sacrificed. The heart was
photographed at postmortem examination
(fig. 6); the area of infarction corresponds in
size and shape to the area of deficient
perfusion indicated by scintiphotographs in
figure 5. The autopsy picture in figure 6 also
shows the position of the occluding plug in the
coronary artery. Scintiphotograpbs obtained
in control studies and after occlusion of the
wH
CANNON ET AL.
282
DOG P
CONTROL STUDY
DOG P STUDY AFTER INFARCTION
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Icm
Figure 6
b Area Perf used
C
Additional Area Perfused in C ontroI Study
Figure 5
Perfnision patterns produced byl '33Xe during a con7trol stuidy of normal myocardial perf-usion (top) and
after experinmental anterior rniyocardial infarction (bottoniI) in dog P. The gray stippling in the schematic
representation after infarc tion depicts that region of
left ventricular m!yocardiumi dep)rived of its nutrient
blood sulpply. (The cir-cular spot wchich is apparent on
the scintiphotographs is a radioactive marker tapedl
to the animal's chest).
left anterior descending branch of dog T are
presented in figure 7.
In five dogs posterior myocardial infarctions
were produced by plug occlusion of the
posterior circumflex artery. Figure 8 demonstrates the characteristic electrocardiographic
changes induced by this proceduire. Figure 9
shows the typical control isotope perfusion
pattern observed after the injection of 13XIXe
into the posterior circumflex artery and also
depicts the loss of the distal perfusion larea
which occurred after plug occlusion of tbt
artery. The gray stippled area on the schemnatic view represents that portion of myocardium
no longer receiving adequate nutitrient )lood
supply after the infarction.
The heart of dog P. The plug occluding the anterior
descenidinig branch of the left coronary artery is indicated hy the arrow. The area of infarction corresponds
to that portion of the control '33Xe perfusion image in
figure 5 w, hich is no longer visible after plhg occlusion
of the artery.
Discussion
Because of its high diffusibility, short
biologic half-life and low garmma energy,
133Xe was the isotope employed in the present
studies of myocardial perfusion. Herd and
associates"8 and Ross and co-workers20 first
used radioactive ineit gases to study myocardial nutrient blood flow; these workers demonstrated that blood flow per gram of heart
calculated from the uniexponential washout
curve of "'Xe or 85Kr when multiplied by
cardiac weight equaled the total coronary flow
measured by a flow meter.
The measure of blood flow per unit volume
of heart muscle provided by these methods
has not been of significant diagnostic value in
the evaluation of patients with angina peetoris, possibly for two reasons: (1) It is likely
that both heart muscle mass and blood flow
can decline simultaneously in coronary heart
disease,42 a change which would be uinde,
tected by these methods. (2) The measureCircutanon, Volume XL, September 1969
X_*+.=STiI T<!4FiZt~ .
MYOCARDIAL PERFUSION BY SCINTIPIJOTOGRAPHY
Dog T. Control Study
DOG T
DUG U
283
CONTROL STUDY
AFTER INFARCTION
STUDY
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Z
Area Perfused
Area Perfused
Additionol Area Perfused in Control Study
AdditionaI Area Perfused in Control Study
Figure 9
Figure 7
Contiol atid experimental scintiphotographs of the
Perf4tsiori patterns produced by 1'3Xe in the ntyocardijuni of dog U before and after experimental posterior
hteart of dog T in which an anterior myocardial infarcin qocardial infarction.
tion1 was produced.
POSTERIOR MYOCARDIAL INFARCTION
STANDARD LEADS
i t -t:
... ...
..
,
*s
7, 7r
41
.1'
___
.F S '4_
....
...
_d
-.
t..
_
.
_9,_1t
1
.s
_t
'' -1
.__ _ _ _
._. _.n
__ . _,
.:
Figure 8
Electrocardiograp/tic changes itn the stanidard leads in dog 0 10 min after experimental occlusion
of the posterior circumrflex artery appears in the bottom of the figure. The characteristic pattern
of an acite posterior inifarction is visible.
Circulation, Volume XL, September 1969
284
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ment obtained after injection of either isotope
into the coronary arteries gives no information
concerning myocardial perfusion in various
areas of the ventricle perfused by the coronary
artery studied. Two recent reports have
suggested that significant differences in regional myocardial blood flow may exist in
patients with coronary heart disease. Sullivan
and associates'2 found that the rate of
washout of 85Kr (injected locally into the
ventricular mass at time of thoracotomy)
varied significantly in different areas of the
hearts of such patients, and Klocke and
associates22 showed that heterogeneous myocardial blood flow in animals or patients with
varying degrees of coronary occlusion caused
the slope of the cardiac washout curve of an
inert gas to deviate significantly from a single
exponential.
In the present experiments, 133Xe dissolved
in saline solution was deposited in myocardial
tissue through a fine catheter positioned in the
left anterior descending or posterior circumflex coronary arteries, and the heart was
photographed with a gamma scintillation
camera to define the regions of left ventricle
supplied by the various branches of the left
coronary artery. Because of its high diffusibility, 133Xe, when injected into the branch of the
coronary artery, did not remain within the
blood vessel but rapidly diffused into the
tissue supplied by that arterial segment. Since
the radioactivity images recorded by the
camera were generated by the presence of
isotope within myocardial cells, the resulting
scintiphotographs corresponded to the tissue
bed which derives its nutrient blood supply
from the vessel injected. Control 133Xe scintiphotographs thus delineated regions of left
ventricle receiving adequate capillary perfusion and were therefore different from the
coronary cineangiograms which defined the
anatomy of large and medium-sized coronary
blood vessels. The distinctive appearance and
the absence of significant overlap of perfusion
patterns suggest that few intercoronarv anastomoses exist in the normal canine heart.
Use of a fine radiopaque indwelling
catheter for injection of isotope was not
CANNON ET AL.
necessary for successful visualization of myocardial perfusion by the present technic. Such
a catheter was employed merely to facilitate
serial measurements of coronary perfusion in
the dog, a species in which it is technically
difficult to maintain an arteriographic catheter
in the main left coronary artery. Preliminary
studies had demonstrated that placement of
the coronary catheter did not alter myocardial
blood flow. Other preliminary studies indicated that, if 133Xe was injected inadvertently
into the left ventricle or aorta, the isotope was
washed downstream rapidly in 2 to 10 sec; in
the latter situations a radioisotope image of
the cardiac chamber or aorta, or both, was
visualized on the television monitor.
The fact that the maximal size of the
image of '33Xe distribution in the normal
myocardium coincided with the peak counts
per second monitored externally provides
evidence for an assumption concerning the
inert gas technic for measuring coronary blood
flow,20 namely, that blood-myocardial tissue
equilibration of xenon is almost instantaneous.
133Xe was not visualized clearly on 1-sec
scintiphotographs taken 45 to 90 sec after
peak tissue activity in dogs with a normal
washout of isotope from heart muscle (nutrient flow, 70 to 120 ml/ lOOg/min). The chance
observation in one dog who spontaneously
developed ventricular fibrillation shortly after
the isotope was injected, that scintiphotographs of 1"3Xe in myocardium persisted
unchanged for over 3 min, supports another
assumption concerning these methods, namely, that the inert gas leaves heart tissue almost
entirely by way of the venous drainage.
The closed-chest technic utilized for producing acute myocardial infarctions in the animals43 was reproducible, and infarction was
demonstrated at postmortem examination in
all dogs who developed characteristic electrocardiographic changes. Scintiphotographs of
133Xe in myocardium after experimental infaretions showed that the radioisotope images
were smaller and altered in shape in all
studies, and the portion of the control isotope
image no longer visible after the infarcts
corresponded to the shape of the myocardial
Circulation, Volume XL, September 1969
MYOCARDIAL PERFUSION BY SCINTIPHOTOGRAPHY
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infarction at autopsy when the heart was
viewed from the left side of the animal.*
Thus, the technic was capable of demonstrating areas of myocardium which were no
longer receiving nutrient blood flow in the
intact animal.
Several other isotope technics for localizing
myocardial infarctions have been developed in
the past decade. Injections of macroaggregates of human serum albumin labeled
with 1311 have been employed to visualize the
coronary vascular bed in dogs43; however, the
potential hazards of this procedure for patients with coronary insufficiency have precluded extensive use of this substance in man.
Infarcted tissue takes up increased amounts of
radioactive chlormerodrin and a derivative of
mercurochrome labeled with 203Hg; hence
external scans after injection of these isotopes
have been reported to indicate areas of
infarcted myocardium.4 The present technic
is not dependent upon the presence of actual
tissue necrosis since the distribution of 133Xe is
a function of nutrient blood supply. Thus, it is
likely that not only areas of tissue death, but
also relatively avascular regions of myocardium which are not necrotic (for example,
areas of fibrosis or ventricular aneurysms) can
be detected with the new method.
Normal myocardial tissue is known to
extract 86rubidium, 131cesium, and oleic acid
labeled with 131I from coronary artery blood.
Precordial scans obtained after injection of
any one of these substances have indicated
diminished uptake of tracer in areas of
myocardial infarction.4>49 The present technic
appears to afford several advantages over
*In studies in which isotope was injected into the
anterior descending artery, resolution was probably
not significantly altered by curvature of the ventricle
because the surface of the anterior left ventricular
wall was parallel to and less than 4 cm beneath the
inferior plane of the collimator of the scintillation
camera. In studies after injection into the posterior
circumflex artery, however, the anesthetized animal
was not repositioned to make the posterior-inferior
surface of the heart parallel to the plane of the
collimator; hence in these studies resolution diminished directly with the degree of curvature of the
ischemic area.
Circulation, Volume XL, September 1969
285
these methods, however: (1) The speed of the
scintillation camera (30 frames/ sec) far exceeds
that of currently available rectilinear scanning
equipment; hence dynamic studies of isotope
arrival and washout can be obtained. (2) The
resolving power of the detection system is
slightly greater than that of such scanning
procedures. (3) The shorter biologic half-life
of '33Xe and the low energy of its gamma
emission will reduce the possibility of radiation hazard to the patient if this technic, or a
variation thereof, is used in man.20' 31
Two disadvantageous aspects of the technic employed in the present studies are related
to the less-than-optimal effective resolution of
the isotope imaging system and to the absence
of quantitative regional blood flow data.
Ideally one would desire the imaging system
to have an effective resolution less than 0.5
cm. Although the resolving power of the
system used in these experiments was sufficiently great to detect in vivo the myocardial
infarctions produced in the dog hearts,
nevertheless phantom studies indicated that
the effective resolution with 133Xe was only
slightly less than 1 cm.41 It is possible,
however, that with improved collimators, this
scintillation camera may be able to detect
even smaller avascular areas in myocardium
because its intrinsic tube resolution is 2 mm.
Quantitation of gamma intensity during
133Xe washout from different regions of the
myocardium was not possible with the particular equipment employed in the present
experiments, even though the design of the
Ter-Pogossian image intensifier tube is such
that the intensity of the photoemission recorded by the system is proportional to the
amount of radioactivity in the tissue under
study. If, in the future, quantitation of isotope
activity in different areas of the scintillation
detector becomes technically feasible, it is
anticipated that it will then be possible to
obtain quantitative measurements of the rate
of myocardial blood flow in regions of the
myocardium where vascular disease has reduced but not abolished blood flow. Currently, experiments are under way in this laboratory to develop methods for quantitative
CANNON ET AL.
286
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estimation of regional myocardial blood flow
employing 133Xe, scintillation photography,
and a variation of the procedures employed in
the present preliminary studies.
Potential clinical applications of the approach to assessment of regional myocardial
perfusion with radioactive inert gases and
scintillation photography are several. They
include the visualization and definition of
functionally avascular regions of the myocardium, the assessment of adequacy of collateral
circulation beyond coronary artery occlusions,
study of diseases which affect the coronary
microcirculation,50 and the critical evaluation
of surgical procedures now employed to
revascularize the myocardium. It is anticipated that such assessments would supplement but not replace the definition of
coronary vascular anatomy obtained by cine-
angiography.
Acknowledgment
The authors wish to thank Dr. B. J. Clark of Neisler
Laboratories, Inc. for generously providing some of
the 133Xe utilized in these studies.
References
1. VINEBERG, A. M., AND WALKER, J.: Surgical
treatment of coronary artery disease by internal
mammary implantation: Report of 140 cases
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Circulation, Volume XL, September 1969
MYOCARDIAL PERFUSION BY SCINTIPHOTOGRAPHY
of radioactive inert gas into the coronary
arteries. Circulation Research 15: 28, 1964.
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Chains of Tradition in Scientific Journals
The great defect of the scholastic philosophers in Bacon's view was that they
placed too much emphasis on existing texts, neglecting their own powers of observation.
The characteristic work of the pre-scientific period was the compilation and the commentary. In the era before printing this may have grown to some extent out of the fact
that a manuscript is unique and that in the act of copying and transmitting a manuscript
a scholar might not be able to resist yielding to the temptation of annotating and commenting on the omissions and deficiencies of the basic text. The scarcity of copies
would lead to scholars compiling collections of notes from the sources they consulted
much in the same way a scholar might today accumulate collections of notes. The
availability of the original sources today would make the publication of such collections
of little value, while in a period of scarcity they might have had an important function
to perform. The change from manuscript to printing introduced new problems in the
transmission of information but there was a considerable carry over from the manuscript,
just as the printed character was an attempt to reproduce the hand drawn character.
The practice of lengthy citation from original sources that persists in scholarship even
today may perhaps be regarded as another example of the persistence of tradition. ...
-DAVID A. KRONICK: A History of Scientific and Technical Periodicals. New York, The
Scarecrow Press, Inc., 1962, p. 45.
Circulation, Volume XL, September 1969
Visual Assessment of Regional Myocardial Perfusion Utilizing Radioactive Xenon
and Scintillation Photography
P. J. CANNON, J. I. HAFT and P. M. JOHNSON
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Circulation. 1969;40:277-288
doi: 10.1161/01.CIR.40.3.277
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