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THE
AMERICAN
OF
ROENTGENOLOGY RADIUM
JOURNAL
THERAPY
NUCLEAR
AN
Bj
DAVID
MEDICINE JUNE,
I 24.
VOL.
INVESTIGATION FOR INFORMATION FROM TOMOGRAPHY
EXTRACTING COMPUTERIZED SCANS*
F. REESE, PAUL
PH.D., GEORGE C. McCULLOUGH,
M.D., PETER R. GERDING,
C. O’BRIEN, and EDWIN
HE computerized tomographic scan is presented as an 8o by 8o matrix of numbers whose value is directly related to the x-ray attenuation coefficients of unit volumes of brain. Each unit measures 3 by 3 by 13 mm. deep. These attenuation coefficient numbers are printed out on large sheets of computer paper and are difficult for a radiologist to analyze in terms of normal and pathologic anatomy. Through a digital to analogue converter (Fig. i), this information is displayed on a cathode ray tube as representations of axial brain slices. These displays are more intelligible to the eye than are the printed sheets; from this scope and the photographic prints taken of it, diagnoses are made. But one may ask the question, “Is there more information on the numerical printout sheet (that is, in the attenuation coefficient numbers) than can be displayed Presented
at the Seventy-fifth
Annual
Meeting
W.
2
MORE
BEELER, PH.D.
JR.,
PH.D.,
MINNESOTA
T
*
No.
1975
ROCHESTER,
27,
AND
and perceived on the cathode ray tube?” This paper is an early report on our attempt to answer that question. There are many approaches to the problem of increasing the diagnostic yield of the attenuation coefficient numbers. Different formats of display are one. For example, Thompson and Ethier2 have produced a three-dimensional display of the individual brain slices, and Ackerman’ has combined 6 slices and displayed them simultaneously on a TV monitor in both the sagittal and coronal projections. Our approach has been directed toward statistical analysis and redisplay in the form of histograms. METHOD
Using material generated by the EM! brain scanner, we analyzed 20 normal scans and 5 abnormal scans of proved pathology.
of the American
Roentgen
Ray
Society,
San
Francisco,
California,
September
a.-
1974.
From the Mayo Clinic and Mayo Foundation, Rochester, Minnesota. This investigation was supported in part by Research Grants CA-159o2 Institutes of Health, Public Health Service.
‘77
and RRoooo7
and Contract
CB-43982
from
the National
Reese,
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178
1
K K
‘.
..
K1;;
O’Brien,
K.:
:.
K.2
:;
;.
‘:
:::
#{149}
.
L
L
and
McCullough
JUNE,
1975
K
K K K
.
:
#{149}
II
K #{149}#{149}.
Gerding
::
I
:
Jr.,
:
:
:: K I
Beeler,
I :
2 .
:
.
4;#{149}
.
‘
#{149};..:
: :,
and analogue
representation
LLI Fic.
i.
Digital
Our scanner is equipped with a tape deck option and all scan data are placed on industry compatible digital magnetic tape for archival purposes. These tapes are studied on a different computer system, where a master tape of selected slices is created and used for redisplay and analysis of picture content. Although histograms of the attenuation coefficient numbers of the entire image can be made, the region of diagnostic interest is the intracranial portion of the image (Fig. 2). The remaining numbers representing the calvarium, the surrounding water, and air in the hair are unimportant and in some way must be deleted. To this end, the computer program scans each line and column of the image from the periphery inward, seeking the skull (defined as attenuation coefficient numbers greater than ioo). This amplitude test is used to define the inner margins of the skull. Data values within 2 pixels of this margin, and all data outside this margin, are discarded from statistical consideration. The remainder of the data is divided into the left and right hemispheres, based on a subjective designation of the midline.
of left hemispheric
glioma.
RESULTS
We have not yet analyzed all the levels in each of the 20 normal patients. Rather, we chose the 2A slice in each instance. This level is anatomically quite complex and includes portions of many structures such as the frontoparietal and occipital lobes, lateral and third ventricles, and the basal ganglia. Also, abnormalities are frequently found at this level. The analysis of 20 normal scans is shown in Table i. Table i shows numerical data from each hemisphere, applying 3 basic statistics: the mean; the standard deviation; and the skewness coefficient of the attenuation coefficient numbers. The analysis in terms of means is given in the first 3 columns. /=XR-XL is the difference in mean attenuation coefficient number between the right and left hemispheres. The standard deviation (Columns 4 to 6) measures the degree of heterogeneity, large values of the standard deviation representing a great degree of heterogeneity. Column 6 gives the ratio (R) of the standard deviation of the right hemisphere to that of the left.
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VOL.
124,
No.
2
Extracting
Information
from
Columns 7 to i 2 relate to the third descriptive statistic, the coefficient of skewness. These coefficients for the right and left hemispheres are given in Columns 7 and 8, respectively. The skewness coefficients, adjusted for standard error, are given in Columns 10 and ii. A large positive skewness coefficient indicates unusually large attenuation coefficient numbers; a negative value indicates unusually small attenuation coefficient numbers. In addition to describing brain attenuation coefficient number patterns in normal subjects, these data may well provide a basis for distinguishing normals from abnormals. The degree of symmetry between right and left hemispheres is indicated by Columns 3, 6, , and 12. Large values (either positive or negative) for in Column 3 indicate that, on the average, one hemisphere attenuates more x-rays than the other. Similarly, large values for R in Column 6 indicate that the right hemisphere is more heterogeneous than the left. (The converse would be associated with values for R close to o.) Differences in skewness between right and left hemispheres are indicated in Columns 9 and 12. In summary, the above statistics should be useful in detecting abnormal scans in 3 ways: i. Differences in means between right and left hemispheres: for detecting scans in which one side has a higher or lower average x-ray attenuation relative to the other side. 2. The ratio of standard deviations: for detecting scans in which one side has both extremely high and low x-ray attenuation relative to the other side. 3. The difference between skewness coefficients: for detecting scans in which one side has either extremely high or low x-ray attenuation (but not both) relative to the other side. At this time, the skewness coefficients are of uncertain value. However, in Column 3, with one exception, the absolute differences of the means in the two hemispheres are less than i. The only exception, control Patient
Computerized
Tomography
Scans
‘79
Fic.
2. Numerical printout before and after deletion of superfluous attenuation coefficient numbers representing water, air, and bone. The remaining numbers represent intracranial contents only.
14, has a difference in mean value of attenuation coefficient number of -1.98. This may represent an abnormality. The ratios of the standard deviations are seen in Column 6. These are approximately equal to i, with the highest ratio equal to 1.27 and the lowest equal to 0.79. By summarizing the data obtained on each subject in terms of these basic descriptive statistics, one is able to make comparisons among subjects rather easily, determine normal ranges, and thus quickly spot abnormal scans with values lying outside the limits for normal subjects. However, such a condensation of data results in a loss of information when studying the distribution of attenuation coefficient numbers of individual subjects. A more informative method for comparing right and left hemispheres for a given subject is obtained by constructing frequency polygons as in Figures 3 to 9. Along the X axis are the
I
Reese,
8o
O’Brien,
Beeler,
Jr., TABLE
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SUMMARY
STATI5TIC5
ON
ATTENUATION
(right
Subject
XL
SDR
SDL-R
JUNE,
1975
NUMBERS
FOR
20
NORMALS
hemispheres)
GIR*
G1L*
TG1Rt
TOILt
I
24.82
15.76
0.9165
0.1091
-0.2386
0.35
1.30
15.88
0.42
3.5852 3.454!
3.9117
16.30
3.3631
2.0271
0.1223
-0.106!
0.23
1.32
1.12
3
‘9.73 17.92 16.94 16.92
19.27
4.5758 4.7865
5.2202
0.003
1.69
2.70
-0.0!
5.5060
0.8766 0.8693
o.i6ii
17.16
0.46 0.76
1.2001
-1.15
12.95
-12.45
17.53
0.59
4.1795
4.4111
0.9475
-0.3828
0.0497
-0.33
4.40
-o.6
-3.84
16.94
0.02
3.9722
4.3707
-0.2323
0.4557
-0.69
7 8 9
16.47 16.33
16.36 i6.8
0.!!
3.5538
3.67!!
o.o88 0.9680
0.4020
4.8! -4.46
-7.25 0.48
1.0879
17.49
5.1027
0.9166
10
i6.86
4.4616 4.6769 4.0336 4.3228
4.1012
17.55
4.0708
0.9909
-0.3669 -o.o8 -0.3368 0.2488
-2.44 3.98 -0.67
5.4905
0.7873
-0.0590
3.8145
3.3170
1.1500
-0.5971
4.997! 4.9253
4.9365
1.0123
4.6439 4.4236
1.0584 0.9254
0.1939
6
-0.94
SDL
left
McCullough
I COEFFICIENT
and
and
2
4 5
-0.52 0.06
0.0473
0.1583
0.0089 -0.3443
o.2o6
-0.07
4.07
-o.io 0.38
i.6 -0.64
2.70
-5.23
-0.26
-6.75 3.37
-3.85 25.96
-1.17
4.79 -2.62
17.43
‘3
i6.oi i8.z
14
15.20
17.18
15
26.45
27.35
0.9O
4.0935
i6
18.52 18.73
18.82 i8.6o
-0.30
4.8377 7.0769
5.060!
0.9560
0.3616
0.0328
0.33
5.5862
3.9150
0.5052
3.41
i8 ‘9
16.40
i6.,o
-o.o
5.2024
-o.66
25.90
15.94
-0.04
3.6495
5.5456 3.8596
1.2669 0.938!
0.9456
-0.1325
20
27.46 ‘9.73 24.82
17.43
0.03
5.0064
0.898!
19.27
0.96 1.98
4.4963 7.08
3.45
3.3!
0.79
3.9! -o.66
17.02
17.17
4.43
4.58
0.97
0.26
Max Mm Mean
Skewness
t T-
coefficient,
15.76
0.96 0.44
1.98
0.23
-0.15
1.27
0.4425
-0.3365
2.9878 -0.1079
0.0115
0.4513 -0.2359
-0.3815 0.2208
i.8 -o.6 0.43
2.2! 4.22 42.20
-0.28
-.oi -i.6
-0.35
-0.1987
0.2!
0.22
1.40
3.41
42.20
-0.44 0.10
0.10
-3.95
II
-0.0!
-2.75
0.0!
12
-0.71
0.50
0.04
‘7.57 16.47 i6.oa 18.07
‘7
*
XR
Gerding
-1.15
-7.0!
o.i6
2.85
0.40 5.40
4.05 2.44
-0.77 0.22 -2.05
4.49 -2.90
28.4!
5.96 4.83 3.82 36.80
-3.98
-3.03
2.53 -2.16 25.96 -5.23
-4.09
1.03
2.28 36.80 -22.45 2.82
Gi.
Gi/SEoi.
values of the attenuation coefficient numbers, which in normal brain range from about + 10 to +30. Cerebrospinal fluid has attenuation coefficient numbers between I to +3 and gray matter has relatively high attenuation coefficient numbers (+25 to +30). The Y axis shows the percentage occurrence of the various attenuation coefficient numbers. These charts were done by hand, using a class interval of , but in time it will be possible to chart these on the computer with a cathode ray display, with class intervals of any desired width. Nineteen of the 20 control patients had left and right hemispheres that matched almost exactly. The only exception is Patient 14; it can be seen in the histogram (Fig. 3, Uper left; and 4) that the right hemisphere has less x-ray attenuation than the left. According to the statistical chart previously presented, the mean attenuation coefficient number difference between the two hemispheres was almost 2, whereas none of the other normals had an absolute mean differ-
ence of greater than i On reviewing this patient’s history, we noted that she had had a severe concussion and skull fracture over the right hemisphere 25 years previously. Now she has a Grade i EEG dysrhythmia in the right cerebral hemisphere, the significance of which is unknown. The right hemisphere seems to have some post-traumatic atrophy. Analysis of Abnormal Scans.-Five scans of known pathology were chosen for analysis. The first scan represents a meningioma of the falx before and after the injection of Renogralin (Fig. 5 and 6). In the first scan, there is a distortion of Zone 2 of the right lateral ventricle, but it is difficult to actually visualize the tumor. The histogram shows symmetry of the attenuation coefficient numbers below 20, but the right hemisphere has a higher proportion of attenuation coefficient numbers between 20 and 30 than does the left hemisphere. The difference in the means is 1.64, with the right side having higher x-ray attenuation. .
VOL.
No.
i,
2
Extracting
0
10
Information
from
Computerized
Tomography
Scans
i8i
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40
30
20
10 I’.’ I.. 3
‘I
50
40
30
20
10
0 -10
20
30
40
50
60
-10
0
10
20
30
40
50
60
Densities
Fic. 3. Histograms
superimposing left
shows
2 hemispheres: 19 ot 20 were symmetric. asymmetry of density of 2 hemispheres.
Remember that in 19 of the 20 normals there was no difference greater than i, thus indicating that the scan for this patient may be abnormal. The statistics do not show that the right lateral ventricle is less visible than the left, but the eye does. After the injection of Renografin, the tumor is obvious. The statistics are also quite abnormal. The mean difference in the two lobes is now 7.98 and the ratio of standard deviations is 2.05. The highest normal difference in standard deviation was 1.3. It is of interest that the difference in skewness coefficients between the two hemispheres was i.6, whereas we had some differences in normal subjects that were as high as 36. This casts doubt on the use of skew as a method of analysis for detecting this type of abnormality. The next patient (Fig. 7) had a cm. left sphenoid meningioma. This tomographic
Histogram
on upper
scan was read as negative, and it may indeed be negative. The level may not have been low enough to pick up the left sphenoid wing. In any event, the statistical analysis showed no abnormality. The x-ray attenuations of the 2 hemispheres match almost exactly. The scan in Figure 8 shows a typical glioma in the left temporal fossa. There are zones of increased and decreased x-ray attenuation and a mass effect on the ventricles. However, the statistical analysis is disappointing. The difference in the average x-ray attenuation coefficient numbers between the 2 hemispheres is 0.48 (considerably less than i); the ratio of standard deviation is nearly i and well within the range observed in normals. The histogram also suggests no abnormality. Apparently, the higher and lower x-ray attenuations of the tumor averaged out and masqueraded
Reese,
182
O’Brien,
Beeler,
Jr.,
Gerding
and
McCullough
JUNE,
2975
50
LH RH
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-
40 #{188}.
q)
20
10
0 0
-10
10
20
30
40
50
60
Densities I
SDR Subject 267
*Skees$
R
L
15.20
17.18
coefficient,
SDR -1.98
4.9153
SDL 4439
G1 10584
G
tT
-0.1079
t 04513
R
-0.56
-0.2391
T1
Gi
1 -1.17
4.79
-5.96
G /SE i
i
Fic. . The right hemisphere is less dense than the left and the difference in the means greater than i. The visual appearance of the scan was normal, but the statistics imply diffuse abnormality of the right hemisphere relative to ancient trauma.
is -1.98, that there
which is may be a
50
LH RH
-
40
#{188}.
20 q)
10
Densities
Subject Slide *Sk.e$$
067,
34
R
k
16.82
15.18
coefficient,
SDR 1.64
4.3788
SDL SLRj 4.8321
G
‘T I
Fic.
5. Scan
made
Gi i1
0.9062
0.5635
G1 -0.689
1.25
R
TG1
-0.8175
6.01
G /SE I
before
the
contrast
medium
injection
(see
text).
T61 -6.91
12.92
VoL.
No.
ii,
Extracting
2
from
Computerized
Tomography
LH RH
.
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Information
40
Scans
183
#{149}U6-2E 121C
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20 q)
10
Densities
I
Slide *Skees$
1067,
I Ik I I I I2672118.741 19.923114.8308 12.05411 XR
Subject 2
B
SD
SDL
fE:RJ
7.98
coefficient,
Fic.
G1
6. Scan
GIR
:
j
0.50481
GIL *
0.43921 0.07
I 1
R
1.1494
ITGIRITGI
15.141
I
L:
3.5811.56
‘T= GI/SEG made
after
the
contrast
medium
injection.
---RH I’)
#{188}.
Densities SDR Subject 394
*Skewness
Fic.
7. Left
XR 16.92
L 16.94
coefficient,
sphenoid Scan
SDR -0.02
3.9722
SDL 4.3707
0.9088
G1
wing meningioma. cut is probably
tT Scan above
the
G1
G1
L
-.2323
.4557
-0.69
R -0.5098
I Gi 1-2.44
G1/SE6
is negative and statistics tumor and is, indeed,
show normal.
no abnormality.
TGI L 4.81
-7.25
1
Reese,
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184
O’Brien,
Beeler,
Jr.,
Gerding
and
McCullough
LH RH
-
.
JUNE,
568-
1975
2A
40 #{188})
Densities 1
SDR XR
Lubiect 1
16.40
568
*Skewness
FIG.
8. Left
L. 16.88
coefficient,
temporal coefficient
-0.48
SDR
SDL
3.6087
3.6234
G1
glioma with increased numbers equal those
G1 j
G1 0.9959
0.7096-00560
L 0.77
I
R -12671
Gi
4j
R
8.44
TGI L -0.68
9.12
‘T= GI/SEG
and decreased x-ray in the right temporal
as normal brain x-ray attenuation when considered over the entire hemisphere. Finally, another glioma of the right posterotemporal lobe (Fig. 9) is presented; it contains areas of increased and decreased x-ray attenuation, but mostly decreased. The histogram shows that the right hemisphere is less attenuating to x-rays than the left hemisphere. The absolute difference in means is +1.75, which is above the limit of i. The ratio of standard deviations is 1.2, which is suggestive of an abnormality. DISCUSSION
This project was the first step in an attempt to use a computer to aid the visual diagnosis of the computerized tomographic scan. It is envisioned that as the radiologist observes the conventional cathode ray tube with its anatomic representation, he will simultaneously have, on a second tube, the
attenuation, lobe. Statistics
whose are
average normal.
attenuation
statistical data as well as histograms representing a particular slice of brain tissue. This would either aid him in the diagnosis of specific lesions or alert him to the fact that there may be a statistical difference between an area in one hemisphere and the corresponding area in the other. Early results are encouraging but equivocal. It does not appear that this method will work in lesions whose average x-ray attenuation is equal to normal tissue. It is also postulated that midline symmetric lesions such as pontine and corpus callosum tumors and third ventricular masses will not be detected, at least by the comparison of means. As a result of this study, we will take 2 steps. The first will be to make more detailed comparisons of the histograms. The comparisons, in a case such as the first meningioma, might reveal a significant dif-
VOL.
Extracting
No.
124,
Information
from
Computerized
Tomography
Scans
i
85
50
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LH RH
40 #{188}) #{188}.
30
Q.)
20
:3 Q)
10
,u/ ,
-
-10
I
0
I
10
20
30
40
I
50
60
Densities
[
Subject
I I
*Skewness
coefficient,
I
XR
17.14
Fic.
I
L
11a891-1.75
I SDR
I
ISD
RI
SDL
nizing
sensitive
statistical
abnormal
methods
glioma. Difference
Right hemisphere in means of the
computerized their
information
for
tomography in
digital
0.361 -1741621
GlRITG1LI 3881-0.21
I
1
4.09
scans
average is -
density 1.75.
David
F. Reese, M.D. Clinic and Mayo Rochester, Minnesota
Foundation 5590!
REFERENCES i.
recog-
form,
shows lower hemispheres
2
Mayo
2.
Because
R
the information is in a natural format for statistical and mathematical analyses and redisplay in various forms. \Ve have chosen histograms as a redisplay format. Further refinements and experience will be necessary before the method is clinically applicable.
scans. CONCLUSIONS
produce
1
‘T= GI/SEG
ference in the x-ray attenuation coefficient numbers in the 20’s and 30’s. A second step will be to subtract individual points of the left hemisphere from spatially symmetric individual points of the right hemisphere. The left temporal glioma missed by the study of means may become apparent by this method. To date, we have studied only one 13 mm. thick slice of brain. Integrating the slice or slices above and below will give us larger volumes of both normal and abnormal brain. The resultant additional information may lead to the development of more
G
11.25611 R I o.343jo.ol97I IR i
16.023114.7952
G1
9. Right posterior temporal than does left hemisphere.
G
L. Frontal and lateral projections of EM! scans. Read at the Montreal First International Symposium on Computerized Axial Tomography, May 31-June I, 1974. tHoMPsoN, C., and ETHIER, R. Topographic and density displays of EM! scans. Read at the Montreal First International Symposium on Computerized Axial Tomography, May 31-
ACKERMAN,
J tIflC
I,
1974.
THE
AMERICAN
OF
ROENTGENOLOGY RADIUM
JOURNAL
THERAPY
NUCLEAR
AN
Bj
DAVID
MEDICINE JUNE,
I 24.
VOL.
INVESTIGATION FOR INFORMATION FROM TOMOGRAPHY
EXTRACTING COMPUTERIZED SCANS*
F. REESE, PAUL
PH.D., GEORGE C. McCULLOUGH,
M.D., PETER R. GERDING,
C. O’BRIEN, and EDWIN
HE computerized tomographic scan is presented as an 8o by 8o matrix of numbers whose value is directly related to the x-ray attenuation coefficients of unit volumes of brain. Each unit measures 3 by 3 by 13 mm. deep. These attenuation coefficient numbers are printed out on large sheets of computer paper and are difficult for a radiologist to analyze in terms of normal and pathologic anatomy. Through a digital to analogue converter (Fig. i), this information is displayed on a cathode ray tube as representations of axial brain slices. These displays are more intelligible to the eye than are the printed sheets; from this scope and the photographic prints taken of it, diagnoses are made. But one may ask the question, “Is there more information on the numerical printout sheet (that is, in the attenuation coefficient numbers) than can be displayed Presented
at the Seventy-fifth
Annual
Meeting
W.
2
MORE
BEELER, PH.D.
JR.,
PH.D.,
MINNESOTA
T
*
No.
1975
ROCHESTER,
27,
AND
and perceived on the cathode ray tube?” This paper is an early report on our attempt to answer that question. There are many approaches to the problem of increasing the diagnostic yield of the attenuation coefficient numbers. Different formats of display are one. For example, Thompson and Ethier2 have produced a three-dimensional display of the individual brain slices, and Ackerman’ has combined 6 slices and displayed them simultaneously on a TV monitor in both the sagittal and coronal projections. Our approach has been directed toward statistical analysis and redisplay in the form of histograms. METHOD
Using material generated by the EM! brain scanner, we analyzed 20 normal scans and 5 abnormal scans of proved pathology.
of the American
Roentgen
Ray
Society,
San
Francisco,
California,
September
a.-
1974.
From the Mayo Clinic and Mayo Foundation, Rochester, Minnesota. This investigation was supported in part by Research Grants CA-159o2 Institutes of Health, Public Health Service.
‘77
and RRoooo7
and Contract
CB-43982
from
the National
Reese,
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178
1
K K
‘.
..
K1;;
O’Brien,
K.:
:.
K.2
:;
;.
‘:
:::
#{149}
.
L
L
and
McCullough
JUNE,
1975
K
K K K
.
:
#{149}
II
K #{149}#{149}.
Gerding
::
I
:
Jr.,
:
:
:: K I
Beeler,
I :
2 .
:
.
4;#{149}
.
‘
#{149};..:
: :,
and analogue
representation
LLI Fic.
i.
Digital
Our scanner is equipped with a tape deck option and all scan data are placed on industry compatible digital magnetic tape for archival purposes. These tapes are studied on a different computer system, where a master tape of selected slices is created and used for redisplay and analysis of picture content. Although histograms of the attenuation coefficient numbers of the entire image can be made, the region of diagnostic interest is the intracranial portion of the image (Fig. 2). The remaining numbers representing the calvarium, the surrounding water, and air in the hair are unimportant and in some way must be deleted. To this end, the computer program scans each line and column of the image from the periphery inward, seeking the skull (defined as attenuation coefficient numbers greater than ioo). This amplitude test is used to define the inner margins of the skull. Data values within 2 pixels of this margin, and all data outside this margin, are discarded from statistical consideration. The remainder of the data is divided into the left and right hemispheres, based on a subjective designation of the midline.
of left hemispheric
glioma.
RESULTS
We have not yet analyzed all the levels in each of the 20 normal patients. Rather, we chose the 2A slice in each instance. This level is anatomically quite complex and includes portions of many structures such as the frontoparietal and occipital lobes, lateral and third ventricles, and the basal ganglia. Also, abnormalities are frequently found at this level. The analysis of 20 normal scans is shown in Table i. Table i shows numerical data from each hemisphere, applying 3 basic statistics: the mean; the standard deviation; and the skewness coefficient of the attenuation coefficient numbers. The analysis in terms of means is given in the first 3 columns. /=XR-XL is the difference in mean attenuation coefficient number between the right and left hemispheres. The standard deviation (Columns 4 to 6) measures the degree of heterogeneity, large values of the standard deviation representing a great degree of heterogeneity. Column 6 gives the ratio (R) of the standard deviation of the right hemisphere to that of the left.
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VOL.
124,
No.
2
Extracting
Information
from
Columns 7 to i 2 relate to the third descriptive statistic, the coefficient of skewness. These coefficients for the right and left hemispheres are given in Columns 7 and 8, respectively. The skewness coefficients, adjusted for standard error, are given in Columns 10 and ii. A large positive skewness coefficient indicates unusually large attenuation coefficient numbers; a negative value indicates unusually small attenuation coefficient numbers. In addition to describing brain attenuation coefficient number patterns in normal subjects, these data may well provide a basis for distinguishing normals from abnormals. The degree of symmetry between right and left hemispheres is indicated by Columns 3, 6, , and 12. Large values (either positive or negative) for in Column 3 indicate that, on the average, one hemisphere attenuates more x-rays than the other. Similarly, large values for R in Column 6 indicate that the right hemisphere is more heterogeneous than the left. (The converse would be associated with values for R close to o.) Differences in skewness between right and left hemispheres are indicated in Columns 9 and 12. In summary, the above statistics should be useful in detecting abnormal scans in 3 ways: i. Differences in means between right and left hemispheres: for detecting scans in which one side has a higher or lower average x-ray attenuation relative to the other side. 2. The ratio of standard deviations: for detecting scans in which one side has both extremely high and low x-ray attenuation relative to the other side. 3. The difference between skewness coefficients: for detecting scans in which one side has either extremely high or low x-ray attenuation (but not both) relative to the other side. At this time, the skewness coefficients are of uncertain value. However, in Column 3, with one exception, the absolute differences of the means in the two hemispheres are less than i. The only exception, control Patient
Computerized
Tomography
Scans
‘79
Fic.
2. Numerical printout before and after deletion of superfluous attenuation coefficient numbers representing water, air, and bone. The remaining numbers represent intracranial contents only.
14, has a difference in mean value of attenuation coefficient number of -1.98. This may represent an abnormality. The ratios of the standard deviations are seen in Column 6. These are approximately equal to i, with the highest ratio equal to 1.27 and the lowest equal to 0.79. By summarizing the data obtained on each subject in terms of these basic descriptive statistics, one is able to make comparisons among subjects rather easily, determine normal ranges, and thus quickly spot abnormal scans with values lying outside the limits for normal subjects. However, such a condensation of data results in a loss of information when studying the distribution of attenuation coefficient numbers of individual subjects. A more informative method for comparing right and left hemispheres for a given subject is obtained by constructing frequency polygons as in Figures 3 to 9. Along the X axis are the
I
Reese,
8o
O’Brien,
Beeler,
Jr., TABLE
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SUMMARY
STATI5TIC5
ON
ATTENUATION
(right
Subject
XL
SDR
SDL-R
JUNE,
1975
NUMBERS
FOR
20
NORMALS
hemispheres)
GIR*
G1L*
TG1Rt
TOILt
I
24.82
15.76
0.9165
0.1091
-0.2386
0.35
1.30
15.88
0.42
3.5852 3.454!
3.9117
16.30
3.3631
2.0271
0.1223
-0.106!
0.23
1.32
1.12
3
‘9.73 17.92 16.94 16.92
19.27
4.5758 4.7865
5.2202
0.003
1.69
2.70
-0.0!
5.5060
0.8766 0.8693
o.i6ii
17.16
0.46 0.76
1.2001
-1.15
12.95
-12.45
17.53
0.59
4.1795
4.4111
0.9475
-0.3828
0.0497
-0.33
4.40
-o.6
-3.84
16.94
0.02
3.9722
4.3707
-0.2323
0.4557
-0.69
7 8 9
16.47 16.33
16.36 i6.8
0.!!
3.5538
3.67!!
o.o88 0.9680
0.4020
4.8! -4.46
-7.25 0.48
1.0879
17.49
5.1027
0.9166
10
i6.86
4.4616 4.6769 4.0336 4.3228
4.1012
17.55
4.0708
0.9909
-0.3669 -o.o8 -0.3368 0.2488
-2.44 3.98 -0.67
5.4905
0.7873
-0.0590
3.8145
3.3170
1.1500
-0.5971
4.997! 4.9253
4.9365
1.0123
4.6439 4.4236
1.0584 0.9254
0.1939
6
-0.94
SDL
left
McCullough
I COEFFICIENT
and
and
2
4 5
-0.52 0.06
0.0473
0.1583
0.0089 -0.3443
o.2o6
-0.07
4.07
-o.io 0.38
i.6 -0.64
2.70
-5.23
-0.26
-6.75 3.37
-3.85 25.96
-1.17
4.79 -2.62
17.43
‘3
i6.oi i8.z
14
15.20
17.18
15
26.45
27.35
0.9O
4.0935
i6
18.52 18.73
18.82 i8.6o
-0.30
4.8377 7.0769
5.060!
0.9560
0.3616
0.0328
0.33
5.5862
3.9150
0.5052
3.41
i8 ‘9
16.40
i6.,o
-o.o
5.2024
-o.66
25.90
15.94
-0.04
3.6495
5.5456 3.8596
1.2669 0.938!
0.9456
-0.1325
20
27.46 ‘9.73 24.82
17.43
0.03
5.0064
0.898!
19.27
0.96 1.98
4.4963 7.08
3.45
3.3!
0.79
3.9! -o.66
17.02
17.17
4.43
4.58
0.97
0.26
Max Mm Mean
Skewness
t T-
coefficient,
15.76
0.96 0.44
1.98
0.23
-0.15
1.27
0.4425
-0.3365
2.9878 -0.1079
0.0115
0.4513 -0.2359
-0.3815 0.2208
i.8 -o.6 0.43
2.2! 4.22 42.20
-0.28
-.oi -i.6
-0.35
-0.1987
0.2!
0.22
1.40
3.41
42.20
-0.44 0.10
0.10
-3.95
II
-0.0!
-2.75
0.0!
12
-0.71
0.50
0.04
‘7.57 16.47 i6.oa 18.07
‘7
*
XR
Gerding
-1.15
-7.0!
o.i6
2.85
0.40 5.40
4.05 2.44
-0.77 0.22 -2.05
4.49 -2.90
28.4!
5.96 4.83 3.82 36.80
-3.98
-3.03
2.53 -2.16 25.96 -5.23
-4.09
1.03
2.28 36.80 -22.45 2.82
Gi.
Gi/SEoi.
values of the attenuation coefficient numbers, which in normal brain range from about + 10 to +30. Cerebrospinal fluid has attenuation coefficient numbers between I to +3 and gray matter has relatively high attenuation coefficient numbers (+25 to +30). The Y axis shows the percentage occurrence of the various attenuation coefficient numbers. These charts were done by hand, using a class interval of , but in time it will be possible to chart these on the computer with a cathode ray display, with class intervals of any desired width. Nineteen of the 20 control patients had left and right hemispheres that matched almost exactly. The only exception is Patient 14; it can be seen in the histogram (Fig. 3, Uper left; and 4) that the right hemisphere has less x-ray attenuation than the left. According to the statistical chart previously presented, the mean attenuation coefficient number difference between the two hemispheres was almost 2, whereas none of the other normals had an absolute mean differ-
ence of greater than i On reviewing this patient’s history, we noted that she had had a severe concussion and skull fracture over the right hemisphere 25 years previously. Now she has a Grade i EEG dysrhythmia in the right cerebral hemisphere, the significance of which is unknown. The right hemisphere seems to have some post-traumatic atrophy. Analysis of Abnormal Scans.-Five scans of known pathology were chosen for analysis. The first scan represents a meningioma of the falx before and after the injection of Renogralin (Fig. 5 and 6). In the first scan, there is a distortion of Zone 2 of the right lateral ventricle, but it is difficult to actually visualize the tumor. The histogram shows symmetry of the attenuation coefficient numbers below 20, but the right hemisphere has a higher proportion of attenuation coefficient numbers between 20 and 30 than does the left hemisphere. The difference in the means is 1.64, with the right side having higher x-ray attenuation. .
VOL.
No.
i,
2
Extracting
0
10
Information
from
Computerized
Tomography
Scans
i8i
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40
30
20
10 I’.’ I.. 3
‘I
50
40
30
20
10
0 -10
20
30
40
50
60
-10
0
10
20
30
40
50
60
Densities
Fic. 3. Histograms
superimposing left
shows
2 hemispheres: 19 ot 20 were symmetric. asymmetry of density of 2 hemispheres.
Remember that in 19 of the 20 normals there was no difference greater than i, thus indicating that the scan for this patient may be abnormal. The statistics do not show that the right lateral ventricle is less visible than the left, but the eye does. After the injection of Renografin, the tumor is obvious. The statistics are also quite abnormal. The mean difference in the two lobes is now 7.98 and the ratio of standard deviations is 2.05. The highest normal difference in standard deviation was 1.3. It is of interest that the difference in skewness coefficients between the two hemispheres was i.6, whereas we had some differences in normal subjects that were as high as 36. This casts doubt on the use of skew as a method of analysis for detecting this type of abnormality. The next patient (Fig. 7) had a cm. left sphenoid meningioma. This tomographic
Histogram
on upper
scan was read as negative, and it may indeed be negative. The level may not have been low enough to pick up the left sphenoid wing. In any event, the statistical analysis showed no abnormality. The x-ray attenuations of the 2 hemispheres match almost exactly. The scan in Figure 8 shows a typical glioma in the left temporal fossa. There are zones of increased and decreased x-ray attenuation and a mass effect on the ventricles. However, the statistical analysis is disappointing. The difference in the average x-ray attenuation coefficient numbers between the 2 hemispheres is 0.48 (considerably less than i); the ratio of standard deviation is nearly i and well within the range observed in normals. The histogram also suggests no abnormality. Apparently, the higher and lower x-ray attenuations of the tumor averaged out and masqueraded
Reese,
182
O’Brien,
Beeler,
Jr.,
Gerding
and
McCullough
JUNE,
2975
50
LH RH
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-
40 #{188}.
q)
20
10
0 0
-10
10
20
30
40
50
60
Densities I
SDR Subject 267
*Skees$
R
L
15.20
17.18
coefficient,
SDR -1.98
4.9153
SDL 4439
G1 10584
G
tT
-0.1079
t 04513
R
-0.56
-0.2391
T1
Gi
1 -1.17
4.79
-5.96
G /SE i
i
Fic. . The right hemisphere is less dense than the left and the difference in the means greater than i. The visual appearance of the scan was normal, but the statistics imply diffuse abnormality of the right hemisphere relative to ancient trauma.
is -1.98, that there
which is may be a
50
LH RH
-
40
#{188}.
20 q)
10
Densities
Subject Slide *Sk.e$$
067,
34
R
k
16.82
15.18
coefficient,
SDR 1.64
4.3788
SDL SLRj 4.8321
G
‘T I
Fic.
5. Scan
made
Gi i1
0.9062
0.5635
G1 -0.689
1.25
R
TG1
-0.8175
6.01
G /SE I
before
the
contrast
medium
injection
(see
text).
T61 -6.91
12.92
VoL.
No.
ii,
Extracting
2
from
Computerized
Tomography
LH RH
.
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Information
40
Scans
183
#{149}U6-2E 121C
#{188}) #{188}.
20 q)
10
Densities
I
Slide *Skees$
1067,
I Ik I I I I2672118.741 19.923114.8308 12.05411 XR
Subject 2
B
SD
SDL
fE:RJ
7.98
coefficient,
Fic.
G1
6. Scan
GIR
:
j
0.50481
GIL *
0.43921 0.07
I 1
R
1.1494
ITGIRITGI
15.141
I
L:
3.5811.56
‘T= GI/SEG made
after
the
contrast
medium
injection.
---RH I’)
#{188}.
Densities SDR Subject 394
*Skewness
Fic.
7. Left
XR 16.92
L 16.94
coefficient,
sphenoid Scan
SDR -0.02
3.9722
SDL 4.3707
0.9088
G1
wing meningioma. cut is probably
tT Scan above
the
G1
G1
L
-.2323
.4557
-0.69
R -0.5098
I Gi 1-2.44
G1/SE6
is negative and statistics tumor and is, indeed,
show normal.
no abnormality.
TGI L 4.81
-7.25
1
Reese,
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184
O’Brien,
Beeler,
Jr.,
Gerding
and
McCullough
LH RH
-
.
JUNE,
568-
1975
2A
40 #{188})
Densities 1
SDR XR
Lubiect 1
16.40
568
*Skewness
FIG.
8. Left
L. 16.88
coefficient,
temporal coefficient
-0.48
SDR
SDL
3.6087
3.6234
G1
glioma with increased numbers equal those
G1 j
G1 0.9959
0.7096-00560
L 0.77
I
R -12671
Gi
4j
R
8.44
TGI L -0.68
9.12
‘T= GI/SEG
and decreased x-ray in the right temporal
as normal brain x-ray attenuation when considered over the entire hemisphere. Finally, another glioma of the right posterotemporal lobe (Fig. 9) is presented; it contains areas of increased and decreased x-ray attenuation, but mostly decreased. The histogram shows that the right hemisphere is less attenuating to x-rays than the left hemisphere. The absolute difference in means is +1.75, which is above the limit of i. The ratio of standard deviations is 1.2, which is suggestive of an abnormality. DISCUSSION
This project was the first step in an attempt to use a computer to aid the visual diagnosis of the computerized tomographic scan. It is envisioned that as the radiologist observes the conventional cathode ray tube with its anatomic representation, he will simultaneously have, on a second tube, the
attenuation, lobe. Statistics
whose are
average normal.
attenuation
statistical data as well as histograms representing a particular slice of brain tissue. This would either aid him in the diagnosis of specific lesions or alert him to the fact that there may be a statistical difference between an area in one hemisphere and the corresponding area in the other. Early results are encouraging but equivocal. It does not appear that this method will work in lesions whose average x-ray attenuation is equal to normal tissue. It is also postulated that midline symmetric lesions such as pontine and corpus callosum tumors and third ventricular masses will not be detected, at least by the comparison of means. As a result of this study, we will take 2 steps. The first will be to make more detailed comparisons of the histograms. The comparisons, in a case such as the first meningioma, might reveal a significant dif-
VOL.
Extracting
No.
124,
Information
from
Computerized
Tomography
Scans
i
85
50
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LH RH
40 #{188}) #{188}.
30
Q.)
20
:3 Q)
10
,u/ ,
-
-10
I
0
I
10
20
30
40
I
50
60
Densities
[
Subject
I I
*Skewness
coefficient,
I
XR
17.14
Fic.
I
L
11a891-1.75
I SDR
I
ISD
RI
SDL
nizing
sensitive
statistical
abnormal
methods
glioma. Difference
Right hemisphere in means of the
computerized their
information
for
tomography in
digital
0.361 -1741621
GlRITG1LI 3881-0.21
I
1
4.09
scans
average is -
density 1.75.
David
F. Reese, M.D. Clinic and Mayo Rochester, Minnesota
Foundation 5590!
REFERENCES i.
recog-
form,
shows lower hemispheres
2
Mayo
2.
Because
R
the information is in a natural format for statistical and mathematical analyses and redisplay in various forms. \Ve have chosen histograms as a redisplay format. Further refinements and experience will be necessary before the method is clinically applicable.
scans. CONCLUSIONS
produce
1
‘T= GI/SEG
ference in the x-ray attenuation coefficient numbers in the 20’s and 30’s. A second step will be to subtract individual points of the left hemisphere from spatially symmetric individual points of the right hemisphere. The left temporal glioma missed by the study of means may become apparent by this method. To date, we have studied only one 13 mm. thick slice of brain. Integrating the slice or slices above and below will give us larger volumes of both normal and abnormal brain. The resultant additional information may lead to the development of more
G
11.25611 R I o.343jo.ol97I IR i
16.023114.7952
G1
9. Right posterior temporal than does left hemisphere.
G
L. Frontal and lateral projections of EM! scans. Read at the Montreal First International Symposium on Computerized Axial Tomography, May 31-June I, 1974. tHoMPsoN, C., and ETHIER, R. Topographic and density displays of EM! scans. Read at the Montreal First International Symposium on Computerized Axial Tomography, May 31-
ACKERMAN,
J tIflC
I,
1974.
