U.S. patent application number 09/798756 was filed with the patent office on 2001-10-25 for computer-aided diagnosis system and method.
Invention is credited to Wang, Shih-Ping.
Application Number | 20010033681 09/798756 |
Document ID | / |
Family ID | 25174186 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033681 |
Kind Code |
A1 |
Wang, Shih-Ping |
October 25, 2001 |
Computer-aided diagnosis system and method
Abstract
An x-ray system acquires an initial low-contrast, wide latitude
(G=2.5, or G=2 or less) x-ray image of a breast. A processing
system automatically finds suspected abnormalities in the breast by
processing the low contrast initial image, and then automatically
converts the initial x-ray image to a high-contrast, narrow
latitude image at the locations of the found abnormalities to
thereby facilitate diagnosis and patient care. The technology
includes effective ways to produce, process and display the various
images, and can be extended to other types of images.
Inventors: |
Wang, Shih-Ping; (Los Altos,
CA) |
Correspondence
Address: |
Ivan S. Kavrukov
Cooper & Dunham LLP
1185 Avenue of the Americas
New York
NY
10036
US
|
Family ID: |
25174186 |
Appl. No.: |
09/798756 |
Filed: |
March 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09798756 |
Mar 2, 2001 |
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08980254 |
Nov 28, 1997 |
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09798756 |
Mar 2, 2001 |
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08579802 |
Dec 28, 1995 |
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5828774 |
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09798756 |
Mar 2, 2001 |
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08438432 |
May 10, 1995 |
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5729620 |
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09798756 |
Mar 2, 2001 |
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08129255 |
Sep 29, 1993 |
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Current U.S.
Class: |
382/132 |
Current CPC
Class: |
G06T 5/50 20130101; G06T
2207/10116 20130101; G06T 7/0012 20130101; G16H 30/40 20180101;
G06T 5/009 20130101; H05G 1/60 20130101; G16H 40/63 20180101; G06T
2207/30068 20130101; G16H 15/00 20180101; G16H 50/20 20180101; G06T
5/40 20130101 |
Class at
Publication: |
382/132 |
International
Class: |
G06K 009/00 |
Claims
1. A method comprising the steps of: acquiring a low-contrast,
wide-latitude x-ray film image characterized by a contrast gradient
G of 2 or less using a medical imaging modality; converting the
film image to a low-contrast, wide-latitude digital image;
processing the low-contrast, wide-latitude digital image by
computer to automatically identify suspected abnormalities therein;
using information regarding suspected abnormalities identified in
the processing step to automatically find a relatively narrow
exposure range that includes an exposure range related to at least
one of the abnormalities; converting the low-contrast,
wide-latitude digital image to a high-contrast, narrow-latitude
version display image conforming to said relatively narrow exposure
range; and displaying the display image on a display device.
2. A method as in claim 1 in which said displaying comprises
printing said high-contrast, narrow-latitude image on photographic
film.
3. A method as in claim 1 in which said displaying comprises
displaying said high-contrast, narrow-latitude image on an
electronic monitor.
4. A system comprising: a medical imaging unit acquiring a film
image having a relatively low contrast and relatively wide exposure
range characterized by a contrast gradient G of 2 or less and
converting the film image to a low-contrast, wide latitude digital
image; a programmed computer processing the low-contrast,
wide-latitude digital image to automatically identify suspected
abnormalities therein and to automatically find at least one
relatively narrow exposure range that includes an exposure range
related to at least one of the abnormalities and converting the
low-contrast, wide-latitude digital image to a display image that
is high-contrast in at least one narrow latitude related to said at
least one narrow exposure range; and a display device for
displaying said display image.
5. A system as in claim 4 in which said display device comprises a
film printer printing said display image on photographic film.
6. A system as in claim 4 in which said display device comprises an
electronic monitor.
7. A system as in claim 4 in which said medical imaging unit
acquires a film image having an exposure range characterized by a
contrast gradient of less than 2.
8. A system as in claim 4 in which the display image is
characterized by a contrast gradient G of at least 3 in said narrow
latitude.
9. A system as in claim 4 in which the display device displays a
latitude exposure range of less than about 25.
10. A system as in claim 4 in which: the medical imaging unit is a
mammography unit; the computer identifies suspected speculated
lesion and microcalcification cluster type abnormalities and
produces information for an annotated map comprising symbols
identifying the type and location of the abnormalities; and the
display image includes the annotated map.
11. A method comprising the steps of: producing a low-contrast,
wide-latitude digital x-ray image characterized by a contrast
gradient G or 2 or less using a medical imaging modality;
processing the digital image by computer to identify suspected
abnormalities therein; finding, through computer processing that
does not require window and/or level selection by an operator, a
relatively narrow exposure range which includes at least one
exposure range related to at least one of the abnormalities;
computer-generating a high-contrast, narrow-latitude version of
said image conforming to said at least one relatively narrow
exposure range, using information regarding said relatively narrow
exposure range provided without operator intervention; and
displaying said high-contrast, narrow-latitude version of said
image on a display device.
12. A method as in claim 11 in which said displaying comprises
printing said high-contrast, narrow-latitude version of said image
on photographic film.
13. A method as in claim 11 in which said displaying comprises
displaying said high-contrast, narrow-latitude version of said
image on an electronic monitor.
14. A method as in claim 11 in which said acquiring comprises
acquiring a digital image that has a latitude exposure range of
more than about 25.
15. A method as in claim 11 in which said acquiring comprises
acquiring a digital image that has a latitude exposure range of
more than about 100.
16. A method as in claim 11 in which said displaying comprises
displaying an image that has a latitude exposure range of less than
about 25.
17. A system comprising: a medical imaging unit acquiring a
low-contrast, wide-latitude digital x-ray image characterized by a
density gradient G no greater than 2.5; a programmed computer
processing the digital image to automatically identify suspected
abnormalities therein and to find at least one relatively narrow
exposure range which includes an exposure range of at least one of
the abnormalities; said programmed computer further using
information regarding at least one of said abnormalities to
automatically, without requiring window and/or level selection by
an operator, convert the digital image to a high-contrast, narrow
latitude display image that includes said at least one relatively
narrow exposure range; and a display device for displaying said
display image.
18. A system as in claim 17 in which said display device comprises
a film printer printing said display image on photographic
film.
19. A system as in claim 17 in which said display device comprises
an electronic monitor displaying said display image.
20. A system as in claim 17 in which: the medical imaging unit is a
mammography unit; the computer identifies suspected speculated
lesion and microcalcification cluster type abnormalities and
produces information for an annotated map comprising symbols
identifying the type and location of the abnormalities; said
display image comprises a mammogram; and the display device
displays the annotated map in addition to displaying said
mammogram.
21. A method comprising: imaging a breast with x-rays to produce an
initial image characterized by a contrast gradient G no greater
than 2.5; processing the initial image with a programmed computer
to identify suspected abnormalities; using information resulting
from the processing step to identify a latitude narrower than that
of the initial image; converting the initial image to a display
image characterized by a density gradient G or at least 3 within
said narrower latitude; and displaying the display image.
22. A method as in claim 21 in which the processing step includes
generating an annotated map of said abnormalities, and the
displaying step comprises displaying said map as a part of or
adjacent said display image.
23. A method as in claim 17 in which said imaging comprises imaging
at KVp in the range of 40-55.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of parent
application Ser. No. 08/890,254 filed on Nov. 28, 1997 (to be
abandoned as of the filing date accorded to this application). Ser.
No. 08/890,254 is in turn is a continuation-in-part of copending
parent applications Ser. Nos. 08/579,802 filed on Dec. 28, 1995
(now U.S. Pat. Nos. 5,828,774) and 08/438,432 filed on May 10, 1995
(now U.S. Pat. No. 5,729,620). In turn, Ser. No. 08/579,802 is a
continuation, and Ser. No. 08/438,432 is a continuation-in-part, of
parent application Ser. No. 08/129,255 filed on Sep. 29, 1993
(abandoned). This application hereby incorporates by reference the
entire disclosure, drawings and claims of each of said parent
applications as though fully set forth herein.
FIELD, BACKGROUND, AND SUMMARY OF THE DISCLOSURE
[0002] This patent specification relates to displaying radiological
images and other information in a manner believed to assist users
such as physicians in reading such images and other information.
More specifically, it relates to a computer-aided diagnosis "CAD")
system and method for detection and identification of abnormalities
in radiological images, and to using the results to produce images
that provide more useful diagnostic information and better patient
care. The images can be viewed in conventional format but in
conjunction with viewing an annotated road map of the location
and/or the identification of suspected abnormalities found through
computer processing of radiological images. The annotated map
highlights and/or identifies suspected abnormalities to help the
image reader better assess the presence and/or meaning and
significance of abnormalities in the radiological image.
[0003] The utility of the system and method is further improved by
initially acquiring an x-ray image that is low-contrast but
wide-latitude (G=2.5, or G=2 or less). In the case of breast
imaging, a low-contrast, wide latitude x-ray image makes it
possible to include in the image significant information about both
very dense and much less dense tissue whereas normal x-ray film
(typically G=3) may not record sufficient information about dense
breast tissue. On the other hand, a low-contrast image may not be
as suitable for viewing, and laws and regulations may prohibit the
use of film of G less than 3 for breast diagnosis. In a preferred
embodiment, the low-contrast image is automatically processed in
the electronic domain to find suspected abnormalities, taking
advantage of the fact that the wide latitude may allows the film to
contain more information than conventional images. Resulting
information regarding such abnormalities is in turn used as a guide
in automatically converting the initial, low contrast image to a
display image that is high-contrast at areas of the suspected
abnormalities, to thereby facilitate diagnosis and patient
care.
[0004] The detection of abnormal anatomic regions in radiological
images using a computer system comprising specialized software and
possibly specialized hardware has been reported. For example, in
the area of mammography, representative reports are: Giger et al in
the May 1993 issue of RadioGraphics, pages 647-656; Giger et al in
Proceedings of SPIE, Volume 1445 (1991), pages 101-103; Doi et al
in U.S. Pat. No. 4,907,156; and Giger et al in U.S. Pat. No.
5,133,020. See, also, the disclosure of and in prior art cited in
said parent applications. In particular, in the area of detecting
spiculated or stellate lesions in mammograms using convergent line
detectors as the principal abnormal feature detection algorithm,
representative reports are: N. Karssemeijer in the book entitled
"Digital Mammography", edited by A. G. Gale et al, published by
Elsevier in 1994, pages 211-219; and Kegelmeyer et al in Volume 191
(1994) of Radiology, pages 331-337. In the area of detecting
clusters of microcalcifications in mammograms using thresholding
and a clustering kernel as the principal abnormal feature detection
algorithm, representative report are: Nishikawa et al in Volume 20
(1993) of Medical Physics, pages 1661-1666; and Feig et al in
Volume 33 (1995) of Radiological Clinics of North America, pages
1205-30. See, also, co-pending patent applications Ser. No.
08/676,660 filed on Jul. 10, 1966 entitled "Method and apparatus
for fast detection of spiculated lesions in digital mammograms,"
and Ser. No. 08/901,541 filed on Jul. 28, 1997 entitled "Method and
system for using local attenuation in the detection of
abnormalities in digitized medical images." These two patent
applications and each of the other references cited in this patent
specification are incorporated herein by reference as though fully
set forth herein. These systems are generally referred to as
Computer-Aided Diagnosis ("CAD") systems, and are believed to be
particularly useful to radiologists in the diagnostic process and
particularly in screening radiological procedures. R2 Technology,
Inc. of Los Altos, Calif. offers technology under the trade name
ImageChecker and a system under the trade name ImageChecker M 1000
to assist physicians in their review of screening mammograms by
identifying image areas that might require further review.
Information on this technology is available at www.r2tech.com.
[0005] In a screening radiological procedure, such as screening
mammography, the patients typically are asymptomatic and true
abnormalities (e.g. cancers) are said to occur at a typical rate of
about one case per one hundred patient examinations. Reading of the
mammograms, when most of them are negative, can be a tedious task
that can make it difficult to maintain a constantly high attention
level. Some detectable abnormalities can be missed or misdiagnosed,
which can result in delayed or more costly treatment, and can even
result in a reduction of patient's longevity or chance of survival.
According to an article in the May 26, 1993 issue of JAMA, pages
2616-2617, the misdiagnosis rate in mammograms can be in the range
of 15 to 63%. The CAD system, serving as an electronic reminder or
second reader, as a spell-checker can be in a word processor, can
assist radiologists in attaining higher detection rate (higher
sensitivity) for abnormalities or reducing the misdiagnosis rate
(lowering the false-negative rate).
[0006] Applicant understands that a current procedure using a CAD
mammographic system proceeds as follows. The physician views a
radiological image, reaches a preliminary diagnostic decision, and
then views a separate second image displayed on a CAD system. This
second image is marked or annotated with a localized identification
of the abnormalities that the CAD system has detected through
computer analysis of a digitized version of the conventionally
obtained radiological image. After a reexamination the area of the
radiological image that corresponds to the position of the detected
abnormalities displayed on the CAD system, the physician makes the
final diagnostic decision. This final diagnostic decision may or
may not be the same as the preliminary decision, depending on
whether the physician found the additional diagnostic information
provided by the CAD system to be significant and, if so, what
significance the physician ascribed to it. Following the final
diagnostic decision, and perhaps depending on the degree of
suspicion for malignancy, the physician can recommend a course of
further action, which can include no further action or further
follow-up examinations or biopsy.
[0007] In the process of detecting abnormal anatomic features in
radiological images using a CAD system as described in the above
cited references, the radiological film image of a patient is
processed through a film digitizer to generate a digitized image
which is input as such into the system. The digitized image is then
analyzed by a digital image processing computer with specialized
software and perhaps also specialized hardware for abnormal
anatomic feature detection. If abnormalities are detected, an
annotated radiological image is displayed on a special TV monitor,
with markers placed around or adjacent the detected abnormalities.
This TV monitor typically has a large dimension (typically a screen
diagonal of 12 inches or larger) and a high spatial resolution
(typically more than 1000.times.1000 pixels). Because of the large
dimension and high spatial resolution, this TV monitor typically is
positioned at some distance away from the film. Typically the
center of the monitor is more than 12 inches from the center of the
film on the conventional film illumination box. In addition, this
special TV monitor typically has a low brightness and a high
cost.
[0008] It is believed that the display method using a
high-resolution TV monitor has certain shortcomings that make the
process inconvenient and inefficient. The high-resolution TV
monitor is expensive, its spatial resolution although high for
monitors is still less than that of the original x-ray film, and
its brightness and dynamic range are also inferior to those of an
x-ray film viewed on a light box. Therefore, it is believed that a
physician might not wish to rely solely on the image displayed on
the TV monitor to make diagnosis, but typically would repeatedly go
back to the conventional film illumination box to view the original
film image. This can lead to the loss of valuable time and can be
uncomfortable at least because of the different brightness levels
and spatial resolution levels of the two images. In addition, it is
believed that diagnostic errors can arise from the need for the
physician to shuttle back and forth between two different displayed
images. Even when a potentially true abnormality (cancer) is
detected and pointed out by the CAD system to the physician, the
fatigue and eye discomfort and other effects due to viewing two
images of such different characteristics may still cause the
physician to miss the significance of the corresponding area on the
original x-ray film and to fail to notice or appreciate the
abnormal features of the detected abnormality and decide to ignore
the detected abnormality.
[0009] Accordingly, one object of this patent specification is to
provide an improved combined display of an x-ray radiological image
and CAD-detected abnormalities from the x-ray image. A more
specific object is to provide the CAD user with further processed,
annotated and enhanced image representations of regions around the
CAD detected abnormalities in order to emphasize abnormal image
features of these detected abnormalities. Another more specific
object is to produce an initial image that is low-contrast but wide
latitude and use it to automatically find suspected abnormalities,
and use information about the suspected abnormalities to
automatically convert the initial image to a display image that is
high-contrast at the density range of the found abnormalities. The
ultimate goal is to help the user (physician) better assess the
type and degree of abnormality of these detected abnormalities in
the radiological image.
[0010] Another objective is to present the further processed image
of the area around the CAD detected abnormalities on a display such
as a small TV monitor located close to the x-ray film during
viewing of the x-ray film. The term TV monitor is used generically,
to refer to any type of electronic display, for example a flat
panel display. The two images should be so close and should
otherwise match each other such that eye and other discomfort due
to viewing two different images alternately would be reduced. Still
another object is to print the annotated road map and/or the
further processed image representations of areas around the CAD
detected abnormalities on the same sheet of photographic film that
contains a printout of the radiological image.
[0011] This patent specification describes in detail, toward the
end, the preferred embodiment that derives a low-contrast, wide
latitude image, automatically extracts information about suspected
abnormalities therefrom, and uses that information to automatically
produce a display image that is high-contrast at the areas of the
suspected abnormalities. Earlier parts of the patent specification
describe embodiments involving primarily various ways to obtain an
x-ray image, extract information regarding suspected abnormalities,
and display that information in ways that facilitate diagnosis and
treatment.
[0012] In an exemplary and non-limiting first embodiment, the
further processed image of areas around the CAD detected
abnormalities from a radiological film is presented on a small TV
monitor, located in close proximity to the radiological film being
viewed at the light box. The display of this further processed
image shares (e.g., is toggled on) the small TV monitor with the
display of a miniaturized annotated road map. On demand by the CAD
user, e.g. the physician using a toggle switch, the miniaturized
annotated road map image and the further processed image
representations such as tiles of areas around the CAD detected
abnormalities are displayed alternatively on the small TV.
[0013] In an exemplary and non-limiting second embodiment, the
miniaturized annotated road map image is presented on a small TV
monitor and further processed image tiles of areas around the CAD
detected abnormalities are presented on a second and separate small
TV monitor. Both small monitors preferably are located in close
proximity to the radiological film being viewed at the light
box.
[0014] In an exemplary and non-limiting third embodiment, the
radiological image is acquired through digital means, and thus is
in digital form initially. The radiological image can be displayed
as an electronic image on a high-resolution monitor. The annotated
map and, if desired the tiles as well, can be displayed on the same
monitor, at an area that does not overlap with the areas of
interest of the displayed radiological image. In some cases, the
digitally acquired radiological image is printed on a sheet of
photographic film for later viewing on a light box. In that case,
the annotation road map and, if desired the tiles as well, can be
printed on the same sheet of photographic film, at an area that
does not obscure relevant parts of the radiological image.
[0015] In an exemplary and non-limiting fourth embodiment, a CAD
system is used to enhance the informational content of image
displays, by taking an initial radiographic image that has a low
contrast but wide latitude. This allows imaging well on the same
film or other imaging system of tissues that differ greatly in
density. The initial image is processed to identify area of
possible interest, such as areas of suspected abnormalities. Based
on characteristics of these areas, the initial image is converted
to a display image that has high contrast at the density range(s)
of the already identified areas of possible interest and thus can
provide enhanced diagnostic information and assist in any further
treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a block diagram illustrating a CAD system and its
output display according to a first embodiment.
[0017] FIG. 2 is a block diagram illustrating a CAD system and its
output display according to a second embodiment.
[0018] FIG. 3 is a block diagram illustrating a CAD system and a
first method of output display according to the third
embodiment.
[0019] FIG. 4 is a block diagram illustrating a CAD system and a
second method of output display according to the third
embodiment
[0020] FIG. 5 is a block diagram illustrating a CAD system and an
output display according to a fourth embodiment.
[0021] FIG. 6 illustrates displaying an output according to the
fourth embodiment.
[0022] FIG. 7 compares film characteristics of wide latitude films
used in the fourth embodiment with characteristics of the prior art
film.
DETAILED DESCRIPTION
[0023] Referring to FIG. 1, a preferred but non-limiting example of
a first embodiment generates an annotated road map of CAD-detected
abnormalities and a further processed image of the area around the
CAD detected abnormalities from a radiological film. The annotated
road map and/or the further processed image are displayed on one or
more small TV monitors located in close proximity to the
radiological film being viewed at a light box. In this example, the
radiological film is in the form of a mammographic x-ray film
acquired with a conventional mammographic film-screen imaging
system. The original analog two-dimensional mammographic x-ray film
10, with a patient information label 12 printed at an edge of the
film, is sent through a film digitizer 30 of a CAD (computer-aided
diagnosis) system 20. This system 20 can be the system disclosed in
the U.S. patent applications incorporated by reference herein, and
generates a digitized two-dimensional mammographic image 40.
Preferably, the film digitizer 30 should be a laser film digitizer
or a high performance CCD based film digitizer and should have a
dynamic range and a spatial resolution comparable to those of the
original mammographic film. Such film typically has a dynamic range
of 10,000:1 and spatial resolution of approximately 50 microns per
pixel (or about 4,000.times.5,000 pixels for 8-inch.times.10-inch
film. The identity of the original mammographic image 10 is entered
into the CAD system at this point to identify the digitized
mammographic image 40 and thus the original film 10. An useful
option at this point is to automatically input the identity of the
original mammographic image 10 into the CAD machine. This can be
accomplished in many ways--for example, by labeling the
mammographic film 10 with a code such as a bar code close to the a
patient information label 12 printed on the edge of the film, or by
incorporating the bar code into the patient information label 12.
The label can then be read into the CAD system 20 with an optional
ID bar code reader 15 as the mammographic film 10 is being fed into
the film digitizer 30.
[0024] The digitized mammographic image 40 is then sent through an
abnormal feature detection stage 50 of the CAD system, or CAD
machine, 20. The findings or results, positive or negative in
nature, from the abnormal feature detection stage 50 typically are
in the form of a two-dimensional annotation map 55. The map
identifies the locations and types of the CAD-detected
abnormalities 56 and 57 (in this illustrative example) present in
the original film image 10. For the purposes of an illustration,
let the abnormality 56 be a spiculated lesion and lei, its location
on the annotated map be marked with a star-shaped marker. Let the
abnormality 57 be a cluster of microcalcifications and let its
location on the annotated map be marked with a triangular shaped
marker. Thus, the markers identify not only the detected location
but also the detected nature of the suspected abnormality
identified at this stage. The annotation map 55 can be scaled down
to a sub-sampled image, say 512.times.512 pixel in size and 8-bit
in gray scale, as the digitized image 40. The two superimposed
images, 55 and 40, in registration with each other, form a
miniaturized annotated road map image 58. Enhanced image areas or
tiles 66 and 67 are centered around the CAD-detected abnormalities
56 and 57, respectively, and can be, for example, 512.times.512
pixel in size and 8-bit in gray scale. They are generated by
further image processing the regions in the digitized image 40
which correspond to the CAD detected abnormalities 56 and 57. The
CAD-generated annotation map 55, the miniaturized annotated road
map image 58, the enhanced image tiles 66 and 67, together with the
digitized image 40 and its corresponding identification, can be
stored for later use in an optional memory storage unit 70.
[0025] The annotation road map 58 and the enhanced image tiles 66
and 67 are transferred to an output display section of the system
for display. The output display section of the CAD system can be a
part of the total CAD system, in which case the data transfer can
be through a dedicated shielded cable. Or, the output display
section can be a separate system, in which case additional data
storage memory can be added to the unit to store the transferred
interim data, and the data transfer can be through a dedicated
shielded cable or an existing network where the equipment is
installed.
[0026] It is important to point out and emphasize the abnormal
features of the CAD detected abnormalities to the physician. The
reason is that the physician, even after seeing the location of the
CAD detected abnormalities on the miniature road map 58, may still
fail to notice or appreciate corresponding abnormal features on the
original the x-ray film. By pointing these abnormal features out,
with further emphasis, to the physician, it is believed that the
physician would be in better position to assess the level and
nature of abnormality of these CAD detected abnormalities. The
principal abnormal feature detection algorithms used in the
abnormal feature detection stage 50 to detect the abnormalities can
be used to further emphasize the abnormal features of the CAD
detected abnormalities. For example, in the case of the abnormality
56, the principal abnormal feature used to detect the spiculated
lesion can be a set of convergent lines. Since the presence of the
convergent lines around a lesion raises the probability of
malignancy, it is believed that there would be less a chance that
the physician could ignore the lesion if the convergent lines were
made more noticeable. Therefore, this set of convergent lines
around the spiculated lesion could be contrast and edge enhanced to
form the image tile 66. For example,
[0027] FIG. 3(B) of Karssemeijer article cited shows a set of
detected pixels pointing to the center of a suspected spiculated
lesion. Superimposing these detected pixels on the image can form
the image tile 66. In the case of the abnormality 57, the principal
abnormal feature used to detect the cluster of microcalcifications
can be the small clustering of three or more high contrast spots.
This small clustering of high contrast spots can be enhanced in
brightness to form the image tile 67. The formation of this small
clustering of bright spots can be of great interest to the
physician. This is because the probability of malignancy is higher
for a linear or branching formation. Therefore, this small
clustering of high contrast spots can also be magnified in size,
for example by a factor of 2 or more, to form the image tile 67 in
order to help the physician see the formation of these bright spots
clearly in the image tile 67. In this manner, it is believed that
the CAD user, the physician, after seeing the enhanced abnormal
image features of these detected abnormalities and reexamining the
original x-ray image, can better assess the level of abnormality of
these detected abnormalities in the x-ray image.
[0028] Also shown in FIG. 1 is an illustration of a CAD output
display consisting of a conventional film illuminator, commonly
called a light box, 100 and a small TV monitor 200 according to the
first embodiment. In this exemplary embodiment, the miniaturized
annotated road map 58 and the enhanced image tiles 66 and 67 are
alternatively or sequentially displayed as images 300x, by
operating a toggle switch 90 to display one image at a time (where
x=a, b and c) on the small TV monitor 200 located in close
proximity to the original film 10. Respectively, the image 300a
represents the miniaturized annotated road map 58, the image 300b
represents the enhanced image tile 66 around the CAD detected
spiculated lesion, and the image 300c represents the enhanced image
tile 67 around the CAD detected cluster of microcalcifications. If
more abnormalities were detected, there would be images 300d, 300c,
etc. to be toggled through the small TV monitor.
[0029] The dimensions of the display screen of the small TV monitor
200 in this example preferably, but not necessarily, are of the
order of 1/4 to 1/2 of the dimensions of original film 10. In
addition, the small TV monitor 200 should preferably be located as
close as practical to the light box 100 displaying the original
film 10. Preferably the center of the small TV monitor 200 should
be less than 12 inches from the center of the original film 10 on
the conventional film illumination light box 100. The preferred
position, as shown in FIG. 1, for mounting the small TV monitor 200
is just beneath the light box 100 that displays the original image
10. It is also convenient to display a pair of images on each TV
monitor, since frequently a pair of the original mammographic films
10, such as the mammograms of the left and right breasts, are
displayed and viewed next to each other. In this manner, the
physician still has to minimally move his or her eyes back and
forth between the original radiological film image 10 on the film
illuminator 100 and the images 300x displayed on the small TV
monitor 200. The spatial resolution of the small TV monitor 200 can
be in the range of 500 TV lines, or comparable to that of NTSC or
PAL. The brightness level of the small TV monitor 200 should be
similar to that of the average brightness transmitted through the
original film 10, so that the observer would not be bothered by a
change in brightness. In using the CAD system as a second reader in
a screening situation, it is sometimes preferred that the display
on the small TV monitor 200 can be easily toggled with on-off with
a switch 90 by the observer. As a variation, more than one monitor
200 can be used; for example, one can display the annotated map 58
and at least one other monitor can display one or more of the
tiles. The tiles can be displayed on a single monitor, by toggling
from one to another, or each of two or more tiles can be displayed
at a respective monitor. The one or more monitors can be placed at
positions relative to the light box other than those illustrated in
FIG. 1
[0030] FIG. 2 is similar to FIG. 1 in many respects, and similarly
labeled components serve a similar function and therefore will not
be described again in detail. FIG. 2 shows a CAD output display
comprising a conventional film illuminator 100 and, in this case,
two small TV monitors 200 and 250, according to a second
embodiment. In this exemplary embodiment, the annotated information
58 is presented as a miniaturized annotated road map image 300a on
the first small TV monitor 200, located in close proximity to the
original film 10. The enhanced image tiles 66 and 67 are
alternatively or sequentially presented, by operating a toggle
switch 90, as images 300b and 300c on the second small TV monitor
250, located next to the first small TV monitor 200 and in close
proximity to the original film 10. It is sometimes preferred that
two or more small TV monitors are used, in place of monitor 250, to
display the further processed image tiles 66 and 67 such that each
detected abnormality is displayed on a separate small TV monitor at
the same time. The small TV monitors 200 and 250 can be placed at
other positions relative to the light box 100, e.g. to the side or
above light box 100. More than one monitor can be used to display
the tiles.
[0031] Referring to FIG. 3, a preferred but non-limiting example
according to a third embodiment receives radiological images which
already are in the digital format, detects abnormalities on these
radiological images with a CAD system, and prints out the
radiological images together with CAD results on photographic film.
Again, components labeled the same as in FIGS. 1 and 2 serve
similar functions and therefore will not be described again in
detail. Digital imaging systems that provide images in digital form
include but are not limited to magnetic resonance imaging ("MRI")
systems, computed tomography ("CT") systems, ultrasound imaging
systems, scintillation cameras, computed radiography ("CR") systems
(such as Fuji's CR system based on stimulated emission phosphor
detector), and recently reported and introduced digital radiography
and digital mammography systems (for example, see Feig article
cited earlier; using CCDs or amorphous silicon array detectors),
and recently popular digital mammography and other x-ray systems
using flat panel x-ray detectors. In this example, the radiological
image is in the form of a digital mammogram, which is acquired with
a digital mammography system. This digital mammogram 14, already
having properly encoded identification and patient information 12,
is reformatted into the digitized mammographic image 40 and is sent
through the abnormal feature detection stage 50 of the CAD machine
20. If the information is already properly formatted for the CAD
machine 20, it is sent directly to and through the abnormal feature
detection stage 50 of the CAD machine 20 without reformatting. The
initial film digitization step used in the first and second
embodiments for analog mammograms is not needed in this case. As in
the first and second embodiments, the findings or results, positive
or negative in nature, from the abnormal feature detection stage 50
are in the form of a two-dimensional annotation map 55 showing the
locations and types of the CAD-detected abnormalities 56 and 57.
For the purposes of an illustration, let the abnormality 56 be a
spiculated lesion and let its location on the annotated map be
marked by a star shaped marker. Let the abnormality 57 be a cluster
of microcalcifications and let its location on the annotated map be
marked by a triangular shaped marker. The annotation map 55 can be
scaled down to the same size of a sub-sampled image, say
512.times.512 pixel in size and 8-bit in gray scale, of the
digitized image 40, and the two superimposed images in registration
with each other form a miniaturized annotated road map image 58.
Enhanced image tiles 66 and 67, centered respectively around the
CAD-detected abnormalities 56 and 57, say 512.times.512 pixel in
size and 8-bit in gray scale, are generated by further image
processing the regions in the digitized image 40 which correspond
to the CAD detected abnormalities 56 and 57. The CAD-generated
annotation map 55, the miniaturized annotated road map image 58,
the enhanced image tiles 66 and 67, and together with the digitized
image 40 and its corresponding identification, can be stored for
later use in an optional memory storage unit 70.
[0032] The annotation road map 58 and the enhanced image tiles 66
and 67 are transferred to the output display section of the system
for display. There are several methods to display the CAD results
and the digitally acquired mammogram. Since the digital system
produces no film to start with at the acquisition, the first method
is a totally filmless display by using a high resolution TV monitor
400. The resolution should be at least 1000.times.1000 pixels. In
this method the annotation road map 58, the enhanced image tiles 66
and 67, and the digital mammogram 40 are all displayed on the same
TV monitor as a combined digital image 450 as shown in FIG. 3. The
annotation road map 58 and the enhanced image tiles 66 and 67 are
shown placed at the edge or margin of the combined digital image
450. Patient information 12 can also be displayed at the same edge
or margin of the combined digital image 450. The annotation road
map 58 may alternatively be displayed by overlaying it on top of
the digital mammogram 40. This overlay may be toggled (switch not
shown) on and off so that the digital mammogram 40 can be examined
without obstruction. The enhanced image tiles 66 and 67 can also be
toggled (switch not shown) on and off. Alternatively, the map and
tiles can be displayed on one or more monitors as in the previously
disclosed embodiments.
[0033] The second method of display, shown in FIG. 4, where the
same reference numerals have the same significance as in the
earlier Figures, makes a photographic film printout of the digital
mammogram 40, the miniaturized annotation road map 58 and the
enhanced image tiles 66 and 67 all on a same sheet of film 500. The
printout film 500 is viewed on a light box 550. Since, at the
present time, physicians usually are more accustomed to a
photographic film, which typically conveys information with higher
spatial and contrast resolution and gray scale range than a high
resolution TV monitor, the second method of display can be
preferred over the first method. The annotation road map 58 and the
enhanced image tiles 66 and 67 are shown in FIG. 4 placed at the
same edge or margin of the printout film as the patient information
label 12. The photographic film printout, typically having a
resolution of 4000.times.5000 pixels, can be made with a high
resolution laser film printer 580. Such high resolution,
4000.times.5000 pixels, laser film printers are commercially
available with a resolution of 40 microns per pixel for 8
inch.times.10 inch size films and 100 microns per pixel for 14
inch.times.17 inch size films. It is sometimes preferred that only
the miniaturized annotation road map 58 be printed at the edge of
the printout film 500. Alternatively, monitors can be used to
display the annotated map and the tiles as in the preceding
embodiments.
[0034] Digital radiological images, such as, without limitation, in
the case of images from magnetic resonance imaging ("MRI"),
computed tomography ("CT"), digital fluorography ("DF"), and
computed radiography ("CR"), are sometimes printed out on sheets of
4000.times.5000 pixels photographic film for later viewing on a
light box. Since MRI images are typically formatted into
256.times.256 pixels, CT images into 512.times.512 pixels, DF
images into 1024.times.1024 pixels, and CR images into
2048.times.2048 pixels, many images from MRI or CT or CR modalities
can be printed as small tiles in an array on one sheet of
4000.times.5000 pixels photographic film. Therefore, the CAD
findings from these images can be printed as one or several of the
tiles. A further refinement on the use of CAD is to reduce the
number of images to be presented to the physician, for example by
not presenting radiological images on which no suspected
abnormalities are found by the CAD system, or by not presenting
such radiological images for a second opinion or review by another
professional.
[0035] Although the embodiments discussed above have been described
in terms of preferred structures involving a single sheet of film,
it should be apparent to those skilled in the art that this patent
disclosure applies to viewing of multiple films on a multiple-film
viewing station or an alternator (a multiple film viewer having
pre-loaded films and a transport belt), to allow several x-ray
films 10 or printout films 500 to be viewed at the same time or
different times, with or without their respective annotation maps
58 and the enhanced image tiles 66 and 67.
[0036] FIG. 5 illustrates a system in accordance with a fourth
embodiment. In this example, an initial radiographic image is a
low-contrast but high-latitude film image. Again, the same
reference numerals have the same meanings as in the earlier
Figures. The FIG. 5 system comprises an analog film-screen
acquisition system and a CAD system similar to the first and second
embodiments. However, in the fourth embodiment, the radiological
image is acquired on a low-contrast but wide-latitude mammographic
film 600. This embodiment and the third embodiment differ in the
source of the digitized image 40. The acquisition system, in this
example, uses a relatively inexpensive conventional mammographic
intensifying screen cassette 620. The cost ratio between this
screen cassette 620 and a typical current digital mammographic
system can be several orders of magnitude, e.g., approximately 1000
times. The standard screen-film acquisition and exposure technique
and the conventional mammographic x-ray system (not shown here)
will be unchanged for use in this embodiment. The high voltage of
the x-ray generator typically is in the range of 25 to 35 KVp
(kilovolt peak) or, as discussed below, can be raised to a level in
the 40 to 55 KVp range. By reducing the average contrast gradient G
of the mammographic film 600 say from about 3.0 to about 2.0, or to
1.5 or even less, we pick up substantial gain in exposure
latitude.
[0037] This concept of "wide latitude" is illustrated in FIG. 7,
where the optical density of the film is plotted against the base
10 logarithm of the x-ray exposure (logE). The latitude is defined
as the usable range of x-ray exposure, which is often expressed as
the width in LogE. The conventional "prior art" mammography film is
represented by the curve 702 in FIG. 7. The prior art film is shown
to have a latitude of about 25 (a width of 1.4 in logE), a maximum
optical density of approximately 4.2, and an average G of
approximately 3.0 (maximum usable optical density divided by the
width in LogE). Two examples in the range of the "wide latitude"
films used in this preferred embodiment are represented by the
curves 704 and 706. The 704 film has a latitude of about 125 (a
width of 2.1 in logE), a maximum optical density (similar to the
prior art film) of approximately 4.2, and an average G of
approximately 2.0 (in this example, 4.2/2.1=2.1). The 706 film has
a latitude of about 625 (a width of 2.8 in logE), a maximum optical
density of 4.2, and an average G of approximately 1.5
(4.2/2.8=1.5). These are only examples, and it should be understood
that this embodiment can use films of different G ratings that are
substantially below 3. Preferably, the G rating of the film is 2.5
or below. More preferably, it is 2 or below. G ratings that are 1.5
and below also can be used in this embodiments.
[0038] Applicant believes that physicians may not use mammography
films that have an average G rating below 3 for diagnostic viewing
in mammography screening in this country. This is so because
applicant understands the Congress of the United States passed a
law entitled "Mammography Quality Standards Act ("MQSA") in 1992 to
establish national quality standards for mammography. Mammography
films with average G of less than 3 would not be able to pass the
quality tests, which require the visualization of certain low
contrast objects on a standard test phantom. Thus, the low-contrast
but high latitude films of this embodiment are not intended for use
directly for diagnostic viewing by the physician without the
additional image processing described below.
[0039] The low-contrast, wide-latitude films can be produced in
several ways. One way is to start with a film manufactured such
that it is inherently a low-contrast, wide-latitude x-ray film and
use a conventional x-ray mammograph with conventional settings to
take an x-ray image. Another way is to use the same prior art film
with a G rating of about 3, but to process the exposed film at a
much lower temperature than conventional so that the contrast is
purposely lowered to correspond to the lower G ratings discussed
above. However, this approach may not be desired in at least some
circumstances because the film would not be processed in the manner
for which it was designed and conventional processing procedures
would have to be changed. Still another way is to again use the
same prior art film having a G rating of about 3, but to raise the
x-ray generator high voltage substantially, say to the range of 40
to 55 KVp. The contrast of the breast is thus substantially
reduced, achieving an x-ray image similar to that produced with a
film having the lower G ratings discussed above. This approach has
the added benefit of improved penetration of dense breast, which
presently can accounts for about 40% of the screening population.
The lower contrast in the breast image can be recovered by
subsequent image processing because the better x-ray penetration
also brings quantum statistics.
[0040] Referring again to FIG. 5, because of the low contrast (low
G) effects deliberately achieved as discussed above, physicians
would not be expected to make diagnosis by viewing this low
contrast and wide latitude mammogram 600. The low-contrast
mammographic film 600 is digitized through the film digitizer 30
and is thereby converted into a digitized image 40 that can be put
through the CAD abnormal feature detection stage 50. This detection
can be optimized for use with low-contrast, wide-latitude images.
The result, as in earlier embodiments, is an annotated map 58 of
suspected abnormalities, but in this case derived from the
low-contrast image and, if desired, tiles 66 and 67. The
information generated up to this point can be stored at unit 70.
Depending on the setting of a switch 71, the information can be
used in one of two ways. One involved displaying the low-contrast
radiographic image together with the annotated map and, if desired,
the tiles. To this end, the low-contrast but wide latitude image is
fed through a high-resolution film printer 580 and printed out as a
conventional high contrast mammogram 650. The respective annotated
road maps 58 and the enhanced image tiles 66 and 67 can also be
printed at the edge or margin of the mammogram 650. The physician,
as in earlier embodiments, finally reads the mammogram on the light
box 550. Using the miniaturized road map 58 as a guide, the
physician reexamines the mammogram 650 to see if any of the CAD
detected abnormalities suggest further action. The enhanced image
tiles 66 and 67 provide the physician with further information by
emphasizing the abnormal features of the CAD detected
abnormalities. It is sometimes preferred that only the miniaturized
annotation road map 58 be printed at the margin of the mammogram
650. Alternatively, depending on the setting of a switch 73, the
radiological image, annotated map and tiles can be displayed at 900
in one of the ways described in connection with FIGS. 1, 2, and
3.
[0041] In order to provide an enhanced way of displaying the more
relevant information, the switch 71 is set to send the
low-contrast, wide latitude radiological image and information
about the suspected abnormalities through a processor 72, that is
explained in more detail in connection with FIG. 6. This processor,
which can be a part of the same programmed computer that does some
of all of the processing involved in the embodiment of FIG. 5, uses
information regarding the suspected abnormalities that were
automatically found by unit 50 to automatically convert the
low-contrast radiological image to a high-contrast image at the
density range(s) corresponding to the abnormalities. This produces
a display image that can be fed to printer 580 to produce a film
for display at light box 550, preferably together with a display of
the annotated map alone or with the tiles. Again, depending on the
setting of switch 73, the display can be additionally, or instead,
on a unit 900.
[0042] FIG. 6 illustrates how a CAD system in accordance with a
fourth embodiment can be used to convert a low-contrast,
wide-latitude digital radiographic image to an image that has
high-contrast at areas of interest, e.g., the areas of suspected
abnormalities. One of the major problems in digital imaging is how
to display all the information contained in the digitally acquired
images. Typically, according to Feig et al in Volume 33 (1995) of
Radiological Clinics of North America, pages 1205-30, and other
sources, the exposure range of the latitude (the ratio of the
exposure at the highest signal region to that at the lowest signal
region) of the digitally acquired image is of the order of 100 to
over 1000, which is much broader than that of the display media. By
comparison, if a radiogram is to be displayed on a photographic
film, the exposure range of the latitude (the ratio of exposure at
the highest signal region to that at the lowest signal region where
the display gradient is significant) is of the order of 25 and the
exposure range of the latitude of a TV monitor is less than 10.
[0043] As illustrated in FIG. 6, a CAD system 20, which can be a
part of unit 72 in FIG. 5, is used guide into two different display
media the display resulting from converting a low-.contrast image
into a high-contrast image where needed, as determined by
information about abnormalities found through processing the
low-contrast image. A wide latitude digitally acquired image 800 is
formatted for example such that the base10 log of its output signal
(with an exposure range of over 1000) is encoded into 12 bits (4096
levels of gray). In this example, the CAD system determines how the
digital, wide-latitude radiogram 800 should be printed on a
photographic film 830 (having a display latitude of, for example,
25) and displayed on a high-resolution TV or computer monitor 860
(having a display latitude of, for example, 10). The radiogram 800
can be the digitized image 40 in FIG. 5. As illustrated in FIG. 6,
this is done by centering the display latitude of the display
medium (photographic film 830 or monitor 860) at and around the
relative exposure level of the CAD detected abnormality identified
at 890 on the wide latitude image 800. That is, only the range of
say the relative exposure 10 to 100, around the CAD detected
abnormality 890, say around relative exposure 30, is provided at
the optimum contrast gradient (say G=3.0) while other image
content, above or below the exposure range of the CAD detected
abnormality 890, are compressed in display latitude and are
displayed with reduced contrast gradient (e.g. 2.5 or less) on film
830 and/or monitor 860. The monitors would normally display the
processed x-ray images; for the purposes of illustration only, FIG.
6 shows curves illustrating the relative log exposure centered
around the level of interest, as determined by the fact that in
this example a suspected abnormality has been detected at a
relative log exposure of 30 and gray level of 890.
[0044] Although the subject matter of this patent specification has
been described above in terms of preferred structures, methods and
processes, it should be apparent to those skilled in the art that
various alterations and modifications can be made without departing
from the scope thereof and that such modifications and alterations
are intended to be considered to be within the spirit and scope of
the inventions defined by the appended claims.
* * * * *
References