U.S. patent application number 11/869324 was filed with the patent office on 2008-05-08 for method, code, and system for assaying joint deformity.
Invention is credited to Xiaoli Bi, Joon Shim.
Application Number | 20080107322 11/869324 |
Document ID | / |
Family ID | 30771147 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080107322 |
Kind Code |
A1 |
Bi; Xiaoli ; et al. |
May 8, 2008 |
METHOD, CODE, AND SYSTEM FOR ASSAYING JOINT DEFORMITY
Abstract
A method, machine-readable storage medium embodying
computer-readable code and automated system for assaying or
monitoring the extent of joint or bone deformity reported by a
summarized score that may include joint space narrowing, bone
erosion and periarticular osteoporosis in a joint-degenerative or
joint-damaging disease in a subject are disclosed. From a digitized
image of one of the subject's straight bone terminated with a joint
such as fingers, coordinates of right and left bone contours of a
selected middle or proximal phalange are determined, and these
coordinates are in turn used to determine the coordinates of a
minimum width in the middle region of the phalange and one or more
apices in a region adjacent at least one side of a joint of the
selected phalange. These latter coordinates are used in selecting a
reference joint contour representing normal-bone contour for that
phalange, or the contour of the patient phalange from an earlier
x-ray image. Guided by the reference joint contour, a region of the
selected joint of the patient is analyzed to assay or monitor the
extent of joint or bone deformity in the subject.
Inventors: |
Bi; Xiaoli; (Cerritos,
CA) ; Shim; Joon; (Fremont, CA) |
Correspondence
Address: |
PERKINS COIE LLP
P.O. BOX 2168
MENLO PARK
CA
94026
US
|
Family ID: |
30771147 |
Appl. No.: |
11/869324 |
Filed: |
October 9, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10625444 |
Jul 22, 2003 |
7280683 |
|
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11869324 |
Oct 9, 2007 |
|
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60397943 |
Jul 22, 2002 |
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Current U.S.
Class: |
382/132 ;
378/4 |
Current CPC
Class: |
A61B 5/4509 20130101;
G06K 9/6203 20130101; A61B 6/505 20130101; G06K 2209/055 20130101;
A61B 5/4528 20130101 |
Class at
Publication: |
382/132 ;
378/004 |
International
Class: |
G06K 9/64 20060101
G06K009/64; G01N 23/083 20060101 G01N023/083; G06K 9/48 20060101
G06K009/48 |
Claims
1. An automated method of assaying or monitoring the extent of
joint or bone deformity in a joint-degenerative or joint-damaging
disease in a subject, comprising the steps of (a) determining from
a digitized x-ray image of a patient's selected straight bone that
terminates at a joint, coordinates of at least one of the right and
left bone contours of a selected bone, (b) determining from bone
contour coordinates determined in step (a), the coordinates of one
or more apices in a region adjacent at least one side of the joint
formed by the selected bone, and, optionally, the coordinates of a
minimum width in the middle region of the bone, (c) using the
coordinates determined in step (b) for selecting a reference joint
contour corresponding to one of (i) the contours of confronting
joint portions of adjacent straight bones in a normal joint formed
by the selected bone; (ii) the contour of a normal joint in a joint
region formed by the selected bone; and (iii) the contour from
previous x-ray of the subject's bone in the region of the joint,
and (d) guided by the reference joint contour selected in step (c),
analyzing a region of the selected joint of the patient, to assay
or monitor the extent of bone or joint deformity in the
subject.
2. The method of claim 1, wherein the selected bone is a finger
phalange terminating in a finger joint, or a toe phalange
terminating in a toe joint.
3. The method of claim 2, wherein step (c) includes matching
contour coordinates for a selected patient phalange determined from
step (b) with one or more of a plurality of normal-phalange
templates from a library of templates.
4. The method of claim 3, wherein each normal-phalange template in
a library has been generated, for given patient characteristic(s)
related to one or more of gender, age, ethnic group, hand size and
body size, as a statistical average of a plurality of
normal-phalange templates for the given patient
characteristic(s).
5. The method of claim 2, wherein the selected bone is the middle
or proximal phalange of a patient's finger.
6. The method of claim 5, for use in assaying or monitoring joint
space width in a patient joint, wherein step (c) includes (ci)
matching the coordinates of a minimum width in the middle region of
the phalange and one or more apices on at least one side of the
selected phalange adjacent said joint with corresponding
coordinates in a normal-finger template, to identify a
normal-finger template that matches the subject phalange, (cii)
superimposing the normal-finger template phalange on the image of
the patient-finger phalange, and (ciii) using the contours of the
template finger to identify a scanning box at one of the joints of
the selected phalange, and step (d) includes (di) scanning one of
the joints of the selected phalange within said scanning box, in
scanning directions substantially parallel to the axis of the
finger, to generate contours of the confronting ends of the
phalanges in said joint, (dii) generating profiles of the distances
between said confronting phalange bone-end contours within said
scan box, and (diii) analyzing said profiles from (ii) to determine
the extent of bone loss at said joint, as an indicator of extent or
progression of joint-damaging disease in said subject.
7. The method of claim 6, wherein the selected phalange is the
middle phalange, and the scanning box is placed at the middle
phalange/proximal phalange (MP/PP) joint.
8. The method of claim 7, wherein step (ci) includes using the
coordinates of the minimum middle phalange width to determine a
scaling factor for superimposing the template finger of the image
of the patient finger.
9. The method of claim 7, wherein step (ci) further includes
matching the determined coordinates of a patient-finger middle
flange with the corresponding coordinates of the middle phalange of
each of a set of template fingers, assessing the difference between
the two, and based on this difference, either accepting the
template or matching another template from the set.
10. The method of claim 7, wherein step (ciii) includes finding a
first line extending through the widest portion of the middle
phalange in the region of the MP/PP joint, finding a second line
parallel to the first which extends through the widest portion of
the adjacent phalange in the region of the same joint, and
connecting the two lines with parallel connecting lines to form a
rectangular scanning box defined by said widest bone portions.
11. The method of claim 5, wherein step (d) includes successively
scanning across said joint, in a direction substantially parallel
to the finger axis, and the scan line an incremental distance along
the width of the scan box, until scans along the entire width of
the box have been taken.
12. The method of claim 11 wherein the selected phalange is the
middle phalange, and the scanning box is placed at the middle
phalange/proximal phalange (MP/PP) joint, and step (dii) includes
comparing the distances at each point along the scan box in said
profile with those representative of a normal-subject MP/PP joint
from the same finger as the patient finger.
13. The method of claim 5, for use in assaying or monitoring bone
erosion in a patient joint, wherein step (c) includes (ci) from the
determined coordinates of the contours of the selected phalange,
identifying a pair of apices on at least one side of the selected
phalange adjacent said joint, and (cii) constructing a straight
line between each the apices in each pair, where said straight line
represents a reference joint contour adjacent the joint region of
the selected phalange, and step (d) includes comparing the straight
line contour between a pair of apices with the actual patient
contour between the same two points, to determine the extent of
concavity of said region with respect to the straight line
extending between the two apices.
14. The method of claim 5, for use in assaying or monitoring bone
erosion in a patient joint, wherein step (c) includes (ci) matching
the coordinates of a minimum width coordinate in the middle region
of the phalange and one or more apices on at least one side of the
selected phalange adjacent said joint with corresponding
coordinates in a partial or complete normal-finger template, to
identify a joint region of a normal-finger phalange template that
matches the subject finger joint region, and (cii) superimposing
the contour of the template phalange joint region on the image of
the patient-finger phalange joint region, where the template
contour represents a reference joint contour adjacent the joint
region of the selected phalange, and step (d) includes comparing
the template line contour in the joint region with the actual
patient contour in the same region, to determine the extent to
which the actual patient contour deviates from the normal-phalange
contour.
15. The method of claim 5, for use in assaying or monitoring bone
erosion in a patient joint, wherein step (c) include (ci) matching
the coordinates of a minimum width coordinate in the middle region
of the phalange and one or more apices on at least one side of the
selected phalange adjacent said joint with corresponding
coordinates in a previous patient x-ray image of the finger
phalange, and (cii) superimposing the contour of the previous x-ray
image phalange joint region on the image of the patient-finger
phalange joint region, where the previous-patient contour
represents a reference joint contour adjacent the joint region of
the selected phalange, and step (d) includes comparing the
previous-image contour in the joint region with the actual patient
contour in the same region, to determine the extent to which the
actual patient contour deviates from the previous-image
contour.
16. The method of claim 15, wherein the selected phalange is the
proximal phalange, and the joint is the MP/PP joint.
17. A machine readable storage medium embodying computer-readable
code which is operable, when used to control the operation of an
electronic computer, to assay or monitor the extent of joint or
bone deformity in a joint-degenerative or joint-damaging disease in
a subject, by the steps of (a) determining from a digitized x-ray
image of a patient's selected straight bone that terminates at a
joint, coordinates of at least one of the right and left bone
contours of a selected bone, (b) determining from bone contour
coordinates determined in step (a), the coordinates of one or more
apices in a region adjacent at least one side of the joint formed
by the selected bone, and, optionally, the coordinates of a minimum
width in the middle region of the bone, (c) using the coordinates
determined in step (b) for selecting a reference joint contour
corresponding to one of (i) the contours of confronting joint
portions of adjacent straight bones in a normal joint formed by the
selected bone; (ii) the contour of a normal joint in a region
adjacent at least one side of the joint formed by the selected
bone. and (iii) the contour of the subject's joint in a region
adjacent at least one side of the joint formed by the selected
bone, and (d) guided by the reference joint contour selected in
step (c), analyzing a region of the selected joint of the patient,
to assay or monitor the extent of joint or bone deformity in the
subject.
18. The storage medium of claim 17, wherein the selected bone is a
finger phalange defining a finger joint, or a toe phalange defining
a toe joint.
19. The storage medium of claim 18, wherein the selected bone is a
middle or proximal phalange of a patient's finger.
20. The storage medium of claim 19, for use in assaying or
monitoring joint space width in a patient joint, wherein step (c)
includes (ci) matching the coordinates of a minimum width in the
middle region of the phalange and one or more apices on at least
one side of the selected phalange adjacent said joint with
corresponding coordinates in a normal-finger template, to identify
a normal-finger template that matches the subject phalange, (cii)
superimposing the normal-finger template phalange on the image of
the patient-finger phalange, and (ciii) using the contours of the
template finger to identify a scanning box at one of the joints of
the selected phalange, and step (d) includes (di) scanning one of
the joints of the selected phalange within said scanning box, in
scanning directions substantially parallel to the axis of the
finger, to generate contours of the confronting ends of the
phalanges in said joint, (dii) generating profiles of the distances
between said confronting phalange bone-end contours within said
scan box, and (diii) analyzing said profiles (ii) to determine the
extent of bone loss at said joint, as an indicator of extent or
progression of joint-damaging disease in said subject.
21. The storage medium of claim 19, for use in assaying or
monitoring bone erosion in a patient joint, wherein step (c)
includes (ci) from the determined coordinates of the contours of
the selected phalange, identifying a pair of apices on at least one
side of the selected phalange adjacent said joint, and (cii)
constructing a straight line between each the apices in each pair,
where said straight line represents a reference joint contour
adjacent the joint region of the selected phalange, and step (d)
includes comparing the straight line contour between a pair of
apices with the actual patient contour between the same two points,
to determine the extent of concavity of said region with respect to
the straight line extending between the two apices.
22. The storage medium of claim 19, for use in assaying or
monitoring bone erosion in a patient joint, wherein step (c)
includes (ci) matching the coordinates of a minimum width
coordinate in the middle region of the phalange and one or more
apices on at least one side of the selected phalange adjacent said
joint with corresponding coordinates in a partial or complete
normal-finger template, to identify a joint region of a
normal-finger phalange template that matches the subject finger
joint region, and (cii) superimposing the contour of the template
phalange joint region on the image of the patient-finger phalange
joint region, where the template contour represents a reference
joint contour adjacent the joint region of the selected phalange,
and step (d) includes comparing the template line contour in the
joint region with the actual patient contour in the same region, to
determine the extent to which the actual patient contour deviates
from the normal-phalange contour.
23. The storage medium of claim 19, for use in assaying or
monitoring bone erosion in a patient joint, wherein step (c)
include (ci) matching the coordinates of a minimum width coordinate
in the middle region of the phalange and one or more apices on at
least one side of the selected phalange adjacent said joint with
corresponding coordinates in a previous patient x-ray image of the
finger phalange, and (cii) superimposing the contour of the
previous x-ray image phalange joint region on the image of the
patient-finger phalange joint region, where the previous-patient
contour represents a reference joint contour adjacent the joint
region of the selected phalange, and step (d) includes comparing
the previous-image contour in the joint region with the actual
patient contour in the same region, to determine the extent to
which the actual patient contour deviates from the previous-image
contour.
24. An automated system for use in assaying or monitoring the
extent of joint or bone deformity in a joint-degenerative or
joint-damaging disease in a subject, comprising (A) an electronic
computer, and (B) machine readable storage medium embodying
computer-readable code which is operable, when used to control the
operation of the computer to carry out the steps in the method of
claim 1, where the selecting step in the claimed method includes
matching contour coordinates for a selected patient phalange
determined from step (b) with each of a plurality of
normal-phalange templates from a library of templates, and (C).a
library of normal-phalange templates which is accessible by said
code for use in carrying out step (c) in the method.
25. The system of claim 23, wherein each normal-phalange template
in a library has been generated, for given patient
characteristic(s) related to one or more of gender, age, ethnic
group, hand size and body size, as a statistical average of a
plurality of normal-phalange templates for the given patient
characteristic(s).
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/625,444 filed on Jul. 22, 2003, now
allowed, which claims the benefit of U.S. Provisional Patent
Application No. 60, 397,943 filed on Jul. 22, 2002, now abandoned,
both of which are incorporated in their entirety herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an automated method and
system for assaying or monitoring the extent or progression of
joint or bone deformity in a joint-degenerative or joint-damaging
disease, such as osteoarthritis or deformity joint disease such as
rheumatoid arthritis.
BACKGROUND OF THE INVENTION
[0003] There are a variety of joint-degenerative and joint-damaging
diseases, such as various forms of arthritis and osteoporosis, that
have important health and quality-of-life consequence to patients.
Since these diseases tend to be progressive, it is also important
to be able to monitor change in joint or bone deformity, for
example, in monitoring treatment methods.
[0004] A variety of biochemical and physical analysis tools are
available for monitoring bone and joint resorption and degeneration
conditions. These methods suffer various limitations relating to
ability to pinpoint and accurately quantitate joint-degenerative
conditions in an automated or substantially automated way.
SUMMARY OF THE INVENTION
[0005] The invention includes, in one aspect, an automated method
of assaying or monitoring the extent of joint or bone deformity in
a joint-degenerative or joint-damaging disease such as
osteoarthritis or osteoporosis, or deformity joint disease such as
rheumatoid arthritis, in a subject. The method includes first
determining from a digitized image of a patient's selected straight
bone that terminates at a joint, coordinates of at least one of the
right and left bone contours of a selected bone, and determining
from the bone contour coordinates above, one or more apices in a
region adjacent at least one side of a joint of the selected bone,
and, optionally, the coordinates of a minimum width in the middle
region of the bone.
[0006] The coordinates so determined are used for selecting a
reference bone contour corresponding to one of (i) the contours of
confronting joint portions of adjacent straight bones in a normal
joint formed by the selected bone; (ii) the contour of a normal
joint in a joint region formed by the selected bone; and (iii) the
contour from previous x-ray of the subject's bone in the region of
the joint. Guided by the reference bone contour, a region of the
selected bone of the patient is analyzed to assay or monitor the
extent of bone deformity in the subject.
[0007] The selected bone may be a finger phalange defining a finger
joint, or a toe phalange defining a toe joint. An exemplary bone is
the middle or proximal phalange of a patient's finger. The step of
selecting a reference bone contour may include matching contour
coordinates for a selected patient phalange with one or more of a
plurality of normal-phalange templates from a library of templates.
The normal-phalange templates in the library may generated, for
given patient characteristic(s) related to one or more of gender,
age, ethnic group, hand size and body size, as a statistical
average of a plurality of normal-phalange templates for the given
patient characteristic(s).
[0008] In one general embodiment (Embodiment 1) for use in assaying
or monitoring joint space width in a patient joint, the selecting
step may include (i) matching the coordinates of a minimum width in
the middle region of the phalange and one or more apices on at
least one side of the selected phalange adjacent the joint with
corresponding coordinates in a normal-finger template, to identify
a normal-finger template that matches the subject phalange, (ii)
superimposing the normal-finger template phalange on the image of
the patient-finger phalange, and (iii) using the contours of the
template finger to identify a scanning box at one of the joints of
the selected phalange.
[0009] Selecting step (i) may include using the coordinates of the
minimum phalange width to determine a scaling factor for
superimposing the template finger of the image of the patient
finger. This step may further include matching the determined
coordinates of a patient-finger flange with the corresponding
coordinates of the phalange from one or more of a set of template
phalanges, assessing the difference between the two, and based on
this difference, either accepting the template or matching another
template from the set.
[0010] Selecting step (iii) may include finding a first line
extending through the widest portion of the middle phalange in the
region of the MP/PP joint, finding a second line parallel to the
first which extends through the widest portion of the adjacent
phalange in the region of the same joint, and connecting the two
lines with parallel connecting lines to form a rectangular scanning
box defined by the widest bone portions.
[0011] The analyzing step may include scanning one of the joints of
the selected phalange within the scanning box, in scanning
directions substantially parallel to the axis of the finger, to
generate contours of the confronting ends of the phalanges in the
joint, (ii) generating a profile of the distances between the
confronting phalange bone-end contours within the scan box, and
(iii) analyzing the profile from (ii) to determine the distance
between the confronting ends of the phalanges defining the joint
space width and the extent of bone loss at the joint, as an
indicator of extent or progression of joint-damaging disease in the
subject.
[0012] The analyzing step may further include successively scanning
across the joint, in a direction substantially parallel to the
finger axis, and the scan line an incremental distance along the
width of the scan box, until scans along the entire width of the
box have been taken.
[0013] One exemplary phalange is the middle phalange, and the
scanning box is placed at the middle phalange/proximal phalange
(MP/PP) joint, and scanning step (ii) includes comparing the
distances at each point along the scan box in the profile with
those representative of a normal-subject MP/PP joint from the same
finger as the patient finger.
[0014] In an embodiment (Embodiment 2) for use in assaying or
monitoring bone erosion in a patient joint, the selecting step may
include (i) from the determined coordinates of the contours of the
selected phalange, identifying a pair of apices on at least one
side of the selected phalange adjacent the joint, and (ii)
constructing a straight line between the apices in each pair, where
the straight line represents a reference joint contour adjacent the
joint region of the selected phalange. The analyzing step includes
comparing the straight-line contour between a pair of apices with
the actual patient contour between the same two points, to
determine the extent of concavity of said region with respect to
the straight line extending between the two apices.
[0015] In another embodiment (Embodiment 3) for use in assaying or
monitoring bone erosion in a patient joint, the selecting step may
include (i) matching the coordinates of a minimum width coordinate
in the middle region of the phalange and one or more apices on at
least one side of the selected phalange adjacent the joint with
corresponding coordinates in a partial or complete normal-finger
template, to identify a joint region of a normal-finger phalange
template that matches the subject finger joint region, and (ii)
superimposing the contour of the template phalange joint region on
the image of the patient-finger phalange joint region, where the
template contour represents a reference joint contour adjacent the
joint region of the selected phalange. The analyzing step includes
comparing the template line contour in the joint region with the
actual patient contour in the same region, to determine the extent
to which the actual patient contour deviates from the
normal-phalange contour.
[0016] In still another embodiment (Embodiment 4) for use in
assaying or monitoring bone erosion in a patient joint, the
selecting step may include (i) matching the coordinates of a
minimum width coordinate in the middle region of the phalange and
one or more apices on at least one side of the selected phalange
adjacent the joint with corresponding coordinates in a previous
patient x-ray image of the finger phalange, and (ii) superimposing
the contour of the previous x-ray image phalange on the image of
the patient-finger phalange, where the previous-patient contour
represents a reference contour of the selected phalange. The
analyzing step includes comparing the previous-image contour in the
joint region with the actual patient contour in the same region, to
determine the extent to which the actual patient contour deviates
from the previous-image contour.
[0017] In another aspect, the invention includes machine-readable
storage medium embodying computer-readable code which is operable,
when used to control the operation of an electronic computer, to
carry out the steps in the above method for assaying or monitoring
the extent of joint or bone deformity in a joint-degenerative or
joint-damaging disease.
[0018] Also disclosed is an automated system for use in assaying or
monitoring the extent of joint or bone deformity in a
joint-degenerative or joint-damaging disease, such as arthritis or
osteoporosis. The system includes an electronic computer, and
machine-readable storage medium embodying computer-readable code
which is operable, when used to control the operation of the
computer to carry out the steps in the above method, where the
selecting step in the method includes matching contour coordinates
for a selected patient phalange with one or more of a plurality of
normal-phalange templates from a library of templates. The system
also includes a library of normal-phalange templates that is
accessible by the code for use in carrying out the selecting step
in the method. The library forms yet another aspect of the
invention.
[0019] These and other objects and features of the invention will
become more fully apparent when the following detailed description
of the invention is read in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows an x-ray image of a patient hand, with a
calibration wedge in the image shown at the upper right in the
figure;
[0021] FIGS. 2A and 2B are flow diagrams of the operation of the
system in carrying out Embodiment 1 of the invention;
[0022] FIG. 3 is a portion of an x-ray image of a patient finger,
showing scanning boxes at the MP/PP and PP/MC joints;
[0023] FIG. 4 is an enlarged view of the of the MP/PP joint scan
box shown in FIG. 3;
[0024] FIG. 5 is a flow diagram of steps in carrying out Embodiment
2 of the invention;
[0025] FIG. 6 illustrates apical-point reference and patient-bone
contours in the distal joint region of PP;
[0026] FIG. 7 is a flow diagram of steps in carrying out Embodiment
3 of the invention;
[0027] FIGS. 8A and 8B show minimum width (N) and apical points (P)
in a patient phalange joint region (8A) and corresponding template
joint region (8B);
[0028] FIGS. 9A and 9B show lines connecting minimum width (N) and
apical points (P) in a patient phalange joint region (9A) and
corresponding template joint region (9B), for purposes of
determining a scaling factor between the two contours;
[0029] FIGS. 10A and 10B show the superposition of a scaled
template phalange on a patient phalange before (10A) and after
(10B) application of a rotation matrix;
[0030] FIG. 11 shows erosion assessment after partial template
overlay, in accordance with the method of Embodiment 3;
[0031] FIG. 12 is a flow diagram of steps in carrying out
Embodiment 4 of the invention;
[0032] FIG. 13 illustrates patient reference and patient-bone
contours in the distal joint region of the PP, for assessing bone
erosion by the method of Embodiment 4; and
[0033] FIGS. 14A-4E show steps in correcting finger axis in
severely curved finger.
DETAILED DESCRIPTION OF THE INVENTION
[0034] As described above, the invention includes an automated
method for monitoring or assessing the extent of joint or bone
deformity in a joint-degenerative or joint-damaging disease, such
as arthritis or osteoporosis or deformity joint disease such as
rheumatoid arthritis, and a system and machine-readable code for
carrying out, or assisting medical personnel in carrying out the
method. The code is in the form of a machine-readable storage
medium embodying computer-executable code which is operable to
control an electronic computer, as will be readily understood from
the description of the operation of the code herein. The method
will be illustrated with respect to four general embodiments:
[0035] Embodiment 1 is intended for use in measuring the joint
space width (JSW) in a selected joint, e.g., the MP/PP joint
between the middle phalange (MP) and the proximal phalange (PP)
and/or the joint PP/MC joint between the PP and metacarpal (MC)
bone in a patient's hand. In particular, the method is intended to
assay or monitor damage in this joint, as evidenced, for example,
by a less-than-normal JSW in the joint.
[0036] Embodiments 2-4 are each designed for assaying bone erosion
in the joint region of one or both bones forming the joint, e.g.,
the regions adjacent the confronting joint regions of the MP or PP,
or adjacent the confronting joint regions of the PP and MC. In all
three embodiments, bone erosion is measured as the difference
between a reference contour in the joint region of the selected
bone and the actual patient contour in the same region of the bone.
The reference contour in Embodiment 2 is a straight line between a
pair of apical points on one or both sides of the joint region of
the bone; in Embodiment 3, the reference contour corresponds to a
normal-bone template, either partial or complete, that is
superimposed on the patient joint region; and in Embodiment 4, the
reference contour is generated from an earlier x-ray image of the
same patient bone, allowing a change in bone erosion over time to
be monitored.
[0037] The method is based on computer analysis of digitized x-ray
images of joints in a patient's long bones, typically one or more
flanges or the patient's finger of toe bones, but optionally
including other long or elongate bones that terminate in a joint,
such as the long bones of the arm or legs. For purposes of
description, the method will be described with particular reference
to images of a patient's hand, it being understood how the method
would be applied to other long bones.
[0038] The x-ray or fluoroscopic image of a patient's hand may be
obtained using conventional x-ray methods. At a minimum, the x-ray
image should include at least one and preferably three fingers on
at least one hand of the patient, where the image of each finger
includes all of the middle phalange (MP), all of the proximal
phalange (PP), and therefore the MP/PP joint, and enough of the
metacarpal phalange or bone (MC) to provide an image of the PP/MC
joint for that finger. A preferred image contains three digits of a
hand and a calibration wedge, as illustrated for example in FIG. 1
and detailed with respect to FIG. 3 and in column 6, lines 37-49 of
co-owned U.S. Pat. No. 6,246,745 B1 ('745 patent). The '745 patent
is incorporated herein in its entirety. FIG. 1 is an x-ray image 20
of a patient's left hand, showing fingers such as index finger 22,
and phalanges, such as the middle phalange (MP) 24, proximal
phalange (PP) 26, and the metacarpal bone (MC) 30. Also shown in
the figure is a calibration radio-opaque wedge 32.
[0039] The x-ray image is digitized, according to known methods,
such as disclosed in the '745 patent, for example, at column 10,
lines 21-27, yielding, for example, a 12-bit grey scale image with
a resolution of at least 230 dpi. A segmentation and processing
module (also forming part of the machine-readable storage medium
embodying computer-readable code of the present invention), such as
described in the above '745 patent, column 12, line 47 to column
13, line 23, and in related passages describing processing steps
160, 164, 168, 174, 178, and 184) then carries out the following
image processing steps:
[0040] (1) The three digits, e.g., the index, second, and third
fingers, and the calibration wedge are segmented from the
background (processing step 160).
[0041] (2) The contour points (x,y coordinates) of the three digits
and wedge are stored (processing step 164).
[0042] (3) The central axis of each of the three digits is
determined and stored (processing steps 168 and 174).
[0043] (4) The left bone edge and the right bone edge of each digit
are determined (processing step 178).
[0044] (5) The contour points (x,y coordinates) of the left and
right bone edges are stored (processing step 184).
[0045] Once these operations have been performed, the program
operates to determine the coordinates of one or more apices, i.e.,
points of maximum lateral extension or projection, adjacent at
least one side of a joint of that phalange, e.g., at least one side
region of the middle phalange MP/PP joint. The apices may be local
maxima, allowing for more than one apex along each side region of a
joint. Optionally, the program also determines the coordinates of
the minimum width in the middle region of a selected phalange,
e.g., the MP or PP. As will be seen below, both apical and minimum
width coordinates are typically used in selecting reference
contours, although in one embodiment (Embodiment 2), minimum-width
coordinates may not be required.
[0046] The coordinates determined from above are then used in
selecting reference contours that are employed in the joint or bone
analysis. For Embodiment 1, the reference contours are the contours
of confronting portions of adjacent phalanges in a normal-finger
joint. In Embodiments 2 and 3, the reference contours selected are
the contours of a normal-finger joint in a region adjacent at least
one side of a joint of the selected phalange. The "normal-finger"
contour may be represented either by a straight line between a pair
of apical joints adjacent the joint region (Embodiment 2), or a
contour from a normal-bone template in that joint region
(Embodiment 3). In Embodiment 4, the reference contour is derived
from an earlier patient x-ray image of the same bone region.
[0047] Guided by the reference joint contours identified as above,
a region of the selected joint of the patient is then scanned to
assay or monitor the extent of joint or bone degeneration in the
subject.
A. EMBODIMENT 1
Measuring JWS
[0048] FIGS. 2A and 2B show a flow diagram of steps performed by
the machine-readable storage medium embodying computer-readable
code of the invention, in carrying out the method of Embodiment 1.
As indicated by box 34 in the figure, the coordinates that are
determined from the x-ray images are the coordinates at the left
and right edges of the bone at its narrowest width (Min), and the
apical coordinates corresponding to coordinates at the ends of a
line through the widest portion of the phalange (Max) adjacent one
or both joints of that phalange, for example, the greatest widths
at the top and bottom joint regions of the middle flange.
[0049] The coordinates are determined by using the left and right
bone edge contours to find the minimum bone width of the middle
phalange. Starting from the first coordinate of the left bone edge
contour, the program finds the corresponding coordinate that has
the same Y coordinate from the right bone edge contour. The width
at this Y coordinate will be the difference between the two X
coordinates. After creating the width profile, the middle phalange
minimum width coordinates and the coordinates at the widest points
of both top and bottom joint regions are determined. Embodiment 3
below details the algorithm for finding minimum width coordinates.
The same approach is used for finding coordinates at a maximum
width in the joint regions of the selected phalange.
[0050] Once these coordinates are determined, the program operates
at 36 to find a normal-bone template that closely matches the
selected patient phalange, e.g., the MP, in size and shape. The
templates are selected from a library 38 of normal-bone phalanges.
Each template in library 38 is a collection of contour points of a
phalange, and is defined as T(x.sub.i, y.sub.i), i=0, 1, . . . n,
where n is the total number points of the contour.
[0051] The template may be generated statistically or arbitrarily.
A statistical template can be made after sampling a large number of
normal phalange data and "averaging" them. This requires a large
set of "good representative" data. An arbitrary template is created
using a selected phalange contour. This is possible when the shape
of an object of interest is uniform and regular. The statistical
template will preferably be specific for gender, height and/or hand
size. In order to cover minor variations in shape of phalanges
depending on gender and age group, there is a preferable set of
templates for each finger's every phalange. In an exemplary method,
and based on the matching time and the shape variances, five to six
templates for each set are chosen.
[0052] A selected template from the set is then overlaid on a real
bone image. The minimum width of the middle phalange found from
above is used as an anchor point to overlay the template. A scale
factor (SF) is calculated at 40 based on the size of the finger,
i.e., the height and the minimum width of the patient's middle
phalange. It is defined as SF = max .function. ( y ) .di-elect
cons. T .function. ( x , y ) - min .function. ( y ) .di-elect cons.
T .function. ( x , y ) max .function. ( y ) .di-elect cons. R
.function. ( x , y ) - min .function. ( y ) .di-elect cons. R
.function. ( x , y ) ##EQU1## where T(x,y), R(x,y) represent the
template and real bone respectively. With the anchor point as well
as the scale factor, the template is shrunk or expanded to fit the
real phalange. The scaled template is superimposed on the patient
phalange for template matching, as at 41. An error parameter r (box
42) is used to evaluate the "goodness" of the match. r = i = 1 n
.times. R .function. ( x i , y i ) - T .function. ( x i , y i ) 2
##EQU2##
[0053] All the templates in an appropriate set will participate in
the matching process by repeating the matching steps as described.
The logic of the template selection is shown at 44-50 in FIG. 2A.
Briefly, a minimum error function r for all templates tested is
stored. This lowest error function is compared with the error
function of the latest template match at 44. If the latest template
match is lower than the stored error function, the new match is
saved to file 46, along with its error function. If the latest
template error function is higher than the existing function, the
program proceeds to test the next template, through the logic of
48, 49, until all of the library templates have been tested against
the selected patient phalange. When this process is completed, the
template having the lowest error function is identified as the best
match template, at 50. That is, if the error parameter of the match
between the patient-image middle phalange and the template is
within a predefined range, the template is retained; otherwise, a
new template is evaluated, and the process repeated until an
appropriate template is found, either as a good-match or as the
best-match, i.e., the one with the minimum error.
[0054] The template that generates the minimum error parameter is
selected for the next stage operations, which are given in flow
diagram form in FIG. 2B. Once a MP template is found, it is
superimposed on the patient template, at 52, and using the outlines
of the template, the program constructs a rectangular scan box 53
(Box 1, the upper box in FIG. 3) for the MP/Proximal phalange (PP)
joint is defined by
[0055] (a) two parallel lines 54, 56 (see also FIG. 4) extending
between the widest portions of MP and PP.
[0056] (b) two parallel lines 58, 60 (see also FIG. 4) extending
between the ends of the MP widest-portion line and extensions of
the PP widest-portion line.
[0057] The construction of the scanning box is indicated at 64 in
FIG. 2B. A scanning and profile analysis algorithm given in FIG. 2B
is now employed to scan the patient MP and PP bone-end contours, by
scanning in a direction parallel to the bone axis, across the
entire length of Box 1. Inside the scan box is a small sub-image as
shown in FIG. 4 including joints between either MP and PP, or
joints between PP and MCP. A series of mathematical image processes
including Unsharp Mask, Local Equalization and Median Filter are
then be applied to the sub-image for the purpose of enhancing image
quality by reducing both the high and low frequency noise.
[0058] With reference to FIG. 4, which shows scanning box 53 in
enlarged view, the start point will be the center point of the scan
box, indicated by scan line 62. The program scans line-by-line
parallel to the bone axis (vertical in FIG. 3) toward each side of
the box until reaches the two ends. This operation is indicated at
66 in FIG. 2B. A gray level profile is then created for each
scanned line.
[0059] For each profile, its optical density curve is analyzed to
extract JSW after a Sobel operator is applied, as shown at 68 in
FIG. 2B. The concept of the Sobel operator is to find the gradient
of a function f at coordinates (x,y). It is defined as: .DELTA.
.times. .times. f = [ .differential. f .differential. x
.differential. f .differential. y ] ##EQU3## and the magnitude of
this vector is .DELTA. .times. .times. f = mag .function. ( .DELTA.
.times. .times. f ) = [ ( .differential. f .differential. x ) 2 + (
.differential. f .differential. y ) 2 ] 1 / 2 ##EQU4##
[0060] By analyzing each profile using this operator, an interface
between the end of MP bone and the joint area as well as the end of
PP bone and the joint area can be detected. Let y.sub.j be the y
coordinate at the bottom bone outline of the upper phalange, and
y.sub.i be the y coordinate at the top bone outline of the bottom
phalange, marking two coordinates per profile (R(x.sub.i,y.sub.i)
and R(x.sub.j,y.sub.j)), MP and PP bone end contours will be formed
from the bone/joint interface coordinates. The contours of a MP/PP
joint are shown in the corresponding scan box in FIG. 4, and the
operation of determining JSW for each scan profile, indicated at 70
in FIG. 2B. The joint space width w(x.sub.i) at coordinates
(x.sub.i.y.sub.i) is defined as:
w(x.sub.i)=abs(y.sup.i-y.sup.j)
[0061] The distances between the contours of MP/PP joint are
averaged, as at 72 in FIG. 2B, to create the MP/PP joint space
width, JSW = i = 1 n .times. w .function. ( x i ) .times. .times. i
= 1 , 2 , .times. .times. n ##EQU5##
[0062] A similar approach is used to determine the joint space
narrowing at the PP/MCP bone joints. Based on the top portion of
the PP contour from the operation above, the MP width and height,
the program calculates a scale factor for the PP. With this scale
factor, a PP template (preferably taken from the same template set
for the MP) is overlaid. The match process is similar to that
described above for the MP. This approach assumes that the axis of
the finger is a straight line. If this is not the case, the PP
template has to be rotated with respect to the MP until the two
template phalanges are aligned with the patient phalanges.
[0063] In particular, once the PP template is overlaid, it is
possible to
[0064] 1. Define a scan box (lower box in FIG. 3) from the widest
portions confronting MP and MCP bones;
[0065] 2. Scan the PP/MCP joint in directions parallel to the
finger axis, to generate bone-end contours;
[0066] 3. Generate a profile across the joint of the distance
between the bone-end contours, and
[0067] 4. Use this profile to assess the degree of joint loss
between the PP and MCP.
[0068] This score provides another indicator of the extent or
progression of joint loss in the patient hand.
B. EMBODIMENT 2
Measuring Joint Bone Erosion
[0069] Erosion happens in early stages in RA patients and it
rapidly gets worse in the first few years of the disease. When a
patient is first seen, the physician's objective is to detect the
existence and the severity of bone erosion. At this time the
contours of the interested bones are obtained for the first time
and saved as baseline results for future monitoring purpose.
Embodiment 2 described in this section and Embodiment 3 described
in the next sections are designed to assess the extent of bone loss
in the joint region of a selected bone, e.g., phalange, using
normal-bone contours to as reference contours. In follow-up visits,
the patient's own earlier x-ray images may be used as the reference
contours, for assessing the change in bone erosion over time. This
approach is detailed below as Embodiment 4.
[0070] When the patient's bone contours are obtained for the first
time, there are no pre-existing contours to reference in the
database. Since there are wide variances in the shape of bones of
interest, it may not be straightforward to use templates in order
to detect erosion in this situation. To overcome this difficulty,
the method of Embodiment 2 utilizes a method of determining
convex--concave property of the top portion of the lateral bone
contours.
[0071] FIG. 6 shows the concave property of a PP phalange 74 having
a contour 76 shown in black trace. In an AP (anterior-posterior)
fingers x-ray, with no excessive rotation of the fingers along the
center axis, the normal shape of the top portion of the bones of
interest exhibits an outward convex. If erosion has taken place, it
is possible to detect various concave shapes in those areas. Using
two points and a straight line that connects them, it is possible
to determine how concave the contour is in the area and thus the
existence of erosion.
[0072] To illustrate the algorithm in detail, consider only one
side, e.g., the left top quarter of the bone contour in FIG. 6. In
this illustration, contour 76 of the phalange has two distinctive
apices (maxima), point P and point Q. Apical point P, indicated at
78, is found by the algorithm below, corresponding to box 80 in
FIG. 5, which is a flow diagram of the steps in the method. By
scanning the left lateral portion of the contour from its upper tip
down through one quarter of its full length, the point on this
segment with its X.sub.i coordinate value smaller than X.sub.i+1
identifies point P. P=(x.sub.i,y.sub.i).epsilon.B.sub.L where
B.sub.L is a defined portion of the left side bone contour. In this
case, the algorithm uses a quarter length of the whole contour in
this study, and x.sub.i<x.sub.i+1, where
(x.sub.i+1,y.sub.i+1).epsilon.B.sub.L, and m.ltoreq.i.ltoreq.q,
where (x.sub.m,y.sub.m).epsilon.B.sub.L and
ym=min(y).epsilon.B.sub.L(Xq y.sub.q).epsilon.B.sub.L and y 4 = max
.function. ( y ) .di-elect cons. B L - min .function. ( y )
.di-elect cons. B L 4 ##EQU6##
[0073] The second point, Q, shown at 82 in FIG. 6, is determined by
the same method as described above but by scanning the contour in a
bottom-up direction. These steps are generally represented by box
84 in FIG. 5. Q=(x.sub.j,y.sub.j).epsilon.B.sub.L Where
xj<x.sub.j+1 and (x.sub.j+1,y.sub.j+1).epsilon.B.sub.L and
yi.noteq.y.sub.j, and q.gtoreq.j.gtoreq.m, m and q are defined the
same as above.
[0074] Once points P and Q are found, the program constructs a
straight line 83 between the points, as indicated by box 86 in FIG.
5. This line represents a "normal" bone contour in this region (As
indicated above, a normal bone may be slightly convex in this
region). The points making up the patient bone contour segment
between points P and Q can then be compared to the number of pixels
making up the strait line connecting points P and Q (red trace in
FIG. 4), to analyze the deviation between the straight line and the
patient contour between the same two points. One measure of this
deviation is the number of pixels contained in the each contour
between points P and Q, the straight line contour represented the
smallest pixel number between the two points, and the number of
pixels in the patient contour being related to the extent of
concavity in the contour. This operation is indicated at 88 in FIG.
5. The comparison of pixel numbers in the two contours can be
expressed with criteria for a certainty or confidence factor (CF),
as at 90 in FIG. 5. The system by default determines that the
erosion exists if the CF exceeds a certain threshold, e.g., 60%,
which can be determined by matching the automated algorithm to
expert's assessment.
C. EMBODIMENT 3
Measuring Joint Bone Erosion
[0075] The method in this embodiment uses a portion of MP or PP
templates to predict or estimate a normal contour (without
erosion). Then, the current contour can be compared against the
estimated contour to determine the existence and severity if the
erosion.
[0076] From a MP or PP template, the algorithm defines two landmark
points (described below in detailed steps) and applies a matching
algorithm only on the contour points between them. By "copying
over" the shape of the template's contour--the points between the
two landmarks--for the area of interest (the area the erosion is
supposed to occur), it is possible to partially overlay two
contours and compare. The algorithm is shown in flow diagram in
FIG. 7.
[0077] As a first step, indicated at box 92 in FIG. 7, the program
finds the coordinates for an apical point P, as carried out in
Embodiment 2, and the coordinates for the minimum width of the
phalange (points N), as discussed below. These points are shown at
P and N for a patient middle phalange 108 in FIG. 8A, and at
P.sub.t and N.sub.t, for a normal-bone template 110 in FIGS.
8B.
N=(x.sub.n,y.sub.n).epsilon.B.sub.c, where B.sub.c is the current
phalange contour
(x.sub.a, y.sub.n).epsilon.B.sub.c, (x.sub.b,
y.sub.n).epsilon.B.sub.c, min(|x.sub.a-x.sub.b|) in all x.sub.i,
where 1.ltoreq.i.ltoreq.N, N is the number of contour points
[0078] That is, the program examines, for each y coordinate along
the length of the bone, a coordinate for which the absolute value
of x.sub.a-x.sub.b on opposite sides of the bone that has a minimum
value. The pair of x,y coordinates so identified are designated N.
A similar algorithm finds the y coordinates adjacent at least bone
end for which the absolute value x.sub.a-x.sub.b is a maximum, and
designates the corresponding x,y values as points P. These
algorithms are also applied in Embodiments 1 and 4 for finding
minimum-width coordinates and maximum-width apical coordinates.
[0079] In the operation of the program. and with reference again to
FIG. 7, a template is selected at 94 from a library of templates
96, constructed as described with respect to Embodiment 1. In
determining whether the template is a good match for the patient
contour, the program first calculates at 98 a scaling factor SF
coordinates N, N.sub.t, P, and P.sub.t determined for the patient
and template contours as above. The scaling factor is calculated as
the as the ratio of distances between P and N vs P.sub.t and
N.sub.t.
[0080] In addition to a scaling factor, the program calculates a
rotation matrix for orienting the template and patient contours in
the same plane, as indicated by box 100 in FIG. 7. This is done, as
illustrated in FIGS. 9A and 9B, by forming lines P-N and N-N in the
patient contour and corresponding lines P.sub.t-N.sub.t and
N.sub.t-N.sub.t in the template contour. The rotation matrix is
then determined by calculating the rotation angle, .theta., as the
angle between the line connecting P and N, and P.sub.t and N.sub.t,
respectively. That is .theta. is the difference between the angle
N-N-P in the patient contour and N.sub.t-N.sub.t-P.sub.t in the
template contour. The rotation matrix is R = [ cos .times. .times.
.theta. sin .times. .times. .theta. - sin .times. .times. .theta.
cos .times. .times. .theta. ] ##EQU7##
[0081] FIGS. 10A and 10B show the superimposition of the template
contour on the patient contour before and after application of the
rotation matrix.
[0082] The program now determines, at 102, a translation vector T
for transforming each point between P.sub.t and P.sub.t of the
template contour into the corresponding contour region between P
and P in the patient contour.
[0083] The final matrix transform M for superimposing the template
contour on the patient contour is now calculated as: M=sM.sub.R+T
where s is a scaling factor, R is a rotation matrix and T is a
translation vector defined in the above steps. FIG. 11 shows the
superposition of a template contour on a patient contour employing
the matrix. As seen, the matrix has the effect of superimposing the
template points N.sub.t and P.sub.t on the corresponding patient
contour point N and P, respectively, for templates that have a good
fit with the patient contour.
[0084] The above template matching is repeated for one or more
templates in the library until a template that gives a best-fir
superposition of the corresponding points N, P and N.sub.t, P.sub.t
between patient and template contours is found, as indicated at box
104 in FIG. 7.
[0085] After selection of a best-fit template, the extent of
erosion of the patient bone is analyzed, as at 106, by comparing
the template line contour in the joint region with the actual
patient contour in the same region, to determine the extent to
which the actual patient contour deviates from the normal-phalange
contour. In particular, the program analyzes the differences in
contours between N and P on the left side of the bone, P and P
across the top of the bone, and P and on the right side of the
bone. In the N-P analysis, the algorithm scans in the y direction,
recording for each y coordinate, the difference between the patient
and contour x coordinate positions. Across the top of the bone, the
scan is in the x direction, the difference value is for the contour
y coordinates. When the scan is complete, an erosion value is
determined, e.g., the average value of "negative" contour
differences, that is, contour differences in which the template
value is greater than the patient contour value.
[0086] The above method may be employed with either partial or
total template. This method employs basically the same technique as
described below for Embodiment 4, except that due to shape and size
variances between the template and the real phalange contour, a
number of small non-matched regions might exist. The subsequent
necessary step is to analyze each of those regions and determine if
it is generated by the minor variances or actual erosion. The
criteria used is based on a shape analysis algorithm: long and thin
regions are most likely generated by the minor variances, while
jogged areas are erosions.
D. EMBODIMENT 4
Measuring Joint Bone Erosion
[0087] If A patient has the bone contour obtained and stored in the
previous visit or analysis, it is possible to accurately monitor
the progression of erosion by using it as a template. The contour
of the previous analysis is retrieved from the database and used as
a shape template by overlaying it on the current contour, as shown
at 112 in FIG. 13. The black contour represents the result of the
current analysis, and the yellow one obtained in the previous
analysis, respectively. The orange area indicates increased erosion
development whereas the green area on the right shows improvement
in erosion.
[0088] The operation of the algorithm in this method is shown in
FIG. 12. Initially, the program constructs the current patient
contour (box 114), according to previously discussed methods. This
contour is then matched at 116 with one or more earlier
patient-phalange contours stored at 118. The operation of the
algorithm for matching the current (B.sub.c) and previous (B.sub.p)
bone contours, and for assessing the differences between the two
are as follows:
[0089] Given that the x-ray will be re-taken according to
consistent AP guidelines, it is reasonable to expect that the
contours in comparison should be almost identical in shape except
for the areas of erosion. Therefore, it is possible to perform an
accurate overlay of the template on the current bone contour,
employing a scaling factor (SF) and anchoring points.
[0090] The scaling factor indicates how much the template should be
expanded or shrunk. This is simply calculated by comparing lengths
of bones in the two contours. Since these two contours are from the
same patient, they are expected to yield a value close to 1. SF =
max .function. ( y ) .di-elect cons. B c - min .function. ( y )
.di-elect cons. B c max .function. ( y ) .di-elect cons. B p - min
.function. ( y ) .di-elect cons. B p ##EQU8##
[0091] The anchoring points determine whether a translation and/or
rotation are needed. They are used to align the shape template with
the current contour. In this case, axes of each contour are aligned
to achieve the overlay. Suppose there is a point that belonged to
the previous contour, (x,y).epsilon.B.sub.p, and there is a
corresponding point (x',y') belongs to the current contour,
(x',y')=SF*(x-.DELTA..sub.x,y-.DELTA..sub.y)
where
[0092] .DELTA..sub.x=x.sub.c-x.sub.p, (x.sub.p,y).epsilon.B.sub.p,
and (x.sub.c,y).epsilon.B.sub.c
[0093]
.DELTA..sub.y=min(y).epsilon.B.sub.c-min(y).epsilon.B.sub.p
[0094] Since the angles of axes are expected to be almost
identical, very little translation and/or rotation of the template,
if any, will be needed.
[0095] Once the two contours are superimposed (box 116 in FIG. 12)
the program determines an overlay function which is used in
assessing the differences in the areas of the two contours (box 120
in FIG. 12). The overlay function has the form:
O(B.sub.c,B.sub.p)=A.sub.i where A.sub.i represents an area created
from the contour overlay difference, where 0.ltoreq.i.ltoreq.n, n
is the total number of areas. Assuming there is a point inside the
area Ai, which is (x.sub.i,y.sub.i).epsilon.A.sub.i and
y.sub.m.ltoreq.y.sub.i.ltoreq.y.sub.q where y.sub.m and y.sub.q are
similarly defined as in the concave test in the previous section.
Erosion treatment improvement is then defined as (for left side) I
.function. ( B c , B p ) = { true .times. .times. if .times.
.times. all .function. ( x i , y i ) .times. B c and .times.
.times. x i .ltoreq. x j , ( x j , y j ) .di-elect cons. B p false
otherwise ##EQU9##
[0096] Once B.sub.c and B.sub.p are overlaid, the numbers of points
in B.sub.c that are inside (closer to the axis) of B.sub.p are
counted. The confidence factor can be represented as (from area Ai)
cf = n .function. ( ( x c , y ' ) .di-elect cons. B c ) max
.function. ( y ) .di-elect cons. A i - min .function. ( y )
.di-elect cons. A i + 1 ##EQU10## such that x.sub.c<x.sub.p,
(x.sub.p, y').epsilon.B.sub.p., n((x,y)) is a function that returns
the number of points.
[0097] These points indicate erosion has occurred.
E. CORRECTION FOR SEVERELY CURVED FINGERS
[0098] The method described above assumes that fingers are almost
straight or only slightly curved. If the finger to analyze is
severely curved, as it can be in joint degenerative or
joint-damaging disease, the analysis may initial require a
correction to place the bones, e.g., phalanges forming the joint
being analyzed along the same long axis.
[0099] The correction method described below is based on the
observation that an axis of a finger is composed of a straight line
axis of a distal phalange, that of a middle phalange and that of a
proximal phalange. Therefore, even if the overall axis of a finger
may be severely curved, its axis can be obtained by composing each
of the three straight line axes for the three bones inside a
finger.
[0100] Each step can be elaborated as follows. First, obtain a
contour of a finger, and obtain an approximate straight line axis
of a finger using any conventional method, as indicated in FIG.
14A, which shows a severely curved finger 122, a straight-line axis
124 determined from the distal and middle phalanges, and the outer
contour of the finger at 126. One algorithm calculates a central
axis of the finger based on the center of gravity of the finger as
determined from the outer contour. The entire finger is then
rotated to an upright position along this axis, as indicated in
FIG. 14A, that is, the center axis is oriented to a vertical
line.
[0101] Next, the program scans the finger along the length of the
axis (the y axis) to determine a midpoint along each scan line
(x-axis direction). These steps are illustrated in FIG. 14B, which
shows midpoints 130,134 for scan lines 128, 132, respectively. The
program now connects the first and last midpoints, to give line
131.
[0102] With reference to FIG. 14C, the program now calculates the
distance between line 131 and each midpoint. The point on the scan
line having the maximum distance from line 131 is determined,
referred to herein as P.sub.1, and is identified at 144 in FIG.
14C. As seen, point P.sub.1 is close to the MP/PP joint in this
figure. Next, the program constructs a line 136 from the highest
midpoint to point P.sub.1, and a second line 142 from point P.sub.1
to the lowest scan line midpoint.
[0103] This same procedure is repeated to find a second point
P.sub.2 used in generating another phalange axis. This is done by
determining the maximum distance of each scan midpoint from line
136 or from line 142. The greater of these maxima will define point
P.sub.2 at the midpoint on a scan line intersected by one of the
two lines 136 or 142. In the present case, P2 is identified at
point 147, corresponding roughly to the joint between the middle
and distal phalanges, as seen in FIG. 14D. Line 136 is now divided
into two lines, a line 146 between the dital tip and point P2, and
a line 148 between points p1, and P2.
[0104] Each finger phalange is now rotated, as shown in FIG. 14E,
to bring the line segment assigned to it into line with center axis
124. The program then operates to connect the three rotated
phalanges from top to bottom to obtain artificially composed
straight finger contour. This "straightened" contour is then is for
further analysis in the method above.
[0105] The invention thus includes a method for orienting a
severely curved finger into a straightened condition, for purposes
of establishing a more normal orientation of the finger preliminary
to the method steps above, where the bone contour is matched with
template of previous-patient contours. The method includes
constructing horizontal scan lines along the length of the finger,
and determining midpoints of these scan lines. These midpoints are
then used find points of maximum deviation of a line connecting the
end midpoints with the midpoints themselves, as a basis for
dividing the connecting line into two lines intersecting at this
point of maximum deviation. Once the one or more points of maximum
deviation are found, the separate portions of the finger may be
rotated to bring each connecting line into conformity with a common
vertical axis.
F. PERIARTICULAR OSTEOPOROSIS MEASUREMENT
[0106] Applying the existing OsteoGram technology to the scan box
region, BMD adjacent to the joint space (or inside the scan box
described above) is calculated pixel-by-pixel (U.S. Pat. No.
6,246,745). This BMD is a local bone loss value that is different
from the comprehensive phalange BMD reported from the patent 745.
It only evaluates the BMD adjacent to the joint area so that it
will reflect the progression of the joint degeneration more
precisely. In addition, this local BMD can be further separated to
trabecular(axial) and cortical (peripheral) BMD, while the combined
cortical thickness near the joint is considered as a better
indicator for early RA disease.
[0107] Two possible algorithms can be used to automatically
distinguish the two bone tissues:
[0108] Threshold algorithm: A local histogram profile is created
for the region inside the scan box shown in FIG. 4. A cortical
threshold is defined and a binary image will be created based on
this threshold. A bug-following algorithm from pending patent Ser.
No. 09/430,054 is then used to extract the cortical area.
[0109] Region-growing algorithm. This algorithm starts with a set
of cortical seed points that selected immediately from the phalange
confront ends to grow regions by appending to each seed point those
neighboring pixels that have similar gray levels.
[0110] An overall radiological score for monitoring the progression
of the bone deformity disease will be reported after an X-ray
radiograph is analyzed using the above method. The score will
include the information of JSW, bone erosion and periarticular BMD
status.
[0111] From the foregoing, it will be appreciated how various
objects and features of the invention are met. The method allows
for accurate quantitative determination and monitoring of both
joint deformity and bone erosion, using only standard patient x-ray
images for analysis. The method, as embodied in the code and system
of the invention, is carried out in a nearly fully automated
manner, allowing rapid and relatively assessment of joint and bone
degeneration.
[0112] Although the application has been described with respect to
certain embodiments and applications, it will be appreciated how
various changes and modifications may be made without departing
from the invention as claimed.
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