 |
Claims  |
|
|
Having thus described the preferred embodiment, the invention is now
claimed to be:
1. A CT scanner system comprising:
a source of radiation for irradiating an examination region from a
plurality of directions;
a radiation detection means disposed across the examination region from the
radiation source for receiving radiation that has traversed the
examination region;
an examined object support means for supporting and moving an object
axially through the examination region such that a volumetric region of
the object is examined;
a reconstruction means for reconstructing data values representing voxels
of the volumetric region;
an object memory means for storing the data values from the reconstruction
means;
a transform means for transforming polygonal surfaces of the volumetric
region into transformed polygonal surfaces on a viewing plane which
transformed polygonal surfaces represent projections of the volumetric
region polygonal surfaces on the viewing plane and for reversely
transforming locations on the viewing plane into corresponding coordinates
in the volumetric region;
a two-dimensional display means for generating a two-dimensional
human-readable display corresponding to the viewing plane, the
human-readable display including a two-dimensional array of pixels, the
transforming means reversely transforming the locations of the pixels into
corresponding coordinates of the volumetric region;
an image processor means for converting the data values corresponding to
the reversely transformed pixel coordinates into image values displayed at
the corresponding pixels of the two-dimensional display means;
a cursor positioning means for selecting a location on the two-dimensional
display at which a cursor is displayed, the cursor positioning means being
operatively connected with the image processor means for causing the
cursor to be displayed at the selected cursor location and with the
transform means for reversely transforming the selected cursor location to
a corresponding cursor coordinate in the volumetric region;
a plane defining means operatively connected with the transform means for
defining at least two of transverse, coronal, and sagittal planes through
the volumetric region which intersect at the reversely transformed cursor
coordinate, the data values corresponding to the defined planes being
supplied to the image processor means which converts the data values
corresponding to the defined planes into image values which are displayed
on the two-dimensional display means, whereby human-readable images of a
projection view of the volumetric region and at least two of intersecting
transverse, coronal, and sagittal planes are displayed concurrently, the
human-readable images of the planes changing substantially in real time as
the cursor positioning means moves the cursor.
2. An image display system comprising:
an object memory means for storing data values from a three-dimensional
image data source representing voxels of a three-dimensional volumetric
region;
a transform means for transforming polygonal surfaces of the volumetric
region into transformed polygonal surfaces on a viewing plane which
transformed polygonal surfaces represent projections of the volumetric
region polygonal surfaces on the viewing plane and for reversely
transforming locations on the viewing plane into corresponding coordinates
in the volumetric region;
a two-dimensional display means for generating a two-dimensional
human-readable display corresponding to the viewing plane, the
human-readable display including a two-dimensional array of pixels, the
transforming means reversely transforming the locations of the pixels into
corresponding image pixel coordinates of the volumetric region;
an image processor means for converting the data values corresponding to
the reversely transformed image pixel coordinates into image values
displayed at the corresponding pixels of the two-dimensional display
means;
a cursor positioning means for selecting a location on the two-dimensional
display at which a cursor is displayed, the cursor positioning means being
operatively connected with the image processor means for causing the
cursor to be displayed at the selected location and with the transform
means for reversely transforming the selected cursor location to a
corresponding cursor coordinate in the volumetric region;
a plane defining means operatively connected with the transform means for
defining at least two planes through the volumetric region which intersect
at the reversely transformed cursor coordinate, data values corresponding
to the defined planes being supplied to the image processor means which
converts the data values corresponding to the defined planes into image
values which are displayed on the two-dimensional display means, whereby
human-readable images of a projection view of the volumetric region and at
least two intersecting planes in the volumetric region are displayed
concurrently with the human-readable images of the planes changing as the
cursor positioning means moves the cursor.
3. The system as set forth in claim 2 further including an operator
controlled transform control means operatively connected with the
transform means for selectively adjusting a spatial relationship between
the volumetric region and the viewing plane.
4. The system as set forth in claim 3 wherein the operator controlled
transform control means includes an operator controlled viewing angle
rotation means for selectively rotating an angle from which the viewing
plane views the volumetric region, the viewing angle control means being
operatively connected with the transform means for adjusting the transform
in accordance with changes in the selected viewing angle.
5. The system as set forth in claim 4 wherein the transform control means
includes a scaling means for selectively enlarging and diminishing the
displayed two-dimensional image representation by a scaling factor, the
scaling means being operatively connected with the transform means for
adjusting the transform in accordance with the scaling factor.
6. The system as set forth in claim 2 wherein the three-dimensional image
data source includes a CT scanner.
7. The system as set forth in claim 6 further including:
an axial position indicating means for indicating positions along an axial
direction of the CT scanner; and,
wherein the cursor positioning means includes means for selecting
horizontal and vertical positions along the two-dimensional display, the
axial position indicating means and the cursor positioning means being
connected with the transform means such that the indicated axial position
and the indicated horizontal and vertical positions are reverse
transformed into the cursor coordinate supplied to the plane defining
means.
8. The system as set forth in claim 7 wherein the plane defining means
includes a transverse plane defining means for defining a transverse plane
orthogonal to the axial direction through the cursor coordinate, a
sagittal plane defining means for defining a sagittal plane orthogonal to
the transverse plane through the cursor coordinate, and a coronal plane
defining means for defining a coronal plane orthogonal to the transverse
and sagittal planes through the cursor coordinate.
9. The system as set forth in claim 8 further including a display memory
means having a first memory portion for storing image values corresponding
to the projection image representation, a second memory portion for
storing the values from the object memory means corresponding to the
defined transverse plane, a third memory portion for storing the data from
the object memory means corresponding to the defined coronal plane, and a
fourth memory portion for storing values corresponding to the defined
sagittal plane, portions of the display memory means being updated as the
cursor is moved, the image processor being connected with the display
memory means.
10. The system as set forth in claim 2 further including a depth
determining means for determining a relative depth in a viewing direction
from the selected cursor location to a point of intersection of a ray
extending through the selected cursor location in the viewing direction
and a viewed voxel of the volumetric region, the depth defining means
being operatively connected with the transform means such that the
transform means transforms the selected location of the cursor on the
display and the determined relative depth into the reversely transformed
cursor coordinate.
11. In an image display system which includes an object memory for storing
data values representing voxels of a three-dimensional volumetric region,
a transform means for transforming voxel coordinates of the volumetric
region which define polygonal surfaces into transformed polygonal surfaces
on a viewing plane, which transformed polygonal surfaces represent
projections of the volumetric region polygonal surfaces onto the viewing
plane and for reversely transforming locations on the viewing plane into
corresponding voxel coordinates in the volumetric region, a
two-dimensional display means for generating a two-dimensional
human-readable display, the human-readable display including a
two-dimensional array of pixels, the transforming means reversely
transforming locations of the pixels on the view plane into corresponding
pixel coordinates in the volumetric region, and an image processor means
for converting the data values corresponding to the reversely transformed
pixel coordinates into image values for display at the corresponding
pixels of the two-dimensional display means, the improvement comprising:
a cursor positioning means for selecting a location on the two-channel
display at which a cursor is displayed, the cursor positioning means being
operatively connected with the image processor means for causing the
cursor to be displayed at the selected location on the two-dimensional
display and being operatively connected with the transform means for
reversely transforming the selected cursor location to a corresponding
cursor coordinate in the volumetric region;
a plane defining means operatively connected with the transform means for
defining at least two planes through the volumetric region, which planes
intersect at the cursor coordinate, the data values corresponding to the
defined planes being supplied to the image processor means to be converted
into the image values which are displayed on the display means.
12. In the system set forth in claim 11, the improvement further
comprising:
an axial position indicating means for selecting positions along a first
axis, which first axis extends away from the viewing plane; and,
wherein the cursor positioning means includes a means for selecting
horizontal and vertical positions along the two-dimensional display, the
axial position indicating means and the cursor positioning means being
connected with the transform means such that the indicated axial position
and the indicated horizontal and vertical display positions are reversely
transformed into the cursor coordinate.
13. In the system as set forth in claim 12, the improvement further
comprising the plane defining means including:
a transverse plane defining means for defining a transverse plane through
the cursor coordinate;
a coronal plane defining means for defining a coronal plane orthogonal to
the transverse plane through the cursor coordinate; and,
a sagittal plane defining means for defining a sagittal plane orthogonal to
the transverse and coronal planes through the cursor coordinate.
14. In the system as set forth in claim 13, the improvement further
comprising a means for supplying the cursor coordinate to the image
processor means such that a cursor indication is superimposed on the
two-dimensional display of the transverse, coronal, and sagittal planes.
15. A method of concurrently displaying a projection image of a volumetric
region and at least two intersecting planes through the volumetric region,
the method comprising:
displaying the projection image on a portion of a two-dimensional display
means;
displaying a cursor at a selected location on the projection image;
transforming the selected cursor location into a corresponding cursor
coordinate of the volumetric region;
defining a first plane through the volumetric region which intersects the
cursor coordinate;
defining a second plane through the volumetric region which intersects the
first plane and the cursor coordinate;
generating a display of data values corresponding to the first plane in a
second portion of the two-dimensional display means;
generating a display of the data values corresponding to the second plane
in a third region of the display means.
16. The method as set forth in claim 15 further including moving the
location of the cursor on the projection image such that the transforming
step transforming the moved cursor location into a new cursor coordinate
as the cursor is moved, and the plane defining step redefining the planes
as the cursor coordinate is changed, whereby the displayed planes are
updated by re-slicing the volume according to the position of the cursor.
17. The method as set forth in claim 16 further including defining a third
plane through the cursor coordinate.
18. The method as set forth in claim 17, wherein the first, second, and
third planes are orthogonal to each other.
19. The method as set forth in claim 17, further including converting the
cursor location into a human-readable display on the two-dimensional
display means.
20. The method as set forth in claim 17 wherein the two-dimensional display
means is a single video monitor and wherein the display step includes
converting the data values into a video signal. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
BACKGROUND OF THE INVENTION
The present invention pertains to the image display art. It finds
particular application in conjunction with the display of CT medical
diagnostic images on video monitors and will be described with particular
reference thereto. However, it is to be appreciated that the invention is
also applicable to medical diagnostic images from magnetic resonance,
nuclear, and other imaging modalities, to quality assurance and other
three-dimensional, non-medical images, and the like. The invention is also
applicable to hard copy displays, film image displays, and other display
formats.
Heretofore, CT scanners have irradiated a planar region of a subject from
various angles and detected the intensity of radiation passing
therethrough. From the angle and radiation intensity information,
two-dimensional image representations of the plane were reconstructed. A
typical image representation included a 512.times.512 pixel array,
although coarser and finer arrays are also known.
For three-dimensional imaging, the patient was moved along a longitudinal
axis of the CT scanner either continuously for spiral scanning or
incrementally, to generate a multiplicity of slices. The image data was
reconstructed, extrapolating or interpolating as necessary, to generate CT
numbers corresponding to each of a three-dimensional array of voxels. For
simplicity of illustration, each of the CT numbers can be conceptualized
as being addressable by its coordinate location along three orthogonal
axes, e.g. x, y, and z-axes of the examined volume.
Typically, the volume data was displayed on the planar surface of a video
monitor. Various planar representations of the volume data are now
commonly available. Most commonly, the examined volume was a six sided
prism with square or rectangular faces. The operator could select a
display depicting any one of the six faces of the prism or any one of the
slices through an interior of the prism along one of the (x,y), (x,z) or
(y,z) planes. Some display formats also permitted oblique planes to be
selected. Display formats were also available which permitted two or three
sides of the prism to be displayed concurrently on a two-dimensional (i,j)
image plane with appropriate visual cues to give the impression of a
perspective view in three dimensions. That is, the visible faces were
foreshortened (or extended) and transformed from rectangles to
parallelograms by a sine or cosine value of an angle by which the viewing
direction was changed. In this manner, each face of the prism was
transformed into its projection along the viewing direction onto the
viewing plane. This gives the faces the appearance of extending either
parallel to the viewing plane or video monitor screen or extending away
from the screen at an oblique angle. Some routines added shading to the
view to give further visual cues of depth.
More specifically, the operator could typically cause a selected surface,
such as a transverse (x,y) plane on the face (z=0) of the examined volume
to be displayed. The operator could then cause a selected number of
transverse planar slices to be peeled away or deleted by indexing along
the z-axis (z=1,2,3, . . . ,n) to view the nth interior transverse planes.
The operator could then position the cursor on the (x,y) or transverse
plane to select a coronal or (x,z) plane. The selected coronal plane would
then be displayed. The operator would then position the cursor on the
displayed coronal plane to select a sagittal or (y,z) plane. Prior art
medical image workstations commonly permitted the transverse, coronal, or
sagittal planes or views to be displayed concurrently on the same screen.
Some also permitted the three-dimensional projection image to be displayed
concurrently as well.
One of the disadvantages of these prior art systems is that they did not
permit simultaneous, interactive adjustment of the selected transverse,
coronal, and sagittal planes. These prior art adjustments were commonly
based on a two-dimensional reference plane which was always co-planar with
the transverse, sagittal, or coronal planes, therefore restricting the
sectioning cursor to two-dimensional movements. In the display format in
which all three planes were displayed concurrently, the operator moved the
cursor to one of the views, which then became the "active" view. By moving
the cursor on the active view, the next planar slice could be reselected.
By moving the cursor to the readjusted planar slice, the next slice could
be readjusted. Thus, readjusting the displayed transverse, coronal, and
sagittal views was sequential and, therefore, relatively slow and time
consuming.
The present invention contemplates a new and improved method and apparatus
for displaying images which permits concurrent, real-time readjustment of
the transverse, coronal, and sagittal view displays by using a rotatable
3D object (or volume) and its projection view as a three-dimensional
reference surface which allows the sectioning cursor to move in three
dimensions.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a volume object
memory means is provided for holding data values indicative of each voxel
of a volumetric region of the object. An affine transform means rotates,
scales, and translates points, lines, and surfaces of the volumetric
region (object space) into transformed points, lines, and surfaces of a 3D
projection view when displayed on the pixels of a two-dimensional image
plane or video display (image space). The transform means also supplies a
reverse of the selected transform to transform the display pixels into
corresponding locations of the object volumetric region. A video processor
generates a video display of the data values that correspond to the
reverse transformed locations in the volumetric region. An operator uses a
cursor control means to move a cursor on the video display. The transform
means also reversely transforms coordinates of the cursor from the image
plane to a corresponding location in the volumetric region. A plane
defining means defines orthogonal planes, preferably, transverse, coronal,
and sagittal planes, which intersect the reversely transformed location in
the volumetric region. The video processor means receives data values from
the object memory lying along each of the planes and converts them into a
corresponding video image. Preferably, the video processor converts the
two-dimensional projection image representation and the planar images into
images which are displayed concurrently in a common video display.
In accordance with another aspect of the present invention, a third image
space coordinate is determined in accordance with a relative distance
along the viewing direction from the screen pixel at the cursor to a point
of intersection with a displayed voxel of the object.
One advantage of the present invention is that the relationship between the
volume projection view and the transverse, coronal, and sagittal section
(re-sliced) planes is maintained when the volume view is rotated for
better visualization. These planes intersect at the cursor in both object
and image space. The reverse transform between these spaces enables the
planes to be updated correctly in object space regardless of the rotating
(or view direction or orientation) of the volume projection view.
Another advantage of the present invention is that it permits interactive
and simultaneous adjustment of the transverse, coronal, and sagittal
planes.
Another advantage of the present invention is that it assists the operator
in relating the position of the displayed transverse, sagittal, and
coronal planes with their locations through a perspective type view of the
volume.
Another advantage of the present invention is that it permits the operator
to select the intersection point of the transverse, coronal, and sagittal
planes in three dimensions in object space by using a cursor on a
two-dimensional screen.
Still further advantages of the present invention will become apparent to
those of ordinary skill in the art upon reading and understanding the
following detailed description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may take form in various components and arrangements of
components, and in various steps and arrangements of steps. The drawings
are only for purposes of illustrating a preferred embodiment and are not
to be construed as limiting the invention.
FIG. 1 is a diagrammatic illustration of an image data display system in
accordance with the present invention;
FIG. 2 is a diagrammatic illustration of a preferred video display
generated by the present invention;
FIG. 2A illustrates a transverse plane through the volumetric region;
FIG. 2B illustrates a coronal plane through the volumetric region;
FIG. 2C illustrates a sagittal plane through the volumetric region;
FIG. 3 is a diagrammatic explanation of the transverse, sagittal, and
coronal planes relative to a human subject;
FIG. 4 is analogous to FIG. 2 but illustrates a projection view that has at
least one obliquely cut surface;
FIG. 5 is analogous to FIG. 4 but with the perspective view rotated to
another viewing orientation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. 1, a diagnostic imaging device A non-invasively
examines a polyhedral volumetric region of a subject and generates a data
value indicative of each voxel within the volumetric region. The data
values corresponding to voxels of the polyhedron are stored in a
three-dimensional object memory means B. The shape and size of the
volumetric region is generally defined by the diagnostic imaging device.
In the embodiment illustrated in FIG. 2, the region is illustrated as a
rectangular prism, i.e. a six-sided volume having rectangular or square
orthogonal faces. With continuing reference to FIG. 2 and further
reference to FIG. 3, the volumetric region is defined by x, y, and
z-coordinates which are defined in terms of a transverse plane 10, coronal
plane 12, and sagittal plane 14 of a patient or other examined object. For
each voxel within the polyhedral examined volumetric region, the imaging
device A generates a data value, e.g. a CT number, which, for simplicity
of illustration, is retrievable from the object memory B by addressing the
object memory with the (x,y,z) coordinates of the voxel. A data processing
system C processes the three-dimensional object data to generate a video
display D in accordance with instructions input by the operator on an
operator control console or system E.
With reference to FIG. 2, the video display D includes a video display
screen 20 having a plurality of, e.g. four, view ports. Each view port
displays an independently changeable video image. In the preferred
embodiment, a first view port 22 displays a projection image depicting a
projection of the imaged volume onto the video screen or viewing plane 20.
The video screen or viewing plane includes a two-dimensional array of
pixels defined by coordinates (i,j). A third coordinate k is defined in a
direction orthogonal to the i, j-coordinates of the viewing plane. Faces
24, 26, 28 of the 3D projection image are "distorted" to give visual cues
indicative of the depth or distance along the k-axis between the viewing
screen and each point on the surface. The rectangular faces in the
illustrated projection image are displayed as parallelograms with the
angles at the corners changed from orthogonal in proportion to the
relative angular orientation or rotation of the viewing plane relative to
the examined object region. The dimensions of the parallelograms are
likewise foreshortened in accordance with the angular orientation or
rotation. Note that if a face is orthogonal to the viewing plane, it is
displayed full size with 90.degree. corners. However, as the faces appear
to become obliquely oriented toward the viewing screen, the faces are
foreshortened and the change in the angles at the corners of the
parallelograms becomes more pronounced.
With reference to FIGS. 4 and 5, the operator may conveniently position or
rotate the 3D projection image with a selected apparent orientation when
viewed from the viewing plane; conversely, the viewer may re-orient or
rotate the viewing plane around the polyhedral imaged volume. The volume
may be rotated about a selected axis to bring previously hidden faces into
view.
With continuing reference to FIG. 2 and further reference to FIG. 3, the
operator positions a cursor 30 at a selectable location on the first view
port or portion 22 of the video display D. A second view port 32 displays
the data along the transverse plane 10 through the position of the cursor.
In the coordinate system of FIG. 2, the transverse plane is also the (x,y)
plane. In a CT scanner in which a human patient is disposed in a prone
position, the transverse plane is also known as an axial plane. Because
the x, y, and z-coordinates in object space are fixed, the displayed (x,y)
plane is selected by adjusting the selected distance along the z-axis. A
third view port 34 displays an image of the coronal plane 12, i.e. the
(x,z) plane. A fourth view port 36 displays the (y,z) or sagittal plane 14
through the imaged volume which intersects the (x,y,z) position of the
cursor 30.
To index through the available coronal planes, the operator moves the
cursor 30 across face 24 along track 38c. By moving the cursor along track
38s, the sagittal plane is re-positioned left and right in the
illustration of FIG. 2C. To index the transverse planes with the coronal
and sagittal planes, the operator uses either a transverse slice selection
means other than a cursor or tracks along one of paths 38t and 38t'. The
examined volumetric region illustrated at FIG. 2 is through the pelvic
region of the patient. The pelvic bone 40 and lumbar vertebrae 42 are
visible on the surface of the projection image of the first view port 22.
The operator's view of the pelvic bone, lumbar vertebrae, and other
associated tissue is adjusted by moving the cursor 30 until the
transverse, coronal, and sagittal images are optimized for the selected
diagnostic procedure.
Of course, the examined volume may not coincide precisely with the region
that the operator wants to examine. Other tissues and structures such as
air and the patient couch, are commonly examined and imaged along with the
patient. An editing means 44 enables the operator to make an effective
removal of unwanted voxels from the examination region. Although removing
a single selected voxel is conceptually simplest, the operator more
typically removes or edits larger groups of voxels. As is conventional in
the art, the operator may define cutting planes, either parallel to one of
the transverse, coronal, or sagittal planes, or oblique cutting planes.
The operator may also define curved cutting surfaces. A volumetric region
edited into a polygon with at least one oblique surface is illustrated in
FIGS. 4 and 5. Rather than editing voxels based on spatial location, the
operator can also edit voxels based on other criteria. For example, air,
soft tissue, bone, and other types of imaged subject matter have CT
numbers in distinct ranges. The operator can delete all voxels with CT
numbers corresponding to air, for example. As another example, the
operator may choose to edit all voxels except those with CT numbers
corresponding to bone. This provides a skeletal display in the projection
image. As yet another option, the operator may perform a separate editing
for the projection image and the three orthogonal slice images. For
example, the projection image may be a tissue specific depth image with
shading and the three orthogonal images can be interpolated CT number
images. As another example, the projection image can be edited for tissue
type to "peel away" selected tissue types, thereby providing a new surface
for the cursor to traverse. This can be achieved by duplicating the object
memory and accessing the memory holding data edited with one editing
function for the projection image and accessing the memory edited with the
other editing function to display the orthogonal slices. In this manner,
the operator can display, for example, a projection view of a section of
the patient's skeleton to facilitate accurate placement of the cursor
while viewing images of all tissue in the orthogonal slices through the
cursor position.
With reference to FIGS. 4 and 5, in many instances, the displayed
projection image of the volume has one or more oblique surfaces 46. As the
cursor 30 moves along an oblique surface, such as along track 48, all
three of the transverse, coronal, and sagittal planes are indexed
concurrently. Even after the transverse, coronal, and sagittal views are
selected, the operator can rotate the viewing plane or imaged object, such
as between the positions of FIGS. 4 and 5, without affecting the
orientation or other aspects of the display of the transverse coronal and
sagittal planes. The rotation can expose surfaces that were not previously
visible.
With reference again to FIG. 1, the non-invasive examination means A, in
the illustrated embodiment, is a CT scanner. However, other sources of
three dimensional image data both outside the medical imaging field and in
the medical imaging field, such as magnetic resonance imagers, are
contemplated. The non-invasive medical diagnostic apparatus A includes an
examination region 50 for receiving the subject supported on a patient
couch or support 52. An irradiating means 54, such as an x-ray tube,
magnets, or radio frequency coils, irradiates the patient. A radiant
energy receiving means 56, such as radiation detectors, radio frequency
receiving coils, or the like, receive medical diagnostically encoded
radiant energy. In the illustrated CT scanner example, the source of
radiant energy is an x-ray tube which generates a fan-shaped beam of
x-rays. The fan-shaped beam of x-rays passes through the subject in the
examination region 50 impinging upon a ring of x-ray detectors of the
radiant energy detection means 56. The x-ray tube is mounted for rotation
by a motor or other rotating means about the examination region such that
the patient is irradiated from a multiplicity of directions. The radiation
detectors are positioned either in a stationary ring surrounding the
examination ring or in an arc which rotates with the x-ray tube to receive
the radiation that has traversed the patient.
An image reconstruction means 58 reconstructs an image representation from
the received radiation. For example, the image reconstruction means may
reconstruct a 512.times.512 array of data values, each data value being
representative of a radiation transmissive property of a corresponding
voxel of the one plane or slice of the volumetric region. The patient
couch is indexed axially through the examination region between scans to
generate a plurality of slices of image data. Optionally, the patient
couch may be translated continuously such that the x-ray beam passes
through the patient along a spiral path. If spiral data is generated, a
conventional, spiral data reconstruction means is utilized to convert the
spiral data into data values corresponding to each of a three-dimensional
orthogonal array of voxels, e.g. an x, y, z array where x, y, and z are
the coordinate axes of object space. Object space is the (x,y,z)
coordinate system of the patient in the scanner; whereas, image space is
the (i,j, k) coordinate system of the projection image presented in the
first port 22.
The data processing system C includes transform means 60 which translates,
rotates, and scales coordinates, lines, curves, and surfaces from object
space to image space and reversely transforms locations, lines, curves,
and surfaces from image space to object space. More specifically, the
affine transform is a matrix which translates coordinates or vectors x, y,
z in object space to corresponding coordinates or vectors i, j, k in image
space, i.e.:
##EQU1##
Conversely, the reverse of the affine transform matrix converts
coordinates or vectors in image space to corresponding coordinates or
vectors in object space, i.e.:
##EQU2##
The k-coordinate of the projection image is uniquely defined by the i,
j-coordinate. For example, the planes of the polyhedral volumetric region
are mathematically defined in the process of editing the data or otherwise
preparing the data for display. Accordingly, the k value can be retrieved
from a look-up table or otherwise uniquely calculated from this a priori
information. When the viewing angle is changed, the values of the
transform matrix are modified in accordance with trigonometric functions
of the angle of rotation.
The operator control means E includes a mouse, trackball, or other angular
orientation input means 62.sub..theta.x, 62.sub..theta.y, and 62.sub.74 z
for inputting a degree of rotation of the viewing angle about the x, y,
and z-axes to rotate the 3D projection image as illustrated by way of
example in FIGS. 2--4. Viewing angle buffers 64.sub..theta.x,
64.sub..theta.y, and 64.sub..theta.z store the selected viewing angle. A
one-dimensional joystick or other scale input means 66 controls
enlargement and reduction of the viewed 3D volume image. A scale or
magnification buffer 68 stores the selected scale factor. Optionally,
other controls may be provided for translating the viewed 3D volume
projection image.
The affine transform means 60 adds the indicated x, y, and z-translation
factors, multiplies the length and angle of the polyhedral faces from the
volume space by sine and cosine values of the indicated rotation angles,
and multiplies the dimensions by the scale factor. An image space memory
means 70 stores the transformed face polygons and a grid indicative of the
(i,j) pixel locations on the video display D. A data retrieval means 72
identifies each pixel location which falls within one of the polygonal
faces and determines its location relative to that polygon.
A depth from the viewing plane determining means 74 determines a depth or
distance k in the viewing direction from the viewing plane to a point of
intersection with a viewed voxel of the imaged volume. More specifically,
the depth determining means 74 determines the distance from the cursor
pixel of the viewing plane to a point of intersection with the underlying
face. The depth may be determined, for example, from a look-up table
addressed by (i,j), by the conventional ray tracing technique in which a
length of a ray projected in the viewing direction from the corresponding
pixel of the viewing plane to a point of intersection with the object is
determined, or the like. It is to be appreciated, that the point of
intersection need not be on the surface 26. As indicated above, some
voxels of the object may be given a value which renders them invisible to
the viewer. For example, only data values within object space which have a
CT number corresponding to a selected tissue type, such as bone, may be
displayed in a surface rendered image based on a depth image. In this 3D
appliation, 3D tissue surfaces are created by allowing the operator to
select a tissue type such as bone, and then other tissue types are
segmented out. In this 3D technique, the depth from the screen to the
surface is commonly looked-up from a visible surface memory buffer, or is
determined with a suitable ray tracing technique. Data values
corresponding to air and other tissue types are set to zero, or another
value which indicates that they are not displayed. As the cursor 30 moves
across the patient's face, such as across the patient's nose, the depth
from the viewing plane to the viewable voxels changes, causing a
corresponding change in the location of the transverse plane. If the
cursor moves obliquely across face 24 as well, all three displayed planes
change concurrently.
The data retrieval means 72 accesses the transform means 60 and the depth
means 74 to cause the image space pixel locations to be transformed with
the reverse of the transform indicated by the buffers 64, 68. The reverse
transform of the (i,j,k) pixel location provides a corresponding (x,y,z)
coordinate in object space. A memory access means 76 uses the object space
coordinates to retrieve the corresponding data values from the object
memory B.
Although reversely transformed coordinates of the 3D projection image can
fall directly on voxels of object space, the coordinates in many instances
will fall in between. To this end, an interpolating means 80 interpolates
the data values corresponding to the two, four, or eight closest voxels to
the reversely transformed coordinates, in inverse proportion to the
relative proximity.
The retrieved, interpolated values from the object memory B are converted
by a video processor 82 into a video display on a video display means D.
If the video processor can generate images with more than one pixel
format, it is connected with the image space memory 70 for supplying an
indication of the selected pixel grid. Optionally, a video memory 84 may
be provided. The video memory has a first portion 86 corresponding to the
first video port into which the data for the projection image is loaded.
The video processor 82 then converts the data from the video memory into a
video signal to drive the video display.
The operator control panel E further includes a cursor positioning means
90, such as a mouse or trackball for indicating the (i,j) location of the
cursor relative to the projection image. A cursor image control means 92
is connected between the cursor positioning means and the video processor
82 to cause the cursor 30, such as a crosshair, to be displayed at the
selected (i,j) coordinates indicated by the cursor positioning means.
Optionally, the transverse (or other) slice may be selected by a z- (or
other) axis control 94 including associated circuitry or buffers 96. As
the z-control is indexed, slices on the front face 24 of the displayed
three-dimensional object are "peeled away". That is, the displayed front
face is removed and the next plane down becomes the frontmost face of the
volumetric region. This process is repeated until a selected transverse
plane is reached. The cursor control 90 increments the i and j-coordinates
of the cursor crosshair, causing the crosshair to be shifted vertically
and horizontally across the video display. The k-coordinate is selected
either from the depth measuring means 74 or the z-control 94.
The i, j, and k-coordinate corresponding to the cursor is conveyed to the
transform means 60 which performs a reverse of the selected transform on
cursor location to transform it from image space to the corresponding x,
y, z-coordinate of object space.
A transverse or (x,y) plane defining means 100 converts the designated
(x,y,z) coordinate into an identification of the transverse or (x,y)
plane. As illustrated in FIG. 2A, the transverse or (x,y) plane has a
fixed orientation in object space. Only the z-location in object space is
necessary to identify the (x,y) plane. A coronal or (x,z) plane defining
means 102 defines the addresses of the selected coronal plane in the
object memory B. Again, as illustrated in FIG. 2B, because the orientation
of the coronal cursor coordinate in object space is fixed, the position of
the plane along the y-axis determines the coronal plane. Analogously, a
sagittal or (y,z) plane defining means 104 converts the received cursor
coordinates into the appropriate addresses in the object memory for the
sagittal plane. The CT or other data values at the addresses for t | | |
