U.S. patent application number 17/320579 was filed with the patent office on 2021-11-11 for method of reducing the x-ray dose in an x-ray system.
This patent application is currently assigned to 3SHAPE A/S. The applicant listed for this patent is 3SHAPE A/S. Invention is credited to Henrik OJELUND.
Application Number | 20210345982 17/320579 |
Document ID | / |
Family ID | 1000005738753 |
Filed Date | 2021-11-11 |
United States Patent
Application |
20210345982 |
Kind Code |
A1 |
OJELUND; Henrik |
November 11, 2021 |
METHOD OF REDUCING THE X-RAY DOSE IN AN X-RAY SYSTEM
Abstract
A method of reducing the x-ray dose of a patient in an x-ray
system includes defining a region of interest of the patient,
obtaining at least two tracking images of a tracking element taken
with at least one camera having a known positional relationship
relative to an x-ray source and/or sensor, determining any movement
of the tracking element between the acquisition of at least two
tracking images, adjusting the collimator of the x-ray source to
compensate for any movement of the tracking element between the
acquisition of the at least two tracking images, providing that the
field of exposure of the x-ray source is confined to the region of
interest and obtaining at least one x-ray image of the region of
interest after the adjustment of the collimator.
Inventors: |
OJELUND; Henrik; (Kgs.
Lyngby, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3SHAPE A/S |
Copenhagen K |
|
DK |
|
|
Assignee: |
3SHAPE A/S
Copenhagen K
DK
|
Family ID: |
1000005738753 |
Appl. No.: |
17/320579 |
Filed: |
May 14, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16701604 |
Dec 3, 2019 |
11020082 |
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17320579 |
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16452601 |
Jun 26, 2019 |
10524759 |
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16701604 |
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15561739 |
Sep 26, 2017 |
10376231 |
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PCT/EP2016/056387 |
Mar 23, 2016 |
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16452601 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 6/582 20130101;
A61B 6/486 20130101; A61B 6/488 20130101; A61B 6/501 20130101; A61B
5/721 20130101; A61B 6/14 20130101; A61B 6/542 20130101; A61B 6/547
20130101; A61B 6/0487 20200801; A61B 6/469 20130101; A61B 5/1127
20130101; A61B 6/545 20130101; A61B 6/032 20130101; A61B 6/0492
20130101 |
International
Class: |
A61B 6/00 20060101
A61B006/00; A61B 6/03 20060101 A61B006/03; A61B 6/04 20060101
A61B006/04; A61B 6/14 20060101 A61B006/14; A61B 5/11 20060101
A61B005/11; A61B 5/00 20060101 A61B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2015 |
DK |
PA 2015 70179 |
Claims
1-11. (canceled)
12. A method of obtaining medical images of a patient using a
medical imaging device, the method comprising: defining a region of
interest of the patient; obtaining at least two tracking images of
a tracking element taken with at least one camera having a known
positional relationship relative to the medical imaging device;
determining any movement of the tracking element between the
acquisition of at least two tracking images; obtaining a plurality
of images of the region of interest simultaneously with the
tracking images; and dynamically adjusting the medical imaging
device to compensate for any movement of the tracking element
between the acquisition of the at least two tracking images.
13. The method of claim 12, wherein the medical imaging device
obtains an x-ray image.
14. The method of claim 12, wherein the medical imaging device is a
magnetic resonance imaging device.
15. The method of claim 12, wherein the medical imaging device
comprises is a positron emission tomography device.
16. The method of claim 12, wherein the medical imaging device is a
cone beam computed tomography (CBCT) scanner.
17. The method of claim 16, wherein the at least one medical image
are x-ray images defining a panoramic trajectory, wherein the
method further comprises: adjusting the CBCT scanner to follow the
determined panoramic trajectory based on the determined movement
from the tracking element.
18. The method of claim 16, wherein the cone beam computed
tomography system is configured to take one of a panoramic x-ray
image, a cephalometric image, or any other type of 2-dimensional
x-ray image or a 3D cone beam computed tomography scan of the
patient.
19. The method of claim 12, wherein dynamically adjusting comprises
dynamically adjusting a collimator of a radiation source of the
cone beam computed tomography scanner.
20. The method of claim 12, wherein a scout image is taken with a
lower resolution/image quality using the medical imaging device,
and the region of interest is defined using the scout image.
21. The method of claim 12, wherein a scout image is taken using a
face scanner, an intra-oral scanner and/or a surface contour laser
scanner, and the region of interest is defined using the scout
image.
22. The method of claim 12, wherein a scout image is taken using an
imaging device to obtain a 2-D image, and the region of interest is
defined using the scout image.
23. The method of claim 12, wherein the tracking element comprises
a predefined geometry and/or predefined information.
24. The method of claim 12, wherein determining any movement of the
tracking element between the acquisition of at least two tracking
images comprises: recognizing a plurality of fiducial markers in
each tracking image; obtaining a digital representation in a
database of the known predefined pattern and/or shape of the
fiducial markers; and recognizing the pattern of the fiducial
markers in each image to achieve a best fit to the known predefined
pattern of the fiducial markers on the tracking element from each
tracking image.
25. The method of claim 24, wherein determining any movement of the
tracking element between the acquisition of at least two tracking
images comprises: recognizing a plurality of the individual
fiducial markers in each tracking image; using classification of
the indices of the fiducial markers; and matching the known pattern
of the fiducial markers on the tracking element to the pattern of
the fiducial markers on the tracking image using the classification
of the indices of the fiducial markers.
26. The method of any claim 12, wherein the images are combined to
make a digital medical model.
27. A system for obtaining medical images of a patient, the system
comprising: a medical imaging device; one or more tracking image
cameras configured to take tracking images of a tracking element; a
computer device comprising a microprocessor and a computer readable
medium; a visual display unit; and input means for controlling the
medical imaging device; wherein the computer device is configured
to the medical imaging device in response to determined movement of
the tracking element.
28. The system of claim 27, wherein the computer device is further
configured to adjust the medical imaging device by changing the
geometry of the medical imaging device.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 16/701,604, filed on Dec. 3, 2019, which is a continuation of
U.S. application Ser. No. 16/452,601, filed on Jun. 26, 2019, Now
U.S. Pat. No. 10,524,759, which is a continuation of U.S.
application Ser. No. 15/561,739, filed on Sep. 26, 2017, now U.S.
Pat. No. 10,376,231, which is a national stage application of
International Application No. PCT/EP2016/056387, filed on Mar. 23,
2016, and which claims the priority of Danish Patent Application
No. PA 2015 70179, filed on Mar. 27, 2015. The contents of U.S.
application Ser. No. 16/701,604, U.S. application Ser. No.
16/452,601, U.S. application Ser. No. 15/561,739, International
Application No. PCT/EP2016/056387, and Danish Patent Application
No. PA 2015 70179 are incorporated herein by reference.
TECHNICAL FIELD
[0002] This invention generally relates to a system and method for
controlling the collimator in a medical imaging device. More
particularly, the invention relates to the tracking of patient
movements during image acquisition in a medical imaging device, in
particular in Cone Beam Computed Tomography (CBCT) scanners, and
using this information to direct the x-rays to a defined Region of
Interest (ROI).
BACKGROUND
[0003] Computed tomography, particularly x-ray computed tomography
(CT), is a widely used volumetric imaging principle. In general
terms, a radiation source and a radiation-sensitive image sensor
are arranged on a line, with the subject of the examination
positioned in between. The subject attenuates the radiation. The
source-detector arrangement is typically moved into several
positions, often on a circle or segment thereof, around the subject
of the examination, and images are taken at every position. The
spatial, volumetric distribution of the attenuation coefficient
within the subject can then be reconstructed from all images, for
example using the filtered back projection algorithm, generating a
3D digital model of the subject. Often, the image sensor is a 2D
sensor, such as in cone beam computed tomography (CBCT). In
medicine, x-ray CT scanners are valuable non-invasive diagnostic
devices.
[0004] A major concern related to the use of CT scanners in
medicine is radiation dose. Accordingly, a large body of research
has focused on volumetric reconstruction algorithms that exploit
the image data in an optimal way, allowing fewer images to be
taken, or a lower dose per image, for a given quality of the
reconstruction. While filtered back projection is a direct
algorithm, many refined algorithms are iterative ones. Because the
volumetric reconstruction problem is ill-posed, various
regularization approaches have been suggested, e.g., total
variation. Maximum-likelihood estimation has also been proposed,
for example with a prior based on material assumptions. Several
proposed reconstruction algorithms contain some of the above
elements, or all of them.
[0005] Another way to lower the needed dose in a CBCT system is to
make sure the patient does not move during image acquisition. This
is because for a given needed accuracy, the signal-to-noise ratio
will be greater when the patient does not move. Also, when the
patient moves, motion artifacts such as for example streaks and
aliasing may deteriorate the image quality. Therefore, in general,
the image quality will be better when patient movement is kept to a
minimum.
[0006] In prior art CBCT systems, various forms of head fixation
devices have been employed to keep the patient fixated during the
x-ray recording. These systems all have the goal of minimizing
effects from motion blur and patient movement, thereby achieving a
higher accuracy of the final images. However, all these systems
have the disadvantage that it may be uncomfortable for the patient
to be fixated for the duration of the scan, in particular for
patients that may suffer from claustrophobia. It therefore remains
a problem to achieve a high accuracy of CBCT images without having
to fixate the patient.
[0007] Yet another way to lower the used dose in a CBCT system is
to accurately define a region of interest (ROI). Many existing CT
scanners allow the selection of a region of interest, but the
selection is made schematically, and in order to ascertain that the
relevant volume is covered, the region of interest suggested by the
system is often larger than necessary for a particular patient.
Also, since there is a risk that the patient moves during x-ray
image acquisition, the chosen ROI is often larger than ideally
necessary, in order to make certain that the whole ROI is covered
in a single scan. It may be useful if the CT scanner allowed
realization of the adjustment of the region of interest by for
example four independent collimator shutters for the top, bottom,
left, and right sides of the beam.
SUMMARY
[0008] In one aspect there is disclosed a method of obtaining
medical images of a patient using a medical imaging device, the
method comprising: [0009] defining a region of interest of the
patient; [0010] obtaining at least two tracking images of a
tracking element taken with at least one camera having a known
positional relationship relative to a radiation source and/or
sensor; [0011] determining any movement of the tracking element
between the acquisition of at least two tracking images; [0012]
adjusting the medical imaging device based on the determined
movement of the tracking element between the acquisition of the at
least two tracking images so that the radiation passes through the
region of interest; and [0013] obtaining at least one medical image
of the region of interest after the adjustment of the medical
imaging device.
[0014] In this way, it is insured that even if the patient moves
during the acquisition of medical images, the radiation is confined
to the region of interest, thereby making it possible to for
example define a smaller region of interest.
[0015] In another aspect there is disclosed a method of obtaining
one or more x-ray images of a patient, the method comprising:
[0016] defining a region of interest of the patient; [0017]
obtaining at least two tracking images of a tracking element taken
with at least one camera having a known positional relationship
relative to an x-ray source and/or sensor; [0018] determining any
movement of the tracking element between the acquisition of at
least two tracking images; [0019] adjusting the collimator of the
x-ray source to compensate for any movement of the tracking element
between the acquisition of the at least two tracking images,
providing that the field of exposure of the x-ray source is
confined to the region of interest; and [0020] obtaining at least
one x-ray image of the region of interest after the adjustment of
the collimator.
[0021] In X-ray optics, a collimator is a device that filters a
stream of rays so that only those traveling parallel to a specified
direction are allowed through. Collimators are used in X-ray optics
because it is not yet possible to focus radiation with such short
wavelengths into an image through the use of lenses as is routine
with electromagnetic radiation at optical or near-optical
wavelengths. Without a collimator, rays from all directions will be
recorded; for example, a ray that has passed through the top of the
specimen but happens to be travelling in a downwards direction may
be recorded at the bottom of the plate, resulting in a blurred
image.
[0022] Accordingly, it is thus possible to compensate for any
unwanted movement the patient makes during acquisition of the x-ray
images. The movement of the tracking element corresponds to a
movement of the patient, and since there is a feedback between the
determination of the movement of the tracking element and the
collimator, it is possible to focus the x-rays on the region of
interest, even if the patient has moved.
[0023] In some embodiments a scout image is taken of the patient.
The scout image may be taken with a lower resolution/image quality
using the x-ray source and sensor, or the scout image may be taken
using a surface imaging device, for example using a face scanner,
an intra-oral scanner and/or a surface contour laser scanner, and
the region of interest is defined using the scout image.
[0024] In this way, the region of interest chosen will correspond
to the exact geometry of the patient, rather than using a generic
or standard geometry to define the region of interest.
[0025] In some embodiments, the predefined information of the
tracking element comprises at least one fiducial marker, such as a
plurality of fiducial markers in a predefined pattern, size, shape
and/or colour.
[0026] When the placement, size, shape and/or colour of the
fiducial markers are already known with very high accuracy before
any images are taken, it is possible to determine with very high
accuracy the movement of the tracking element between images. In
prior art systems, landmarks on the patient have been used to track
any movement of the patient. However, this is not as accurate as
using a tracking element, for example comprising fiducial markers
placed on the tracking element with a very high and known
placement, because unlike in the current disclosure, the landmarks
have to first be determined or marked by an operator or by computer
software. This means that the exact position of the landmarks will
not be as accurate as using a tracking element. Also, when taking
for example a series of chest x-rays, the breathing of the person
will affect the relative positions of the landmarks, so that this
in itself will lead to a less accurate result.
[0027] In some embodiments, the tracking images and the x-ray
images are time stamped using the same clock.
[0028] One way to correlate the movement of the patient with the
x-ray data, is to map the movement of the tracking element in time
with the recording of the x-ray data. In principle, the cameras
recording the tracking element and the x-ray sensor could be run
using two separate processors with each their own clock. However,
in this case, the two clocks would have to be synchronized in order
to be able to map exactly the movement of the patient with the
medical imaging data. A simpler solution is to have both the
cameras and the x-ray device run using the same clock. This can be
accomplished for example by running the cameras and the x-ray
device from the same computer processor. The computer processor may
be a stand-alone desktop or laptop computer or any other type of
computer means, or it may be integrated in the scanner.
[0029] In some embodiments, determining the position and
orientation of the tracking element at each time stamp comprises:
[0030] recognizing a plurality of the individual fiducial markers
in each tracking image; [0031] obtaining a digital representation
in a database of the known predefined pattern and/or shape of the
fiducial markers; [0032] recognizing the pattern of the fiducial
markers in each image to achieve a best fit to the known predefined
pattern of the fiducial markers on the tracking element from each
tracking image.
[0033] In order to determine the orientation and position of the
tracking element, image analysis algorithms can be used. For
example, if the fiducial markers are in the form of dots of a known
size, the algorithms can be used to detect where there are dots and
what size they have. The method used may for example be principal
component analysis (PCA), although other methods are also possible
and known to the person skilled in the art.
[0034] Since the fiducial markers have a known size, shape and/or
predefined pattern on the tracking element, once the size, shape
and position of each found dot is determined, a mask comprising the
known predefined pattern of the fiducial markers can by loaded from
a database, be overlayed on the tracking image, and the fit of the
tracking image to the mask can be determined, thereby finding the
orientation and position of the tracking element.
[0035] In some embodiments there may be more than one camera, such
as two cameras or three cameras for recording the movement of the
tracking element. The reason for this, is that if only one camera
is used, it is difficult to unambiguously determine how far away
from the camera the fiducial marker is. If two cameras are used, it
is difficult to unambiguously determine the position of the
tracking element in a direction that is parallel to a line
connecting the two cameras. If, on the other hand, three cameras
are used, possibly but not necessarily, placed for example at the
points of an equilateral triangle, the position of the tracking
element in all three dimensions can be unambiguously
determined.
[0036] Determining the position and orientation of the tracking
element using three cameras, can be accomplished for example by
having the images from the three cameras time stamped so that at
each time t, there are three images taken of the element,
recognizing the fiducial markers in each image, determining a best
fit to the known predefined pattern of the fiducial markers on the
tracking element in each image, determining the position and
orientation of the tracking element in each of the three images of
the tracking element at each time stamp, and computing a weighted
average of the position and orientation of the tracking element
from the three images.
[0037] In some embodiments, determining the position and
orientation of the tracking element at each time stamp comprises:
[0038] recognizing a plurality of the individual fiducial markers
in each tracking image; [0039] using classification of the indices
of the fiducial markers; and [0040] matching the known pattern of
the fiducial markers on the tracking element to the pattern of the
fiducial markers on the tracking image using the classification of
the indices of the fiducial markers.
[0041] Matching the known pattern of the fiducial markers may for
example be accomplished using a computer device, where the tracking
images are loaded, and the fiducial markers are recognized and/or
segmented in the tracking images. Then, the position of the
fiducial markers in the tracking image are indexed, and the index
of the fiducial markers in the tracking image are compared to the
known index of the fiducial markers on the tracking element. Since
the distance between the fiducial markers on the tracking element
is known, the distances between the fiducial markers in the
tracking images can be compared to the known distances, and known
mathematical algorithms can be used to determine the position and
rotation of the tracking element in the tracking images.
[0042] In some embodiments, the camera position and rotation of
each camera is calibrated or determined; [0043] the intrinsic
parameters such as the focal length, skew, principal point and lens
distortion are calibrated or determined for each camera; [0044] the
tracking images from the three cameras are acquired simultaneously
such that at each time t, there are three images taken of the
tracking element; [0045] the fiducial markers are recognized in
each tracking image and the position of each fiducial marker is
determined directly in the camera co-ordinate frame; [0046] the
position and/or orientation of the tracking element from the three
images is determined using a cost function to minimize the
difference in the determined position of the fiducial markers in
each of the tracking images.
[0047] Since extrinsic parameters of the cameras are known (i.e.
the position and rotation of the cameras with relation to the
medical imaging device), and the fiducial markers are recognized in
each image and the position of the fiducial markers are determined
directly in the co-ordinate frame of the camera, the determination
of the position and rotation of the tracking element relative to
the medical imaging device will be more accurate.
[0048] In some embodiments, the tracking element is attached to a
headband, which can be placed on the patient's head. It is an
advantage if the headband is adjustable, since it should be
possible to securely attach the headband to patients with different
head sizes such as children and adults, without any risk of the
headband moving during the exposure time.
[0049] The tracking element may have only one fiducial marker, but
preferably should have a plurality of fiducial markers on its
surface, for example in the form of dots or circles. There may be
any number of fiducial markers, for example more than 10, more than
100, more than 200 or more than 400 dots. Preferably there should
be enough dots to make it simple to find the position and size of
the dots, but not so many that it would take too much processing
time.
[0050] In some embodiments, there are asymmetrical features on the
tracking element or the tracking element itself is asymmetrical. In
principle, it is possible to determine the position and orientation
of the tracking element even if the fiducial markers are all placed
in a completely symmetrical pattern. In this case, it would be
assumed that the tracking element has moved the shortest possible
distance that is consistent with the pattern of the fiducial
markers, between each time stamp. However, if the fiducial markers
are placed asymmetrically, or if the tracking element itself is
asymmetrical, there is no ambiguity in when overlaying the mask of
the known predefined pattern with the image of the tracking
element.
[0051] The adjustment of the collimator should take place
substantially in real time during acquisition of the x-ray images.
In this way, any movement of the patient will be reflected in the
adjustment of the collimator. The adjustment of the collimator may
comprise tilting the collimator, moving the collimator in a
horizontal and/or vertical direction and/or any other direction,
and/or changing any other characteristics of the collimator such as
the size of the opening of the collimator.
[0052] There are many different designs of collimators, and any
collimator can be used with this invention. The collimator may for
example be a set of four lead plates that can be individually
adjusted, to change the size of the opening and the direction of
the x-rays, or it may be a grid of rods that can be adjusted to
create a similar effect, or any other design that is capable of
directing the x-rays.
[0053] The inventive concept of this specification can be used
advantageously in any medical imaging device where it is important
that the patient is still during imaging, such as standard x-ray,
magnetic resonance imaging, positron emission tomography, etc.
However, it is particularly useful in CBCT systems where it is very
important to get a very high accuracy of the scan, and where it is
important to achieve a low dose of x-ray exposure.
[0054] In some embodiments, the fiducial markers are in the form of
circular dots. Dots or circles are simple geometrical features,
that are easily recognized by computer algorithms.
[0055] In some embodiments, the x-ray images are combined to form a
digital medical model.
[0056] In some embodiments, the system may include a mouthpiece for
helping the patient stay still during the exposure. The mouthpiece
may be in the form of a plate attached to the medical imaging
device, and configured to allow the patient to bite onto the
plate.
[0057] The tracking element in this specification can be made from
any material such as plastic, glass, metal or the like. It is,
however important that the tracking element is made out of a
material that is substantially rigid, so that the known pattern of
fiducial markers will not be distorted over time.
[0058] In some embodiments, the tracking element is made of coated
glass, and the fiducial markers are printed on the surface of the
glass. This material is both rigid, and it is relatively simple to
etch or print fiducial markers on the surface of the glass with
high accuracy.
[0059] In some embodiments, disclosed is a method of reducing the
x-ray dose of a patient in an x-ray system, the method comprising:
[0060] defining a region of interest of the patient; [0061]
obtaining a first tracking image of a tracking element taken with
at least one camera having a known positional relationship relative
to an x-ray source and/or sensor, said tracking images depicting at
least a part of the tracking element; [0062] obtaining a second
tracking image of the tracking element taken with the at least one
camera; [0063] determining any movement of the tracking element
between the acquisition of the first and second tracking images;
[0064] adjusting the collimator of the x-ray system to compensate
for any movement of the tracking element between the acquisition of
the first and second tracking images providing that the field of
exposure of the x-ray source is confined to the region of
interest.
[0065] Since the collimator is adjusted to compensate for any
movement of the patient, the region of interest can be defined more
narrowly than if there was no compensation for the movement of the
patient. Therefore, the effective x-ray dose the patient receives
will be less than if there was no collimator adjustment.
[0066] In some embodiments, the x-ray system is configured to
obtain one of a panoramic x-ray image, a cephalometric image, or
any other type of 2-dimensional x-ray image.
[0067] In some embodiments, the x-ray system is configured to
obtain a 3-dimensional digital model of at least a part of the
patient, such as for example a CBCT scan.
[0068] In this way, the use of the feedback between the tracking
element and the collimator of the x-ray source can be used to
reduce the dose and/or raise the accuracy of any x-ray image,
whether it is a 2D-image or a 3D digital model.
[0069] In another aspect, disclosed is a method of controlling the
region of interest of a patient imaged using a medical imaging
device, the method comprising:
[0070] defining a region of interest of the patient;
[0071] obtaining a first tracking image of a tracking element taken
with at least one camera having a known positional relationship
relative to a radiation source and/or sensor, said tracking image
depicting at least a part of the tracking element;
[0072] obtaining a second tracking image of the tracking element
taken with the at least one camera;
[0073] determining any movement of the tracking element between the
acquisition of the first and second tracking images;
[0074] adjusting the position of the radiation source and/or
radiation sensor of the medical imaging system to compensate for
any movement of the tracking element between the acquisition of the
first and second tracking images providing that the field of
exposure of the radiation source is confined to the region of
interest.
[0075] In this way it is possible to confine the field of exposure,
for example of an x-ray source to the region of interest on the
patient without adjusting the collimator, but instead by changing
the geometry of the medical imaging device. For example, in the
case of a CBCT system, the x-ray source and x-ray sensor are placed
on a ring capable of rotating around the patient. In this way, if
the patient has moved as determined from the position of the
tracking element in a series of tracking images, the ring
containing the x-ray source and sensor can be rotated to better
align the x-rays with the region of interest. Of course, depending
on the movement of the patient and the exact geometry of the setup
of the medical imaging device, the x-ray source may not be confined
completely within the region of interest of the patient. However,
it will in most cases be better confined to the region of interest
using this setup.
[0076] In some embodiments, the medical imaging device is a CBCT
scanner, and the at least one medical image are x-ray images
defining a panoramic trajectory, wherein the method further
comprises: [0077] adjusting the CBCT scanner to follow the
determined panoramic trajectory based on the determined movement
from the tracking element.
[0078] In some cases, it is desired to obtain a panoramic x-ray. A
panoramic x-ray is a two-dimensional image that captures the entire
oral area in one image, including teeth, upper and lower jaws, and
the surrounding structures and tissues. When using a CBCT system, a
panoramic trajectory is defined, so that the patient is exposed to
the x-rays in a predetermined path that allows for capturing the
panoramic x-ray. If the patient moves during this time, the
panoramic trajectory may no longer be in correspondence with the
actual trajectory, meaning that the resulting panoramic image may
be blurred. In this case, the panoramic trajectory can be corrected
based on the determined movement of the tracking element. This can
be accomplished by adjusting the position and/or exposure of the
x-ray source and/or sensor based on the determined movement of the
tracking element. In another aspect, disclosed herein is a system
for obtaining medical images of a patient, the system comprising:
[0079] a medical imaging device comprising; [0080] one or more
tracking image cameras configured to take tracking images of a
tracking element; [0081] a computer device comprising a
microprocessor and a computer readable medium; [0082] a visual
display unit; [0083] input means for controlling the medical
imaging device; wherein the computer device is configured to adjust
the medical imaging device in response to determined movement of
the tracking element.
[0084] This system comprises the means for performing the methods
according to the previous aspects and embodiments.
[0085] In some embodiments, the computer device is configured to
adjust the medical imaging device by adjusting a collimator of the
medical imaging device.
[0086] In this way, the computer device can adjust for example the
beam of an x-ray source, by adjusting the collimator of the x-ray
machine.
[0087] In some embodiments, the computer device is configured to
adjust the medical imaging device by changing the geometry of the
medical imaging device.
[0088] In this case, instead of adjusting a collimator of the
medical imaging device, the geometry of the medical imaging device
can be changed. For example, in a CBCT scanner, the ring on which
the x-ray sensor and x-ray source are attached, the computer device
can adjust the position of the ring, so that the x-ray sensor
and/or x-ray source are moved relative to the patient.
[0089] In the context of this specification, the term medical
imaging device covers any device capable of taking medical images
of a patient, such as x-ray, magnetic resonance imaging, computed
tomography, positron emission tomography, cone beam computed
tomography etc.
[0090] In the context of this specification, the term tracking
element should be understood to mean any device that can be
attached to the patient for the purpose of determining their
movement, and should therefore not be confined to mean only a flat
rectangular piece of metal or plastic. In principle, the form of
the tracking element could be for example circular, semi-circular,
pyramidal, triangular, or any other shape. The tracking element
could even be a complex three dimensional shape, where the shape of
the tracking element itself is used as the fiducial markers.
EMBODIMENTS
[0091] 1. A method of obtaining medical images of a patient using a
medical imaging device, the method comprising: [0092] defining a
region of interest of the patient; [0093] obtaining at least two
tracking images of a tracking element taken with at least one
camera having a known positional relationship relative to a
radiation source and/or sensor; [0094] determining any movement of
the tracking element between the acquisition of at least two
tracking images; [0095] adjusting the medical imaging device based
on the determined movement of the tracking element between the
acquisition of the at least two tracking images so that the
radiation passes through the region of interest; and [0096]
obtaining at least one medical image of the region of interest
after the adjustment of the medical imaging device.
[0097] 2. The method according to embodiment 1, wherein adjusting
the medical imaging device based on the determined movement of the
tracking element between the acquisition of the at least two
tracking images comprises adjusting the collimator of the radiation
source to compensate for any movement of the tracking element
between the acquisition of the at least two tracking images,
providing that the field of exposure of the radiation is confined
to the region of interest.
[0098] 3. The method according to embodiment 1, wherein adjusting
the medical imaging device based on the determined movement of the
tracking element between the acquisition of the at least two
tracking images comprises changing the geometry of the medical
imaging device, so that either the radiation sensor and/or source
is moved relative to the region of interest, based on the
determined movement of the tracking element.
[0099] 4. The method according any of the preceding embodiments,
wherein the medical imaging device comprises an x-ray source and
sensor, and a scout image is taken with a lower resolution/image
quality using the x-ray source and sensor, and the region of
interest is defined using the scout image.
[0100] 5. The method according to any of the preceding embodiments,
wherein a scout image is taken using a face scanner, an intra-oral
scanner and/or a surface contour laser scanner, and the region of
interest is defined using the scout image.
[0101] 6. The method according to any of the preceding embodiments,
wherein the tracking element comprises a predefined geometry and/or
predefined information.
[0102] 7. The method according to any of the preceding embodiments,
wherein determining any movement of the tracking element between
the acquisition of at least two tracking images comprises; [0103]
recognizing a plurality of fiducial markers in each tracking image;
[0104] obtaining a digital representation in a database of the
known predefined pattern and/or shape of the fiducial markers;
[0105] recognizing the pattern of the fiducial markers in each
image to achieve a best fit to the known predefined pattern of the
fiducial markers on the tracking element from each tracking
image.
[0106] 8. The method according to any of embodiments 1-7, wherein
determining any movement of the tracking element between the
acquisition of at least two tracking images comprises: [0107]
recognizing a plurality of the individual fiducial markers in each
tracking image; [0108] using classification of the indices of the
fiducial markers; and [0109] matching the known pattern of the
fiducial markers on the tracking element to the pattern of the
fiducial markers on the tracking image using the classification of
the indices of the fiducial markers.
[0110] 9. The method according to any of the preceding embodiments,
wherein the x-ray images are combined to make a digital medical
model.
[0111] 10. The method according to any of the preceding
embodiments, wherein the medical imaging device is a cone beam
computed tomography scanner.
[0112] 11. The method according to embodiment 10, wherein the at
least one medical image are x-ray images defining a panoramic
trajectory, wherein the method further comprises: [0113] adjusting
the CBCT scanner to follow the determined panoramic trajectory
based on the determined movement from the tracking element.
[0114] 12. The method according to embodiment any of the preceding
embodiments, wherein the x-ray system is configured to take one of
a panoramic x-ray image, a cephalometric image, or any other type
of 2-dimensional x-ray image or a CBCT scan of the patient.
[0115] 13. A system for obtaining medical images of a patient, the
system comprising: [0116] a medical imaging device comprising;
[0117] one or more tracking image cameras configure to take
tracking images of a tracking element; [0118] a computer device
comprising a microprocessor and a computer readable medium; [0119]
a visual display unit; [0120] input means for controlling the
medical imaging device; wherein the computer device is configured
to adjust the medical imaging device in response to determined
movement of the tracking element.
[0121] 14. The system according to embodiment 13, wherein the
computer device is configured to adjust the medical imaging device
by adjusting a collimator of the medical imaging device.
[0122] 15. The system according to embodiment 13, wherein the
computer device is configured to adjust the medical imaging device
by changing the geometry of the medical imaging device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0123] The above and/or additional objects, features and advantages
of the present invention, will be further described by the
following illustrative and non-limiting detailed description of
embodiments of the present invention, with reference to the
appended drawings, wherein:
[0124] FIG. 1 shows a flow chart of a method according to an
embodiment of this invention.
[0125] FIG. 2 shows a flow chart of a method according to an
embodiment of this invention.
[0126] FIG. 3 shows a tracking element according to an embodiment
of this invention.
[0127] FIG. 4 shows a CBCT scanning system according to an
embodiment of this invention.
[0128] FIG. 5 shows a stylized view of a collimator according to an
embodiment of this invention.
[0129] FIG. 6 shows a schematic of a system according to an
embodiment of the invention.
DETAILED DESCRIPTION
[0130] An embodiment of the method disclosed herein is shown in
FIG. 1.
[0131] In step 101, a scout image is taken of the patient using the
x-ray source and sensor, typically at a lower resolution and/or
image quality than what is used in the subsequent exposure. Lower
resolution and/or image quality may comprise for example using a
lower x-ray dose, if the scout image is taken using x-rays. While
the scout image is taken, a head tracking system is started. The
head tracking system comprises at least one camera, which is
configured to take images of a tracking element attached to the
head of the patient. The position and orientation of the tracking
element is determined in step 102, and at subsequent times,
tracking images are taken of the tracking element, and the position
and orientation of the tracking element is determined. Based on
this determination, the movement of the tracking element, and
therefore the movement of the patient, may be determined
substantially continuously. In step 103, a region of interest is
defined using the scout image. The scout image may for example be
displayed on a touch screen or on a computer that has controls for
the x-ray scanner, and the region of interest may be defined
interactively by the operator, or it may be suggested automatically
by the system. Once the region of interest is defined, the
resolution of the x-ray scanner may be set to a higher
resolution/image quality, if this is needed for the final x-ray
images. In step 104, the collimator controlling the path of the
x-rays is dynamically adjusted based on the determined movement of
the patient, so that the x-rays are confined to expose the region
of interest. In this way, even if the patient moves during the
x-ray image generation, which could comprise one or more of a CBCT
scan, a panoramic image, a cephalometric image or any other type of
x-ray, only the region of interest will be subject to x-ray
exposure. Therefore, the region of interest can be set to be as
small as possible, giving the patient a lower x-ray dose. In step
105, one or more x-ray images at the higher resolution/image
quality is taken of the patient using the x-ray scanner. Since the
region of interest was defined using the scout image, and the
tracking element is attached to the patient during subsequent
exposures, any movement of the tracking element can be correlated
with a movement of the region of interest.
[0132] FIG. 2 shows a flow chart representing an embodiment of the
method disclosed herein. In step 201, a tracking element, here in
the form of a plate, with at least one fiducial marker is attached
to the head of a patient. The fiducial markers may be any shape,
for example a circle, triangle, ellipse, or any other geometrical
shape. In step 202, a scout image is taken using either the x-ray
source, a face scanner, a video camera, or any other imaging
device. If the scout image is taken using the x-ray source, the
scout image will typically be taken with a lower resolution/image
quality than the final x-ray images. In step 203a, the medical
imaging device acquires medical images of the patient. Concurrently
with step 203a, in step 203b, tracking images of the plate are
taken using one or more cameras that are placed in a known spatial
relationship with the medical imaging source and sensor. The
cameras may be integrated into the medical imaging device, or they
may be a separate system. In step 204, the position, size and tilt
of the fiducial markers is determined. This can for example be done
by using principal component analysis. If, for example the fiducial
markers are in the form of circular dots, when there is an angle
between a normal vector of the plate and a linear axis between the
plate and the camera, the circular dots will look slightly deformed
in the tracking image. In this case, principal component analysis
can be used to determine whether what is observed in the image is a
dot, and where the center of the dot is located. In step 205, a
mask of the known predefined pattern of the fiducial markers is
loaded from a database, and compared with the determined pattern of
fiducial markers in each tracking image. This comparison can be
done using any method known in the art. This allows the position
and orientation of the plate to be determined. It may be
advantageous to determine the orientation of the midpoint of the
plate, since this will allow the highest accuracy. However, the
position and orientation of any point on the plate may be used, for
example the corner of the plate.
[0133] If there is more than one camera, a tracking image from each
camera will be taken at each time t. Each of these tracking images
will then have a determined position and orientation of the plate
at each time t. The position and orientation determined from each
tracking image at time t may be slightly different because of the
particular geometry of the situation, for example one camera may
have a more acute angle towards the plate than another. The
determined position and orientation from each tracking image at
time t may then be combined into a single determined position and
orientation. This combination can for example be done by performing
a weighted average of the position and orientation measurement from
each tracking image at time t.
[0134] The weighted average can for example be computed by starting
with the found position and orientation of the tracking element
from one image, determining the difference between this starting
position and the position and orientation of the tracking element
in each of the other two images, and iteratively adjusting the
starting position and orientation of the tracking element to an
adjusted position and orientation, until the combined error or
difference between the position and orientation of the tracking
element in each image and the adjusted position and orientation is
minimized.
[0135] Alternatively, the starting position and orientation of the
tracking element could be a standard default position and
orientation, and the difference between this standard position and
orientation and the position and orientation determined in each of
the three images can be computed. Then the starting position and
orientation of the tracking element can be iteratively adjusted
until the combined error or difference between the position and
orientation of the tracking element in each image and the adjusted
starting position is minimized.
[0136] Therefore the accuracy of the determined position and
orientation of the plate will be better when more than one camera
is used.
[0137] An alternative approach to the comparison step 205 may be
accomplished as follows. Instead of having a database containing a
mask of the known predefined pattern of the fiducial pattern or
markers, there may instead be a classification of the indices of
each of the fiducial markers, as explained in relation to FIG. 3.
In this way, the 3D position and orientation of the element is then
found such that the classification indices of the known pattern is
matched with the determined indices of the fiducial markers on the
image sensor after projecting. Here it is important to note that
the field of view of each camera, should be large enough to
unambiguously determine which part of the element is in the image.
In the case of more than one camera, there may be ambiguities as to
the exact position and orientation of the element as determined
from the tracking images taken with different cameras. In this
case, a cost function may be used, so that the position and
orientation determination is optimized using information from all
cameras.
[0138] In step 206, the movement of the plate between different
times t is determined, and the determined movement of the plate is
correlated to a movement of the region of interest. Since the
positional relationship between the cameras and the medical imaging
source and sensor is known, any movement of the plate can be
directly translated into a corresponding movement of the patient,
and therefore the region of interest.
[0139] In step 207, any determined movement of the region of
interest is used to adjust the collimator so that the x-rays
converge on the region of interest. Alternatively, instead of
adjusting the collimator, the x-ray source and or sensor may be
adjusted or moved based on the determined movement of the region of
interest. This will typically be the case if a larger movement of
the patient has occurred, for example if the movement is 1 cm or
more. However, no matter the value of the actual determined
movement of the patient, the collimator and/or the x-ray sensor
and/or the x-ray source may be moved or adjusted.
[0140] In FIG. 3, a tracking element 1 according to embodiments of
this disclosure is shown. The tracking element has the form of a
rectangular plate, made of a rigid material. The plate has a
plurality of fiducial markers 2, in a predetermined pattern, layout
or configuration. The pattern should be known to a very high degree
of accuracy, so that matching subsequent tracking images taken of
the plate, can be matched with a mask of the same pattern saved in
a database. In CBCT systems today, typical accuracy is in the range
75-350 microns at the moment. Therefore, the accuracy of the known
placement of each fiducial marker should at least be within this
range in order to achieve a higher accuracy in the digital medical
model. Of course, the higher the accuracy of the placement of the
fiducial markers, the more the accuracy will be improved.
[0141] Each fiducial marker may be classified using a
classification index. For example, the fiducial marker closes to
one corner could be defined as having the index (0,0), the next one
in the same row could have the index (0,1) and in general the
fiducial markers could have an index defined as (i,j), with I going
from 0 to n, and j going from 0 to m. In this way, the fiducial
markers will have a known classification index, which can then be
compared to tracking images to match the actual pattern of the
fiducial markers on the element to the fiducial markers in the
tracking images.
[0142] However, when the system is used for example for a
cephalometric image or a panoramic image or any 2-dimensional
x-ray, a lesser accuracy may be sufficient. For example, if a
patient moves several millimeters or centimeters, any accuracy
better than the movement of the patient will yield a more accurate
final x-ray image/model. The plate may also comprise an
asymmetrical feature 3. This will make it easier for computer
algorithms to unambiguously match the pattern from the database to
the tracking images, and therefrom derive the actual position and
orientation of the tracking element in each tracking image. In the
case where the fiducial markers are classified using a
classification index, the asymmetrical feature will mean that it
will be easier to make sure that each tracking camera has a view of
the element wherein the position and orientation of the element in
the field of view of the camera can more easily be unambiguously
derived. That is, once the fiducial markers have been segmented in
the tracking images, for example using PCA, they can be classified
according to the classification index. If, on the other hand, the
field of view of the tracking camera only covered an ambiguous
subset of the fiducial markers, it would be impossible to
unambiguously derive the position and orientation of the element in
the tracking image.
[0143] The tracking element may be made of any rigid material such
as plastic, metal or glass. When using coated glass for the
element, it is easy to print or etch the fiducial markers onto or
into the surface of the element.
[0144] Although illustrated here as a rigid plate on which the
fiducial markers are printed or etched, the tracking element may
also for example be a plate with holes, with lights placed
underneath the holes, so that the position of the lights can be
picked up by a sensor. The lights could for instance use infrared
wavelengths, and the sensor could be an infrared sensor. Another
option could be to have an active plate where lights are placed on
the surface of the plate, and the position of these lights could be
picked up by a sensor. For example, the light could be LED
lights.
[0145] Turning now to FIG. 4, a system according to an aspect of
this disclosure is shown. The system comprises a medical imaging
device in the form of a CBCT scanner 10, where the CBCT scanner
comprises a sensor 11, and a radiation source 12. The sensor and/or
the radiation source are able to turn substantially around a full
circle around the patient's head. The system may also comprise a
chin rest 13 for the patient to rest his/her chin. The system may
also include a face scanner (not shown), the face scanner
configured to record a 3D model of the patient's face. The system
further comprises a tracking element 1, here shown as a plate
attachable to the patient's head. Also comprised in the system is
one or more cameras, for example located inside the ring 15. The
cameras should be mounted with a known geometrical relationship to
the sensor 11 and radiation source 12. Often, this will be near or
in the center of the ring 15, since the patient will usually be
positioned underneath the center of the ring 15. The cameras are
configured to be used to take tracking images of the tracking
element 1 simultaneously with the CBCT scanner taking x-ray images.
In front of, or integrated in the radiation source is a collimator,
which can be adjusted to focus or converge or point the x-rays in a
certain direction.
[0146] FIG. 5 shows a stylized view of the adjustable collimator 17
as disclosed herein. The x-ray source 12 provides x-rays 18, and
the collimator 17 is fully adjustable, so that the x-rays 18 can be
directed towards the region of interest 16. The collimator can have
any form, for example it can be composed of four independent
shutters controlling the top, bottom, left and right of the x-ray
beam.
[0147] FIG. 6 shows a schematic of a system according to an
embodiment of the invention. The system 600 comprises a computer
device 602 comprising a computer readable medium 604 and a
microprocessor 603. The system further comprises a visual display
unit 605, input means for entering data and activating digital
buttons visualized on the visual display unit 605. In some
embodiments as shown here, the input means may be a computer
keyboard 606 and a computer mouse 607. The visual display unit 605
can be a computer screen, or a tablet computer, or any other
digital display unit. In some cases when the visual display unit is
for example a tablet computer, the input means may be the touch
screen of the tablet computer.
[0148] The computer device 602 is capable of obtaining medical
images recorded with one or more medical imaging devices 601a and
tracking images recorded by one or more cameras 601b. The obtained
medical images and tracking images can be stored in the computer
readable medium 604 and provided to the processor 603. In some
embodiments system 600 may be configured for allowing an operator
to control the medical imaging device using the computer device
602. The controls may displayed digitally on the visual display
unit 605, and the user may control the medical imaging device, as
well as the tracking cameras using the computer keyboard 606 and
computer mouse 607.
[0149] The system may comprise a unit 608 for transmitting the
medical images, the tracking images and/or the digital medical
model via the internet, for example to a cloud storage.
[0150] The medical imaging device 601a may be for example a CBCT
unit located for example at a dentist office.
[0151] Although some embodiments have been described and shown in
detail, the invention is not restricted to them, but may also be
embodied in other ways within the scope of the subject matter
defined in the following claims. In particular, it is to be
understood that other embodiments may be utilized and structural
and functional modifications may be made without departing from the
scope of the present invention.
[0152] In device claims enumerating several means, several of these
means can be embodied by one and the same item of hardware. The
mere fact that certain measures are recited in mutually different
dependent claims or described in different embodiments does not
indicate that a combination of these measures cannot be used to
advantage.
[0153] A claim may refer to any of the preceding claims, and "any"
is understood to mean "any one or more" of the preceding
claims.
[0154] The term "obtaining" as used in this specification may refer
to physically acquiring for example medical images using a medical
imaging device, but it may also refer for example to loading into a
computer an image or a digital representation previously
acquired.
[0155] It should be emphasized that the term "comprises/comprising"
when used in this specification is taken to specify the presence of
stated features, integers, steps or components but does not
preclude the presence or addition of one or more other features,
integers, steps, components or groups thereof.
[0156] Some features of the method described above and in the
following may be implemented in software and carried out on a data
processing system or other processing means caused by the execution
of computer-executable instructions. The instructions may be
program code means loaded in a memory, such as a RAM, from a
storage medium or from another computer via a computer network.
Alternatively, the described features may be implemented by
hardwired circuitry instead of software or in combination with
software.
* * * * *