U.S. patent application number 16/652031 was filed with the patent office on 2020-08-20 for a method and system for obtaining operating parameters for 3d x ray acquisition.
The applicant listed for this patent is TROPHY. Invention is credited to Stephane ALRIC, Laurent BOUTTE, Aude LAGARDERE, Olivier NESME, Stephane VARLET.
Application Number | 20200261039 16/652031 |
Document ID | 20200261039 / US20200261039 |
Family ID | 1000004825622 |
Filed Date | 2020-08-20 |
Patent Application | download [pdf] |
United States Patent
Application |
20200261039 |
Kind Code |
A1 |
VARLET; Stephane ; et
al. |
August 20, 2020 |
A METHOD AND SYSTEM FOR OBTAINING OPERATING PARAMETERS FOR 3D X RAY
ACQUISITION
Abstract
The invention concerns a method for obtaining operating
parameters for an x-ray CBCT imaging apparatus in view of acquiring
a set of data of a patient's maxillofacial region. The method
comprises: --identifying a patient's maxillofacial first region of
interest (ROI1), --determining a height of a horizontal plane of
said patient's maxillofacial first region of interest (ROI1) when
the patient is in an occlusion position or bites a patient
positioning accessory, --acquiring through a slit-shaped collimator
window a first set of data relative to said patient's maxillofacial
first region of interest (ROI1) including the horizontal plane
using x-ray CBCT imaging, --reconstructing an axial CBCT slice
comprising the horizontal plane based on the first set of data
relative to the reconstructed the patient's maxillofacial first
region of interest (ROI1), --displaying the reconstructed axial
CBCT slice of the patient's maxillofacial first region of interest
(ROI1) from the acquired first set of data, --defining at least
partially a second region of interest (ROI2) based on the displayed
reconstructed axial CBCT slice of the patient's maxillofacial first
region of interest (ROI1) and intersecting the latter, --obtaining
operating parameters for an x-ray CBCT imaging apparatus based on
at least the defined second region of interest (ROI2) in view of
acquiring a second set of data including the defined second region
of interest (ROI2).
Inventors: |
VARLET; Stephane;
(Chenehutte, FR) ; NESME; Olivier;
(Nogent-sur-Marne, FR) ; BOUTTE; Laurent;
(Ozoir-la-Ferriere, FR) ; ALRIC; Stephane; (Paris,
FR) ; LAGARDERE; Aude; (Paris, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TROPHY |
Croissy-Beauboung |
|
FR |
|
|
Family ID: |
1000004825622 |
Appl. No.: |
16/652031 |
Filed: |
September 26, 2018 |
PCT Filed: |
September 26, 2018 |
PCT NO: |
PCT/EP2018/076172 |
371 Date: |
March 28, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 6/06 20130101; A61B
6/04 20130101; A61B 6/14 20130101; A61B 6/032 20130101; A61B 6/485
20130101; A61B 6/4085 20130101; A61B 6/5217 20130101; A61B 6/469
20130101; A61B 6/488 20130101 |
International
Class: |
A61B 6/14 20060101
A61B006/14; A61B 6/00 20060101 A61B006/00; A61B 6/03 20060101
A61B006/03; A61B 6/04 20060101 A61B006/04; A61B 6/06 20060101
A61B006/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2017 |
EP |
17306306.6 |
Claims
1. A method for obtaining operating parameters for an x-ray CBCT
imaging apparatus in view of acquiring a set of data of a patient's
maxillofacial region, the method comprising: identifying a
patient's maxillofacial first region of interest (ROI1),
determining a height of a horizontal plane of said patient's
maxillofacial first region of interest (ROI1) when the patient is
in an occlusion position or bites a patient positioning accessory,
acquiring through a slit-shaped collimator window a first set of
data relative to said patient's maxillofacial first region of
interest (ROI1) including the horizontal plane using x-ray CBCT
imaging, reconstructing an axial CBCT slice comprising the
horizontal plane based on the first set of data relative to the
patient's maxillofacial first region of interest (ROI1), displaying
the reconstructed axial CBCT slice of the patient's maxillofacial
first region of interest (ROI1) from the acquired first set of
data, defining at least partially a second region of interest
(ROI2) based on the displayed reconstructed axial CBCT slice of the
patient's maxillofacial first region of interest (ROI1) and
intersecting the latter, obtaining operating parameters for an
x-ray CBCT imaging apparatus based on at least the defined second
region of interest (ROI2) in view of acquiring a second set of data
including the defined second region of interest (ROI2).
2. The method of claim 1, wherein defining at least partially the
second region of interest (ROI2) based on the displayed
reconstructed axial CBCT slice of the patient's maxillofacial first
region of interest (ROI1) includes defining the position of the
second region of interest (ROI2) in the x, y plane of the axial
slice.
3. The method of claim 2, wherein defining the second region of
interest (ROI2) further includes defining the position of the
second region of interest (ROI2) along a z axis (height) that is
perpendicular to the x, y plane of the axial slice.
4. The method of claim 3, wherein defining the z-axis position of
the second region of interest (ROI2) includes beforehand one of the
following: acquiring a lateral x-ray scout view comprising the
patient's maxillofacial first region of interest (ROI1); acquiring
an optical image comprising the patient's maxillofacial first
region of interest (ROI1) including landmarks; performing physical
measurements on the patient's maxillofacial first region of
interest (ROI1) using a patient positioning device.
5. The method of claim 4, wherein the method further comprises
adjusting the height of the second region of interest (ROI2) based
on the lateral scout view, the optical image or the performed
physical measurements.
6. The method of claim 3, wherein the z-axis position of the second
region of interest (ROI2) is predetermined.
7. The method of any of claims 1 to 3, wherein the second region of
interest (ROI2) has a size that is selected among a set of
predetermined values.
8. The method of any of claims 3 to 5, wherein defining the z-axis
position of the second region of interest (ROI2) is based on
determining the height of an horizontal plane of said patient's
maxillofacial first region of interest (ROI1) when the patient is
in an occlusion position or bites a patient positioning
accessory.
9. The method of any of claims 1 to 8, wherein determining a height
of an horizontal plane of said patient's maxillofacial first region
of interest (ROI1) when the patient is in an occlusion position or
bites a patient positioning accessory includes beforehand one of
the following: acquiring a lateral x-ray scout view comprising the
patient's maxillofacial first region of interest (ROI1); acquiring
an optical image comprising the patient's maxillofacial first
region of interest (ROI1) including landmarks; performing physical
measurements on the patient's maxillofacial first region of
interest (ROI1) using a patient positioning device.
10. The method of any of claims 1 to 9, wherein the first set of
data is acquired while the patient is maintained in a first
position through a patient positioning device, said first patient
position being defined by a set of setting parameters for the
patient positioning device.
11. The method of claim 10, wherein it comprises prior adjusting
the setting parameters of the patient positioning device before
acquiring the second set of data.
12. The method of any of claims 1 to 11, wherein the first set of
data and the second set of data are separate in time.
13. The method of any of claims 1 to 12, wherein the x-ray CBCT
imaging apparatus comprises an x-ray source and an x-ray sensor
that are both operable to simultaneously move around the patient's
head along a predetermined trajectory and obtaining operating
parameters for the x-ray CBCT imaging apparatus based on the
defined second region of interest (ROI2) comprises adjusting a
trajectory for both x-ray source and x-ray sensor based on the
defined second region of interest ROI2.
14. A system for obtaining operating parameters for x-ray CBCT
imaging a patient's maxillofacial region, comprising: an x-ray
source and at least one x-ray sensor that are configured to move
around a patient's maxillofacial first region of interest (ROI1)
while irradiating the latter with a slit-shaped x-ray beam so as to
acquire a first set of data relative to said patient's
maxillofacial first region of interest (ROI1) when the patient is
in an occlusion position or bites a patient positioning accessory,
said patient's maxillofacial first region of interest (ROI1)
including an horizontal plane, a microprocessor configured to:
reconstruct an axial CBCT slice comprising the horizontal plane
based on the first set of data relative to the patient's
maxillofacial first region of interest (ROI1), display the
reconstructed axial CBCT slice of the patient's maxillofacial first
region of interest (ROI1) from the acquired first set of data with
a view to defining at least partially a second region of interest
(ROI2) that is based on the displayed reconstructed axial CBCT
slice and intersects the latter, obtain operating parameters for an
x-ray CBCT imaging apparatus based on at least the defined second
region of interest (ROI2) in view of acquiring a second set of data
including the defined second region of interest (ROI2).
15. A computer storage medium having instructions stored therein
for causing a computer or a microprocessor to perform the method of
any of claims 1 to 13.
Description
TECHNICAL FIELD
[0001] The disclosure relates generally to the field of dental
x-ray imaging and in particular to the field of x-ray CBCT (Cone
Beam Computed Tomography) imaging. More specifically, the
disclosure relates to a method for obtaining operating parameters
for an x-ray CBCT imaging apparatus and a system for obtaining
operating parameters for x-ray CBCT imaging a patient's
maxillofacial region.
BACKGROUND
[0002] Conventional methods and systems for obtaining a
radiographic image of a patient's maxillofacial region through
x-ray CBCT imaging very often require irradiating local areas of
reduced size relative to the size of the whole patient's
maxillofacial region with an x-ray dose during a certain exposure
time in order to obtain details on teeth, specific areas, etc. that
are of interest to the practitioner.
[0003] Predefined apparatus settings corresponding to an average
patient allow to reach the desired local areas.
[0004] However, image retaking may occur due to variation between
patients regarding the average predefined settings, thereby leading
to an increase in the x-ray dose received by the patient.
[0005] While such systems may have achieved certain degrees of
success in their particular applications, there is nevertheless a
need to improve these methods and systems.
SUMMARY
[0006] An object of the present disclosure is to avoid unnecessary
x-ray doses for the patients when undergoing an x-ray CBCT
examination.
[0007] Another object of the present disclosure is to improve the
positioning accuracy of a patient's data volume acquired through an
x-ray CBCT data acquisition while limiting the patient dose
exposure.
[0008] Still another object of the present disclosure is to
optimize the adjustment of operating or acquisition parameters of
an x-ray CBCT imaging apparatus before submitting a patient to an
x-ray CBCT examination.
[0009] These objects are given only by way of illustrative example,
and such objects may be exemplary of one or more embodiments of the
invention. Other desirable objectives and advantages inherently
achieved by the invention may occur or become apparent to those
skilled in the art. The invention is defined by the appended
claims.
[0010] According to one aspect of the disclosure, there is provided
a method for obtaining operating parameters for an x-ray CBCT
imaging apparatus in view of acquiring a set of data of a patient's
maxillofacial region, the method comprising: [0011] identifying a
patient's maxillofacial first region of interest ROI1, [0012]
determining a height of an horizontal plane of said patient's
maxillofacial first region of interest ROI1 when the patient is in
an occlusion position or bites a patient positioning accessory,
[0013] acquiring through a slit-shaped collimator window a first
set of data relative to said patient's maxillofacial first region
of interest ROI1 including the horizontal plane using x-ray CBCT
imaging, [0014] reconstructing an axial CBCT slice comprising the
horizontal plane based on the first set of data relative to the
patient's maxillofacial first region of interest ROI1, [0015]
displaying the reconstructed axial CBCT slice of the patient's
maxillofacial first region of interest ROI1 from the acquired first
set of data, [0016] defining at least partially a second region of
interest ROI2 based on the displayed reconstructed axial CBCT slice
of the patient's maxillofacial first region of interest ROI1 and
intersecting the latter, [0017] obtaining operating parameters for
an x-ray CBCT imaging apparatus based on at least the defined
second region of interest ROI2 in view of acquiring a second set of
data including the defined second region of interest ROI2.
[0018] The method according to an embodiment of the invention is a
novel method which makes it possible to reduce the patient exposure
to x-rays.
[0019] The method according to an embodiment of the invention is a
novel method which uses a first x-ray "pre-shoot" with an x-ray
dose to obtain and reconstruct a CBCT slice comprising the
patient's maxillofacial first region of interest ROI1 and that
enables selection or definition of a more specific area or region
of interest by the practitioner. This definition or selection of a
more specific area or region of interest makes it possible to
obtain adapted operating or acquisition parameters that will be
used for another "shoot" or second x-ray CBCT data acquisition.
[0020] Typically a low dose is used for the "pre-shoot". A low is a
dose that does not exceed 20%, preferably less than 10% and more
preferably less than 5% of the default or standard dose (obtained
with default or standard parameters) that is used for a known x-ray
examination (3D, panoramic etc.). A low dose may be used since the
CBCT slice does not need many details as in a default or
conventional acquisition and the patient must not be too much
exposed to x-rays. However, the CBCT slice information has to be
sufficient to provide morphology information (ex: location of
teeth, geometry of teeth, etc.) enabling selection of a more
specific area or region of interest by the practitioner. The
information that is contained in the CBCT slice is proper to the
patient. Use of such information therefore enables more adapted
and/or accurate definition of a more specific area or region of
interest. This way of proceeding is clearly not based on averaged
patient's data as in the past. The operating or acquisition
parameters that are obtained based on such a more specific area or
region of interest of the patient will thus be more reliable and
accurate since they will be representative of the patient. The CBCT
slice may be a thin slice that includes the ROI1. The slice may be
less than 100 .mu.m thick or high or a slice integrated over a
certain thickness or height typically in the order of a few
mms.
[0021] The patient is preferably in a repeatable position during
the "pre-shoot", thereby meaning that for a subsequent "shoot" or
acquisition with the obtained parameters the patient will be in the
same or in a very close position. In this respect, the setting
parameters of the x-ray apparatus for positioning the patient are
kept in memory.
[0022] According to possible features or aspects: [0023] defining
at least partially the second region of interest ROI12 based on the
displayed reconstructed axial CBCT slice of the patient's
maxillofacial first region of interest ROI1 includes defining the
position of the second region of interest ROI12 in the x, y plane
of the axial slice; [0024] defining the second region of interest
ROI12 further includes defining the position of the second region
of interest ROI12 along a z axis (height) that is perpendicular to
the x, y plane of the axial slice; [0025] defining the z-axis
position of the second region of interest ROI12 includes beforehand
one of the following:
[0026] acquiring a lateral x-ray scout view comprising the
patient's maxillofacial first region of interest ROI1; the scout
view may be used to position both the height of the horizontal
plane of ROI1 and the height and the size in the y, z plane of
ROI12;
[0027] acquiring an optical image comprising the patient's
maxillofacial first region of interest ROI1 including
landmarks;
[0028] performing physical measurements on the patient's
maxillofacial first region of interest ROI1 using a patient
positioning device; [0029] the method further comprises adjusting
the height of the second region of interest ROI12 based on the
lateral scout view, the optical image or the performed physical
measurements; [0030] the z-axis position of the second region of
interest ROI12 is predetermined; [0031] the second region of
interest ROI2 has a size that is selected among a set of
predetermined values; [0032] defining the z-axis position of the
second region of interest ROI2 is based on determining the height
of an horizontal plane of said patient's maxillofacial first region
of interest ROI1 when the patient is in an occlusion position or
bites a patient positioning accessory; [0033] determining a height
of an horizontal plane of said patient's maxillofacial first region
of interest ROI1 when the patient is in an occlusion position or
bites a patient positioning accessory includes beforehand one of
the following:
[0034] acquiring a lateral x-ray scout view comprising the
patient's maxillofacial first region of interest ROI1;
[0035] acquiring an optical image comprising the patient's
maxillofacial first region of interest ROI1 including
landmarks;
[0036] performing physical measurements on the patient's
maxillofacial first region of interest ROI1 using a patient
positioning device; [0037] the first set of data is acquired while
the patient is maintained in a first position through a patient
positioning device, said first patient position being defined by a
set of setting parameters for the patient positioning device;
[0038] the method comprises prior adjusting the setting parameters
of the patient positioning device before acquiring the second set
of data; [0039] the first set of data and the second set of data
are separate in time; [0040] the x-ray CBCT imaging apparatus
comprises an x-ray source and an x-ray sensor that are both
operable to simultaneously move around the patient's head along a
predetermined trajectory and obtaining operating parameters for the
x-ray CBCT imaging apparatus based on the defined second region of
interest ROI2 comprises adjusting a trajectory for both x-ray
source and x-ray sensor based on the defined second region of
interest ROI2.
[0041] According to another aspect of the disclosure, there is
provided a system for obtaining operating parameters for x-ray CBCT
imaging a patient's maxillofacial region, comprising: [0042] an
x-ray source and at least one x-ray sensor that are configured to
move around a patient's maxillofacial first region of interest ROI1
while irradiating the latter with a slit-shaped x-ray beam so as to
acquire a first set of data relative to said patient's
maxillofacial first region of interest ROI1 when the patient is in
an occlusion position or bites a patient positioning accessory,
said patient's maxillofacial first region of interest ROI1
including an horizontal plane of the patient in an occlusion
position or a plane parallel thereto, [0043] a microprocessor
configured to:
[0044] reconstruct an axial CBCT slice comprising the occlusal
plane or the plane parallel thereto based on the first set of data
relative to the patient's maxillofacial first region of interest
ROI1,
[0045] display the reconstructed axial CBCT slice of the patient's
maxillofacial first region of interest ROI1 from the acquired first
set of data with a view to defining at least partially a second
region of interest ROI2 that is based on the displayed
reconstructed axial CBCT slice and intersects the latter,
[0046] obtain operating parameters for an x-ray CBCT imaging
apparatus based on at least the defined second region of interest
ROI2 in view of acquiring a second set of data including the
defined second region of interest ROI2.
[0047] The microprocessor may also be configured to perform any of
the steps, operations, features or aspects of the above method.
[0048] According to still another aspect of the disclosure, there
is provided a computer storage medium having instructions stored
therein for causing a computer or a microprocessor to perform the
method as briefly mentioned above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] The foregoing and other objects, features, and advantages of
the invention will be apparent from the following more particular
description of the embodiments of the invention, as illustrated in
the accompanying drawings.
[0050] The elements of the drawings are not necessarily to scale
relative to each other.
[0051] FIG. 1 shows an overall schematic perspective view of an
x-ray CBCT imaging apparatus according to an embodiment of the
invention;
[0052] FIG. 2 shows main functional components or assemblies of an
x-ray CBCT imaging system according to an embodiment of the
invention;
[0053] FIG. 3 shows an algorithm of a method according to an
embodiment of the invention;
[0054] FIG. 4 shows different processes to perform the FIG. 3 step
S1;
[0055] FIG. 5 shows the possible positions of the ROI1 and ROI2 in
a y, z plane with a lateral scout view;
[0056] FIG. 6A illustrates possible relative positions between the
ROI1 and the x-ray source;
[0057] FIG. 6B shows an axial view of the reconstructed CBCT slice
with the ROI2;
[0058] FIG. 7 shows an example of a trajectory for both an x-ray
source and an x-ray sensor.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0059] The following is a detailed description of the preferred
embodiments, reference being made to the drawings in which the same
reference numerals identify the same elements of structure in each
of the several figures.
[0060] FIG. 1 illustrates an embodiment of an x-ray imaging
apparatus, in particular an extra-oral imaging apparatus 10.
Apparatus 10 comprises a support structure that includes a support
frame 12 which may be a support column.
[0061] The support structure also includes a horizontal mount 14
that may be supported or held by the vertical column 12. Horizontal
mount 14 extends away from vertical column 12 and may be
substantially perpendicular thereto. Horizontal mount 14 can move
vertically relative to the vertical column 12.
[0062] More particularly, horizontal mount 14 is fixedly mounted on
a vertical part 12a that is slidably mounted over a fixed vertical
part 12b. For example, an actuator, e.g. of the electric type,
located behind the vertical column (not represented in the drawing)
can be commanded to drive the horizontal mount 14 into a vertical
movement in a controlled manner.
[0063] Horizontal mount 14 can support a gantry 16. Gantry 16 is
movable relative to the support structure, and more particularly to
horizontal mount 14. Gantry 16 may more particularly be rotatable
relative to horizontal mount 14. Gantry 16 may be rotatable about a
vertical axis of rotation which may be stationary during the
operation of the imaging process or may follow one among several
predetermined trajectories in accordance with the selected imaging
process. A driving known mechanism (not represented in the drawing)
for driving the gantry 16 into a given movement is integrated
inside horizontal mount 14. By way of example, such driving
mechanism includes motors for imparting a first movement in an x, y
plane, e.g. two step-by-step motors, and a motor for imparting a
rotational movement about the vertical axis z, e.g. a brushless
motor.
[0064] Gantry 16 supports both an x-ray source 18 and at least one
x-ray sensor 20 that is arranged in correspondence with the x-ray
source. X-ray source 18 and the at least one x-ray sensor 20 may be
arranged facing each other. Gantry 16 may include two opposite
downwardly extending arms: a first arm 16a supports x-ray source 18
that is attached thereto and a second opposite arm 16b supports the
at least one x-ray sensor 20 that is attached thereto.
[0065] X-ray source 18 includes a conventional collimator (not
represented in FIG. 1). The position of the collimator along the
vertical axis z and the opening of the slit collimator window may
be adjusted so that the collimated x-ray beam irradiates a region
of interest of the patient's head or patient's maxillofacial
region.
[0066] When activated x-ray source 18 emits an x-ray beam which
here irradiates an imaging area of a patient's maxillofacial region
(or patient's maxillofacial region of interest) before impinging
the at least one x-ray sensor 20.
[0067] In the present embodiment, x-ray source 18 and the at least
one x-ray sensor 20 are configured to move around the patient's
maxillofacial region along a predetermined trajectory, while
irradiating the imaging area of the patient's maxillofacial
region.
[0068] In the present embodiment, the apparatus 10 is used in an
x-ray CBCT operating mode and here, more particularly, in a CBCT
operating mode for obtaining a 3D CBCT slice as will be seen
subsequently. The apparatus 10 may be considered as an x-ray CBCT
imaging apparatus to perform volumetric or computerized tomography
and obtain 3D images.
[0069] However, the apparatus 10 may also function according to one
or several other operating modes or imaging processes, such as
panoramic, cephalometric, etc.
[0070] The apparatus 10 is also able to operate according to such
different operating modes or only some of them.
[0071] In this respect, another sensor or other sensors may be used
and the x-ray may be collimated accordingly to irradiate a region
of the patient's head as the patient's maxillofacial region of
interest (or the whole patient's head) with a specific shape
depending on the selected operating mode and choice of the
practitioner.
[0072] The at least one x-ray sensor 20 includes a sensor that is
adapted to one of the operating modes of the apparatus. For
instance, the sensor may be adapted to perform a CBCT scan, e.g. a
volumetric or computerized sensor (e.g. rectangular,
square-shaped), or several sensors of the previous type.
[0073] The support structure may also include a patient positioning
accessory support member 22 which here is an arm. Arm 22 is
connected to the support frame, and more particularly to the
vertical column 12. The patient positioning arm 22 is movable
relative to the support frame. More particularly, arm 22 can slide
along the vertical column 12 so as to move up or down upon command
through appropriate actuator(s) e.g. of the electric type. The
patient positioning arm 22 extends from an arm support 22a that is
slidably mounted relative to the fixed vertical part 12b. The
patient positioning arm 22 extends along the apparatus in a
direction that is substantially in correspondence with the
direction of extension of horizontal mount 14. Patient positioning
arm 22 is here arranged sideways relative to the apparatus in a
substantial parallel relationship with horizontal mount 14.
[0074] Patient positioning arm 22 serves to position the patient in
the apparatus at a given location.
[0075] Patient positioning arm 22 may include one of several
patient positioning accessories generally located at a free end 22b
of the arm or proximate thereto. These accessories may also or
alternatively be considered as holding systems.
[0076] These patient positioning accessories allow to position the
anatomical structures of the patient's head according to different
orientations and to immobilize the patient's head during the
examination so as to reduce any possible movement.
[0077] There exists one or several types of patient positioning
accessories for each type of specific examination to be carried out
by the apparatus according to different operating modes. The arm 22
is configured to accommodate each of these patient positioning
accessories of different types, generally one at a time.
[0078] As illustrated in FIG. 1, one of these patient positioning
accessories, noted 24, includes two temporal holding members that
extend upwardly from the arm 22 to which they are removably
attached. Only one temporal holding member is represented, the
other one being hidden by the arm 16b.
[0079] The patient positioning accessory 24 may also include a chin
rest 26 that extends upwardly from the arm 22 to which it is
removably attached. The chin rest 26 is located between the two
temporal holding members to position a patient's head for a
panoramic examination. A standard bite block may be further added
to the chin rest.
[0080] Alternatively, a Frankfort guide bite block may be used for
panoramic examination.
[0081] Other possible types of patient positioning accessories may
be envisaged: a nasal support for conducting a temporal mandible
joint examination with open and closed mouth, a bitten support for
3D examination (bit type), a frontal support for 3D examination
(frontal type), a combination of a bite support and a frontal
support, etc.
[0082] In addition, a seat (not represented in the drawing) may be
used for the patient according to the type of examination. This
arrangement may help to set the position of the patient and also
the repeatability of this position in the future, for subsequent
data acquisition. Even though subsequent data acquisition is not
performed on the same apparatus, the setting parameters defining
the patient's position (including the position relative to the
seat) may be stored in memory.
[0083] As illustrated in FIG. 1, a handle assembly 34 may be
positioned at the free end 22b of the arm, underneath the arm and
in a parallel relationship with the arm. This handle assembly 34
includes two vertical separate handle portions 34a, 34b which can
be grasped by the patient when undergoing an imaging process so as
to remain motionless.
[0084] Overall this handle assembly 34 has a U-shape which includes
a horizontal base portion 34c and two vertical upwardly-extending
branches 34a, 34b that are fixed to the arm 22. Each branch plays
the role of a vertical handle portion.
[0085] Other handle assemblies may alternatively be used for
handling the arm 22.
[0086] Patient positioning arm 22 may also support a monitor or
display assembly 36 which makes it possible for a practitioner of
the apparatus to view images displayed thereon, interact therewith
and drive certain functions of the apparatus.
[0087] FIG. 2 is a schematic view of main functional components or
assemblies of a system for obtaining operating parameters 40 that
will be used in the present embodiment.
[0088] Some or all of these components or assemblies may be part of
the apparatus 10 or not.
[0089] In the present embodiment system 40 is located in the
apparatus 10.
[0090] System 40 comprises an acquisition assembly 42 that includes
the x-ray source and x-ray sensor of FIG. 1 apparatus.
[0091] System 40 comprises a control assembly 44 that is connected
to acquisition assembly 42 and configured to control operation of
the latter according to embodiment methods of the invention.
[0092] Control assembly 44 may also be used to enable operation of
the apparatus 10 and its different components/assemblies in a more
conventional manner, in particular to perform CBCT scans and
reconstruct 3D volumes (3D x-ray image data) and perform panoramic,
cephalometric, etc. data acquisition.
[0093] Control assembly 44 includes in particular a microprocessor
and possibly one or more storage medium for storing a computer
program having instructions for controlling system 40 to practice
one or several embodiment methods according to the present
invention. When the microprocessor executes the computer program
stored in the one or more storage medium the microprocessor is
considered as being configured to perform steps or operations of
the embodiment method according to the present invention.
[0094] An aspect of the present invention is also directed to a
computer program product including the one or more storage
medium.
[0095] The above one or more storage medium may be, for example;
magnetic storage media such as magnetic disk (such as a floppy
disk) or magnetic tape; optical storage media such as optical disk,
optical tape, or machine readable bar code; solid-state electronic
storage devices such as random access memory (RAM), or read-only
memory (ROM); or any other physical device or media employed to
store such a computer program.
[0096] The stored computer program(s) or other stored computer
program(s) may have also instructions for controlling the apparatus
10 to practice more conventional methods such as conventional
methods for obtaining a 3D volume.
[0097] System 40 may also comprise one or more external storage
medium 46 that store, here, different volumes of data reconstructed
by the apparatus in the course of x-ray imaging processes, e.g.
CBCT imaging processes. The one or more external storage medium 46
may also be of the same type as described above.
[0098] The one or more external storage medium 46 may also store
the above computer program(s) for controlling system 40 and/or,
more generally, for controlling the apparatus 10 instead of the one
or more storage medium inherent to control assembly 44.
[0099] System 40 further comprises a display assembly 48, here a
monitor or screen or several of them, that may correspond to
display assembly 36 of FIG. 1. Display assembly 48 is connected to
control assembly 44.
[0100] Display assembly 48 may display, automatically or on demand,
selected images of a patient's maxillofacial region obtained from
an x-ray CBCT imaging process performed by the apparatus 10.
[0101] Display assembly operates under control of control assembly
44.
[0102] System 40 may further comprise a user interface assembly 50
that is connected to display assembly 48 and control assembly 44.
User interface assembly 50 allows a user, e.g. a practitioner or
technician, to interact with the display assembly 48, and possibly
control assembly 44 that executes image processing/algorithms, in
order to perform different tasks.
[0103] The user interface assembly 50 may include one or more
interaction devices connected to display assembly 48, such as, but
not limited to, a pointing device, e.g. a computer mouse joystick,
a stylet, a keypad, a touchpad etc.
[0104] Other types of interaction devices or tools (user interface
tools) may alternatively, or in addition, be used: a touch screen,
tool icons displayed or that may be displayed on command on the
screen, etc.
[0105] Assemblies 44, 46, 48 and 50 may be located in whole or in
part in the arm 22 of apparatus 10 or remotely-located relative to
the apparatus (e.g. in the same room or in a separate room or in
another place). If control assembly 44 is not located in the
apparatus 10, another control assembly may be present in the
apparatus so as to control the acquisition assembly 42 and, in a
general manner, the operation of the apparatus. However, the whole
description applies equally whatever the location of the
assemblies.
[0106] The above also applies if assemblies 42, 44, 46, 48 and 50
pertain to another x-ray imaging apparatus.
[0107] An embodiment method according to the invention will now be
described with reference to FIG. 3 which depicts an algorithm of
the corresponding computer program(s). This algorithm makes
reference to other algorithms that are illustrated on other figures
and that may be part of the same computer program or correspond to
other computer programs.
[0108] For its operation the embodiment method makes use of
functional components or assemblies that can be those described
above in connection with FIG. 1 apparatus 10 and FIG. 2.
Alternatively, the functional components or assemblies necessary to
perform the method may be those of another x-ray imaging apparatus
although they may be in accordance with the configuration of FIG. 2
(all the components of FIG. 2 may not be present).
[0109] A patient is first positioned in the working space of
apparatus 10 between the x-ray source 18 and x-ray sensor 20 of
acquisition assembly 42, e.g. in a sitting position. The method
starts with an identification step S1 for identifying a patient's
maxillofacial first region of interest denoted ROI1. The
practitioner identifies ROI1 based on predetermined criteria such
as the type of examination to be carried out on a second region of
interest ROI2 of the patient's maxillofacial region, the second
region of interest ROI2 itself, etc.
[0110] For example, ROI1 may include the upper and lower jaws, part
of both jaws, only one jaw, part of a single jaw etc. depending on
the interest of the practitioner.
[0111] The method further comprises a height determination step S2.
For the performance of this step the patient may bite in a patient
positioning member or accessory and his/her teeth are then spaced
from a few millimeters. Such a patient positioning member or
accessory may be attached to the arm 22 in a releasable manner.
Such a patient positioning member or accessory may be a bite block,
e.g. a Frankfurt guide bite block used for panoramic examination, a
standard bite block, a bitten 3D support etc.
[0112] FIG. 5 illustrates ROI1 that has been identified/selected by
the practitioner on a previously acquired lateral scout view LSV of
the patient's maxillofacial region (mere projection of data
acquired through a lateral x-ray data acquisition). On FIG. 5 the
patient's face is also illustrated as a background. The resulting
view may be displayed on display assembly 48.
[0113] On FIG. 5 the biting block has not been represented for the
sake of clarity.
[0114] Alternatively, the patient may be in an occlusion position,
i.e. his/her upper and lower jaws have to be in contact with each
other. His/her head may be maintained in position through a chin
rest, a frontal support including a chin rest etc. The identified
ROI1 may include the occlusal plane in this alternative
arrangement.
[0115] The aim of this step is to determine a height of a
horizontal plane within ROI1. This height will be used next for a
first x-ray data acquisition to be described later on.
[0116] This horizontal plane may be a median plane of ROI1 or
another plane within ROI1.
[0117] For the performance of this step the patient may also be
positioned so that his/her Camper plane be horizontal.
[0118] FIG. 4 shows different ways for determining the height of
the horizontal plane.
[0119] A first way is to acquire an x-ray lateral scout view of the
patient (step S2.1) through the acquisition assembly 42 operated
under the control of control assembly 44 of FIG. 2. The position of
the scout view relative to the patient's jaw may have been
previously determined based on predetermined mean values.
[0120] FIG. 5 that has been already mentioned above schematically
illustrates an x-ray lateral scout view of the patient that has
been acquired in a conventional manner. Such a view provides here
information on the location of the upper and lower jaws and shows
the above-discussed patient's maxillofacial first region of
interest ROI1 that has been identified by a practitioner. ROI1
includes here the upper part of the lower jaw of the patient and
extends to the back of the patient's head. However, the extension
of ROI1 may be shorter along y axis. Alternatively, ROI1 may have
been positioned differently by the practitioner relative to the
jaws and its extension may be or not shorter along y axis.
[0121] An horizontal plane of interest of ROI1 may be positioned on
display by the practitioner or determined by computation. The
horizontal plane may be the median plane of ROI1 as already
mentioned above.
[0122] Next, at step S2.2 the height of this horizontal plane is
determined in a conventional manner based on the known position of
the scout view relative to the used patient's positioning accessory
(here a bite block) and the known position of the latter relative
to the x-ray apparatus, in particular the arm 22 or any other
reference part of the apparatus. To be noted that the position of
the x-ray source relative to the arm is also known.
[0123] FIG. 5 illustrates the z axis position of the
above-mentioned horizontal plane by the line denoted L.
[0124] Two other ways for determining the height of a horizontal
plane are illustrated on FIG. 4.
[0125] A second way (step S2.3) makes provision for acquiring at
least one optical image of the patient (in a biting position or in
the occlusal position) comprising the patient's maxillofacial first
region of interest ROI1 including landmarks. The at least one image
is more particularly a facial image taken by a camera and the
landmarks may be of the anatomical type (ex: the corners of the
mouth or landmarks that have been added on the patient's face. The
camera may be positioned on the apparatus 10, e.g. on the arm 22 or
independent from the apparatus. On FIG. 1 an example of a camera 52
is located next to x-ray source 18. Another location for a camera
may alternatively or in addition be selected.
[0126] Alternatively, a lateral optical image of the patient may be
convenient instead of the facial one.
[0127] The landmark or landmarks are representative of a
geometrical position that is known or can be easily known by
computation relative to the teeth roots.
[0128] As a consequence, the height of a horizontal plane (ex:
median plane) of ROI1 that can be used for the first x-ray data
acquisition can therefore be determined by computation based on the
position of the landmark or landmarks (step S2.2).
[0129] A third way (step S2.4) makes provision for performing
physical measurements on the patient (in a biting position or in
the occlusal position), more particularly on the patient's
maxillofacial first region of interest (ROI1), using a patient
positioning device or accessory.
[0130] A patient positioning accessory attached to the arm 22 of
FIG. 1 may be used, e.g. a bite block or the like. The bite block
is attached to the arm in a fixed position and the height of the
bite block relative to the arm is known or can be measured. The
mean size (height) of teeth for a given patient (adult, child etc.)
are also known, which makes it possible to situate the position of
teeth roots and therefore their position relative to the teeth
extremities, i.e. the bite block.
[0131] Consequently, the height or position of the horizontal plane
of ROI1 relative to the arm may be determined by measurements
and/or computation based on the above.
[0132] Alternatively, a sensor located in the bite block or the
like may provide appropriate measurement data and the height or
position of the occlusal plane relative to the arm may next be
determined therefrom.
[0133] Then, the height of a horizontal plane of ROI1 that can be
used for the first x-ray data acquisition can be determined based
on the position of the occlusal plane (step S2.2).
[0134] This prior determination phase aims at determining the
height at which the first set of data relating to ROI1 will be
acquired.
[0135] Once the height of the horizontal plane has been determined,
the apparatus 10 is set by control assembly 44 in a configuration
that enables acquisition of the first set of data relative to ROI1
as provided by step S3 of FIG. 3. The first set of data may
correspond to the whole ROI1 or to a selected portion thereof.
[0136] Two ways are used for setting the apparatus in the
acquisition configuration/ [0137] firstly, the set of x-ray source
and x-ray sensor is commanded by control assembly 44 to be moved to
the determined height so that the x-ray source be at the
appropriate height for the acquisition; this arrangement makes it
possible to reduce the x-ray dose easily; [0138] secondly, the
x-ray source remains at the same altitude and the x-ray collimator
is moved so as to orientate the x-ray beam upwardly towards the
determined height of the plane.
[0139] For this first data acquisition the patient remains in the
biting position (or occlusal position) as provided for at previous
step S2. The patient may also be positioned so that his/her Camper
plane be horizontal as for step S2.
[0140] The patient is placed in an appropriate position (first
position) for this first data acquisition, e.g. using a patient
positioning device or accessory of the apparatus (here a bite
block) and possibly a seat.
[0141] The different setting parameters that define the first
position of the patient, such as the accessory used, the position
of this accessory on the apparatus if several position settings are
available (ex: different possible heights for a support) and the
accessory position relative to the patient (ex: if several width
values are possible in accordance with the patient's face width),
the height of the possible seat if this parameter is adjustable,
etc. are recorded or stored by the practitioner (ex: in a storage
medium through the user interface assembly) with a view to being
used again for a subsequent data acquisition.
[0142] For this first data acquisition the apparatus 10 is in an
operating CBCT mode under the control of control assembly 44.
[0143] According to this mode the x-ray collimator opening is
adjusted as a slit-shaped collimator window so as to produce a slit
shaped x-ray beam focused on the patient's maxillofacial first
region of interest (ROI1) including the horizontal plane.
[0144] This slit shape for the beam is adjusted so as to cover the
ROI1 and preferably a thin volume in height.
[0145] The horizontal plane of ROI1 is aimed at thanks to the
adjustment in the collimator position and the collimator window
opening.
[0146] FIG. 6A illustrates two different relative positions between
the x-ray source 18 and ROI1 (ROI1 could alternatively be replaced
by a portion thereof and the remainder of the description applies
equally) with different openings for the x-ray collimator 19. As
represented, the x-ray source 18 is in alignment with the lower end
of the sensor 20.
[0147] The axis of rotation A of the set composed of the source and
the sensor has also been illustrated. In order to capture and
reconstruct a CBCT slice, the opening of the collimator in the
vertical direction depends on the position of the collimator
relative to the source-sensor alignment. The smallest opening is
obtained when the source-sensor axis passes by the collimator. In
other words, the median plane of the collimated x-ray beam may be
adjusted so as to obtain for the collimator the smallest opening
that is necessary for the slice reconstruction.
[0148] Preferentially, the source-sensor axis passes by the basis
of the collimator window and the lower edge or boundary of
ROI1.
[0149] The x-ray source is operated with a first x-ray dose that
may be qualified as a low dose with respect to the x-ray dose that
will be used for a subsequent second data acquisition.
[0150] The first x-ray dose is selected so as to minimize x-ray
exposure for the patient. The x-ray dose depends on the volume of
patient data to be acquired. The volume is preferably as small as
possible and does not need high resolution for data acquisition
since the useful information that is needed for the remainder of
the method lies in the morphological characteristics or data of the
patient maxillofacial first region of interest (location of the
teeth, characteristic dimensions, etc.). Preferably, such
information does not require many details in the acquired data.
However, the volume is not necessarily thin and its size depends on
the resolution of the image. A compromise between the size and
resolution of the volume has generally to be made if the dose is to
be low.
[0151] Typically, the first x-ray dose does not exceed 20% of the
second dose that will be used for a subsequent second data
acquisition.
[0152] Preferentially, the first x-ray dose does not exceed 10% of
the second dose and, more preferentially, does not exceed 5% of the
second dose.
[0153] For example, a first x-ray dose may be in the order of 4
.mu.Sv for generating a CBCT slice.
[0154] The information that is needed in the data volume to be
acquired during this first acquisition (CBCT slice) will be used
for appropriately positioning the data volume to be acquired during
a subsequent second acquisition.
[0155] Reverting to FIG. 3, the third step S3 for acquiring a first
set of data (3D volume) is based on the above settings and
adjustments. This first acquisition may be viewed as a "pre-shoot"
for providing useful information that will be used for a "shoot".
The exposure time for this pre-shoot may be rather low, e.g. in the
order of 5 s.
[0156] Next step S4 is a reconstruction step for reconstructing a
CBCT slice based on the acquired first set of data using
conventional CBCT data processing techniques (e.g. the FDK
algorithm).
[0157] The reconstructed CBCT slice comprises the horizontal plane
of ROI1 and is based on the acquired first set of data relative to
the patient's maxillofacial first region of interest (ROI1).
[0158] As an example of a low resolution in the first acquired data
a voxel size around 500 .mu.m in the reconstructed CBCT slice can
be obtained. For example, the thickness or height of the slice lies
between 10 and 30 voxels, thereby corresponding to a range between
1 and 15 mm. Preferentially, a range between 1 and 5 mm may be
selected.
[0159] The reconstructed CBCT slice may take the shape of a
cylinder (another shape may be used) with a diameter lying between
120 mm (for small skull dimensions) and 160 mm.
[0160] Smaller diameters may be convenient. The CBCT slice may be
qualified here as a thin slice. In other example embodiments
acquisition of the whole dental arch may be aimed at.
[0161] The method further comprises a display step S5 for
displaying on display assembly 48 of FIG. 2 an axial slice of the
reconstructed 3D volume (CBCT slice of the patient's maxillofacial
first region of interest ROI1) as illustrated on FIG. 6B
(horizontal plane). Additional views may also be displayed where
necessary, e.g. a sagittal view.
[0162] The method further comprises a step S6 for defining at least
partially a second region of interest ROI2 based on the
reconstructed and displayed axial CBCT slice of the patient's
maxillofacial first region of interest ROI1.
[0163] The second region of interest ROI2 is defined or selected so
as to intersect the first region of interest ROI1 in the x, y plane
of the axial slice.
[0164] The second region of interest ROI2 is defined or selected by
the practitioner through user interface assembly or Graphical User
Interface 50. For instance, the practitioner selects, through
activating a user input tool such as clicking on a mouse, the
display of a menu or set of icons and further selects an icon that
can be moved to the desired position on the displayed slice thanks
to the movement of the mouse cursor. The icon is represented here
by a circle C on FIG. 6B since in this embodiment the second volume
of data to be subsequently acquired is a cylinder. The circle
appearing on the view has the dimensions of the second volume of
data to be acquired.
[0165] In addition, the second volume of data to be subsequently
acquired may take another shape and the landmark or icon that helps
defining the ROI2 may take another shape in register therewith.
[0166] Reverting to FIG. 6B, the position and the size of the
circle on the displayed axial slice define the second region of
interest ROI2 that intersects the first region of interest ROI1 in
the x, y plane of this Figure.
[0167] On FIG. 6B, the circle (ROI2) has been positioned in part on
a group of teeth.
[0168] As illustrated, the position of the ROI2 can be adjusted
according to x and y coordinates in the plane of FIG. 6B (see the
corresponding left, right, up and down arrows) so as to define the
desired position in accordance with the practitioner needs (step
S6.1). In particular, he/she may need to focus on one tooth or a
group of teeth for the next and more accurate data acquisition.
[0169] To be noted that the size of the circle (here its diameter)
may be adjusted where necessary to enlarge or reduce the size of
the second region of interest ROI2 to be defined. The size may be
varied e.g. by scrolling the mouse wheel for example. The size of
the circle may be changed by selecting a value among a set of
predetermined values.
[0170] The above-described size and/or position adjustments of ROI2
may be viewed on display in real time by the practitioner, which
makes it possible to further adjust the size and/or position where
necessary.
[0171] All that has been described above in connection with a
circle and a mouse equally applies to other displayed landmarks and
user input tools, as well as the operation of both landmarks and
user input tools to define the second region of interest.
[0172] In step S6.2 the position of the ROI2 can also be defined or
adjusted according to an axis z that is perpendicular to the x, y
plane of FIG. 6B so as to finish defining the desired position of
the second volume of data in accordance with the practitioner
needs.
[0173] The z-axis position or height of ROI2 (Field Of View or FOV)
may be defined or adjusted based on a lateral scout view. The
lateral scout view may advantageously be that used for determining
the height of the horizontal plane of interest at step S2 above and
illustrated on FIG. 5 (LSV).
[0174] The lateral scout view LSV provides the practitioner with
additional morphological information such as indication about the
location of teeth and their geometries in a vertical plane (y, z
plane). This may help the practitioner to further define the
position of the ROI2 relative to the maxillofacial region, in
particular as regards the z-axis position. In addition, the y-axis
position of the ROI2 may also be better defined or adjusted thanks
to lateral scout view LSV.
[0175] The height or size in height of ROI2 may have a
predetermined value and may be changed upon command by the
practitioner so as to increase or reduce the second volume of data
to be acquired. The same process as that described above for the
size (e.g. diameter for a circle) of the circle C may also apply
here for modifying the z-axis position. To be noted that the
practitioner may flip back and forth between the views of FIGS. 5
and 6B to manually adjust x, y and/or z-axis positions of ROI2
and/or size thereof.
[0176] The height or size in height of the ROI2 may be changed by
selecting a value among a set of predetermined values.
[0177] In the present embodiment, as already mentioned above the
second volume of data to be acquired may take the shape of a
cylinder whose dimensions may vary according to the practitioner's
needs.
[0178] To be noted that defining the geometric position of the ROI2
sets the position of the center of the ROI2.
[0179] It has been explained above how to define or adjust the
z-axis position or height of ROI2 based on a lateral scout
view.
[0180] However, more generally, the z-axis position or height of
ROI2 may be defined or adjusted based on determining the height of
the horizontal plane of interest as described at step S2 above. In
particular, other processes than the lateral scout view may be used
such as acquiring an optical image or performing physical
measurements as described above at steps S2.3 and S2.4.
[0181] Alternatively, the z-axis position or height of ROI2 may be
defined or adjusted independently from the determination of the
height of the plane of interest as described at step S2 above. The
z-axis position or height of ROI2 may then be defined or adjusted
based on one of the following that is performed on purpose for
achieving this goal: [0182] acquiring a lateral x-ray scout view
comprising the patient's maxillofacial first region of interest
(ROI1); [0183] acquiring an optical image comprising the patient's
maxillofacial first region of interest (ROI1) including landmarks;
[0184] performing physical measurements on the patient's
maxillofacial first region of interest (ROI1) using a patient
positioning device.
[0185] The above steps are identical to those described above in
connection with steps S2.1, S2.2, S2.3 and S2.4. However, in this
alternative embodiment method the same step may be performed twice,
one for determining the height of the plane of interest and the
other for defining the z-axis position of the ROI2.
[0186] As a variant embodiment, the step for defining or adjusting
the z-axis position of ROI2 may be different from that performed at
step S2. For example, a lateral scout view is acquired to be used
for defining or adjusting the z-axis position of ROI2 whereas step
S2 has been carried without using a lateral scout view.
[0187] It is to be noted that the size in height of the ROI2 may
extend beyond the height of the CBCT slice which is here rather
thin, e.g. in the order of 1-15 mm, preferably, 1-5 mm.
[0188] The method further comprises a step S7 for obtaining
operating parameters based on at least the thus defined ROI2.
[0189] As seen above the ROI2 has been defined by its x, y and z
spatial coordinates which set the spatial or geometric position of
the center of the ROI2 and size. This position and size information
on the ROI2 has thus been obtained with accuracy based on patient's
data and not on averaged patient's data. This therefore makes it
possible for the practitioner to adjust the trajectory of both the
x-ray source and x sensor to subsequently acquire a 3D volume
(second set of data including the ROI2) based on the ROI2 position
and size. To be noted that the trajectory may be based on the ROI2
position only. Both the x-ray source and x sensor will be operable
to simultaneously move around the patient's head along this
trajectory. Preferably, the 3D volume corresponds to the volume of
data of the ROI2. However, other configurations may be
envisaged.
[0190] Through this adjustment the position of the center of
rotation of the set of the x-ray source and x sensor may be
modified in accordance with the targeted anatomy (ex: ROI2).
[0191] An example of a possible trajectory for both x-ray source 18
and x sensor 20 is illustrated on FIG. 7 on which the following
notations have been used:
[0192] C: center of rotation of the gantry;
[0193] N: nose of the patient;
[0194] SP: sagittal plane of the patient;
[0195] T: trajectory followed by the center C;
[0196] V: 3D volume that is reconstructed/obtained through
describing trajectory T.
[0197] In a general manner, the position and size of the ROI2 are
operating parameters as well as the shape of the ROI2 which is here
a cylinder in the example embodiment.
[0198] If the 3D volume to be subsequently acquired does not
correspond to the ROI2, the operating parameters to be used during
this subsequent acquisition may differ from the above.
[0199] The obtained operating parameters make it possible to
determine a plurality of trajectories which each make it possible
to obtain the desired 3D volume.
[0200] The obtained operating or acquisition parameters of step S7
can then be stored while waiting for being used.
[0201] All the operating parameters are obtained based on the
defined ROI2 which accurately represents the region of interest for
the practitioner without any unnecessary details (optimization of
the position of the ROI or 3D volume to be subsequently
acquired).
[0202] Therefore the obtained operating parameters are tailored to
the specific needs of the practitioner and reduce as much as
possible the patient's area that will be exposed to x-rays as well
as the x-ray dose to be used.
[0203] To be noted that a few steps (other than manual steps S1 and
S6) may be performed automatically by control assembly 44 of FIG. 2
in the embodiment method of FIG. 3.
[0204] The operating or acquisition parameters that have been
obtained at step S7 may be used in the course of a subsequent step
S8 for acquiring a second set of data relating to the patient's
maxillofacial second region of interest (ROI2) and including the
latter using a second x-ray dose. This second set of data to be
acquired corresponds to the above 3D volume of data.
[0205] This acquisition step will be performed with an x-ray CBCT
imaging apparatus that is not necessarily the apparatus 10. This
acquisition step may be separate in time from the first steps S1 to
S7, e.g. by several hours, days, months, etc. It will be assumed
that the patient's maxillofacial region has not changed between the
two acquisitions.
[0206] Here the method step S8 comprises a prior patient
positioning step before acquiring a second set of data, using the
recorded or stored different setting parameters defining the first
position of the patient (see above steps S2 and S3). This prior
step makes provision for adjusting the setting parameters in the
x-ray CBCT imaging apparatus, in particular of the patient
positioning device or accessory used at step S3, so that the
patient be positioned in the same first position or close to in
view of this second data acquisition.
[0207] The obtained operating or acquisition parameters (ex:
trajectory, x-ray dose, etc.) are next used at step S8 to adjust or
set the x-ray CBCT imaging apparatus in view of acquiring a 3D
volume of data including the ROI2 relative to the patient's
maxillofacial region.
[0208] The x-ray dose that is used for this second data acquisition
is higher than the first x-ray dose for generating a slice: the
first x-ray dose is less than or equal to 20% of the second x-ray
dose, preferably less than or equal to 10% and more preferably less
than or equal to 5%.
[0209] By way of example, the first x-ray dose is 4 .mu.Sv and the
second x-ray dose is: [0210] 200 .mu.Sv for a 3D examination with a
large field of view (17.times.13 cm); [0211] 20 .mu.Sv for a 3D
examination with a 5.times.5 cm field of view.
[0212] By way of example, the duration of the exposure to x-ray for
the second data acquisition is between 5 and 20 s for a 3D
examination compared with an approximately 5 s duration for the
first data acquisition.
[0213] By way of example, the resolution of the image(s) obtained
through the second data acquisition is defined by a 100m voxel size
for a 3D examination compared with a 500m voxel size for the first
data acquisition.
[0214] The invention has been described in detail, and may have
been described with particular reference to a suitable or presently
preferred embodiment, but it will be understood that variations and
modifications can be effected within the spirit and scope of the
invention. The presently disclosed embodiments are therefore
considered in all respects to be illustrative and not restrictive.
The scope of the invention is indicated by the appended claims, and
all changes that come within the meaning and range of equivalents
thereof are intended to be embraced therein.
* * * * *