U.S. patent application number 10/760627 was filed with the patent office on 2004-11-04 for computed tomogrophy scanning.
Invention is credited to Brown, Kevin John, Jaffray, David, Siewerdsen, Jeffrey H., Sonke, Jan-Jakob, van Herk, Marcel.
Application Number | 20040218719 10/760627 |
Document ID | / |
Family ID | 32773963 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040218719 |
Kind Code |
A1 |
Brown, Kevin John ; et
al. |
November 4, 2004 |
Computed tomogrophy scanning
Abstract
Artefacts in the reconstructed volume data of cone beam CT
systems can be removed by the application of respiration
correlation techniques to the acquired projection images. To
achieve this, the phase of the patients breathing is monitored
while acquiring projection images continuously. On completion of
the acquisition, projection images that have comparable breathing
phases can be selected from the complete set, and these are used to
reconstruct the volume data using similar techniques to those of
conventional CT. Any phase can be selected and therefore the effect
of breathing can be studied. It is also possible to use a feature
in the projection image(s) such as the patient's diaphragm to
determine the breathing phase. This feature in the projection
images can be used to control delivery of therapeutic radiation
dependent on the: patient's breathing cycle, to ensure that the
tumour is in the correct position when the radiation is
delivered.
Inventors: |
Brown, Kevin John; (Crawley,
GB) ; Jaffray, David; (Etobicoke, CA) ;
Siewerdsen, Jeffrey H.; (Toronto, CA) ; van Herk,
Marcel; (Amsterdam, NL) ; Sonke, Jan-Jakob;
(Amsterdam, NL) |
Correspondence
Address: |
BROMBERG & SUNSTEIN LLP
125 SUMMER STREET
BOSTON
MA
02110-1618
US
|
Family ID: |
32773963 |
Appl. No.: |
10/760627 |
Filed: |
January 20, 2004 |
Current U.S.
Class: |
378/95 |
Current CPC
Class: |
G06T 2207/30061
20130101; G06T 2207/20068 20130101; G06T 7/0016 20130101; G06T
2211/412 20130101; G06T 2207/30096 20130101; G06T 11/005 20130101;
A61N 5/1064 20130101; G06T 2207/10081 20130101; G06T 2207/20192
20130101; G06T 5/009 20130101; G06T 5/003 20130101; G06T 7/20
20130101 |
Class at
Publication: |
378/095 |
International
Class: |
H05G 001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2003 |
GB |
0301278.8 |
Nov 28, 2003 |
GB |
0327675.5 |
Claims
1. A method of cone beam CT scanning in which respiration
correlation techniques are applied to the acquired two-dimensional
projection images.
2. A method of cone beam CT scanning according to claim 1 in which
the phase of the patient's breathing is monitored continuously
during acquisition of projection images.
3. A method of cone beam CT scanning according to claim 2 in which
projection images that have comparable breathing phases are
selected from the complete data set on completion of the
acquisition and are used to reconstruct the volume data.
4. A method of cone beam CT scanning according to claim 2 in which
a feature in the projection image(s) is used to determine the
breathing phase.
5. A method of cone beam CT scanning according to claim 4 in which
the feature is the position of the patient's diaphragm.
6. A method of cone beam CT scanning according to claim 1 in which
visual and/or audible prompts are provided for the patient's
breathing.
7. A method of cone beam CT scanning according to claim 1 in which
therapeutic radiation is delivered during the scan at times
correlated with the patient's breathing cycle.
8. A cone beam CT scanner including means for acquiring information
as to the patient respiration cycle and means for selection of
acquired two-dimensional projection images from the set of data
acquired during a scan on the basis of the respiration cycle
information.
9. A cone beam CT scanner according to claim 8 adapted to monitor
the phase of the patient's breathing continuously during
acquisition of projection images.
10. A cone beam CT scanner according to claim 9 arranged to select
projection images that have comparable breathing phases from the
complete data set on completion of the acquisition and to use these
to reconstruct the volume data.
11. A cone beam CT scanner according to claim 9 including means for
detecting a respiration-cycle-correlated feature in the projection
image(s) thereby to determine the breathing phase.
12. A cone beam CT scanner according to claim 11 in which the
feature is the position of the patient's diaphragm.
13. A cone beam CT scanner according to claim 7 including means to
provide visual and/or audible prompts for the patient's
breathing.
14. A radiotherapy device comprising a cone beam CT scanner and a
source of therapeutic radiation, in which the CT scanner applies
respiration correlation techniques to the acquired two-dimensional
projection images and therapeutic radiation is delivered during the
scan at times correlated with the patient's breathing cycle.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to scanning by computed
tomography (CT).
BACKGROUND ART
[0002] CT scanning is a process for imaging the internal structure
of a patient. In conventional CT scanning, a beam of x-rays is
projected through the patient and its attenuation is measured. At
the same time, the apparatus is rotated about an axis passing
longitudinally through the patient. Thus, data is acquired as to
the attenuation of the beam in each direction in the plane in which
rotation takes place. From this data, the internal structure of the
patient on that plane can be computed. The patient or apparatus is
then indexed along the axis and a further plane (known as a
`slice`) is then investigated. A three dimensional image of the
patient can then be constructed from the various slices.
[0003] One problem is that over the time required to acquire the
necessary slices, the patient is not motionless. Gross motor
movement can be avoided by suitable instruction to the patient, but
even so each slice is acquired at a different phase of the
breathing cycle. This results in a beating artefact due to the
different frequency of breathing and slice acquisition.
[0004] Two ways have been used to solve this problem. On is to
trigger the CT on a particular phase of the patients breathing.
This is termed `respiration gated CT` and implies that one CT slice
is acquired for every breath. This means that it takes a long time
to acquire a complete volume of data.
[0005] Another technique is to monitor the phase of the patients
breathing whilst acquiring CT slices continuously. Once the data is
acquired, slices that have comparable breathing phase are selected
from the complete set and these are then used to visualise the
volume. This has the advantage that any phase can be selected
retrospectively and therefore the effect of breathing can be
studied. This is termed `respiration correlated CT`.
[0006] Conventional CT scans have the disadvantage that the
resolution along the axis is poor since it corresponds to the slice
thickness. It is theoretically straightforward to increase this,
but doing so results in a correspondingly longer acquisition time,
or the need to rotate the apparatus correspondingly faster. Both
options also give rise to an attendant reduction in contrast in the
measured beam. Accordingly, `cone beam CT` methods have been
developed, in which a conical beam of radiation is directed at the
patient and a two-dimensional image acquired via a flat panel
detector. This apparatus is then rotated around the patient axis
and a three-dimensional image is reconstructed from the set of
two-dimensional images. As the individual slices are eliminated,
there is the same resolution in all directions of the image.
Likewise, as there are no slices the above-mentioned breathing
artefact is absent since there can be no variation in patient
position between slices.
SUMMARY OF THE INVENTION
[0007] We have however found that there are other artefacts in the
reconstructed volume data of cone beam CT systems, which we have
traced to patient breathing movements. In addition, the motion is
not measurable in the reconstructed volume data. This can be a
particular problem in cone beam systems due to the long time
required for acquisition, typically 1-2 minutes.
[0008] The techniques used in conventional CT scanners cannot be
used directly in a cone beam system as the data is acquired in 2D
projection images, and therefore slices cannot be selected from the
resulting data. However, respiration correlation techniques could
be applied to the acquired projection images rather than the
reconstructed CT volume. To achieve this, we propose monitoring the
phase of the patients breathing while acquiring projection images
continuously. On completion of the acquisition, projection images
that have comparable breathing phases can be selected from the
complete set, and these are used to reconstruct the volume data
using similar techniques to those of conventional CT. An advantage
is that any phase can be selected and therefore the effect of
breathing can be studied.
[0009] Breath control systems are available, intended for use in
conventional CT scanning, and which could be used to monitor the
patient's breathing. As an alternative, however, it is possible to
use a feature in the projection image(s) to determine the breathing
phase. A suitable feature is the position of the patient's
diaphragm. This can then be used to select the relevant images to
be used in the projection process.
[0010] It is known in the field of conventional CT scanning to be
advantageous to prompt the patient visually and audibly in order to
ensure a regular amplitude and pattern of breathing. Techniques
such as these could usefully be applied in the present
invention.
[0011] Furthermore this feature in the projection images can be
used to control delivery of therapeutic radiation dependent on the
patient's breathing cycle, to ensure that the tumour is in the
correct position when the radiation is delivered. This will provide
a direct measure of the patient's breathing phase, a significant
improvement as compared to current methods that use external
markers affixed to the patient. The use of a 3D volume data set
generated using the same patient position and contemporaneous with
the treatment will remove significant uncertainties.
[0012] The present invention further provides a radiotherapy device
comprising a respiration correlated cone beam CT scanner and a
source of therapeutic radiation, in which therapeutic radiation is
delivered during the scan at times correlated with the patient's
breathing cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] An embodiment of the present invention will now be described
by way of example, with reference to the accompanying figures in
which;
[0014] FIG. 1 is a view of a cone beam CT scanner according to the
present invention, viewed along the axis of rotation thereof;
[0015] FIG. 2 is a schematic view of the system incorporating such
a scanner; and
[0016] FIG. 3 shows a treatment apparatus including the scanner of
the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENT
[0017] FIG. 1 shows a cone beam CT scanner. A patient 10 is
supported on a couch 12 which may be of any suitable design.
Couches typically allow the elevation and longitudinal position of
the patient to be adjusted and this may be provided for as
desired.
[0018] An x-ray source 14 is arranged to project a wide beam 16 of
radiation generally directed towards the isocentre 18 of the
patient. The source 14 is rotatable around the isocentre 18 on a
rotational support 20. The support can; for example, be in the form
of a ring or annulus around the patient 10 and couch 12 in which
the source is mounted, or it can be a C-arm, or any suitable
support allowing the source to rotate, or any combination
thereof.
[0019] A two-dimensional flat-panel detector 22 is also mounted on
the support 20, opposite the source 14 and arranged to rotate in
synchronism therewith. If the support includes a C-arm then this
can be achieved by mounting the detector on the opposite arm.
[0020] Thus, radiation emitted by the source 14 is partially
absorbed by the patient and the attenuated signal is detected by
the flat panel detector 22. The source 14 and detector 22 are then
indexed rotationally and a fresh image obtained. This is repeated
until sufficient images are acquired to reconstruct the volume
data, typically one complete rotation.
[0021] FIG. 2 shows the system as a whole. The scanner of FIG. 1 is
shown, together with cables linking the source 14, detector 22 and
rotational support 20 to a plurality of computing means 24, 26
which process the data generated including the images, source
intensity (etc), and rotational support position. Data is output
via any suitable means, depicted generally as a monitor 28 but not
limited thereto, and the system is controlled by any suitable input
means, again depicted generally as a keyboard 30 but likewise not
especially limited thereto.
[0022] As mentioned above, we have found that there are artefacts
in the reconstructed volume data of cone beam CT systems, which we
have traced to patient breathing movements. To overcome or
alleviate these, respiration correlation techniques are applied to
the acquired projection images by the computing means 24, 26. This
differs from conventional respiration-correlated CT scanning in
acting on the acquired projection images rather than the
reconstructed CT volume.
[0023] To assist in this process, a breath control system is
provided at 32 to monitor the phase of the patients breathing while
the projection images are acquired. On completion of the
acquisition, projection images that have comparable breathing
phases can be selected from the complete set, and these are used to
reconstruct the volume data using cone beam CT techniques. As a
result, any phase or range of phases can be selected and therefore
the effect of breathing can be studied if desired.
[0024] As an alternative to the breath control system, it is
possible to use a feature in the projection image(s) to determine
the breathing phase, such as the position of the patient's
diaphragm. This can then be used to select the relevant images to
be used in the projection process.
[0025] An alert system including a light 34 and a buzzer 36 is
provided, to prompt the patient visually and audibly in order to
ensure a regular amplitude and pattern of breathing. Other alerts
could of course be employed, such as other forms of visible prompts
including (for example) movable devices, and other forms of audible
prompts including (for example) speakers, percussive devices or any
other form of controllable sound generation apparatus.
[0026] FIG. 3 shows a system including a therapeutic source of
radiation 38 arranged to emit a suitably collimated beam of
therapeutic radiation 40. This allows simultaneous scanning and
treatment. If the radiation from source 14 continues during the
treatment the selected feature (above) in the projection images can
be used to control delivery of therapeutic radiation from the
source 38, dependent on the patient's breathing cycle. This ensures
that the tumour is in the correct position when the radiation is
delivered. This will provide a direct measure of the patient's
breathing phase, a significant improvement as compared to current
methods that use external markers affixed to the patient. The use
of the same direct measure of the patient's breathing phase and
patient position to generate the 3D volume data set and control the
treatment delivery will remove significant uncertainties.
[0027] It will of course be understood that many variations may be
made to the above-described embodiment without departing from the
scope of the present invention.
* * * * *