Title of Invention	EXACT VOLUME IMAGING INVOLVING MULTIPLE PARTIAL SCANS
Abstract	The invention relates to a method for performing an exact volume imaging with a C-arm digital x-ray imaging system by moving the source through two partial circular scans which form a complete source trajectory. The partial circular scans form a complete source trajectory when the plane defined by the C-arm is repositioned for the second scan at an angle equal to the cone angle with respect to the long axis of the patient.

Title of Invention

EXACT VOLUME IMAGING INVOLVING MULTIPLE PARTIAL SCANS

Abstract

The invention relates to a method for performing an exact volume imaging with a C-arm digital x-ray imaging system by moving the source through two partial circular scans which form a complete source trajectory. The partial circular scans form a complete source trajectory when the plane defined by the C-arm is repositioned for the second scan at an angle equal to the cone angle with respect to the long axis of the patient.

Full Text	EXACT VOLUME IMAGING INVOLVING MULTIPLE PARTIAL SCANS BACKGROUND OF THE INVENTION Field of the Invention This invention relates generally to x-ray imaging systems with a C-arm which can be used for volume imaging. More specifically, this invention relates to scanning methods and algorithms used for volume reconstruction. Background and Prior Art Digital x-ray systems include C-arm volume imaging systems. These C-arm imaging systems have a source and detector that are 180 degrees opposite of each other at the ends of a C-arm. The C-arm itself is capable of being translated along the axis of the patient (the z-axis) (or the patient table can be translated) and capable of being rotated about that axis. The x-ray sources of these C-arm imaging systems can be modeled as projecting a cone of x-ray radiation through a volume of a patient to be detected by a detector having an area. These C-arm imaging systems have been used to generate three dimensional reconstructions of volumes within patients. Such C-arm imaging systems usually rely on partial circle scans over an angular interval for 180 degrees plus the cone angle within a single plane. This angular interval typically ranges up to 200 degrees. Such a trajectory can exactly reproduce a disk with radius r inside the mid-plane define by the rotation of the line between the source and the detector center. However the volume outside the mid-plan only provides enough information for an approximate reconstruction. In order to provide an exact reconstruction of an arbitrary volume within a patient, a complete source trajectory is required. A particular complete source trajectory can be seen in Fig. 1. as a "wobble." Various other source trajectories have been combined to provide composites which are complete source trajectories and are well known in the art. Examples include a circle and line, two orthogonal circles, a circle an arc, and a number of other trajectories which involve moving the source in a number of different dimensions. Once projections have been acquired over a complete source trajectory, an appropriate beam reconstruction algorithm can be used a known in the art. However, the above complete source trajectories are impractical to achieve with the current C-arm imaging systems. Further it is preferable that the source move with a constant speed. This avoids significant complications in implementing the reconstruction algorithm. Accordingly, there remains a need in the art for a complete source trajectory which can be practically implemented in current C-arm x-ray imaging systems. SUMMARY OF THE INVENTION A method for performing an exact volume imaging with a C-arm digital x-ray imaging system by moving the source through two partial circular scans which form a complete source trajectory. The partial circular scans form a complete source trajectory when the plane defined by the C-arm is repositioned for the second scan at an angle equal to the cone angle with respect to the long axis of the patient. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and are not limitative of the present invention, and wherein: Figure 1 is the graph of a wobble complete source trajectory; Figure 2 is a graph of two source trajectories which when combined form a complete source trajectory; Figure 3 is a diagram of a patient defining a coordinate system and angles; Figure 4 is a diagram of a coordinate system defined by a source and a detector; Figure 5(a)-5(d) are successive views in time of a C-arm imaging system performing a first scan; Figure 6(a)-6(d) are successive views in time of a C-arm imaging system performing a second scan. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, a method for providing a complete source trajectory to achieve an exact reconstruction of a scan field of view is provided. See Fig. 2. In essence, a first partial circle scan is used for source trajectory 21, and then the plane of the C-arm is rotated at an angle to the z-axis. Then a second partial circle scan 22 is performed. Together these constitute a complete source trajectory. Such a complete source trajectory can be completed with current C-arm systems and at constitute source speed. The angle between the planes defined by the two partial (or short) circle scans is p. The angle of the cone from the source to encompass a volume r within or partially within the patient is the the angle βcone. According to the present invention, β=βcone. Fig. 3 defines the x,y,z coordinates and the a angle with respect to a patient body 31. Fig. 4 defines the angle p. where the z,y,z and x',y,z' represent the two coordinate systems created by the rotation of angle p. According to the present invention, the angle rotated by the source a must define a partial circle. More particularly, to achieve an exact reconstruction a must finish at 180 degree + βcone. Note, however, even a scan for a rotation less than this value if repeated at an angle βcone from the z-axis provides a more complete reconstruction than a full rotation a without the second scan at an angle. More precisely, looking to Fig. 4, we candefine the source trajectory as where D is the distance to source. The above has assumed that the angle with the Z axis of the patient body starts at zero. However, as a more general proposition, as long as the angle between the two plans formed by the two partial circular scans is βcone or greater, the initial start position can vary. Particularly where βcone is large, the initial scan may need to start at angle for -βcone/2, with the second scan at +βcone/2. In an embodiment of the present invention, a sequence of steps of steps is performed. The C-arm is placed in a start position, with α=αstart and β=0°. A scan is performed where a goes from αstart to αstart+180°+βcone. See Fig. 5. Then β is set to βcone and a reset to a new αstan. Then a goes from astan to αstart+180°+βcone again. Normal reconstruction algorithms can now be applied. See Fig. 6. The invention having been thus described, it will be obvious to those skilled in the art that the same may be varied in many ways without departing from the spirit and scope of the invention. We Claim: 1. A c-arm imaging system for performing a volume imaging to obtain an exact three-dimensional reconstruction of the acquired volume images within a patient, the system comprising a source for x-ray radiation, at least one detector to detect a substantially complete source trajectory of X-ray radiation through the volume of the patient, a c-arm enabled to be translated along an axis of the patient, and a software structure to generate three dimensional reconstruction of volumes within the patient, the system is configured to: - define a cone angle for the volume to be reconstructed, - define a plane by the source, the c-arm, and the detector; - position the c-arm such that said plane is orthogonal to a long axis of the patient; - perform a partial circular scan by rotating the source to an angle equaling to 180° plus the value of said cone angle; - reposition the c-arm such that the orthogonal of the plane in the repositioned configuration forms an angle equal to the value of the cone angle with the long axis; and - calculate the reconstructed volume within the patient body. ABSTRACT TITLE: EXACT VOLUME IMAGING INVOLVING MULTIPLE PARTIAL SCANS The invention relates to a method for performing an exact volume imaging with a C-arm digital x-ray imaging system by moving the source through two partial circular scans which form a complete source trajectory. The partial circular scans form a complete source trajectory when the plane defined by the C-arm is repositioned for the second scan at an angle equal to the cone angle with respect to the long axis of the patient.

Full Text

EXACT VOLUME IMAGING INVOLVING MULTIPLE PARTIAL SCANS
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to x-ray imaging systems with a C-arm
which can be used for volume imaging. More specifically, this invention relates to
scanning methods and algorithms used for volume reconstruction.
Background and Prior Art
Digital x-ray systems include C-arm volume imaging systems. These C-arm
imaging systems have a source and detector that are 180 degrees opposite of
each other at the ends of a C-arm. The C-arm itself is capable of being translated
along the axis of the patient (the z-axis) (or the patient table can be translated)
and capable of being rotated about that axis. The x-ray sources of these C-arm
imaging systems can be modeled as projecting a cone of x-ray radiation through a
volume of a patient to be detected by a detector having an area.
These C-arm imaging systems have been used to generate three
dimensional reconstructions of volumes within patients. Such C-arm imaging
systems usually rely on partial circle scans over an angular interval for 180
degrees plus the cone angle within a single plane. This angular interval typically
ranges up to 200 degrees. Such a trajectory can exactly reproduce a disk with
radius r inside the mid-plane define by the rotation of the line between the source
and the detector center. However the volume outside the mid-plan only provides
enough information for an approximate reconstruction.
In order to provide an exact reconstruction of an arbitrary volume within a
patient, a complete source trajectory is required. A particular complete source
trajectory can be seen in Fig. 1. as a "wobble." Various other source trajectories
have been combined to provide composites which are complete source
trajectories and are well known in the art. Examples include a circle and line, two
orthogonal circles, a circle an arc, and a number of other trajectories which
involve moving the source in a number of different dimensions. Once projections
have been acquired over a complete source trajectory, an appropriate beam
reconstruction algorithm can be used a known in the art.

However, the above complete source trajectories are impractical to achieve
with the current C-arm imaging systems. Further it is preferable that the source
move with a constant speed. This avoids significant complications in
implementing the reconstruction algorithm. Accordingly, there remains a need in
the art for a complete source trajectory which can be practically implemented in
current C-arm x-ray imaging systems.
SUMMARY OF THE INVENTION
A method for performing an exact volume imaging with a C-arm
digital x-ray imaging system by moving the source through two partial circular
scans which form a complete source trajectory. The partial circular scans form a
complete source trajectory when the plane defined by the C-arm is repositioned
for the second scan at an angle equal to the cone angle with respect to the long
axis of the patient.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed
description given herein below and the accompanying drawings which are given
by way of illustration only, and are not limitative of the present invention, and
wherein:
Figure 1 is the graph of a wobble complete source trajectory;
Figure 2 is a graph of two source trajectories which when combined form a
complete source trajectory;
Figure 3 is a diagram of a patient defining a coordinate system and angles;
Figure 4 is a diagram of a coordinate system defined by a source and a
detector;
Figure 5(a)-5(d) are successive views in time of a C-arm imaging system
performing a first scan;
Figure 6(a)-6(d) are successive views in time of a C-arm imaging system
performing a second scan.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the present invention, a method for providing a complete
source trajectory to achieve an exact reconstruction of a scan field of view is
provided. See Fig. 2. In essence, a first partial circle scan is used for source
trajectory 21, and then the plane of the C-arm is rotated at an angle to the z-axis.
Then a second partial circle scan 22 is performed. Together these constitute a
complete source trajectory. Such a complete source trajectory can be completed
with current C-arm systems and at constitute source speed. The angle between
the planes defined by the two partial (or short) circle scans is p. The angle of the
cone from the source to encompass a volume r within or partially within the
patient is the the angle βcone. According to the present invention, β=βcone.
Fig. 3 defines the x,y,z coordinates and the a angle with respect to a
patient body 31. Fig. 4 defines the angle p. where the z,y,z and x',y,z' represent
the two coordinate systems created by the rotation of angle p.
According to the present invention, the angle rotated by the source a must
define a partial circle. More particularly, to achieve an exact reconstruction a
must finish at 180 degree + βcone. Note, however, even a scan for a rotation less
than this value if repeated at an angle βcone from the z-axis provides a more
complete reconstruction than a full rotation a without the second scan at an
angle.
More precisely, looking to Fig. 4, we candefine the source trajectory as

where D is the distance to source.
The above has assumed that the angle with the Z axis of the patient body
starts at zero. However, as a more general proposition, as long as the angle
between the two plans formed by the two partial circular scans is βcone or greater,
the initial start position can vary. Particularly where βcone is large, the initial scan
may need to start at angle for -βcone/2, with the second scan at +βcone/2.
In an embodiment of the present invention, a sequence of steps of steps is
performed. The C-arm is placed in a start position, with α=αstart and β=0°. A scan
is performed where a goes from αstart to αstart+180°+βcone. See Fig. 5. Then β is set

to βcone and a reset to a new αstan. Then a goes from astan to αstart+180°+βcone
again. Normal reconstruction algorithms can now be applied. See Fig. 6.
The invention having been thus described, it will be obvious to those skilled
in the art that the same may be varied in many ways without departing from the
spirit and scope of the invention.

We Claim:
1. A c-arm imaging system for performing a volume imaging to obtain an
exact three-dimensional reconstruction of the acquired volume images
within a patient, the system comprising a source for x-ray radiation, at
least one detector to detect a substantially complete source trajectory of
X-ray radiation through the volume of the patient, a c-arm enabled to be
translated along an axis of the patient, and a software structure to
generate three dimensional reconstruction of volumes within the patient,
the system is configured to:
- define a cone angle for the volume to be reconstructed,
- define a plane by the source, the c-arm, and the detector;
- position the c-arm such that said plane is orthogonal to a long axis of the
patient;
- perform a partial circular scan by rotating the source to an angle equaling
to 180° plus the value of said cone angle;
- reposition the c-arm such that the orthogonal of the plane in the
repositioned configuration forms an angle equal to the value of the cone
angle with the long axis; and
- calculate the reconstructed volume within the patient body.

ABSTRACT

TITLE: EXACT VOLUME IMAGING INVOLVING MULTIPLE PARTIAL SCANS
The invention relates to a method for performing an exact volume imaging with
a C-arm digital x-ray imaging system by moving the source through two partial
circular scans which form a complete source trajectory. The partial circular scans
form a complete source trajectory when the plane defined by the C-arm is
repositioned for the second scan at an angle equal to the cone angle with
respect to the long axis of the patient.

Documents:

01824-kolnp-2006-abstract.pdf

01824-kolnp-2006-asignment.pdf

01824-kolnp-2006-claims.pdf

01824-kolnp-2006-correspondence other.pdf

01824-kolnp-2006-correspondence others-1.1.pdf

01824-kolnp-2006-description (complete).pdf

01824-kolnp-2006-drawings.pdf

01824-kolnp-2006-form-1.pdf

01824-kolnp-2006-form-2.pdf

01824-kolnp-2006-form-3.pdf

01824-kolnp-2006-form-5.pdf

01824-kolnp-2006-international publication.pdf

01824-kolnp-2006-international search authority report-1.1.pdf

01824-kolnp-2006-international search report.pdf

01824-kolnp-2006-pct form.pdf

1824-KOLNP-2006-(16-02-2012)-CORRESPONDENCE.pdf

1824-KOLNP-2006-(16-02-2012)-FORM-1.pdf

1824-KOLNP-2006-ABSTRACT.pdf

1824-KOLNP-2006-AMANDED CLAIMS.pdf

1824-KOLNP-2006-CORRESPONDENCE 1.1.pdf

1824-KOLNP-2006-CORRESPONDENCE OTHERS 1.1.pdf

1824-KOLNP-2006-CORRESPONDENCE-1.2.pdf

1824-KOLNP-2006-DESCRIPTION (COMPLETE).pdf

1824-KOLNP-2006-DRAWINGS.pdf

1824-KOLNP-2006-Examination Report Reply Recieved.pdf

1824-KOLNP-2006-EXAMINATION REPORT.pdf

1824-KOLNP-2006-FORM 1.pdf

1824-KOLNP-2006-FORM 18 1.1.pdf

1824-kolnp-2006-form 18.pdf

1824-KOLNP-2006-FORM 2.pdf

1824-KOLNP-2006-FORM 26.pdf

1824-KOLNP-2006-FORM 3 1.1.pdf

1824-KOLNP-2006-FORM 3.pdf

1824-KOLNP-2006-FORM 5.pdf

1824-KOLNP-2006-GPA.pdf

1824-KOLNP-2006-GRANTED-ABSTRACT.pdf

1824-KOLNP-2006-GRANTED-CLAIMS.pdf

1824-KOLNP-2006-GRANTED-DESCRIPTION (COMPLETE).pdf

1824-KOLNP-2006-GRANTED-DRAWINGS.pdf

1824-KOLNP-2006-GRANTED-FORM 1.pdf

1824-KOLNP-2006-GRANTED-FORM 2.pdf

1824-KOLNP-2006-GRANTED-SPECIFICATION.pdf

1824-KOLNP-2006-OTHERS 1.2.pdf

1824-KOLNP-2006-OTHERS-1.1.pdf

1824-KOLNP-2006-OTHERS.pdf

1824-KOLNP-2006-PA.pdf

1824-KOLNP-2006-PETITION UNDER RULE 137.pdf

1824-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf

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Patent Number

253271

Indian Patent Application Number

1824/KOLNP/2006

PG Journal Number

28/2012

Publication Date

13-Jul-2012

Grant Date

10-Jul-2012

Date of Filing

30-Jun-2006

Name of Patentee

JOHN HOPKINS UNIVERSITY

Applicant Address

3400 N.CHARLES STREET BALTIMORE, MARYLAND 21218

Inventors:

#	Inventor's Name	Inventor's Address
1	STROBEL, Norbert, Karl	Stanford West Apartments, 1163 Clark Way, Palo Alto California 94304
2	RAMAMURTHI, Krishnakumar	3800 Canterbury Road, APT. C, Baltlmore, Maryland 21218

PCT International Classification Number

A61B6/03; A61B6/00

PCT International Application Number

PCT/US05/010865

PCT International Filing date

2005-03-30

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/557,475	2004-03-30	U.S.A.
2	11/091,992	2005-03-29	U.S.A.