System and method for real-time MRI-guided object navigation
A magnetic resonance method and system are provided for magnetic resonance (MR) image-guided insertion of an object into a biological tissue along a predetermined trajectory. The trajectory provides a path between a starting point and a target site within the tissue. Sufficiently high resolution images can be generated in real time to precisely guide the needle placement. A compressed sensing approach is used to generate the images based on minimization of a cost function, where the cost function is based on the predetermined needle path, artifact effects associated with the needle, the negligible changes in the images away from the trajectory, and the limited differences between successive images. The improved combination of spatial and temporal resolution facilitates an insertion procedure that can be continuously adjusted to accurately follow a predetermined trajectory in the tissue, without interruptions to obtain verification images.
1. A method for directing an object from a starting point to a target site in a biological tissue using real-time magnetic resonance imaging (MRI) guidance, comprising the steps of:
generating a high-resolution planning image of a region of the biological tissue that includes the starting point and the target site;
determining a trajectory from the starting point to the target site using the planning image;
generating and displaying a series of images of the region of the biological tissue and of an artifact based on the position of the object using a compressed sensing technique, wherein the series of images is generated and displayed substantially in real time;
wherein each image of the series of images is generated using a compressed sensing technique based on minimization of a cost function that includes:
a difference between the current image and the corresponding raw image data based on a particular MRI sampling operator;
a difference between the current image and a sum of a baseline image and a predicted artifact; and
a difference between the current image and the most recent image.
2. The method of claim 1 , further comprising:
introducing a distal end of the object into the starting point in a direction substantially corresponding to the direction of the trajectory; and
advancing the object further into the biological tissue along the trajectory toward the target site, wherein a direction of the advancement is based on the displayed series of images.
3. The method of claim 1 , wherein the cost function is denoted as ƒ(x t ) and has the form:
f
(
x
t
)
=
1
2
Ax
t
-
y
2
2
+
λ
1
x
t
-
(
x
ref
+
x
^
Needle
,
t
)
1
+
λ
2
x
t
-
x
t
-
1
1
wherein x t represents the current image being computed at time t, A represents an MRI sampling operator, y represents measured (raw) k-space data, X ref represents a predicted image without the presence of needle artifacts, {circumflex over (x)} Needle,t represents a predicted needle artifact, x t-1 represents the previous image that was computed at time t- 1 , and λ 1 and λ 2 are weighting coefficients.
4. The method of claim 3 , wherein a value for λ 1 is between 0.5 and 1.5.
5. The method of claim 3 , wherein a value for λ 2 is between 0.5 and 1.5.
6. The method of claim 1 , wherein each image of the series of images includes a representation of the trajectory.
7. The method of claim 1 , wherein the series of images is generated at a rate that is between 0.5 and 15 images per second.
8. The method of claim 1 , wherein each image of the series of images has an in-plane resolution that is between 0.5 mm and 2 mm.
9. The method of claim 1 , wherein each image of the series of images is generated using a radial sampling trajectory in k-space.
10. The method of claim 1 , wherein each image of the series of images is generated using a spiral sampling trajectory in k-space.
11. The method of claim 1 , wherein each image of the series of images is generated using a steady-state free precession technique.
12. The method of claim 1 , wherein each image of the series of images is generated using a balanced steady-state free precession technique.
13. An MRI system configured to facilitate directing an object from a starting point to a target site in a biological tissue using real-time magnetic resonance imaging (MRI) guidance, comprising:
a radio frequency (RF) signal generator and a magnetic field gradient generator which are together configured to provide an imaging protocol comprising a plurality of imaging pulse sequences that further comprise a plurality of RF pulse sequences and magnetic field gradient sequences for acquisition of image data; and
an image processing unit configured to generate a series of images based on the image data,
wherein the MRI system is configured to:
generate a high-resolution planning image of a region of the biological tissue that includes the starting point and the target site;
determine a trajectory from the starting point to the target site based on the planning image; and
generate and display the series of images of the region of the biological tissue and of an artifact using a compressed sensing technique, wherein each image is based on a current position of the object, and wherein the series of images is generated and displayed substantially in real time;
wherein each image of the series of images is generated using a compressed sensing technique based on minimization of a cost function that includes:
a difference between the current image and the corresponding raw image data based on a particular MRI sampling operator;
a difference between the current image and a sum of a baseline image and a predicted artifact; and
a difference between the current image and the most recent image.
14. The system of claim 13 , wherein the cost function is denoted as ƒ(x t ) and has the form:
f
(
x
t
)
=
1
2
Ax
t
-
y
2
2
+
λ
1
x
t
-
(
x
ref
+
x
^
Needle
,
t
)
1
+
λ
2
x
t
-
x
t
-
1
1
wherein x t represents the current image being computed at time t, A represents an MRI sampling operator, y represents measured (raw) k-space data, x ref represents a predicted image without the presence of needle artifacts, {circumflex over (x)} Needle,t represents a predicted needle artifact, x t-1 represents the previous image that was computed at time t- 1 , and λ 1 and λ 2 are weighting coefficients.
15. The system of claim 14 , wherein at least one of λ 1 and λ 2 has a value that is between 0.5 and 1.5.
16. The system of claim 13 , wherein each image of the series of images includes a representation of the trajectory.
17. The system of claim 13 , wherein the system is configured to generate the series of images at a rate that is between 0.5 and 15 images per second.
18. The system of claim 13 , wherein the system is configured to generate each image of the series of images with an in-plane resolution that is between 0.5 mm and 2 mm.
19. The system of claim 13 , wherein the system is configured to generate each image of the series of images using at least one of a spiral sampling trajectory or a radial sampling trajectory in k-space.
20. The system of claim 13 , wherein the system is configured to generate each image of the series of images using a steady-state free precession technique.