Method for using three points to define a 2D MR imaging section

Details Method for using three points to define a 2D MR imaging section Method for using three points to define a 2D MR imaging section

1998-11-25

2001-08-14

Oda, Christine (Department: 2862)

Electricity: measuring and testing

Particle precession resonance

Using a nuclear resonance spectrometer system

C600S410000, C324S309000

Reexamination Certificate

active

06275035

ABSTRACT:

FIELD OF THE INVENTION
The field of the invention is nuclear magnetic resonance imaging methods and systems. More particularly, the invention relates to MRI imaging systems equipped for real-time imaging and methods for assisting the operator to interactively position the excitation profile for subsequent acquisition of the desired anatomical imaging section.
BACKGROUND OF THE INVENTION
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field Bo), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but process about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B
1
) which is the x-y plane and which is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment M. A signal is emitted by the excited spins after the excitation signal B
1
is terminated and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (G
x
, G
y
and G
z
) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
When attempting to define the volume of coverage for an MRI scan, the NMR system operator may desire to prescribe a specific two dimension scan plane within the total volume of coverage. This process can be particularly useful when prescribing a double oblique, off axis two dimensional scan plane of complex anatomy such as vasculature.
Typically, two dimensional axial, sagittal and coronal “scout” images are first acquired. Such scout images are stored for later use. To use, the operator calls up the scout image and either graphically or explicitly (using geometry coordinates) prescribes the imaging volume directly on the scout images. The imaging volume may be either a two dimensional stack of slices or a three dimensional slab of the structure of interest. The drawback of this technique is that the operator does not actually see the results of the prescribed geometry until the subsequent imaging volume is acquired. Further, complex double oblique views are not easily visualized from standard scout images which makes the task of prescribing such sections difficult and time consuming.
SUMMARY OF THE INVENTION
In accordance with the present invention, Applicant provides a method and apparatus for producing an imaging plane on an image of a structure of interest, such as an anatomical structure, positioned in an MRI system. An operator interactively pages through real-time, planar sections of the structure of interest. Using an input device, the operator selects three separate points in up to three different planar sections of the structure under study. Within approximately one second of selection of the third point, the method of the present invention determines the imaging plane containing the three selected points, determines the centroid of the imaging plane centered on a triangle defined by the three selected points, sends such imaging geometry and in-plane offsets of the imaging plane directly to the MRI system to generate a new imaging plane optimally positioned with respect to the selected points on the structure of interest and displaying such new imaging plane. The operator can also selectively maneuver the imaging plane on the image of the structure of interest. The operator uses a graphical user interface in conjunction with the input device and a display screen for producing the imaging plane on the structure of interest. Such graphical user interface is referred to as a three point tool.
It is a principal object of the present invention to rapidly localize views on an image of a structure of interest displayed on a screen of a MRI system. Another object of the present invention is to calculate the unique plane that intersects three selected points on a structure of interest and direct real-time scan plan geometry to intersect such selected points and provide a unique, potentially double oblique view, centered on the centroid of the triangle defined by the three selected points.
Other principal features and advantages of the present invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.


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