Method and apparatus for projecting diagnostic images from non-isotropic volumed diagnostic data

• US 5,331,552 A
• Filed: 12/04/1992
• Issued: 07/19/1994
• Est. Priority Date: 07/14/1992
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Lloyd, Robert F., Kennedy, Thomas E., Wilbricht, Christopher J.
• Primary Examiner(s): Envall, Jr., Roy N.
• Assistant Examiner(s): Tran, Khai
• Application Number:
  US07/985,389
• Time in Patent Office: 592 Days
• Field of Search: 364/413.15, 364/413.22, 364/413.09, 364/413.21, 128/708, 128/710, 128/712
• US Class Current: 378/15
• CPC Class Codes: G01R 33/56 Image enhancement or correction, e.g. subtraction or averaging techniques , e.g. improvement of signal-to-noise ratio and resolution
• CPC Class Codes: G06T 15/08 Volume rendering
• CPC Class Codes: H05G 1/26 Measuring, controlling or protecting measuring X-ray radiation G01T

Abstract

A computer program for manipulating diagnostic images obtained with computed tomography or magnetic resonance systems spatially compresses acquired non-isotropic data to isotropic coordinates as stored in computer memory. A view axis along which a projected image is to be displayed is adjusted to reflect this distortion. After projecting the voxel data to pixels of an image, the data is decompressed to remove any distortion. The decompression operates over the limited number of pixels rather than the entire set of voxels providing faster image generation.

Claims

1. A method of generating a diagnostic image of a body comprising the steps of:

directing a radiated energy through a region of interest of the body;

detecting an interaction of the energy with the body to acquire data at a plurality of voxels, the voxels having actual spatial coordinates in dimensions of a coordinate system and being located within the region of interest of the body wherein a value of the datum of each voxel corresponds to a physical property of the body at the spatial coordinates, wherein the spatial coordinates of the voxels are not equally spaced along each of the dimensions;

storing the data of the voxels in addresses in an electronic memory wherein the addresses are related to scaled spatial coordinates of the voxels, the scaled spatial coordinates being the actual spatial coordinates of the voxels transformed by multiplying at least one coordinate by a scaling factor;

determining a desired view axis with respect to the actual spatial coordinates of the voxels along which to view the voxels, the desired view axis defined by three rotative coordinates;

calculating an effective view axis from the desired view axis and the scaling factor, so that a ray directed along the effective view axis intersects the same voxels at the scaled spatial coordinates as the desired view axis would intersect the voxels at the actual spatial coordinates;

transforming the scaled spatial coordinates of each voxel by at least one rotation to produce rotated spatial coordinates so that the effective view axis is normal to an imaging plane;

projecting the voxels along the view axis to pixels in the image plane having image coordinates corresponding to the rotates spatial coordinates; and

displaying pixel data at the image coordinates in an image.

2. The method of claim 1 including the additional step of rescaling the pixels of the image plane after the projecting step so that the image coordinates of the pixels correspond to the actual spatial coordinates of the voxels.

3. The method of claim 2 wherein the step of rescaling also rotates the pixels about the view axis.

4. The method of claim 1 wherein the data of the voxels x-ray attenuation data produced in a three-dimensional field by a computed tomography scanner.

5. The method of claim 1 wherein the data of the voxels is nuclear magnetic resonance data produced in a three-dimensional field by magnetic resonance imaging equipment.

6. The method of claim 1 wherein the effective view axis is calculated by:

##EQU10## where r_eff is an angle of rotation of the effective axis, t_eff is an angle of tilt of the effective axis,

r is an angle of rotation of the view axis,

t is an angle of tilt of the view axis, and

1/a is the scaling factor.

7. The method of claim 2 where the rescaling is accomplished by multiplying each image coordinate x'"'"' and y'"'"' of a pixel by the matrix M_d where:

##EQU11## where r_eff is an angle of rotation of the effective axis, t_eff is an angle of tilt of the effective axis,

r is an angle of rotation of the view axis,

t is an angle of tilt of the view axis, and

1/a is the scaling factor.

8. An apparatus generating a diagnostic image of a body comprising:

a means for directing a radiated energy through a region of interest of the body;

a means for detecting an interaction of the energy with the body to acquire data at a plurality of voxels, the voxels having spatial coordinates located within the region of interest of the body wherein a value of the datum of each voxel corresponds to a physical property of the body at the spatial coordinates, wherein the voxels are not equally spaced along each of the dimension;

an electronic memory means for storing the data of the voxels in addresses wherein the addresses are related to scaled spatial coordinates of the voxels, the scaled spatial coordinates being the actual spatial coordinates of the voxels transformed by multiplying at least one coordinate by a scaling factor;

a means for determining a desired view axis with respect to the actual spatial coordinates of the voxels along which to view the voxels to an image plane, the desired axis defined by three rotative coordinates;

a means for calculating an effective view axis from the desired view axis and the scaling factor, so that a ray directed along the effective view axis intersects the same voxels at the scaled spatial coordinates as the desired view axis would intersect the voxels at the actual spatial coordinates;

a means for transforming the scaled spatial coordinates of each voxel by at least one rotation to produce rotated spatial coordinates so that the effective view axis is normal to an image plane;

a means for projecting the voxels along the view axis to pixels in the image plane having image coordinates corresponding to the rotated spatial coordinates; and

a means for displaying pixel data at the image coordinates in an image.

9. The apparatus of claim 8 wherein the means for transforming the scaled spatial coordinates includes means for rescaling the pixels of the image plane after projecting by the projecting mans so that the image coordinates of the pixels correspond to the axis spatial coordinates of the voxels.

10. The apparatus of claim 9 wherein the means for rescaling also rotates the pixels about the view axis.

11. The apparatus of claim 8 wherein the directing means is an x-ray tube and wherein the detecting means is an array of x-ray detectors to provide voxel data related to the attenuation of the x-rays by the body.

12. The apparatus of claim 8 wherein the directing means is an RF coil for transmitting RF energy and the detecting means is an RF antenna for receiving NMR signals to provide voxel data related to the precessing of protons caused by the RF energy.