Method and apparatus for volumetric projection rendering using reverse ray casting

• US 5,226,113 A
• Filed: 02/28/1992
• Issued: 07/06/1993
• Est. Priority Date: 10/30/1989
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Dumoulin, Charles L., Cline, Harvey E., Ludke, Siegwalt, Souza, Steven P.
• Primary Examiner(s): Harkcom, Gary V.
• Assistant Examiner(s): JANKUS, ALMIS R
• Application Number:
  US07/844,983
• Time in Patent Office: 494 Days
• Field of Search: 364/518-521, 364/414, 364/413.3, 364/413.22, 364/413.13-413.16, 324/309, 324/306, 395/119, 395/120, 395/124, 395/125, 395/127, 395/139
• US Class Current: 345/424
• CPC Class Codes: G06T 17/00 Three dimensional [3D] modelling, e.g. data description of 3D objects

Abstract

A method for providing a volumetrically-rendered projection image using reverse ray casting, uses the steps of: acquiring, from an object volume of interest, a set of data sampled from each volume element (voxel) therein responsive to a selected characteristic of that object volume; storing the data for each object voxel in a corresponding data volume element; scanning sequentially through each data voxel within the data volume corresponding to the object volume of interest; projecting each scanned data voxel to an image plane, at a solid angle determined from the solid angle at which the object volume is viewed; storing a value for each image plane pixel, responsive to a selected criteria, from the values of all projected data voxel values impingent upon that image plane pixel; and then scaling the dimensions of each image plane pixel responsive to the dimensions of the corresponding object volume shape, and the involved projection solid angle, to correct for anisotropy.

Claims

1. Apparatus for creating a volumetrically-rendered projection image of a sample object, comprising:

address generator means for providing a sequential series of addresses within a selected object volume of interest;

three-dimensional data memory means for storing data voxel values at each of a multiplicity of addresses, each data voxel value corresponding to a physical characteristic of one voxel of a plurality of slices of the sample object in an object volume, and also for providing a data voxel value upon receipt of an address from said address generator means;

means for rotating a set of input viewing angle parameters and an address of a sample object voxel then being output from said address generator means, to obtain an address of a corresponding pixel location at which a ray cast according to the input viewing angle parameters through the sample object voxel at a point will impinge;

image plane memory mean for storing a projection data value at each of a multiplicity of image plane addresses, each corresponding to one pixel of the image plane;

means for processing the data voxel values from the three-dimensional memory means the processing means employing the data voxel values in updating the image plane memory means at the image plane address corresponding to the viewing angle parameters and the specific data voxel being processed; and

scaling the updated values in the image plane memory means; and

a display means for displaying the scaled values in the image plane memory means.

2. The apparatus of claim 1, wherein the image plane memory means is reset prior to the providing of a sequence of addresses by the address generator means.

3. The apparatus of claim 2, wherein said processing means includes means for retaining in the image plane memory means the larger of a value of each datum newly-provided form said three-dimensional memory means and (b) a data value already stored in said image plane memory means for a specific pixel, for any voxel projected to impinge upon that image plane pixel.

4. The apparatus of claim 3, wherein said retaining means includes a data comparator, receiving the data value already stored in the image plane memory means and the data value then being output from the three-dimensional memory means, and causing the image plane memory to store the larger of the two input data values.

5. The apparatus of claim 4, wherein the image plane memory means replaces the already stored data only if the data value then being output from the three-dimensional memory means is larger than the stored data value.

6. The apparatus of claim 2, wherein said processing means includes means for summing up, and then storing in the image plane memory means, a value of each datum newly-provided from said three-dimensional memory means and a data value already stored in said image plane memory means for a specific pixel, and also for storing the number of summations carried out for each pixel;

the summation data stored for each image plane pixel being divided by the number of summations for that pixel, after all addresses in a sequence have been provided by said address-providing means, to obtain an average data value for that pixel.

7. The apparatus of claim 1, further comprising CPU means for scaling the image plane memory means data representing each object voxel height H by an effective scale factor E_s to obtain a scaled height H'"'"' of an associated pixel in the image plane.

8. The apparatus of claim 7, wherein the effective scale factor E_s =sqrt((Acosγ

)₂ +sin² γ

), γ

is an angle of elevation in the object slice thickness T to an actual object voxel side S.

9. Apparatus for creating a volumetrically-rendered projection image of a sample object comprising:

data acquisition means for acquiring a three-dimensional data volume comprised of data, each data voxel corresponding to an object volume element of said sample object and each representing a physical characteristic of the corresponding object volume element, and each data voxel having a three-dimensional address corresponding to a location of the corresponding sample object volume;

three-dimensional data memory means connected to the data acquisition means for receiving and storing each data voxel at its three-dimensional address, the three-dimensional memory means also providing a data voxel upon receiving its three-dimensional address;

view matrix means for receiving from a user a pair of viewing angles at which to view an output image and for creating a view matrix;

address generator means connected to the three-dimensional memory means, for providing a three-dimensional address to the three-dimensional memory means and repeating with different three-dimensional addresses until all three-dimensional addresses have been provided only once;

rotate means connected to the address generator means and the view matrix means for receiving the three-dimensional addresses form the address generator means and the view matrix and creating a calculated image plane address representing a point at which each object volume element would be projected onto an image plane from viewing angles;

image plane memory means for storing each image plane pixel at the calculated image plane address, the image plane memory also providing an image plane pixel at the calculated image plane address upon receiving the calculated image plane address;

image processor means connected to the image plane memory means and the three-dimensional memory means for receiving a data voxel from the three-dimensional memory means, and for receiving the image plane pixel from the image plane memory means at the calculated image plane address from the rotate means, and processing the data voxel and the image pixel to produce updated image plane pixel which is stored in the image plane memory means at the calculated image plane address;

central processor unit for scaling each image plane pixel in the image plane memory means to correct for anisotropy introduced by the difference in shape between the object volume element and the corresponding data voxel; and

display means for displaying the scaled image plane pixels to produce an X-ray-like projection image.

10. The apparatus for creating a volumetrically-rendered projection image of claim 9 wherein the image processor means is a data comparator means that compares each data voxel with the the image plane pixel at the calculated address and replaces the image plane pixel with the data voxel if the the data voxel is larger than the image plane pixel.

11. The apparatus for creating a volumetrically-rendered projection image of claim 9 wherein the image processor means is an adder means that adds the data voxel with the image plane pixel at the calculated image plane address.

12. The apparatus for creating a volumetrically-rendered projection image of claim 9 wherein the image processor means is an averager means that adds the data voxel to the image plane pixel to create a sum, and counts the data voxels added, divides the sum by the count to create an average and replaces the image plane pixel with the average.