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SLOPED WIRE PHANTOM FOR MEASURING CT SLICE SENSITIVITY PROFILE

IP.com Disclosure Number: IPCOM000126275D
Publication Date: 2005-Jul-12
Document File: 7 page(s) / 635K

Publishing Venue

The IP.com Prior Art Database

Abstract

In an embodiment according to this invention, a wire with a small slope is used to provide good measurement resolution, but the wire is repeated in such a way to also provide good axial coverage and, as well, several measurements at varying radial locations. Accordingly, there are two sets of oppositely sloped wires with each set containing five parallel wires that lie in the same plane. In this example, the slope of the wires is 1:4 (14°) so that a magnification factor of 4 is obtained. Therefore, a 0.625 mm slice thickness yields a wire length of 2.5 mm in the reconstructed CT image, which is significantly larger than the limiting resolution of approximately 1.2 mm when using the "Standard" reconstruction filter on VCT scanners.

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SLOPED WIRE PHANTOM FOR MEASURING CT SLICE SENSITIVITY PROFILE

FIELD OF THE INVENTION

[0001]               This invention relates generally, to measuring a sensitivity profile, and more particularly to, a sloped wire phantom for measuring CT slice sensitivity profile in medical imaging.

BACKGROUND OF THE INVENTION

[0002]               The slice sensitivity profile (SSP) or slice thickness of a CT image is an important parameter that affects how clearly small anatomy or objects can be imaged.  The SSP can vary depending on where in the CT image it is measured.  For example, the slice thickness near the center of the circular CT image may be different than the slice thickness nearer the edge.  The SSP can also vary on multi-slice CT scanners depending on which slices contribute toward the reconstructed image.  For example, on a 64-slice VCT scanner, data from rows 1 to 3 may contribute toward an axial image reconstructed at one location, while only data from row 32 may contribute toward an axial image reconstructed at a different location.  The slice profile for each image can therefore be slightly different.  A method is thus needed to measure the slice profile at various image locations and also simultaneously on many images.

[0003]               One method of measuring the slice profile uses a disc [Patent #6,490,336, Siemens].  This method is suitable for helical scanning where images can be reconstructed at intervals much smaller than the slice thickness.  However, for axial scanning this method is not practical.  This method also requires that the slice profile be identical from image-to-image, and is not suitable when this condition is not satisfied.

[0004]               Another method of measuring the slice thickness uses a sloped wire that slopes across the scan plane.  The length of the wire that appears in the reconstructed CT image is proportional to the thickness of the slice, with the constant of proportionality determined by the slope of the wire.  As the thickness of the slices becomes smaller, the slope of the wire must be smaller in order to maintain a measurable length in the reconstructed CT image.  However, as the slope of the wire becomes smaller, the wire covers a smaller axial distance and fewer slices can be measured

[0005]                 This invention describes a phantom design that addresses the challenges of accurately measuring slice profiles using wires with small slope, performing these measurements on many simultaneous slices, and providing measurements at several locations within the image.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]               FIG. 1 shows a schematic top view and end view of the Slice Sensitivity Profile phantom according to an example of this invention.  In this example, there are 5 parallel wires sloped in one direction, and 5 parallel wires below them sloped in the opposite direction.  The slope is 1:4.  The wires are strung around rods for ease of manufacturability and to maintain constant spacing. 

[0007]               FIG. 2 shows two representative CT images from...