Method and apparatus for measuring bone density

A method of measuring the density of a bone in a body part, the body part comprising bone and soft tissue, the method comprising the steps of:

• obtaining a high-energy image of the body part and a hard tissue reference and a soft tissue reference by irradiating the body part and the references with high-energy radiation;
• obtaining a low-energy image of the body part and the references by irradiating the body part and the references with low-energy radiation;
• determining high-energy and low-energy radiation transmissivity characteristics of varying thicknesses of the hard tissue reference and the soft tissue reference from the high-energy and low-energy images;
• and
• determining a density of the bone based on at least one pixel that corresponds to bone in the high-energy image, a corresponding at least one pixel in the low-energy image, and the determined transmissivity characteristics.

A method of measuring the density of a bone in a body part, the body part comprising bone and soft tissue, the method comprising the steps of:

• computing a first function that relates a high-energy radiation transmissivity of a hard tissue reference to a low-energy radiation transmissivity of the hard tissue reference, based on detected amounts of high-energy radiation and low-energy radiation transmitted through the hard tissue reference for at least some of a plurality of pixels located under the hard tissue reference;
• computing a second function that relates a high-energy radiation transmissivity of a soft tissue reference to a low-energy radiation transmissivity of the soft tissue reference, based on detected amounts of high-energy radiation and low-energy radiation transmitted through the soft tissue reference for at least some of a plurality of pixels located under the soft tissue reference;
• selecting a high-energy set of pixels from a high-energy image of the body part, and a corresponding low-energy set of pixels from a low-energy image of the body part;
• computing a hard tissue value for the set of pixels based on the high-energy set, the low-energy set, the first function, and the second function;
• computing a third function that relates an amount of radiation detected at a given pixel to the thickness of the hard tissue reference above the given pixel, based on an amount of radiation detected at each of a plurality of certain pixels and known thicknesses of the hard tissue reference above the certain pixels;
• and
• computing a bone density based on the third function and the hard tissue value for at least one pixel that corresponds to bone.

A method of measuring the density of a bone in a body part, the body part comprising bone and soft tissue, the method comprising the steps of:

• irradiating a hard tissue reference and a soft tissue reference with high-energy radiation;
• detecting an amount of high-energy radiation transmitted through each tissue reference for each of a plurality of pixels located under each tissue reference;
• irradiating the tissue references with low-energy radiation;
• detecting an amount of low-energy radiation transmitted through each tissue reference for each of the plurality of pixels located under each tissue reference;
• computing a first function that relates the high-energy radiation transmissivity of the hard tissue reference to the low-energy radiation transmissivity of the hard tissue reference, based on the detected amounts of high-energy radiation and low-energy radiation transmitted through the hard tissue reference for at least some of the plurality of pixels located under the hard tissue reference;
• computing a second function that relates the high-energy radiation transmissivity of the soft tissue reference to the low-energy radiation transmissivity of the soft tissue reference, based on the detected amounts of high-energy radiation and low-energy radiation transmitted through the soft tissue reference for at least some of the plurality of pixels located under the soft tissue reference;
• irradiating the body part with high-energy radiation;
• obtaining a high-energy image by detecting an amount of high-energy radiation transmitted through the body part for each of a plurality of pixels located under the body part;
• irradiating the body part with low-energy radiation;
• obtaining a low-energy image by detecting an amount of low-energy radiation transmitted through the body part for each of the plurality of pixels located under the body part;
• selecting a set of high-energy pixels from the high-energy image, and a corresponding set of low-energy pixels from the low-energy image;
• computing a hard tissue value for the set of pixels based on the high-energy set, the low-energy set, the first function, and the second function;
• computing a third function that relates an amount of radiation detected at a given pixel to the thickness of the hard tissue reference above the given pixel, based on an amount of radiation detected at each of a plurality of certain pixels and known thicknesses of the hard tissue reference above the certain pixels;
• and
• computing a bone density based on the third function and the hard tissue value for at least one pixel that corresponds to bone.

An apparatus for measuring the density of a bone in a body part, the body part comprising bone and soft tissue, comprising:

• means for obtaining a high-energy image of the body part and a hard tissue reference and a soft tissue reference by irradiating the body part and the references with high-energy radiation;
• means for obtaining a low-energy image of the body part and the references by irradiating the body part and the references with low-energy radiation;
• means for determining high-energy and low-energy radiation transmissivity characteristics of varying thicknesses of the hard tissue reference and the soft tissue reference from the high-energy and low-energy images;
• and
• means for determining a density of the bone based on at least one pixel that corresponds to bone in the high-energy image, a corresponding at least one pixel in the low-energy image, and the determined transmissivity characteristics.

A method of determining the radiation transmissivity of a bone in a body part, comprising the steps of:

• reading at least one pixel of interest in a high-energy image of the body part;
• reading a corresponding at least one pixel in a low-energy image of the body part;
• accessing a first function that relates a high-energy radiation transmissivity of a hard tissue reference to a low-energy radiation transmissivity of the hard tissue reference;
• accessing a second function that relates a high-energy radiation transmissivity of a soft tissue reference to a low-energy radiation transmissivity of the soft tissue reference;
• and
• calculating a hard tissue value based on the at least one pixel of interest in the high-energy image, the corresponding at least one pixel in the low-energy image, the first function, and the second function.

An apparatus for determining the radiation transmissivity of a bone in a body part, comprising:

• means for reading at least one pixel of interest in a high-energy image of the body part;
• means for reading a corresponding at least one pixel in a low-energy image of the body part;
• memory means for storing a first function that relates a high-energy radiation transmissivity of a hard tissue reference to a low-energy radiation transmissivity of the hard tissue reference and a second function that relates a high-energy radiation transmissivity of a soft tissue reference to a low-energy radiation transmissivity of the soft tissue reference;
• and
• calculating means for calculating a hard tissue value based on the at least one pixel of interest in the high-energy image, the corresponding at least one pixel in the low-energy image of the body part, the first function, and the second function.

A method of determining the radiation transmissivity of a bone in a body part using a pixel of interest in a first-energy image of the body part, a corresponding pixel in a second-energy image of the body part, a first function that relates the first-energy radiation transmissivity of a first tissue reference to the second-energy radiation transmissivity of the first tissue reference, and a second function that relates the first-energy radiation transmissivity of a second tissue reference to the second-energy radiation transmissivity of the second tissue reference, the method comprising the steps of:

• (a) estimating a first-energy radiation transmissivity of the first tissue for a pixel of interest;
• (b) determining a first-energy radiation transmissivity of the second tissue for the pixel of interest based on the estimated first-energy radiation transmissivity of the first tissue and a measured first-energy transmissivity of the pixel of interest;
• (c) calculating, for the pixel of interest, a second-energy radiation transmissivity of the first tissue and a second-energy radiation transmissivity of the second tissue based on the estimated first-energy radiation transmissivity of the first tissue, the determined first-energy radiation transmissivity of the second tissue, the first function, and the second function;
• (d) calculating a composite second-energy transmissivity for the pixel of interest based on the calculated second-energy radiation transmissivity of the first tissue and the second-energy radiation transmissivity of the second tissue;
• (e) comparing the calculated composite second-energy transmissivity to a measured second-energy transmissivity of the pixel of interest, and determining whether the calculated composite is sufficiently close to the measured value;
• and
• (f) adjusting the estimate of the first-energy radiation transmissivity of the first tissue and repeating steps (b) through (f) when it is determined, in said comparing step, that the calculated composite is not sufficiently close to the measured value.