Method and apparatus for measuring long bone density of small-animals
View Patent ↗A method and apparatus are disclosed for measuring long bone density of small animals. A phosphor screen or plate is provided of a type that transduces incident ionizing radiation to emitted light. A small animal is positioned before the phosphor screen or plate and exposed to soft X-radiation having an energy level in the range of 11 to 16 Kev. Light emitted by the phosphor screen or plate is captured using a digital camera and a digital X-ray image is prepared of a long bone of the animal. The X-ray image is transformed into an X-ray density image and a region of interest is defined on the long bone in the X-ray density image. At least one row of pixels is scanned within the region of interest of the X-ray density image. A nonlinear least squares analysis of data obtained from the scanning step is conducted using a cylindrical model for the long bone within the region of interest.
1. A method for measuring long bone density of small animals, comprising:
providing a phosphor screen or plate of a type that transduces incident ionizing radiation to emitted light;
positioning a small animal before the phosphor screen or plate;
exposing the animal to X-radiation having an energy level in the range of 10 to 16 Kev;
capturing light emitted by the phosphor screen or plate using a digital camera and preparing a digital X-ray image of a long bone of the animal; and
using a computer to perform the steps of:
transforming the X-ray image into an X-ray density image;
defining a region of interest of the long bone in the X-ray density image;
scanning at least one row of pixels within the region of interest of the X-ray density image; and
conducting a nonlinear least squares analysis of data obtained from the scanning step using a virtual, cylindrical model for the long bone within the region of interest and adjusting values of parameters of the model so as to minimize the chi square of a residual between the data and the model.
2. A method according to claim 1 , wherein the phosphor screen has a spatial resolution of >25 line pairs/mm 2 at 50% MTF.
3. An apparatus for measuring long bone density of small animals, comprising:
a phosphor screen or plate of a type that transduces incident ionizing radiation to emitted light;
a source of X-radiation having an energy level in the range of 10 to 16 Kev;
a stage for supporting a small animal between the screen or plate and the source;
a digital camera for capturing light emitted by the phosphor screen or plate from a small animal positioned on the stage and producing a digital X-ray image of a long bone of the animal; and
a computer for receiving the digital X-ray image, the computer comprising:
means for transforming the digital X-ray image into an X-ray density image;
means for defining a region of interest of the long bone in the X-ray density image;
means for scanning at least one row of pixels within the region of interest of the X-ray density image; and
means for conducting a nonlinear least squares analysis of data obtained from the scanning step using a virtual, cylindrical model for the long bone within the region of interest and adjusting values of parameters of the model so as to minimize the chi square of a residual between the data and the model.
4. An apparatus according to claim 3 , wherein the phosphor screen has a spatial resolution of >25 line pairs/mm 2 at 50% MTF.
5. A method for measuring long bone density of small animals, comprising steps of:
providing a phosphor screen or plate of a type that transduces incident ionizing radiation to emitted light;
positioning a small animal before the phosphor screen or plate;
exposing the animal to X-radiation having an energy level in the range of 10 to 16 Kev;
capturing light emitted by the phosphor screen or plate using a digital camera and preparing a digital X-ray image of a long bone of the animal;
transforming the X-ray image into an X-ray density image;
defining a region of interest of the long bone in the X-ray density image;
scanning at least one row of pixels within the region of interest of the X-ray density image; and
conducting a nonlinear least squares analysis of data obtained from the scanning step using a virtual, cylindrical model for the long bone within the region of interest, wherein the cylindrical model is according to the following relationship:
CASE 1: if (abs(x−xin)<Rin), then
D= 2 d bone (√{square root over ( R out 2 −( x out −x ) 2 )}−√{square root over ( R in 2 −( x in −x ) 2 )})+2 d marrow √{square root over ( R in 2 −( x in −x ) 2 )}+ bx+a
CASE 2: else if (abs(x−xout)<Rout), then
D= 2 d bone √{square root over ( R out 2 −( x out −x ) 2 )}+ bx+a
CASE 3: else,
D=bx+a,
Wherein
D=measured X-ray density
d bone =excess column density of the bone above background column density;
d marrow =excess column density of the marrow above background column density;
R out =outer radius of the bone
R out R in =inner radius of the bone;
x out =x coordinate of the center of the outer radius of the bone;
x in =x coordinate of the center of the outer radius of the bone;
b=slope of linear background density; and
a=intercept of linear background density.
6. A method according to claim 5 , wherein the phosphor screen has a spatial resolution of >25 line pairs/mm 2 at 50% MTF.
7. An apparatus for measuring long bone density of small animals, comprising:
a phosphor screen or plate of a type that transduces incident ionizing radiation to emitted light;
a source of X-radiation having an energy level in the range of 10 to 16 Kev;
a stage for supporting a small animal between the screen or plate and the source;
a digital camera for capturing light emitted by the phosphor screen or plate from a small animal positioned on the stage and producing a digital X-ray image of a long bone of the animal;
means for transforming the digital X-ray image into an X-ray density image;
means for defining a region of interest of the long bone in the X-ray density image;
means for scanning at least one row of pixels within the region of interest of the X-ray density image; and
means for conducting a nonlinear least squares analysis of data obtained from the scanning step using a virtual, cylindrical model for the long bone within the region of interest, wherein the cylindrical model is according to the following relationship:
CASE 1: if (abs(x−xin)<Rin), then
D= 2 d bone (√{square root over ( R out 2 −( x out −x ) 2 )}−√{square root over ( R in 2 −( x in −x ) 2 )})+2 d marrow √{square root over ( R in 2 −( x in −x ) 2 )}+ bx+a;
CASE 2: else if (abs(x−xout)<Rout), then
D= 2 d bone √{square root over ( R out 2 −( x out −x ) 2 )}+ bx+a
CASE 3: else,
wherein:
D=bx+a;
where
D=measured X-ray density
d bone =excess column density of the bone above background column density;
d marrow =excess column density of the marrow above background column density;
R out =outer radius of the bone;
R in =inner radius of the bone;
x out =x coordinate of the center of the outer radius of the bone;
x in =x coordinate of the center of the outer radius of the bone;
b=slope of linear background density; and
a=intercept of linear background density.
8. An apparatus according to claim 7 , wherein the phosphor screen has a spatial resolution of >25 line pairs/mm 2 at 50% MTF.