Method and apparatus for improving the spatial resolution in molecular breast tomosynthesis
An apparatus and method for reducing the blurriness of tomographic (3D) images constructed from a gamma camera system with one or more VASH (variable-angle slant-hole) collimators. A conventional gamma camera with a VASH collimator exhibits a loss of spatial resolution from the fact that the gamma-ray is entering the detector element at an angle other than normal to the surface. This depth dependence of the spatial localization causes a blurring of the spatial resolution, which is dependent on the incident angle relative to the normal, on the thickness of the detector element and on the stopping length of the gamma-ray in the detector element material. The invention provides an apparatus and method for correcting the spatial location where the gamma ray is recorded to improve the spatial resolution of the system.
1. A method for correcting the blurring of the spatial location in a molecular breast tomosynthesis system including a variable-angle slant-hole (VASH) collimator and a gamma-ray sensitive element, comprising:
collecting gamma ray events with the gamma-ray sensitive element while varying the angle of the VASH collimator;
recording the recorded pixel location (RP), the depth of the gamma-ray interaction (DEP) within the recorded pixel, the angle (A) of the holes in the slant-hole collimator, and the pixel pitch (PP); and
calculating the True Pixel location (TP) of each gamma-ray event according to the equation
TP=RP +INT( DEP *Tan( A )/ PP );
where INT (DEP*Tan(A)/PP) is a function that returns the largest integer value less than the decimal value of the expression within the parenthesis.
2. The method of claim 1 wherein the gamma-ray sensitive element is a solid-state element; and the method further comprises calculating the depth from the ratio of the electrical signals on an anode and a cathode of the solid state element.
3. The method of claim 1 wherein the gamma-ray sensitive element is a scintillation crystal element; and the method further comprises calculating the depth from the ratio of the light signals recorded at the top and bottom of the scintillation crystal.
4. A molecular breast tomosynthesis system for producing three-dimensional (3D) images with correction for blurring of spatial location, comprising:
at least one gamma camera comprising a collimator system, a gamma-ray sensitive element to collect gamma ray events and electronics in operative connection with the gamma-ray sensitive element, said collimator system comprising a variable-angle slant-hole (VASH) collimator including a plurality of holes which are adjustable together to an angle (A) over a range of various angles; and
an electro-mechanical mechanism to control and record the angle (A) of the plurality of holes in the VASH collimator; and
a computer configured to record the characteristics of each gamma ray event, said characteristics comprising the pixel location (RP) of a gamma-ray event, a depth of the gamma-ray interaction (DEP) within the recorded pixel, and the angle (A) of the holes in the VASH collimator, and the pixel pitch (PP), said computer further configured to calculate a True Pixel location (TP) of each gamma-ray event according to the equation:
TP=RP +INT( DEP *Tan( A )/ PP ):
wherein TNT (DEP*Tan(A)/PP) is a function that returns the largest integer value less than the decimal value of the expression within the parenthesis.
5. The molecular breast tomosynthesis system of claim 4 wherein the gamma-ray sensitive element is a solid-state element and the depth of the gamma-ray interaction is calculated from the ratio of the electrical signals on an anode and a cathode of the solid-state element.
6. The molecular breast tomosynthesis system of claim 5 wherein the solid-state element is cadmium zinc telluride (CZT).
7. The molecular breast tomosynthesis system of claim 4 wherein the gamma-ray sensitive element is a scintillation crystal element, and the depth of the gamma-ray interaction is calculated from the ratio of the light signals recorded at the top and the bottom of the scintillation crystal element.
8. The molecular breast tomosynthesis system of claim 7 , wherein the scintillation crystal element is thallium doped sodium-iodide (NaI(Tl)).