Radiation image processing device and radiation image processing method
A radiation image processing device ( 100 ) includes an image processor ( 6 ) configured to calculate an adjustment coefficient (I ideal /I real ) for adjusting a signal reduction rate (D scat ) due to removal of a scattered component in a subject (S) of radiation transmitting through the subject (S) acquired based on a luminance value (I nogrid ) of a radiation image (X nogrid ) captured with the radiation radiated to the subject (S) without a grid ( 8 ) being arranged, the luminance value (I nogrid ) of the radiation image (X nogrid ) containing a signal of a scattered ray.
1. A radiation image processing method comprising:
storing a signal reduction rate of radiation due to a scattered ray generated by the radiation transmitting through a subject, and a correspondence relationship between a thickness of the subject and a scattered dose;
calculating an ideal luminance value in accordance with the correspondence relationship;
capturing an actual radiation image without using a grid configured for removing a scattered ray therefrom;
calculating an actual luminance value for the radiation image in accordance with the signal reduction rate;
calculating an adjustment coefficient by calculating a ratio of the ideal luminance value to the actual luminance value; and
removing a signal component of the scattered ray superimposed on the
actual captured radiation image based on the calculated adjustment coefficient.
2. The radiation image processing method according to claim 1 , wherein the removing the signal component of the scattered ray includes removing the signal component of the scattered ray superimposed on the radiation image captured without the grid being arranged, and calculating a luminance value I est (x, y) estimated assuming that the grid is arranged based on a following formula (1):
I
est
(
x
,
y
)
=
I
nogrid
(
x
,
y
)
×
D
prim
×
I
ideal
I
real
×
D
scat
,
(
0
≤
D
prim
≤
1
,
0
≤
D
scat
≤
1
)
(
1
)
where I nogrid (x, y) represents a luminance value at coordinates (x, y) of the radiation image captured without the grid being arranged, the radiation image containing the signal of the scattered ray, D prim represents a signal reduction rate due to passage through the grid, D scat represents the signal reduction rate of the radiation stored in a database unit, I ideal represents the ideal luminance value under a specific imaging condition, and I real represents the luminance value based on the radiation image actually captured, and I ideal /I real represents the adjustment coefficient.
3. The radiation image processing method according to claim 2 , wherein
the storing the signal reduction rate of the radiation and the correspondence relationship between the thickness of the subject and the scattered dose includes storing a characteristic of a relationship between the thickness of the subject corresponding to a reduction rate of a luminance value of a pixel corresponding to a subject region in which the radiation transmits through the subject with respect to a luminance value of a pixel corresponding to a non-subject region in which the radiation does not transmit through the subject in the radiation image captured without the grid being arranged, and a signal reduction rate due to removal of a scattered component; and
the removing the signal component of the scattered ray includes calculating the I real based on the stored characteristic of the relationship between the thickness of the subject and the signal reduction rate of the radiation, and the luminance value of the radiation image actually captured.
4. The radiation image processing method according to claim 3 , wherein the removing the signal component of the scattered ray includes calculating the D prim based on a ratio of a luminance value of the non-subject region in the radiation image captured in advance with the grid being arranged to a luminance value of the non-subject region in the radiation image captured without the grid being arranged.
5. The radiation image processing method according to claim 4 , wherein the removing the signal component of the scattered ray includes calculating the D scat based on a ratio of a luminance value of each pixel to a luminance value of the non-subject region in the radiation image captured without the grid being arranged.
6. The radiation image processing method according to claim 5 , wherein the removing the signal component of the scattered ray includes calculating a subject thickness index corresponding to the thickness of the subject based on a following formula (2):
(
1
-
I
nogrid
(
x
,
y
)
I
nogrid
(
air
)
)
(
2
)
where I nogrid (air) represents the luminance value of the non-subject region in the radiation image captured without the grid being arranged.
7. The radiation image processing method according to claim 1 , wherein calculating the actual luminance includes using a value of Dprim as well as the signal reduction rate for the calculation, the value of Dprim being a ratio of a luminance value of a non-subject region in the radiation image captured in advance with the grid being arranged to a luminance value of the non-subject region in the radiation image captured without the grid being arranged.