X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
2001-11-08
2002-07-16
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S098900, C378S098120
Reexamination Certificate
active
06421419
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an energy subtraction processing method and apparatus, wherein energy subtraction processing is performed on a plurality of image signals representing radiation images of an object. This invention also relates to a recording medium, on which a program for causing a computer to execute the energy subtraction processing method has been recorded and from which the computer is capable of reading the program.
2. Description of the Related Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet, on which the radiation image has been stored, is then exposed to stimulating rays, such as a laser beam, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into a digital image signal. The image signal is then processed and used for the reproduction of the radiation image of the object as a visible image on a recording material.
Also, techniques for performing energy subtraction processing on radiation images have heretofore been known. (The energy subtraction processing techniques are disclosed in, for example, U.S. Pat. Nos. 4,855,598 and 4,896,037, 5,485,371.) With the energy subtraction processing techniques, an object is exposed to several kinds of radiation having different energy distributions. Alternatively, the energy distribution of the radiation carrying image information of an object is changed after the radiation has been irradiated onto one of a plurality of radiation detecting means (e.g., the stimulable phosphor sheets described above), after which the radiation impinges upon the second radiation detecting means. In this manner, a plurality of radiation images, in which different images of a specific structure of the object are embedded, are obtained. Thereafter, image signal components of the image signals representing the plurality of the radiation images, which image signal components represent corresponding pixels in the radiation images, are multiplied by appropriate weight factors, and the thus weighted image signal components are subjected to a subtraction process. From the subtraction process, a difference signal, which represents only the image of the specific structure of the object, is obtained. By the utilization of the thus obtained difference signal, a visible radiation image, which represents only the specific structure of the object, is capable of being reproduced.
In the aforesaid radiation image recording and reproducing systems utilizing the stimulable phosphor sheets, the radiation image having been stored on the stimulable phosphor sheet is read out directly as an electric image signal. Therefore, with the radiation image recording and reproducing systems, the energy subtraction processing is capable of being performed easily. In cases where the energy subtraction processing is to be carried out by using the stimulable phosphor sheets, radiation images may be stored on, for, example, two stimulable phosphor sheets such that the parts of the radiation images corresponding to a specific structure may be different in the two radiation images. For such purposes, a two-shot energy subtraction processing technique may be employed wherein the operation for recording a radiation image is performed twice with two kinds of radiation having different energy distributions. Alternatively, a one-shot energy subtraction processing technique may be employed wherein, for example, two stimulable phosphor sheets placed one upon the other (they may be in contact with each other or spaced away from each other) are simultaneously exposed to radiation, which carries image information of an object, such that the two stimulable phosphor sheets are exposed to radiation having different energy distributions. In cases where the two-shot energy subtraction processing technique is employed, and radiation images are to be recorded on an increased number of the stimulable phosphor sheets, the same number of image recording operations as that of the stimulable phosphor sheets are performed. For example, in cases where the two-shot energy subtraction processing technique is employed, and radiation images are to be recorded on three stimulable phosphor sheets, three image recording operations are performed. Therefore, in this specification, the energy subtraction processing technique, in which multiple image recording operations are performed, is referred to as the multi-shot energy subtraction processing technique (including the two-shot energy subtraction processing technique).
With the energy subtraction processing techniques utilizing the stimulable phosphor sheets, for example, in cases where the object is a human body, two radiation images of the human body may be formed on the stimulable phosphor sheets with two kinds of radiation having different energy distributions (i.e., radiation having a high energy level and radiation having a low energy level), and two image signals representing the two radiation images may be obtained. Also, the two image signals may be weighted with appropriate weight factors, and the difference signal may be obtained by performing a subtraction process on the weighted image signals. In this manner, a radiation image, in which only the pattern of a soft tissue of the human body is illustrated, and a radiation image, in which only the pattern of a bone of the human body is illustrated, are capable of being obtained. The operation processing is performed in the manner described below. Specifically, the first stimulable phosphor sheet, upon which the radiation having a low energy level impinges, may be represented by IP
1
, and the second stimulable phosphor sheet, upon which the radiation having a high energy level impinges, may be represented by IP
2
. Also, a logarithmic value of a radiation dose (i.e., a logarithmic radiation dose), which the first stimulable phosphor sheet IP
1
receives, may be represented by L, and the logarithmic value of the radiation dose (i.e., the logarithmic radiation dose), which the second stimulable phosphor sheet IP
2
receives, may be represented by H. In such cases, L and H may be represented respectively by Formula (1) and Formula (2) shown below.
L=−{overscore (&mgr;
S
+L )}
t
S
−{overscore (&mgr;
B
+L )}
t
B
+L
0
(1)
H=−{overscore (&mgr;
S
+L )}′
t
S
−{overscore (&mgr;
B
+L )}′
t
B
+H
0
(2)
wherein
{overscore (&mgr;
B
+L )} represents the mean attenuation coefficient of the bone with respect to the first stimulable phosphor sheet IP
1
,
{overscore (&mgr;
S
+L )} represents the mean attenuation coefficient of the soft tissue with respect to the first stimulable phosphor sheet IP
1
,
{overscore (&mgr;
B
+L )}′ represents the mean attenuation coefficient of the bone with respect to the second stimulable phosphor sheet IP
2
,
{overscore (&mgr;
S
+L )}′ represents the mean attenuation coefficient of the soft tissue with respect to the second stimulable phosphor sheet IP
2
,
t
S
represents the thickness of the bone,
t
B
represents the thickness of the soft tissue, and
each of L
0
and H
0
represents the fixed number depending upon the radiation source.
As the logarithmic radiation doses L and H, the image signals having been obtained from the stimulable phosphor sheets IP
1
and IP
2
may be employed respectively.
A substance has a radiation attenuation coefficient depending upon radiation energy. Also, in cases where the radiation irradiated to the object is not monochromatic and is distributed over a certain energy range, the energy distribution of the detected
Bruce David V.
Fuji Photo Film Co. , Ltd.
Hobden Pamela R.
Sughrue & Mion, PLLC
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