X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2000-12-22
2003-02-11
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C250S370090
Reexamination Certificate
active
06519314
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an X-ray based measuring device, and more particularly to a technique which can be suitably applied to an X-ray measuring device having a planar X-ray detector.
BACKGROUND ART
In a conventional X-ray based measuring device, after an X-ray image transmitted through an inspection object is first converted into an optical image by an X-ray II (X-ray image intensifier), the optical image is converted into an analog image signal. The analog image signal is converted into a digital image signal (image data) by an A/D converter, is then subjected to known image processing such as filtering and contour enhancement by an image processing circuit, and is displayed on an display as an X-ray image. In recent years, there has been a strong demand for rendering the X-ray based measuring device compact, and attempts have been made to render the device compact through the improvement of an X-ray source and its power supply. Meanwhile, in order to pick up an X-ray image of a large area in one imaging, an imaging system including the X-ray II and a television camera has tended to be large in size, and the X-ray II, in particular, has constituted a large hindrance to the miniaturization of the device because of its basic principle. As a means for overcoming this problem, the development of planar X-ray detectors has been undertaken energetically in recent years, and a method has been developed in which an X-ray image is converted into visible light (optical image) by a scintillator such as a CsI, and after the visible light is converted into electrical signals by photodiodes formed of such as a-Si (amorphous silicon), the electrical signals are sequentially read by a TFT (thin film transistor) or CMOS (complementary) circuit. In a case where a reading circuit is formed by TFTs, the planar X-ray detector makes it possible to make the screen large. On the other hand, in a case where the reading circuit is formed by a CMOS circuit, a planar X-ray detector of a large screen can be constructed by combining a plurality of CMOS X-ray detectors.
DISCLOSURE OF INVENTION
As a result of studying the conventional art, the present inventors found out the following problems. Conventional measuring devices using planar X-ray detectors have suffered from problems in that the dynamic range is narrow and that the imaging speed is slow.
FIGS. 25
,
26
,
27
, and
28
are diagrams explaining a schematic configuration of an example of a conventional X-ray based measuring device. In a case where, in chest roentgenography of a subject, an interested area C (
901
c
) including both the heart and the lung filed and indicated by slanting lines is imaged as an interested area, as shown in
FIG. 27
, with the conventional measuring device using a planar X-ray detector, a minimum value C
1
and a maximum value C
2
of detector output values in the interested area C are respectively made to correspond to a minimum value (LSB) and a maximum value (MSB) of an A/D converter which can be subjected to analog-to-digital conversion, so as to make maximum use of the capability of the A/D converter. The thick line
209
shown in
FIG. 28
shows the relationship between the range (C
1
-C
2
) of the value of the detector output (x-axis) and the range (LSB-MSB) permitting the input (y-axis) to the A/D converter. In the case of the conventional measuring device. thus set, however, as shown in
FIG. 25
, for example, in the measurement of an interested area A (
901
a
) which includes only a portion close to the heart, i.e., a portion (C
1
-A
1
) where pixel values are small, values greater than the maximum value A
1
are not inputted to the A/D converter. Similarly, as shown in
FIG. 26
, in the measurement of an interested area B (
901
b
) in the heart field which includes only a portion (B
1
-C
2
) where pixel values are large, values smaller than the minimum value B
1
are not inputted to the A/D converter. Hence, effective use is not made of the A/D converter. Thus, with the conventional X-ray based measuring device, there has been a problem in that the detectable range (dynamic range) of the detector is not effectively used in the measurement of areas where the interested areas are small.
The object of the present invention is to provide a technique which makes it possible to enlarge the dynamic range of the measuring device using a planar X-ray detector and permits high-speed imaging, and to provide an X-ray based measuring device which makes it possible to make effective use of the dynamic range of the planar X-ray detector and improve the quality of the image measured. A brief description will be given below of outlines of typical configurations in accordance with the present invention.
(1) An X-ray based measuring device in accordance with the present invention is characterized by comprising: X-ray imaging means which have their detection areas divided into a plurality of detector units, detect X-rays transmitted through an inspection object, and pick up an X-ray image in an interested area of the inspection object; conversion means for converting analog image signals read from the detector units into digital image data under specified conversion conditions for each of the detector units; and re-conversion means for converting the digital image data obtained for each of the detector units under re-conversion conditions corresponding to the specified conversion conditions, wherein the analog image signals are A/D converted into the digital image data under optimum conversion conditions for each of the detector units, and X-ray images in the interested area of the inspection object are sequentially picked up.
(2) The X-ray based measuring device in accordance with the present invention is characterized by comprising: X-ray imaging means which have their detection areas divided into a plurality of detector units, detect X-rays transmitted through an inspection object, and pick up an X-ray image in an interested area of the inspection object; conversion means for converting analog image signals read sequentially from the detector units starting with detecting elements of the detector units which are close to a position where two of the detector units contact with each other into digital image data under specified conversion conditions for each of the detector units; and re-conversion means for converting the digital image data obtained for each of the detector units under re-conversion conditions corresponding to the specified conversion conditions, wherein the analog image signals are converted into the digital image data under optimum conversion conditions for each of the detector units, and X-ray conditions for ensuing imaging are set on the basis of the X-ray image of the inspection object detected by each of the detector units, so as to sequentially pick up X-ray images in the interested area.
Further, the X-ray based measuring devices in (1) and (2) above are also characterized in that (a) setting means is further provided for setting the specified conversion conditions for each of the detector units on the basis of the analog image signals in the interested area set in advance, so as to convert the analog image signals read by each of the detector units into the digital image data; (b) the conversion means has an A/D converter, and a range of an input signal to the A/D converter and a range of a signal detected by the detector unit are made to agree with each other; (c) the conversion means has an A/D converter and linear amplification means for linearly amplifying the signal detected by the detector unit and/or nonlinear amplification means for nonlinearly amplifying the same, so as to change an operating condition of the A/D converter by one of first parameters including a gain and an offset of the linear amplification means and second parameters including a gain and nonlinearity of an input output characteristic of the nonlinear amplification means, or by a combination of the first and second parameters; (d), in (c), the nonlinear amplification means is formed by logarithm
Baba Rika
Ueda Ken
Church Craig E.
Hitachi Medical Corporation
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