Radiographic image detector and controlling method therefor

• US 8,983,035 B2
• Filed: 11/21/2012
• Issued: 03/17/2015
• Est. Priority Date: 11/25/2011
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Inventors: Noma, Kentaro, Iwakiri, Naoto, Kitano, Kouichi, Watanabe, Keita, Nakamura, Kenji
• Primary Examiner(s): Vanore, David A
• Application Number:
  US13/683,428
• Publication Number:
  US 20130136234A1
• Time in Patent Office: 846 Days
• Field of Search: 250/370.09, 250/370.08, 250/366, 250/371, 250/394, 250/205, 250/208.1, 250/214.P, 250/338.4, 250/363.01, 250/370.07, 250/370.11, 250/395, 250/580, 250/585, 250/591, 378/98.8, 378/109, 378/114, 378/169, 378/116, 378/182, 378/189, 378/91, 378/97
• US Class Current: 378/97
• CPC Class Codes: A61B 6/548 Remote control of the apparatus or devices
• CPC Class Codes: G01T 1/171 Compensation of dead-time counting losses see provisionally also G01T1/17
• CPC Class Codes: H04N 23/30 for generating image signals from X-rays
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 5/32 Transforming X-rays cameras or camera modules for generating image signals from X-rays H04N23/30; circuitry of SSIS for transforming X-rays into image signals H04N25/30
• CPC Class Codes: H05G 1/64 Circuit arrangements for X-ray apparatus incorporating image intensifiers

Abstract

A flat panel detector has pixels for obtaining image signals and detective pixels for detecting the amount of incident x-rays. A signal processing circuit is of a pipeline-type, wherein first and second buffer memories are connected to the output of an A/D converter. In a dose detecting operation, the signal processing circuit repeats primary cycles alternately with secondary cycles of a shorter length than the primary cycles. In the primary cycle, a dose detection signal based on electric charges from the detective pixels is input in the first buffer memory and, simultaneously, a dummy signal is output from the second buffer memory. In secondary cycle, the dose detection signal is output from the first buffer memory and, simultaneously, a second dummy signal is input in the second buffer memory. On the basis of the dose detection signals, a start-of-radiation detector detects the start of x-ray radiation.

Claims

1. A radiographic image detector for detecting radiographic images of a subject, comprising:

a flat panel detector having an imaging area in which a plurality of columns of pixels for accumulating electric charges corresponding to the amounts of radioactive rays incident on the pixels, a dose sensor generating electric charges corresponding to the amount of radiated radioactive rays radiated from a radiation source, and signal lines provided for respective columns of the pixels are arranged in an array, wherein the pixels and the dose sensor are connected to the signal lines to output the electric charges accumulated in the pixels as image signals and the electric charges generated from the dose sensor as a dose detection signal through the signal lines;

a pipeline-type signal processing circuit comprising a plurality of integrating amplifiers provided for the respective signal lines, to integrate and convert electric charges to voltage signals, and first and second signal holding devices for temporarily holding two sets of voltage signal as successively read out from the integrating amplifiers, wherein a set of voltage signal is being input to one of the first and second signal holding devices while a preceding set of voltage signal is being output from the other of the first and second signal holding devices;

a memory for storing the image signal and the dose detection signal as voltage signals output from the signal processing circuit; and

a controller for controlling operation timings of the flat panel detector, the signal processing circuit and the memory,

wherein the controller controls the signal input and output of the first and second signal holding devices to be repeated in ordinary cycles of a constant length, which corresponds to an integrating session from a start of integration of electric charges till resetting the integrating amplifiers, in a reading operation for outputting the image signal to the memory,

whereas the controller controls the signal input and output of the first and second signal holding devices to be repeated in two kinds of cycles, including primary cycles and secondary cycles of a shorter length than the primary cycles, in such a manner that at least one secondary cycle is conducted in between two primary cycles in a dose detecting operation for outputting the dose detection signal to the memory.

2. The radiographic image detector as claimed in claim 1, wherein the dose detection signal is used for at least one of determination of whether the radiation source has started radiation, determination of whether the radiation source has stopped radiation, automatic control of radiographic exposure, and gain control on the image signal in the reading operation.

3. The radiographic image detector as claimed in claim 1, wherein each of the integrating amplifiers integrates electric charges of one pixel per one signal line to output the image signal for one line in each ordinary cycle.

4. The radiographic image detector as claimed in claim 1, wherein the dose sensor comprises a plurality of elements dispersed over the imaging area, the integrating amplifiers integrate electric charges from the plurality of elements of the dose sensor all at once in the primary cycle and in the secondary cycle.

5. The radiographic image detector as claimed in claim 1, the primary cycle is longer than the ordinary cycle.

6. The radiographic image detector as claimed in claim 1, wherein, in the dose detecting operation, among of the two sets of voltage signal as being successively read out from the integrating amplifiers, only one set of voltage signal which is input in the first signal holding device or the second signal holding device is treated as the dose detection signal, and the other set of voltage signal is not treated as the dose detection signal but as a dummy signal containing useless data.

7. The radiographic image detector as claimed in claim 1, wherein one integrating session of the integrating amplifiers, which is set for the dose detecting operation, is divided between the primary cycle and the secondary cycle.

8. The radiographic image detector as claimed in claim 1, wherein one integrating session of a corresponding length is allotted to each of the primary and secondary cycles.

9. The radiographic image detector as claimed in claim 1, wherein the signal processing circuit further comprises CDS circuits connected to respective outputs of the integrating amplifiers, to sample and hold an analog voltage signal from the integrating amplifiers;

and an A/D converter for converting the analog voltage signal sampled and held in the CDS circuits to a digital voltage signal.

10. The radiographic image detector as claimed in claim 9, the first and second signal holding devices are two buffer memories connected in parallel with each other in between the A/D converter and the memory.

11. The radiographic image detector as claimed in claim 9, wherein the CDS circuits are connected in pairs to the respective outputs of the integrating amplifiers, the CDS circuits of each pair being connected in parallel with each other to constitute the first and second signal holding devices respectively.

12. The radiographic image detector as claimed in claim 1, wherein the controller conducts the primary cycles and the secondary cycles alternately.

13. The radiographic image detector as claimed in claim 9, wherein one and the other of a pair of buffer memories, which are connected in parallel with each other in between the A/D converter and the memory, and one and the other of a pair of the CDS circuits, which are connected in parallel with each other to the output of each integrating amplifier, constitute the first signal holding devices and the second signal holding devices, respectively.

14. The radiographic image detector as claimed in claim 13, wherein the controller conducts two secondary cycles in between two primary cycles.

15. The radiographic image detector as claimed in claim 1, wherein the controller cuts the length of the secondary cycle shorter than the primary cycle by controlling the numbers or intervals of operation control signals applied to the signal processing circuit.

16. The radiographic image detector as claimed in claim 1, wherein some of the pixels serve as the dose sensor.

17. The radiographic image detector as claimed in claim 16, wherein the pixels include ordinary pixels that accumulate signal charges responding to radioactive rays and output the signal charges to the signal lines upon switching elements being turned on, and detective pixels connected directly to the signal lines without intermediate switching elements, the detective pixels serving as the dose sensor.

18. The radiographic image detector as claimed in claim 16, wherein the pixels include ordinary pixels that accumulate signal charges responding to radioactive rays and output the signal charges to the signal lines upon switching elements being turned on, and detective pixels provided with such switching elements that are driven independently of the switching elements of the ordinary pixels, the detective pixels serving as the dose sensor.

19. The radiographic image detector as claimed in claim 1, wherein the radiographic image detector is an electronic cassette containing the flat panel detector in a portable housing.

20. A method of operating a radiographic image detector for detecting radiographic images of a subject, the radiographic image detector comprising:

a flat panel detector having an imaging area in which a plurality of columns of pixels for accumulating electric charges corresponding to the amounts of radioactive rays incident on the pixels, a dose sensor generating electric charges corresponding to the amount of radiated radioactive rays radiated from a radiation source, and signal lines provided for respective columns of the pixels are arranged in an array, wherein the pixels and the dose sensor are connected to the signal lines to output the electric charges accumulated in the pixels as image signals and the electric charges generated from the dose sensor as a dose detection signal through the signal lines;

a pipeline-type signal processing circuit comprising a plurality of integrating amplifiers provided for the respective signal lines, to integrate and convert electric charges to voltage signals, and first and second signal holding devices for temporarily holding two sets of voltage signal as successively read out from the integrating amplifiers, wherein a set of voltage signal is being input to one of the first and second signal holding devices while a preceding set of voltage signal is being output from the other of the first and second signal holding devices;

a memory for storing the image signal and the dose detection signal as voltage signals output from the signal processing circuit; and

a controller for controlling operation timings of the flat panel detector, the signal processing circuit and the memory, wherein the method comprising the steps of;

making the controller, in a reading operation for outputting the image signal to the memory, control the signal input and output of the first and second signal holding devices to be repeated in ordinary cycles of a constant length corresponding to an integrating session from the start of integration of electric charges to resetting the integrating amplifiers; and

making the controller, in a dose detecting operation for outputting the dose detection signal to the memory, control the signal input and output of the first and second signal holding devices to be repeated in two kinds of cycles, including primary cycles and secondary cycles of a shorter length than the primary cycles, in such a manner that at least one secondary cycle is conducted in between the (N−

1)^th primary cycle and the N^th primary cycle.