WO2010018497A1

WO2010018497A1 - A mammography detector for the medical examining of a female breast

Info

Publication number: WO2010018497A1
Application number: PCT/IB2009/053434
Authority: WO
Inventors: Roelf Van Der Wal; Abhishek Kumar; Chiel Smit; Onno J. Wimmers
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-08-14
Filing date: 2009-08-06
Publication date: 2010-02-18

Abstract

The application describes a mammography detector for the medical examining of a female breast, wherein the detector comprises an image sensor, wherein the image sensor comprises a first group consisting of at least two image sensing pixels, and a first multiplexer, which is adapted to address directly a first image sensing pixel out of the first group. Further the application deals with a method for scanning a female breast, comprising the step of scanning with the help of a detector according to the application. Furthermore, the application deals with a programme element, which, when being executed by a processor, is adapted to carry out the method according to the application. A further aspect of the application is a computer readable medium having stored the programme element according to the application.

Description

A MAMMOGRAPHY DETECTOR FOR THE MEDICAL EXAMINING OF A FEMALE BREAST

FIELD OF THE INVENTION

The present invention relates to a mammography detector for the medical examining of a female breast, and in particular to a method for scanning a female breast. Further, the present invention relates to a programme element, which, when being executed by a processor, is adapted to carry out the method according to the present invention. Furthermore, the present invention relates to a computer readable medium having stored the inventive programme element. BACKGROUND OF THE INVENTION The person skilled in the art knows mammography detectors, which comprise photo diodes (pixels) for scanning the female breast. The photo diodes generate charges in case of e.g. X-rays. These charges can be evaluated by charge sensitive amplifiers. For selecting the different photo diodes in order to evaluate the corresponding charges there are control lines.

SUMMARY OF THE INVENTION

The aim is to realize a full field digital mammography detector. For mammography it is important to distinguish small details. To make this possible, it is necessary to have a detector with small pixels, while maintaining high signal to noise ratio. A very cost effective technology for realizing such a detector is amorphous silicon technology.

When the pixel sizes become less than 100 μm, two major problems will arise. The first problem is the number of interconnects and the small pitch of these interconnects. All the rows and columns of the pixel array have to be connected with the control electronics. This is mostly done with flex foils. These are bonded to the detector plate with for instance an ACF process. Due to the small bonding pitch that is necessary and the large number of connections that are necessary, the assembly will take a long time, and the yield will be small. The second problem is the noise. Due to the small pixels, the signal of each pixel will be small, and therefore the signal-to-noise ratio will be small. To overcome this problem, one possibility is to increase the filling factor of a pixel. This can be realized with multi level technology. In this technology, the photo diode is patterned in a second layer on top of the thin film transistor. In this way, the thin film transistor is not occupying a part of the filling factor of the photo diode. After maximizing the filling factor, the signal-to noise ratio can be further improved by decreasing the electronic noise. A major part of the electronic noise is due to the data- column capacitance. The input noise of the charge sensitive amplifier (CSA) is multiplied with the ratio of the data-column capacitance and the integration capacitance of the CSA. The higher the data-column capacitance is, the higher the electronic noise. In most common pixel designs, the data-column capacitance is e.g. determined by the capacitance of all the thin film transistors in the pixels connected to the data-column.

The inventive concept is to minimize the number of thin film transistors connected to one data-column by applying multiplex thin film transistors in the pixel array.

According to a first aspect of the invention a mammography detector for the medical examining of a female breast is proposed, wherein the detector comprises an image sensor, wherein the image sensor comprises a first group consisting of at least two image sensing pixels, and a first multiplexer, which is adapted to address directly a first image sensing pixel out of the first group.

The mammography detector according to the invention could be also used as an universal/general detector. The mammography detector could be applied e.g. for examining mechanical parts e.g. instead of scanning female breasts because of suspicion of cancer. The detector comprises a group of photo diodes. Typically, according to the present invention the total amount of photo diodes will be divided in groups of photo diodes, wherein the groups of photo diodes comprise the same number of photo diodes. For instance one group comprises four photo diodes then the image sensor comprises normally a total number of photo diodes, which is divisable by the divisor 4. It is also possible to divide the quantity of photo diodes of an image sensor into groups of e.g. 2, 6 or any other integer number of photo diodes. The single members of a group of photo diodes will be addressed by a multiplexer, wherein the multiplexer addresses typically one member of the group of photo diodes of every group. The multiplexer controls the members of the groups directly, what means that there is no further device e.g. a logic unit between the multiplexer and the addressed image sensing pixel. The control signals, which are emitted by the multiplexer serve to control the switches of the array of pixels, in order to evaluate the charges of the photo diodes. The output signals of the multiplexer define directly which switch is closed and which charge will be read out. Typically, image sensing pixels are photo diodes.

For instance the array of photo diodes could comprise 512 rows of photo diodes and 512 columns of photo diodes. Then, there would be a total of 262144 photo diodes. In case the photo diodes would be shaped in groups of 4 photo diodes there were 65536 groups of photo diodes. Every group of photo diodes is arranged along two different rows and two different columns (every group is arranged as an array of 2 x 2 photo diodes). Therefore, there is an array of 256 x 256 groups of photo diodes. Assuming that there are 256 charge sensitive amplifiers there would be 256 control lines necessary to select one group for every amplifier. As a result according to the inventive concept there would be necessary 256 control lines and 4 control lines of the multiplexer, which leads to a total amount of 260 control lines. According to the prior art there would be necessary 512 amplifiers and 512 control lines to select the corresponding row of photo diodes. Therefore, the arrangement according to the prior art requires additional 256 amplifiers and additional 252 control lines to select one photo diode for every amplifier compared with the arrangement according to the inventive concept.

According to a second aspect of the invention it is proposed a method for scanning a female breast, comprising the step of scanning with the help of a detector according to one of claims 1 to 8.

According to a third aspect of the invention it is proposed a programme element, which, when being executed by a processor, is adapted to carry out the method of claim 9. According to a fourth aspect of the invention it is proposed a computer readable medium having stored the programme element of claim 10.

Further embodiments are incorporated in the dependent claims. It should be noted that the following described exemplary embodiments of the invention apply also for the method, the programme element and the computer readable medium.

According to the present invention it is provided a detector, wherein the image sensor comprises a second group consisting of at least two image sensing pixels, and a second multiplexer, which is adapted to address directly a second image sensing pixel out of the second group.

Typically, all pixels of the sensor are grouped in groups of e.g. 2, 4, 6 photo diodes. These groups can be addressed by one or several multiplexers. The output of the multiplexers addresses the switches of the corresponding photo diodes in order to evaluate the charges of the photo diodes. According to an exemplary embodiment it is provided a detector, wherein the first multiplexer is identical to the second multiplexer. The inventive concept comprises arrangements with only one or several multiplexers for selecting one photo diode of every group. Usually, there is only one mutliplexer.

According to another exemplary embodiment it is provided a detector, wherein first resulting image sensing pixels are addressed by the first multiplexer, wherein second resulting image sensing pixels are addressed by the second multiplexer, wherein the detector comprises a control line, wherein the control line is adapted to address selected image sensing pixels out of the group consisting of the first resulting image sensing pixels and the second resulting image sensing pixels. According to another exemplary embodiment it is provided a detector, comprising a charge sensitive amplifier, which is adapted to detect the charge of an image sensing pixel out of the group consisting of the selected image sensing pixels, wherein the charge of the image sensing pixel is generated in case the image sensing pixel is exposed to light. There are drivers for controlling switches with the help of control lines, wherein the charge of a photo diode can be evaluated if the corresponding switch is closed. The charges will be evaluated with amplifiers, which comprise typically a low- pass filter.

According to another exemplary embodiment it is provided a detector, wherein the image sensing pixels of the first group are arranged adjacent. Typically the single photo diodes of a group are arranged adjacent in order to minimize the length of control lines and connections to the photo diodes. A further effect is the minimization of connections to the switches and capacitors, which belong to the photo diodes of the group.

According to another exemplary embodiment it is provided a detector, wherein the image sensing pixels of the second group are arranged adjacent.

According to another exemplary embodiment it is provided a detector, wherein the first group consists of an integer number of image sensing pixels. It is senseful to use groups of 2, 4, 6 or any other integer number of photo diodes to form groups of photo diodes. It may be seen as a gist of the present invention to reduce the necessary number of control lines of an array of photo diodes. By reducing the number of photo diodes it is possible to arrange an increased number of photo diodes in the same area. This effect results in an increased resolution of the image sensing detector, wherein very small details can be distinguished. It should be noted that the above features may also be combined. The combination of the above features may also lead to synergetic effects, even if not explicitly described in detail.

These and other aspects of the present invention will become apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described in the following with reference to the following drawings.

Fig. 1. shows the grouping of e.g. four pixels, wherein the pixels of every group of four pixels is selected by one multiplexer, Fig. 2. shows voltage diagrams of switches, wherein a high voltage means a closed switch,

Fig. 3. shows an embodiment of a sensor,

Fig. 4. shows an embodiment of a sensor,

Fig. 5. shows an embodiment of a sensor,

Fig. 6. shows an embodiment of a sensor,

Fig. 7. shows an embodiment of a sensor,

Fig. 8. shows an arrangement of photo diodes according to the prior art,

FFiigg.. 99.. shows an arrangement of groups of photo diodes according to the inventive concept,

Fie. 10. shows the processing of the charge of an photo diode.

DETAILED DESCRIPTION OF EMBODIMENTS Fig. 1 shows three groups of four photo diodes 106. Every single photo diode 106 is connected with a switch 107. A group of photo diodes is formed by joining the outputs of switches 107. The photo diode 106 can generate a charge due to exposure of e.g. visible ligt or X-ray radiation. In case the switch 107 is closed the charge of the photo diode 106 can be detected from the node of the switches, which belong to the grouped photo diodes 106. The switches of the group is selected e.g. by a multiplexer 104, wherein the multiplexer 104 selects one photo diode 106 of every group of photo diodes 106. The multiplexer 104 drives control lines A, B, C, D, which select one of the switches 107. The groups of photo diodes 106 are selected by switches E, F, G, wherein these switches are controlled by control lines 101. As a result the charge of one photo diode 106 can be detected via the data column 102. This charge will be processed with the help of the charge sensitive amplifier 103.

Fig. 1 shows an embodiment of an inventive circuit, wherein one multiplex switch is connecting four pixels. In this way, the number of thin film transistors connected to one data column is reduced with 75%. And therefore the data- column capacitance is reduced significantly. A second advantage is that the number of gate line drivers is also reduced with 75%. This reduces the number of interconnects significantly without reducing the read-out speed much. In the embodiment, one of the four diodes of a pixel cluster is selected in the whole array. Then the complete array is scanned. Subsequently, the second diodes are selected, the complete array is scanned for the second time, and unto the last diode is selected and read-out by the CSA. Fig. 2 shows a diagram of voltages, wherein a high voltage means that the corresponding switch is conducting. The first diagram shows the high voltage 201 during a first period of time. Therefore, during this period of time one single photo diode from every group of photo diodes 106 is selected. Now it is necessary to select the group of photo diodes 106, in order to receive the charge of only one single photo diode 106. This is achieved by controlling one of the switches E, F or G. Therefore, during the first period of time 201 it can be selected one of the switches E, F or G. During the period of time 205 the first group of photo diodes is selected and one single photo diode of this group is selected by the high voltage, which drives the switch A. During the period of time 202 another photo diode 106 of the groups of photo diodes can be selected according to the voltages 205, 206, 207. The voltages 201, 202, 203 and 204 provide the possibility to select single photo diodes 106 of the groups of photo diodes. During this periods of time the selection of the group of photo diodes is achieved by the switches E, F and G. The switches E, F and G are controlled by the voltages 205, 206, 207. Fig. 3 shows an arrangement of photo diodes and the corresponding

PCB-layout. Further, it is shown a circuit with one multiplex switch connecting four pixels. However, the number of pixels connected by one multiplex switch can vary from two unto a very high number. The theoretical minimum in data column capacitance occurs when the number of multiplex switches equals the root of the total number of pixels in one column. However this is an impractical high number.

Fig. 3 shows an implementation from a circuit with one multiplexer connecting two pixels. The fig. 3 shows the gate drivers 302, 303 and the drivers 304, 305, that have to select all of the odd or even pixels. There need to be only two of these drivers 304, 305 on the complete array. The gate-lines, which are starting from the gate drivers 302, 303, are shown together with the gates of the thin film transistors. Fig. 3 shows the CSAs (charge sensitive amplifiers) 301, wherein the CSAs are supplied by the data columns 306. The bars 307 show the local data columns, together with the drain and source of the thin film transistors. The circles 308 show the connection vias to the photo diode. The circles 309 show the vias connecting the thin film transistor with the data column 306. The photo diodes on top and the common bars are not shown in this picture, to get a more clear view.

Due to the multi level technology, the photo diode is placed on top, and therefore the extra multiplex switch does not reduce the filling factor.

Fig. 4 shows an arrangement of photo diodes. The gate drivers 402 and 403 in combination with the drivers 404, 405 by which one single photo diode for every charge sensitive amplifier 401 can be selected. The gate- lines, which are starting from the gate drivers 402, 404 are shown together with the gates of the thin film transistor. It is also shown the charge sensitive amplifiers 401, wherein the charge sensitive amplifiers are supplied by the data columns 406. The bars 407 show the local data columns together with the drain and source of the thin film transistors. The circles 408 show the connection vias to the photo diode. The circles 409 show the vias connecting the thin film transistor with the data column 406. The photo diodes on top and the common bars are not shown.

In this example, extra gate lines are necessary to connect the multiplex switches. Fig. 4 shows an embodiment, wherein it is not necessary if the gate line of the lowest pixel from the upper pixel-group is combined with the gate line of the upper pixel from the lower pixel-group.

In this way, the number of gate columns can be kept the same as without the multiplex switches. In this example, the pitch of the gate drivers is increased with 100%. However, the pitch of the CSAs still equals the pixel pitch. Fig. 5 shows how this can be solved by placing the CSAs on both sides of the array. Fig. 5 shows the gate drivers 502, 503 as well as the drivers 504 and 505. The charge sensitive amplifiers 501 are supplied by the data columns 506, wherein the data columns 506 are connected with the help of vias 509 with the thin film transistor. The bars 507 are local data columns. The same tricks are possible with other multiplex factors, like 1 to 4. This is shown in the figs. 6 and 7. In this case, the pitch of the CSAs is kept the same, while the pitch of the drivers is four times the pixel pitch.

Fig. 6 shows gate drivers 602, 603 and drivers 604, 605, 610, 611 for selecting one single photo diode for every charge sensitive amplifier 601. The charge sensitive amplifiers 601 are supplied by the data columns 606. The bars 607 are the local data columns. The data columns 606 are connected with thin film transistors by vias 609.

Fig. 7 shows charge sensitive amplifiers 701, which are supplied by data columns 706. The data columns 706 are connected with thin film transistors with the help of vias 712. The bars 707 are local data columns.

The groups of pixels read out by one multiplex switch can be chosen in such a way that both the pixel pitch of the drivers and of the CSAs become twice the pixel pitch. This is shown in the fig. 7. The advantage of this scheme is that there is no need to place the CSAs at both sides of the panel. This gives more design freedom. It is now for example possible to chose the data columns to be the shortest lines of the panel, or to divide the panel in two halves while placing CSA's at both sides of the panel to reduce the data column length with 50%. The drawback is a more complex pixel reordering. Fig. 8 shows an array of photo diodes 802, 805 according to the prior art, wherein capacitors 806, 809 are arranged parallel to the photo diodes 802, 805 in order to load the charge of the photo diodes 802, 805. The gate drivers 810 of the part 808 select one row of photo diodes 802, 805, wherein a corresponding row of charge sensitive amplifiers 801 evaluates the charges generated by the photo diodes 802, 805. The gate drivers 810 are switching on the switches 803, 804 via the control lines 807. The switches 803, 804 can be shaped as a thin film transistor. According to the prior art it is necessary to arrange two rows of amplifiers 801, wherein every row of amplifiers comprises the same number of amplifiers compared with a row of photo diodes. In this case it is necessary to arrange so many amplifiers to reduce the length of the data columns 811 in order to reduce the capacitance of the data column 811. By lowering the capacitance of the data columns 811 the noise will be reduced also. Fig. 9 shows an arrangement of photo diodes 905 according to the inventive concept. According to the depicted embodiment of the invention groups 902 of four photo diodes 905 are arranged. A group 902 of photo diodes 905 is selected by the gate drivers 908 of the part 904. The gate drivers 908 can switch on the corresponding group 902 of photo diodes 905 with the help of the control lines 903. Further, a multiplexer is selecting one single photo diode 905 of every group 902 of photo diodes 905. The charge of the selected photo diodes 905 will be transmitted to the charge sensitive amplifiers 901 with the help of the data columns 910. According to the inventive concept the arrangement comprises only half the number of the arrangement of the prior art, depicted in the figure 8. Due to the grouping of photo diodes 905 the length of the data columns 910 can be reduced, which results in a reduced capacitance and therefore reduced noise. Parallel to the photo diodes 905 there are capacitors 906 in order to load the charge of the photo diode 905. The switches 907 will be controlled by the multiplexer 909. The switches 911 will be controlled by the part 904. The switches 907 and/or 911 can be thin film transistors, e.g..

Fig. 10 shows a circuit comprising a photo diode 1002 for generating a charge and a charge sensitive amplifier. The charge sensitive amplifier comprises an amplifier 1001, wherein one input of the amplifier 1001 is supplied by a constant voltage source 1005 with the voltage Uo. The second input of the amplifier 1001 will be supplied by a capacitor 1006 that is also connected to the output of the amplifier

1001. In case the switch 1003 is closed the capacitor transforms the charge of the photo diode 1002 into a voltage. Further, there is a capacitor 1004 which represents the data column capacitance.

The invention can be applied in any amorphous silicon X-ray detector where noise or the number of interconnects is an important issue. This includes cardio and vascular, general X-ray and mammography. In those applications where speed is an even more important specification point, it is less likely that the invention will be used, because of the higher resistance in series with the pixel capacitance (2 x thin film transistor in series). For very small pixels however, there is no other choice in amorphous silicon, due to the very high number of interconnects. For very small pixels, the time constant determined by the pixel capacitance and the thin film transistor resistance will not increase. Although the resistance is increased, because the pixel capacitance of small pixels is very small, the total time constant will not increase.

It should be noted that the term 'comprising' does not exclude other elements or steps and the 'a' or 'an' does not exclude a plurality. Also elements described in association with the different embodiments may be combined.

It should be noted that the reference signs in the claims shall not be construed as limiting the scope of the claims.

LIST OF REFERENCE SIGNS

101 control line

102 data column

103 charge sensitive amplifier (CSA) 104 multiplexer

105 low potential

106 photo diode

107 switch

201 time period of high voltage of output A of a multiplexer 202 time period of high voltage of output B of a multiplexer

203 time period of high voltage of output C of a multiplexer

204 time period of high voltage of output D of a multiplexer

205 time period of high voltage for controlling the switch E

206 time period of high voltage for controlling the switch F 207 time period of high voltage for controlling the switch G

301 charge sensitive amplifier

302 gate driver

303 gate driver

304 driver 305 driver

306 data column

307 bar

308 via

309 via 401 charge sensitive amplifier

402 gate driver

403 gate driver

404 driver

405 driver 406 data column

407 bar 408 via

409 via

501 via

502 gate driver

503 gate driver

504 driver

505 driver

506 data column

507 bar

508 via

509 via

601 charge sensitive amplifier

602 gate driver

603 gate driver

604 driver

605 driver

606 data column

607 bar

608 via

609 via

610 driver

611 driver

701 charge sensitive amplifier

702 gate driver

703 gate driver

704 driver

705 driver

706 data column

707 bar

708 via

709 charge sensitive amplifier 710 dnver

711 driver

801 charge sensitive amplifier

802 photo diode

803 switch

804 switch

805 photo diode

806 capacitor

807 control line

808 part

809 capacitor

810 gate driver

811 data column

901 charge sensitive amplifier

902 group of four photo diodes

903 control line

904 part

905 photo diode

906 capacitor

907 switch

908 gate driver

909 multiplexer

910 data column

911 switch

1001 amplifier

1002 photo diode

1003 switch

1004 capacitor

1005 constant voltage source

1006 capacitor

Claims

CLAIMS:

1. A mammography detector for the medical examining of a female breast, wherein the detector comprises an image sensor, wherein the image sensor comprises a first group consisting of at least two image sensing pixels (106, 905, 1002), and a first multiplexer (104, 909), which is adapted to address directly a first image sensing pixel (106, 905, 1002) out of the first group.

2. The detector according to claim 1 , wherein the image sensor comprises a second group consisting of at least two image sensing pixels, and a second multiplexer, which is adapted to address directly a second image sensing pixel out of the second group.

3. The detector according to claim 2, wherein the first multiplexer is identical to the second multiplexer.

4. The detector according to one of the claims 2 to 3, wherein first resulting image sensing pixels (106, 905, 1002) are addressed by the first multiplexer (104, 909), wherein second resulting image sensing pixels are addressed by the second multiplexer, wherein the detector comprises a control line, wherein the control line is adapted to address selected image sensing pixels out of the group consisting of the first resulting image sensing pixels (106, 905, 1002) and the second resulting image sensing pixels.

5. The detector according to claim 4, comprising a charge sensitive amplifier (103, 901, 1001), which is adapted to detect the charge of an image sensing pixel out of the group consisting of the selected image sensing pixels, wherein the charge of the image sensing pixel is generated in case the image sensing pixel is exposed to light.

6. The detector according to one of the preceding claims, wherein the image sensing pixels of the first group are arranged adjacent.

7. The detector according to one of the claims 2 to 6, wherein the image sensing pixels of the second group are arranged adjacent.

8. The detector according to one of the claims 2 to 7, wherein the first group consists of an integer number of image sensing pixels.

9. A method for scanning a female breast, comprising the step of scanning with the help of a detector according to one of the preceding claims.

10. Programme element, which, when being executed by a processor, is adapted to carry out the method of claim 9.

11. Computer readable medium having stored the programme element of claim 10.