GB2305095A - Imaging system with support for imaging devices - Google Patents

Abstract

An imaging support 22 for supporting imaging devices 20 in respective positions to define an imaging surface is arranged to permit the imaging devices 20 to be mounted on the support in a non-destructive, removable manner. The removable mounting is preferably achieved by providing a source of reduced air pressure through an aperture 8 behind the imaging devices 20 to suck the devices onto the support 22 so that the devices are accurately located in a non-destructive manner. The imaging devices are removable without damage to the device to be removed, the surrounding devices or the support. Devices can readily and quickly be replaced on the same or a different imaging support. The devices may be semiconductor pixel detectors, and may be secured by sockets, clips of magnets instead of suction.

Description

IMAGING SYSTEM AND METHOD The invention relates to an imaging system and method. The invention finds particular application to large area imaging.

Imaging systems are used in a wide range of applications, particularly for imaging for medical diagnosis, in biotechnology and in industrial applications for nondestructive testing and on-line product quality control.

For all of these fields of application, the prevailing means of performing imaging is with the use of radiation, usually X-rays, gamma-rays and beta-rays.

Radiation is detected by some sort of imaging plane, which need not be planar.

Accordingly, the term imaging surface will be used hereinafter. Images are formed either directly on the imaging surfaces (e.g. projection imaging) or data are processed and images are reconstructed in a computer (e.g.. computerized tomography or coded aperture imaging in nuclear medicine).

The traditional imaging surface was formed by a film in a cassette. Other imaging surface solutions have been developed over the past 40 years offering digital imaging. Such examples are Nal scintillating screens, Nal scintillating crystals, BGO crystals, wire gas chambers, digital imaging plates etc. More recently, semiconductor imaging solutions such as Charged Coupled Devices, Si microstrip detectors and semiconductor pixel detectors have been developed.

Typically, in all of the above cases, when a large imaging area is needed it is made either as a monolithic structure (e.g.. films, digital imaging plates, NaI screens etc.) or as a mosaic of smaller pieces (tiles) put together and fixed on a support surface (e.g.. gamma cameras with NaI crystals).

When a monolithic large imaging surface is employed, if a part of the surface is defective then the whole surface needs to be changed. Unfortunately, the most precise digital on-line imaging devices proposed so far involve pixel-based semiconductors which cannot be manufactured in large areas (larger than a few square cm at most). Moreover, it would not be desirable to manufacture, for example, a monolithic 30cm by 30cm digital imaging semiconductor surface because the yield would be low. If a portion of the expensive imaging area became defective, then the whole surface would have to be replaced.

It has been proposed to provide a large area imaging surface (larger than a few square mm) using a tiling approach. In a recent patent application (EP 0 577 487 Al) semiconductor pixel detectors are tiled together to form a larger fixed surface. Using such an approach, individual imaging devices are arranged in a mosaic on an imaging support to form an imaging mosaic. Outputs from the individual imaging devices can be processed to provide a single output image corresponding substantially to the whole area covered by the imaging surface. The imaging devices are fixed to the imaging support in an essential permanent manner by soldering or the like so that it is difficult or impossible to remove the imaging devices without damage to the devices and/or the support and/or the devices surrounding the device to be removed.

It is seen from the above that solutions to large imaging areas proposed so far rely either on monolithic structures or on fixed tiling solutions. As high resolution semiconductor imaging solutions are progressively introduced in radiation imaging there is a need for an efficient way of assembling large imaging areas. Semiconductor imaging solutions are quite expensive both because of the semiconductor cost and also because of the integrated readout electronics. Therefore it is important to maximize the effective use of each square unit of imaging area.

An object of the invention is to provide an imaging system and method which, while providing the advantages of the tiling approach, remove or at least mitigate the problems of the prior art.

In accordance with a first aspect of the invention, there is provided an imaging support for supporting a plurality of imaging devices in respective positions to define an imaging surface, the imaging support comprising means for removably mounting the imaging devices on the imaging support in a non-destructive, removable manner.

In accordance with another aspect of the invention, there is provided a method of forming an imaging array comprising: - providing an imaging support for supporting a plurality of imaging devices in respective positions to define an imaging surface; and - removably mounting the imaging devices on the support in a non-destructive, removable manner.

Unlike prior art large area imaging systems, the imaging devices are removable without damage to the device to be removed, the surrounding devices or the support.

In this manner, defective devices can readily and quickly be replaced. Moreover, correctly functioning imaging devices can easily be removed and re-used on the same or a different imaging support. Thus, with a set of imaging devices and a number of different supports, different imaging surfaces can be constructed without needing to have enough imaging devices for each of the imaging supports. As a result, modular imaging surfaces can easily and cost effectively be assembled and maintained.

In a preferred embodiment, the imaging devices comprise a semiconductor pixel detector and its associated readout chip.

Preferably, the imaging devices are removable and are temporarily kept in place on the master plane by means of a reduced air pressure (vacuum).

Embodiments of the invention are described hereinafter, by way of example only, with reference to the accompanying drawings in which: Figure 1A is a schematic cross-sectional view of an imaging device; Figure 1B is a schematic cross-sectional view of part of an imaging support; Figure I C is a schematic cross-sectional view of the imaging device located on the imaging support; Figure 2 is a schematic plan view of the imaging support; Figure 3 is a schematic view of an imaging system; and Figure 4 is a schematic view of an alternative imaging support with the imaging device located thereon.

Embodiments of the invention provide a new imaging mosaic system and a method for producing imaging mosaics using a plurality of imaging devices (tiles) and an imaging support. The imaging devices are positioned and held on the support in a reversible and non-destructive way. The removable positioning/fixing means allow individual imaging devices to be removed multiple times so that the same imaging device can be used in a different imaging support or it can be replaced if found to be defective without damaging the imaging support and without affecting the operation of any other imaging device on the imaging support.

As individual imaging devices can be removed and re-positioned any number of times the same imaging devices can be used in a number of applications. For example imaging devices used for mammography can be quickly transferred on a different imaging support for chest X-rays. A variety of imaging supports can have different sizes and shapes but only one set of imaging devices is needed. Additionally replacing an imaging device can be done by a non-expert and maintenance costs are minimized. Accordingly, contrary to the prior art where large imaging areas have monolithic imaging means or a fixed tiled imaging plane, the invention introduces a new large area imaging system where the imaging mosaic is made of removable imaging devices allowing for multi-purpose use and re-use of the individual imaging devices, while also allowing cost effective maintenance of the imaging areas.

In a preferred embodiment, by way of example only, the imaging devices comprise Active Semiconductor Imaging Devices (ASIDs) as described in the present applicant's patent application PCT/EP95/02056. An ASID is an active, dynamic semiconductor pixel imaging device with dimensions from possibly few square mm to several square cm.

A cross-section of one such imaging device (tile) 20 is shown schematically in Figure 1A. Radiation enters the semiconductor detector 1 from one face (the top face in Figure 1A) and upon absorption creates an electric charge. On the exit face of the detector electrode pads define the detector cells or pixels. Charge created from successive radiation hits is accumulated on the corresponding pixel circuits 3 which are connected to the detector pixels via conductive microbumps 2 (e.g. indium bumps).

Each such imaging device 20 has tens of thousands of pixels but only needs around 5-10 external lines that will provide control signals, supply voltage and will readout the signal. These lines are provided on the imaging support 22 on which the imaging device 20 is mounted.

The imaging device 20 itself carries an equal number of contacts 5 in the form of, for example, small metal spheres or bumps. As shown in Figure 1A and 1B these metal spheres match an equal number of small appropriately sized metal spherical holes or cavities 7 on a circuit board 9 of the imaging support 22. The cavities on the imaging support 22 are connected to the aforementioned control, supply and signal lines (not shown).

The imaging devices 20 are mounted on the imaging support 22 in a nondestructive manner so that the imaging device 20 can easily be re-positioned on a different imaging support 22 if needed or the imaging device 20 can be changed. In this embodiment, non-destructive mounting is provided by an additional small aperture 8 on the imaging support 22 through which air from beneath the imaging device 20 can be extracted, so that the imaging device 20 is held onto the imaging support by the pressure differential between atmospheric pressure on the upper surface of the imaging device 20 and the reduced air pressure below the imaging device 20.At each mounting location on the imaging support, a gasket 6 formed from a flexible impervious sealing material in a ring shape (e.g. an 'O'-ring) is provided to ensure that the air pressure differential between the upper and lower surfaces of the imaging device 20 are maintained.

Additionally, alignment pins Sa and alignment holes Sb are provided on the imaging device 20 and the imaging support 22, respectively, to assist in locating the imaging device 20 on the imaging support 22 (better than 10pm positional accuracy is achievable) before suction. Pins Sa will ensure that the contacts S on the imaging device 20 will properly match the female connectors 7 on the imaging support 22 after suction. Moreover, because of the close tolerances between the pins Sa and holes Sb, these pins and holes will help to prevent the imaging devices 20 from falling out of the mounting locations (sockets) for the imaging devices 20 when the arrangement shown in Figure 1 is at an angle to the horizontal or even inverted.

Figure 2 shows a plan view of the imaging support 22, which provides a support surface, or plane (e.g., a PCB 9) with a plurality of mounting locations (sockets) for the imaging devices 20. It should be noted that the imaging devices 20 have been arranged in a linear array of columns, with adjacent columns being displaced in the column direction. This way the small inactive space between imaging devices 20 will be covered when the imaging support 22 moves in a direction perpendicular to the column axis as described in patent application PCT/EP95/02056.

In practice the mounting locations will be closer than illustrated, schematically, in Figure 2.

In accordance with this example of the invention, all the imaging devices 20 are provided with an aperture for suction and only one common vacuum pipe is needed per imaging support 22 as shown in Figure 3. In the same Figure, a valve 12 controls the vacuum condition which is monitored from a gauge 14. A vacuum container 13 acts as a vacuum buffer to further enhance the vacuum condition when needed. The vacuum pump 15 can be located remotely so that it does not cause any disturbance by its presence or as a result of noise.

If a particular example, e.g., mammography, is considered, an imaging surface of 30cm by 30cm (about 600 imaging devices of the type described in patent application PCTXEP95/02056) will be needed. The 600 imaging devices will be mounted on a printed circuit board 9 of the imaging support 22. In accordance with this example of the invention, one aperture 8 is provided for each imaging device 20.

All the apertures are connected to a common vacuum pipe for simultaneously sucking all the imaging devices 20 into position. The vacuum condition is easily monitored with a gauge 14 or pressure threshold sensor and additional air can be sucked out via the buffer container 13. Once imaging devices 20 have been sucked in, the vacuum pipe may be removed from vacuum switch 12 since the gaskets 6 are air-tight.

When an imaging device 20 needs to be removed, all is needed is to open the vacuum switch 12 and one or more or indeed all of the imaging devices 20 are ready to be removed and relocated or substituted. As mentioned above, the engagement of the pins 5a in the holes 5b will assist in retaining imaging devices 20 until physically removed by the operator.

In this example, all the apertures 8 are connected via passages 28 in a support structure 10 of the imaging support 22 to a common valve 12. However, a plurality of valves could be provided so that the vacuum can be supplied individually to apertures 8 or groups of apertures 8 for respective mounting locations. Selectively removing or applying suction could be used to assist in the individual mounting or removal of imaging devices 20. Also, rather than a manual valve, electronically controlled valves could be provided under the control, for example, of a control computer or other control mechanism.

Figure 4 illustrates an alternative to the imaging support of Figure 1. Figure 4A is a schematic cross-sectional view of an imaging device 24 similar to that of Figure 1A. Figure 4B is a schematic cross-sectional view of part of the alternative imaging support 26. Figure 4C is a schematic cross-sectional view of the imaging device 24 located on the alternative imaging support 26. Figure 4D is a schematic plan view of the alternative imaging support 26.

As illustrated in Figure 4, an air-tight gasket 16 is provided at the surface of each of the contacts 17 of the imaging support 26. The gaskets 16 are made of a flexible impervious sealing material which is electrically conductive. Any suitable material can be used which is either conductive in itself, or made conductive, for example by impregnating it with conductive material in a suitable manner as will be apparent to one skilled in the art.

An aperture 18 is provided for each contact 17. Each gasket 16 surrounds the respective aperture 18 and is also connected to the corresponding lines or wires 19 on the imaging support 26. In this example, as in the example described above, the apertures 18 can be connected to a common vacuum pipe via a common valve, or via separate valves, etc, as required.

Accordingly, the Figure 4 embodiment differs from the Figure 1 embodiment in that a separate gasket is provided for each contact, rather than each imaging device.

The use of the individual conducting gaskets 16 which are directly connected to the imaging support lines ensures good contact of each and every bump connector 5 on the imaging device to the corresponding female connector 17 on the imaging support 26.

Although no alignment pins and holes corresponding to the pins/holes 5a, Sb of the first embodiment are shown in the Figure 4 embodiment, these can additionally be provided in the Figure 4 embodiment to aid accurate location and/or retention of the imaging devices 24.

Using an embodiment of the invention, for example one of the embodiments described above, it is thus possible to configure a variety of clinical equipment with the imaging supports ready and mounted on the corresponding systems awaiting for the imaging devices. Imaging devices can be properly packaged and supplied separately from the rest of the imaging system and any average technical employee can handle them and relocate them from one plane to another. In this way, the use of the relatively expensive pixel semiconductor imaging devices is optimized by requiring less imaging devices than are needed simultaneously to equip all systems. In addition, maintenance becomes cost effective. A defective imaging device can be substituted rather than the whole imaging surface (mosaic) and this can be done easily by an average technical employee.

The invention can be used for any radiation type in any radiation imaging field where areas larger than a few square mm are needed. In particular it finds application in medical diagnosis imaging with X-rays and gamma-rays, in biotechnology imaging with beta-rays (where isotopes are used as labels on the samples to be imaged) and in industrial applications for non-destructive testing and product quality control.

There has, therefore been described a mosaic imaging system and a method for assembling a mosaic imaging plane made of individual imaging devices (tiles).

The method comprises the following steps: 1) manufacturing individual imaging devices (tiles) and packaging them so as to have access through a number of contacts to all needed control, supply and readout signals on the imaging device; 2) manufacturing an imaging support (master plane) having contacts for each contact on the imaging device, the imaging support contacts being connected to appropriate control, supply and readout signal lines for connection to external circuitry, the imaging support contacts preferably also serving to aid alignment of the imaging device by co-operation with the imaging device contacts; 3) positioning each one of the imaging devices on the master plane with the corresponding contacts being aligned;; 4) removably securing the position of each of the individual imaging devices to the imaging support in a non-destructive manner such that the imaging devices may subsequently be removed individually without damage.

The removable securing is achieved in a non-destructive way such that an imaging devices may be secured to and removed from an imaging support a plurality of times leaving the imaging device, the board(s) and corresponding contacts in substantially the same state.

The removable mounting may be achieved using alternative techniques including: - reduced air pressure, or vacuum as described above, whereby the imaging devices are sucked into position; - a socket configuration (preferably zero-insertion force socket means) whereby the imaging devices have pins that plug into corresponding sockets on the imaging support; - clips, whereby the imaging devices are kept in position with mechanical clips, strings or the like; - magnets, whereby small magnets, either on the imaging support or on the imaging devices, or both, secure the imaging devices to the imaging plane; - other mechanical arrangements.

While specific embodiments have been described, it is to be understood that many modifications and alternatives can be made without departing from the invention.

For example imaging mosaic planes may comprise other than semiconductor pixel devices, such as removable NaI crystals or small scale wire gas chambers.

Also the removable mounting may be achieved without the use of vacuum, for example by clips, socket arrangements, magnets etc.

Also, rather than providing contact spheres or bumps on the imaging devices, and matching holes or cavities on the imaging support, at least some or all of the bumps could be provided on the imaging support with cooperating formations on the imaging devices. Indeed, rather than bumps and holes, other contact configurations (e.g., pins or plates) could be used in other embodiments.

Claims (19)

1. An imaging support for supporting a plurality of imaging devices in respective positions to define an imaging surface, said imaging support comprising means for removably mounting said imaging devices on said imaging support in a nondestructive, removable manner.

2. An imaging support according to claim 1, comprising a plurality of imaging device locations, said removable mounting means removably mounting a respective imaging device at each said location.

3. An imaging support according to claim 2, wherein each imaging device location comprises a plurality of imaging support contacts, each for co-operating with a respective imaging device contact for a transfer of signals between said imaging device support and said imaging device.

4. An imaging support according to claim 3, wherein said imaging support contacts comprise recesses for receiving correspondingly shaped bumps on a said imaging device or bumps for receiving correspondingly shaped recesses on a said imaging device.

5. An imaging support according to any one of claims 2 to 4, wherein said removable mounting means comprises an air passage at a said mounting location, said air passage being connected or connectable to pressure reduction means.

6. An imaging support according to claim 5, wherein each air passage for a plurality of mounting locations are connected to a common pressure reduction means.

7. An imaging support according to claim 6, wherein each mounting location is surrounded by a seal to maintain reduced pressure under an imaging device at said mounting location.

8. An imaging support according to any one of claims 2 to 4, wherein said removable mounting means comprises an air passage at each contact position in a said mounting location on said imaging support, said air passages being connected or connectable to pressure reduction means.

9. An imaging support according to claim 8, wherein each air passage for a plurality of mounting locations are connected to a common pressure reduction means.

10. An imaging support according to claim 8 or claim 9, wherein each said contact position is surrounded by a conductive seal to maintain reduced pressure under corresponding contact of a said imaging device at said mounting location.

11. An imaging support according to claim 10, wherein said seal is conductive to electrically connect said corresponding contact of said imaging device to conductors on said imaging support.

12. An imaging system comprising an imaging support according to any one of the preceding claims with a plurality of imaging devices for mounting at said mounting locations.

13. An imaging system according to claim 12 comprising a plurality of different imaging supports according to any one of claims 1 to 11 and a common set of imaging devices which are mountable on a selected imaging support at any one time, but are removable whereby they may be mounted on another one of said imaging supports.

14. A method of forming an imaging array comprising: - providing an imaging support for supporting a plurality of imaging devices in respective positions to define an imaging surface; and - removably mounting said imaging devices on said imaging support in a nondestructive, removable manner.

15. A method of forming an imaging array according to claim 14 comprising: - providing a plurality of imaging supports, each for supporting a plurality of imaging devices in respective positions to define an imaging surface; and - removably mounting said imaging devices on a first one of said imaging supports in a non-destructive, removable manner at a first time; - removing at least some of said imaging devices from said first support and removably mounting said imaging devices on a second one of said imaging supports in a non-destructive, removable manner at a second time.

16. A method of forming an imaging array according to claim 14 or claim 15, wherein the step of removably mounting said imaging devices comprises providing a source of reduced pressure behind said imaging devices on said imaging support and sucking said imaging devices onto said imaging support to accurately locate said imaging devices on said support in a removable, non-destructive manner.

17. An imaging support substantially as hereinbefore described with reference to the accompanying drawings.

18. An imaging system substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of forming an imaging array substantially as hereinbefore described with reference to the accompanying drawings.