GB2110037A - A radiographic examination system - Google Patents

Abstract

A system for performing radiographic examination, particularly of large items such as international container units is disclosed. The system is formed as an installation comprising housings (25, 26) for respective linear accelerators (35) transmitting a beam of radiation across the path of a conveyor (38) along which the units can be displaced continuously or incrementally. On either end of the installation are container handling areas including roller conveyors (11, 29) with drag chains and transverse manipulators, and the whole installation is secured within automatically operated doors (21, 22) which seal the high energy region when a container on the conveyor (38) is being subjected to examination. The radiation transmitted through a container (34) is detected in a detector system (39) incorporating a fluoroscopic screen (40) light output from which is detected in a camera system (42) such as a television camera, and transmitted as coded pulsed signals by a coding transfer unit (43) to display screens where an image of the transmitted information can be displayed and/ or recorded for further use. <IMAGE>

Description

SPECIFICATION A radiographic examination system The present invention relates to a radiographic examination system which is particularly adapted for the repeated examination of large items. The present invention finds particular utility in connection with the examination and verification of the contacts of goods traffic containers, particularly useful for customs authorities, port authorities, border posts, security services and similar groups in charge of supervision of goods movements at critical points, particularly for verification of the contents and for avoiding the movement of contraband or illegal goods.

The requirement for increasing mechanisation in the transport of goods has led in recent years to the introduction of standardised container units which can be moved individualiy by road on the trailers of articulated lorries, and which can be stacked regularly within the holds of ships to maximise the utilsation of space. Such containers are loaded and closed at their departure point and provide the not inconsiderable advantage of being relatively inviolate so that loss of contents due to misplacement of the goods or pilfering is substantially reduced due to the fact that the enclosure of the goods within the containers makes them relatively inaccessible.It also means that supervision of the movement of goods for customs and excise purposes, and for verification of the contents by the appropriate authorities at the ports is made more difficult, particularly if the containers are packed with a large quantity of relatively small items since the problem of unpacking a large container (and these can be up to 40 ft long and 8 ft in width and height) create substantial problems.

Similar problems of investigating the interior of otherwise closed containers or items which for one reason or another cannot be opened, and for gaining information about components at inaccessible locations it is known to use long range sensors with electromagnetic radiation of a wavelength which can be propagated through the material of the items under investigation. For example, radiographic examination of the interior of the human body has been undertaken for some considerable time and these techniques are used for diagnostic and prophylactic purposes as well as in medical research. Images generated by such techniques are formed on fixed film receptors between which and the X-ray source the subject for exposure is placed.A similar technique is used for the examination of hand baggage at airport security control check stations where, however, instead of photographic film, a fluoroscopic screen is used to provide an immediate image of the information generated by transmitting X-radiation through the hand baggage.

For testing the quality of welds it has been known to use linear accelerators to generate high energy electromagnetic radiation which is transmitted through the welded components. Again, fixed film exposure to the transmitted radiation is used to provide optically detectable images.

The object of the present invention is that of enabling radiographic examination of large containers such as the international container units used for the international transport of goods to be effected safely and accurately.

It is a further object of the present invention to provide an examination system using a radiographic linear accelerator which will permit customs authorities, security services, port authorities or the like to examine, if necessary in great detail, the contents of containers of any sort for the purpose of comparing the contents displayed on imaging screens with written descriptions thereof, such as in bills of lading, without it being necessary to open the containers for a conventional visual examination unless the radiographic examination reveals suspicious discrepancies between the apparent contents and the bills of lading.

According to one aspect of the present invention, therefore, there is provided a radiographic examination system in which items to be examined are positioned between a radiation source and detector units which operates directly or indirectly to produce optical images from the detected radiation, in which means are provided for transmitting information signals from the primary detectors to a remote location where the information can be displayed on a screen for visual inspection and recorded either photographically or electronically.

Because of the scale of international container units it is necessary to use extremely high energy radiation in order to generate satisfactory images. Moreover, repeated narrow scans of the containers must be made in order to generate the overall pictures and for this reason display systems able to provide a recording function are necessary so that a single fixed image generated by an extended scan, perhaps taking between five and twenty minutes to complete, can be obtained.

Radiographic examination of large containers can be undertaken utilising the system of the present invention to enable simple and speedy identification of the contents thereof to be obtained. Advantageously, therefore, the presence of possible contraband goods mixed with normal merchandise can be identified readily so that suspect containers can be isolated for conventional visual inspection after opening.

In a preferred embodiment of the invention the radiation source is a linear accelerator generating X-rays and the primary detectors include fluoroscopic screens and/or photosensitive diodes which produce optical signals and/or electrical signals, the former of which represent a visual image and the latter of which can be converted to represent a visual image of the incident radiation. The image in practic is created by interposing the subject under examination between the radiation source and the detectors; such image therefore represents a radiation "shadow" of the subject exposed to the radiation. Calibrating electronic integrating and analysing equipment will be required if arrays of photodiodes are used.

Because of the high energies involved it is necessary for the containers to be exposed to the radiation at a "safe" location which is remote from the operating personnel and suitably shielded by radiation absorbing materials such as lead or mass concrete. Conventional visual examination of the fluoroscopic screens cannot, therefore be undertaken and in order to transmit visual energies from the radiographic exposure point to a safe location the optical signals generated by the fluoroscopic screens are detected by a camera incorporating an electronic tube operable to convert the incident optical signals to electrical signals for transmission.A pulse code moduiation of signals is preferably used to transmit the information from the cameras to a remote viewing location where suitable receivers convert the coded electrical signals into an optical display on a screen. Image intensifiers oporat- ing on the electrical signals can be used to improve the perceived quality of the image to facilitate ready identification of the contents of the containers under examination.

The coded electrical signals may also be recorded electromagnetically for storage and/ or for subsequent playback to generate optical images for comparison with images produced during a subsequent scan of the same or a similar subject under investigation.

In the prior art radiographic examination systems, for example those for investigating the quality of welded joints, it is usual to provide a motorised yoke and overhead bridge crane for positioning the acclerator with respect to the container. This involves problems in locating the target film accurately and the present invention seeks to overcome such potential difficulties by providing relatively fixed positioning of the linear accelerator and the detectors, and by displacing the items under investigation into position between them using a heavy duty transport conveyor which is nevertheless capable of positioning the subjects for investigation reasonably accurately between the X-ray source and the detectors.By "reasonably accurately" is intended to mean positioning to within tolerances sufficient to enable fine adjustment to be made by movement of the X-ray source and detectors only over a range of a few mm. This can be effected by carrying the X-ray source and detectors on a massive A-frame spanning the investigation point at which the containers are located in sequence for examination.

It is envisaged that basic self-aligning roller table systems, operating in conjunction with fixed chain link conveyors where necessary will be employed as the primary means for moving the items under investigation forwardly from a storage area to the inspection point. Intermediate drag chains and dogs for major side movements of containers may also be employed.

Transport of the containers may be effected by means of roller tables built up from individual rollers having a length of up to 3.5 metres for effecting the main forward and reverse movement of containers from a lorry unloading point through a storage region to the inspection point, and from the inspection point to a subsidiary inspection point and/or to a cleared collection and dispatch area.

It is envisaged that systems of the present invention will use two parallel inspection lines drawing containers from a common storage area along parallel track and/or roller conveyors, there being provided means for transporting a container from one inspection line to another for secondary radiographic examination in the event of the primary examination giving rise to grounds for suspicion that the contents of the container need further investigation.

The invention will be better understood from a consideration of the following detailed description with reference to the accompanying drawings which illustrates a preferred embodiment of the invention, and in which: Figure 1 is a schematic plan view of an installation incorporating the radiographic examination system of the present invention; and Figure 2 is an expanded block diagram illustrating the X-radiation exposure and imaging system.

Referring now to the drawings the installation shown comprises two examination lines generally indicated 11, 1 2 for conveying containers from respective initial delivery and/ storage areas 13, 14 through respective radiographic examination stations 15, 1 6 to respective output or despatch areas 1 7, 18.

Each of the radiographic examination systems on the two lines 11, 1 2 is identical and consequently only one will be described in detail herein. Between the two initial arrival areas 13, 14 is a container turnaround area 1 9 housing a turn-around crane of conventional type which, together with lateral transfer means (not illustrated) enables a container to be transferred laterally from one conveyor line to the other and at the same time to be reversed so that upon transfer from one line to the other the container can passed through the investigation unit facing in the opposite direction. The purpose of this facility will be explained in further detail below.

Along the length of the conveyor line 11, for example, the installation will be enclosed with a suitable encircling wall 20 with motorised main input doors 21 and exit doors 22 which are automatically controlled and interlocked with the operation of the accelerators.

In the embodiment illustrated there are provided two accelerator installations 23, 24 one on either side of the line 11 and two detector houses 25, 26 for receiving electromagnet radiation transmitted across the line 11 from the respective accelerators 23, 24.

In the embodiment illustrated in Fig. 1 the conveyor lines 11, 1 2 comprise sets of selfaligning roller table systems, operating in conjunction with fixed chain link conveyors. For effective lateral transfer of containers from the conveyor lines 11, 1 2 to the turn around area 1 9 or from the delivery of arrival areas 13, 1 4 there are provided intermediate drag chain and dog conveyors (not shown) such conveyor systems are, known from heavy steel rolling mill practice where it is quite common for steel ingots and slabs weighing up to 60 tons to be conveyed by means of such roller table and drag chain conveyor systems.It can be demonstrated that by suitably choosing the dimensions of the rollers for the roller conveyors of the lines 11, 12, and appropriately spacing them along the lines, the shock loads on each roller as a fully loaded container up to its maximum weight are substantially less than corresponding shock loads experienced by rollers used in rolling mills. It is considered, therefore, that such existing technology could readily be adapted for the purposes of the present invention.

The sections of the conveyor lines 11, 1 2 between the arrival and/or storage area 13, 14 and the turnaround area 1 9 comprise 1 6 metres of roller track having rollers of, for example, 2.75 to 3.25 metres in length, under which secondary support rollers are fitted in at least two equidistant positions in order to reiieve the shock loads which can occur during the transfer of the containers onto the roller table. Interspaced between the rollers is a drag link dog conveyor system (not shown) which permits the rapid and semiautomatic centring of containers on the rollers.To facilitate transfer of containers from the lorries on which they arrive at the deliver/sotrage areas 13, 14 there are provided skid banks fitted with drag link chains which transfer the containers to the conveyor lines 11, 1 2. In this way it is unnecessary for the drivers of the container lorries accurately to place the containers at a given position since the positioning of the container is effected automatically by the container transfer system.

At the end of the initial section of the roller conveyor line 11 is a short section, for example about 4 metres, of tapering single grooved rollers which accurately centre the container and convey it into the main close tolerance roller conveyor 28 on which the container is carried past the high energy scanning station, and which extends between the entry door 21 and the exit door 22. Incremental movement of the container past the linear accelerator or accelerators takes place during scanning and once scanning has been completed the container is transferred through the exit door 22 and onto a further 4 metre section of roller table 28 from where the container is transferred to a further 1 6 metre long section roller conveyor 29 which transports the containers past a recheck area 30 on one side and an intermediate hold area 31 on the other.A short junction roller table 32 transfers containers from the intermediate roller conveyor 29 to a further 1 6 metre long output conveyor 33 which conveys the containers to the despatch areas 17, 18.

At the end of this last run of 1 6 metres of despatch roller tables a further drag chain/dog link conveyor (not illustrated is provided to draw the containers laterally onto a slightwardly downward sloping skid bank on either side of the roller table. Again, the skid banks are not illustrated in Fig. 1; they have the capacity of carrying six 40 ft long containers thereby ensuring adequate storage for the containers which have been inspected and cleared, allowing a degree of latitude in the final transfer of the inspected and released containers onto their road transport trailers so that removal of the containers does not have to keep pace exactly with the examination.

The scanning system itself will be discussed in further detail below, but first the procedure for dealing with containers which are found, upon examination, to have contents at variance with the description, and which must therefore be subjected to more detailed examination. First, the possibility of a faulty or anomalous scan has to be eliminated. This is effected by reversing the conveyor line on which the suspect container is carried, and returning it to the section of conveyor adjacent the delivery area from where it is transferred laterally onto the turn-around area 1 9 and conveyed onto the other line when this has completed examination of any containers already on it. The container is then passed through the examination station of the other line and the results of the scan compared with a record of the original scan.If the second scan does not clear the container it is stopped at the intermediate roller conveyor 29 and displaced laterally into the recheck area 30 where further and more detailed checks on the container contents can be effected by means of aromatic examination, and visual examination subsequent on opening the container are undertaken. Again, the recheck area 30 containers skid banks into which the container is laterally displaced by a drag chain/dog link conveyor system from the roller table 29.

In an alternative arrangement three sets of scans are undertaken for comparison before a container is passed to the recheck area 30.

This is effected by first transferring a container from the intermediate roller table 29 into the intermediate hold area 31 by means of lateral drag chain/dog link conveyors from where the container is transferred to the other line when this is suitably cleared. The line is reversed to pass the container backwardly through the said other line to the input area and it is then transferred across, via the turnaround area 19, where it is turned around as before, to its original line passing through the inspection station associated with this line in the opposite orientation from its initial pass.

This triple scan system avoids any possibility of anomalous operation of the linear accelerators or electromagnetic detectors giving rise to spurious indications.

It is to be noted that the rollers and chain link systems for the arrangements described hereinabove would require to be of special hard wearing steels in order to ensure resistance to abrasion, and that reversing roller drives would be required on the majority of the roller tables and conveyor systems. The conveyors located within the perimeter wall 20, and which may be subjected to significant amounts of radiation must be lubricated with lithium and sodium free greases in order to prevent degradation due to radiation. The spacing between the rollers must be selected so that adequate support for short containers is provided, especially if these are heavily laden, and it is considered that a minimum of 6 rollers should support a single container at any one time.The drives for the roller tables are preferably electric motors which, in practice require to be of a class H or class F type in order to meet the requirements which will be placed on them in operation.

Finally, the section of the roller conveyor housed within the perimeter wall 20, and which transfers the containers past the scanning station must be capable of close tolerance speed control in both directions in order to ensure that accurate successive scans of the container and contents can be made since, as mentioned above, the linear accelerator and detection system are movable only over a very limited range for fine adjustment.

Turning now to Fig. 2 there can be seen a container 34 mounted on the scan station roller table 38. Housed in the accelerator housing 24 is a linear accelerator 35. Since an X-ray source can be considered as a point source it is necessary for the accelerator 35 to include a collimator schematically indicated by the box 36 and to ensure evenness of energy distribution across the width of the beam a flattening filter 37 is also provided. The scanning radiation is transmitted across the scan station roller table through the space which in operation is occupied by the container 34 and is received by a detector system 39. This includes a fluoroscopic screen 40 which produces a visual image from the received radiation.A prism 41 transmits light from the fluoroscopic screen 40 to a camera system 42 which is located to one side of the beam and well out of the penumbra of the transmitted radiation beam. This is necessary to avoid interference between the high energy electromagnetic radiation transmitted by the linear accelerator and the lower energy electromagnetic radiation constituting the light emitted by the fluoroscopic screen and to which the camera system 42 is sensitive.

The output from the camera 42, in the form of electrical signals, is transmitted to a pulse signal transfer coding unit 43 from which the signals are transmitted away from the dangerously high energy level area within the detector housing 26 to a suitable operator consol and supervision chamber 44 remote from the detector housing which is protected by high density concrete shielding walls 45.

The camera system 42 is one including an electronic tube similar to a television camera system but using a "novecon" or similar type of tube capable of low level light detection and high definition. Such cameras cannot be placed directly into a high energy X-ray beam, nor in an area too near to the penumbra of the beam as mentioned above in order to avoid electromagnetic interaction and interference from distorting or destroying the images produced by the camera.

As illustrated in Fig. 1 each inspection line has housings for two accelerators and two detector systems. These can be provided as secondary back up systems for use in the event of operational failure of the primary system, or can be used to increase the rate of through put of containers. Additionally, a third accelerator (not shown) could be mounted above the roller conveyor 38 with detectors mounted beneath this conveyor to provide a vertical scan to supplement the horizontal scan or scans provided by the accelerators mounted in the housings 23 and 24.

It will be appreciated that for medical investigation and research work for which high energy accelerators have previously been used, as in the radiographic examination of metal welds, the quality of resolution has had to be extremely high in order to produce photographs including fine detail. It is not anticipated that this standard of quality will be necessary for container inspection since the inspection is performed, in fact, merely as supervising operation to check that the contents of the container agree with the stated contents in the bill of lading.

The system also incorporates safety interlocks on the X-ray source in the accelerator rooms to ensure that the scanning X-ray beam is only in operation when the acclerator is aligned along the centre line, and only pointing from the accelerator housing 24 towards the detector housing 26 with its high density concrete shielding 45. Additional safety precautions to ensure that all personnel are outside the high energy area defined by the perimeter wall 20 and the entrance and exit doors 21, 22 are also required. These safety precautions are reinforced by the fact that the control consols of the system are located closely adjacent the entrance and exit doors so that supervising personnel can maintain a constant surveillance over the movements of personnel to ensure that any repair or maintenance staff have vacated the premises before the high energy electromagnetic radiation is generated in operation of the device.

Claims (11)

1. A radiographic examination system in which items to be examined are positioned between a radiation source and radiation detection means comprising primary radiation detectors and display means, the said radiation detection means being operable directly or indirectly to produce optical images from the detected radiation, in which means are provided for transmitting information signals from the said primary detectors to the said display means at a location remote therefrom, the said display means including a screen on which the information is displayed as optical images for signal inspection, and from which the information can be recorded either photographically or electronically.

2. A radiographic examination system as claimed in claim 1, in which the radiation source is a linear accelerator generating x-rays and the primary detectors include a fiuoroscopic screen which produces optical signals representing a visual image of the incident radiation.

3. A radiographic examination system as claimed in claim 2 in which the optical signals generated by the fluoroscopic screen are detected by a camera incorporating an electronic picture tube operable to convert the incident optical signals into electrical signals.

4. A radiographic examination system as claimed in claim 1 or claim 2, in which the radiation detection means include an array of photodiodes.

5. A radiographic examination system as claimed in any of claims 1 to 3, in which a pulse code modulation of the signals is used to transmit the information from the primary detectors to a remote viewing location where suitable receivers of the display means convert the coded electrical signals into an optical display on a screen.

6. A radiographic examination system as claimed in claim 5, in which there are further provided image intensifiers acting on the signals supplied to the display means.

7. A radiographic examination system as claimed in claim 5 or claim 6, in which the coded electrical signals are also recorded electromagnetically for storage and/or subsequent playback to generate optical images for comparison with images produced during a subsequent scan of the same or a similar item under investigation.

8. A radiographic examination system as claimed in any preceding claim adapted for examining the contents of international container units, in which there are provided heavy duty transport conveyors for accurately positioning the container units for investigation between the x-ray source and the detection means.

9. A radiographic examination system as claimed in any preceding claim in which the detectors and x-ray source are together movable over a limited range for fine positioning with respect to the subject under investigation.

1 0. A radiographic examination system as claimed in claim 8, in which the said conveyors include roller conveyors for transporting items under investigation past the x-ray source.

11. A radiographic examination system as claimed in claim 8 or claim 10, in which there are further provided means for displacing containers laterally of the length of a conveyor to or from a container-carrier lorry drawn up alongside the conveyor.

1 2. A radiographic examination system as claimed in any of the claims 8, 10 or 11, in which there are provided at least one chain link conveyor in association with a roller table for effecting transport of containers or other articles under investigation past the radiation source.

1 3. A radiographic examination system as claimed in claim 12, in which the, or each, roller table is a self-aligning roller table.

1 4. A radiographic examination system as claimed in any preceding claim formed as an installation with a fixed housing for the radiation source incorporating a radiation shield extending partially around the source.

1 5. A radiographic examination system substantially as hereinbefore described with reference to the accompanying drawings.