GB2278765A

GB2278765A - Imaging arrangements

Info

Publication number: GB2278765A
Application number: GB9311415A
Authority: GB
Inventors: Brian Philip Allen
Original assignee: EEV Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1993-06-03
Filing date: 1993-06-03
Publication date: 1994-12-07
Also published as: GB9311415D0

Abstract

In an imaging arrangement, such as a radiological system, an X-ray source is moved relative to an object to be irradiated simultaneously with a sensor array. The sensor array comprises a plurality of sensors (4, 6) which are arranged such that adjacent sensors overlap in the scan direction. This enables image information to be acquired across the entire width of the sensor array. The sensors (4) may be arranged in two or more parallel lines (Fig 2) normal to the scan direction with sensors in one line overlapping those in the other. In (Fig. 3) a single line of sensors (6) is used, the sensors having a parallelogram configuration such that one sensor overlaps adjacent sensors in the direction of scan. <IMAGE>

Description

IMAGING ARRANGEMENTS This invention relates to imaging arrangements and more particularly, but not exclusively, to radiology systems primarily for medical purposes.

Radiology is an important discipline within the medical screening and analysis fields and is usually carried out with an X-ray generator and a detector system which records a transmitted image through a patient to form an X-ray shadowgraph. The detector is conventionally a film which may also include a laminated X-ray scintillator screen. However, such films require chemical processing subsequent to the image recording, prohibiting immediate observation. An additional disadvantage is that electronic image processing and enhancement may only be carried out after converting the image captured on film into an electronic signal.

Solid state detectors are available such as CCDs, silicon photodiodes and other semiconductor devices which could be used in radiology systems as they can be made both X-ray sensitive and provide a representative electronic signal. However, such detectors are limited in size because of practical constraints and cost limitations.

Hence they have not yet found acceptance in fields such as mammography where large areas must be imaged.

The present invention seeks to provide a solid state imaging system which is suitable for X-ray imaging. The invention is particularly suitable for use with radiology systems used for medical purposes, especially mammography. It is envisaged that the invention may also be applicable to arrangements used for other medical applications and in other fields, for example, for inspection purposes in industrial manufacturing plants.

According to the invention there is provided an imaging arrangement for scanning an object comprising: a source of radiation, an array of sensors, each sensor having a plurality of radiation sensitive detector elements, and means for scanning the sensor array relative to the object, the sensor array being configured such that sensors overlap in the scan direction.

As the sensors overlap, they may be arranged in a configuration which offers a continuous region of radiation sensitive detectors across the entire width of the imaged area. The invention thus enables a number of relatively small sensors to be used to capture image information over a large image width without loss of information. Costs are therefore acceptable as smaller sensors are readily available.

Furthermore use of the invention may enable a larger area to be fully imaged compared to what would be possible using the largest solid state sensors currently available. The invention therefore permits image sizes to be detected which are comparable to those acquired using conventional film techniques whilst allowing the signal processing available with solid state devices to be utilized and permitting immediate viewing of the region under inspection.

In a scanning system, the sensor array is moved relative to the object being investigated. The object or the sensor array or both may be moved to obtain the required scanning effect, depending on what is convenient for a particular application.

Where the radiation used is potentially harmful in large doses, such as at X-ray energies, then it is desirable to move the source relative to the object in unison with the sensor array to ensure that only radiation useful to the image acquisition is used to irradiate the object under examination.This technique is already used in particular in mammography and panoramic dental X-ray examinations. The source and sensor array are both scanned simultaneously with the object between them.

In one advantageous embodiment of the invention, the sensor array comprises a plurality of lines of sensors, the lines being normal to the scan direction, and the sensors of one line being offset relative to those of another line in the scan direction.

Two or more lines of sensors may be used. The "building brick" or "mosaic" pattern of this sensor configuration ensures that when the sensor lines are scanned relative to the object, then any dead space between sensors in one line is covered by the active areas of sensors in another line. The signals from each line of sensors are added electronically whilst preserving the spatial relationship of image information across the image width.

In another advantageous embodiment of the invention, the sensor array comprises a line of sensors in which edges of each sensor are oblique to the scan direction and directly adjacent sensors overlap in the scan direction. By "oblique" it is meant that an edge is at a non-parallel and non-normal orientation relative to the scan direction. The sensors may be arranged to have a parallelogram configuration in which two edges of each sensor are normal to the scan direction and the other two edges oblique to it. The oblique edges are advantageously arranged to be at 450 to the scan direction. The sensors may have parallel oblique edges or the oblique edges may be in a non-parallel configuration. Only one line of sensors is necessary to implement this geometry, although more than one may be employed. The configuration and the above described "mosaic" geometry may be combined in a particular imaging arrangement.

Preferably, the detector elements of each sensor are arranged in columns parallel to the scan direction and rows normal to it. Such an arrangement facilitates signal processing when information from overlapping regions of the sensors is transferred from one sensor to another as the scan progresses or is combined. Other element configurations could be used but more complicated signal processing would then be required.

Preferably, the columns of one sensor are aligned with those of an overlapping sensor to provide optimum resolution.

The radiation is advantageously X-ray energy. However, the invention may be advantageously employed in systems which image radiation in other parts of the electromagnetic spectrum.

Advantageously, the sensors are COD devices or photodiode devices. Other semiconductor devices may be suitable.

Preferably the sensors lie in substantially the same plane, which may be flat or curved. However, they could be arranged such that one lies partly behind another in the radiation path, but this may lead to difficulties in processing and interpreting imaging information and also to unused imaging capability.

In one arrangement in accordance with the invention, means are included for performing time delay and integrate signal acquisition and processing (TDI). In this arrangement, the image information acquired by the sensor array is moved electrically from one row of each sensor to the next, such that the image is transferred at the same speed as the mechanical scan but in the opposite direction. Thus, the electrical representation of the image within the sensor array is increased as the scan progresses.

In another arrangement, means are included for performing stepwise frame signal acquisition and processing. This technique is similar to TDI processing except the motion of either or both the mechanical and electrical scans is not linear but may be stepped.

Some ways in which the invention may be performed are now described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of an arrangement in accordance with the invention; Figure 2 schematically shows an arrangement of sensors used in the arrangement of Figure 1; and Figure 3 illustrates an alternative arrangements of sensors for use in the arrangement of Figure 1.

With reference to Figure 1, an X-ray imaging arrangement used for examination purposes includes an X-ray source 1 and a solid state sensor array 2 of COD detecting elements. The subject to be scanned is placed between them in the plane indicated at 3. The X-rays impinge on the sensor array 2 after passing through the subject to generate a charge distribution at the sensor array 2 which is processed to give an image for analysis by a user of the equipment. The shape of the X-ray beam is collimated to give a rectangular transverse section, the length of the rectangle defining the width of the image field and the width of the rectangle being arranged to cover the width of the sensor array. The source 1 and sensor array 2 are moved relative to the subject to enable a relatively large area of the subject to be examined.

The relative movement between the subject and the source 1 and sensor array 2 is achieved by moving the source 1 and sensor array 2 simultaneously in the direction shown by the arrow, which is the scan direction.

The sensor array 2 is shown in greater detail in Figure 2 which is a plan view, radiation being incident on the array from a direction normal to the plane of the paper.

The sensor array 2 comprises a plurality of sensors 4, each of which includes an array of rectangular detector elements 5 arranged in rows and columns. Typically, each sensor 4 has detector elements 5 arranged in three rows and ten columns, the columns being arranged parallel to the scan direction as indicated by the arrow. The sensors are arranged in two lines in this embodiment of the invention but more than two lines could be used. The sensors in one line A are offset relative to those in the other line B in the scan direction, the columns of overlapping sensors on lines A and B being aligned.

The arrangement of Figure 1 may be operated in a time delay and integrate (TDI) mode or a stepwise frame mode.

In the TDI mode, the X-ray source 1 and sensor array 2 are both scanned simultaneously with the subject between them, the scan direction being perpendicular to the orientation of the rows in the sensor array. The image information contained within the detector elements 5 of the sensors 4 is moved electrically from one row to the next in each sensor at the same speed as the mechanical scan but the opposite direction. Thus, the electrical representation of the image within the sensors 4 is increased as the scan progresses. The image information is transferred from the last row of detector elements of each sensor 4 in the first line A to the first row of detector elements 5 in the sensors 4 in the second line B where there is an overlap. Thus, it is possible to obtain image information across the entire width of the sensor array because the overlapping sensors enable what would otherwise be dead space to be made radiation sensitive.

The signal in the first line of sensors is added to the signal from the second line of sensors when the signal is shifted electronically from one sensor to the next at the same speed as the sensor array is mechanically scanned across the image. The resultant image from a column therefore has an increased signal to noise ratio due to the composition of information from a multiplicity of rows. However, where one line of sensors has no sensitive area, because of the gap between the sensors, then the signal to noise ratio is reduced accordingly and limited by the actual number of sensors covering that area.

An alternative sensor array in accordance with the invention is illustrated in Figure 3 which is a plan view. Only one line of sensors is required, although more than one may be used if desired. Again, the arrow indicates the scan direction. Each sensor 6 of the array is a parallelogram shape having edges which are normal to the scan direction and edges which are oblique to the scan direction, in this case at 45".

Each sensor 6 comprises a plurality of detector elements 7 arranged in rows and columns, the rows being normal to the scan direction and the columns being parallel to it. The sensors 6 are arranged sufficiently close to each other that there is an overlap between adjacent sensors in a direction transverse to the scan direction. This ensures that the image information may be captured over the whole width of the sensor array as the scan progresses. Although there are gaps between adjacent sensors these are not parallel to the scan direction but as the columns are aligned parallel with the scan direction image information is obtained over the width of the array. The columns of adjacent sensors 6 are arranged to be aligned in the overlap region.

In a stepwise frame mode of operation, the motion of either or both the mechanical or electrical scan is not linear but may be stepped. Such a technique may also be used with an arrangement in accordance with the invention.

Claims

1. An imaging arrangement for scanning an object comprising: a source of radiation, an array of sensors, each sensor having a plurality of radiation sensitive detector elements, and means for scanning the sensor array relative to the object, the sensor array being configured such that sensors overlap in the scan direction.

2. An arrangement as claimed in claim 1 wherein the sensor array comprises a plurality of lines of sensors, the lines being substantially normal to the scan direction, and the sensors of one line being offset relative to those of another line in the scan direction.

3. An arrangement as claimed in claim 1 or 2 wherein the sensor array comprises a line of sensors in which edges of each sensor are oblique to the scan direction and directly adjacent sensors overlap in the scan direction.

4. An arrangement as claimed in claim 3 wherein the line is substantially normal to the scan direction.

5. An arrangement as claimed in claim 1, 2, 3 or 4 wherein the detector elements of each sensor are arranged in columns parallel to the scan direction and rows normal to it.

6. An arrangement as claimed in claim 5 wherein columns of one sensor are aligned with those of an overlapping sensor.

7. An arrangement as claimed in claim 5 or 6 and including means for transferring image information from a row of one sensor to a row of another overlapping sensor for those columns included in the overlapping parts of those sensors.

8. An arrangement as claimed in any preceding claim wherein the sensors are arranged in substantially the same plane.

9. An arrangement as claimed in any preceding claim wherein the radiation is Xray energy.

10. An arrangement as claimed in any preceding claim wherein the sensors are COD devices.

11. An arrangement as claimed in any of claims 1 to 9 wherein the sensors are photodiode devices.

12. An arrangement as claimed in any preceding claim and including means for scanning the source in synchronism with the sensor array.

13. An arrangement as claimed in any preceding claim and including means for performing time delay and integrate signal acquisition and processing on signals representative of radiation detected by the detector elements.

14. An arrangement as claimed in any of claims 1 to 12 and including means for performing stepwise frame signal acquisition and processing on signals representative of radiation detected by the detector elements.

15. An arrangement as claimed in any preceding claim and adapted for medical imaging.

16. An imaging arrangement substantially as illustrated and described with reference to the accompanying drawings.