WO1997014359A1

WO1997014359A1 - Method and apparatus to produce three-dimensional x-ray images

Info

Publication number: WO1997014359A1
Application number: PCT/GB1996/002505
Authority: WO
Inventors: Simon Richard Dodds
Original assignee: INTEGRATED DYNAMICS Ltd
Current assignee: INTEGRATED DYNAMICS Ltd
Priority date: 1995-10-16
Filing date: 1996-10-14
Publication date: 1997-04-24
Anticipated expiration: 1998-04-16
Also published as: EP0858290A1; AU7309496A

Abstract

The present invention provides a method for generating a perceived three-dimensional image of the internal structure of a subject from a series of two-dimensional images, which method comprises directing a beam of X-rays or other penetrating radiation at the subject and capturing the image of the resultant radiation passing through, absorbed, emitted, reflected, scattered and/or diffracted by the internal structure of the subject and viewing a plurality of such images, characterised in that: a) the images are generated by directing penetrating radiation at the subject from a number of points displaced angularly from one another along a path relative to the subject; b) the images are captured for some or all of the said points; c) the images are stored as a sequence of discrete images in a machine readable storage medium having sufficient capacity to store more than two of the images concurrently; d) the images from the storage medium are presented, without significant reconstruction of the individual images, as a series of individual images or pairs of images to an observer, preferably in pairs as if they were stereoscopic pairs of images; and e) the observer selects the speed of presentation of the images and/or the relative direction within the stored sequence of the images at which the images are presented to the observer so as to optimise the three-dimensional depth perceived by the observer. The invention also provides apparatus for use in the method of the invention.

Description

METHOD AND APPARATUS TO PRODUCE THREE DIMENTIONAL X-RAY IMAGES .

The present invention relates to a method and apparatus for use in that method , notably to a method for presenting X ray images and to an apparatus for presenting stored digitised X ray images to an observer .

BACKGROUND TO THE INVENTION :

In making an X ray image , a beam of X rays from a source is directed onto a subj ect and the X rays are absorbed to dif ferent extents by the subj ect . This provides an image of the radiation which pas ses through the subj ect whose intensity varies according to the amount of radiation absorbed or scattered by the internal structure of the subj ect . This image is captured on a photographic plate to give a single image fixed in time , but which offers a high resolution image which can be stored for future use . However , such an image is a purely two dimensional image and lacks any shading or other clues which would give an observer any impression of depth in the image . Thus , an observer can deduce very little about the three dimensional composition of the internal structure of the subj ect .

It has therefore been proposed to take a second image with the X ray source displaced at a known angle from the f irst to provide a pair of images . This pair of images can then be viewed together through a suitable stereoscopic viewer to give the observer a measure of depth perception . However , this requires that two images be taken , which increases the dosage of X rays to which the subj ect is exposed , which may be unacceptable .

In order to reduce the radiation dosage to which the subj ect is exposed , i t has been proposed to subj ect the image to an intensification process, for example by locating the film which captures the image between two photoluminescent screens which illuminate the film when they are excited by being struck by X rays. It has also been proposed to capture the images using an array of phosphors to create a visible image which is then viewed through a photomultiplier by a camera or other image capture device. In this way a low radiation level can be used to produce an image of low intensity and the effect of the photomultiplier is to enhance the image for capture. Whilst such a system reduces the radiation dosage to which the subject is exposed, it reduces the definition of the image captured.

Furthermore, even with a single stereoscopic pair of images, the depth perception is poor and it has been proposed to increase the number of images taken so as to create a series of stereoscopic pairs of images which can be viewed in sequence so as to increase the viewers comprehension of the internal structure of the subject. However, thε images are presented in the same order as that in which they are taken and at a specific speed of presentation, typically in the sequence and at the rate at which they arε captured. Several forms of such a display system are known and include ones in which the images are captured via an image intensifiεr and displayed on a video display screen as the images are captured. The memory unit in such a system thus typically stores the data for only one or two images at a time. Such a system requires that a number of images be taken to create the sequence of images which arε observed, thus increasing the potential radiation dose administered to the subject and does not envisage the storage of the images for future use and reference.

In a modification of such a system, the images are digitised and held in a digital memory for subsequent replay as a series of images, and the image can be processed to provide other forms of image, for example subtractive images. It has been proposed in US Patent No 5 090 038 to vary the angular separation of the im.ages presented to an observer from such a digitised store of the images for the left and right eyes. It was stated that the perception of depth for the internal structure of the subject was enhanced by varying the angular separation of the two series of images until the optimum separation for the observer was obtained.

However, such techniques all require the taking of stereoscopic pairs of images and cannot be applied to mono- scopic single images. As a result, the dosage received by the subject and cost and complexity of the image capture, storage and display devices is increased.

It has been proposed in what is known as a CAT scanner, to direct a series of pencil beams of high intensity radiation through the subject from a series of locations angularly displaced about the subject. The images from such beams are captured individually and are fed to a computer which creates a two dimensional synthetic image of the whole slice of the subject being scanned. Due to the collimated nature of the beam and the high intensity of the X ray radiation used, the images are of high definition, but are only of a specific path through the subject and require considerable computer processing to combine the data from each beam image to create the image of the slice, which is viewed at 90° to the plane of the slice image created.

Such a system provides sufficient data from which the computer can create an image of the transverse slice through the subject which can be rotated, enlarged or otherwise processed by the computer to give the observer flexibility as to how thε imace is examined. However, a CAT scanner exposes the subj ect to high radiation doses in order to achieve the requisite number of images . Furthermore , a CAT scanner does not give a broad picture of the interior of the subj ect and it is necessary to capture a number of images not only around the subj ect to create the image of a slice , but to capture further images at axially displaced positions along the subj ect to create the data for a series of slices from which a complete image can be created . This further increases the radiation dosage to which the εubj ect is exposed and requires yet more computer processing power to handle the data and create the images for viewing by the observer . A CAT scanner is therefore an expensive and complex piece of equipment which cannot readily be transported from one site to another .

We have now devised a method of capturing and presenting X ray images which reduces the cost and complexity problems of a CAT scanner and does not require the high dosage rates required to produce the series of images from which an improved perception of depth can be obtained , thus enhancing the confidence with which a viewer can identify the nature and relative position of items within the internal structure of the subj ect . Surpris ingly, the method of the invention can be applied to ono- scopic images and does not require the capture of stereoscopic pairs of images as hitherto considered necessary .

SUMMARY 0? THE INVENTION :

Accordingly , thε present invention provides a method for generating a perceived three dimensional image of the internal structure of a subj ect f rom a series of two dimensional images , which method comprises directing a beam of X rays or other penetrating radiation at thε subj ect and capturing the image of the resultant radiation passing through, absorbed , emitted , reflected , scattered and/or diffracted by the internal structure of the subj ect and viewing a plurality of such images , characterised in that : a . the images are generated by directing penetrating radiation at the subj ect from a number of points displaced angularly from one another along a path relative to the subj ect ; b . the images are captured for some or all of the said points ;

- c . the images are stored as a εequence of discrete images in a machine readable storage medium having sufficient capacity to store more than two of the images concurrently ; d . thε images from the storage medium are presented, without significant reconstruction of the individual images , as a series of individual images or pairs of images to an observer, preferably in pairs as if they were stereoscopic pairs of images ,- and e . the observer selects the speed of presentation of the images and/or the relative direction within the stored sequence of the images at which the images are presented to the observer so as to optimise the three dimensional depth perceived by the observεr .

By sεlecting the speed of presentation of the images to the observer, we have found that perception of the relative positions of items within the internal structure of the subj ect presented in two dimensions is surprisingly enhanced and the observer can deduce more than would have been expected from such a series of images than from observation of the individual images . Surprisingly, this enhancement can be achieved even with a series of single , or mono- scopic , images and does not require the presεntation of the images as stereoscopic pairs . Where thε sequence of images from the storage medium is presented first in one order then in the reverse order and/or the direction of presentation iε repeatedly changed , the perception of the relativε position of itεms in the internal structure of the subj ect iε further enhanced . If such speed and/or direction of presentation is applied to pairs of images presented as stereoscopic pairs , the perception is further enhanced . Where thε observer is al so provided with means whereby he can select images out of the strict sequence in which they are held in the storage medium, so aε to vary the perceived angular εeparation between the two imageε- in a pair of imageε presented to the obεerver, the perception of both depth and the relative poεition of the features of the internal structure of the subj ect is enhanced yet further . By varying the speed, direction and relative separation of successive images presented to the observer from within the sequence as stored, the observer can optimise the perception of relative positions and depth to suit his subj ective requirements . Thiε will increase the confidence with which he can identify the relative position of items within the subj ect and hence hiε diagnoεiε of the condition of the εubj ect .

The invention thuε provides a simple and ef fective meanε for enhancing thε three dimensional information which an obεerver can obtain from a series of two dimensional images which does not expose the subj ect to excessive radiation doses and does not require large computing power since the images are presented in substantially the form in which they are stored and are not subj ected to dis -assembly and re - aεεembly as is required with a CAT scanner image . The necessary hardware and sof tware required to operate the invention can readily be connected to an existing X ray machine with little or no modif icat ion cf the machine , thus converting machines which had hitherto baer. cons idered suitable only f or taking individual images or low resolut ion pairs of images into more versatile machines capable of providing the user with more information than had hitherto been considerεd poεεible.

Since the images are stored in a machine readable form, for example in a computer memory or data disc, the observer can alεo freeze the imageε during presentation for more detailed static image inspection. The observer can also enlarge areaε of the image or superimpose images to provide total flexibility in the manner in which the imageε are presented so as to extract maximum information therefrom in a manner beεt εuited to hiε individual requirements.

It is particularly preferred to store the images in digital form, in a frame store which is accesεed by a computer and to provide the computer with meanε for εelecting thε order and εpeed at which the images are to be viewed by the obεεrver. We have found that the imageε can be held at a reεolution of from 256 by 256 pixelε upwards and that a typical pair of imageε will require about 128 kilobyteε of memory for its storage. We prefer to present at least 10, notably at least 20, images or pairs of images to the observer and this will require about 1.2 megabyte of storage on a conventional 3.5 inch high denεity magnetic disc. The invention thuε rεadily lends itself to operation on a PC based syεtem connected to a known CCD array or other image capture device .

Where the imageε are taken at 4° intervalε, then a εerieε of images along a path extending over an arc of rotation of 88° about the subject can be accommodated. By allowing dynamic, interactive display of imageε from thiε seriεs a better percεption of depth can be achieved for this sequence than either a single high resolution 1024 x 1024 image or a stereo-pair of images of about 700 by 700 pixels. The invention thus also provides apparatus for use in the method of the invention, which apparatus comprises : a . meanε for generating and directing a beam of X rays or other penetrating radiation onto a subject from a number of locations around a subj ect ; b . means for capturing a series of the individual images of the intensity of the radiation passing through, absorbed, emitted, reflected, scattered and/or diffracted by the internal structure of the εubj ect for each of at leaεt - some of the said points around the subj ect ; c . machine readable storage means for storing the series of individual imageε in identified locationε within a εequence of captured images ; d . meanε for presenting images from said storage means to an observer either singly or in pairs ,- and e . observer controlled means for selecting the speed of presentation of the imageε and/or the poεition within the said sequence from which the successive images presented to the obεerver are εelected from εaid sequence of images in said storage means .

The invention can be applied to a wide range of types of penetrative radiation which pass through and/or are absorbed, emitted, reflected, scattered and/or diffracted by items of the internal structure of the subj ect . Since the imageε which are captured represent transmission or shadow imageε , there are not normally any of thε normal visual clues , such as εurface folds , textures or thε likε , which an observer can use to assess the shape and structure of a subj ect . However , the invention can also be applied to other forms of image where other cluεs as to relative position of features and of three dimensional shape are available , for example in images from magnetic resonance imaging cr ultrasound imaging . For convenience , the invention will be described hereinafter in terms of the uεe of X rayε to generate shadow images of internal εtructureε within a human patient as the subject caused by abεorption of the X rayε by the individual itemε of thε internal εtructure.

The X ray beam can be generated by a conventional εingle X ray source which is caused to travel around the subject^' on an arcuate path centred on an axiε of the εubject. For example, the X ray generator iε carried upon a C frame which rotateε under the influence of a manual, elεctric, hydraulic or other drive meanε so that the generator follows a substantially circular path about the εubject. Preferably, thε path extends for at least 30 to 120° about the longitudinal axis of the subject and the images are taken at intervals of up to 10° along that path. The optimum angular separation between the points at which images are taken depends, inter alia, upon the εpeed of movement of thε X ray generator and the manner in which the images are to be presented to the observer. In general, the faster the movement of the X ray generator, the greater the angular separation at a given time interval between generation of successive X ray beams. However, if the resultant imageε are presented to an observer as a series of individual images, the image will appear jerky and the enhancement of position perception may be reduced if the angular separation between the points at which the X ray images are taker- exceeds 10°. It is usually preferred to provide images which are at from 2 to 5° separation and to take those at a ratε of 6 to 10 images per second, iε . over an arc of travel of about 30° per εecond. Such angular separations and rates of arcuate travel can be achieved using a conventional C arm X ray devicε using conventional control means. A typical example cf such a frame is shown in Figure 1 of the accompanying drawings . The X ray generator can provide a continuous beam of radiation which is a divergent conical beam of radiation as is typically obtained f rom a conventional X ray source . However, it is preferred to operate the generator intermittently so as to reduce the total radiation dose to which the εubj ect iε exposed and to generate the X ray beam at each location at which an image is to be captured .

The radiation passing through the subj ect is captured by any suitable medium, for example by means of an image intenεifier and plumbicon tube aε uεed with a conventional f luoroεcopic imaging ^' X ray machine . Alternatively, the image can be captured using a radiation senεitivε array of individual sεnsors , each capturing a pixel or a component of a pixel of the image to be stored in the εtorage medium . Thuε , for a 256 by 256 pixel frame store memory, the image capture device will comprise an array of radiation sensitive transistorε or diodeε on a grid pattern of 256 by 256 or more . Such image capture deviceε are commercially known and have been propoεed for use in capturing X ray imageε and may be uεed in their commercially available formε in the preεent invention .

It will usually be desired to minimise the dosage to which the subj ect is exposed , and it haε been proposed to employ a comparatively low level of radiation, ie . a low power X ray εource , and to enhance the image of the radiation paεεing through the subj ect by suitable means . For example , the image can be reduced in s ize to achieve a smaller image having a greater intens ity of image so as to increase the contrast in thε grey shades , typically 256 or more shadeε of grey, obεervεd by the image capture device . Alternatively , the radiation passing through the εubj ect can fall upon a screen of phosphors to create a visible image which is viewed through a photomul ipl ier by a suitable camera to capture the visible image created on thε phosphor screen. Such image capture and intensifier devices can be of conventional design and construction and may be used in the method and apparatus of the invention with little or no modification.

Surprisingly, we have found that, despite the reduction in resolution which is caused by the use of a low intensity radiation source, the three dimensional perception of resultant image using the method and apparatus of the invention is enhanced as compared to conventional static mono-scopic or εtereoεcopic scanning of the images.

The phosphor screen and image intensifier are preferably mounted in asεociation with the image capture dεvicε at the diametrically oppoεed end of the C frame carrying the X ray generation device deεcribed above.

The X ray generation device and the image intensification/ collection device are caused to preceεε about thε subject by any εuitable meanε εo that individual imageε can bε captured at a εerieε of locations about the subject. The precesεion can be continuouε or stepwise and the X ray generation and/or image collection devices operated intermittently so as to capture images at intervals of at least 2° angular separation about the subject. Preferably, the X ray generation device iε located radially with respect to the subject and has itε axiε of rotation substantially co¬ incident with the longitudinal axis of the subject. However, if desired, the X ray generator can be rotated about an axis pasεing through a εpecific point within the εubject which iε radially off εet from the longitudinal axiε of the εubject, or can bε located at one end of the εubjεct and directed axially with respect to the εubjεct and rotated about an axis co-incident with or parallel to the longitudinal axiε of the subj ect .

For convenience , the invention will be deεcribεd in terms of rotating a radially orientated C frame about the longitudinal axiε of the subj ect .

The image collection device can be a εingle array of εenεors which travel with the X ray generator as deεcribed above . However , it iε within the scope of the preεent invention to provide a εtationary arcuate array of senεors upon which the beam of X rayε passing ^' through the subj ect falls at each operation of the X ray generator upon its diametrically opposed arcuate path of travel . It is also within thε εcopε of the present invention to provide a series of X ray generators mounted upon an arc about the subj ect and to operate those generators in series to provide the individual images . However , it is preferred to provide a single X ray generator which moves about the subj ect in opposition to a corresponding moving diametrically opposed image capture/intensif ication device .

The image from the image collection device will typically be in analog form and requires to be εtored for future viewing by the observer . However , it may be desired to observe the images are they are generated to ensure that any abnormality in the images can be corrected , if due to incorrect set up or operation of the apparatus . Alternatively, where the abnormality is due to some feature of interεst within the internal structure of the εubj ect , the set up and operation of the apparatus can be del iberately altered to concentrate on the f eature of interest , for example by altering the longitudinal pos ition of the apparatus with respect to the subj ect and/or al tering the arc swept around the subj ect by the apparatus . Such real time display of the images being generated can be achieved using any appropriate method , for example a video εcreen receiving itε εignalε from the image capture device . However , in εuch a case the images will be displayed in the sequence in which they are captured and the obεerver will not have the control over the sequence and rate of diεplay of the imageε which the apparatuε of the invention can achieve . I t may therefore be desirεd to fεed any real time diεplay of the imageε being generated from the obεerver controlled εelection device described below εo that the obεerver can make use of the features of the invention, whi-lst εtill ef fectively being able to review thε imageε in pεeudo real time .

The image may alεo be pas sed to an analog data εtorage device , f or example a photographic f ilm or electromagnetic recording tape , for interim storage prior to digitisation of the images for storage in the machine readable format . For convenience , the invention will be deεcribed hereinaf ter in termε of a method and apparatuε in which the signals from the image capture device are in an analog format and are fed directly to a digital signal storage device .

Thus , the signals f rom the CCD array or other image capture device are fed to an analog to digital convertor in which the signals representing the shadeε of grey, typically 256 εhadeε of grey , are converted to digital signals for storage , wherε the image capture device does not already digitise the image it has captured , aε iε thε case with a solid εtate camera . Such analog to digital conversion can be carried out uεing convent ional techniques and equipment . If deεired, the imageε may be εubj ected to initial pre- or poεt treatment . For example , the image can be subj ected to f iltering to remove background noise or extranεous signalε outsidε thε f requency range which it is desirεd to monitor . The resultant cleaned image can be subj ected to image processing to enhancε the captured image , for example to complete portions of the image which have been rendered unclear due to the use of low levels of radiation intensity reεulting in loεε of reεolution in the image captured. It may alεo be deεired to incorporate meanε by which one image may be εubtracted from another to present a resultant image which εhowε only the changed εubject matter of the two imageε, for example the presence of dye or opacity in a blood vesεel. Such subtraction is preferably done upon the digitised image and εuch digital subtraction can be achieved uεing conventional software techniqueε.

Such treatmentε can be of conventional nature and can be carried out uεing known techniques and equipment. However, such treatments do not incorporate disaεεembly of the image and reconstruction of the image from modified data as occurs when a synthetic image is computed in a CAT scanner. For convenience, the invention will be described herεinaftεr in terms of the direct conversion, where necessary, of the signals from the image capture/intensification device and their storage in an electromagnetic εtorage device.

The storage device can be a memory chip or other device for storing digital data in a machine readable form. However, as indicated above, the memory requirement for the εtorage of a εerieε of 20 images will be about 1.2 megabyte and it iε thus poεsible to use a conventional magnetic disc as the data εtorage medium for the preεent invention. Thuε, it iε preferred to capture the image using a conventional frame grabber device and to store the data from each frame in a frame store device to ensure that the data for each individual image is retained aε a unit and can be given a unique address for its location in the sεriεs of i agεε generated by the X ray generator/image collection deviceε . Such a frame grabber and frame store devices can bε cf conventional design and operation. The imageε from the machine readable εtorage medium can be called up by the uεer as a series of individual images. In thiε case the depth perception is achievεd by thε user recognising the clueε to the relative positions of items within the succeεεion of two dimensional images presented to him by the changeε between successive images due to the apparent rotation of the subject as the series of images iε preεented. It iε preferred that the imageε are preεented at such a rate that there is a visually εmooth tranεition from one orientation of the εubject to the next. As indicated above, thiε will not be achieved at angular εeparations between the points at which the images are captured of more than 10°. Typically, it is preferred to present the imageε at εuch a rate and at such angular separation that the subject appearε to rotate through 30° per second and the rotation is through about 60 to 90° over 20 to 30 images which are taken at angular separations of from 2 to 3°. As indicated above, it iε alεo preferred to provide the obεerver with meanε for reversing the direction of the flow of images so that he can back-track through part or all of the sequence of images being presented. This ability to travel to and fro within the sequence of images and to vary the εpεed at which εuch travel occurs enhances the perception of the relativε positionε of items within the εtructure of the εubject. Surprisingly, this enhancεment of perception is achieved even with εingle images and it is not necessary to use stereo pairs of images.

The observεr controlled means for selecting the speed and direction of diεplay of the εequence cf imageε will incorporate meanε for identifying the addressεs in the memory store from which the individual images are to be retrieved and will incorporate εuitable software or other control means by which the images are retrieved and presented at the desired rate and in the desired order. Such means is of conventional form and thε software for controlling its operation can be written using conventional programming techniques .

We have found that such dynamic perception of the rela_tive positions of items within thε structure of the subject can be further enhanced if the images are viewed as stereoscopic pairs of images . In this case , the images are stored as two serieε of imageε , one for the lef t eye and one for the righ_t eye. In practice the- two series may be held in a single memory store and are identified by their addresses within that single store . The pairs of images are viewed through a εuitable stereoεcopic viewer to give a threε dimenεional perception of the subj ect . Typically, the angular separation between each image in a stereoscopic pair will be up to 8° . The angular separation between successive images in the εequence aε εtored and between individual imageε in a pair of imageε can be fixed, for example can correspond to the angular εeparation of the succesεive εtereo images as captured and stored. However, we have found that it is desirable to be able to vary the angular separation between the images , either within the pair as presented or between εucceεsive pairε of images . The ability to vary the angular εeparation of the images enhances the three dimenεional perception of the images and gives the observer greater confidence that he has correctly identifiεd the three dimensional structure of the subj ect .

The imageε may be preεented as pairs , one to εach eye , by any suitable optical meanε . For example , one image may be tinted red, the other green and the obεerver wears appropriately coloured glasses . Alternatively, by imposing a delay on the presεntation of the image to one eye as opposed to the other , a perception of depth may alεo be created . However , it is preferred to present the imageε as black and white imageε εimul taneouεly through εeparate pathε to each eye of the observer , f or example using a εuitable mirror path to achieve the desired lateral separation of the imageε and to create the illuεion that they are generated f rom a common εource . Typically , the eyeε of an obεerver require the pairε of images in a true εtereo- εcopic pair to be generated f rom pos itions separated by f rom less than 8° , typically 2 to 6° angular diεplacement .

Where εtereo- εcopic pairs of imageε are to be viewed , it will uεually be necessary to provide εome sort of viewing device by which the images can be presented separately to the observer' ε eyeε . Such a device may take the form of a mirror arrangement by which the uεer can observe separate images on a video screen or screens ,- or electronically εhutterεd εpectacleε f or delivering separate images to the lef t and right eyes of the observer . Typically, the optical pathε to each eye will be εcreened from one another to minimise cross - talk between the paths . Such stereo-εcopic viewing devices are readily available or can be made using conventional optical techniqueε and equipment .

In the apparatuε and method of the invention, thε obεerver can εelect which images are to be viewed together f rom the εequence in the series aε stored by selecting the required locationε in the addreεses in the f rame store so that he can f ine tune the angular separation in the pairs observed by him . For example , one observer may find that the depth perception is enhanced when he views image 1 with image 4 in thε series as stored rather than image 1 with its companion image 2 . Another obεerver may f ind that viewing imageε 1 aε a stereo pair combined with the scrolling of the series of images gives optimal depth perception .

The user can select the order or pairing cf the imageε presεnted to him by any suitable means . For example , by suitable programming , the keyboard of the PC can be usεd to prεεεnt εimultaneouε images ( ie . image 1 with image 1 ) at pressing key 0 , succeeding images ( ie . image 1 with image 2 ) on keying key 1 , imageε εeparated by one position in the sequencε as stored ( ie . image 1 with image 3 ) by keying key 2 and so on . Alternatively, a j oyεtick, touch εenεitive ecreen , mouse or voice activated syεtem can be used ^' to provide the physical interface upon which the observer acts to -control the selection of the order and pairing of the imageε .

Such programming of the selection of the images and their order of presentation can be achieved using any suitable method by those skilled in the programming art . The programming can also be used to dictate other features in the presentation of the images singly or in pairs to the observer . For example , the duration of each display and the time interval before the next display can also be controlled by the observer so that he can scroll rapidly or εlowly through the sεlected εequence of images εo as to achieve a perception of rotation of the subj ect being observed; the scrolling can be stopped to review a particular image ,- and means can be provided for identifying areas of the image of principal interest and for present ing enlarged portionε of the images as εtored to concentrate on those areas . Again such operations can be achieved by conventional programming techniques .

As indicated above , the apparatus of the invention pref erably incorporates a conventional computer or microprocessor device operat ing under the control of specific sof tware to act as the f rame grabber/store and to read the data from the storage medium for manipulation by the obεerver prior to diεplay upon a video εcreen or other diεplay device . If neceεεary, the computer or microproceεεor can bε provided with the neceεεary additional proceεsor board to enable it to act as the frame grabber/εtore . The invention can thuε readily be carried out uεing exiεting X ray generating and image capture devicεε and a conventional computer or microproceεsor and frame grabber/store equipment .

The invention thuε alεo provideε a computer adapted to control the capture and presentation of images from X ray inεpection of a subj ect , characterised in that the computer is programmed to select the speed and/or direction of presentation, and optionally also the order and separation of images to be presented, to an obεerver from a sequence of images held in a computer accessible memory unit .

The invention also provides a program for controlling operation of a computer, which program includes instructions for operating the computer to select images at a εelected rate and order, and optionally also out of sequence , from a εequencε of imageε held in a computer accessible memory unit . Preferably, the program iε carried on a portable storage means . However, the program may be held in a master memory unit which is accessible to many users of the program.

The additional apparatus , for example the frame grabber/store , the data εtore , the microprocessor required to operate thoεe and the stereo-εcopic scanning device together with the asεociated software required to operate the apparatus can readily be incorporated into existing designε of X ray generator/image capture deviceε during manufacture or can be readily applied to existing X ray generator/image capture deviceε with liεtie or no modif ication of the exiεting device . The invention can be applied to the generation of imageε from a wide range of εubjectε for a wide range of purpoεeε . Typically, the method and apparatuε of the invention will be uεed in the analyεiε of X ray images of human patients, for example to locate tumours, heart disorders, bone and other fractures, blood clots and vascular or arterial blockages or malfunctions. In such cases it will usually be desired to minimiεe the radiation dose to which the patient iε expo^'εed and it will uεually be necessary to uεe an image intenεifier to enable a εatiεfactory image to be captured. Whilεt εuch an image iε of lower resolution than when a high intenεity radiation source is used, the ability of the observer to adjust the εpεed of presentation and the order in which images are preεented enables the obεerver to identify itemε and their relative poεitions within the subject with greater confidence than hitherto. X Rayε are typically used in medical applications. However, the invention may be applied to other applications of X rays to scan human beings, for example in airport security scanners.

The invention can also be applied to inanimate objects where the level of dosage exposure is not material. For example, the invention can be applied to X ray analysis of internal flaws or cracks in metal castings or welds in tubes. In such cases, there is no need to reduce the radiation intensity of the X ray beam and no need to use an image intensifier to enable a satisfactory image to be captured.

DESCRIPTION OF THE DRAWINGS :

The method and apparatus of thε invention will now be illustrated by way of illustration only with respect to the accompanying drawings in which Figure 1 iε a diagrammatic representation of an X ray generation/image collection device; and Figure 2 iε a block diagram representation of the f ra ε storε and image selection equipment f or use in selecting the image to be viewed by the observer .

DESCRIPTION OF THE PREFERRED EMBODIMENT :

The X ray generation and image collection device for scanning a εubj ect 1 comprises a conventional X ray gun 2 mounted at one end of a C shaped arm 4 which is mounted generally radially with respect to the longitudinal axiε of the εubj ect 1 . The C shaped arm extends over an arc of about 180° and the other , diametrically opposed , end of the arm carries a phosphor screen , a photomultiplier and CCD array camera collectively shown as 3 and referred to hereaf ter as the camera , for collecting the X ray radiation which passes through the subj ect and for presenting an image in machine readable form . The arm 4 iε rotated about the longitudinal axiε of the subj ect by a motor 5 . In this way , the relative position of the X ray source 2 and the camera 3 with reεpect to the subj ect is kept substantially constant .

The output from the camera will usually be an analog electrical signal representing the intenεity of the X ray image obεervεd by the CCD array in 256 εhadεs of grey and will typically have a resolution of 256 by 256 pixel s per square inch . However , other forms of image presentation may be used, for example a full colour picture at higher resolution if desired . The analog εignal requirεε to be converted to a digital e ignal , where thiε has not already been done within the camera circuitry, for storage in a εuitable storage meanε 6 . Such conversion may bε carried out at any suitable point in the proceε sing of thε image and using conventional techniques and equipment . Typically, the analog tc digital convers ion iε carried out within the camera circuitry to provide a digitised output f rom the camera . However, the analog signal may be stored, for example on an electromagnetic tape , to provide an analog record of the imageε for display uεing a conventional video recorder and televiεion, or a video screen for real time display . However, it is preferred to feed the digital signals to a frame store or other electronic memory store .

The frame store typically comprises a serieε of individual memory cell addresses each large enough to accommodate the data for a single image from device 3 . This frame store and its individual cell addresses is schematically represented as item 10 in Figure 2 and haε εufficient capacity to εtore from 10 to 40 imageε concurrently . The identity and speed, direction and εequence of recall of data from the individual cell addrεεεes iε selected by an observer via input device 12 , for example the keyboard, touch screen panel or mouse of a computer (not shown) . This controls the operation of a suitable selection and addressing device 11 , for example the computer itself , which transfers the data from the selected cell addresε to a visual display device 13 . The visual display device iε a mono-scopic device in which individual imageε are diεplayed at the deεired rate and in the deεired εequence according to the selection made at the input device 12 . However, in an alternative embodiment , the imageε may be presented as pairs of images and Figure 2 shows a εtereo- εcopic viεual diεplay device in which two images from the εtore 10 are diεplayed simultaneously to the observer .

In operation, the C arm 4 is caused to rotate about the subj ect 1 and the X ray gun 2 is operated at preset time intervals on the path of the arm to provide images which are captured by the camera 3 at angular intervals about the subj ect . Typically , these intervals are from 3 to 6° , but may be more or less frequent . The imageε captured at the camera are fed aε digital imageε to the frame store 10 . Whilst real time images may be taken directly from the output of the camera, such imageε will be presented in the order in which they are captured and at the rate at which they are captured. It may therefore be preferred to take the images from the data in the frame store 10 and to uεe the input device 12 to control the image preεεnted. Whilst this will allow the images to be presented in real time in the ordεr in which they are captured, it will also allow ^'the observer to modify the presentation if this is necesεary and to back track over the -images captured to allow imageε to be retaken if a problem haV been encountered or a specific area of interest within the subject identified and further images are rεquired. This may enable the observer to take extra images whilεt the εubject is still in position within the C arm and avoid the need to recall the εubject at a later date.

The uεer can εelect the identity of the cell addreεεeε required to be obεerved and the optimum rate and direction of preεentation required to maximiεe hiε perception of the three dimenεional internal structure of the subject by virtue of thε dynamic sequence of the changing imageε. The user may also εelect to view the imageε aε εtereo pairε and to εεlect the εequence and the pairing of the cell addreεεeε of the pairε of imageε presented to him εo as further to enhance the depth perception created by not only the dynamic εequence of the changing imageε by alεo by the prεεentation of the imageε aε εtereo-εcopic pairε.

Typically, the imageε will be preεentεd at thε rate of from 5 to 15 images per second so aε to give the impression of smooth rotational movement of the subject. However, the observer can increase cr slow down thε rate of presentation and can increase or decrease the separation of the cell addrεsεes within the seσuence in the frame storε so as to optimise the perception of depth in the observed images_. Typically, the separation of the cell addresεes wi_ll correspond to angular separationε of the imageε of from pluε or minus 2 to 3°.

Claims

CLAIMS :

1 . A method for generating a perceived three dimenεional image of the internal structure of a subj ect from a εerieε of two dimenεional imageε , which method compriseε directing a beam of X rays or other penetrating radiation at the subj ect and capturing the image of the resultant radiation paεεing through, absorbed , emitted, reflected, scattered and/or diffracted by the internal structure of the subj ect and viewing a plurality of such images , characterised in that : a . the images are generated by directing penetrating radiation at the subj ect from a number of points displaced angularly from one another relative to the subj ect along a path relative to thε subj ect ; b . the imageε are captured for εome or all of the εaid points ; c . the images are stored as a εequεnce of diεcrete imageε in a machine readable εtorage medium having sufficient capacity to εtore more than two of the images concurrently; d . the images from the εtorage medium are preεented, without εignificant reconεtruction of the individual images , aε a series of individual images or pairs of images to an observer ,- and e . the observer εelectε the εpeed of presεntation of thε i agεs and/or the relative direction within the stored sequence of the imageε at which the images arε presented to the obεerver , εo aε to optimiεe the three dimensional depth perceived by the obεerver .

2 . A method aε claimed in claim 1 wherein the imageε are transmission images obtained by passing radiation through the εubj ec .

3 . A method as claimed in claim 1 for generating a perceived three dimenεional image of thε internal structure of a subj ect f rom a series of two dimensional imageε , which method comprises pasε ing a beam of X rays through the εubj ect and capturing the image of the resultant beam af ter it has passed through the subj ect , characterised in that _: a . the X ray beam is directed at the subj ect from a number of points displaced angularly from one another along a path relative to the subj ect ; b . the imageε of- the intensity of the resultant beamε after they have passed through the subject are captured for some or all of the said points from which the X rays are directed at the subj ect ; c . the images are εtored as a sequence of discrete images in a machine readable storage medium having sufficient capacity to store more than two of the images concurrently ; d . the images from the storage medium are presented, without significant reconstruction of the individual images , as a series of individual images or pairs of images to an observer ; e . the observer selects the speed of presεntation of the images and/or the relative direction within the εtored εequence of the imageε at which thε imageε are presented to the observer so as to optimise the three dimensional depth perceived by him.

4 . A method as claimed in any one of the preceding claims , wherein the images arε presented to the observer in pairs aε if they were εtereoεcopic pairs of imageε

5 . A method aε claimεd in any one of the preceding claimε , wherein the source of radiation is carried upon a C frame which rotates under the influence of a manual , electric , hydraulic or other drive meanε so that the generator follows a substantially circular arcuate path about the subj εct .

6 . A mεthod aε claimed in claim 5 , wherein the path extends for at least 30 to 120° about the longitudinal axis of the εubj ect and thε imagεε are taken at intervalε of up to 10° along that path .

7 . A mεthod aε claimed in any one of the preceding claimε , wherein the obεerver selects both the speed and direction of presentation of the images to him and the relative position of succeεεive imageε presented to him from the εequence of images in thε machine ^' readable εtorage medium.

8 . A method aε claimed in any one of the precεding claimε , whεrein thε obεεrver selects the speed and/or direction of presentation of the images and the relative position of the successive images presented to him from the sequence in the storage medium by means of a computer means programmed to control the presentation of images from a data store operatively associated with the computer means .

9 . Apparatus for use in the method of claim 1 , which apparatuε comprises : a . means for generating and directing a beam of X rays or other penetrating radiation onto a subj ect from a number of location points around a subj ect ; b . means for capturing a εerieε of the individual images of thε intensity of the radiation paεεing through, abεorbed, emitted, reflected, scattεrεd and/or dif fracted by the internal εtructure of thε subj ect for each of at least εome of the εaid points around the subj ect ,- c . machine readable εtorage means for storing the series of individual images in identified locations within a seσuence of caotured imaσes ; d . means for presenting imageε f rom said εtorage means to an observer either singly or in pairs ,- and e . observer controlled meanε for selecting the speed of presεntation of the images and/or the position within the said sequence from which the εuccesεive imageε preεented to thε obεerver are εelected from said sequence of images in said storage means .

10 . Apparatus as claimed in claim 9 , wherein the observer controlled means is adapted also to εelect thε relative position within the εaϊα sequence of images in εaid εtorage means at which the successive images presented to the observer .

11 . A computer adapted to control the presentation of plurality of two dimensional images from a computer acceεεible memory unit containing a plurality of the imageε obtained by directing penetrating radiation at a subj ect and capturing thε imageε of the radiation passing through, absorbed, emitted, reflected, scattered and/or diffracted by the internal structure of the subj ect , said images being held in the memory unit in a specified sequence , characterised in that the computer is programmed to selεct the speed of presentation of the images and/or the relative direction within the stored εequence of the imagεε at which the imageε are preεented to the observer so as to optimise the three dimensional depth perceived by him.

12 . A program for controlling operation of a computer which iε to present to an observer images from a machine readable memory unit containing a plurality of two dimensional images obtained by directing penetrating radiation at a subj ect and capturing the images of the radiation passing through, absorbed , emitted, reflected , scatterεd and/or diffracted by the internal structure of the subj ect , said images being held in the memory unit in a εpecified εe uence, which program includes instructions for operating the computer to εelect the εpeed of preεentation of the images and/or the relative direction within the εtored εequence of the imageε at which the imageε are presented to the observer so as to optimise the three dimensional depth perceivεd by the observer.