Imaging of objects using x-rays is well known. In a simple device an x-ray beam is passed through an object, and the shadow of the object is projected onto an image intensifier. Magnification of the object can be achieved by moving the object relative to the x-ray source, or by moving the image intensifier relative to the object.

Real-time imaging can be achieved by placing the object on a support plate movable in translation and rotation. The support plate is usually horizontal so that the object to be imaged is retained in position by gravity as the support plate moves. Viewing of the object at an angle may for example be achieved by arranging the x-ray source and image intensifier non-perpendicularly with respect to the object.

Laminography is the technique of sequentially imaging an object obliquely in more than one direction, digitising the images formed at the image intensifier, and summing the images so as to isolate features at a predetermined layer in the object.

Various laminography techniques have been proposed for example by Samsung, Hewlett Packard and Nicolet. These techniques generally require rotation of more than one component of an x-ray imaging device so as to provide multiple two-dimensional images for subsequent software manipulation. Such techniques generally lead to somewhat bulky and complex machinery which is inevitably expensive.

Typically a prior art imaging device will require rotation of two of the three main elements, namely the x-ray source, the support table for the object to be imaged, and the image intensifier. High precision is essential, and co-ordinated movement of the two rotatable elements is a prerequisite. Accordingly a stiff machine frame and high precision rotary bearings and drives are essential.

In one prior example the x-ray source is circulated in a relatively fixed plane above a fixed object, so that the x-ray beam impinges on the object at an angle, and the image intensifier is circulated in a parallel plane below the object so as to be in a position to receive the shadow cast by the x-ray beam at several angular positions.

What is required is a simplified arrangement which reduces the cost, complexity and bulk of the laminography device, yet is capable of imaging the required slice at the same resolution as the prior art.

According to the invention there is provided an x-ray imaging device comprising a frame, an x-ray source fixed relative to said frame, an image intensifier fixed relative to said frame and facing said source, and a support for an object to be imaged, said support being between said source and image intensifier and being rotatable, wherein said source, object and image intensifier are arranged such that an x-ray beam generated by said source is adapted to strike said object obliquely.

In such an arrangement both the source and image intensifier are relatively fixed whereas only the support is rotatable. The x-ray beam is arranged to strike the object obliquely, and by rotating the support table, several different oblique images can be acquired. Using conventional techniques these images can be overlaid to depict a particular layer in the object.

By fixing the relatively complex x-ray source and intensifier, the design of the device is greatly simplified. A simple motor driven rotary support suffices, and there is no problem of synchronization, which is a consequence of two rotatable components.

Furthermore the device can be relatively slim compared with the prior art devices since the x-ray beam is arranged on a single fixed axis with respect to the relatively fixed image intensifier. This has the advantage of substantially reducing the overall size of the device, and of reducing the area of lead sheathing required; in turn these features substantially reduce the mass of the device, which is an important consideration.

Preferably the image intensifier is flat, and in the preferred embodiment the plane thereof is oblique with respect to the centre of the x-ray beam. In the preferred embodiment the image intensifier is in a plane parallel to the plane of rotation of the support.

In the preferred embodiment the support face is planar, and the centre of the x-ray beam is arranged to strike the support face obliquely.

Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompanying drawings in which:-

Fig. 1 is a schematic representation of a prior art x-ray laminography device; Fig. 2 is an illustration of overlaid images, on a reduced scale; Fig. 3 is a schematic representation of a laminography device according to the present invention; Fig. 4 is an illustration of realigned images obtained from the device of Fig. 3; and Fig. 5 is an illustration of the image of Fig. 4 after combining.

Fig. 1 illustrates a typical prior laminography device having two relatively rotatable components.

An x-ray source 11 is schematically represented by a spot, and is adapted to be circulated in a horizontal plane above an object 10 having multiple horizontal layers represented by (in descending order) A, B and C. Four spot positions 11 a-lid are illustrated, at 90° intervals on the circular path 12 of the source.

Beneath the object, which is itself on a suitable support, is an image intensifier 13 which is rotatable on a horizontal circular path 14 so as to be in line with both the object 10 and the source 11. As will be appreciated, the image intensifier 13 is 180° out of phase with rotation of the source. The support is relatively fixed with respect to the source and image intensifier.

The image intensifier 13 is illustrated for reasons of clarity in only one position, in line with spot position 1 la. Also for reasons of clarity, the shape of the image intensifier is somewhat distorted and the effect of magnification and perspective is not accurately depicted.

With the spot in position 1 la an image 15a of the object 10 is projected on the image intensifier 13 as illustrated, with the letters A, B and C arranged from right to left.

Other images 15b, 15c, 15d correspond to spot positions llb, lie, lid at appropriate positions of the image intensifier.

At each position of the image intensifier 13, the projected image is digitized, and these images may be overlaid using known computer software techniques to reinforce the features of a desired layer. Such an overlay is illustrated on a reduced scale in Fig. 2, and shows reinforcement of the image of the letter B whereas other letters (A and C) are inevitably overlaid in a manner which is not useful.

In this way the image of a specified layer of an object (letter B) can be represented. The technique of laminography has important applications, particularly in the inspection of hidden electrical joints of microprocessor devices.

In practice a device does not have discrete layers A, B and C, but the operator selects a depth corresponding to a particular plane of interest. In the example described the image at plane B is reinforced by this technique so as to give enhanced clarity over all other planes through the object.

It will be appreciated that the object and source, or the object and image intensifier may be rotated with the third element stationary in order to achieve the same effect. In all cases however either the top or bottom element must be rotated, with the result that the radial dimension of the device is usually rather large.

The present invention is illustrated in Fig. 3. In this arrangement both the source 21 and the image intensifier 22 are fixed, and the object 23 is rotatable on a suitable support (not illustrated) as represented by arrow 25. The source and image intensifier are not vertically aligned, but are arranged to illuminate the object at an angle to the vertical. In the position illustrated in Fig. 3 a first image 24a is produced. By rotating the object 23 additional images 24b, 24c and 24d can be produced without changing the position of the source and image intensifier. These additional images 24b-24d produced by successive 90° movements of the object 23, are illustrated in a digitised form, and it will be noted that the letters A, B, C face, in each case, in a different direction. For clarity and comparison purposes, the images are shown in a single column, though each image will of course be formed on the image intensifier 22 without movement thereof.

Fig. 4 illustrates notional rotation of the images of Fig. 3, which are then superimposed in the manner represented in Fig. 5 to reinforce the part of the images corresponding to the layer of interest. Digitization and manipulation of the images using software techniques is not part of this invention, but uses substantially the same method and means as that proposed in the prior art devices. The images illustrated in Fig. 4 are

corrected for rotation-the rotation of the image caused by rotating the object is removed by applying the reverse rotation to the image, and thus causes the images to appear in the same manner as illustrated in Fig. 1.

The use of the terms'horizontal'and'vertical'relate to a conventional embodiment in which an object is placed on a rotatable support, and retained by gravity. Provided suitable means are provided for holding the support relative to the source and image intensifier, there is no reason why the invention could not be used in other orientations.

For example the x-ray beam could be arranged in a generally horizontal plane.

Furthermore the source could be below the object and the image intensifier above the object.