This invention relates generally to imaging systems and more particularly to imaging systems employing X-ray fan beams.
Imaging systems that form images based upon interaction of a target object and X-rays are known. In many cases the formed image relies upon detecting X-rays as pass through the target object. Various materials (and quantities of materials) absorb varying amounts of X-rays as the X-rays pass through the target object and the resultant transmission X-rays as emerge from the target object will exhibit corresponding variations with respect to intensity. These changes in intensity with respect to the initial transmission are used to develop the target object image.
Not all X-ray beams in such a scenario are partially or fully absorbed, however. In many cases some of the X-ray energy is deflected by the target object. Such deflection is commonly referred to as scatter and there can be back scatter, side scatter, and/or forward scatter depending upon the characteristics of the target object itself. Ordinarily the prior art has sought to eliminate scatter as much as possible, partly because scatter can create unwanted radiation exposure to nearby personnel and partly because scatter can create so-called background fog in the resultant image. Such fog can obscure faint objects and detract from image resolution and clarity.
In some cases, however, scatter has been employed in a more positive manner. Proposals exist, for example, to employ back scatter detectors in conjunction with a moving X-ray pencil beam. Such an approach, however, tends towards complexity. Perhaps more significantly, the moving X-ray pencil beam illuminates the target object with an effective duty cycle of only about 1%. As a result, and depending upon the nature of the target object itself, this can result in relatively poor images, or can require either a considerable expenditure of energy and/or time in order to obtain a relatively decent image.
The above needs are at least partially met through provision of the method and apparatus to facilitate formation of a two-dimensional image using X-ray fan beam scatter described in the following detailed description, particularly when studied in conjunction with the drawings, wherein:
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.
Generally speaking, pursuant to these various embodiments, one directs an X-ray fan beam towards a target. A first linear array of detectors serve to detect X-ray fan beam scatter as occurs when at least portions of the X-ray fan beam interact with the target. The resultant scatter-based target information is then used, in conjunction to with relative motion between then x-ray source and the target, to form a two-dimensional view of the target.
By one approach the linear array of detectors comprises a linear array of back scatter detectors. By another approach the linear array of detectors comprises a linear array of side scatter detectors or forward scatter detectors. If desired, a plurality of such detector arrays can be employed. For example, two linear arrays of back scatter detectors can be deployed with one on either side of the X-ray fan beam. Depending upon the needs and/or requirements of the application setting, these detectors can be placed on the sides of the X-ray fan beam or can be placed above and/or below the X-ray fan beam as well. One may also employ the use of scatter detectors in conjunction with a more traditional transmission detector as well if desired.
The X-ray fan beam offers the advantage of illuminating the target 100% of the time. This contrasts sharply, of course, with a scanning X-ray pencil beam. The resultant structure tends towards relative simplicity. This, in turn, favors both ease of use and maintenance. Such teachings are also readily employed to permit relatively quick and effective scanning of large, difficult targets (such as truck, maritime, and railroad containers and cars).
These and other benefits may become clearer upon making a thorough review and study of the following detailed description. Referring now to the drawings, and in particular to
X-ray fan beams are also known in the art. Such beams tend to be wide in a first dimension and relatively narrow in a dimension that is normal to the first dimension. In many prior art applications the wide dimension comprises a horizontally aligned dimension. For these present purposes, however, it may be desirable to orient the X-ray fan beam such that the wide dimension is vertically aligned. With momentary reference to
Referring again to
Those skilled in the art will understand that such a detector effectively serves to convert X-ray photons into electronic signals. There are various ways known in the art by which this may be accomplished including scintillator and direct conversion detectors as are frequently found in modern applications. As such detectors are well known in the art, and further as these teachings are relatively non-dependent upon the use of any particular detection technology or approach, for the sake of brevity further elaboration will not be provided here regarding such detectors.
As shown in the illustrative schematic depiction of
By one approach, and referring now momentarily to the schematic representation at
So configured, and referring momentarily to
So configured, this second linear array of scatter detectors 209 is suitably positioned to also receive at least some back scatter 402 as occurs through interaction of the X-ray fan beam 202 with the target 205. As with the first linear array of scatter detectors 207, it may be useful to orient the longitudinal axis of the second linear array of scatter detectors 209 substantially parallel to the X-ray fan beam plane 204 and with its x-ray sensitive face substantially normal to at least some of the back scatter 402.
As will be discussed below in more detail, additional linear arrays of scatter detectors and/or alternative placements are possible and may be used as appropriate to suit the needs and/or requirements of a given application.
Referring again to
A processor 208 of choice can receive the scatter-based target information from the linear array of scatter detectors 207 (and 209 when present). Such processors are known in the art and serve to collect and process target information as corresponds to a plurality of individual views to thereby form an aggregate two-dimensional view of the target. Such a two-dimensional view can be provided to a user, for example, using a display technology of choice (not shown). Such views can also be stored, transmitted to a remote location, and/or printed if desired.
Referring again to
If desired, the latter processor 211 can comprise the same processor 208 as processes the scatter-based target information. Also if desired, the resultant images from the two processors 208 and 211 can be combined into an aggregate image or can be used as independent views of the same target 205.
As noted earlier, there are various alterations that one may introduce with respect to these teachings. To illustrate, and referring now to
As another illustrative example, and referring now to
As yet another illustrative example, and referring now to
Those skilled in the art will appreciate that when one set of scatter detectors is placed on either side of the plane of the X-ray fan beam and also above (or below) the X-ray fan beam, then it is possible to obtain, presuming target motion, three-dimensional information regarding the target (such as, for example, three-dimensional information regarding the relative position of one or more objects within a cargo container). As the target moves a first linear array of side scatter detectors disposed above or below the X-ray fan beam provides a corresponding two-dimensional view from above or below the X-ray fan beam. Additional detectors (such as back scatter, side scatter, and/or forward scatter detectors) that are aligned normal to the direction of propagation of the target can then provide vertical position information regarding scattered target. Together these two two-dimensional views provide three-dimensional information (though not necessarily a three-dimensional image) regarding the target. Such three-dimensional information can also be similarly attained by using side scatter detectors as disclosed above in conjunction with a transmission detector.
These teachings are well suited to megavolt systems intended for use with large scale inspection systems such as cargo inspection systems. In comparison with back scatter at several hundred kilovolts, it has been noted that back scatter coefficients are often eight to ten times lower in the megavolt region. This, however, is substantially offset by the latter's higher photon rates. Further, the voltage of the back scatter near 180 degrees from 200 kV to 450 kV sources is near 100 kV, while that from megavolt sources is over 200 kV. Accordingly, the higher-voltage back scatter from megavolt sources can emerge from greater depths. This, in turn, can comprise an important advantage for larger or denser targets. Much the same applies to side scatter near 90 degrees, where the scattered energy from 200 kV to 450 kV sources is mostly below 200 kV while that from megavolt sources is over 400 kV.
These teachings offer considerable benefit when employed in conjunction with a security-based inspection system. Traditional transmission detection, for example, cannot readily discern the difference between a relatively low-density object that is thick and a relatively high density object that is thinner. The resulting image will typically look the same for both as both can absorb the same amount of total X-ray intensity. Some materials of concern, however, such as many explosives, tend to exhibit relatively high scatter coefficients. Consequently, although a certain quantity, and/or thickness shape, of explosive material may look identical to a lump of steel of different quantity, shape and/or thickness when viewed using transmission detection, the two objects will look considerably different from one another when viewed using scatter-based detection.
Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept. For example, in the illustrative examples offered above, the detectors have a substantially rectangular-shaped cross-sectional form factor. For at least some applications, however, it may be desirable to use a wedge-shaped cross-sectional form factor instead.