A METHOD OF DESIGNING AN X-RAY EMITTER PANEL

Abstract

A method of designing an x-ray emitter panel 100 including the step of determining a pitch scale, r, to be used in placing x-ray emitter elements 110 on the panel 100, thereby arriving at a specific design of x-ray emitter panel 100 suitable for a specific use.

Claims

1. A method of designing an x-ray emitter panel including an array of x-ray emitters for use as a distributed x-ray source, the x-ray emitter panel for use with an x-ray detector panel, the method comprising the steps of choosing a predetermined total number of photons produced by a charge available for a single exposure, E.sub.tot; and choosing a predetermined surface area of the emitter panel, F; choosing a predetermined absorption factor due to tissue placed between the emitter panel and the detector panel, η.sub.bre; choosing a predetermined maximum emitter-detector panel separation, D.sub.max; choosing a predetermined minimum number of photons that is required to arrive at a detector in the detector panel in order to obtain a viable image, E.sub.min; choosing a predetermined density of detectors in the detector panel, ρ.sub.det; choosing a predetermined dimensionless constant having a value between approximately 10 and 20, A; solving an inequality of the form: $\frac{{\left(\frac{r}{D_{\max }}\right)}^2}{{\left(1+{\left(\frac{r}{D_{\max }}\right)}^2\right)}^{\frac{3}{2}}}\ge \frac{A.Math..Math.{\rho }_{\det }.Math.{\mathrm{FE}}_{\min }}{E_{\mathrm{tot}}.Math.{\eta }_{\mathrm{bre}}}$ for r; selecting a pitch scale corresponding to a value of r determined from the solution of the inequality.

2. The method of claim 1, wherein solving the inequality comprises finding an approximate solution.

3. The method of claim 1, wherein solving the inequality comprises selecting a minimum value of the pitch scale r which satisfies the inequality.

4. The method of claim 1, wherein solving the inequality comprises solving the equation: $\frac{{\left(\frac{r}{D_{\max }}\right)}^2}{{\left(1+{\left(\frac{r}{D_{\max }}\right)}^2\right)}^{\frac{3}{2}}}=\frac{A.Math..Math.{\rho }_{\det }.Math.{\mathrm{FE}}_{\min }}{E_{\mathrm{tot}}.Math.{\eta }_{\mathrm{bre}}}$

5. The method of claim 4, wherein solving the equation comprises applying Newton's method.

6. The method of claim 1, further comprising the step of selecting a collimation angle, α, that is less than or equal to twice the arctangent of the ratio of the selected pitch scale r to the maximum emitter-detector panel separation D.sub.max; that is: $\alpha \le 2.Math.{\tan }^{-1}.Math.\frac{r}{D_{\max }}$

7. The method of claim 6, further comprising the step of selecting a collimation angle α, that is substantially equal to twice the arctangent of the ratio of the selected pitch scale r to the maximum emitter-detector panel separation D.sub.max; that is: $\alpha =2.Math.{\tan }^{-1}.Math.\frac{r}{D_{\max }}$

8. The method of claim 1, further comprising the steps of: choosing a predetermined desired stand-off distance of the emitter panel from the tissue placed between the emitter panel and the detector panel, δ.sub.design; choosing a predetermined factor representative of a multiplicity of overlapping conelets from adjacent x-ray emitters on a given part of the tissue, M.sub.design; and solving a second inequality of the form: $\alpha \ge 2.Math.{\tan }^{-1}.Math.\frac{{\mathrm{rM}}_{\mathrm{design}}}{4.Math.{\delta }_{\mathrm{design}}}$ selecting a collimation angle corresponding to a value of α, determined from the solution of the second inequality.

9. The method of claim 8, further comprising the steps of: choosing a predetermined desired thickness of tissue placed between the emitter panel and the detector panel, d.sub.design; choosing a predetermined desired emitter-detector panel separation, D.sub.design, less than D.sub.max; and determining M.sub.design by solving the further equation: $M_{\mathrm{design}}=4-\frac{d_{\mathrm{design}}}{D_{\mathrm{design}}}$

10. The method of claim 1, wherein D.sub.max is determined based on an imaging modality.

11. The method of claim 1, further comprising the steps of: choosing a predetermined maximum thickness of tissue placed between the emitter panel and the detector panel, d.sub.max; and choosing a predetermined minimum value of a factor, M.sub.min representative of a multiplicity of overlapping conelets from adjacent x-ray emitters on a given part of the tissue, wherein M.sub.min has a value between 1 and 4; determining D.sub.max by solving the further equation: $D_{\max }=\frac{4.Math.d_{\max }}{4-M_{\min }}$

12. The method of claim 11, wherein M.sub.min is determined based on a consideration of the specific image reconstruction approach used and the desired speed of imaging.

13. The method of claim 11, when dependent on claim 8, wherein M.sub.min is determined based on a minimum value of M.sub.design.

Description

[0071] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

[0072] FIG. 1 is a schematic cross-sectional representation of an emitter array in use.

[0073] FIG. 2 is a schematic cross-sectional representation of an emitter array in use.

[0074] FIG. 3 is a schematic plan-view representation of an emitter array.

[0075] The present invention will be described with respect to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. Each drawing may not include all of the features of the invention and therefore should not necessarily be considered to be an embodiment of the invention. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0076] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that operation is capable in other sequences than described or illustrated herein.

[0077] Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that operation is capable in other orientations than described or illustrated herein.

[0078] It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

[0079] Similarly, it is to be noticed that the term “connected”, used in the description, should not be interpreted as being restricted to direct connections only. Thus, the scope of the expression “a device A connected to a device B” should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. “Connected” may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

[0080] Reference throughout this specification to “an embodiment” or “an aspect” means that a particular feature, structure or characteristic described in connection with the embodiment or aspect is included in at least one embodiment or aspect of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, or “in an aspect” in various places throughout this specification are not necessarily all referring to the same embodiment or aspect, but may refer to different embodiments or aspects. Furthermore, the particular features, structures or characteristics of any embodiment or aspect of the invention may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments or aspects.

[0081] Similarly, it should be appreciated that in the description various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Moreover, the description of any individual drawing or aspect should not necessarily be considered to be an embodiment of the invention. Rather, as the following claims reflect, inventive aspects lie in fewer than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0082] Furthermore, while some embodiments described herein include some features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form yet further embodiments, as will be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0083] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0084] In the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of said values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.

[0085] The use of the term “at least one” may mean only one in certain circumstances.

[0086] The principles of the invention will now be described by a detailed description of at least one drawing relating to exemplary features of the invention. It is clear that other arrangements can be configured according to the knowledge of persons skilled in the art without departing from the underlying concept or technical teaching of the invention, the invention being limited only by the terms of the appended claims.

[0087] FIG. 1 shows an emitter array 100 including a plurality of emitter elements 110. Each emitter element 110 is configured to emit x-rays 140 over a collimation angle α. The emitter array 100 is shown in use such that x-rays 140 from the emitter elements 110 may pass through a body 120 having an approximate thickness d, spaced a distance δ from the emitter array 100, to be detected by a detector panel 130 that is spaced a distance D from the emitter array 100.

[0088] FIG. 2 shows an emitter array 200 including a first and second plurality of emitter elements (not shown). X-rays 240 (shown in solid lines) from an emitter element in the first plurality of emitter elements are arranged such that they do not overlap with x-rays from adjacent emitter elements in the first plurality of emitter elements before arriving at a detector panel 230 (after passing through tissue to be examined 220). This prevents multiple images being formed of a single feature in the tissue 220. Similarly, x-rays 250 (shown in dotted lines) from an emitter element in the second plurality of emitter elements are arranged such that they do not overlap with x-rays from adjacent emitter elements in the second plurality of emitter elements before arriving at a detector panel 230 (after passing through tissue to be examined 220). By using each plurality of emitter elements separately (i.e. spaced in time, temporal separation), a greater coverage of the tissue 220 may be made. In the arrangement shown in FIG. 2, at least one further plurality of emitter elements may also be used to build complete coverage of the tissue 220 in a similar way.

[0089] FIG. 3 is a schematic plan-view representation of an emitter array 300. Each emitter element 310 is arranged with its centre at node points of a grid of equilateral triangles. That is, the centres are located at points:

[00014]$2.Math.r\left(k.Math.\stackrel{.fwdarw.}{e_1}+l.Math.\stackrel{.fwdarw.}{e_2}\right),k,l\in \mathbb{Z}$$\mathrm{where}.Math.\text{:}$$\stackrel{.fwdarw.}{e_1}=\left(\begin{array}{c}1\\ 0\end{array}\right)$$\stackrel{.fwdarw.}{e_2}=\left(\begin{array}{c}\cos .Math.\frac{\pi }{3}\\ \sin .Math.\frac{\pi }{3}\end{array}\right)$

[0090] and denotes the set of integers such that the defined points fit on a given panel. This pattern is shifted such that the panel is covered homogenously by 48 exposures enumerated by the formula

f+4(g−1)+16(h−1), (f=1, . . . , 4; g=1, . . . , 4; h=1, . . . , 3)

[0091] The centres of circles that are fired simultaneously in exposure (f, g, h) are given by:

[00015]$r\left(\frac{f-1}{2}.Math.\stackrel{.fwdarw.}{e_1}+\frac{g-1}{2}.Math.\stackrel{.fwdarw.}{e_2}+\frac{h-1}{2.Math.\sqrt{3}}.Math.\stackrel{.fwdarw.}{e_3}+2.Math.k.Math.\stackrel{.fwdarw.}{e_1}+2.Math.l.Math.\stackrel{.fwdarw.}{e_2}\right)$$\mathrm{where}.Math.\text{:}$$\stackrel{.fwdarw.}{e_3}=\left(\begin{array}{c}\cos .Math.\frac{\pi }{6}\\ \sin .Math.\frac{\pi }{6}\end{array}\right)$

[0092] The first 16 exposures (corresponding to h=1) are obtained by shifting the parent pattern to the nodes obtained by bisecting the grid of equilateral triangles twice.

[0093] The second and third group of 16 exposures are centred where the first set of exposures left holes (regions not covered by radiation). There are twice as many holes as disks in any given exposure, which leads to the three sets of 16.

[0094] Note that all emitters except those near the boundary of the panel are equidistant to their six nearest neighbours, the distance being

[00016]$\left(\frac{r}{\sqrt{12}}\right).$

[0095] We call this distance emitter pitch, while we refer to r as the emitter scale. The emitter scale also has the interpretation as radius of the non-overlapping disks of radiation that reach the detector panel simultaneously in any given exposure. r may be chosen such that these disks are just touching.