Obtaining three-dimensional structural information inside objects in nondestructive way has been challenging. The most common approach is conventional computed tomography (CT) where either the object is rotated around one axis, or the x-ray source and detector are rotated around the object. Then the object structure is determined using a computation algorithm. This limits the application to cases where the object and structure inside the object is not changing over the time period needed to perform the scan. Furthermore, the resolution is determined by the x-ray source and detector characteristics.

A new 3D x-ray imager combines two different hardware pieces. The first is an x-ray optic with a depth of field that is small compared to the object under investigation. Reflective Wolter type x-ray optics are one such design. These hollow optics have a relatively large collection efficiency and can be designed with a large field of view. The depth of focus, which is the distance over which a feature can be resolved along the imaging direction, is relatively small for these optics — typically small compared to the field of view. These optics have been used extensively in x-ray astronomy and in some cases for x-ray microscopy.

The short depth of field distance is often considered a drawback to the design; however, when combined with a three-dimensional x-ray detector, it is possible to take advantage of the short depth of field to obtain additional information about the 3D structure of an object. One simple version of the 3D detector uses film. The x-rays are partially transmitted and partially absorbed through a piece of x-ray film. This allows the recording of multiple images along one line of sight and simultaneously.

This technology overcomes the limitation of obtaining three-dimensional structural information by providing multiple views with one exposure without moving parts. It relies on a 3D detector, which can be as simple as a stack of film plates, and a focusing x-ray optic. The x-ray optic allows collection of x-rays from a localized volume, just like an ordinary optical lens, and the stacked film plate or other 3D detector design allows collection of the multiple focal plane information from one line of sight. Acquiring images simultaneously from a single line of sight reduces the motion blurring and reconstruction artifacts due to the system motion.

For more information, contact Genaro Mempin in the Innovation and Partnerships Office at This email address is being protected from spambots. You need JavaScript enabled to view it..

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This article first appeared in the December, 2020 issue of Tech Briefs Magazine.

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