Computed tomography is an imaging technique mainly applied for visualization of the interior of objects non-destructively. This technique uses computer-processed combinations of multiple X-ray measurements taken from different angles to produce tomographic images. As such, X-ray computed tomography continues to have a transformative effect on clinical diagnostics, preclinical research, and nondestructive testing. A major strength of this imaging technique is the wide range of spatial resolution regimes that can be accessed (on the macro-, micro-, and even the nanoscale). Nonetheless, while a high resolution is always desirable, its achievement requires dedicated hardware, which can be an inflexible constraint. Consequently, the tomographic scanner must be equipped with an x-ray source with an adequately small focal spot and/or a detector with appropriately sized pixels that suffer little crosstalk. Although certain specialized x-ray sources feature a variable focal spot, allowing to increase resolution more flexibly, their use is not the norm in a variety of applications. Likewise, detectors with small pixels exist, but these typically impose a small field of view, often no larger than a few centimeters.CCD cameras with variable optics can enable fast resolution switching but resolution is again coupled to the field of view. Hence, high-resolution imaging may only be possible locally for very small sections of the scanned sample. These aspects prove to be a restrictive factor, especially with an increasing number of applications requiring a flexible, ideally multiscale, approach to tomographic imaging.
To address this, University College London researchers: Dr. Charlotte K. Hagen, Dr. Fabio A. Vittoria, Oriol Roche i Morgó, Dr. Marco Endrizzi and Professor Alessandro Olivo developed a novel method by which the in-slice resolution (at a constant slice thickness) in a CT image can be increased in a flexible and efficient manner without having to utilize specialized sources and detectors and without relying on geometric magnification. Their work is published in the research journal, Physical Review Applied.
Technically, their concept was enabled through the synergy of two advances in terms of the tomographic scanner layout and the data acquisition strategy. In their approach, instead of probing the sample using the full X-ray beam, the sample was probed by an array of beamlets generated by a mask with narrow slit-shaped apertures.
Since the mask apertures were smaller than the combined blur of the x-ray source and detector, and that there was no significant overlap between adjacent beamlets, higher spatial frequencies could be introduced into the image-formation process.The team reported that the application of a cycloidal acquisition scheme, by which the sample was simultaneously rotated and translated within the in-slice plane, facilitated an efficient exploitation of the frequencies and their reconstruction into high-resolution tomographic images. In a statement to Advances in Engineering, Dr. Charlotte K. Hagen, first author, explained that method’s compatibility with so-called fly-scans was of paramount importance. In such scans, the sample is rotated without interruption, which implies that scans can be fast as dead times are minimized.
Charlotte K. Hagen, Fabio A. Vittoria, Oriol Roche i Morgó, Marco Endrizzi, Alessandro Olivo. Cycloidal Computed Tomography. Physical Review Applied: volume 14, 014069.