Abstract
Optical CT is a method that can potentially provide both accurate dosimetry at high spatial resolution and 3-D visualisation over a large field-of-view in a single dataset. The major factors limiting spatial resolution in previous studies are analysed here and it is shown that improvements in equipment specification can overcome many of these. The need for ultra-high spatial resolution in the verification of microbeam radiation therapy verification is demonstrated and example images of a PRESAGE® sample are presented.
Highlights
It is well established that normal tissues can tolerate high doses of radiation over small volumes
We have previously described the construction of an optical CT microscope [7]; we have developed a protocol for measuring the modulation transfer function of an optical CT scanner [8]; and we have presented preliminary results of the application of this protocol to our optical CT microscopy system, together with examples of the measurement of a synchrotron microbeam treatment applied to a PRESAGE® dosimeter [9]
For the two wider slit patterns (416 and 208 μm), the gradients of figure 1(d) are very similar, whereas for the 108 μm slit pattern, the gradient is around 40% lower. This is a straightforward manifestation of the effect of the modulation transfer function, but illustrates the fact that significant changes in pixel value occur even for structures that are several times the nominal spatial resolution
Summary
It is well established that normal tissues can tolerate high doses of radiation over small volumes. Optical CT is exciting, because of the possibility of obtaining data with microscopic resolution, over the entire field-of-view of a macroscopic object This would allow the entire microbeam treatment to be visualised with accurate dosimetry at each 3-D location. Unlike the case of MRI, in which a small sub-volume can be excited and imaged within a larger object, it is not straightforward ( some techniques do exist) to obtain zoomed images of small regions using CT. This means that to obtain high spatial resolution images of extended objects, one needs to acquire projection images with large matrix sizes. Visualisation and display of the results of imaging with such large 3-D matrix sizes has been, and to a certain extent still is, difficult
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