1 mm
3 volume element. With a SPECT-like pinhole collimator (0.01% sensitivity),
366 fluorescent photons per 1 mm
3 image voxel would be collected. Those statistics
are sufficient for accurate image reconstruction.
7.4 High-Resolution 2D Imaging
Besides clinical and preclinical in vivo imaging, molecular imaging analysis of
surgically removed tumors with high-resolution planar imaging is a potential application for XF or XL imaging. Currently, resected tumors are analyzed by pathologists which requires staining of the tissue with elaborate techniques. This procedure
is cumbersome and time-consuming. In a 2D XF imaging approach, small tumor
samples can be analyzed quickly with resolution ranging from 5 to 100 μm by
translating the sample with a bilinear motion stage across a narrow pencil beam.
Such imaging can be performed close to the operating room and return feedback
about the analysis of the sample to the surgeon before closing the surgical site.
The analysis of small samples allows the use of low energetic X-rays which can
be manipulated with X-ray optics made of hollow glass tubes. With classic collimation, the imaging process can take up to hours, but with polycapillary optics, the
X-ray flux can be increased by orders of magnitude and stimulate a proportionally
sizable fluorescent response [51]. This makes imaging within minutes possible.
7.5 Coded-Aperture Compressed XLCT
The pencil-beam XLCT approach provides a simple image reconstruction problem,
but commonly the scanning time is prohibitive for in vivo imaging. In codedaperture compressive XLCT (CAC-XLCT), a binary pseudorandom aperture mask
encodes the X-ray excitation field for each angular projection. In this case, instead of
exciting the sample one pencil beam at a time, the sample is simultaneously excited
by a subset of multiple pencil beams. The specific excitation pattern created by the
coded aperture mask is incorporated into the sensing matrix, and image reconstruction is performed using sparse regularization. This compressed-sensing image
reconstruction approach that combines a pseudorandom coded aperture mask and
sparse regularization allows for reconstructing high-quality images with far fewer
measurements than what traditional sampling dictates. It was demonstrated that
CAC-XLCT performance using five coded aperture masks per angular projection
with a mask transmission of 20% can locate all target lesions in a mouse-sized
phantom with good image quality. For comparison purposes, an image reconstructed
with cone beam XLCT is not able to recover the true nanophosphor distribution.
CAC-XLCT allows for accurately retrieving the nanophosphor distribution with
400 times fewer measurements than pencil-beam XLCT would require, indicating
a 400-times faster acquisition time.
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141
3 volume element. With a SPECT-like pinhole collimator (0.01% sensitivity),
366 fluorescent photons per 1 mm
3 image voxel would be collected. Those statistics
are sufficient for accurate image reconstruction.
7.4 High-Resolution 2D Imaging
Besides clinical and preclinical in vivo imaging, molecular imaging analysis of
surgically removed tumors with high-resolution planar imaging is a potential application for XF or XL imaging. Currently, resected tumors are analyzed by pathologists which requires staining of the tissue with elaborate techniques. This procedure
is cumbersome and time-consuming. In a 2D XF imaging approach, small tumor
samples can be analyzed quickly with resolution ranging from 5 to 100 μm by
translating the sample with a bilinear motion stage across a narrow pencil beam.
Such imaging can be performed close to the operating room and return feedback
about the analysis of the sample to the surgeon before closing the surgical site.
The analysis of small samples allows the use of low energetic X-rays which can
be manipulated with X-ray optics made of hollow glass tubes. With classic collimation, the imaging process can take up to hours, but with polycapillary optics, the
X-ray flux can be increased by orders of magnitude and stimulate a proportionally
sizable fluorescent response [51]. This makes imaging within minutes possible.
7.5 Coded-Aperture Compressed XLCT
The pencil-beam XLCT approach provides a simple image reconstruction problem,
but commonly the scanning time is prohibitive for in vivo imaging. In codedaperture compressive XLCT (CAC-XLCT), a binary pseudorandom aperture mask
encodes the X-ray excitation field for each angular projection. In this case, instead of
exciting the sample one pencil beam at a time, the sample is simultaneously excited
by a subset of multiple pencil beams. The specific excitation pattern created by the
coded aperture mask is incorporated into the sensing matrix, and image reconstruction is performed using sparse regularization. This compressed-sensing image
reconstruction approach that combines a pseudorandom coded aperture mask and
sparse regularization allows for reconstructing high-quality images with far fewer
measurements than what traditional sampling dictates. It was demonstrated that
CAC-XLCT performance using five coded aperture masks per angular projection
with a mask transmission of 20% can locate all target lesions in a mouse-sized
phantom with good image quality. For comparison purposes, an image reconstructed
with cone beam XLCT is not able to recover the true nanophosphor distribution.
CAC-XLCT allows for accurately retrieving the nanophosphor distribution with
400 times fewer measurements than pencil-beam XLCT would require, indicating
a 400-times faster acquisition time.
X-Ray Excited Fluorescent Materials for Medical Application
141