XFCT, it will be sufficient to catch a cancerous lump of micrometric dimensions
[14]. The method allows quantifying element concentrations in the active biological
environment without the cumbersome and time-consuming analysis of sacrificed
animals.
Potential challenges of XFCT imaging are currently molecular sensitivity, acquisition time, scatter contamination, and cost-effectiveness. The drawback of XFCT
and XLCT is that ionizing radiation is used for the imaging which is harmful if used
in high doses. This limits the sensitivity of the imaging modalities as only clinically
and ethically acceptable doses can be used.
2 Combination of XFCT or XLCT with Transmission CT
Imaging
Transmission X-ray and CT imaging are indispensable in preclinical and clinical
studies, and CT imaging became a cornerstone for the evolution of tomographic
imaging. The modality, however, falls short in providing sufficient contrast for
probing the molecular bases of diseases. Combined with transmission CT, XFCT
or XLCT offers an unprecedented method for visualizing subtle molecular processes
in living subjects within a CT-based anatomical frame of reference. The establishment of fully integrated XF- or XLCT and CT imaging systems will allow the
simultaneous acquisition of anatomical and molecular information in the same scan.
By empowering X-ray imaging with the ability to extract molecular signatures
through the simultaneous measurement of XF or XL signals, the molecular information can be extracted without additional dose for the patient. Due to the low mass
attenuation coefficient of dilutions with low concentrations of XF or XL contrast
agents, these probes are not detectable in transmission X-ray or CT images. The
emergence of fully integrated XFCT/CT systems in laboratories and clinics using
conventional polychromatic X-ray sources will satisfy the ever-growing interest in
imaging of high atomic number (Z > ~30) elements.
On top of the benefits of multimodal imaging by combining anatomical and
molecular information into one imaging system, CT images can also be used to
improve the performance of XFCT imaging. The probability of Compton scatter at a
given point is a function of the underlying material. As the material and density
distributions are known from the CT images, the dual-modality implementation
presents a unique opportunity for advanced attenuation and scatter correction (see
also chapter “Scatter and Attenuation Correction”). While the CT image can directly
be used for attenuation correction, the scatter corrections require more elaborate
processing steps. The CT image can be used to run analytical or semi-analytical
simulations to generate a scatter estimate as the CT pixel data provides the probability for the angle and energy of deflection for scattered X-rays given by the KleinNishina differential cross-section. The scatter estimate can then be used in one of the
abovementioned scatter correction methods.
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D. Vernekohl and L. Xing
[14]. The method allows quantifying element concentrations in the active biological
environment without the cumbersome and time-consuming analysis of sacrificed
animals.
Potential challenges of XFCT imaging are currently molecular sensitivity, acquisition time, scatter contamination, and cost-effectiveness. The drawback of XFCT
and XLCT is that ionizing radiation is used for the imaging which is harmful if used
in high doses. This limits the sensitivity of the imaging modalities as only clinically
and ethically acceptable doses can be used.
2 Combination of XFCT or XLCT with Transmission CT
Imaging
Transmission X-ray and CT imaging are indispensable in preclinical and clinical
studies, and CT imaging became a cornerstone for the evolution of tomographic
imaging. The modality, however, falls short in providing sufficient contrast for
probing the molecular bases of diseases. Combined with transmission CT, XFCT
or XLCT offers an unprecedented method for visualizing subtle molecular processes
in living subjects within a CT-based anatomical frame of reference. The establishment of fully integrated XF- or XLCT and CT imaging systems will allow the
simultaneous acquisition of anatomical and molecular information in the same scan.
By empowering X-ray imaging with the ability to extract molecular signatures
through the simultaneous measurement of XF or XL signals, the molecular information can be extracted without additional dose for the patient. Due to the low mass
attenuation coefficient of dilutions with low concentrations of XF or XL contrast
agents, these probes are not detectable in transmission X-ray or CT images. The
emergence of fully integrated XFCT/CT systems in laboratories and clinics using
conventional polychromatic X-ray sources will satisfy the ever-growing interest in
imaging of high atomic number (Z > ~30) elements.
On top of the benefits of multimodal imaging by combining anatomical and
molecular information into one imaging system, CT images can also be used to
improve the performance of XFCT imaging. The probability of Compton scatter at a
given point is a function of the underlying material. As the material and density
distributions are known from the CT images, the dual-modality implementation
presents a unique opportunity for advanced attenuation and scatter correction (see
also chapter “Scatter and Attenuation Correction”). While the CT image can directly
be used for attenuation correction, the scatter corrections require more elaborate
processing steps. The CT image can be used to run analytical or semi-analytical
simulations to generate a scatter estimate as the CT pixel data provides the probability for the angle and energy of deflection for scattered X-rays given by the KleinNishina differential cross-section. The scatter estimate can then be used in one of the
abovementioned scatter correction methods.
128
D. Vernekohl and L. Xing