7.6 XFCT with Polarized X-Ray
It is possible to perform XFCT imaging with polarized X-rays. In synchrotrons,
for example, X-rays are naturally emitted with a preferred polarization direction. For
excitation it is possible to have an optimized setup with a detector positioning for
suppressed scatter contamination. The reconstructed images in Fig. 4 show how this
is beneficial for XFCT imaging performance.
8 Figures of Merit for Performance Analysis
The direct performance comparison of different systems and imaging modes is a
delicate exercise as different studies utilize different system parameters for their
experiments and different figures of merit for the performance analysis. The imaging
sensitivity and resolution are commonly assessed in phantom experiments. Here, we
propose some imaging configurations and figure of merits which have been proven
useful for the performance analysis.
The molecular sensitivity is usually determined by measuring various mediumsized cylinders with different concentrations of contrast agent. The lowest detectable
contrast agent concentration is then retrieved by a linear least square fit to the
contrast-to-noise ratio (CNR) to concentration ratio where a contrast-to-noise ratio
of 5 (Rose Criterion) is considered the minimal detection limit. In this context, the
CNR is defined by:
CNR ¼
μ ROI À μ bkg
σ bkg
,
where μ ROI , μ bkg , and σ bkg are the average voxel intensity of the region of interest
(ROI) and background (bkg) and the standard deviation of the voxel intensity within
the background region, respectively. Usually, the background region is a ROI sized
region defined in the center of the field of view (FOV).
A figure of merit for spatial accuracy is the Dice coefficient (DC). For phantoms
without background concentration, the coefficient extracts the precision of the image
acquisition and reconstruction to correctly position the contrast agent into the image
and the ability of the image reconstruction to reduce scatter background and noise.
The DC is calculated as follows:
DC ¼
2
P I ROIs
P I ROIs þ 2
P I ROIs
,
where I ROIs is the voxel intensity inside the ROIs and I ROIs the voxel intensity
outside of the ROIs. If no contrast agent is located outside of the ROIs, then a perfect
acquisition and reconstruction results in a DC of one.
142
D. Vernekohl and L. Xing
It is possible to perform XFCT imaging with polarized X-rays. In synchrotrons,
for example, X-rays are naturally emitted with a preferred polarization direction. For
excitation it is possible to have an optimized setup with a detector positioning for
suppressed scatter contamination. The reconstructed images in Fig. 4 show how this
is beneficial for XFCT imaging performance.
8 Figures of Merit for Performance Analysis
The direct performance comparison of different systems and imaging modes is a
delicate exercise as different studies utilize different system parameters for their
experiments and different figures of merit for the performance analysis. The imaging
sensitivity and resolution are commonly assessed in phantom experiments. Here, we
propose some imaging configurations and figure of merits which have been proven
useful for the performance analysis.
The molecular sensitivity is usually determined by measuring various mediumsized cylinders with different concentrations of contrast agent. The lowest detectable
contrast agent concentration is then retrieved by a linear least square fit to the
contrast-to-noise ratio (CNR) to concentration ratio where a contrast-to-noise ratio
of 5 (Rose Criterion) is considered the minimal detection limit. In this context, the
CNR is defined by:
CNR ¼
μ ROI À μ bkg
σ bkg
,
where μ ROI , μ bkg , and σ bkg are the average voxel intensity of the region of interest
(ROI) and background (bkg) and the standard deviation of the voxel intensity within
the background region, respectively. Usually, the background region is a ROI sized
region defined in the center of the field of view (FOV).
A figure of merit for spatial accuracy is the Dice coefficient (DC). For phantoms
without background concentration, the coefficient extracts the precision of the image
acquisition and reconstruction to correctly position the contrast agent into the image
and the ability of the image reconstruction to reduce scatter background and noise.
The DC is calculated as follows:
DC ¼
2
P I ROIs
P I ROIs þ 2
P I ROIs
,
where I ROIs is the voxel intensity inside the ROIs and I ROIs the voxel intensity
outside of the ROIs. If no contrast agent is located outside of the ROIs, then a perfect
acquisition and reconstruction results in a DC of one.
142
D. Vernekohl and L. Xing