Soft Tissue Visualization Using a Highly Efficient Megavoltage Cone ...

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(a): 0.025cGy receptor 1 (b): 0.035cGy receptor 2 3.2 Reconstructed Images 3.2.1 Phantom Images Figure 3: QC-3V phantom images Figure 4 shows the QUASAR and contrast/spatial resolution (ball) phantom images that were acquired with receptor 1. The total delivered dose was 18cGy and no preprocessing filtering used. From Figure 4(a) 2% electron density variation between acrylic and trabecular bone is resolvable without applying the adaptive filtering. Applying the resolution/dose adaptive filter will reduce the standard deviation in pixel intensities by a factor of ~0.5. <strong>Using</strong> the ratio of pixel intensity difference (due to density difference) to root mean square uncertainty in pixel intensities of receptor 1, it can be estimated that the receptor 2 due to its higher CNR compared to receptor 1 and in combination with preprocessing adaptive filtering is capable of resolving 1% contrast with radiation doses as low as 10cGy. The left image on figure 5 illustrates that muscle insert with contrast of 0.5% is resolvable with receptor 1 using 163cGy dose and without applying dose/resolution adaptive filtering. By using only the odd projections used for the previous reconstruction (163cGy) that corresponds to the dose value of 81.5cGy (center image of figure 5), the 0.5% contrast is still detectable. The right hand image of figure 5 shows that the minimum required dose in which the 0.5 % contrast becomes discernible with receptor 1 and by applying the adaptive filter is ~41MU (threshold of detection of 0.5% contrast). Note that all figure 5 images have the cupping artefacts that are due to the scattered, and no scatter/beam profile corrections have been applied to these images. Figures 4(b) and 6(a) illustrate that the 2mm air holes and gold seeds implanted (1mm x 3mm) within a head phantom are resolvable. Figure 6 (a) shows axial, coronal and sagittal images of a head phantom that is acquired with receptor 2 by delivering only 1cGy. Figure 6 (b) displays the raw image (no adaptive filtering) of the 2D projection of this phantom acquired with 0.005cGy. The mean/standard deviation (SD) ratios of this 2D projection (on open field regions) before and after applying dose/resolution adaptive filter are 26 and 68, respectively. This indicates the possibility of the use of receptor 2 for 4D-CT.
(a) 18cGy QUASAR (b) 18cGy contrast/spatial resolution ball phantom Figure 4: QUASAR and contrast/spatial resolution phantom images with receptor 1 (without preprocessing adaptive filtering) Figure 5: Contrast/spatial resolution phantom images with receptor 1. Left: 163cGy, Center: 81.5cGy, Right: 41cGy with adaptive filtering (a) 1cGy reconstructed images (b) Projection image with 0.005cGy
Page 1 and 2: Soft Tissue Visualization Using a H
Page 3 and 4: Two image receptors that were used
Page 5: 3.1 2D QC-3V phantom Projections Fi
Page 9 and 10: Figure 8: Axial view of the pelvic
Page 11 and 12: Figure 13 shows neck/chest MVCT axi

Soft Tissue Visualization Using a Highly Efficient Megavoltage Cone ...

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