An in-vivo feasibility study of potentially improved atherosclerosis CT imaging is presented. By administration of two
different contrast agents to rabbits with induced atherosclerotic plaques we aim at identifying both soft plaque and vessel
lumen simultaneously. Initial injection of iodinated nanoparticle (INP) contrast agent (N1177 - Nanoscan Imaging), two
to four hours before scan, leads to its later accumulation in macrophage-rich soft plaque, while a second gadolinium
contrast agent (Magnevist) injected immediately prior to the scan blends with the aortic blood. The distinction between
the two agents in a single scan is achieved with a double-layer dual-energy MDCT (Philips Healthcare) following
material separation analysis using the reconstructed images of the different x-ray spectra. A single contrast agent
injection scan, where only INP was injected two hours prior to the scan, was compared to a double-contrast scan taken
four hours after INP injection and immediately after gadolinium injection. On the single contrast agent scan we observed
along the aorta walls, localized iodine accumulation which can point on INP uptake by atherosclerotic plaque. In the
double-contrast scan the gadolinium contributes a clearer depiction of the vessel lumen in addition to the lasting INP
presence. The material separation shows a good correlation to the pathologies inferred from the conventional CT images
of the two different scans while performing only a single scan prevents miss-registration problems and reduces radiation
dose. These results suggest that a double-contrast dual-energy CT may be used for advanced clinical diagnostic
applications.
We have analyzed 144 ECG wave-forms that were taken during cardiac CT exams to determine in retrospect the
optimized timing for updating the gantry rotation-time. A score was defined, according to the number of heart beats
during X-ray on, which fulfill the temporal resolution (tR)condition, tR<100mSec. The temporal resolution calculation
was based on dual-cycle π/2 sector segmentation, where the data required for any image is collected during two heart
cycle. The results yield a significant improvement of the tR score with the rotation-time update method relative to using
a fixed minimal rotation-time of the gantry. The analysis suggest that full heart scan with better than 100mSec temporal
resolution per slice can routinely be achieved in 128 slices MSCT scanner by performing gantry rotation-time -update
after patient starts its breath hold. At these conditions the required breath-hold time is expected to be less than 15
seconds.
Cone beam reconstructed cardiac CT images suffer from characteristic streak artifacts that affect the quality of coronary artery imaging. These artifacts arise from inhomogeneous distribution of noise. While in non-tagged reconstruction inhomogeneity of noise distribution is mainly due to anisotropy of the attenuation of the scanned object (e.g. shoulders), in cardiac imaging it is largely influenced by the non-uniform distribution of the acquired data used for reconstructing the heart at a given phase. We use a cardiac adaptive filter to reduce these streaks. In difference to previous methods of adaptive filtering that locally smooth data points on the basis of their attenuation values, our filter is applied as a function of the noise distribution of the data as it is used in the phase selective reconstruction. We have reconstructed trans-axial images without adaptive filtering, with a regular adaptive filter and with the cardiac adaptive filter. With the cardiac adaptive filter significant reduction of streaks is achieved, and thus image quality is improved. The coronary vessel is much more pronounced in the cardiac adaptive filtered images, in slab MIP the main coronary artery branches are more visible, and non-calcified plaque is better differentiated from vessel wall. This improvement is accomplished without altering significantly the border definition of calcified plaques.
A dose optimization tool for CT scanners is presented using patient raw data to calculate noise. The tool uses a single patient image which is modified for various lower doses. Dose optimization is carried out without extra measurements by interactively visualizing the dose-induced changes in this image. This tool can be used either off line, on existing image(s) or, as a pre - requisite for dose optimization for the specific patient, during the patient clinical study. The algorithm of low-dose simulation consists of reconstruction of two images from a single measurement and uses those images to create the various lower dose images. This algorithm enables fast simulation of various low dose (mAs) images on a real patient image.
Fast 16-slice spiral CT delivers superior cardiac visualization in comparison to older generation 2- to 8-slice scanners due to the combination of high temporal resolution along with isotropic spatial resolution and large coverage. The large beam opening of such scanners necessitates the use of adequate algorithms to avoid cone beam artifacts. We have developed a multi-cycle phase selective 3D back projection reconstruction algorithm that provides excellent temporal and spatial resolution for 16-slice CT cardiac images free of cone beam artifacts.
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