The O-arm is a cone beam imaging system designed primarily to support orthopedic surgery and is also used for image-guided and
vascular surgery. Using a gantry that can be opened or closed, the O-arm can function as a 2-dimensional (2D) fluoroscopy device or
collect 3-dimensional (3D) volumetric imaging data like a CT system. Clinical applications of the O-arm in spine surgical procedures,
assessment of pedicle screw position, and kyphoplasty procedures show that the O-arm 3D mode provides enhanced imaging
information compared to radiographs or fluoroscopy alone. In this study, the image quality of an O-arm system was quantitatively
evaluated. A 20 cm diameter CATPHAN 424 phantom was scanned using the pre-programmed head protocols: small/medium (120
kVp, 100 mAs), large (120 kVp, 128 mAs), and extra-large (120 kVp, 160 mAs) in 3D mode. High resolution reconstruction mode
(512×512×0.83 mm) was used to reconstruct images for the analysis of low and high contrast resolution, and noise power spectrum.
MTF was measured using the point spread function. The results show that the O-arm image is uniform but with a noise pattern which
cannot be removed by simply increasing the mAs. The high contrast resolution of the O-arm system was approximately 9 lp/cm. The
system has a 10% MTF at 0.45 mm. The low-contrast resolution cannot be decided due to the noise pattern. For surgery where
locations of a structure are emphasized over a survey of all image details, the image quality of the O-arm is well accepted clinically.
MRI applications often require high spatial and/or temporal resolution within a region of interest (ROI) such as for perfusion studies.
In theory, both spatial resolution and temporal resolution can be significantly improved using a ROI-focused MRI data acquisition
scheme. However, in radial MRI, there is no such acquisition-based solution available. Traditional reconstruction methods to image
the ROI by reducing the field of view produce aliasing artifacts when the dataset becomes truncated. Here we propose an interior
MRI methodology to perform ROI reconstruction without artifacts. Methods: In contrast to the conventional wisdom that the interior
problem does not have a unique solution, interior tomography has been recently proposed as an exact and stable solution to this longstanding
problem. In this project, a ROI-focused radial MRI data acquisition scheme was developed, aided by a dedicated digital
filter. We implemented this method in a 4T 90 cm bore Oxford magnet with a GE phantom and a transceiver TEM head coil. The
parameters were 4 gauss/cm sonata gradients, 5 mm slice thickness, TE=30 ms, TR=200 ms, FOVs of 40 cm and 12 cm respectively.
Results: Both numerical simulation and phantom experiments have demonstrated that the proposed interior MRI method can exactly
reconstruct a ROI with increased spatial resolution (~4 fold) while keeping the same temporal resolution. The image artifacts from
truncated projections are effectively eliminated. No crosstalk with the outside ROI region is involved using the proposed method.
Conclusions: Our interior radial MRI method can be used for zoomed-in and fast
Purpose: To develop robust, novel segmentation and co-registration software to analyze
temporally overlapping CT angiography datasets, with an aim to permit automated measurement
of regional aortic pulsatility in patients with abdominal aortic aneurysms.
Methods: We perform retrospective gated CT angiography in patients with abdominal aortic
aneurysms. Multiple, temporally overlapping, time-resolved CT angiography datasets are
reconstructed over the cardiac cycle, with aortic segmentation performed using a priori anatomic
assumptions for the aorta and heart. Visual quality assessment is performed following automatic
segmentation with manual editing. Following subsequent centerline generation, centerlines are
cross-registered across phases, with internal validation of co-registration performed by
examining registration at the regions of greatest diameter change (i.e. when the second derivative
is maximal).
Results: We have performed gated CT angiography in 60 patients. Automatic seed placement is
successful in 79% of datasets, requiring either no editing (70%) or minimal editing (less than 1
minute; 12%). Causes of error include segmentation into adjacent, high-attenuating, nonvascular
tissues; small segmentation errors associated with calcified plaque; and segmentation of
non-renal, small paralumbar arteries. Internal validation of cross-registration demonstrates
appropriate registration in our patient population. In general, we observed that aortic pulsatility
can vary along the course of the abdominal aorta. Pulsation can also vary within an aneurysm as
well as between aneurysms, but the clinical significance of these findings remain unknown.
Conclusions: Visualization of large vessel pulsatility is possible using ECG-gated CT
angiography, partial scan reconstruction, automatic segmentation, centerline generation, and coregistration
of temporally resolved datasets.
The radiant quantum efficiency (RQE) of x-ray phosphors is defined as the ratio of the emitted luminescent power and
the power absorbed by the material. For a given x-ray imaging technique, a high RQE phosphor means a lower x-ray
exposure to patients and a better image quality. To improve RQE, phosphors such as LiF and BaFX:Eu ( X = Br, Cl, I)
host lattices, which are commonly used in medical dosimetry and imaging system, are always doped with Cu, Ti, or Tb.
Experimental observations showed that these dopants can increase phosphor RQE significantly. In this study, we
theoretically investigated the effect of additional dopants on the RQE of LiF:Mg and BaFX:Eu host lattices using
Density Functional Theory (DFT) in the Local Density Approximation (LDA). Self-consistent charge density
calculations were performed. The energy loss function L(w) was obtained and used to calculate the RQE for different
phosphors. The results showed that additional dopants produced changes in the optical properties of the phosphors,
particularly the energy loss function L(w). Doping with more substitutional impurities increased the RQE of all host
lattices except the BaFI lattice where the RQE decreased.
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