This research addresses the problem of determining the location of a pulmonary nodule in a radiograph with the aid of a
pre-existing computed tomographic (CT) scan. The nodule is segmented in the radiograph using a level set segmentation
method that incorporates characteristics of the nodule in a digitally reconstructed radiograph (DRR) that is calculated
from the CT scan. The segmentation method includes two new level set energy terms. The contrast energy seeks to
increase the contrast of the segmented region relative to its surroundings. The gradient direction convergence energy is
minimized when the intensity gradient direction in the region converges to a point. The segmentation method was tested
on 23 pulmonary nodules from 20 cases for which both a radiographic image and CT scan were collected. The mean
nodule effective diameter is 22.5 mm. The smallest nodule has an effective diameter of 12.0 mm and the largest an
effective diameter of 48.1 mm. Nodule position uncertainty was simulated by randomly offsetting the true nodule center
from an aim point. The segmented region is initialized to a circle centered at the aim point with a radius that is equal to
the effective radius of the nodule plus a 10.0 mm margin. When the segmented region that is produced by the proposed
method is used to localize the nodule, the average reduction in nodule-position uncertainty is 46%. The relevance of this
method to the detection of radiotherapy targets at the time of treatment is discussed.
Patient setup error is one of the major causes of tumor position uncertainty in radiotherapy for extracranial targets,
which can result in a decreased radiation dose to the tumor and an increased dose to the normal tissues. Therefore, it
is a common practice to verify the patient setup accuracy by comparing portal images with a digitally reconstructed
radiograph (DRR) reference image. This paper proposes a practical method of portal image and DRR fusion for
patient setup verification. As a result of the mean intensity difference between the inside and outside of the actual
radiation region in the portal image, the image fusion in this work is fulfilled by applying an image registration
process to the contents inside or outside of the actual radiation region in the portal image and the relevant contents
that are extracted, accordingly, from the DRR image. The image fusion can also be fulfilled statistically by applying
two separate image registration processes to the inside and outside of the actual radiation regions. To segment the
image registration contents, automatic or semiautomatic region delineation schemes are employed that aim at
minimizing users' operation burden, while at the same time maximizing the use of human intelligence. To achieve
an accurate and fast delineation, this paper proposes using adaptive weight in the conventional level-set contour-finding
algorithm for the automatic delineation scheme, as well as the use of adaptive banding in the conventional
Intelligent Scissors algorithm for the semiautomatic delineation scheme.
Blue-noise dither halftoning methods have been found to produce images with pleasing visual characteristics. Results similar to those generated with error-diffusion algorithms can be obtained using an image processing algorithm that is computationally much simpler to implement. The various techniques that have been used to design blue-noise dither matrices are reviewed and compared. In particular, a series of visual cost function based methods and several techniques that involve designing the dither matrices by analyzing the spatial dot distribution are discussed. Ways to extend the basic blue-noise dither techniques to multilevel and color output devices are also described, including recent advances in the design of jointly optimized color blue-noise dither matrices.
Recent experiments that measure the effects of the photoinduced generation and transport of charge on the refractive index of polymeric films having a second-order nonlinear optical response are reported. Two approaches were taken to observe these effects. In the first approach, the photoconductive and light refraction processes were separated by confining these functions to separate layers in a multilayer structure. In the second approach, photoconduction and refraction functions were combined in the same layer. The modulation of the refractive index was then measured in response to photoconductions.
Langmuir-Blodgett films have been fabricated of a prepolymerized amphiphile containing a chromophore of high second-order nonlinear optical activity. Thick films, containing as many as 262 layers of noncentrosymmetric structure have been prepared by alternate deposition of the dye polymer and several different materials. In contrast to previous literature reports on Langmuir-Blodgett films of other polymeric dyes, these films show the theoretically expected quadratic dependence of second harmonic generation with film thickness. Polarization studies of the second harmonic generation demonstrate that the chromophores are highly ordered in these films. In addition, by using all-polymeric materials it has been possible to fabricate a waveguide of these films with optical attenuation of about 1 dB cm-1, substantially lower than has been previously reported for Langmuir-Blodgett films even without a noncentrosymmetric structure.
We have prepared Langmuir-Blodgett monolayer and multilayer films of a polymeric amphiphile with a side chain containing a chromophore of high molecular hyperpolarizability for second order nonlinear optics. Using optical techniques including polarized transmission and attenuated total reflectance spectroscopies, second harmonic generation, and ellipsometry, we have characterized the orientational order of the chromophore and other polymer groups in the films. The high degree of chromophoric order seen in these films indicates that such polymers are good candidates as materials to fabricate Langmuir-Blodgett films for nonlinear optical applications.
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