STATISTICAL SHAPE ANALYSIS OF BRAIN STRUCTURES USING SPHERICAL WAVELETS

We present a novel method of statistical surface-based morphometry based on the use of non-parametric permutation tests and a spherical wavelet (SWC) shape representation. As an application, we analyze two brain structures, the caudate nucleus and the hippocampus, and compare the results obtained to shape analysis using a sampled point representation. Our results show that the SWC representation indicates new areas of significance preserved under the FDR correction for both the left caudate nucleus and left hippocampus. Additionally, the spherical wavelet representation provides a natural way to interpret the significance results in terms of scale in addition to knowing the spatial location of the regions.

On the psychophysics of the shape triangle

We earlier introduced an approach to categorical shape description based on the singularities (shocks) of curve evolution equations. We now consider the simplest compositions of shocks, and show that they lead to three classes of parametrically ordered shape sequences, organized along the sides of a shape triangle. By conducting several psychophysical experiments we demonstrate that shock-based descriptions are predictive of performance in shape perception. Most significantly, the experiments reveal a fundamental difference between perceptual effects dominated by when shocks form with respect to one another, versus those dominated by where they form. The shock-based theory provides a foundation for unifying tasks as diverse as shape bisection, recognition, and categorization.

Postradiation therapy adenosquamous cell carcinoma of the prostate

The objective of this study was to present two cases of adenosquamous cell carcinoma of the prostate following radiation therapy. Two patients with history of prostate cancer treated with radiation therapy presented with rectal bleeding and a large ulcerated rectal mass. The rectal biopsy revealed on both cases squamous cell carcinoma. The initial diagnosis was invasive squamous cell carcinoma from anal origin. Both patients underwent pelvic exenteration with continent urinary diversion. After extensive histological sampling and immuno-histochemisty, they were correctly diagnosed of adenosquamous cell carcinoma of the prostate with invasion of the rectum. The patients died 6 and 16 months after surgery with widespread metastases. A review of the literature is presented. Adenosquamous cell carcinoma of the prostate is an unusual histological variant of prostate cancer. To our knowledge, only three cases of adenosquamous cell carcinoma of the prostate following radiation therapy have been reported. The unusual clinical and histopathological features of the two cases reported here led to an initial mistaken diagnosis. Adenosquamous cell carcinoma of the prostate should be considered in the differential diagnosis when a patient with prostate cancer develops a rectal mass or rectal bleeding following radiation therapy and the rectal biopsy reveals squamous cell carcinoma. Prostate Cancer and Prostatic Diseases (2000) 3, 53-56

Nondistorting flattening maps and the 3-D visualization of colon CT images

In this paper, we consider a novel three-dimensional (3-D) visualization technique based on surface flattening for virtual colonoscopy. Such visualization methods could be important in virtual colonoscopy because they have the potential for noninvasively determining the presence of polyps and other pathologies. Further, we demonstrate a method that presents a surface scan of the entire colon as a cine, and affords the viewer the opportunity to examine each point on the surface without distortion. We use certain angle-preserving mappings from differential geometry to derive an explicit method for flattening surfaces obtained from 3-D colon computed tomography (CT) imagery. Indeed, we describe a general method based on a discretization of the Laplace-Beltrami operator for flattening a surface into the plane in a conformal manner. From a triangulated surface representation of the colon, we indicate how the procedure may be implemented using a finite element technique, which takes into account special boundary conditions. We also provide simple formulas that may be used in a real-time cine to correct for distortion.

Knowledge-based segmentation of SAR data with learned priors

An approach for the segmentation of still and video synthetic aperture radar (SAR) images is described. A priori knowledge about the objects present in the image, e.g., target, shadow and background terrain, is introduced via Bayes' rule. Posterior probabilities obtained in this way are then anisotropically smoothed, and the image segmentation is obtained via MAP classifications of the smoothed data. When segmenting sequences of images, the smoothed posterior probabilities of past frames are used to learn the prior distributions in the succeeding frame. We show with examples from public data sets that this method provides an efficient and fast technique for addressing the segmentation of SAR data.

On the Laplace-Beltrami operator and brain surface flattening

In this paper, using certain conformal mappings from uniformization theory, we give an explicit method for flattening the brain surface in a way which preserves angles. From a triangulated surface representation of the cortex, we indicate how the procedure may be implemented using finite elements. Further, we show how the geometry of the brain surface may be studied using this approach.

Area and length minimizing flows for shape segmentation

A number of active contour models have been proposed that unify the curve evolution framework with classical energy minimization techniques for segmentation, such as snakes. The essential idea is to evolve a curve (in two dimensions) or a surface (in three dimensions) under constraints from image forces so that it clings to features of interest in an intensity image. The evolution equation has been derived from first principles as the gradient flow that minimizes a modified length functional, tailored to features such as edges. However, because the flow may be slow to converge in practice, a constant (hyperbolic) term is added to keep the curve/surface moving in the desired direction. We derive a modification of this term based on the gradient flow derived from a weighted area functional, with image dependent weighting factor. When combined with the earlier modified length gradient flow, we obtain a partial differential equation (PDE) that offers a number of advantages, as illustrated by several examples of shape segmentation on medical images. In many cases the weighted area flow may be used on its own, with significant computational savings.

Electroencephalogram activity in the anoxic turtle brain

The anoxia-tolerant turtle brain slowly undergoes a complex sequence of changes in electroencephalogram (EEG) activity as the brain systematically downregulates its energy demands. Following N2 respiration, the root mean square voltage rapidly fell, reaching approximately 20% of normoxic levels after approximately 100 min of anoxia. During the first 20- to 40-min transition period, the power of the EEG decreased substantially, particularly in the 12- to 24-Hz band, with low-amplitude slow wave activity predominating (3-12 Hz). Bursts of high voltage rhythmic slow (approximately 3-8 Hz) waves were seen during the 20- to 100-min period of anoxia, accompanied by large sharp waves. During the next 400 min of N2 respiration, two distinct patterns of electrical activity characterized the anoxic turtle brain: 1) a sustained but depressed activity level, with an EEG amplitude approximately 20% of the normoxic control and with total EEG power reduced by one order of magnitude at all frequencies, and 2) short (3-15 s) periodic (0.5-2/min) bursts of mixed-frequency activity that interrupted the depressed activity state. We speculate that the EEG patterns seen during sustained anoxia represent the minimal or basic electrical activities that are compatible with the survival of the anoxic turtle brain as an integrated unit, which allow the brain to return to normal functioning when air respiration resumed.

Does inflammation contribute to the eradication of basal cell carcinoma following curettage and electrodesiccation?

BACKGROUND

Curettage and electrodesiccation (C&D) is probably the technique most frequently utilized by dermatologists to treat basal cell carcinomas (BCC). From histologic studies, it appears C&D does not completely mechanically remove all nests of BCC in a substantial number of cases. Nevertheless, the reported 5-year reoccurrence rate following C&D is significantly less than this histologically observed residual tumor frequency immediately following C&D. Among the multiple possibilities that exist to explain why these residual nests do not appear as recurrent tumor more frequently is the theory that inflammation developing after C&D clears residual tumor.

OBJECTIVE

To test the hypothesis that inflammation developing after C&D clears residual tumor not mechanically removed by the procedure.

METHODS

The frequency of residual BCC detected histologically immediately following C&D was compared with the frequency 1 month after the C&D, an amount of time in which an effect (if any) of inflammation could occur.

RESULTS

Twenty-two of 29 primary BCC < 1 cm treated by C&D were tumor free immediately following the procedure (clearance rate, 75.9%). Eleven of 14 primary BCC < 1 cm treated by C&D then allowed to granulate 1 month before excision and histologic analysis were tumor free, for a clearance rate of 78.6%. Examination of larger tumors immediately following C&D revealed size is a significant variable for clearance rates. Eleven primary BCC > 1 cm but < 2 cm were examined histologically immediately following C&D; only three were tumor free for a clearance rate of 27.3%. Only one of five tumors > 2 cm thus treated was tumor free, for a clearance rate of 20%. Nine recurrent BCC of various sizes were treated by C&D and immediately examined histologically. Two were tumor free for a clearance rate of 22.2%. Two recurrent BCC were allowed to heal 1 month following C&D; one of these was tumor free when excised.

CONCLUSION

For primary BCC < 1 cm, no evidence was found that inflammation occurring over 1 month following C&D clears residual tumor. It was also noted that C&D fails to completely remove tumor in a large majority of primary BCC > 1 cm, and in recurrent BCC.

A geometric snake model for segmentation of medical imagery

In this note, we employ the new geometric active contour models formulated in [25] and [26] for edge detection and segmentation of magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound medical imagery. Our method is based on defining feature-based metrics on a given image which in turn leads to a novel snake paradigm in which the feature of interest may be considered to lie at the bottom of a potential well. Thus, the snake is attracted very quickly and efficiently to the desired feature.

Behavioral analysis of anisotropic diffusion in image processing

In this paper, we analyze the behavior of the anisotropic diffusion model of Perona and Malik (1990). The main idea is to express the anisotropic diffusion equation as coming from a certain optimization problem, so its behavior can be analyzed based on the shape of the corresponding energy surface. We show that anisotropic diffusion is the steepest descent method for solving an energy minimization problem. It is demonstrated that an anisotropic diffusion is well posed when there exists a unique global minimum for the energy functional and that the ill posedness of a certain anisotropic diffusion is caused by the fact that its energy functional has an infinite number of global minima that are dense in the image space. We give a sufficient condition for an anisotropic diffusion to be well posed and a sufficient and necessary condition for it to be ill posed due to the dense global minima. The mechanism of smoothing and edge enhancement of anisotropic diffusion is illustrated through a particular orthogonal decomposition of the diffusion operator into two parts: one that diffuses tangentially to the edges and therefore acts as an anisotropic smoothing operator, and the other that flows normally to the edges and thus acts as an enhancement operator.

Report of the working group on inhalation carcinogenesis, with special reference to cigarette smoke. Prepared by the Working Group of the Commission on Experimental Oncology, International Union Against Cancer

The working party served to bring together for 3 days a number of people who were either actually engaged in the field of inhalation carcinogenesis or in pertinent related areas. Sufficient time was available for an open, frank discussion of the problems and pitfalls, the design of equipment for exposing animals to fresh cigarette smoke, and the suitability of various species for bioassay of cigarette smoke.