Recovery of 3D volume from 2-tone images of novel objects

In 2-tone images (e.g., Dallenbach's cow), only two levels of brightness are used to convey image structure-dark object regions and shadows are turned to black and light regions are light regions are turned white. Despite a lack of shading, hue and texture information, many 2-tone images of familiar objects and scenes are accurately interpreted, even by naive observers. Objects frequently appear fully volumetric and are distinct from their shadows. If perceptual interpretation of 2-tone images is accomplished via bottom-up processes on the basis of geometrical structure projected to the image (e.g., volumetric parts, contour and junction information) novel objects should appear volumetric as readily as their familiar counterparts. We demonstrate that accurate volumetric representations are rarely extracted from 2-tone images of novel objects, even when these objects are constructed from volumetric primitives such as generalized cones (Marr, D., Nishihara, H.K., 1978. Proceedings of the Royal Society London 200, 269-294; Biederman, I. 1985. Computer Vision, Graphics, and Image Processing 32, 29-73), or from the rearranged components of a familiar object which is itself recognizable as a 2-tone image. Even familiar volumes such as canonical bricks and cylinders require scenes with redundant structure (e.g., rows of cylinders) or explicit lighting (a lamp in the image) for recovery of global volumetric shape. We conclude that 2-tone image perception is not mediated by bottom-up extraction of geometrical features such as junctions or volumetric parts, but may rely on previously stored representations in memory and a model of the illumination of the scene. The success of this top-down strategy implies it is available for general object recognition in natural scenes.     

3D visualization library for multimodal medical images

To clarify the control mechanism of ventilation during posture change, ventilatory parameters, PETCO2, and ventilatory response to CO2 were examined in 11 healthy male subjects at supine (0 degrees) and 75 degrees head-up tilt positions. Minute expiratory ventilation (V.E), tidal volume (VT), respiratory frequency (f), end-tidal and transcutaneous PCO2 and CO2 output (V.CO2), and ventilatory response to CO2 were measured during a steady state condition. V.E (V.A) and VT increased significantly at 75 degrees tilt with significant decrease in PETCO2 from 40.1 mmHg (0 degrees) to about 36.1 mmHg (75 degrees). Transcutaneous PCO2 also decreased during tilt, by 3.3 mmHg. Physiological dead space (VD/VT) and V.CO2, however, remained unchanged, and ventilatory equivalent (V.E/V.CO2, V.A/V.CO2) increased significantly. The CO2-ventilatory response curve shifted upward (or leftward) without significant change in the response slope. At 75 degrees tilt, EMG activity of gastro-cnemius muscle increased. These findings suggested that PETCO2 decreased because of increased V.E (V.A) with a leftward shift of CO2-ventilatory response curve. Various signals such as afferents from lower extremities might have net stimulatory effects on a CO2-ventilation control system to reset the controlled level of PETCO2 to a lower range, but without significant change in CO2-ventilatory response during upright position.     

Watershed-based segmentation of 3D MR data for volume quantization

The aim of this work is the development of a semiautomatic segmentation technique for efficient and accurate volume quantization of Magnetic Resonance (MR) data. The proposed technique uses a 3D variant of Vincent and Soilles immersion-based watershed algorithm that is applied to the gradient magnitude of the MR data and that produces small volume primitives. The known drawback of the watershed algorithm, oversegmentation, is strongly reduced by a priori application of a 3D adaptive anisotropic diffusion filter to the MR data. Furthermore, oversegmentation is a posteriori reduced by properly merging small volume primitives that have similar gray level distributions. The outcome of the proceeding image processing steps is presented to the user for manual segmentation. Through selection of volume primitives, the user quickly segments of first slice, which contains the object of interest. Afterwards, the subsequent slices are automatically segmented by extrapolation. Segmentation results are contingently manually corrected. The proposed segmentation technique is tested on phantom objects, where segmentation errors less than 2% are observed. In addition, the technique is demonstrated on 3D MR data of the mouse head from which the cerebellum is extracted. Volumes of the mouse cerebellum and the mouse brains in toto are calculated.     

Visualizing 3D objects from 2D cross sectional images displayed in-situ versus ex-situ.

The present research investigates how mental visualization of a 3D object from 2D cross sectional images is influenced by displacing the images from the source object, as is customary in medical imaging. Three experiments were conducted to assess people’s ability to integrate spatial information over a series of cross sectional images in order to visualize an object posed in 3D space. Participants used a hand-held tool to reveal a virtual rod as a sequence of cross-sectional images, which were displayed either directly in the space of exploration (in-situ) or displaced to a remote screen (ex-situ). They manipulated a response stylus to match the virtual rod’s pitch (vertical slant), yaw (horizontal slant), or both. Consistent with the hypothesis that spatial colocation of image and source object facilitates mental visualization, we found that although single dimensions of slant were judged accurately with both displays, judging pitch and yaw simultaneously produced differences in systematic error between in-situ and ex-situ displays. Ex-situ imaging also exhibited errors such that the magnitude of the response was approximately correct but the direction was reversed. Regression analysis indicated that the in-situ judgments were primarily based on spatiotemporal visualization, while the ex-situ judgments relied on an ad hoc, screen-based heuristic. These findings suggest that in-situ displays may be useful in clinical practice by reducing error and facilitating the ability of radiologists to visualize 3D anatomy from cross sectional images. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

3D surface rendering of images from multiple MR pulse sequences in the pre-operative evaluation of hepatic lesions

PURPOSE: To develop a method for making three-dimensional (3D) reconstructions of liver vessels and hepatic lesions from different MR data sets. MATERIAL AND METHODS: To reduce the time required for segmentation and reconstructions, we used T1, T2 and phase contrast angiography, optimised for liver, lesion and vessels respectively. Following segmentation and reconstruction, the different volumes were combined on the same workstation and presented to the surgeon. RESULTS AND CONCLUSION: Segmentation and reconstruction took 1-2 h. To be able to combine the volumes from the different data sets, certain criteria had to be fulfilled: a) the field of view had to be constant; b) the same volume had to be scanned every time which meant that the slice thickness and the number of slices could be adjusted as long as the volume covered was the same; and c) the positioning of each volume had to be identical between every scan. The resulting 3D reconstruction gave the surgeon a clear appreciation of the different lesions and their relation to the different liver segments in the pre-operative planning of hepatic resections.     

A method for selecting data subsets from large medical data bases

Response of tissues to homeostatic signals may play a role in the mediation of nutrient partitioning effects of somatotropin. To investigate this, the effects of exogenous porcine somatotropin (pST) on the metabolic responses to a series of intravenous challenges with dextrose, insulin and epinephrine were examined in twelve crossbred barrows (65 kg). In addition, the hyperinsulinemic-euglycemic clamp technique was used to further explore effects of pST on insulin resistance in eight of these animals. Pigs received daily sc injections of either pituitary-derived pST (120 micrograms/kg bw) or an equivalent volume of excipient for 28 d. Treatment with pST resulted in a chronic elevation of plasma glucose, insulin and non-esterified fatty acid concentrations and lowered glucagon concentrations. Acute iv challenges of dextrose (100 mg/kg bw), insulin (1.0 micrograms/kg bw), and epinephrine (2.2 micrograms/kg bw) were administered on days 21, 22, and 23 of the treatment period, respectively. Hyperinsulinemic-euglycemic clamps were carried out on day 28. Effects of pST were most dramatic for responses associated with insulin. In pST-treated pigs, insulin response to dextrose infusion was enhanced, while glucose response to insulin was attenuated and glucose clearance rate was reduced. During the hyperinsulinemic-euglycemic clamp, dextrose infusion rate required to maintain euglycemia during physiologic elevations of insulin was reduced in pST-treated pigs to 28% of control. In pST-treated pigs, glucose response to epinephrine challenge was halved, while insulin response was increased three-fold. Therefore, one mechanism by which pST shifts the nutrient partition is by altering metabolic responses to homeostatic signals. In growing pigs, this is especially evident for glucose response to insulin.     

A reproducible method for automated extraction of brain volumes from 3D human head MR images

PURPOSE: To assess the frequency and prognosis of skin recurrences after breast-conserving therapy (BCT) compared with other breast recurrences. MATERIALS AND METHODS: From 1968 to 1986, 1,624 patients with unilateral stage I or II breast cancer treated with BCT at the Joint Center for Radiation Therapy (Boston, MA) underwent gross tumor excision and received a dose of > or = 60 Gy to the tumor bed. Skin recurrences (SR) were defined as breast recurrences without associated parenchymal disease. An invasive breast recurrence with any parenchymal disease noted clinically or radiographically was scored as an other breast recurrence (OBR). Median follow-up for survivors was 137 months. RESULTS: SR represented 8% (18 of 229) of all breast recurrences and occurred in 1.1% of all patients. The outcome after local recurrence was different for patients with SR and invasive OBR. Patients with SR more frequently had uncontrolled local failure (50%; 9 of 18) than did patients with OBR (14%; 26 of 188) (P = .0007). Forty-four percent (8 of 18) of patients with SR had distant metastasis simultaneously or within 2 months of the recurrence compared with 5% (9 of 188) of invasive OBR patients (P < .0001). For patients without distant metastasis at the time of recurrence, the 5-year actuarial rate of development of distant metastasis was 60% for SR patients compared with 39% for invasive OBR patients (P = .07), and the corresponding 5-year actuarial survival rates beyond the time of local failure were 51% and 79%, respectively (P = .06). CONCLUSION: In contrast to other types of invasive breast recurrence after breast-conserving therapy, skin recurrences are rare and are associated with a significantly higher rate of distant metastasis and uncontrolled local disease as well as a lower rate of survival.     

Applicability of semi-automatic segmentation for volumetric analysis of brain lesions

Acute maxillary sinusitis is a common condition requiring broad-spectrum therapy to prevent development of chronic disease. A randomised, double-blind, multicentre study was performed to compare the efficacy and safety of cefuroxime axetil 250 mg twice daily (n = 185) and clarithromycin 250 mg twice daily (n = 185), both administered for 10 days, in the treatment of patients with acute sinusitis. Efficacy was determined by assessment of clinical response at post-treatment and follow-up, and by radiological assessment at pre-treatment and follow-up. Assessment of days absent from work due to illness was also made. In the cefuroxime axetil group, 169/185 (91%) patients were cured/improved at post-treatment, as were 172/185 (93%) patients receiving clarithromycin and, of these, 137/169 (81%) and 143/172 (83%) maintained their response at follow-up. Follow-up radiography showed a reduction in incidence of air fluid level and/or opacification from 96% to 15% (cefuroxime axetil) and from 96% to 11% (clarithromycin), and a decrease in frequency of mucosal thickening from 58% to 28% (cefuroxime axetil) and from 56% to 29% (clarithromycin). Only 10% of patients in either group experienced adverse events and days absent from work were comparable. This study demonstrated clinical equivalence between twice-daily cefuroxime axetil and clarithromycin, both treatments being effective and well tolerated.     

A review of compression methods for medical images in PACS

As an introduction to Section C2 (medical imaging) of track C (Images and PACS) of MIE '97, an appropriate and timely topic concerns the coding for the transmission of medical images in PACS. Speed limitations of existing networks along with the explosive growth of image modalities with extremely high volume outputs have combined to make the issue of medical image coding one of the key considerations in the design of future PACS systems. Both lossless and lossy compression schemes are reviewed and compared, and the compression demands are presented of the main digital medical image modalities.     

A cryptologic based trust center for medical images

OBJECTIVE: To investigate practical solutions that can integrate cryptographic techniques and picture archiving and communication systems (PACS) to improve the security of medical images. DESIGN: The PACS at the University of California San Francisco Medical Center consolidate images and associated data from various scanners into a centralized data archive and transmit them to remote display stations for review and consultation purposes. The purpose of this study is to investigate the model of a digital trust center that integrates cryptographic algorithms and protocols seamlessly into such a digital radiology environment to improve the security of medical images. MEASUREMENTS: The timing performance of encryption, decryption, and transmission of the cryptographic protocols over 81 volumetric PACS datasets has been measured. Lossless data compression is also applied before the encryption. The transmission performance is measured against three types of networks of different bandwidths: narrow-band Integrated Services Digital Network, Ethernet, and OC-3c Asynchronous Transfer Mode. RESULTS: The proposed digital trust center provides a cryptosystem solution to protect the confidentiality and to determine the authenticity of digital images in hospitals. The results of this study indicate that diagnostic images such as x-rays and magnetic resonance images could be routinely encrypted in PACS. However, applying encryption in teleradiology and PACS is a tradeoff between communications performance and security measures. CONCLUSION: Many people are uncertain about how to integrate cryptographic algorithms coherently into existing operations of the clinical enterprise. This paper describes a centralized cryptosystem architecture to ensure image data authenticity in a digital radiology department. The system performance has been evaluated in a hospital-integrated PACS environment.     

Segmentation of 2-D and 3-D objects from MRI volume data using constrained elastic deformations of flexible Fourier contour and surface models

This paper describes a new model-based segmentation technique combining desirable properties of physical models (snakes), shape representation by Fourier parametrization, and modelling of natural shape variability. Flexible parametric shape models are represented by a parameter vector describing the mean contour and by a set of eigenmodes of the parameters characterizing the shape variation. Usually the segmentation process is divided into an initial placement of the mean model and an elastic deformation restricted to the model variability. This, however leads to a separation of biological variation due to a global similarity transform from small-scale shape changes originating from elastic deformations of the normalized model contours only. The performance can be considerably improved by building shape models normalized with respect to a small set of stable landmarks (AC-PC in our application) and by explaining the remaining variability among a series of images with the model flexibility. This way the image interpretation is solved by a new coarse-to-fine segmentation procedure based on the set of deformation eigenmodes, making a separate initialization step unnecessary. Although straightforward, the extension to 3-D is severely impeded by difficulties arising during the generation of a proper surface parametrization for arbitrary objects with spherical topology. We apply a newly developed surface parametrization which achieves a uniform mapping between object surface and parameter space. The 3-D procedure is demonstrated by segmenting deep structures of the human brain from MR volume data.     

Split-and-merge segmentation of magnetic resonance medical images: performance evaluation and extension to three dimensions

Intensity- or edge-based methods of segmentation are often insufficiently robust to be applied to images containing complex anatomical objects, such as those seen in high-resolution magnetic resonance imaging systems. Split-and-merge techniques attempt to overcome these difficulties by using homogeneity measures. Simple modifications to the basic 2D split-and-merge method, based on the principles of simulated annealing and controlled boundary elimination, are developed and discussed. Simulated annealing reduced the number of regions by 22% with a further reduction of 21% achieved through boundary elimination. Smoother regional boundaries are also produced. These methods are extended to true 3D and quantitatively compared with their 2D counterparts. The main advantage of 3D methods is that they produce segmented volumes by directly preserving the connectivity between slices, whereas in 2D, segments have to be grouped together in a post-split-and-merge process. Finally, the properties of the 3D approach are demonstrated by the automatic quantitation of brain ventricle volume, producing estimates to within 7% of validated manual methods.     

An image-processing system for qualitative and quantitative volumetric analysis of brain images

In this work, we developed, implemented, and validated an image-processing system for qualitative and quantitative volumetric analysis of brain images. This system allows the visualization and quantitation of global and regional brain volumes. Global volumes were obtained via an automated adaptive Bayesian segmentation technique that labels the brain into white matter, gray matter, and cerebrospinal fluid. Absolute volumetric errors for these compartments ranged between 1 and 3% as indicated by phantom studies. Quantitation of regional brain volumes was performed through normalization and tessellation of segmented brain images into the Talairach space with a 3D elastic warping model. Retest reliability of regional volumes measured in Talairach space indicated errors of < 1.5% for the frontal, parietal, temporal, and occipital brain regions. Additional regional analysis was performed with an automated hybrid method combining a region-of-interest approach and voxel-based analysis, named Regional Analysis of Volumes Examined in Normalized Space (RAVENS). RAVENS analysis for several subcortical structures showed good agreement with operator-defined volumes. This system has sufficient accuracy for longitudinal imaging data and is currently being used in the analysis of neuroimaging data of the Baltimore Longitudinal Study of Aging.     

A 3D sequence-independent representation of the protein data bank

Here we address the following questions. How many structurally different entries are there in the Protein Data Bank (PDB)? How do the proteins populate the structural universe? To investigate these questions a structurally non-redundant set of representative entries was selected from the PDB. Construction of such a dataset is not trivial: (i) the considerable size of the PDB requires a large number of comparisons (there were more than 3250 structures of protein chains available in May 1994); (ii) the PDB is highly redundant, containing many structurally similar entries, not necessarily with significant sequence homology, and (iii) there is no clear-cut definition of structural similarity. The latter depend on the criteria and methods used. Here, we analyze structural similarity ignoring protein topology. To date, representative sets have been selected either by hand, by sequence comparison techniques which ignore the three-dimensional (3D) structures of the proteins or by using sequence comparisons followed by linear structural comparison (i.e. the topology, or the sequential order of the chains, is enforced in the structural comparison). Here we describe a 3D sequence-independent automated and efficient method to obtain a representative set of protein molecules from the PDB which contains all unique structures and which is structurally non-redundant. The method has two novel features. The first is the use of strictly structural criteria in the selection process without taking into account the sequence information. To this end we employ a fast structural comparison algorithm which requires on average approximately 2 s per pairwise comparison on a workstation. The second novel feature is the iterative application of a heuristic clustering algorithm that greatly reduces the number of comparisons required. We obtain a representative set of 220 chains with resolution better than 3.0 A, or 268 chains including lower resolution entries, NMR entries and models. The resulting set can serve as a basis for extensive structural classification and studies of 3D recurring motifs and of sequence-structure relationships. The clustering algorithm succeeds in classifying into the same structural family chains with no significant sequence homology, e.g. all the globins in one single group, all the trypsin-like serine proteases in another or all the immunoglobulin-like folds into a third. In addition, unexpected structural similarities of interest have been automatically detected between pairs of chains. A cluster analysis of the representative structures demonstrates the way the "structural universe' is populated.     

A 3D damage model for trabecular bone based on fabric tensors

Motivated by the role of damage in normal and pathological conditions of trabecular bone, a novel 3D constitutive law was developed that describes anisotropic elasticity and the rate-independent degradation in mechanical properties resulting from the growth of cracks or voids in the trabecular tissue. The theoretical model was formulated within the framework of continuum damage mechanics and based on two fabric tensors characterizing the local trabecular morphology. Experimental validation of the model was achieved by uniaxial and torsional testing of waisted bovine trabecular bone specimens. Strong correlations were found between cumulated permanent strain, reduction in elastic moduli and nonlinear postyield stress, which support the hypothesis that these variables reflect the same underlying damage process.     

A rationale for DSM-III's medical model.

Defends the medical model in treating psychological disorders in response to T. Schacht and P. E. Nathan's (see record 1978-29497-001) etiologic regrouping of Diagnostic and Statistical Manual of Mental Disorders (DSM-III) diagnostic categories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A model for predicting the transmission rate of malaria from serological data

A model is developed to estimate the duration for which malaria antibody levels in the blood remain high in a closed population. This estimate can be used to calculate the transmission rate within a region, in conjunction with the serological information contained in the population. The model is used on data obtained from a study of malaria in the Philippines and shows excellent agreement. It is subsequently utilised for predictions and seems to be an appropriate vehicle for this purpose.