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PubMed2004

Brain tumor target volume determination for radiation treatment planning through automated MRI segmentation.

PURPOSE: To assess the effectiveness of two automated magnetic resonance imaging (MRI) segmentation methods in determining the gross tumor volume (GTV) of brain tumors for use in radiation therapy treatment planning. METHODS AND MATERIALS: Two automated MRI tumor segmentation methods (supervised k-nearest neighbors [kNN] and automatic knowledge-guided [KG]) were evaluated for their potential as "cyber colleagues." This required an initial determination of the accuracy and variability of radiation oncologists engaged in the manual definition of the GTV in MRI registered with computed tomography images for 11 glioma patients. Three sets of contours were defined for each of these patients by three radiation oncologists. These outlines were compared directly to establish inter- and intraoperator variability among the radiation oncologists. A novel, probabilistic measurement of accuracy was introduced to compare the level of agreement among the automated MRI segmentations. The accuracy was determined by comparing the volumes obtained by the automated segmentation methods with the weighted average volumes prepared by the radiation oncologists. RESULTS: Intra- and inter-operator variability in outlining was found to be an average of 20% +/- 15% and 28% +/- 12%, respectively. Lowest intraoperator variability was found for the physician who spent the most time producing the contours. The average accuracy of the kNN segmentation method was 56% +/- 6% for all 11 cases, whereas that of the KG method was 52% +/- 7% for 7 of the 11 cases when compared with the physician contours. For the areas of the contours where the oncologists were in substantial agreement (i.e., the center of the tumor volume), the accuracy of kNN and KG was 75% and 72%, respectively. The automated segmentation methods were found to be least accurate in outlining at the edges of the tumor volume. CONCLUSIONS: The kNN method was able to segment all cases, whereas the KG method was limited to enhancing tumors and gliomas with clear enhancing edges and no cystic formation. Both methods undersegment the tumor volume when compared with the radiation oncologists and performed within the variability of the contouring performed by experienced radiation oncologists based on the same data.

Aged↗
PubMed2005

Atlas-based automatic segmentation of MR images: validation study on the brainstem in radiotherapy context.

PURPOSE: Brain tumor radiotherapy requires the volume measurements and the localization of several individual brain structures. Any tool that can assist the physician to perform the delineation would then be of great help. Among segmentation methods, those that are atlas-based are appealing because they are able to segment several structures simultaneously, while preserving the anatomy topology. This study aims to evaluate such a method in a clinical context. METHODS AND MATERIALS: The brain atlas is made of two three-dimensional (3D) volumes: the first is an artificial 3D magnetic resonance imaging (MRI); the second consists of the segmented structures in this artificial MRI. The elastic registration of the artificial 3D MRI against a patient 3D MRI dataset yields an elastic transformation that can be applied to the labeled image. The elastic transformation is obtained by minimizing the sum of the square differences of the image intensities and derived from the optical flow principle. This automatic delineation (AD) enables the mapping of the segmented structures onto the patient MRI. Parameters of the AD have been optimized on a set of 20 patients. Results are obtained on a series of 6 patients' MRI. A comprehensive validation of the AD has been conducted on performance of atlas-based segmentation in a clinical context with volume, position, sensitivity, and specificity that are compared by a panel of seven experimented physicians for the brain tumor treatments. RESULTS: Expert interobserver volume variability ranged from 16.70 cm(3) to 41.26 cm(3). For patients, the ratio of minimal to maximal volume ranged from 48% to 70%. Median volume varied from 19.47 cm(3) to 27.66 cm(3) and volume of the brainstem calculated by AD varied from 17.75 cm(3) to 24.54 cm(3). Medians of experts ranged, respectively, for sensitivity and specificity, from 0.75 to 0.98 and from 0.85 to 0.99. Median of AD were, respectively, 0.77 and 0.97. Mean of experts ranged, respectively, from 0.78 to 0.97 and from 0.86 to 0.99. Mean of AD were, respectively, 0.76 and 0.97. CONCLUSIONS: Results demonstrate that the method is repeatable, provides a good trade-off between accuracy and robustness, and leads to reproducible segmentation and labeling. These results can be improved by enriching the atlas with the rough information of tumor or by using different laws of deformation for the different structures. Qualitative results also suggest that this method can be used for automatic segmentation of other organs such as neck, thorax, abdomen, pelvis, and limbs.

Algorithms↗
PubMed2005

One or 2 Intacs segments for the correction of keratoconus.

PURPOSE: To evaluate the effect of implanting 1 or 2 intracorneal rings (Intacs, KeraVision) as a device to correct, stabilize, and/or improve the best corrected visual acuity in patients with clear cornea keratoconus oriented by the preoperative corneal topography pattern. SETTING: Vissum/Instituto Oftalmológico de Alicante, Miguel Hernandez University, Alicante, Spain. METHODS: In this prospective comparative consecutive study, Intacs segments were implanted in 26 keratoconic eyes with clear central corneas of 19 consecutive patients (9 women and 10 men). Corneas were divided into 2 groups according to the topographic pattern of the cone. Group I included keratoconus not crossing the 180 degrees meridian and Group II included keratoconus crossing the 180 degrees meridian. The Intacs were horizontally placed through a lateral clear corneal incision. According to the corneal topography 1 segment was implanted 0.45 mm inferior in Group I, and 2 segments were implanted, 1 0.25 mm superior and the other 0.45 mm inferior, in Group II. All cases completed a minimum follow-up of 1 year. Differences between preoperative and postoperative uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and keratometry were clinically and statistically evaluated. RESULTS: Spherical equivalent error and refractive astigmatism were significantly reduced. The mean keratometric values were reduced following Intacs insertion in both groups. At the end of the first year of the postoperative follow-up, Group I (1 segment) had an improvement in mean UCVA to 20/50 (0.4 +/- 0.22 decimal value), which was statistically significant when compared to the preoperative UCVA of 20/100 (0.2 +/- 0.13 decimal value) (P=.011). Mean BSCVA was 20/32 (0.62 +/- 0.24 decimal value), which was also statistically significant when compared to the preoperative BSCVA, which was 20/50 (0.4 +/- 0.21 decimal value) (P=.002). In Group II (2 segments), UCVA after 1 year was 20/63 (0.34 +/- 0.17 decimal value), which was statistically significant when compared to the preoperative UCVA of 20/400 (0.06 +/- 0.02 decimal value) (P=.001). Mean BSCVA was 20/32 (0.62 +/- 0.27 decimal value), which was significantly better than the preoperative UCVA of 20/50 (0.38 +/- 0.22 decimal value) (P=.001). In 4 eyes, the inferior segment was removed because of partial extrusion during the postoperative follow-up. CONCLUSIONS: Treatment of keratoconus with 1 or 2 Intacs segments oriented by the preoperative corneal topography used in this study proved to be effective in decreasing the corneal steepening and astigmatism and improving BSCVA. Further follow-up is needed to determine the final effect of Intacs on the progression of the corneal disease.

Adult↗
PubMed2004

Giant R wave, convex ST-segment elevation, and negative T wave during exercise treadmill test.

The giant R wave syndrome is characterized by giant R wave accompanied by widening of the QRS complex, marked ST segment elevation, QRS axis deviation, and the formation of monophasic QRS-ST complex with obliteration of S wave in leads facing the ischemic zone. This report describes a 65-year-old-man with variant angina who had a transient giant R wave syndrome during an exercise treadmill test. Initially, at peak exercise, there was a convex ST segment elevation ending in a negative T wave in the same (inferior) leads which showed giant R waves. Later, in the recovery period and coinciding with an amelioration of myocardial ischemia, there was a less marked increase of R wave amplitude associated with concave ST segment elevation and positive T wave in the inferolateral leads. Subsequently, a ST segment depression in the inferolateral leads preceded the ECG normalization. The patient had also a concave ST segment elevation and positive T wave in inferolateral leads during a spontaneous episode of variant angina at rest. An emergency coronary arteriography showed a dominant right coronary artery with an 80% and a 75% diameter stenosis of the middle and distal segment, respectively; the other arteries and left ventriculogram were normal. The underlying mechanisms of the different shapes of ST segment elevation and T waveform in the setting of acute transmural myocardial ischemia are discussed.

Aged↗
PubMed2005

Derived 12-lead electrocardiogram in the assessment of ST-segment deviation and cardiac rhythm.

BACKGROUND: There are little data on the validation of 12-lead electrocardiogram (ECG) derived by the EASI lead system used for continuous monitoring in critical care settings. OBJECTIVE: The objectives of this study were to determine the accuracy of 12-lead ECG derived by the EASI lead system in the detection of ST-segment deviation and cardiac rhythm compared with the standard 12-lead ECG. METHODS: All patients admitted to the coronary care unit were studied. Kappa statistics was used to calculate the agreement between both ECG systems in the determination of cardiac rhythm and premature ventricular complex morphology. ST-segment analysis was performed in patients with acute coronary syndromes. Pearson correlation was used to correlate the ST-segment deviation between both techniques. The sensitivity and specificity of the determination of significant ST-segment deviation by the EASI lead system were calculated. RESULTS: There were a total of 282 patients enrolled in this study. There was a complete agreement in the interpretation of cardiac rhythm between the 2 methods (kappa = 1). Analysis of ST-segment deviation of 12-lead ECG also showed a significant correlation (correlation coefficient varied from 0.62 in lead I to 0.823 in lead aVF with a P value of <.001 in all leads) between the 2 methods with very high sensitivity and specificity in the detection of significant ST-segment elevation and depression. CONCLUSION: The 12-lead ECG derived by the EASI lead system is an accurate and reliable information for the assessment of ST-segment deviation and cardiac rhythm in critically ill patients.

Aged↗
PubMed2005

Use of novel interactive input devices for segmentation of articular cartilage from magnetic resonance images.

OBJECTIVE: To study the effect of new interactive computer input devices on cartilage segmentation in terms of time, consistency between input devices, and precision in quantitative magnetic resonance imaging (qMRI). DESIGN: We compared two new input devices, an interactive digitizing tablet and an interactive touch-sensitive screen, to a traditional mouse. Medial tibial and patellar cartilage of six healthy and six osteoarthritic knees were segmented using each input device. Cartilage volume, surface area and mean thickness were assessed using a validated algorithm and used to determine consistency and precision. Segmentation time was also measured. RESULTS: Segmenting with an interactive touch-sensitive screen reduced segmentation time by 15% when compared to the traditional mouse but we found no significant difference in segmentation time between the interactive digitizing tablet and the traditional mouse. We found no difference in consistency or precision of cartilage volume, mean thickness or surface area between the three input devices tested. CONCLUSIONS: We conclude that measurements of cartilage made using articular cartilage segmentation from MR images are independent of the input device chosen for user interaction.

Adult↗
PubMed2006

Pharmacological evaluation of plasma membrane beta-adrenoceptors in rat hearts using the tissue segment binding method.

This study evaluates beta-adrenoceptors in rat atria and ventricle using the tissue segment binding method and compares the results with those obtained using conventional homogenate binding assays. In studies with tissue segment binding, the hydrophilic radioligand [(3)H]-CGP12177 selectively bound to plasma membrane beta-adrenoceptors, and the B(max) levels were significantly higher than those obtained with homogenate binding. However, both binding approaches revealed similar proportions of beta(1)- and beta(2)-adrenoceptors. The regional distribution of plasma membrane beta(1)- and beta(2)-adrenoceptors in rat hearts were also determined using tissue segment binding. Abundance of beta-adrenoceptors and proportion of beta(1)-adrenoceptors were higher in atria than in ventricle, but there was no significant difference between right and left atria or within ventricle (right and left ventricle free walls, apex, and interventricular septum). To establish the ability of the tissue segment binding method to study beta-adrenoceptor regulation such as the internalization of receptors, the effect of prolonged exposure of rat ventricle to (-)-isoprenaline was also investigated by using tissue segments and homogenate binding. Incubation with (-)-isoprenaline for 1 h in vitro caused a concentration-dependent decrease in the density of beta-adrenoceptors, predominantly beta(2)-adrenoceptors, when assessed with tissue segment binding method. In contrast, the subtype-specific change after treatment with (-)-isoprenaline was not detected using homogenate binding. In summary, the tissue segment binding method with [(3)H]-CGP12177 enables a more precise quantitation of plasma membrane beta(1)- and beta(2)-adrenoceptors in rat hearts and is suitable for studying their regulation.

Adrenergic beta-Agonists↗
PubMed2004

Mutual information in coupled multi-shape model for medical image segmentation.

This paper presents extensions which improve the performance of the shape-based deformable active contour model presented earlier in [IEEE Conf. Comput. Vision Pattern Recog. 1 (2001) 463] for medical image segmentation. In contrast to that previous work, the segmentation framework that we present in this paper allows multiple shapes to be segmented simultaneously in a seamless fashion. To achieve this, multiple signed distance functions are employed as the implicit representations of the multiple shape classes within the image. A parametric model for this new representation is derived by applying principal component analysis to the collection of these multiple signed distance functions. By deriving a parametric model in this manner, we obtain a coupling between the multiple shapes within the image and hence effectively capture the co-variations among the different shapes. The parameters of the multi-shape model are then calculated to minimize a single mutual information-based cost criterion for image segmentation. The use of a single cost criterion further enhances the coupling between the multiple shapes as the deformation of any given shape depends, at all times, upon every other shape, regardless of their proximity. We found that this resulting algorithm is able to effectively utilize the co-dependencies among the different shapes to aid in the segmentation process. It is able to capture a wide range of shape variability despite being a parametric shape-model. And finally, the algorithm is robust to large amounts of additive noise. We demonstrate the utility of this segmentation framework by applying it to a medical application: the segmentation of the prostate gland, the rectum, and the internal obturator muscles for MR-guided prostate brachytherapy.

Algorithms↗
PubMed2004

A brain tumor segmentation framework based on outlier detection.

This paper describes a framework for automatic brain tumor segmentation from MR images. The detection of edema is done simultaneously with tumor segmentation, as the knowledge of the extent of edema is important for diagnosis, planning, and treatment. Whereas many other tumor segmentation methods rely on the intensity enhancement produced by the gadolinium contrast agent in the T1-weighted image, the method proposed here does not require contrast enhanced image channels. The only required input for the segmentation procedure is the T2 MR image channel, but it can make use of any additional non-enhanced image channels for improved tissue segmentation. The segmentation framework is composed of three stages. First, we detect abnormal regions using a registered brain atlas as a model for healthy brains. We then make use of the robust estimates of the location and dispersion of the normal brain tissue intensity clusters to determine the intensity properties of the different tissue types. In the second stage, we determine from the T2 image intensities whether edema appears together with tumor in the abnormal regions. Finally, we apply geometric and spatial constraints to the detected tumor and edema regions. The segmentation procedure has been applied to three real datasets, representing different tumor shapes, locations, sizes, image intensities, and enhancement.

Algorithms↗
PubMed2005

Case study: an evaluation of user-assisted hierarchical watershed segmentation.

This paper evaluates the effectiveness of an interactive, three-dimensional image segmentation technique that relies on watersheds. This paper presents two user-based case studies, which include two different groups of domain experts. Subjects manipulate a graphics-based front end to a hierarchy of segmented regions generated from a watershed segmentation algorithm, which is implemented in the Insight Toolkit. In the first study, medical students segment several different anatomical structures from the Visible Human Female head and neck color cryosection data. In the second study, radiologists use the interactive tool to produce models of brain tumors from MRI data. This paper presents a quantitative and qualitative comparison against hand contouring. To quantify accuracy, we estimate ground truth from the hand-contouring data using the Simultaneous Truth and Performance Estimation algorithm. We also apply metrics from the literature to estimate precision and efficiency. The watershed segmentation technique showed improved subject interaction times and increased inter-subject precision over hand contouring, with quality that is visually and statistically comparable. The analysis also identifies some failures in the watershed technique, where edges were poorly defined in the data, and note a trend in the hand-contouring results toward systematically larger segmentations, which raises questions about the wisdom of using expert segmentations to define ground truth.

Algorithms↗
PubMed2004

Segmentation and compartition in the early avian hindbrain.

For the comparative embryologists of the early 20th century, the segment-like bulges that appear transiently during the early stages of vertebrate hindbrain development were both the object of fascination and the subject of vigorous dispute. Conflicting views were held as to the significance of these 'rhombomeres' to brain development and their more general relevance to head evolution. Whether rhombomeres are inconsequential bumps in the embryonic brain or true segments-iterative or metameric units-has only recently been resolved. A number of studies using more modern techniques (such as immunohistochemistry, in situ hybridisation, axonal tracing, single cell labelling, heterotopic and orthotopic grafting, and the manipulation of gene expression by electroporation) have shown that the hindbrain has a truly metameric cellular organisation. The avian embryo has played a particularly prominent role in such studies by virtue of its large size and accessibility, its amenability to microsurgery, and its well-described anatomy. Furthermore, electrophysiological studies, also on avian embryos, have shown that segmentation of the parent neuroepithelium into rhombomeres plays a crucial part in establishing the functional organization of the hindbrain. Segmentation suggests the early allocation of defined sets of precursor cells and is therefore presumed to allow a specific identity for each successive segment to emerge from a common ground plan. This short review will focus on the contribution the avian embryo has made to our understanding of this fly-like region of the vertebrate brain, in respect of its morphology and neuronal architecture, the cellular and molecular mechanisms involved in establishing and maintaining the segments, and the molecular controls of segmental identity.

Animals↗
PubMed2006

Porcine T-cell receptor beta-chain: a genomic sequence covering Dbeta1.1 to Cbeta2 gene segments and the diversity of cDNA expressed in piglets including novel alternative splicing products.

Porcine TCRbeta-chain cDNA clones were isolated from thymic and peripheral blood lymphocytes of piglets. Using these nucleotide sequences, a genomic 18kbp sequence stretch covering Dbeta1 to Cbeta2 gene segments was identified, which revealed that the porcine TCRbeta-chain locus consists of two sets of Dbeta-Jbeta-Cbeta gene groups with each set having a Dbeta gene segment, seven Jbeta gene segments and a down stream Cbeta gene segment composed of four exons. This structure is consistent with other known mammalian TCRbeta-chain loci. With this genomic information, TCRbeta-chain clones from cDNA libraries were analyzed. Sixteen Vbeta gene segments were obtained accompanied by either Dbeta1 or Dbeta2 and by one of the nine Jbeta gene segments. Five different Cbeta cDNA sequences were obtained including four types of Cbeta1 sequences and one type of Cbeta2 sequence. The differences among the Cbeta1 sequences are either allelic polymorphisms or two splice variants, one being a product of exon1 splicing to exon3 (exon2 skipping), and another being an alternative splicing using a splice acceptor site newly discovered inside Cbeta1 exon4. The latter splice acceptor site was also found in human, mouse and horse all giving short cytoplasmic domain with Phe at their C-terminal ends. Other splicing products included trans-splicing of Jbeta2 to Cbeta1, non-functional splicing of two Jbeta gene segments in tandem and a part of Jbeta2.7-Cbeta2 intron to Cbeta2 exon1. Numerous examples of splice variants may suggest the involvement of splicing in generating TCRbeta-chain functional diversity.

Alternative Splicing↗
PubMed2006

Automated segmentation of multiple sclerosis lesion subtypes with multichannel MRI.

PURPOSE: To automatically segment multiple sclerosis (MS) lesions into three subtypes (i.e., enhancing lesions, T1 "black holes", T2 hyperintense lesions). MATERIALS AND METHODS: Proton density-, T2- and contrast-enhanced T1-weighted brain images of 12 MR scans were pre-processed through intracranial cavity (IC) extraction, inhomogeneity correction and intensity normalization. Intensity-based statistical k-nearest neighbor (k-NN) classification was combined with template-driven segmentation and partial volume artifact correction (TDS+) for segmentation of MS lesions subtypes and brain tissue compartments. Operator-supervised tissue sampling and parameter calibration were performed on 2 randomly selected scans and were applied automatically to the remaining 10 scans. Results from this three-channel TDS+ (3ch-TDS+) were compared to those from a previously validated two-channel TDS+ (2ch-TDS+) method. The results of both the 3ch-TDS+ and 2ch-TDS+ were also compared to manual segmentation performed by experts. RESULTS: Intra-class correlation coefficients (ICC) of 3ch-TDS+ for all three subtypes of lesions were higher (ICC between 0.95 and 0.96) than that of 2ch-TDS+ for T2 lesions (ICC = 0.82). The 3ch-TDS+ also identified the three lesion subtypes with high specificity (98.7-99.9%) and accuracy (98.5-99.9%). Sensitivity of 3ch-TDS+ for T2 lesions was 16% higher than with 2ch-TDS+. Enhancing lesions were segmented with the best sensitivity (81.9%). "Black holes" were segmented with the least sensitivity (62.3%). CONCLUSION: 3ch-TDS+ is a promising method for automated segmentation of MS lesion subtypes.

Adult↗
PubMed2004

Changes in keratoconic corneas after intracorneal ring segment explantation and reimplantation.

PURPOSE: To evaluate the outcome and potential reversibility of the changes induced in keratoconic eyes after intracorneal ring segment explantation. DESIGN: Retrospective, interventional case series. PARTICIPANTS: Five eyes of 4 patients who underwent uneventful implantation of one or two intracorneal ring segment segments for the correction of clear corneal keratoconus and who required explantation of one segment due to complications. MAIN OUTCOME MEASURES: Visual acuity, refraction, keratometric readings, and corneal topography. The follow-up was up to 1 year from the primary implantation procedure in all cases. RESULTS: Explantation was performed easily in all cases without intraoperative or postoperative complications. The segments were extracted due to migration and local melting. The visual, refractive, and topographic map findings regressed to approximate the original clinical situation before segment implantation. CONCLUSIONS: Intracorneal ring segments are safely and easily explanted from keratoconic eyes. Most of the visual, refractive, and topographic findings return to near the preimplantation levels.

Adult↗
PubMedDate not supplied

Adjacent segment disease after anterior cervical interbody fusion.

BACKGROUND CONTEXT: There have been many follow-up studies on anterior interbody fusion for cervical nerve root and spinal cord compression, and excellent neurological outcomes have been reported. However, postoperative degenerative changes at adjacent discs may lead to the development of new radiculopathy or myelopathy. In the previous reports, the incidence of symptomatic adjacent segment disease has ranged from 7% to 15%. PURPOSE: The present study was undertaken to investigate the incidence of symptomatic adjacent segment disease after anterior cervical interbody fusion (ACIF) and to identify the factors that are related to the development of this disease. STUDY DESIGN/SETTING: This is a retrospective cohort study. PATIENT SAMPLE: A total of 112 patients were followed up clinically and radiologically for more than 2 years. OUTCOME MEASURES: Follow-up evaluation was primarily by means of clinical visits. The postoperative course of any symptoms, the findings of neurological examination and serial follow-up radiographs were performed in all patients. METHODS: The diagnosis of symptomatic adjacent segment disease was based on the presence of new radiculopathy or myelopathy symptoms referable to an adjacent level, and the presence of a compressive lesion at an adjacent level by magnetic resonance imaging or myelography. We evaluated the correlation between the incidence of symptomatic adjacent segment disease and the following clinical parameters (age at operation, sex, number of the levels fused) and radiological parameters (preoperative cervical spine alignment, preoperative range of motion of C2-C7 cervical spine, anteroposterior spinal canal diameter, preoperative existence of an adjacent segment degeneration on plain radiograph, myelography and magnetic resonance imaging [MRI]). RESULTS: Symptomatic adjacent segment disease developed in 19 of 112 patients (19%) followed. A Kaplan-Meier survival analysis was performed in order to follow the disease-free survival of the entire series of patients. The disease-free survival rates were 89% at 5 years, 84% at 10 years and 67% at 17 years. The incidences of indentation of dura matter on preoperative myelography or disc protrusion on MRI at the adjacent level were significantly higher in disease cases (p=.0087, .0299, respectively; chi-squared test). However, the other parameters did not show a statistically significant difference. There were seven cases (37%) who had failure of nonoperative treatment and additional operations were performed. CONCLUSIONS: The incidence of symptomatic adjacent segment disease after ACIF was higher when preoperative myelography or MRI revealed asymptomatic disc degeneration at that level regardless of the number of the levels fused, preoperative alignment, spinal canal diameter or fusion alignment.

Adult↗
PubMed2004

Effects of cryopreservation and thawing on the structure of vascular segment.

The objective of this study was to analyze the importance of the quality of the vascular segment to be cryopreserved and the influence of storage in a gas phase, a liquid phase, or after accidental immersion in liquid nitrogen. In addition, we investigated the effects of rapid versus slow thawing on the occurrence of fractures and changes in the structure of the vessel wall. The tissue sources were whole thoracic and abdominal aortas from 15 pigs. Each aorta was cut into equal segments and randomly assigned to each study group. One segment of fresh unfrozen aorta of the same size was used as a control. The samples were cryopreserved using a programmed apparatus. After 2 weeks the arterial segments were thawed rapidly or slowly. A great variation in the results was obtained depending on the quality of the control. Although endothelial cells were better preserved in the liquid phase, the internal elastic lamina and elastic lamelli showed better preservation and fewer microfractures in the gas phase. The internal elastic lamina showed a greater number of microfractures when an accidental immersion in liquid nitrogen had taken place. Furthermore, better preservation of the structure of the vascular segment was observed with a slow thawing method. In general, the conditions of storage and the method of thawing seem to damage the structure of vascular segments. It is necessary to use a severe protocol of donor and vascular segment selection to optimize the post-thaw quality of the cryopreserved samples.

Animals↗
PubMed2004

Evo-devo perspectives on segmentation: model organisms, and beyond.

Bilaterian animals show a diverse array of segmental patterns and segmentation processes. Differences in pattern and process emerge both in comparisons of taxa and among sets of serial structures within one animal. Diversity in developmental mechanisms of segmentation and their genetic control is reflected in the modes in which segmentation evolves, which are difficult to accommodate within the traditional concept of segments as modular building blocks. Thus, in spite of the apparent simplicity of segmental patterns, studying the evolution of segmentation requires an approach that, in an adequate comparative framework, combines the efforts of researchers of genes, cells, embryos and post-embryonic stages.

Journal Article↗
PubMed2006

Needle and seed segmentation in intra-operative 3D ultrasound-guided prostate brachytherapy.

In order to guide the needle to the correct location in 3D US-guided brachytherapy, the needle is continuously tracked as it is being inserted. A pre-scan before the needle insertion and a post-scan after the needle insertion are subtracted to obtain a difference image containing the needle. The image is projected along two orthogonal directions approximately perpendicular to the needle, and the 3D needle is reconstructed from the segmented needles in the two projected images. The seeds implanted with the needle are located in the cropped volume along the needle. Thus, the seeds are segmented using a tri-bar model and 3D line segment patterns. Finally, the positions of the seeds are determined using a peak detection technique. Experiments with agar and turkey/chicken phantoms as well as patient data demonstrated that our needle segmentation technique could segment the needle in near real-time with an accuracy of 0.6 mm in position and 1.0 degrees in orientation. The true-positive rate for seed segmentation is 100% for the agar phantom and 93% for the chicken phantom. The average distance to manual seed segmentation was 1.0mm for the agar phantom and 1.7 mm for the chicken phantom.

Algorithms↗