Closely spaced, fast dynamic movements in disparity vergence

Conflicting theories exist describing how symmetrical vergence responses, the inward or outward turning of the eyes, are mediated. Classical theories describe vergence control as mediated by visual feedback. Extensive experimental evidence indicates that two distinct control components comprise the vergence response, and a recent theory supports the concept that one of these components is not visually guided. Occasionally, saccadic eye movements will respond to a single step stimulus with two closely spaced saccades, a behavior that is indicative of its switching control structure. If a portion of the vergence response is controlled in a manner analogous to saccades, then occasional double fast dynamic components might be expected. During this study, eye movements were recorded in response to symmetrical vergence stimuli of 2, 4, 6, 8, and 10 degrees steps. The left and right eye movements were subtracted to yield a net vergence response, and only convergent responses were investigated. Double fast dynamic components associated with high-velocity movements were observed in all four subjects studied. In double high-velocity component responses, the average peak velocity of both fast dynamic movements was always considerably less than the average peak velocity found when the response to the same stimulus was made with only a single component. Response amplitudes of single and double movements showed that if the primary component of a double response did not reach >/=80% of the stimulus amplitude, a secondary component would be generated to aid the movement. Plots of peak velocity as a function of response amplitude for both double and single movements followed the main sequence for vergence eye movements demonstrating that the first-order dynamic characteristics of all high-velocity components were the same. The time at which maximum velocity occurred (relative to stimulus onset) was also the same for both single component responses and the first component of double responses. The similarity in dynamics and timing implies that the high-velocity components were processed by the same controller mechanism. The existence of double high-velocity movements is indicative of an internal, switching mechanism similar to that found in saccades and is difficult to explain with theories that rely on visual feedback control alone.

Assessment of equivalence on multiple endpoints

Some clinical trials aim to demonstrate therapeutic equivalence on multiple primary endpoints. For example, therapeutic equivalence studies of agents for the treatment of osteoarthritis use several primary endpoints including investigator's global assessment of disease activity, patient's global assessment of response to therapy, and pain. In this paper, thoughts on simultaneous equivalence assessment on three endpoints are presented. As pointed out by Berger and Hsu (1996), the conventional intersection-union test can be conservative. Simulation and computation are conducted to provide an insight on the conservativeness. We also provide a method to lower the confidence level and at the same time maintain the type I error when endpoints have normal distributions and are independent. If, in a particular analysis, the goal is to demonstrate equivalence on as many endpoints as possible, a step-up procedure can be used for selecting those endpoints for which equivalence may be demonstrated. This step-up procedure at the same time controls experimentwise error rate. The techniques are illustrated by a data example.

Leukemia cell infiltration causes defective erythropoiesis partially through MIP-1α/CCL3

Leukemia often results in severe anemia, which may significantly contribute to patient mortality and morbidity. However, the mechanisms underlying defective erythropoiesis in leukemia have not been fully elucidated. In this study, we demonstrated that insufficient erythropoiesis in an immunocompetent acute myeloid leukemia (AML) murine model was due to reduced proliferation of megakaryocyte erythroid progenitors and increased apoptosis of erythroblasts. Colony-forming cell assays indicated that the leukemic bone marrow (BM) plasma inhibited erythroid colony formation, whereas they had no inhibitory effect on other types of colonies. Cytokine array analysis demonstrated that the chemokine CCL3 was elevated in the plasma of AML mice and patients. CCL3 inhibited erythroid differentiation of hematopoietic stem cells, common myeloid progenitors and especially megakaryocytic-erythroid progenitors. Administration of the CCR1 antagonist partially recovered the yield of erythroid colonies in the presence of CCL3 or leukemic BM plasma. Mechanistically, we observed an increase of p38 phosphorylation and subsequent downregulation of GATA1 after CCL3 treatment. Furthermore, knockdown of CCL3 attenuated leukemic progression and alleviated anemia. Therefore, our results demonstrate that elevated CCL3 in the leukemic environment suppresses erythropoiesis via CCR1-p38 activation, suggesting a novel mechanism for the erythroid defects observed in leukemia.

ERIC-PCR identification of the spread of airborne Escherichia coli in pig houses

To understand the spread of microbial aerosols in pig houses, with Escherichia coli (E. coli) as indicator, the airborne E. coli in 4 pig houses and their surroundings at different points 10, 50m upwind and 10, 50, 100, 200 and 400m downwind respectively from the pig houses were collected, and the concentrations were calculated at each sampling point. Furthermore, the feces of pigs were collected to separate E. coli. The ERIC-PCR (Enterobacterial Repetitive Intergenic Consensus-Polymerase Chain Reaction) technology was used to amplify the isolated E. coli DNA samples, then the amplified results were analyzed by NTSYS-pc (Version 2.10) to identify the similarity of isolated E. coli. The results showed that the airborne E. coli concentrations in indoor air of the 4 pig houses (21-35CFUm(-)(3) air) were much higher than those in upwind and downwind air (P<0.05), but there were no significant differences (P>0.05) at downwind distances. The ERIC-PCR results also showed that 52.4% of the fecal E. coli (four houses being respectively 2/4, 50%; 2/4, 50%; 3/6, 50%; 4/7, 57.1%) were identical to the indoor airborne E. coli isolates, and there was more than 90% similarity between the majority of E. coli (50%, 21/42) isolated from downwind air at 10, 50, 100 and 200m and those from indoor air or feces. It could be concluded that the aerosols in pig houses can spread to the surroundings, and thus effective measures should be taken to control and minimize the spread of microbial aerosols.

Dynamics of the disparity vergence step response: a model-based analysis

A new method to analyze the dynamics of vergence eye movements was developed based on a reconstruction of the presumed motor command signal. A model was used to construct equivalent motor command signals and transform an associated vergence transient response into an equivalent set of motor commands. This model represented only the motor components of the vergence system and consisted of signal generators representing the neural burst and tonic cells and a plant representing the ocular musculature and dynamics of the orbit. Through highly accurate simulations, dynamic vergence responses could be reduced to a set of five model parameters, each relating to a specific feature of the internal motor command. This dynamic analysis tool was applied to the analysis of inter-movement variability in vergence step responses. Model parameters obtained from a large number of response simulations showed that the width of the command pulse was tightly controlled while its amplitude, rising slope, and falling slope were less tightly regulated. Variation in the latter three parameters accounted for the most of the movement-to-movement variability seen in vergence step responses. Unlike version movements, pulse width did not increase with increased stimulus amplitude, although the other command signal parameters were substantially influenced by stimulus amplitude.

White matter microstructural abnormality in children with hydrocephalus detected by probabilistic diffusion tractography

BACKGROUND AND PURPOSE

Hydrocephalus is a severe pathologic condition in which WM damage is a major factor associated with poor outcomes. The goal of the study was to investigate tract-based WM connectivity and DTI measurements in children with hydrocephalus by using the probabilistic diffusion tractography method.

MATERIALS AND METHODS

Twelve children with hydrocephalus and 16 age-matched controls were included in the study. Probabilistic diffusion tractography was conducted to generate tract-based connectivity distribution and DTI measures for the genu of the corpus callosum and the connectivity index. Tract-based summary measurements, including the connectivity index and DTI measures (fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity), were calculated and compared between the 2 study groups.

RESULTS

Tract-based summary measurement showed a higher percentage of voxels with lower normalized connectivity index values in the WM tracts in children with hydrocephalus. In the genu of the corpus callosum, the left midsegment of the corticospinal tract, and the right midsegment of the corticospinal tract, the normalized connectivity index value in children with hydrocephalus was found to be significantly lower (P < .05, corrected). The tract-based DTI measures showed that the children with hydrocephalus had significantly higher mean diffusivity, axial diffusivity, and radial diffusivity in the genu of the corpus callosum, left midsegment of the corticospinal tract, and right midsegment of corticospinal tract and lower fractional anisotropy in the genu of the corpus callosum (P < .05, corrected).

CONCLUSIONS

The analysis of WM connectivity showed that the probabilistic diffusion tractography method is a sensitive tool to detect the decreased continuity in WM tracts that are under the direct influence of mechanical distortion and increased intracranial pressure in hydrocephalus. This voxel-based connectivity method can provide quantitative information complementary to the standard DTI summary measures.

Indicators of fetal growth and infectious disease in childhood--a birth cohort with hospitalization as outcome

We evaluated the association between indicators of fetal growth and hospitalization with infectious disease during childhood in a cohort of 10,400 newborns. The cohort was based on children born to mothers who at about 36 weeks of gestation attended the midwife centres in Odense and Aalborg, Denmark for a routine examination. Women were recruited to the study from April 1984 to April 1987. After linkage with the National Hospital Registry, the first hospitalization with infectious disease from 6 months up to 12 years of age was identified. The cumulative incidence of hospitalization with infectious disease during follow-up was 18.9%. Preterm birth was associated with an increased risk of being hospitalized with infections during childhood (incidence rate ratio: 1.67, 95% CI: 1.33-2.10); low birth weight had a similar association, but only in preterm birth. Reduced birth length related to the head was correlated with an increased risk of hospitalization with infections. The effect of gestational age was mainly seen in the period close to the time of birth, but the children who were short at birth appeared to remain at increased risk throughout the age interval under analysis. In conclusion, the study suggests that preterm birth was the main factor underlying the association between low birth weight and the increased risk of hospitalization with infectious disease during childhood. However, it could not explain the increased risk in children who were short at birth.

Diffusion tensor imaging findings in young children with benign external hydrocephalus differ from the normal population

PURPOSE

To compare a pediatric population diagnosed with benign external hydrocephalus (BEH) to normal age-matched controls using diffusion tensor imaging (DTI) techniques.

METHODS

We retrospectively identified 17 BEH patients by specific clinical and neuroimaging criteria. Fractional anisotropy (FA) and mean diffusivity (MD) values obtained from DTI scans were compared to a population of age-matched controls and group differences were examined by mixed model analysis. A longitudinal comparison was completed on a subset that underwent multiple scans (n = 8).

RESULTS

In the genu of the corpus callosum (gCC), six of 15 BEH children had an FA value above the upper limit of 95% prediction interval, nine of 15 BEH children had MD values below the lower limit of 95% prediction interval. A similar trend applied to the other regions of interest (ROIs): splenium of the corpus callosum (sCC), ALIC, and PLIC. Statistical analysis demonstrated significant differences in FA within the gCC, sCC, and PLIC and in MD within the sCC between BEH patients and controls given (P = 0.05). No statistical differences were identified at any ROIs at the later scans.

CONCLUSIONS

We found a significant increase in FA and decrease in MD in children with BEH compared with normal children in specific white matter (WM) ROIs, notably in the gCC and sCC; furthermore, in longitudinal comparison, DTI parameters normalized over time. The current study further demonstrates the ability of DTI to distinguish between subtle diffusion changes in periventricular white matter and establishes preliminary objective radiographic parameters for watchful observation of patients with BEH.

Disparity vergence double responses processed by internal error

Disparity vergence eye movements occasionally exhibit two high-velocity components to a single step stimulus (Alvarez, T. L., Semmlow, J. L. & Yuan, W. (1998). Journal of Neurophysiology, 79, 37-44). This research investigates the neural strategy used to trigger the second component of double high-velocity vergence eye movements. Vergence doubles evoked by an experimental protocol that induces post-movement visual error were compared to doubles that occur normally. The second component of a visually evoked response double occurred later, and with slower dynamics, than that of a naturally occurring double. These differences in timing and dynamics indicate that natural double responses are mediated, at least in part, by a mechanism other than visual feedback. The faster dynamics and timing of natural doubles suggest that an internal monitoring process triggers these movements.

Effects of maternal folic acid supplementation on gene methylation and being small for gestational age

BACKGROUND

Being small for gestational age (SGA), a foetal growth abnormality, has a long-lasting impact on childhood health. Its aetiology and underlying mechanisms are not well understood. Underlying epigenetic changes of imprinted genes have emerged as a potential pathological pathway because they may be associated with growth, including SGA. As a common methyl donor, folic acid (FA) is essential for DNA methylation, synthesis and repair, and FA supplementation is widely recommended for women planning pregnancy. The present study aimed to investigate the inter-relationships among methylation levels of two imprinted genes [H19 differentially methylated regions (DMRs) and MEST DMRs], maternal FA supplementation and SGA.

METHODS

We conducted a case-control study. Umbilical cord blood was taken from 39 SGA infants and 49 controls whose birth weights are appropriate for gestational age (AGA). DNA methylation levels of H19 and MEST DMRs were determined by an analysis of mass array quantitative methylation.

RESULTS

Statistically significantly higher methylation levels were observed at sites 7.8, 9 and 17.18 of H19 (P = 0.030, 0.016 and 0.050, respectively) in the SGA infants compared to the AGA group. In addition, the association was stronger in male births where the mothers took FA around conception at six H19 sites (P = 0.004, 0.005, 0.048, 0.002, 0.021 and 0.005, respectively).

CONCLUSIONS

Methylation levels at H19 DMRs were higher in SGA infants compared to AGA controls. It appears that the association may be influenced by maternal peri-conception FA supplementation and also be sex-specific.

Kaempferol inhibited bovine herpesvirus 1 replication and LPS-induced inflammatory response

Plant-derived flavonoids contain large amount of compounds with pharmacological effects. In this study, we showed the compound Kaempferol to have robust antiviral activity against bovine herpesvirus 1 (BoHV-1) replication in vitro. Kaempferol at a concentration of 100 μmol/l completely inhibited viral replication in MDBK cells. It mainly affects the viral replication at the post-entry stages. The inhibition of Akt signaling is a potential mechanism underlying the antiviral effect of Kaempferol. In addition, at a concentration of 25 and 50 μmol/l Kaempferol could significantly reduce the expression of inflammatory mediators such as tumor necrosis factor alpha (TNF-α), interleukin-8 (IL-8) and macrophage inflammatory protein 1 alpha (MIP-1α) in human promonocytic U937 cells-derived macrophages (dU937) in response to lipopolysaccharides (LPS) stimulation. Overall, our results indicated that Kaempferol provides a potent protection against BoHV-1 infection and LPS-induced inflammatory response.

In vitro translational analysis of genomic, defective, and satellite RNAs of Cryphonectria hypovirus 3-GH2

Cryphonectria hypovirus 3-GH2 (CHV3-GH2) is a member of the fungal virus family Hypoviridae that differs from previously characterized members in having a single large open reading frame with the potential to encode a protein of 326 kDa from its 9.8-kb genome. The N-terminal portion of the ORF contains sequence motifs that are somewhat similar to papain-like proteinases identified in other hypoviruses. Translation of the ORF is predicted to release autocatalytically a 32.5-kDa protein. A defective RNA, predicted to encode a 91.6-kDa protein representing most of the N-terminal proteinase fused to the entire putative helicase domain, and two satellite RNAs, predicted to encode very small proteins, also are associated with CHV3-GH2 infected fungal cultures. We performed in vitro translation experiments to examine expression of these RNAs. Translation of three RT-PCR clones representing different lengths of the amino-terminal portion of the ORF of the genomic RNA resulted in autocatalytic release of the predicted 32.5-kDa protein. Site-directed mutagenesis was used to map the processing site between Gly(297) and Thr(298). In vitro translation of multiple independent cDNA clones of CHV3-GH2-defective RNA 2 resulted in protein products of approximately 92 kDa, predicted to be the full-length translation product, 32 kDa, predicted to represent the N-terminal proteinase, and 60 kDa, predicted to represent the C-terminal two-thirds of the full-length product. In vitro translation of cDNA clones representing satellite RNA 4 resulted in products of slightly less than 10 kDa, consistent with the predicted 9.4 kDa product.

Time course for the modulation of hepatic cytochrome P450 after administration of ethylbenzene and its correlation with toluene metabolism

The goal of the present study was to examine the time course for changes in P450 expression and hydrocarbon metabolism after acute treatment with the simple aromatic hydrocarbon ethylbenzene (EB) and to correlate these alterations with the changes observed in alkylbenzene metabolism. Male Holtzman rats were treated with a single intraperitoneal injection of EB, and the effects on specific P450-dependent activities, immunoreactive P450 isozyme levels, and RNA levels were measured at various times after injection. Toluene was used as the test alkylbenzene for examination of the EB-mediated changes on in vitro hydrocarbon metabolism. In untreated rats, toluene was metabolized almost entirely by aliphatic hydroxylation (to benzyl alcohol); however, in EB-treated rats, significant quantities of benzyl alcohol, o-cresol, and p-cresol were produced. Interestingly, 5-10 h after EB treatment, there was a 40% decrease in benzyl alcohol production. By 24 h, rates of benzyl alcohol formation returned to control levels, whereas there was a 7-fold increase in o-cresol and a greater that 50-fold increase in p-cresol production. The changes in the disposition of toluene were then correlated with changes in particular P450 isozymes. Several P450 isozymes were induced after EB administration. P450 2B1/2-dependent testosterone 16 beta-hydroxylation and P450 2B1/2-immunoreactive protein were elevated 30-fold after EB administration, reaching maxima by 24 h and remaining elevated 48 h after exposure. Changes in P450 2B1 and 2B2 RNA preceded those of the proteins. Similar results were observed with P450 1A1. P450 2E1 RNA levels were elevated after a single EB injection. However, the elevation in P450 2E1-dependent activities and immunoreactive protein levels preceded the changes in RNA, suggesting that multiple steps are affected by EB exposure. In contrast to the increases in some isozymes, P450 2C11 protein was rapidly suppressed (within the first 2-10 h) after hydrocarbon exposure, suggestive of a destabilization of the protein. When comparing the changes in P450 isozymes to alterations in toluene metabolism, the immediate suppression in aliphatic hydroxylation of toluene (in the first 5-10 h) was consistent with the decrease in P450 2C11. Subsequent to this effect, P450 2B1/2 and 2E1 were induced, which elevated production of this metabolite to control levels. The increase in the aromatic hydroxylation of toluene to both o, and p-cresol was consistent with the induction of P450s 2B1/2, 2E1, and 1A1.

Insulin-like growth factor-II mediates the steroidogenic and growth promoting actions of follicle stimulating hormone on human ovarian pre-antral follicles cultured in vitro

FSH is important for ovarian antral follicle growth and steroidogenesis, processes in the human that are believed to be mediated by IGF-II. The objective of this study was to determine if human ovarian pre-antral follicles are also FSH- and IGF-II-responsive, since the clinical questions and mechanisms underlying the effects on the pre-antral follicle pool of exogenously administered gonadotropins for fertility therapy and elevated endogenous gonadotropins in the perimenopause remain unanswered. Class 2 preantral follicles were isolated from human premenopausal ovaries (n=6) and cultured in vitro with androstenedione and either no additives or with FSH or IGF-II. FSH (100 ng/mL) stimulated estradiol (E2) production by 3.58 +/- 0.4 fold over 48 hr, compared to controls without FSH. This effect was completely inhibited in the presence of the IGF-II antagonist, IGF binding protein-4 (IGFBP-4). IGF-II also stimulated E2 production by preantral follicles with doses as low as 1 ng/mL and within 24 hr of treatment. Maximal response of 3- to 9-fold above control was achieved with 100 ng/mL of IGF-II between 96-120 hr of culture. IGFBP-4 completely inhibited E2 production to basal levels. FSH stimulated IGF-II mRNA in pre-antral follicles about 4-fold, determined by RT-PCR. FSH also stimulated follicle growth, determined by light microscopy, 50-68% over 48 hr, compared to controls (P<0.001), a process that was inhibited in the presence of IGFBP-4. Cumulatively, these data support IGF-II as a mediator of FSH action on human preantral follicles.

Evidence for separate control of slow version and vergence eye movements: support for Hering's Law

When a visual stimulus changes direction and distance simultaneously, Hering's Law argues that the resulting eye movements are the result of combined version and vergence control processes. Recently, it has been suggested that slow asymmetrical eye movements might be guided by monocular control processes wherein each eye is driven by its own retinal image. Experimental results presented here show behavioral differences between slow version and slow vergence eye movements, indicating that different control processes drive the two "pure" responses. Specifically, version tracking of constant velocity stimuli (i.e., smooth pursuit) is more precise, showing less variation in tracking velocity than movements of equal velocity produced by vergence stimuli. When the two stimuli are combined, the variability in tracking is consistent with the addition of the two components in proportion to their respective stimuli. These results provide support for Hering's Law, at least for low velocity, smooth tracking movements (i.e., slow version and slow vergence.

Complementary Roles of Dynamic Contrast-Enhanced MR Imaging and Postcontrast Vessel Wall Imaging in Detecting High-Risk Intracranial Aneurysms

BACKGROUND AND PURPOSE

Individual assessment of the absolute risk of intracranial aneurysm rupture remains challenging. Emerging imaging techniques such as dynamic contrast-enhanced MR imaging and postcontrast vessel wall MR imaging may improve risk estimation by providing new information on aneurysm wall properties. The purpose of this study was to investigate the relationship between aneurysm wall permeability on dynamic contrast-enhanced MR imaging and aneurysm wall enhancement on postcontrast vessel wall MR imaging in unruptured intracranial aneurysms.

MATERIALS AND METHODS

Patients with unruptured saccular intracranial aneurysms were imaged with vessel wall MR imaging before and after gadolinium contrast administration. Dynamic contrast-enhanced MR imaging was performed coincident with contrast injection using 3D T1-weighted spoiled gradient-echo imaging. The transfer constant (K ^trans) was measured adjacent to intracranial aneurysm and adjacent to the normal intracranial artery.

RESULTS

Twenty-nine subjects were analyzed (mean age, 53.9 ± 13.5 years; 24% men; PHASES score: median, 8; interquartile range, 4.75-10). K ^trans was higher in intracranial aneurysms compared with the normal intracranial artery (median, 0.0110; interquartile range, 0.0060-0.0390 versus median, 0.0032; interquartile range, 0.0018-0.0048 min^-1; P < .001), which correlated with intracranial aneurysm size (Spearman ρ = 0.54, P = .002) and PHASES score (ρ = 0.40, P = .30). Aneurysm wall enhancement, detected in 19 (66%) aneurysms, was associated with intracranial aneurysm size and the PHASES score but not significantly with K ^trans (P = .30). Aneurysms of 2 of the 9 patients undergoing conservative treatment ruptured during 1-year follow-up. Both ruptured aneurysms had increased K ^trans, whereas only 1 had aneurysm wall enhancement at baseline.

CONCLUSIONS

Dynamic contrast-enhanced MR imaging showed increased K ^trans adjacent to intracranial aneurysms, which was independent of aneurysm wall enhancement on postcontrast vessel wall MR imaging. Increased aneurysm wall permeability on dynamic contrast-enhanced MR imaging provides new information that may be useful in intracranial aneurysm risk assessment.

Rap1b is critical for glycoprotein VI-mediated but not ADP receptor-mediated alpha2beta1 activation

BACKGROUND

The platelet alpha2beta1 integrin functions as both an adhesion and signaling receptor upon exposure to collagen. Recent studies have indicated that alpha2beta1 function can be activated via inside-out signaling, similar to the prototypical platelet integrin alphaIIbbeta3. However, signaling molecules that regulate alpha2beta1 activation in platelets are not well defined. A strong candidate molecule is the small GTPase Rap1b, the dominant platelet isoform of Rap1, which regulates alphaIIbbeta3 activation.

OBJECTIVES

We hypothesized that Rap1b positively regulates alpha2beta1 during agonist-induced platelet activation.

METHODS

To test whether Rap1b activates alpha2beta1 downstream of glycoprotein (GP)VI or other platelet receptors, we stimulated platelets purified from Rap1b-/- or wild-type mice with diverse agonists and measured alpha2beta1 activation using fluorescein isothiocyanate-labeled monomeric collagen. We also examined the role of Rap1b in outside-in signaling pathways by analyzing adhesion and spreading of Rap1b-/- or wild-type platelets on monomeric, immobilized collagen. Finally, we monitored the activation status of related Rap GTPases to detect changes in signaling pathways potentially associated with Rap1b-mediated events.

RESULTS

Rap1b-/- platelets displayed comparable ADP-induced or thrombin-induced alpha2beta1 activation as wild-type platelets, but reduced convulxin-dependent alpha2beta1 activation. Rap1b-/- platelets exhibited increased spreading on immobilized collagen but similar adhesion to immobilized collagen compared to wild-type platelets. Rap1b-/- platelets also showed Rap1a and Rap2 activation upon agonist stimulation, possibly revealing functional compensation among Rap family members.

CONCLUSIONS

Rap1b is required for maximal GPVI-induced but not ADP-induced activation of alpha2beta1 in murine platelets.

Semi-automated color segmentation of anatomical tissue

We propose a semi-automated region-based color segmentation algorithm to extract anatomical structures, including soft tissues, in the color anatomy slices of the Visible Human data. Our approach is based on repeatedly dividing an image into regions using Voronoi diagrams and classifying the regions based on experimental classification statistics. The user has the option of reclassifying regions in order to improve the final boundary. Our results indicate that the algorithm can find accurate outlines in a small number of iterations and that manual interaction can markedly improve the outline. This approach can be extended to 3D color segmentation.