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M Marinov

Publications and source records attributed to M Marinov.

At least 19 recordsLinked to original sources
PubMed2006

Virtual simulation of neuroendoscopic procedures: early clinical experience with ventricular lesions.

BACKGROUND: Virtual endoscopy (VE) is a new and promising imaging technology. Applied to neuroendoscopy it allows preoperative simulation of a procedure and evaluation of the individual intraventricular anatomy in selected cases. Along with neuronavigation and real time intraoperative imaging, VE is expected to improve the safety and efficacy of neuroendoscopic procedures. PATIENTS AND METHODS: Between April 2003 and February 2004 VE simulation was performed in 13 randomly selected patients subjected to endoscopic procedures. Pathological entities included 4 cases with aqueduct stenosis, 4 with suprasellar arachnoid cysts, 2 tumors of the posterior third ventricle, 1 colloid cyst, 1 hyperplasia of the choroid plexus and 1 case with multiloculated hydrocephalus due to intraventricular septations. In 8 patients VE was accomplished preoperatively, in another 5 it was done after the operation, using data sets from neuronavigation imaging planning in 4 patients, and in one case using postoperative imaging studies. T (1)-weighted 3D image sets were acquired on a 1.5 T GE Genesis SIGNA MR scanner and VE reconstruction was performed using the General Electric Navigator software. The VE images were compared with the real images obtained during the endoscopic procedures and evaluated for their impact on the planning of the operative approach. RESULTS: VE implementation succeeded in all 13 patients. Major neuroanatomic reference structures were easily recognizable in all cases. Membranous structures such as the thinned floor of the third ventricle or cyst walls were identifiable in only 46 % of the cases. In 6 cases (46 %) VE showed anatomical variants and details relevant for the endoscopic procedure that were not identified on conventional MR images. CONCLUSIONS: VE has proved to be an important adjunct to the preoperative planning of neuroendoscopic procedures and its routine application is suggested.

Adolescent↗
PubMed2003

Continuous-wave lasing of a stoichiometric Yb laser material: KYb(WO4)2.

For the first time to the authors' knowledge, continuous-wave laser emission of the stoichiometric crystal KYb(WO4)2 was achieved at 1068 nm. The 125-microm-thin sample was directly water cooled and pumped at 1025 nm by a Ti:sapphire laser. The maximum output power at room temperature was 20 mW.

Journal Article↗
PubMed2001

The complexity of linkage analysis with neural networks.

As the focus of genome-wide scans for disease loci have shifted from simple Mendelian traits to genetically complex traits, researchers have begun to consider new alternative ways to detect linkage that will consider more than the marginal effects of a single disease locus at a time. One interesting new method is to train a neural network on a genome-wide data set in order to search for the best non-linear relationship between identity-by-descent sharing among affected siblings at markers and their disease status. We investigate here the repeatability of the neural network results from run to run, and show that the results obtained by multiple runs of the neural network method may differ quite a bit. This is most likely due to the fact that training a neural network involves minimizing an error function with a multitude of local minima.

Diabetes Mellitus, Type 1↗
PubMed1999

A comparison of two algorithms, MultiMap and gene mapping system, for automated construction of genetic linkage maps.

Using the GAW11 Problem 2 data set, we compared the performance of two automated map construction algorithms, MultiMap and GMS (Gene Mapping System). The MultiMap algorithm iteratively adds markers in a stepwise manner to the map, while the GMS algorithm seeks to find the best order of the whole set of markers by selective permutations of logically formed subgroups of the markers. While it is difficult to compare these two rather different algorithms, we found that, on these data, GMS performed better than MultiMap, placing more markers in their true order on average, with little order ambiguity. In addition, as the number of markers increased, GMS was less computationally demanding than MultiMap. However, it MultiMap placed a marker, it was almost always in the correct order. In contrast, GMS often placed a group of markers on the wrong end of the map; such incorrect placements occur when the evidence for placement on one end or the other is not strong. Thus, there is room for further algorithmic developments that combine the strengths of both the MultiMap and GMS approaches.

Algorithms↗
PubMed1998

Surgical management of intraosseous skull base tumors with aid of Operating Arm System.

Invasion of bone and critical neurovascular structures often impedes complete resection of intraosseous skull base neoplasms, and these lesions tend to recur unless all infiltrated bone is removed. Evolving experience with image guidance over the past few years indicates the potential value of neuronavigation in skull base lesions diffusely infiltrating or fixed to bone structures. We report our early experience with the Radionics Operating Arm System (OAS), specifically emphasizing its utility as an adjunct in the treatment of intraosseous skull base tumors, mainly meningiomas. In April 1995 the OAS was introduced into clinical use at the neurosurgical university clinic in Münster, Germany. Since then, the system's utility has been explored in 10 patients out of the total neuronavigation series presenting with intraosseous skull base tumors (nine females and one male, mean age 47 years; nine meningiomas, one chordoma). For navigational planning, both 3-mm computed tomography scans and a set of 3-mm fat-suppression magnetic resonance images were chosen. At least four adhesive skin markers were used for system calibration. The system was technically usable in all cases in this small series. Because of the relative immobility of the bone structures and/or the tumor, no significant deviation from the preoperative registration accuracy was noted at the end of the procedures. The main advantages were easier localization and resection of infiltrated bone, which is often not grossly identifiable, even under the microscope. Our preliminary experience with the OAS suggests that image guidance is helpful in this type of lesion, providing better anatomical orientation during surgery and delineating tumor margins and their relation to critical neurovascular structures. The problem of a possible intracranial tumor and brain shift can be neglected in these lesions. The system facilitates resection by volumetric contour information, allowing more aggressive and complete resection.

Adult↗
PubMed1997

Analysis of bipolar disorder using affected relatives.

We have analyzed the GAW10 data from several studies of bipolar affective disorder (BPAD) using the software packages SimIBD and SIMWALK2. SimIBD implements a simulation-based affected-pedigree-member (APM) statistic, called SimAPM, as well as an APM-like statistic, also called SimIBD, that measures identical-by-descent (IBD) sharing. SIMWALK2 uses Markov chain Monte Carlo techniques to compute several IBD-based statistics on the degree of marker-allele clustering among all affected relatives. We have found no strong evidence of linkage to either chromosome 5 or 18. However, we did find that several markers showed p-values less than 0.01 and may deserve further study.

Alleles↗
PubMed1997

Lipofuscin product accumulation, insufficient antioxidant defence in erythrocytes and plasma and enhanced susceptibility to oxidative haemolysis after thermal trauma.

The mechanism of increased susceptibility of red blood cells to oxidative haemolysis in the early post-burn period remains unclear. In this study it was revealed that the accumulation of lipofuscin products in red blood cells was accompanied by the elevation of oxidative haemolysis on the 24th hour after thermal trauma of rats (full thickness skin, on 20% of TBSA). Enhanced thiobarbituric acid reactive substrates (TBARS) and lowered levels of antioxidants such as alpha-tocopherol, ceruloplasmin and albumin were found in plasma. The activity of superoxide dismutase (SOD) and the concentration of alpha-tocopherol and reduced glutathione (GSH) in erythrocytes were also diminished. The results from this study suggest that plasma and intracellular antioxidant deficiency can potentiate oxidative membrane damage. There was a positive correlation (r = 0.72) between increased levels of lipofuscin products and oxidative haemolysis of red blood cells. The enhanced susceptibility of erythrocytes to oxidative haemolysis may be considered as an indirect but sensitive indicator of the impaired antioxidant defence of these blood cells following thermal skin injury. The decreased resistance of red blood cell to oxidative haemolysis under the conditions of reduced antioxidant defence of erythrocytes and blood plasma suggests that adequate antioxidant therapy could prevent all these complications after thermal skin injury.

Animals↗
PubMed1996

Reversible focal ischemia model in the rat: correlation of somatosensory evoked potentials and cortical neuronal injury.

Somatosensory evoked potentials (SEPs) are valuable in experimental stroke studies, but only a few reports have dealt with small rodent models. Our experiments aimed to reproduce SEP monitoring during reversible middle cerebral artery occlusion (MCAo) in a surgical model of open craniotomy and vessel manipulations in the rat. The changes of median nerve SEPs were correlated to the degree of local cortical neuronal injury in the forelimb area. Based on a pilot group (n = 11) both parameters were examined at 2 h after reperfusion in a subsequent study with increase of MCAo time from 1 (n = 7) to 2 h (n = 7); 5 rats were sham operated. A significantly delayed and incomplete recovery of SEPs, expressed as a percentage of the mean preocclusion values was observed with 2 h compared to 1 h MCAo (20.8% versus 6.0% change in the latency and 59.5% versus 2.2% in the amplitude of the primary cortical response). The functional outcome was found to correlate consistently with the degree of neuronal damage in 1 and 2 h reversible MCAo (2.5% versus 79.2% severely damaged neuronal types III and IV). Our findings suggest, that 2 h MCAo followed by 2 h reperfusion produces a submaximal neuronal injury and partial electrical recovery in the periphery of the occluded vascular territory and could be therefore used as a reliable model for assessment of cerebroprotective drug efficacy.

Animals↗
PubMed1993

Answering the connectionist challenge: a symbolic model of learning the past tenses of English verbs.

Supporters of eliminative connectionism have argued for a pattern association-based explanation of language learning and language processing. They deny that explicit rules and symbolic representations play any role in language processing and cognition in general. Their argument is based to a large extent on two artificial neural network (ANN) models that are claimed to be able to learn the past tenses of English verbs (Rumelhart & McClelland, 1986, Parallel distributed processing, Vol. 2, Cambridge, MA: MIT Press; MacWhinney & Leinbach, 1991, Cognition, 40, 121-157). In this article we critically review Rumelhart and McClelland's as well as MacWhinney and Leinbach's ANN models and conclude that they do not succeed in the assigned task of learning the past tenses of English verbs. In order to answer their challenge to the symbolic processing approach, we present our symbolic pattern associator (SPA)-a general-purpose pattern associator that can learn to associate arbitrary discrete patterns. We carried out several experiments with the SPA using the same set of verbs that was used in MacWhinney and Leinbach's simulation with more realistic training and testing procedures. The SPA outperformed the connectionist models by a wide margin in the accuracy of learning, and successful inductive generalizations to unseen verbs. Our SPA has very natural and psychologically realistic explanations to many psychological effects such as U-shaped learning curve, and is much closer to human subjects in predicting past tense of the pseudo-verbs. In contrast to ANNs, whose internal representations are entirely opaque, the SPA can represent the acquired knowledge in the form of production rules that allow for further higher-level processing and integration, resulting in linguistically realistic associative templates for irregular verbs and production rules for regular verbs. In the light of these findings, we conclude that eliminative connectionists' vision of cognition as simple pattern association and pattern recognition without symbolic representation is inadequate. Pattern association as such does not imply rule-less or cue-based models of language acquisition or of human learning in general.

Cognition↗
PubMed1993

[Intracranial meningioma: analysis of radical surgery in 668 patients].

A series of 668 operated intracranial meningiomas is retrospectively analysed with respect to operative radicality and related factors. A total and subtotal resection is reported in 75.8% of cases. Major aspects are localisation, clinical state at the time of surgery and topographical relation of tumours to major neural and vascular structures. A basic reason for incomplete operative resection of tumours we assume to be delayed diagnosis and consecutive extensive tumour growth into relevant brain areas.

Adult↗
PubMed1992

[Effects of nimodipine in experimental permanent focal cerebral ischemia].

In a controlled double blind experiment the influence of a continuous i.v. infusion of Nimodipine (1 microgram kg-1 min-1) upon infarct size, histopathology and neurological outcome in rats with permanent middle cerebral artery (MCA) occlusion was examined. The infusion was started 20 min. before the induction of ischemia and continued 4 hours thereafter. The nimodipine treated animals were subdivided into hypotensive (MABP lower than 85 mmHG for more than 5 minutes after arterial occlusion) and normotensive groups. Infarction size, documented by TTC, H&E and Nissl staining was significantly smaller (p less than 0.001) in nimodipine normtonic rats than the lesions in placebo and saline treated rats, as well as compared with hypotonic nimodipine animals (largest infarction). These differences were found to be entirely at the expense of the cortical (frontoparietal) component of the lesion, suggesting "penumbra" action of the drug. Moreover, nimodipine normotonic rats displayed lower cortical neuronal injury in the periinfarct zone. These findings were corroborated by corresponding better neurological scores. Our results indicate that nimodipine is effective in reducing focal cerebral ischemia, provided the MABP is maintained higher than 85 mmHg.

Animals↗
PubMed1991

Effect of nimodipine in treatment of experimental focal cerebral ischaemia.

Despite the voluminous current literature the potential of nimodipine to modify the outcome in experimental cerebral ischaemia remains a controversial matter. The authors have evaluated in controlled double blind experiments the influence of a continuous i.v. infusion of the drug (1 microgram kg-1 min-1) upon infarct size, histopathology and neurological outcome in rats with permanent middle cerebral artery (MCA) occlusion. The infusion was started 20 min before induction of ischaemia and continued 4 hours thereafter. The nimodipine treated animals were subdivided into hypotensive (MABP lower than 85 mmHg for more than 5 min after arterial occlusion) and normotensive groups. Infarction size, documented by TTC, H&E and Nissl staining was significantly smaller (p less than 0.001) in nimodipine normotonic rats than the lesions in placebo and saline treated rats, as well compared with hypotonic nimodipine animals (largest infarction). These differences were found to be entirely at the expense of the cortical (frontoparietal) component of the lesion, suggesting 'penumbra' action of the drug. Moreover, nimodipine normotonic rats displayed lower cortical neuronal injury in the periinfarct zone. These findings were corroborated by corresponding better neurological scores. Our results indicate that nimodipine is effective in reducing focal cerebral ischaemia, provided the MABP is maintained higher than 85 mmHg.

Animals↗
PubMed1991

Lack of effect of PN 200-110 on neuronal injury and neurological outcome in middle cerebral artery-occluded rats.

We evaluated the influence of a continuous intravenous infusion of 0.24 mg/kg PN 200-110 started 20 minutes before the induction of ischemia and continued for 2 hours on infarct size, histopathology, and neurological outcome in middle cerebral artery-occluded rats treated with PN 200-110 (n = 8), placebo (n = 7), or saline (n = 8). Neurological examination was performed 24 hours after occlusion. We quantified infarct size by 2,3,5-triphenyl-tetrazolium chloride, hematoxylin and eosin, and Nissl staining and by computerized analysis of tracings of the infarcted areas and evaluated neuronal injury at the infarct periphery. The different types of ischemic cell damage were quantified by direct visual counting. We found no differences among saline-, placebo-, and PN 200-110-treated rats regarding infarct size, amount of neuronal alteration, and neurological outcome. Our results indicate the lack of a significant protective effect of this drug in experimental focal ischemia.

Animals↗
PubMed1991

The Dandy-Walker syndrome: diagnostic and surgical considerations.

Thirteen cases of the Dandy-Walker syndrome were seen over a period of 12 years. In this study their preoperative evaluation, surgical treatment and outcome is reviewed. The incidence of hydrocephalus in the series was 77%. Eight of the patients had associated central nervous system anomalies, and the need to identify these abnormalities is stressed. Because the two conditions require different surgical management, during the diagnostic work-up it is crucial to differentiate between the Dandy-Walker syndrome and extra axial cerebrospinal fluid (CSF) filled cysts, and to establish the patency of the aqueduct. The reliability of different diagnostic methods is discussed and the value of metrizamide computed tomographic ventriculography is emphasized. Unsatisfactory results following membrane excision in early cases, and observations of CSF dynamic disturbances confirm the futility of the direct approach for the management of the Dandy-Walker syndrome. The aqueduct was invariably patent and allowed either primary cyst or ventricular shunting, although simultaneous double shunting using a 'Y' connector may need to be carried out later. The mortality rate for the series was 18%. At follow-up 54.5% of the children were judged to have normal IQs.

Brain Damage, Chronic↗
PubMed1990

Intracranial ependymomas in children.

During a 20-year period (1964-1983), the authors managed 60 children with intracranial ependymomas. In 37 patients the tumors were located in the posterior cranial fossa, and in the remaining 23 they were supratentorial. The histological examination in 26 children revealed ependymoblastomas. The average duration of the clinical evolution was 4 months and 5 days in the supratentorial neoplasms and 3 months and 6 days in the subtentorial. Besides the intracranial hypertension, present in about 80% of the patients, specific localizing signs were seen in 70% of the children with subtentorial and in 40% of those with supratentorial tumors. Because of the growth pattern in posterior fossa ependymomas and despite the prevalence of histologically benign neoplasms, radical resection was accomplished in only 21.6% of the cases, as compared with 30.4% in supratentorial tumors. The postoperative mortality remains high: 29.7% in subtentorial tumors and 17.4% in supratentorial. The 1-year survival rate in subtentorial neoplasms was 70.3%, the 3-year survival 29.7%, and the 5-year survival 16.2%. The corresponding figures for supratentorial ependymomas more favorable: 82.6%, 43.5%, and 26.1%, respectively. The most important factors for improving the outcome at the present time appear to be as radical a resection as possible, supplemented with postoperative radiotherapy and chemotherapy.

Brain Neoplasms↗
PubMed1989

An evaluation of the surgical treatment of intracranial arachnoid cysts in children.

In the period 1976-1987, the number of intracranial arachnoid cysts treated at our institute was 60: sylvian, 29; midline supratentorial, 13; subtentorial, 18. The diagnosis was mainly made by means of the results of a combination of CT, dynamic cisternography, and ventriculography. Based on an analysis of the preoperative investigations and operative results, an attempt was made to determine the appropriate treatment more precisely in cysts at different locations. The direct microsurgical approach with membrane excision was mainly used in combination with a preliminary VA shunt to treat hydrocephalus. The direct approach was supplemented with secondary cavity shunting in 5 cases. In more than half of the patients we used membrane excision alone (mainly children with sylvian cysts). In suprasellar cysts we consider the subfrontal approach to be more appropriate than the transventricular one. We restricted the use of primary cyst shunting as an alternative treatment to only 3 infants, with huge cysts. The follow-up reveals that 82.7% of the cases were favorable affected to varying degrees.

Adolescent↗
PubMed1989

Long-term follow-up after surgical treatment of cerebellar astrocytomas in 100 children.

A retrospective study was performed in 100 children, who were operated on between 1954 and 1984 for cerebellar astrocytoma. Twenty-nine patients died during the 1st month after the operation. Of the patients who survived, 24 lived up to 5 years, 17 up to 10 years, and 30 lived 20 or more years. In 22 cases, tumor recurrence was the reason for reoperation. Radiation therapy was used in 25 cases with histological malignancy and/or after partial removal of the tumor. The analysis in 6 cases with brainstem involvement allowed us to conclude that in such cases the prognosis is poor with regard to survival. Although total removal of cerebral astrocytomas appears to be the most effective form of treatment, we are of the opinion that even subtotal excision may be compatible with long-term survival. This suggests that many of these tumors may show benign biological behavior.

Adolescent↗