Generation of individualized thalamus target maps by using statistical shape models and thalamocortical tractography

BACKGROUND AND PURPOSE

Neurosurgical interventions of the thalamus rely on transferring stereotactic coordinates from an atlas onto the patient's MR brain images. We propose a prototype application for performing thalamus target map individualization by fusing patient-specific thalamus geometric information and diffusion tensor tractography.

MATERIALS AND METHODS

Previously, our workgroup developed a thalamus atlas by fusing anatomic information from 7 histologically processed thalami. Thalamocortical connectivity maps were generated from DTI scans of 40 subjects by using a previously described procedure and were mapped to a standard neuroimaging space. These data were merged into a statistical shape model describing the morphologic variability of the thalamic outline, nuclei, and connectivity landmarks. This model was used to deform the atlas to individual images. Postmortem MR imaging scans were used to quantify the accuracy of nuclei predictions.

RESULTS

Reliable tractography-based markers were located in the ventral lateral thalamus, with the somatosensory connections coinciding with the VPLa and VPLp nuclei; and motor/premotor connections, with the VLpv and VLa nuclei. Prediction accuracy of thalamus outlines was higher with the SSM approach than the ACPC alignment of data (0.56 mm versus 1.24; Dice overlap: 0.87 versus 0.7); for individual nuclei: 0.65 mm, Dice: 0.63 (SSM); 1.24 mm, Dice: 0.4 (ACPC).

CONCLUSIONS

Previous studies have already applied DTI to the thalamus. As a further step in this direction, we demonstrate a hybrid approach by using statistical shape models, which have the potential to cope with intersubject variations in individual thalamus geometry.

Technical note: standardized and semiautomated Harris lines detection

Arrest in long bone growth and the subsequent resumption of growth may be visible as radiopaque transverse lines in radiographs (Harris lines, HL; Harris, HA. 1933. Bone growth in health and disease. London: Oxford University Press). The assessment of individual age at occurrence of such lines, as part of paleopathological skeletal studies, is time-consuming and shows large intra- and interobserver variability. Thus, a standardized, automated detection algorithm would help to increase the validity of such paleopathological research. We present an image analysis application facilitating automatic detection of HL. On the basis of established age calculation methods, the individual age-at-formation can be automatically assessed with the tool presented. Additional user input to confirm the automatic result is possible via an intuitive graphical user interface. Automated detection of HL from digital radiographs of a sample of late Medieval Swiss tibiae was compared to the consensus of manual assessment by two blinded expert observers. The intra- and interobserver variability was high. The quality of the observer result improved when standardized detection criteria were defined and applied. The newly developed algorithm detected two-thirds of the HL that were identified as consensus lines between the observers. It was, however, necessary to validate the last one-third by manual editing. The lack of a large test series must be noted. The application is freely available for further testing by any interested researcher.

Modeling intravasation of liquid distension media in surgical simulators

During therapeutic hysteroscopy and transurethral resection of the prostate, intravasation of the liquid distension media into the vascular system of the patient occurs. We present a model which allows the integration of the intravasation process into surgical simulator systems. A linear network flow model is extended with a correction for non-Newtonian blood behavior in small vessels and an appropriate handling of vessel compliance. We employ a fast lookup scheme in order to allow for real-time simulation. Cutting of tissue is accounted for by adjusting pressure boundary conditions for all cut vessels. We investigate the influence of changing distention fluid pressure settings and of the position of tissue cuts. In addition, we quantify the intravasation occurring with different approaches of fluid control, and we compare the performance of direct and iterative solvers applied to the non-linear system of the compliant model. Our simulation predicts significant intravasation only on the venous side, and just in cases when larger veins are cut. The implemented methods allow the realistic control of bleeding for short-term and of the total resulting intravasation volume for long-term complication scenarios. While the simulation is fast enough to support real-time training, it is also adequate for explaining intravasation effects which were previously observed on a phenomenological level only.

Epidural malignant lymphomas of the spine: collected experiences with epidural malignant lymphomas of the spinal canal and their treatment

STUDY DESIGN

Retrospective study of 13 patients treated by the authors.

OBJECTIVE

To examine the course of the disease of malignant lymphoma (ML) presenting in the epidural area of the spine.

SETTING

Department of Neurosurgery, Third Department of Internal Medicine, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary.

SUBJECTS AND METHODS

The epidural presentation in eight patients was heralded by motor signs (paraparesis and plegia), in one by a lesion of the posterior columns of the spinal cord (ataxia), and in three by pain. One patient was free of complaints and symptoms. The affected epidural area was diagnosed previously by myelography and computerized tomography (CT), and later by magnetic resonance (MR), over the course of which the location was verified as thoracic in eight patients, cervical in one, and lumbar in four. The authors recommended surgical intervention in 9 out of 13 cases, in seven cases of Hodgkin's and six cases of non-Hodgkin's lymphoma. Seven patients were treated for recognized manifestations of malignant lymphoma while six were diagnosed by intraoperative-histological examination.

RESULTS AND CONCLUSION

The decompression operations for tumors resulted in limited improvement in seven patients (reduction in pain and return of ability to walk). Four patients were not operated on, two of which had significant improvement in their neurological symptoms. Paraparesis remained unchanged in one patient. One patient remained symptom-free. The authors emphasize the importance of interdisciplinary consultation and weighing individual priorities in the indications for operation on epidural ML.

Non-rigid registration of multi-modal images using both mutual information and cross-correlation

The hierarchical subdivision strategy which decomposes a non-rigid matching problem into numerous local rigid transformations is a very common approach in image registration. While mutual information (MI) has proven to be a very robust and reliable similarity measure for intensity-based matching of multi-modal images, numerous problems have to be faced if it is applied to small-sized images, compromising its usefulness for such subdivision schemes. We examine and explain the loss of MI's statistical consistency along the hierarchical subdivision. Information theoretical measures are proposed to identify the problematic regions in order to overcome the MI drawbacks. This does not only improve the accuracy and robustness of the registration, but also can be used as a very efficient stopping criterion for the further subdivision of nodes in the hierarchy, which drastically reduces the computational cost of the entire registration procedure. Moreover, we present a new intensity mapping technique allowing to replace MI by more reliable measures for small patches. Integrated into the hierarchical framework, this mapping can locally transform the multi-modal images into an intermediate pseudo-modality. This intensity mapping uses the local joint intensity histograms of the coarsely registered sub-images and allows the use of the more robust and computationally more efficient cross-correlation coefficient (CC) for the matching at lower levels of the hierarchy.

4D MR imaging of respiratory organ motion and its variability

This paper describes a method for 4D imaging, which is used to study respiratory organ motion, a key problem in various treatments. Whilst the commonly used imaging methods rely on simplified breathing patterns to acquire one breathing cycle, the proposed method was developed to study irregularities in organ motion during free breathing over tens of minutes. The method does not assume a constant breathing depth or even strict periodicity and does not depend on an external respiratory signal. Time-resolved 3D image sequences were reconstructed by retrospective stacking of dynamic 2D images using internal image-based sorting. The generic method is demonstrated for the liver and for the lung. Quantitative evaluations of the volume consistency show the advantages over one-dimensional measurements for image sorting. Dense deformation fields describing the respiratory motion were estimated from the reconstructed volumes using non-rigid 3D registration. All obtained motion fields showed variations in the range of minutes such as drifts and deformations, which changed both the exhalation position of the liver and the breathing pattern. The obtained motion data are used in proton therapy planning to evaluate dose delivery methodologies with respect to their motion sensitivity. Besides this application, the new possibilities of studying respiratory motion are valuable for other applications such as the evaluation of gating techniques with respect to residual motion.

Patient specific simulation and navigation of ventriculoscopic interventions

In this paper a comprehensive framework for pre-operative planning, procedural skill training, and intraoperative navigation is presented. The goal of this system is to integrate surgical simulation with surgical planning in order to improve the individual treatment of patients. Various surgical approaches and new, more complex procedures can be assessed using a safe and objective platform that will allow the physicians to explore and discuss possible risks and benefits prior to the intervention. A simulation environment extends the pre-operative planning in a natural way, as it allows for direct evaluation of the surgical approach envisioned for each case. In addition, by providing intraoperative navigation based on this simulation, surgeons can carry out the previously optimized plan with higher precision and greater confidence.

Nitric oxide production in striatum and pallidum of cirrhotic rats

Ammonium and manganese are neurotoxic agents related to brain metabolic disturbances observed after prolonged liver damage. The aim of this study was to assess the production of nitric oxide (NO) in the brain of cirrhotic rats exposed to manganese. We induced cirrhosis by bile duct ligation for 4 weeks in rats. From brain, striatum and globus pallidus were dissected out, and NO synthase activity and the content of nitrites plus nitrates (NOx) were determined. In pallidum we found a diminished constitutive NO synthase activity from cirrhotic rats, independently of manganese exposure. This result was confirmed by low levels of NOx in the same brain area (P<0.05, two-way ANOVA). This finding was not related to protein expression of NO synthase since no differences were observed in immunoblot signals between cirrhotic and sham-operated animals. Results from present study suggest that the production of NO is reduced in basal ganglia during cirrhosis.

4D MR imaging using internal respiratory gating

Respiratory organ motion is a key problem in proton therapy and in many other treatments. This paper presents a novel retrospective gating method for 4D (dynamic 3D) MR imaging during free breathing to capture the full variability of respiratory organ deformation. In contrast to other imaging methods, a constant breathing depth or even strict periodicity are not assumed. 3D images of moving organs can be reconstructed for complete respiratory cycles by retrospective stacking of dynamic 2D images using internal image-based gating. Additional noise reduction by combining multiple images significantly increases the signal-to-noise ratio. The resulting image quality is comparable to breath-hold acquisitions. Although the method was developed for proton therapy planning, the new possibilities to study respiratory motion are valuable to improve other treatments and to assess gating techniques, which rely on stronger assumptions about the breathing pattern.

Tumor growth models to generate pathologies for surgical training simulators

Many virtual reality based surgical training simulators have been presented in the last few years. These systems promise to alleviate the lack of realistic training possibilities common to minimally invasive procedures. Virtual reality allows for riskless training on a wide range of findings in a condensed period of time. We investigated different methods for the generation of tumor models suitable for surgical training simulators. The goal of our research is a high fidelity hysteroscopy simulator which provides an individual surgical scene for every training. Emphasis was placed on the modeling of growth processes leading to the generation of macroscopically realistic findings of the most common pathologies in hysteroscopy, namely polyps and myomas found in the uterine cavity. Both a cellular automaton and a particle based tumor growth model are presented and discussed.

A hybrid cutting approach for hysteroscopy simulation

An integral element of every surgical simulator is the ability to interactively cut tissue. A number of approaches have been suggested in the past, the most important being mesh subdivision by introducing new elements and mesh adaptation by adjusting existing topology. In this paper we combine these two methods and optimize them for our training system of hysteroscopic interventions. The basic methodology is introduced in 2D, a first extension to 3D is presented and finally the integration into the simulator described.

Generation of variable anatomical models for surgical training simulators

The generation of variable surgical scenes is a key element for effective training with surgery simulators. Our current research aims at a high fidelity hysteroscopy simulator which challenges the trainee with a new surgical scene in every training session. We previously reported on methods able to generate a broad range of pathologies within an existing healthy organ model. This paper presents the methods necessary to produce variable models of the healthy organ. In order to build a database of uteri, a volunteer study was conducted. The segmentation was carried out interactively, also covering the establishment of an anatomically meaningful correspondence between the individual organs. The variability of the shape parameters has been characterized by principal component analysis. A new method has been developed and tested, allowing the derivation of realistic new instances based on the stochastic model and complying with non-linear shape constraints which are defined and interactively controlled by medical experts.

Hydrometra Simulation for VR-Based Hysteroscopy Training

During hysteroscopy a hydrometra is maintained, i.e. the uterus is distended with liquid media to access and visualize the uterine cavity. The pressure and flow induced by the liquid are crucial tools for he gynecologists during surgery to obtain a clear view of the operation site. This paper presents two different aspects of hydrometra simulation, namely the distension of the uterine muscle and the liquid flow simulation in the cavity. The deformation of the organ's shape is computed offline based on finite element calculations whereas the flow is approximated on the fly by solving the simplified Navier-Stokes equations. The real-time capabilities of the presented algorithms as well as the level of fidelity achieved by the proposed methods are discussed.

Detailed anatomy of the abdomen and pelvis of the visible human female

We report on a virtual anatomical preparation of the abdomen and pelvis of the Visible Human Female (VHF) for laparoscopic surgery training. The detailed cross-sectional image data set from the U.S. National Library of Medicine was used as the basis to build an exemplary model of the female abdomen and pelvis. Segmentation software was developed to delineate organ outlines and more than 300 structures of interest, including organs, blood vessels, bones, muscles, and ligaments, have been segmented and three-dimensionally reconstructed. Analyzing the normal anatomy we found several variations and pathologies of the VHF, such as missing muscles (gemellus superior, psoas minor), additional veins as well as spondylophytes (vertebral column, pubic bone), and colon diverticula. The complete data set may be viewed on the home page of the project (http://www.vision.ee.ethz.ch/projects/Lasso/start.html).

Comparing a simplified FEM approach with the mass-spring model for surgery simulation

Virtual reality based surgical simulators offer a very elegant approach to enhancing traditional training in endoscopic surgery. In this context a realistic soft tissue model is of central importance. The most accurate procedures for modeling elastic deformations of tissue use the Finite Element Method (FEM) to solve the governing mechanical equations. An alternative are mass-spring models which are a crude approximation of the real physical behavior. The main reason given when using the mass-spring approach is the computational complexity of FEM. In this study we show that an optimized linear FEM model requires computation time similar to the mass-spring approach, while giving better results.

Ascending and descending projections of the lateral vestibular nucleus in the rat

The tracer neurobiotin was injected into the lateral vestibular nucleus in rat and the efferent fiber connections of the nucleus were studied. The labeled fibers reached the diencephalon rostrally and the sacral segments of the spinal cord caudally. In the diencephalon, the ventral posteromedial and the gustatory nuclei received the most numerous labeled fibers. In the mesencephalon, the inferior colliculus, the interstitial nucleus of Cajal, the nucleus of Darkschewitch, the periaqueductal gray matter and the red nucleus received large numbers of labeled fibers. In the rhombencephalon, commissural and internuclear connections originated from the lateral vestibular nucleus to all other vestibular nuclei. The medioventral (motor) part of the reticular formation was richly supplied, whereas fewer fibers were seen in the lateral (vegetative) part. In the spinal cord, the descending fibers were densely packed in the anterior funiculus and in the ventral part of the lateral funiculus. Collaterals invaded the entire gray matter from lamina IX up to lamina III; the fibers and terminals were most numerous in laminae VII and VIII. Collateral projections were rich in the cervical and lumbosacral segments, whereas they were relatively poor in the thoracic segments of the spinal cord. It was concluded that the fiber projection in the rostral direction was primarily aimed at sensory-motor centers; in the rhombencephalon and spinal cord, fibers projected onto structures subserving various motor functions.

Postoperative radiotherapy of childhood medulloblastomas

The purpose of this work is to review the result of radiotherapy in the treatment of medulloblastoma in pediatric patients. Between 1986 and 1998, 66 children (45 boys and 21 girls) received postoperative irradiation in our institute. Their mean age was 8.29 years. Irradiation was performed by linear accelerator, 36 Gy were applied in the high risk group (partial tumor resection, tumor cell positivity in the liquor, metastases within the central nervous system) and 30 Gy in the low risk group (total tumor resection, negative liquor cytology, no metastases within the central nervous system) on the entire cerebrum and spinal cord. This was followed in both groups by the application of 20-20 Gy boost irradiation on the posterior scala. Studying the survival it has been found that the surgical radicality did not significantly influence the survival chances of patients, however, with the increase in the tumor size the survival chance significantly decreases (p = 0.03). When predicting life expectancy, however, the stage of tumor, the age of patients, the risk group and the M stage yielded essential information. At the age of 8 years and less, the rate of survivors is 67.6%, for those over 8 years is 75.9% (p = 0.21), however the younger age was not significant. The appearance of metastases considerably deteriorates the chances of survival (from 81.5% to 66.7%, p = 0.02). In the low risk group of patients the 5-year survival is 80%, while in the high risk group it is significantly lower, 67.4% (p = 0.04).

Anteposition of the internal carotid artery for surgical treatment of kinking

BACKGROUND

Kinking of the extracranial portion of the internal carotid artery (ICA) requires surgical reconstruction when it causes neurological symptoms. We suggest a simple surgical reconstruction without arteriotomy.

METHOD

Anteposition of the ICA ventral to the digastric muscle has been performed in three patients. Kinks in the ICAs, proved by angiography, were thought to be responsible for clinical signs and symptoms.

RESULTS

The operations resulted in improvement, both clinically and radiologically.

CONCLUSION

The complications of arteriotomy can be avoided using the technique of ICA antepositioning described in this paper.

An approach to the complexity of the brain

The establishment of ordered neuronal connections is supposed to take place under the control of specific cell adhesion molecules (CAM) which guide neuroblasts and axons to their appropriate destination. The extreme complexity of the nervous system does not provide a favorable medium for the development of deterministic connections. Simon's [112] theorems offer a mean to approach the high level of complexity of the nervous system. The basic tenet is that complex systems are hierarchically organized and decomposable. Such systems can arise by selective trial and error mechanisms. Subsystems in complex systems only interact in an aggregate manner, and no significant information is lost if the detail of aggregate interactions is ignored. A number of nervous activities, which qualify for these requirements, are shown. The following sources of selection are considered: internal and external feedbacks, previous experience, plasticity in simple structures, and the characteristic geometry of dendrites. The role played by CAMs and other membrane-associated molecules is discussed in the sense that they are either inductor molecules that turn on different homeobox genes, or downstream products of genes, or both. These molecules control cellular and tissular differentiation in the developing brain creating sources of selection required for the trial and error process in the organization of the nervous tissue.

Intraoperative monitoring of the motor pathway using transtracheal stimulation of the cervical spine in dogs

Although SEP monitoring of the spinal cord has been a well established method recently, not an ultimate, perfectly developed technique for monitoring of the motor system is known so far, particularly, because of the disturbing effect of narcotic drugs and relaxants on the motor evoked potentials. In this study the upper part of the spinal cord was stimulated in 14 anesthetized and relaxed dogs with a cathode attached to the intratracheal tube and an anode fixed to the cervical spinous processes. Single and serial stimuli were applied. Recordings were obtained from the exposed right femoral nerve and quadriceps muscle. Averaging was necessary when using serial stimulations. Responses were consequent and reproducible during regular anesthesia. The origin of the different responses in the spinal cord is discussed. The method seems to be appropriate for intraoperative monitoring of the thoracolumbar spine.

Somatosensory and motor evoked potentials in patients with tumours in the spinal canal

Motor and sensory evoked potentials were recorded in 27 patients with expanding spinal tumour. The patients were divided into 2 groups: I. tumours at the level of the spinal cord and II. at the level of the cauda equina. On the basis of the localization of the tumour, midline and lateral subgroups were distinguished. The latencies of motor evoked potentials were prolonged in most of the patients, even those without paresis, in both groups. The motor evoked potentials detected subclinical motor lesions in 7 patients. All patients but one manifested sensory deficits, which could not be shown with the somatosensory evoked potentials. Significantly more prolonged cortical motor latencies were found in most of the patients with a laterally located tumour on the tumour side than contralaterally, whereas in somatosensory evoked potentials this difference was not apparent. On the basis of these observations, we concluded that motor evoked potentials, 1. could more reliably detect the neural deficit than somatosensory evoked potentials; 2. could show the side where the tumour was located; 3. proved useful in the detection of subclinical motor lesions. The general conclusion may be drawn that this electrophysiological method can provide useful information for the surgeon.

Transtracheal electrical stimulation of the spinal cord for intraoperative monitoring of the motor pathway

Because of the suppressant effects of anesthetic drugs and muscle relaxants on motor responses elicited by either magnetic or electrical transcranial stimulation, intraoperative monitoring of the motor system, and especially monitoring of lower limb function, presents many difficulties. The upper part of the spinal cord was stimulated in 14 anesthetized and relaxed dogs with a cathode attached to the intratracheal tube and an anode fixed above the upper cervical spinous processes. Action potentials evoked by single and serial stimuli were recorded from the exposed right femoral nerve and quadriceps muscle Averaging was necessary for serial stimulations. Reproducible early and late responses to both single and serial stimulations were recorded during regular anesthesia. The origin of the different responses is discussed. Transtracheal stimulation of the spinal cord is easy to perform and the responses recorded from the peripheral nerve or limb muscle are well reproducible in regular anesthesia. The method seems to be appropriate for intraoperative monitoring of the thoracolumbar spine.

Correlation between central somatosensory conduction time, blood flow velocity, and delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage

In this retrospective study of 67 aneurysmal patients, the predictive role of central conduction time (CCT) on vasospasm occurrence evaluated by means of transcranial Doppler sonography (TCD) and the correlation of CCT to blood flow velocity measured simultaneously in postoperative course were studied. Data about the clinical state of patients at the time of admission (Hunt Hess scale), severity of subarachnoidal hemorrhage on initial CT scan (Fisher grade), timing of surgery (acute or delayed), outcome (Glasgow Outcome Scale), severity of vasospasm graded by highest mean blood flow velocity (BFV) during the entire clinical course and CCT values measured at admission (preoperatively), then postoperatively (one day after surgery) and simultaneously with later TCD investigations were collected from the files. Interhemispheric difference of CCT was also calculated. The results showed that CCT at admission was not predictive for vasospasm. CCT measured either at admission or on the first postoperative day did not differ significantly in the different grades of vasospasm. Similar results were obtained in the acute and in the late operated group of patients. The results also suggest that increased CCT and interhemispheric difference at the time of admission indicate a worse prognosis, but this can be related to higher surgical risk rather than to a higher incidence of late ischemic deterioration. Simultaneous CCT and TCD examinations demonstrated that coincident and statistically significant (p < 0.01) increase of actual CCT (6.7 msec) was found only in the severe grade of vasospasm (BFV 200 cm/s). The authors discuss the role of CCT and TCD monitoring in the management of aneurysmal subarachnoid hemorrhage.

Examinations of the motor conduction time between the motor cortex and the Erb point in patients suffering from tumors of the central nervous system

The cortical latency and the motor conduction time between the motor cortex and the Erb point were investigated in 85 patients with intracranial and in 9 patients with space-occupying spinal tumors. Electrophysiological examinations revealed pathological changes in 19% of intracranial events, and in 100% of cases of spinal tumors. In these latter cases close correlation was registered between the motor evoked potentials and the clinical symptoms of the patients.

Motor and somatosensory conduction time between the cortex and the Erb point in patients suffering from cervical spinal stenosis and tumour

Motor and sensory conduction time between the cortex and the Erb point were examined in patients with cervical cord compression. Patients were divided into two groups: the compression was caused either by cervical extramedullary tumour (9 cases), or by cervical spondylosis or herniated disc (16 cases). In response to median nerve stimulation, pathological somatosensory evoked potentials were recorded in 66% of the patients suffering from tumour and in 60% of the patients suffering from spondylosis. All of the patients disclosed pathological motor evoked potentials. On the basis of these observations it could be concluded that, in cases of cervical spinal cord compression, the involvement of the motor system could be more reliably detected than that of the sensory system with electrophysiological methods.

Multimodal electrophysiological examinations in patients suffering from various tumors of the pineal region

Multimodal electrophysiological examinations: blink-, glabella- and masseter-reflexes, as well as brain stem acoustic, somatosensory and visual evoked potentials were examined in thirteen patients with clear consciousness suffering from extra-axial, chronic, expanding processes in the tectal region. According to the data, the authors came to the conclusion that several modalities were often required to make a correct diagnosis or to the localization of the space occupying processes. Functional disturbances of the whole of the lower brain stem, but especially of the mesencephalon and of the lower pons were found in cases of expanding processes surrounding the tectum.

[Validity of chromosome analysis and bleomycin sensitivity assay in the prevention of head and neck cancer in Hungary]

Because of unfavourable cancer mortality statistics of Hungary, the search of different biomarkers is one of the most important demands of the national primary cancer prevention programme. The aim of this study was to clarify the usefulness of bleomycin sensitivity assay elaborated in the USA, and to find whether it serves under our environmental conditions as a biomarker of individual sensitivity and risk for head and neck cancer, beside chromosomal aberration analysis. The test reflecting mutagen sensitivity is based on the mean values of chromatid breaks induced by bleomycin in vitro in a single lymphocyte (break/cell = b/c). Since cancer formation is influenced by environmental mutagens, in contrast to others, their 111 head and neck cancer patients were matched not only with 230 healthy controls (106 nonsmokers and 124 smokers), but also with 44 strong alcoholic and smoking patients with liver diseases whose lifestyle did not differ from that of the cancer patients. According to the results of conventional chromosome analysis, the aberrant cell frequency was the highest in the cancer patients (3.34%), while in the alcoholics (2.73%) and healthy smokers (2.88%) the values were similar. Thus, the genetic instability occurring in the form of elevated rate of spontaneous chromosomal aberrations was mostly expressed in head and neck cancer patients. Mutagen sensitivity measured by the b/c values of bleomycin assay was significantly higher in both the cancer (1.16 b/c) and the alcoholic patients (1.34 b/c) compared with the controls (1.0 b/c). The bleomycin sensitivity assay, therefore, seems to be the biomarker not only of cancer, but also the disease of the same etiology such as alcohol-related liver disease. However the method is not suitable for the assessment of individual cancer risk because of the high variability of b/c values in each group, and their considerable overlapping with the controls. It can also be supported with extremely high mutagen sensitivity of Hungarian controls (63 and 67%), which is three-fold of US values (23%). The bleomycin sensitivity assay is not a selective biomarker if comparing to the controls, probably due to the action of more complex exposures under Hungarian environmental conditions. When estimating cancer risk, the results of conventional chromosome analysis offer more information than bleomycin sensitivity assay.

Comparative study between the free radicals and tumor markers in patients with gastrointestinal tumors

The tumorous processes, increased level of tumor markers and the change of free radical status are associated in patents with gastrointestinal tumors. The aim of this study was to examine free radical status and tumor markers in patients with gastrointestinal tumors. Two hundered and thirteen patients with gastrointestinal tumor were examined. In the control group 44 non-tumorous patients were examined. The tumor markers (CEA, CA 19-9, CA 72-4, AFP, TPA, AGP) and free radical status (total scavenger capacity) were diagnosed using venal blood (obtained by LIA-kits and chemiluminescent methods, LIA-mAT and the Lumat Berthold instrument). It has been found that: (1) The results showed that the tumor markers, TPA and AGP are the best indicators for the tumorous process; (2) The AGP serum level was in the operable case 91.56+/-38.29 mg/dl meanwhile its value was, 128.46+/-47.62 mg/dl (P<0.001) in the inoperable case; and (3) The TPA value was 118.37+/-155.47 mg/dl in the operable case, (P<0.001) while its value was 227.32+/-244.39 mg/dl in inoperable cases. The significantly high levels of the plasma Chemiluminescent Light Intensity (CLI)=28.12+/-25.96; was obtained in patients with rectal tumors vs. in the control cases CLI= 4.27+/-5.12 RLU% (Relative Light Unit; mean+S.D.; P<0.005). In six of these cases, the free radical status examination indicated the presence of the tumor, even though the level of tumor markers was normal. It has been concluded that the testing of both regular tumor markers and free radical status has an important role in the diagnosis and monitoring of the patients with gastrointestinal tumors.

[Exposure or cancer predisposition? Cytogenetic examination of head and neck squamous cancer patients]

Search of different biomarkers is one of the most important demands of the national cancer prevention programme. We examined the usefulness of bleomycin sensitivity assay, whether it serves as a biomarker of individual sensitivity and risk for head and neck cancer under our environmental conditions. The test is based on the measurement of the means of chromatid breaks induced by bleomycin in vitro in a single lymphocyte (break/cell=b/c). 156 head and neck cancer patients were matched not only with 295 healthy controls (146 non-smokers and 149 smokers), but also with 51 strong alcoholic and smoking patients with liver disease whose lifestyle did not differ from that of the cancer patients. The aberrant cell frequency of cancer patients (2.85%), alcoholics (2.82%) and healthy smokers (2.81%) was similar and higher (p<0.03) than the values of non-smoker controls (2.25%). Thus, the results of conventional chromosome analysis indicate the effect of exposure to mutagens, derived mainly from smoking. Mutagen sensitivity measured by the bleomycin assay was significantly higher in both the cancer- (1.13 b/c) and the alcoholic patients (1.29 b/c) compared with smoker (1.04 b/c) and non-smoker controls (0.98 b/c). The bleomycin sensitivity assay, therefore, seems to be the biomarker not only for the cancer, but also for a disease of the same aetiology such as alcohol-related liver disease. However, the method is not suitable for the assessment of individual cancer risk due to overlapping of b/c values with those of controls. The proportion of mutagen sensitive persons in the group of Hungarian controls is 42-49%, which is two-fold of those in the US and Western Europe. When we estimate the cancer risk, the results of bleomycin sensitivity assay are equivocal under our experimental conditions, and they must be applied cautiously even in combination with the results of chromosome analysis.

[Radiotherapy of childhood brain stem tumours]

STUDY OBJECTIVE: Description and evaluation of radiotherapy of inoperable brain stem tumours. Possibilities of improving therapeutic results. MATERIALS AND METHODS: Between 1987 and 2000 43 patients (23 boys and 20 girls, mean age 8.5+/-4.4 years) with brain stem tumours were treated with 6 MV and 9 MV X-ray. The doses administered ranged from 30 to 66 Gy; mean 50.41+/-7.67 Gy. Treatment in each case was performed according to CT- and /or MR-based radiotherapy plan. Since 2000 3D conformal radiotherapy plans have been prepared by using image fusion. RESULTS: All patients were followed. The mean follow-up period was 19.4 months (range: 1 to 112 months). For survival statistics the 2 to 3-year overall and symptom-free survivals were taken into account, the former ones in the function of tumour localisations. The gender of children did not affect the survival (p>0.74). No significant difference was found as to survival in the function of tumour localisation either (p>0.87). CONCLUSION: According to the literature data the results expected were not achieved by hyperfractionation and by delivering an overall focal dose of 72 to 78 Gy. Results can be improved by precise patient fixation and the routine application of 3D conformal radiotherapy plans prepared by CT- and MR-based image fusion. These together can result the correctly reproducible patient fixation, the homogenous radiation delivery in the target volume and the reduction of injury in the surrounding tissues. Irradiation should be performed also in histologically not verified tumours since a 24.6 month transitory improvement could be achieved in 60.5% of our patients.

Precision of distance determination using 3D to 2D projections: the error of migration measurement using X-ray images

The goal of this study has been to objectively and reliably estimate the precision of measuring 2D migration of hip prostheses. This is the distance change over time between the implant and the bone observable in X-ray images. To reach this goal, a generally valid scheme for determining the standard deviation of distance measurements in 3D to 2D projections has been worked out. The scheme was applied to four previously published methods for measuring the migration of the prosthetic cup using standard radiographs. Applying the scheme yields measures for the sensitivity of the migration measurement towards the relevant sources of error. Inserting previously published data for the amounts of the entering errors, the standard deviation of the migration measurement has been calculated numerically resulting in values up to several millimeters.

[Automatic measurement of dye filling of simultaneous digital ICG- and fluorescein angiography sequences]

BACKGROUND

The ICG filling is supposed to be faster than Fluorescein filling. Interestingly the filling characteristics of these dyes were never correlated directly using precise quantitative methods. Since ICG and Fluorescein are injected as a mixture, the simultaneous 2-channel angiography provides a suitable method to correlate the filling characteristics of the dyes.

MATERIAL AND METHODS

The simultaneous ICG and Fluorescein angiograms were recorded with a Rodenstock Scanning Laser Ophthalmoscope. The angiographic images were digitized real-time with a graphic workstation. Filling characteristics of the two dyes was calculated after off-line eye tracking in different regions of interests (ROIs) on the central retina.

RESULTS

The Fluorescein filling was faster than the ICG filling in 56.5% of our patients. In 26% of our patients was a mixed filling detectable. Depending on the position of the ROIs the Fluorescein or ICG filling was faster. In only 17.5% of our cases was the ICG filling faster than the Fluorescein filling.

CONCLUSION

Our results show that Fluorescein filling in more than 50% of the cases is faster than ICG filling and only a minority of the patients has a faster ICG filling. According to our experience the filling pattern of the two dyes is individual, there is no rule of thumb for the filling.

Exploring the discrimination power of the time domain for segmentation and characterization of active lesions in serial MR data

This paper presents a new method for the automatic segmentation and characterization of object changes in time series of three-dimensional data sets. The technique was inspired by procedures developed for analysis of functional MRI data sets. After precise registration of serial volume data sets to 4-D data, we applied a time series analysis taking into account the characteristic time function of variable lesions. The images were preprocessed with a correction of image field inhomogeneities and a normalization of the brightness over the whole time series. Thus, static regions remain unchanged over time, whereas changes in tissue characteristics produce typical intensity variations in the voxel's time series. A set of features was derived from the time series, expressing probabilities for membership to the sought structures. These multiple sources of uncertain evidence were combined to a single evidence value using Dempster-Shafer's theory. The project was driven by the objective of improving the segmentation and characterization of white matter lesions in serial MR data of multiple sclerosis patients. Pharmaceutical research and patient follow-up requires efficient and robust methods with a high degree of automation. The new approach replaces conventional segmentation of series of 3-D data sets by a 1-D processing of the temporal change at each voxel in the 4-D image data set. The new method has been applied to a total of 11 time series from different patient studies, covering time resolutions of 12 and 24 data sets over a period of about 1 year. The results demonstrate that time evolution is a highly sensitive feature for detection of fluctuating structures.

Modelling of soft tissue deformation for laparoscopic surgery simulation

Virtual reality based surgical simulator systems offer a very elegant solution to the development of endoscopic surgical trainers. While the graphical performance of commercial systems already makes PC-based simulators viable, the real-time simulation of soft tissue deformation is still the major obstacle in developing simulators for soft-tissue surgery. The goal of the present work is to develop a framework for the full-scale, real-time, finite element simulation of elastic tissue deformation in complex systems such as the human abdomen. The key for such a development is the proper formulation of the model, the development of scalable parallel solution algorithms, and special-purpose parallel hardware. The developed techniques will be used for the implementation of a gynecological laparoscopic VR-trainer system.

Parametric estimate of intensity inhomogeneities applied to MRI

This paper presents a new approach to the correction of intensity inhomogeneities in magnetic resonance imaging (MRI) that significantly improves intensity-based tissue segmentation. The distortion of the image brightness values by a low-frequency bias field impedes visual inspection and segmentation. The new correction method called parametric bias field correction (PABIC) is based on a simplified model of the imaging process, a parametric model of tissue class statistics, and a polynomial model of the inhomogeneity field. We assume that the image is composed of pixels assigned to a small number of categories with a priori known statistics. Further we assume that the image is corrupted by noise and a low-frequency inhomogeneity field. The estimation of the parametric bias field is formulated as a nonlinear energy minimization problem using an evolution strategy (ES). The resulting bias field is independent of the image region configurations and thus overcomes limitations of methods based on homomorphic filtering. Furthermore, PABIC can correct bias distortions much larger than the image contrast. Input parameters are the intensity statistics of the classes and the degree of the polynomial function. The polynomial approach combines bias correction with histogram adjustment, making it well suited for normalizing the intensity histogram of datasets from serial studies. We present simulations and a quantitative validation with phantom and test images. A large number of MR image data acquired with breast, surface, and head coils, both in two dimensions and three dimensions, have been processed and demonstrate the versatility and robustness of this new bias correction scheme.

Virtual reality based surgery simulation for endoscopic gynaecology

Virtual reality (VR) based surgical simulator systems offer very elegant possibilities to both enrich and enhance traditional education in endoscopic surgery. However, while a wide range of VR simulator systems have been proposed and realized in the past few years, most of these systems are far from able to provide a reasonably realistic surgical environment. We explore the basic approaches to the current limits of realism and ultimately seek to extend these based on our description and analysis of the most important components of a VR-based endoscopic simulator. The feasibility of the proposed techniques is demonstrated on a first modular prototype system implementing the basic algorithms for VR-training in gynaecologic laparoscopy.

Elastic model-based segmentation of 3-D neuroradiological data sets

This paper presents a new technique for the automatic model-based segmentation of three-dimensional (3-D) objects from volumetric image data. The development closely follows the seminal work of Taylor and Cootes on active shape models, but is based on a hierarchical parametric object description rather than a point distribution model. The segmentation system includes both the building of statistical models and the automatic segmentation of new image data sets via a restricted elastic deformation of shape models. Geometric models are derived from a sample set of image data which have been segmented by experts. The surfaces of these binary objects are converted into parametric surface representations, which are normalized to get an invariant object-centered coordinate system. Surface representations are expanded into series of spherical harmonics which provide parametric descriptions of object shapes. It is shown that invariant object surface parametrization provides a good approximation to automatically determine object homology in terms of sets of corresponding sets of surface points. Gray-level information near object boundaries is represented by 1-D intensity profiles normal to the surface. Considering automatic segmentation of brain structures as our driving application, our choice of coordinates for object alignment was the well-accepted stereotactic coordinate system. Major variation of object shapes around the mean shape, also referred to as shape eigenmodes, are calculated in shape parameter space rather than the feature space of point coordinates. Segmentation makes use of the object shape statistics by restricting possible elastic deformations into the range of the training shapes. The mean shapes are initialized in a new data set by specifying the landmarks of the stereotactic coordinate system. The model elastically deforms, driven by the displacement forces across the object's surface, which are generated by matching local intensity profiles. Elastic deformations are limited by setting bounds for the maximum variations in eigenmode space. The technique has been applied to automatically segment left and right hippocampus, thalamus, putamen, and globus pallidus from volumetric magnetic resonance scans taken from schizophrenia studies. The results have been validated by comparison of automatic segmentation with the results obtained by interactive expert segmentation.

[Occurrence of Helicobacter pylori in patients with gastroesophageal tumors]

Authors examined the occurrence of H. p. retrospectively in bioptic material for three years. Fifty-one oesophageal and gastric tumorous patients were examined and as a control fourty-seven non tumorous patients with chronic gastritis chosen at random. The demonstration of H. p. was performed by modified Giemsa stain. Different types of chronic gastritis, forms and localisation of the tumours as well as their relation with sex and age were investigated. The occurrence of H. p. was higher in chronic gastritis than in tumorous processes. Seventy-one % H. p. positivity was found in the control group against 17.6% in the tumorous patients.

Organization of the motor centres for the innervation of different muscles of the tongue: a neuromorphological study in the frog

Cobalt labelling studies on the localization and morphology of the frog's hypoglossal nucleus have revealed three subnuclei. The dorsomedial subnucleus innervates the geniohyoid, hyoglossus, genioglossus and the intrinsic tongue muscles. The ventrolateral subnucleus supplies the sternohyoid, geniohyoid, omohyoid and intrinsic tongue muscles. The intermediate subnucleus innervates the omohyoid, geniohyoid and intrinsic tongue muscles. Neurons innervating protractor, retractor and intrinsic tongue muscles differ in their soma surface area and in their dendritic arborization pattern. It is concluded that there exists a musculotopic organization in the frog's hypoglossal nucleus and that motoneurons subserving different function in tongue movements disclose characteristic morphological differences.