Biomedical subjects

P Grunert

Publications and source records attributed to P Grunert.

At least 19 recordsLinked to original sources

PubMed1999

Accuracy of stereotactic coordinate transformation using a localisation frame and computed tomographic imaging. Part I. Influence of the mathematical and physical properties of the CT on the image of the rods of the localisation frame and the determination of their centres.

The accuracy of coordinate transformation from the computed tomographic (CT) space to the stereotactic frame space was analysed for frame-based stereotactic systems which use a localisation frame and coordinate transformation based on matrix calculation. The coordinate transformation was divided into three consecutive steps: (1) transforming the localisation frame into the CT image built up from pixels with distinct attenuation values, (2) determining the rod centres of the localisation frame in the CT image, and (3) coordinate transformation from the image to the frame space using the centres of the rods in the image space and algebraic, matrix-based calculation. The error contribution at each step was evaluated separately and its effect on the subsequent mathematical operations was analysed. The first step dealt with the influences of the mathematical and physical properties of the CT on the image of the localisation frame. Noise, slice thickness, convolution filter, dimension of the pixel matrix, and image processing had an influence on the attenuation values in each pixel. Above all, the slice thickness had an effect on the shape of the oblique rods in the CT image. At the second step, the main error contribution was due to the method by which the centre of the rods was calculated. The most accurate method was to determine the centre of gravity using the attenuation values as single mass points (with accuracy in the range of +/-1/10 pixel, or +/-0.125 mm), followed by rounding off the centre of gravity and the highest pixel value in the square matrix R2(N) within 1 pixel. Pointing with a cursor under visual control was accurate to 1 pixel and the pixel with the highest attenuation value showed deviations of up to 2 pixels in the x and y axes. Thus, the methods differed by a factor of 20. The influence of the CT mathematics and physics on the determination of the centre of the fiducials was negligible in comparison to the method of calculation used. There was no systemic error due to the filtred back projection algorithm. Data input errors due to noise were in the range of 1/10 pixel. The effects of the remaining physical influences were all in the range of the error due to noise. In particular these results speak in favour of no influence of slice thickness on coordinate transformation.

Artifacts↗

PubMed1999

Accuracy of stereotactic coordinate transformation using a localisation frame and computed tomographic imaging. Part II. Analysis of matrix-based coordinate transformation.

The accuracy of coordinate transformation from a CT image to a stereotactic frame was investigated for stereotactic systems using a localisation frame and matrix-based coordinate transformation. The main source of error influencing calculation was input data, due to inaccurate calculation of the centres of the rods of the localisation frame in the CT image, and the propagation of this input error during subsequent matrix calculation. Systemic errors during matrix calculation do not exist, and rounding off errors were of subordinate importance compared to the input data error. The influence of input data error on coordinate transformation was studied by geometric methods, computer simulation, and numerical analysis. In the geometric model, input data errors affected the calculation of the centres of the three oblique rods in the frame space and shifted them three points upwards or downwards on the axis of each rod. The three centres of the oblique rods defined the "CT plane" in the 3D space of the stereotactic frame. Displacements of these three centres caused a characteristic tilting of the CT plane. The positions of the correct and tilted CT planes defined the spatial error properties for all target points on the CT plane. The computer simulation investigated the effects on matrix-based transformation of all possible displacement combinations on the three oblique rods by 1 pixel (1. 16 mm) in the x and y directions. A characteristic, space-dependent distribution of the frame-related coordinates was obtained for each target point. In the centre of the frame, we found a maximal deviation of 1.0 mm in the xy direction and 2 mm in the z direction. This corresponded to an error amplification of 0.73 in the xy direction and 1.22 in the z direction relative to the error at the centres of the rods. The maximum deviation (found in the periphery) for all combinations on the three oblique rods was 1.7 mm in the xy direction and 3.3 mm in the z direction. This resulted in an amplification of 1.03 in the xy direction and 2.01 in the z direction. This results had to be multiplied by 2 to obtain a maximal error estimate for displacements including all nine rods of the localisation frame. Numerical analysis showed stable solutions with low error amplification for hexagonal frame arrangements.

Brain↗

PubMed1999

Frameless neuronavigation applied to endoscopic neurosurgery.

OBJECTIVE: We retrospectively analyzed the indications, surgical techniques, and applicability of frameless neuronavigation to endoscopic procedures in a heterogeneous group of 15 patients. MATERIAL AND METHODS: In 8 patients indications for surgery were cystic lesions, in 3 patients intraventricular tumors, and in 4 patients occlusive hydrocephalus. The mean age was 39 years (range 9-76 years). The follow-up period ranged from 5-24 months (mean 10 months). Frameless neuronavigation was accomplished with the "operating arm system" in 10 cases and with the "optical tracking system" in 5 cases (RADIONICS, Burlington, USA). RESULTS: In all 15 cases, neuronavigation sufficiently provided anatomical orientation, preoperative planning, and intraoperative realization of the approach. The calculated mean calibration error was 2.1 mm. There have been no permanent morbidities and no mortalities related to the use of endoscopes and neuronavigation. CONCLUSION: In endoscopic neurosurgery, frameless neuronavigation is a useful tool in planning and realizing the approach and improving intraoperative orientation in selected cases. Indications are small or hidden lesions, impaired visual conditions, abnormal anatomy, and narrow ventricles. Endoscopic procedures include fenestration and resection of intraventricular or intraparenchymal cysts, biopsy of intraventricular tumors, and third ventriculostomy in selected cases.

Adolescent↗

PubMed1999

Endoscopic third ventriculostomy: outcome analysis of 100 consecutive procedures.

OBJECTIVE: Endoscopic third ventriculostomy (ETV) has been shown to be a sufficient alternative in the surgical treatment of occlusive hydrocephalus. To elucidate the ongoing discussion of timing, indication, and surgical technique, a retrospective analysis of 100 consecutive ETVs was conducted. METHODS: One hundred ETVs were performed in 95 patients (43 female and 52 male patients). Their age ranged from 3 weeks to 77 years (mean age, 36 yr). Hydrocephalus was caused by aqueductal stenosis in 40 patients, space-occupying lesions in 42, and intraventricular or subarachnoid hemorrhage in 8. One patient had postinflammatory hydrocephalus, and four patients had occlusive hydrocephalus of unknown origin. In 33 cases, surgery was performed using stereotactic guidance. RESULTS: ETV was accomplished in 98 of 100 cases. The overall success rate was 76%. Patients with benign space-occupying lesions and nontumorous aqueductal stenosis had the highest success rates, which were 95 and 83%, respectively. Complications were arterial bleeding in one case, venous bleeding in three cases, intracerebral bleeding in one case, and infection in one case. There were no permanent morbidities or mortalities. CONCLUSION: ETV is most effective in treating uncomplicated occlusive hydrocephalus caused by aqueductal stenosis and space-occupying lesions. ETV is still effective in two-thirds of the patients with previous infections or intraventricular bleeding. Patients who have previously undergone shunting and who have occlusive hydrocephalus should undergo ETV at the time of shunt failure, with immediate ligation or removal of the shunt device. In selected cases of distorted anatomy or impaired visual conditions, stereotactic guidance is helpful.

Adolescent↗

PubMed1998

Basic principles and clinical applications of neuronavigation and intraoperative computed tomography.

Computed tomography (CT) images in combination with a navigation device enable three-dimensional (3-D) localization of intracranial lesions. Furthermore, CT scanning can be adapted for intraoperative application to actualize the image data and to check the anatomical situation during the operation. Frameless navigation was used in 100 patients. The procedure was performed in 46 cases with an optical navigation system, in 38 cases with a sensory arm, and in 16 cases with a navigated microscope. Six skin markers were used for registration. Mean fiducial registration error was 2.18 mm with a standard deviation of 1.03 mm. The indication for navigation was tumor localization and planning of the craniotomy in 81 cases, stereotactic biopsy in eight cases, and endoscopic procedures in 11 cases. Technical problems with the navigation system were observed in nine cases. In two additional cases the tumor was not found by navigation. All eight biopsy cases were successful, and histologically relevant specimens were obtained without complications. Navigation was helpful in 11 endoscopic cases for choosing an optimal trajectory through the foramen of Monro or for connecting multiple intraventricular cysts. For intraoperative CT imaging, the mobile Philips Tomoscan M was adapted to the needs of the operating environment. The mobile CT was used in 78 cases in the operating room: 16 patients who underwent a stereotactic procedure had only preoperative CT scans, 36 patients had an intraoperative CT during tumor surgery, and 26 patients during the test period of the device had only a postoperative CT investigation. In 10 cases (28%) of the intraoperative group the remaining tumor tissue could be demonstrated on the CT scans. The tumor remnants that were not visible in the microscopical surgical field were subsequently removed. According to our results, intraoperative navigation seems superior for the localization of intracranial lesions and intraoperative CT is more useful when considering the radicality of tumor removal.

Brain Neoplasms↗

PubMed1997

Gene cloning of rat and mouse platelet glycoprotein V: identification of megakaryocyte-specific promoters and demonstration of functional thrombin cleavage.

Platelet glycoprotein (GP) V is a major surface protein cleaved during thrombin-induced platelet activation. GPV associates noncovalently with the GPIb-IX complex to form GPIb-V-IX, a receptor for von Willebrand factor and thrombin. We describe the cloning of the genes coding for rat and mouse GPV and compare them with the human gene. The two rodent genes have a similar structure and resemble the human GPV gene with a coding sequence (approximately 1,700 nucleotides) entirely contained in one exon and a single intron (approximately 900 nucleotides) in the 5' untranslated region. Both genes have megakaryocyte-type promoters with conserved tandem Ets and GATA recognition motifs and lack a TATA box. The mature rat and mouse proteins comprise 551 amino acids, have 70% sequence identity, and contain an additional 8-amino acid intracellular segment as compared with the human protein. As in human GPV, there is an NH2-terminal leucine-rich region of 15 repeats and a thrombin cleavage recognition sequence. Whereas the rat and human thrombin cleavage sites are similar, the mouse cleavage site resembles that of the human thrombin receptor. Functionality of these sites was demonstrated by thrombin cleavage of synthetic peptides and analysis by high-performance liquid chromatography (HPLC) or mass spectrometry. Cleavage of native rat GPV was confirmed by means of a polyclonal antibody directed against the new NH2-terminal peptide exposed after thrombin cleavage. This antibody specifically recognized thrombin-activated rat platelets by fluorescence-activated cell sorting (FACS) analysis. In addition, we raised monoclonal antibodies specific for rat GPV (88 kD), which recognized the NH2-terminal soluble fragment (70 kD) liberated after thrombin cleavage. Knowledge of these rodent GPV genes and availability of species-specific peptides and antibodies will be essential to further studies aiming to define the exact in vivo function of platelet GPV using animal models of thrombosis and gene inactivation experiments.

Amino Acid Sequence↗

PubMed1997

Frame-based and frameless endoscopic procedures in the third ventricle.

Stereotactic guidance is useful for planning an accurate trajectory to the third ventricle. A guiding block with a ball joint was developed for frame-based endoscopy and adaptors for arm-based and armless navigation systems. Between 1992 and 1996, 52 patients were operated on endoscopically in the third ventricle under stereotactic guidance. Thirty-eight ventriculostomies, 13 biopsies and 10 cystic lesions were performed. The coordinates of two points were calculated; one in the foramen of Monro and the second in the third ventricle. The ventriculostomy was performed under endoscopic control bluntly with a Fogarty catheter in front of the basilar artery. Twenty-seven (71%) of the patients had a long-lasting benefit from the operation, 6 (16%) had no benefit, and in 5 (13%) a shunt operation was necessary. Poor outcome was due to closure of the stoma by tumor growth or infection. Three cysts were fenestrated and 7 colloid cysts partly evacuated. One incident of bleeding occurred in the frontal lobe in the path of the endoscope which was treated conservatively with success. Transient memory deficit was noted in one patient and double vision in the second.

Adolescent↗

PubMed1996

Stereotactically guided cavernous malformation surgery.

The incidence of a significant hemorrhage in the natural history of cavernomas is below 1% per year, but the risk of a second hemorrhage in patients with initial bleeding cavernomas is between 14% and 29%. In the light of these figures, all cavernomas ought to be resected if surgical-related morbidity can be minimized. Stereotactically guided neurosurgery offers the advantage of planning the least traumatic approach before craniotomy due to the knowledge of the exact localisation of the lesion. During a 2-year period 12 patients (age 16-54 years) with intracranial supratentorial cavernomas (size 0.5-1.8 cm) were treated by stereotactically guided microsurgery. The cavernomas were seated in a depth between 0.4 and 4.5 cm. 4 patients had an overt hemorrhage in their history. In six cases a seizure was the first symptom (altogether 8 patients had seizures preoperatively). Two patients were asymptomatic. Standard CRW (Cosman, Roberts, Wells) stereotactic system was used in all cases. The skin incision and the osteoplastic craniotomy (mean diameter 2.8 cm) were planned stereotactically. In 11 patients a transsulcal approach was used. The size of the corticotomy could be limited to less than 1 cm. Using the stereotactic method, all cavernomas were found with a high degree of accuracy. After lesionectomy a total of 1 to 2 mm of the surrounding yellow-stained brain tissue was sucked away because it contains hemosiderin and therefore iron, which may have an epileptogenic effect. No relevant surgical-related neurological morbidity was found in any patient a half year after surgery. Seven out of eight patients were free of seizures. One still had problems.

Adolescent↗

PubMed1996

Species specific immunoassays to measure blood platelet and coagulation activation in the rat.

The purpose of this study was to develop specific and sensitive immunoassays to detect early indices of hypercoagulability in the rat. Rat platelet factor 4 (rPF4) and rat fibrinopeptide A (rFPA) assays, tools for the detection of activation of platelets and coagulation respectively, were designed using antibodies raised against purified rPF4 and against synthetic rFPA. The relevance of these new assays and of the commercially available ELISA kit for thrombin-antithrombin III (TAT) complexes was demonstrated in a rat model of a prethrombotic state induced by intravenous infusion of varying doses of thrombo-plastin (90 to 2400 microliters/kg/h). In this model, the immunoassays allowed simultaneous detection of low levels of rFPA and rPF4 which were correlated with fibrinogen and platelet consumption and TAT generation and further proved to be of higher sensitivity than the classical methods of platelet count or measurement of fibrinogen levels. Plasma concentrations of rFPA, rPF4 and TAT were dependent on infusion time and thromboplastin dose, while hirudin (1 mg/kg) prevented their appearance. Thus the new specific immunoassays for rPF4 and rFPA and the commercial human TAT assay represent useful tools for pathophysiological studies or the screening of antithrombotic drugs in rats.

Animals↗

PubMed1995

The need for adjunctive focused radiation therapy in pituitary adenomas.

In pituitary adenomas radiation therapy regardless of the technique should be limited to surgical failures. The delayed onset of beneficial effects and the high rate of pituitary insufficiency have to be weighed against the good surgical and/or medical results in the treatment of these tumours. Unfortunately surgical outcome is almost invariably correlated with invasive growth. Invasiveness is statistically significantly correlated with tumour size, as well as with high proliferation rates, which can be measured by immunohistological methods such as mAB KI-67. Owing to the good results of medical treatment, radiation therapy is usually unnecessary in prolactinomas. Patients with persistent hypersecretion of growth hormone after unsuccessful surgery may represent the ideal candidates for radiation therapy, whereas patients with persistent Cushing's disease need cure for hypercortisolism without delay. In patients with residual tumour due to non functioning adenomas, radiation therapy should only be given if the proliferation rate is high.

Adenoma↗

PubMed1995

Target point calculation in the computerized tomography. Comparison of different stereotactic methods.

The adaptation of computerized tomography for stereotactic operations requires the transformation of the coordinates of the target point from the CT image space into the stereotactic frame space. Two basic solutions for this transformation are realized in the most of the contemporary stereotactical systems. The indirect geometric method adjusts the frame coordinate system mechanically and identifies its origin in the CT image. There are 6 degrees of freedom: 3 of rotation and 3 of translation which have to be taken into consideration. The second method is a based on direct algebraic coordinate transformation and is independent of the explicite knowledge of the relationship between the image and the frame space. A localization frame serves to determine a transformation matrix which, applied to any point in the image, transforms the coordinates directly into the frame coordinate system. Only the algebraic method is independent of the position of the patient in the gantry. All other methods require high mechanical precision of the alignment and stability for the CT table.

Brain Diseases↗

PubMed1994

Results of 200 intracranial stereotactic biopsies.

200 stereotactic biopsies were evaluated. The validity of the intraoperative histopathological results were compared with the final diagnosis using conventional embedding and staining techniques. Further comparison between the histology of the biopsy and the post mortem or open operative findings were possible in 41 cases. Discrepancy was found in one case regarding the tumor detection, and in three cases regarding the tumor grading. The mortality in our patients was 1% and the morbidity 3%. Stereotactical biopsy had a low risk even in deep brain regions such as basal ganglia, mesencephalon, and pons. At the same time the high histologic validity makes the CT-guided stereotactical biopsy recommendable in all lesions not operated by an open resection before any conservative or palliative therapy is started.

Adolescent↗

PubMed1994

Endoscopic procedures through the foramen interventriculare of Monro under stereotactical conditions.

The foramen interventriculare of Monro is an anatomical narrowness for the endoscopic access to the third ventricle. The effective mechanical angle to pass the foramen interventriculare from a frontal bore hole depends on the diameter in the plane of entrance, the depth of the foramen, and the diameter of the endoscope. Under the pathological conditions of a hydrocephalus internus the foramen interventriculare is enlarged. By means of stereotactical guidance, it is possible to reach the third ventricle accurately without damaging anatomical structures around the foramen interventriculare. The endoscopic technique under stereotactical guidance using a rigid endoscope is sufficient and safe to perform ventriculostomies in cases of hydrocephalus occlusus. Best clinical results were obtained in patients with benign aqueduct stenosis or with a tumor in this region compressing the aqueduct. In all patients no further shunt operation was necessary. The path through the foramen interventriculare should be considered also for biopsies in the third ventricle. Calculation of the foramen interventriculare trajectory prevents perforation of the roof of the third ventricle containing the main deep veins. Lesions in the foramen interventriculare like colloid cysts can also be approached very accurately by means of stereotactical calculation. However the endoscopic technique with the at present obtainable instruments does not allow removal of the whole lesion. Even so a free passage to the third ventricle can be achieved by reducing the size of the cyst by means of coagulation and sucking off the colloid material.

Adolescent↗

PubMed1992

CT-guided stereotactic biopsy aided by Doppler ultrasonic vascular monitoring.

The use of a 20 MHz pulsed Doppler technique during stereotactic brain tumour biopsies is described. By means of a miniaturized ultrasonic probe the tissue planned for biopsy was investigated for vessel signals. Out of 41 patients, with this technique a flow-pulse curve in front of the biopsy cannula was registered in 14 cases. In 9 cases one pulse curve was determined and in 5 cases two or more flow curves were found, indicating the presence of arterial vessels. The depth of the vessels signal could be localized and this area avoided for biopsy sampling. In a series of 41 stereotactic biopsies carried out in this way there was no intra-operative haemorrhage or postoperative haematoma.

Adolescent↗

PubMed1991

A new device for interstitial 125Iodine seed implantation.

A new device for interstitial implantation of I125 seeds is presented. The technical details and function of the system are described and compared with well-known commercial systems. Its unique design allows for simple, fast, and safe treatment of most tumor sites including stereotactic implantation of brain. Radiation measurements indicate low exposure to both patients and personnel during implantation.

Brachytherapy↗

PubMed1990

Surgical treatment of epilepsy.

Seventy patients with intractable epilepsy were surgically treated. Thirty-three patients underwent a stereotactic procedure and in all as a first-stage operation fornicotomy was performed. Because of inadequate results in 14 patients, an additional stereotactic intervention was necessary; the targets were amygdala, thalamus, and Forel's H-field, and the final outcome of these patients was 9 (27%) seizure-free, 19 (58%) improved, and 5 (15%) unchanged. In 3 patients a selective amygdalo-hippocampectomy was performed with 2 seizure-free patients and one with improvement. Topectomy in focal epilepsy in 5 patients resulted in freedom from seizures in all cases. In 23 patients a lobectomy was performed; 10 (43%) were seizures-free, 8 (35%) were improved, and 5 (22%) were unchanged. In 6 patients only a pathological lesion was resected. Our results speak in favour of ablative surgery. However, stereotactic operations are indicated in cases with secondary generalization and dissipated foci on the dominant hemisphere.

Adult↗

PubMed1990

[The technique of stereotactic I125 brachytherapy (permanent implants) of brain tumors in Vienna].

Methods of stereotactic target localisation are used in brachytherapy of brain tumors for many years. Since 1987 eight patients with inoperable astrocytomas grade I to III were treated at the Neurosurgical Clinic and Clinic for Radiotherapy of the University Vienna by permanent stereotactic I125-seed implantation. For that purpose a newly developed applicator was used. Preliminary results confine the low risk of operation, but the follow-up time is too short for evaluation of the treatment success. Principal problems of brain brachytherapy are discussed in the light of international data. In general, I125 brachytherapy is a useful and well tolerated way of treatment of low grade astrocytomas, the risk is low, which is especially important for children and old patients.

Astrocytoma↗

PubMed1989

[Stereotaxic biopsy of intracranial processes: validity of histologic diagnosis].

The diagnostic validity of stereotactic intracranial biopsies was investigated in 70 patients retrospectively. In 56 cases (80%) the presence of a neoplastic lesion as well as its grade of malignancy was proved by cytological, histological and immunohistochemical techniques. An inflammatory or vascular lesion was found in 8 patients (11.4%). In 6 patients (8.6%) the nature of the lesion remained unclear because of nonspecific histological findings. In 27 cases a correlation was found between the biopsy specimens and corresponding material obtained during open surgery or autopsy. 24 concordant results were found (88.9%). In one case a malignant tumour was classified only according to the findings obtained at operation. In two cases subsequently diagnosed as glioblastoma biopsy reported a higher differentiated astrocytoma and a non-neoplastic lesion, respectively. These results confirm stereotactic biopsy of intracranial lesions as a method with low complication rate and high diagnostic validity.

Astrocytoma↗