Fluorescence video angiography has recently been introduced in neurosurgery. Such videos are analysed by a new software to allow quantitative characterization of the blood flow during neurovascular operations (clipping an aneurysm, treatment of an angioma). For these purposes the fluorescence dye Indocyanin Green is given intravenously. After activation by a near-infrared light source the fluorescence signal is evaluated by the software. Reference measurements by using a flow phantom were performed to verify the quantitative blood flow results of the software and to validate the software algorithms. The analysis of intraoperative videos provided characteristic biological parameters allowing their implementation in the flow phantom. Under certain conditions the experiments with the help of the flow phantom showed, the results of the software parameter identification algorithmus are within the range of parameter accuracy by the reference method.

A system for optical imaging of intrinsic signals and visualization of functional maps overlaid with the 3D reconstruction of the cortex is presented. Optical imaging of intrinsic signals is an advantageous method for monitoring functional representation of eloquent areas of the cortex. The non-invasive method works free of contact and generates a map of cortical activation with a spatial resolution of less than 1 mm based on the changes in optical parameters of brain tissue during cortical activation. A system containing an illumination device, a surgical microscope, and a camera is described. Computation of the cortical activation map is done by comparison of recordings during rest and stimulation. 3D reconstruction of the cortex and overlay with the optical recording is achieved using the 3D visualization software AMIRA. Optical imaging of intrinsic signals can increase the identification of eloquent regions of the brain. The 3D visualization is beneficial for identifying the region and for inter-individual comparison of the cortical representation of eloquent areas.

Objective: Fluorescence video angiography has recently been introduced to neurosurgery. For intraoperative control, blood flow in the brain vessels can be visualized by means of near-infrared fluorescence dye Indocyanine Green. Until now the sufficiency of the blood flow has to be assessed qualitatively by the surgeon. Therefore, an objective quantification of the blood flow by means of video analysis is desirable.Methods: Two different methods for the determination of the blood flow velocity have been developed, one based on the transit time and the other on the velocity-proportional increase of fluorescence intensity during the inflow process of the dye. Both methods were implemented in software to analyze video data obtained from a digital PAL-standard IR-sensitive imaging system. Verification was realized by means of a flow phantom which emulates the blood flow and fluorescence of the dye in cerebral vessels.Results: Good fluorescence image quality comparable to clinical recordings could be obtained from simulation using the phantom. Determined velocities using transit time exceed the scheduled values by a factor k approximate to 1.5 depending on the vessel diameter and the flow characteristics. The flow profile and the limited penetration depth of the exposing light are supposed to be the cause of this k-factor. After correction, an accuracy of +/- 20 % in velocity determination could be achieved, which is not unusual when comparing with clinical sonographic Doppler measurement. The rise time of fluorescence intensity shows an inverse proportional behavior to flow velocity. The proportionality factor changes according to the vessel diameter.Conclusions: Evaluation of velocity distribution in vessels with variant diameter (e.g. stenosis) solely by means of the rise time is not possible. Transit time measurement is a suitable method for flow velocity determination. The detectable range and accuracy are limited by some further influences on the imaging process. At the moment velocities up to 10 cm/s for a typical visible vessel length of 20 mm can be detected with sufficient accuracy. For clinical studies the algorithms have to be enhanced since an eightfold flow velocity is expected in the large brain arteries. Further investigations are necessary for a robust k-factor correction in-vivo.

Objective In a formerly introduced mathematical model, in-tracranial pressure (ICP) could be non-invasively assessed using cerebral blood flow velocity (FV) and arterial blood pressure (ABP). The current study attempts to check whether the accuracy of the non-invasive ICP assessment (nICP) improves after an initial individual calibration by implanted ICP probes

Hintergrund: Vor einiger Zeit wurde eine Methode zur Berechnung des Hirndrucks (ICP) aus dem arteriellen Blutdruck (ABP) und dem transkraniellen Dopplersignal der A. cerebri media (FV) vorgestellt. In der aktuellen Studie sollte überprüft werden, ob die Genauigkeit dieses nichtinvasiven Verfahrens durch eine einmalige individuelle Kalibrierung mittels implantierter Hirndrucksonde verbessert werden kann.

Study Aims: The purpose of this study was the integration of three-dimensional ultrasound data into a neuronavigation system, in order to allow a guided intraoperative resection control during neurosurgical interventions. Material und Methods: A system for iterative neuronavigation based on 3D-ultrasound (US) has been developed. The main components of the system are the ultrasound device Voluson 730 (GE Healthcare) with a 5-9 MHz probe, the navigation system VectorVision2 (R) (Brain-LAB AG) and a standard PC with Windows XP. The ultrasound data are transferred via DICOM from the ultrasound device to an external computer, where they are processed with a C++ program for representation in the neuronavigation coordinate system. The data transfer between the navigation system and the external computer is performed via the VVLink interface from BrainLAB. The feasibility test of the system was performed with an ultrasound phantom RMI403GS (Gammex-RMI GmbH). Results: The error of homologous points mapping from US datasets to a CT dataset in the neuronavigation system was determined to be 1.9 +/- 0.97 mm. The maximum time required to technically integrate the ultrasound data into the navigation system was 1.5 min. Conclusions: The developed system allows 3D-ultrasound based navigation to be carried out with a commercially available navigation system. The functionality of this system has been proven by technical tests. Recording and integration of the ultrasound data can be repeated at any time during surgery and can be used to update anatomical data and consequently for resection control. Another application is the intraoperative adaptation of preoperative datasets (MRI or CT) in order to compensate for "brain shift" during neurosurgical operations.

Indocyanine green near-infrared-video angiography (ICG-NIR-VA) was recently introduced for measuring perfusion of skin flaps. The prognostic value of this method with regards to post-transfer manipulations of the flap, and subsequently, flap survival is not adequately documented in the literature. In this paper, we report our experience with the ICG-NIR-VA in the intraoperative evaluation and post-operative follow-up of nine flaps (2 large random pattern, 4 pedicled island and 3 free flaps) used in various reconstructive procedures. Two flaps (1 random pattern and 1 free flap) showed delayed intraoperative uptake in ICG-NIR-VA. In the post-operative phase, (days 1-3) six flaps (1 random pattern, 2 axial pattern and 3 free flaps) showed a delay both in the ICG-NIR-VA uptake, as well as clearance. However, a clinical correlate was observed only in 2 of the 6 flaps demonstrating this delay: general and partial venous congestion was seen in a distally based interosseous posterior flap and a free lateral arm flap respectively. Leeches were implemented only based on the clinical signs. In one distally based perforator flap, the decision on perfusion augmentation via microanastomosis was based on the intraoperative ICG-NIR-VA finding. All flaps showed uneventful healing. Based on our observations, the question arises, not whether the ICG-NIR-VA is sensitive for the prognosis of venous congestion, upon which the flap manipulation strategy might rest-but whether it is too sensitive. Further, prospective studies are necessary.

OBJECTIVE:Increased intracranial pressure (ICP) and decreased cerebral blood flow leading to global cerebral ischemia are the primary causes of death after severe subarachnoid hemorrhage (SAH). Hypertonic saline has been demonstrated to exert neuroprotective properties after traumatic brain injury by osmotic mobilization of parenchymal water and improvement of microcirculation. We used a rat model to investigate the effects of hypertonic fluid resuscitation after SAH on ICP, cerebral blood flow, body weight, neurological recovery, and morphological damage. METHODS:Sixty rats were subjected to SAH induced by an endovascular filament. ICP and local cerebral blood flow were recorded continuously. Animals were assigned to three groups: 1) NaCl 0.9%; 2) NaCl 7.5% (4 ml/kg); and 3) NaCl 7.5% plus 6% dextran 70 (4 ml/kg) given 30 minutes after SAH. Body weight and neurological deficits were assessed daily. Morphological damage was evaluated on Day 7. RESULTS:SAH resulted in an immediate increase of ICP to approximately 60 mm Hg initially, and then to approximately 30 mm Hg for the next 90 minutes. Although NaCl 7.5% alone and in combination with dextran led to an immediate, significant, and lasting decrease of ICP to 15 to 20 mm Hg, only the combined therapy significantly increased body weight and improved neurological recovery. Furthermore, the group that received combined therapy exhibited significantly more surviving neurons in hippocampus, cortex, caudoputamen, and cerebellum. Mortality was reduced non-significantly, from approximately 65% in groups I and II to 35% in Group III. CONCLUSION:Treatment with NaCl 7.5% plus 6% dextran 70 is significantly effective for reducing the initial harmful sequelae of SAH. The regimen resulted in lowered ICP, improved neurological recovery, and less morphological damage after SAH in the rat.

OBJECTIVE:The registration of medical volume data sets plays an important role when different images or modalities are used during computer-assisted surgical procedures. Nevertheless, it is often questionable how robust and accurate the underlying algorithms really are. Therefore, the goal is to foster the establishment of methods for an objective evaluation. METHOD:To reliably calculate the accuracy of registration algorithms, a reference transformation must be known. Due to the unknown perfect registration for real clinical data, the simulation of realistic data and successive affine transformations are employed. The simulation is based on models of the respective imaging modality where the dominant physical effects are taken into account. This gives the user full control over all simulation and transformation parameters. Finally, suitable quality measures are applied which allow a systematic evaluation of image registration accuracy by comparing the known theoretical result and the transformation calculated by the algorithm under investigation. RESULTS:During the development of a new registration algorithm, the presented method proved to be a very valuable tool for optimization and evaluation of registration accuracy, since it allows objective numerical comparison of the calculated results. CONCLUSIONS:The presented method can be used during the development of algorithms for optimization and for quantitative comparison of different registration schemes. The respective software tool can automatically generate and transform simulated but realistic data. Employing suitable numerical quality measures, an objective evaluation of registration results can be easily obtained. Still, the validity of the relatively simple models has to be verified to draw reliable conclusions with respect to real data.

OBJECTIVEChanges of major cerebral vessels in patients with subarachnoid hemorrhage (SAH) are well known from routine cerebral angiography. Data on changes in the microcirculation do not exist. This study sought to provide a qualitative and quantitative analysis of the cortical microcirculation after SAH. METHODSBy means of orthogonal polarization spectral imaging, a qualitative and quantitative analysis of cortical microcirculation was performed during aneurysm surgery in 3 patients with an incidental intracerebral aneurysm and 10 patients with SAH. Vessel diameters, red blood cell velocity, and functional capillary density were analyzed before and after the aneurysm was clipped. RESULTSInitial capillary density in patients with an incidental aneurysm was 91.5 ± 36.5 cm−1 (mean ± standard deviation) compared with 30.5 ± 13.8 in patients with SAH (P < 0.05). In patients with SAH, capillary density increased significantly to 53.9 ± 29.1 cm−1 (P < 0.05) during the operation, as did the frequency of venules with a red blood cell velocity greater than 2 mm/s (P < 0.05). No significant change of arteriolar or venular diameters was observed. However, in patients with SAH, mono- and multisegmental microvasospasms in arterioles were observed, with a reduction of vessel diameters up to 75.1%. CONCLUSIONOrthogonal polarization spectral imaging is a suitable method to study cerebral microcirculation during surgery. In patients with SAH, capillary density is significantly decreased and small arteries and arterioles of the cortical surface exhibit vasospasm that cannot be detected by angiography or transcranial Doppler sonography. These changes may contribute to the initial clinical symptoms and may have an influence on the clinical postoperative course.

Article SYSTEMLÖSUNG ZUR IMPLEMENTIERUNG EINES 3D-DISPLAYS IN DIE NEUROCHIRURGIE was published on January 1, 2003 in the journal Biomedical Engineering / Biomedizinische Technik (volume 48, issue s1).

Sl 'MM AK . (nmiing of cerebral auloregulation by the i ' t i l l i lcl lation lesl is believed tu provide kcy informalion lor trcutmcnl oi" patients wilh traumatic brain inlurv On analysing cerebral autoregulaiion with a a>mmerciul lv available transcranial Doppier clevice il coukl be shown that results yielded in poor reproducib ih ty . In many cascs time patterns of autoregulatory response did not correspond to predicted models of scveral authors. We improved test algorithms mainly by considering heart rate and latency of auroregulatory rcsponse. C'erebral autoregulation had been graded by thc autoregulalory Index on a scale between 0 and 9. With mir model we were able to decrease Standard dcviation irom 1.7 to 1.1 in comparison with the aforementioned transcranial Doppier device (n = 1 1 S test cycles with 3 cuff deflation tests).

3-O-Methyl-6-[18F]fluoro-l-DOPA (OMFD) is a major metabolite of 6-[18F]fluoro-L-DOPA. Although synthesis of OFMD was primarily established to study the dopaminergic system, as it is an amino acid analogue, uptake in experimental tumours has been found. The aim of this study was to evaluate the applicability of OMFD for brain tumour imaging and to obtain initial estimates of whole-body biodistribution and radiation dosimetry in humans. Nineteen patients with suspected or confirmed brain tumours were investigated with OMFD and dynamic brain PET, complemented by whole-body PET in seven patients. Tracer kinetics were compared for normal brain and intracerebral lesions. Tissue accumulation was quantified with standardised uptake values (SUVs). Whole-body distribution in combination with tracer kinetics from animal experiments was used for the calculation of radiation dosimetry data. On the basis of OMFD PET, viable brain tumour was suspected in 16 patients with SUVs of 3.0±0.8 and a tumour to non-tumour ratio of 1.9±0.5. Highest tumour and normal brain uptake occurred between 15 and 30 min, with a subsequent slow decrease. Late whole-body tracer distribution was uniform without specific organ accumulation. Elimination occurred via urine. The mean radiation dose to the whole body was estimated at 0.016 mSv/MBq, with the kidneys as dose-critical organ (0.033 mGy/MBq). In conclusion, OMFD enables the visualisation of brain tumours with SUVs similar to other fluorinated amino acids. The whole-body radiation exposure from OMFD is comparable to that from FDG imaging.

Article KONTINUIERLICHES MONITORING DER ZEREBRALEN AUTOREGULATION MIT HILFE DER KREUZKORRELATION was published on January 1, 2003 in the journal Biomedical Engineering / Biomedizinische Technik (volume 48, issue s1).

Article MODELLHINTERGRUND KLINISCHER VERFAHREN ZUR BEURTEILUNG DER ZEREBRALEN AUTOREGULATION was published on January 1, 2003 in the journal Biomedical Engineering / Biomedizinische Technik (volume 48, issue s1).