Accuracy of non-invasive ICP assessment can be increased by an initial individual calibration.

OBJECTIVE: In a formerly introduced mathematical model, intracranial 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. METHODS: Thirteen patients with brain lesions (35-77 years, mean: 58 +/- 13 years) were studied. FV, ABP and ICP signals were recorded at days 1, 2, 4 and 7. nICP was calculated and compared to ICP. In the first recording of each patient the (invasively assessed) ICP signal was used to calibrate the nICP calculation procedure, while the follow-up recordings were used for its validation. FINDINGS: In 11 patients 22 follow-up recordings were performed. The mean deviation between ICP and the original nICP (+/- SD) was 8.3 +/- 7.9 mmHg. Using the calibrated method this deviation was reduced to 6.7 +/- 6.7 mmHg (P < 0.005). CONCLUSIONS: Initial individual calibration of nICP assessment method significantly improves the accuracy of nICP estimation on subsequent days. This hybrid method of ICP assessment may be used in intensive care units in patients with initially implanted ICP probes. After removal of the probes, ICP monitoring can be continued using the calibrated nICP assessment procedure.

Integration of intraoperative 3D-ultrasound in a commercial navigation system.

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 AND 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 (BrainLAB 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 RMI 403GS (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.

Objective evaluation of three-dimensional image registration algorithms--tools for optimization and evaluation.

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.

3-O-methyl-6-[18F]fluoro-L-DOPA and its evaluation in brain tumour imaging.

3-O-Methyl-6-[(18)F]fluoro-L-DOPA (OMFD) is a major metabolite of 6-[(18)F]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.

[Integration of the Aasalid test in an online measurement system for evaluating cerebral autoregulation]. / Integration des Aaslid-Tests in ein Online-Messsystem zur Beurteilung der cerebralen Autoregulation.

An important question during the intensive care of patients with subarachnoid hemorrhage and craniocerebral trauma is the evaluation of the cerebral autoregulation (CA). The so called Aaslid-Test is a standard method which allows the cerebral autoregulation to be classified. As the results under repetitive conditions show a high variation, it has not been yet possible to draw statistically proved conclusions concerning the performance of the CA. To improve the test results the measuring conditions are discussed and systematized. The algorithms of the Aaslid-Test have been implemented to an online measuring system. The error bandwidth has been estimated. To avoid systematically occurring errors an enhanced measuring protocol is provided.

[Comparison of the accuracy of 3-dimensional fusion algorithms]. / Vergleich der Genauigkeit Dreidimensionaler Fusions-Algorithmen.

Recently many algorithms for matching three-dimensional medical data have been developed. Inter- and intramodal fusion of data adds valuable information for planning, controlling and evaluating therapies. This work presents a procedure to evaluate the accuracy of fusion algorithms by numerical means. In contrast to the usual way of visual inspection the developed software tools allow automatic numerical--and thus objective--evaluation of different algorithms using simulated realistic volume data. It is therefore possible to conduct reproducible comparisons of different matching methods. These tools also proved to be very valuable during the development and optimisation of an algorithm employing normalised mutual information.

Surgery of low-grade gliomas near speech-eloquent regions: brainmapping versus preoperative functional imaging.

The identification of eloquent areas is of utmost importance in the surgery of tumors located near speech-eloquent brain areas, since the classical concept of a constant localization was proven to be untrue and the spatial localization of these areas may show large interindividual differences. Some neurosurgical centers apply intraoperative electrophysiological methods that, however, necessitate the performance of surgery in the awake patient. This might be a severe burden both for the patient and the operating team in a procedure that lasts several hours; in addition, electrical stimulation may generate epileptic seizures. Alternatively, methods of functional brain imaging (e.g., PET, fMRI, MEG) may be applied, which allow individual localization of speech-eloquent areas. Matching of these image data with a conventional 3D-CT or MRI now allows the exact transfer of this information into the surgical field by neuronavigation. Whereas standards concerning electrophysiological stimulation techniques that could prevent a permanent postoperative worsening of language are available, until now it remains unclear whether the resection of regions shown to be active in functional brain imaging will cause a permanent postoperative deficit.

Comparison of functional brain PET images and intraoperative brain-mapping data using image-guided surgery.

OBJECTIVE: Knowledge about the spatial localization of eloquent brain areas is essential for resecting lesions in the vicinity of these areas. The classical approach is to perform surgery on the awake patient under local anesthesia using brain-mapping techniques. As an alternative, the location of eloquent areas can be visualized by preoperative functional brain-imaging techniques, for example, positron emission tomography (PET), functional magnetic resonance imaging (fMRI), or magnetoencephalography (MEG). Using functional activation PET, both methods were combined by integration into a frameless navigation system (BrainLAB) and used to map speech-eloquent areas. PATIENTS AND METHODS: Speech-eloquent areas were localized preoperatively in seven patients with a left-sided glioma using 2-[(18)F]-2-desoxy-D-glucose PET. Patients were scanned under silence conditions (i.e., with the patient remaining silent in a sound-proof cabin), and speech was activated using a verb-generation paradigm. The PET data were transferred to the neuronavigation workstation and matched with a preoperative 3D-MRI using an automatic image-fusion algorithm. Intraoperative speech localization was performed using brain-mapping techniques under local anesthesia with bipolar cortical stimulation. The stimulator position was mapped into the MRI/PET data set by neuronavigational tracking of the instrument. RESULTS: Functional PET images were integrated into the MRI-based neuronavigational system and could be transferred exactly to the operative field. By the additional integration of cortical stimulation, intraoperative electrophysiological findings can be directly compared with preoperative functional images. Seven patients with left-sided glioma were operated on using this protocol, confirming the technical feasibility. In three of seven patients, preoperative PET findings were not supported by intraoperative mapping. CONCLUSIONS: This matching and mapping technique is suitable for monitoring eloquent speech areas during surgical resection of extensive left-sided low-grade gliomas, allowing a direct comparison between intraoperative electrophysiological brain mapping and preoperative functional brain-imaging findings. The sensitivity and specificity of functional imaging techniques can now be evaluated by reconciling the data with the intraoperative stimulation results.

Factors influencing the application accuracy of neuronavigation systems.

OBJECTIVE: The overall accuracy of neuronavigation systems may be influenced by (1) the technical accuracy, (2) the registration process, (3) voxel size and/or distortion of image data and (4) intraoperative events. The aim of this study was to test the influence of the registration and imaging modality on the accuracy. METHODS: A plexiglas phantom with 32 rods was taken for navigation targeting. Sixteen fiducials were attached to the surface of the phantom forming two different attachment patterns (clustered vs. diffusely scattered). This model was scanned by MRI and CT (1-mm slices). Registration was performed using different numbers and attachment patterns of the fiducials. Using CT or MRI, the localization error was measured in image space as the Euclidean distance between targets defined in image space and those detected in the physical space. Accuracy was measured with two commercial systems, the Zeiss MKM and the StealthStation. RESULTS: The mean localization error varied between 1.59 +/- 0.29 mm (MKM, 8 scattered fiducials, CT scanning) and 3.86 +/- 2.19 mm (MKM, 4 clustered fiducials, MRI). The worst localization error was 9.5 mm (MKM). In case of an optimal registration, the 95th percentile for the localization error was 2.2 (MKM) and 2.75 mm (StealthStation). The imaging modality has only minor influence on the localization error, with CT increasing accuracy minimally. Both the fiducial number and the attachment pattern critically influence the localization error: 8 fiducials and a generalized attachment pattern increase the accuracy significantly. No correlation between the calculated registration accuracy and the measured localization accuracy was found. CONCLUSION: The application accuracy of different neuronavigation systems critically depends on the registration. The calculated registration accuracy provided by the system does not correspond to the localization error found in reality. The accuracy of frameless neuronavigation systems is comparable to that of classical frame-based stereotactic devices.

Functional neuronavigation with magnetoencephalography: outcome in 50 patients with lesions around the motor cortex.

OBJECT: The authors conducted a study to evaluate the clinical outcome in 50 patients with lesions around the motor cortex who underwent surgery in which functional neuronavigation was performed. METHODS: The sensorimotor cortex was identified in all patients with the use of magnetoencephalography (MEG). The MEG-source localizations were superimposed onto a three-dimensional magnetic resonance image and the image data set was implemented into a neuronavigation system. Based on this setup, the surgeon chose the best surgical strategy. During surgery, the pre- and postcentral gyri were identified by neuronavigation and, in addition, the central sulcus was localized using intraoperative recording of somatosensory evoked potentials. In all cases MEG localizations of the sensory or motor cortex were correct. In 30% of the patients preoperative paresis improved, in 66% no additional deficits occurred, and in only 4% (two patients) deterioration of neurological function occurred. In one of these patients the deterioration was not related to the procedure. CONCLUSIONS: The method of incorporating functional data into neuronavigation systems is a promising tool that can be used in more radical surgery to lessen morbidity around eloquent brain areas.

Functional neuronavigation with magnetoencephalography: outcome in 50 patients with lesions around the motor cortex.

The authors conducted a study to evaluate the clinical outcome in 50 patients with lesions around the motor cortex who underwent surgery in which functional neuronavigation was performed. The sensorimotor cortex was identified in all patients with the use of magnetoencephalography (MEG). The MEG-source localizations were superimposed onto a three-dimensional magnetic resonance image, and the image data set was then implemented into a neuronavigation system. Based on this setup, the surgeon chose the best surgical strategy. During surgery, the pre- and postcentral gyrus were identified by neuronavigation, and in addition, the central sulcus was localized using intraoperative recording of somatosensory evoked potentials. In all cases MEG localizations of the sensory or motor cortex were correct. In 30% of the patients preoperative paresis improved, in 66% no additional deficits occurred, and in only 4% (two patients) deterioration of neurological function occurred. In one of these patients the deterioration was not related to the method. The method of incorporating functional data into neuronavigation systems is a promising tool that can be used in more radical surgery to cause less morbidity around eloquent brain areas.

Intraoperative magnetic resonance imaging with the magnetom open scanner: concepts, neurosurgical indications, and procedures: a preliminary report.

OBJECTIVE: Intraoperative magnetic resonance imaging (MRI) is now available with the General Electric MRI system for dedicated intraoperative use. Alternatively, non-dedicated MRI systems require fewer specific adaptations of instrumentation and surgical techniques. In this report, clinical experiences with such a system are presented. METHODS: All patients were surgically treated in a "twin operating theater," consisting of a conventional operating theater with complete neuronavigation equipment (StealthStation and MKM), which allowed surgery with magnetically incompatible instruments, conventional instrumentation and operating microscope, and a radiofrequency-shielded operating room designed for use with an intraoperative MRI scanner (Magnetom Open; Siemens AG, Erlangen, Germany). The Magnetom Open is a 0.2-T MRI scanner with a resistive magnet and specific adaptations that are necessary to integrate the scanner into the surgical environment. The operating theaters lie close together, and patients can be intraoperatively transported from one room to the other. This retrospective analysis includes 55 patients with cerebral lesions, all of whom were surgically treated between March 1996 and September 1997. RESULTS: Thirty-one patients with supratentorial tumors were surgically treated (with navigational guidance) in the conventional operating room, with intraoperative MRI for resection control. For 5 of these 31 patients, intraoperative resection control revealed significant tumor remnants, which led to further tumor resection guided by the information provided by intraoperative MRI. Intraoperative MRI resection control was performed in 18 transsphenoidal operations. In cases with suspected tumor remnants, the surgeon reexplored the sellar region; additional tumor tissue was removed in three of five cases. Follow-up scans were obtained for all patients 1 week and 2 to 3 months after surgery. For 14 of the 18 patients, the images obtained intraoperatively were comparable to those obtained after 2 to 3 months. Intraoperative MRI was also used for six patients undergoing temporal lobe resections for treatment of pharmacoresistant seizures. For these patients, the extent of neocortical and mesial resection was tailored to fit the preoperative findings of morphological and electrophysiological alterations, as well as intraoperative electrocorticographic findings. CONCLUSION: Intraoperative MRI with the Magnetom Open provides considerable additional information to optimize resection during surgical treatment of supratentorial tumors, pituitary adenomas, and epilepsy. The twin operating theater is a true alternative to a dedicated MRI system. Additional efforts are necessary to improve patient transportation time and instrument guidance within the scanner.

Technical accuracy of a neuronavigation system measured with a high-precision mechanical micromanipulator.

OBJECTIVE: This study was designed to determine and evaluate the different system-inherent sources of erroneous target localization of a light-emitting diode (LED)-based neuronavigation system (StealthStation, Stealth Technologies, Boulder, CO). METHODS: The localization accuracy was estimated by applying a high-precision mechanical micromanipulator to move and exactly locate (+/- 0.1 micron) the pointer at multiple positions in the physical three-dimensional space. The localization error was evaluated by calculating the spatial distance between the (known) LED positions and the LED coordinates measured by the neuronavigator. The results are based on a study of approximately 280,000 independent coordinate measurements. RESULTS: The maximum localization error detected was 0.55 +/- 0.29 mm, with the z direction (distance to the camera array) being the most erroneous coordinate. Minimum localization error was found at a distance of 1400 mm from the central camera (optimal measurement position). Additional error due to 1) mechanical vibrations of the camera tripod (+/- 0.15 mm) and the reference frame (+/- 0.08 mm) and 2) extrapolation of the pointer tip position from the LED coordinates of at least +/- 0.12 mm were detected, leading to a total technical error of 0.55 +/- 0.64 mm. CONCLUSIONS: Based on this technical accuracy analysis, a set of handling recommendations is proposed, leading to an improved localization accuracy. The localization error could be reduced by 0.3 +/- 0.15 mm by correct camera positioning (1400 mm distance) plus 0.15 mm by vibration-eliminating fixation of the camera. Correct handling of the probe during the operation may improve the accuracy by up to 0.1 mm.

Magnetic source imaging combined with image-guided frameless stereotaxy: a new method in surgery around the motor strip.

OBJECTIVE: In this study, information about the localization of the central sulcus obtained by magnetic source imaging (MSI) was intraoperatively translated to the brain, using frameless image-guided stereotaxy. In the past, the MSI results could be translated to the surgical space only by indirect methods (e.g., the comparison of the MSI results, displayed in surface renderings, with bony landmarks or blood vessels on the exposed brain surface). METHODS: Somatosensory evoked fields were recorded with a MAGNES II biomagnetometer (Biomagnetic Technologies Inc., San Diego, CA). Using the single equivalent current dipole model, the localization of the somatosensory cortex was superimposed on magnetic resonance imaging with a self-developed contour fit program. The magnetic resonance image set containing the magnetoencephalographic dipole was then transferred to a frameless image-guided stereotactic system. Intraoperatively, the gyrus containing the dipole was identified as the postcentral gyrus, using neuronavigation, and the next anterior sulcus was regarded as the central sulcus. With intraoperative cortical recording of somatosensory evoked potentials, this assumption was verified in each case. RESULTS: In all cases, the preoperatively assumed localization of the central sulcus and motor cortex with MSI agreed with the intraoperative identification of the central sulcus using the phase reversal technique. CONCLUSION: The combined use of MSI and a frameless stereotactic system allows a fast orientation of eloquent brain areas during surgery. This may contribute to a safer and more radical surgery in lesions adjacent to the motor cortex.

Slow rhythmic oscillations of blood pressure, intracranial pressure, microcirculation, and cerebral oxygenation. Dynamic interrelation and time course in humans.

BACKGROUND AND PURPOSE: Various biological signals show nonpulsatile, slow rhythmic oscillations. These include arterial blood pressure (aBP), blood flow velocity in cerebral arteries, intracranial pressure (ICP), cerebral microflow, and cerebral tissue PO2. Generation and interrelations between these rhythmic fluctuations remained unclear. The aim of this study was to analyze whether stable dynamic interrelations in the low-frequency range exist between these different variables, and if they do, to analyze their exact time delay. METHODS: In a clinical study, 16 comatose patients with either higher-grade subarachnoid hemorrhage or severe traumatic brain injury were examined. A multimodal digital data acquisition system was used to simultaneously monitor aBP, flow velocity in the middle cerebral artery (FVMCA), ICP, cerebral microflow, and oxygen saturation in the jugular bulb (SjO2). Cross-correlation as a means to analyze time delay and correlation between two periodic signals was applied to a time series of 30 minutes' duration divided into four segments of 2048 data points (approximately 436 seconds) each. This resulted in four cross-correlations for each 30-minute time series. If the four cross-correlations were consistent and reproducible, averaging of the original cross-correlations was performed, resulting in a representative time delay and correlation for the complete 30-minute interval. RESULTS: Reproducible cross-correlations and stable dynamic interrelations were found between aBP, FVMCA, ICP, and SjO2. The mean time delay between aBP and ICP was 6.89 +/- 1.90 seconds, with a negative correlation in 81%. A mean time delay of 1.50 +/- 1.29 seconds (median, 0.85 seconds) was found between FVMCA and ICP, with a positive correlation in 94%. The mean delay between ICP and SjO2 was 9.47 +/- 2.21 seconds, with a positive correlation in 77%. Mean values of aBP and ICP did not influence the time delay and dynamic interrelation between the different parameters. CONCLUSIONS: These results strongly support Rosner's theory that ICP B-waves are the autoregulatory response of spontaneous fluctuations of cerebral perfusion pressure. There is casuistic evidence that failure of autoregulation significantly modifies time delay and the correlation between aBP and ICP.

Simultaneous measurement of ocular micro- and macrocirculation, intraocular pressure, and systemic functions.

SIMOMIMA (simultaneous measurement of ocular micro- and macrocirculation) is a 32-channel system for display and analysis of biophysical data on ocular perfusion. Using SIMOMIMA in the real-time mode, several parameters of ocular perfusion and systemic functions were simultaneously measured noninvasively and stored during varying periods of measurement; including ocular macroperfusion (pulsed Doppler sonography: ophthalmic artery), ocular microperfusion (laser Doppler flowmetry; iris, ciliary body, choroid), intraocular pressure, cardiac pulse, respiration, and arterial blood pressure. All data were digitalized and stored by a microcomputer for further data processing. With SIMOMIMA in the off-line mode, several parameters of the ocular and systemic circulation may be examined and correlations between them may be calculated, including absolute values for the ophthalmic-artery blood velocity expressed in centimeters per second; the pulse-wave velocity expressed in centimeters per second; relative values for the microcirculatory blood flow of the iris, ciliary body, or choroid; and absolute values for and the time course of the intraocular pressure, heart rate, and respiration rate. In contrast to the ophthalmic-artery pulse curve, the microcirculatory blood flow in the iris showed no obvious synchronization with the ECG or the respiration rate. The blood-cell velocity and the blood content in the iridal meshwork fluctuated with frequencies ranging between 0.5 and 4 Hz. By a special statistical procedure called averaging laser Doppler flowmetry (ALDF), the influence of the pulsations of the arterial blood pressure (diastolic systolic blood pressure) on the iridial blood flow becomes visible.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral hemodynamics in subarachnoid hemorrhage evaluated by transcranial Doppler sonography. Part 2. Pulsatility indices: normal reference values and characteristics in subarachnoid hemorrhage.

In previous publications on the diagnostic value of transcranial Doppler sonography (TCD), conflicting results concerning predictive capacities for evaluating vasospasm by measuring flow velocities were reported, and the necessity to examine pulsatility indices (PIs) was stressed. PIs are known to give useful information on cerebral hemodynamics in cases of stenosis of the extracranial internal carotid artery and cerebral arteriovenous malformations. Whether the examination of PIs can give additional information in cases of subarachnoid hemorrhage (SAH) and allow prediction of impending delayed ischemic deficits (DIDs) is still unclear. Normal reference values for the Gosling pulsatility index, the Pourcelot resistance index, and the first Fourier pulsatility index were established in a series of 97 normal subjects. A significant increase in the indices was found as age increased, and there was a strong relation between the indices. There were no statistically significant differences between the right and left sides. An inverse relation was found between the flow velocity and PIs in the middle cerebral artery. In a prospective study of 455 follow-up TCD examinations in 66 SAH patients treated routinely with nimodipine, three different groups were analyzed separately: Group I, patients without DIDs; Group II, patients with DIDs; and Group III, patients with neurological deficits not strictly classifiable as DIDs. The analysis of all three groups together showed a typical time course after the onset of SAH: initially elevated PIs normalized around the tenth day after bleeding. According to Fisher grading, the amount of subarachnoid blood influences the increase in PIs significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral hemodynamics in subarachnoid hemorrhage evaluated by transcranial Doppler sonography. Part 1. Reliability of flow velocities in clinical management.

During recent years, the management of subarachnoid hemorrhage (SAH) has changed, resulting in an increase in early operations and routine administration of nimodipine. Both influenced the indication for transcranial Doppler sonography (TCD). Furthermore, investigations detected discrepancies between Doppler findings and neurological status. In a prospective study, the reliability of TCD was investigated in patients with SAH treated with intravenously administered nimodipine. Patients with large hematomas were excluded. Neurological deficits immediately after surgery or within the first 48 hours were classified as not delayed, and therefore not necessarily due to vasospasm. The most remarkable points of this study are that there is no significant difference between the flow velocities for Hunt and Hess Grades I and II when compared with those for Grade III, and that Grades IV and V seem to be affiliated with the lowest velocities. When the flow velocities of 11 patients who developed delayed ischemic deficits (DIDs) were compared with those of patients with no deficit, no significant difference was seen. A significant increase in velocity in the days before the onset of DID was found only in 3 of 11 cases. Eight patients showed either constant high or constant low velocities or even, in some cases, decreasing time courses. High flow velocities did not necessarily mean impending neurological deficits: 8 of 66 patients tolerated flow velocities over 200 cm/s. Therefore, it no longer seems to be justified to proclaim that TCD is able to predict neurological deficits, although it is doubtless able to detect vasospasm.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of cerebral haemodynamics in comatose patients by laser Doppler flowmetry--preliminary observations.

Preliminary observations of laser Doppler flowmetry (LDF) signal changes in comatose patients with severe head injury or higher grade subarachnoid haemorrhage are presented. The data demonstrate that LDF measurements by no means lend themselves to a straightforward and unequivocal interpretation. Three main sources of LDF signal "bias" are tentatively distinguished: (1) properties inherent to the LDF measurement system and (2) spatial as well as (3) temporal heterogeneity of functional responses of the cerebral microvascular bed lead to unexpected, unpredictable and seemingly "paradox" patterns of the LDF signals. Despite the exploratory character of our data, we are convinced that they strongly suggest a more critical and cautious appraisal of the present possibilities of LDF in monitoring comatose patients than suggested by several other recent reports on this topic.