Biomedical subjects

René Krishnan

Publications and source records attributed to René Krishnan.

6 recordsLinked to original sources

PubMed2004

Characterization of the potent combined endothelin(A/B)-antagonist PD 142893 on cerebral vessels.

A disturbed balance between endothelin (ET)-1 and nitric oxide (NO) seems to play a key role in the development of delayed cerebral vasospasm following subarachnoidal hemorrhage. Therefore, the effect of PD 142893 one of the first potent ET(A)- and ET(B)-receptor antagonists was characterized on the contraction and relaxation induced by ET-1 and bigET-1 on rat basilar artery (BA). Concentration-effect curves (CECs) were constructed by cumulative application of ET-1 or big ET-1 on BA ring segments with (E+) and without (E-) functionally intact endothelium. The effect of PD 142893 was determined by the modified pK(b) value and the shift between the CECs. PD 142893 inhibited the contraction by ET-1 and bigET-1. The pK(b)-values were for ET-1: 5.17 (E+) and 5.15 (E-) and for big ET-1: 5.34 (E+) and 5.57 (E-), respectively. A significant relaxation of pre-contracted segments by ET-1 or big ET-1 was neither observed in the presence nor in the absence of the receptor antagonist. The present data suggest a competitive inhibition of the ET(A)-receptor mediated contraction of cerebral arteries by PD 142893. The ET(B)-dependent relaxation of the cerebrovasculature is inhibited by PD 142893 at least in a comparable amount of contraction.

Animals↗

PubMed2004

Functional magnetic resonance imaging-integrated neuronavigation: correlation between lesion-to-motor cortex distance and outcome.

OBJECTIVE: The integration of functional magnetic resonance imaging (fMRI) data into neuronavigation is a new concept for surgery adjacent to the motor cortex. However, the clinical value remains to be defined. In this study, we investigated the correlation between the lesion-to-fMRI activation distance and the occurrence of a new postoperative deficit. METHODS: fMRI-integrated "functional" neuronavigation was used for surgery around the motor strip in 54 patients. During standardized paradigms for hand, foot, and tongue movements, echo-planar imaging T2* blood oxygen level-dependent sequences were acquired and processed with BrainVoyager 2000 software (Brain Innovation, Maastricht, The Netherlands). Neuronavigation was performed with the VectorVision(2) system (BrainLAB, Heimstetten, Germany). For outcome analysis, patient age, histological findings, size of lesion, distance to the fMRI areas, preoperative and postoperative Karnofsky index, postoperative motor deficit, and type of resection were analyzed. RESULTS: In 45 patients, a gross total resection (>95%) was performed, and for 9 lesions (low-grade glioma, 4; glioblastoma, 5), a subtotal resection (80-95%) was achieved. The neurological outcome improved in 16 patients (29.6%), was unchanged in 29 patients (53.7%), and deteriorated in 9 patients (16.7%). Significant predictors of a new neurological deficit were a lesion-to-activation distance of less than 5 mm (P < 0.01) and incomplete resection (P < 0.05). CONCLUSION: fMRI-integrated neuronavigation is a useful concept to assess the risk of a new motor deficit after surgery. Our data suggest that a lesion-to-activation distance of less than 5 mm is associated with a higher risk of neurological deterioration. Within a 10-mm range, cortical stimulation should be performed. For a lesion-to-activation distance of more than 10 mm, a complete resection can be achieved safely. The visualization of fiber tracks is desirable to complete the representation of the motor system.

Adult↗

PubMed2003

Automated fiducial marker detection for patient registration in image-guided neurosurgery.

OBJECTIVE: The registration of applied fiducial markers within the preoperative data is often left to the surgeon, who has to identify and tag the center of each marker. This is both time-consuming and a potential source of error. For this reason, the development of an automated procedure was desirable. In this study, we have investigated the accuracy of a software algorithm for detecting fiducial markers within the navigation data set. The influence of adjustable values for accuracy and threshold on the sensitivity and specificity of the detection process, as well as the time gain, was investigated. PATIENTS AND METHODS: One hundred MP-RAGE MRI data sets of patients with different pathologies who were scheduled for image-guided surgery were used in this study. A total of 591 applied fiducial markers were to be detected using the algorithm of the software VVPlanning 1.3 (BrainLAB, Heimstetten, Germany) on a Pentium II standard PC. The size value of a marker in the y-direction is called "accuracy" and depends on the slice thickness. "Threshold" describes the gray level above which the algorithm starts searching for pixel clusters. The threshold value was changed stepwise on the basis of a constant "accuracy" value. The "accuracy" value was changed on the basis of that threshold value at which all markers were detected correctly. RESULTS: The time needed for automatic detection varied between 12 s and 25 s. An optimum value for adjustable marker size was found to be 1.1 mm, with 8 undetected markers (1.35%) and 7 additionally detected structures (1.18%) out of 591. The mean gray level (Threshold) for all data sets above which marker detection was correct was 248.9. The automatic detection of markers was good for higher gray levels, with 11 missed markers (1.86%). Starting the algorithm at lower gray levels led to a decreased incidence of missed markers (0.17%), but increased the incidence of additionally detected structures to 27.92%. CONCLUSION: The automatic marker-detection algorithm is a robust, fast and objective instrument for reliable fiducial marker registration when used with optimum settings for both threshold and accuracy.

Adolescent↗

PubMed2003

Actual aspects of image-guided surgery.

Use of surgical navigation systems is becoming an increasingly important part of both planning and performing intracranial and spinal surgery. Numerous clinical reports have described neuronavigation as a useful adjunct to surgery that allows neurosurgery to be less invasive and more effective. Although the method of image-guided surgery was introduced more than a decade ago, new technologies have changed and refined the procedure substantially. This chapter summarizes the recent developments of advanced image-guided surgery. For most operations, microscope navigation has replaced pointer navigation. Using the microscope as the localizing device, the workflow is not interrupted and microsurgical procedure can be continued as usual. New chip technology allows integration of magnetic resonance images, angiography findings, endoscopic view, or other pictures in the eyepiece of the microscope. A new method of patient registration is laser scanning and surface matching. When using high-quality images, this new method can be used without additionally acquired images, may reduce costs, simplify the pre-registration procedure, and increase application accuracy compared to skin-fiducial registration. Moreover, integration of other imaging modalities is becoming an increasingly used feature and provides useful information during surgery.

Brain Mapping↗

PubMed2002

Laser surface scanning for patient registration in intracranial image-guided surgery.

OBJECTIVE: To report our clinical experience with a new laser scanning-based technique of surface registration. We performed a prospective study to measure the calculated registration error and the application accuracy of laser surface registration for intracranial image-guided surgery in the clinical setting. METHODS: Thirty-four consecutive patients with different intracranial diseases were scheduled for intracranial image-guided surgery by use of a passive infrared surgical navigation system. Surface registration was performed by use of a Class I laser device that emits a visible laser beam. The Polaris camera system (Northern Digital, Waterloo, ON, Canada) detects the skin reflections of the laser, which the software uses to generate a virtual three-dimensional matrix of the anatomy of each patient. An advanced surface-matching algorithm then matches this virtual three-dimensional matrix to the three-dimensional magnetic resonance therapy data set. Registration error as calculated by the computer was noted. Application accuracy was assessed by use of the localization error for three distant anatomic landmarks. RESULTS: Laser surface registration was successful in all patients. For the surgical field, application accuracy was 2.4 +/- 1.7 mm (range, 1-9 mm). Application accuracy was higher for the surgical field of frontally located lesions (mean, 1.8 +/- 0.8 mm; n = 13) as compared with temporal, parietal, occipital, and infratentorial lesions (mean, 2.8 +/- 2.1 mm; n = 21). CONCLUSION: Laser scanning for surface registration is an accurate, robust, and easy-to-use method of patient registration for image-guided surgery.

Adolescent↗

PubMed2002

Robot-assisted navigated neuroendoscopy.

OBJECTIVE: Major steps in the evolution of advanced neurosurgical techniques include microneurosurgery, neuroendoscopy and its minimally invasive variations, neuronavigation, and advanced intraoperative imaging. With traditional neuroendoscopic techniques (e.g., freehand endoscopy or the use of mechanical arms), definitive controlled movement of the endoscope within the brain depends on the experience and skill of the individual neurosurgeon. METHODS: With the Evolution 1 precision robot (Universal Robot Systems, Schwerin, Germany), a new neurosurgical tool has become available for the precise steering of instruments within the cranium. After preclinical anatomic and precision studies, the system was used for neuronavigated endoscopic procedures for three patients. RESULTS: All robot-assisted, navigated, endoscopic procedures were successfully completed. The time for the registration procedure and setup of the robot decreased from 60 minutes for the first patient to 30 minutes for the third patient. The time for the surgical part of the endoscopic procedure ranged from 17 to 65 minutes. No complications occurred during any procedure. CONCLUSION: The use of robotic technology for neuroendoscopic procedures is a major advance for controlled movement of the endoscope within the cranium. The start-up procedure and calibration of the robot are still time-consuming, but the actual operation time is comparable to that of freehand neuroendoscopic procedures. Steering of the endoscope is facilitated, and the precision of the endoscopic movements is noteworthy.

Adolescent↗