Anwendung der Diffusions-Tensor-Bildgebung in der Neurochirurgie

Classification and Analysis of the Errors in Neuronavigation

There are many different types of errors in neuronavigation, and the reasons and results of these errors are complex. For a neurosurgeon using the neuronavigation system, it is important to have a clear understanding of when an error may occur, what the magnitude of it is, and how to avoid it or reduce its influence on the final application accuracy. In this article, we classify all the errors into 2 groups according to the working principle of neuronavigation systems. The first group contains the errors caused by the differences between the anatomic structures in the images and that of the real patient, and the second group contains the errors occurring in transforming the position of surgical tools from the patient space to the image space. Each group is further divided into 2 subgroups. We discuss 16 types of errors and classify each of them into one of the subgroups. The classification and analysis of these errors should help neurosurgeons understand the power and limits of neuronavigation systems and use them more properly.

Reproducible evaluation of spinal cord DTI using an optimized inner volume sequence in combination with probabilistic ROI analysis

The purpose of this work was to reliably acquire and evaluate diffusion tensor data of the cervical spine. Thereto, we describe an optimized, time-efficient inner-volume echo planar imaging sequence. Multislice capability is achieved by restoring the magnetization in neighbouring slices early during the twice refocused diffusion preparation. The acquired diffusion images showed compelling image quality. To reduce the arbitrariness of conventional region of interest (ROI) analysis, a tissue classification algorithm was applied. The classification was independent of the ROI shape and hence, a reliable and stable evaluation of the diffusion tensor could be achieved. The mean fractional anisotropy (FA) of five healthy subjects decreased from C1 (FA = 0.81 +/- 0.03) to C7 (FA = 0.60 +/- 0.03), while the mean apparent diffusion coefficient (ADC) increased from C1 (ADC= 0.78 +/- 0.08 microm2/ms) to C7 (ADC = 1.08 +/- 0.08 microm2/ms). In subsequent measurements of the individual healthy subjects, the standard deviation of the FA was 0.024 +/- 0.011 and the standard deviation of the ADC was 0.045 +/- 0.017 microm2/ms. The FA values of a patient with acute ischemic spinal trauma were significantly lower and changed more drastically than ADC values. Here, absolute FA ranged from 0.23 to 0.42, showing that DTI of the spine may serve as surrogate marker for tissue integrity and therapy monitoring.