<qa>  What is the third ventricle diameter measurement by transcranial doppler ultrasonographyTranscranial Doppler ultrasonography is usually used in the evaluation and management of patients with brain injury. This noninvasive method measures local blood flow velocity and direction in the proximal portions of large intracranial arteries. The operator requires a short training and experience to perform. The third ventricle diameter measurement by transcranial duplex flow sonography was performed in healthy volunteers . This studies show similar results in those obtained with the MRI or Computer Tomography CT. Currently the third ventricle diameter measurements by transcranial Doppler ultrasonography was not validated for neuro-intensive care unit patients. The investigators propose to used recent ultrasound system to validate the third ventricle diameter measurements in comparison with the standard method CT. 