1 of 4 NON-INVASIVE TECHNOLOGIES FOR INTRACRANIAL PRESSURE/VOLUME MEASUREMENT A. Ragauskas, V. Petkus Telematics Scientific Laboratory, Kaunas University of Technology, Lithuania Abstract – The paper shows that innovative technologies for non- invasive monitoring of the cerebral blood flow autoregulation, cerebral blood flow pulse and slow waves also for the registration of the reactions to the neurodiagnostic tests can be developed on the basis of the precise measurement of brain parenchyma acoustic characteristics. The innovative technological equipment for such measurement has been developed. The clinical studies proving the validity of the concepts chosen have been carried out. For the first time the innovative non-invasive method has been designed for the ICP absolute value measurement without the necessity of individual calibration of system “non-invasive meter – patient”. Keywords - Intracranial pressure, non-invasive monitoring, time-of-flight method, transcranial Doppler. I. INTRODUCTION Head injury has devastating economic and social consequences both to the victim and to the society that supports the victim. The World Health Organization estimate that by the year 2010, one in ten families will have a family member with a head injury. Since head injury is more prevalent in the young and the associated disability does not significantly reduce life expectancy, the result is that the social and economic costs incurred by health and welfare organizations are long term and substantial [1]. Direct measurement of intracranial pressure (ICP) remains the mainstay of detecting brain swelling after the head injury before pressure rises to levels damaging the brain function. At present, the measurement techniques are invasive and require either the placement of a catheter-tip strain gauge device into the brain tissue directly or a fluid filled catheter placed into the cerebral spinal fluid space within the brain. However, the implementation of such procedures is related to entailing the risk of causing intracerebral bleeding, risk of infection inside the brain or other undesirable phenomena that can deteriorate the outcome. To avoid these problems, the non-invasive ICP monitoring technology is needed. The ideas of the measurement of ICP non-invasively have been appearing since 1980. There are many patents [2,3,6- 16], the authors of which attempt to find the objects or physiological characteristics of cerebrospinal system that would be related to the ICP and monitor them non-invasively. Most of the proposed monitoring technologies are based on the ultrasound application and are capable of monitoring physiological properties such as blood flow in intracranial or intraocular vessels, pulsations of the cerebral ventricles, cranium diameter or acoustic properties of the cranium. However, there are a few main questions encountered by a lot of authors of these works: 1) Which biophysical parameter of a cerebrospinal system is a stable and repeatable function of ICP or cerebral perfusion pressure (CPP) only? 2) Is that function linear and more or less independent on such main influential factor as arterial blood pressure (ABP) and how it depends on the cerebral blood flow autoregulation? 3) How to calibrate non-invasively the system "individual patient – non-invasive ICP or CPP meter”? Unfortunately the answers to these questions based on reliable clinical studies still have not been found. Recently, a new method [2] for non-invasive measurement of intracranial volume or pressure has been created in Telematics Scientific Laboratory of Kaunas University of Technology (Lithuania) which uniquely purports to measure the intracranial pulsation of small intracranial blood vessels. This method may be of more clinical value as the microvasculature is the major source of cerebrovascular resistance which determines the intracranial cerebral blood flow and it is responsible for cerebral blood flow autoregulation. Another innovative method [3] includes a means based on the transcranial Doppler multi-depth technique for a non-invasive absolute ICP value measurement without the individual calibration problem. The main applications of these devices are the following: - fast non-invasive diagnosing of brain injury during the first “golden hour” after the casualty case, - non-invasive brain or spinal cord injury physiological monitoring during the intensive care, - non-invasive diagnosing of brain physiological status during the rehabilitation period, - diagnosing and monitoring of the reactions of cerebral blood flow autoregulation system and parenchymal blood volume/ICP on different pharmacological influences or physical loads (space medicine, sport medicine, etc.). Both innovative methods are described in this paper and clinical results are also presented. II. METHODOLOGY The background of the non-invasive intracranial volume or pressure measurement methodology is the relationships between the ultrasound speed in the cerebral parenchymal acoustic path and blood volume inside the cerebral parenchyma (CBV), cerebrovascular resistance (CVR) and also CPP, ABP and ICP. These relationships could be explained by the changes of the diameter of cerebral arterioles as a result of cerebral blood flow autoregulation (Fig. 1). In the case of normal autoregulation (Fig. 1b) the diameter of cerebral arterioles decreases (Fig. 1a) when CPP increases within the linear range of CVR/CPP dependence (Fig. 1c). The blood volume also changes inside the cerebral parenchymal acoustic path (Fig. 1d) as a result of the autoregulatory change of cerebral arterioles diameter. It was 0-7803-7211-5/01$10.00©2001 IEEE Proceedings – 23rd Annual Conference – IEEE/EMBS Oct.25-28, 2001, Istanbul, TURKEY