Ultrasonic non-invasive intracranial wave monitor

The innovative non-invasive intracranial volume wave monitor has been developed in Telematics Scientific Laboratory of Kaunas University of Technology (Lithuania). It is based on the measurement of the human brain parenchyma acoustic properties (ultrasound speed and attenuation) using time-of-flight technique [1,2] and it is capable of measuring different types of intracranial volume wave (slow B waves, respiration waves, pulse waves), also to perform analysis of their shapes and to diagnose different pathophysiological states of the human cerebrovascular system [3]. The diagnostic information about the human cerebrovascular system can be obtained while measuring the dynamics of the acoustic properties of brain parenchyma: 1) slow trends and waves of intracranial pressure (ICP) due to the slow changes of the intracranial media component volumes inside the parenchymal acoustic path, 2) changes of cerebrovascular resistance due to the pathological changes of intracranial component volumes influencing the cerebrospinal fluid (CSF) outflow to the spinal canal which can be determined by measuring the parameters of cerebral blood volume or ICP pulse waves inside brain parenchyma [4]. The essential capability of the monitor is the suitability of continuous and real-time monitoring of human cerebrovascular autoregulation (CA). It is implemented by non-invasively measuring slow B waves of relative ultrasound speed (∆C/C0) in brain parenchyma and applying their correlation with the same waves of arterial blood pressure (ABP) as an index of CA state [3,5]. This correlation coefficient r(∆C/C0;ABP) characterises the cerebrovascular resistance which determines the intracranial cerebral blood flow and can quantitatively represent cerebrovascular autoregulation [6,7]. There could be a few fields of application of the new non-invasive monitor. The intracranial volume monitoring and CA status diagnosing is needed for traumatic brain-injury, spinal cord-injury and hydrocephalus patient treatment. Moreover, the resent clinical studies of factors that influence the outcome of patients with traumatic brain injury show that the cerebrovascular autoregulation state is the most critical factor for the patients outcome [7,8]. The relationship between CA state and the patients’ outcome and their mortality as well was found to be more significant and stronger than the relationships between the outcome and widely used criteria such as Glasgow Coma Scale, mean arterial blood pressure, mean intracranial pressure or mean cerebral perfusion pressure [7,8]. The non-invasive diagnosing and monitoring of the human cerebrovascular autoregulatory system is also important while investigating the reactions to the influences of microgravity/space conditions or physical loads. Other applications of the new non-invasive monitoring system could be the fields of pharmacological investigation, where the introduction of the present technology would open new possibilities to explore different pharmacological influences to the brain and it would help to choose the optimal way for treating the patient.