Intracranial Pressure Monitoring Calibration and Setup Ashish V M
What is intracranial pressure? Intracranialpressure (ICP) is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid (CSF). Normal values: 7-15 mmHg Abnormal values: > 20-25 mmHg Increased ICP indicates Hydrocephalus and Edema Measured during TBI (Traumatic brain injuries )& Neurosurgeries.
Why Calibration… • To determine the functionality of the whole setup and to check whether all the electronics being implemented onto the sensor output is working or not, calibration of sensor is needed. The sensor needs to be exposed to the pressure ranges from 0 to 50mm Hg in order to determine its sensitivity, hysteresis as well as drift in the output voltage with time and pressure. • Need for a Pressure Calibrator: • For stable temperature and pressure characterization of IISc intracranial pressure sensor over a long period of time. • To reproduce an in-vitro environment, this mimics the conditions inside the brain.
ICP calibrator • Water bath assembly for temperature variation • Vertical glass column for pressure variation • Horizontal glass column with standard pressure sensor and multiple ICP sensor insertion points • Temp control and data recording through a PC • Provision to calibrate 10 sensors at a time • Water Bath Assembly • Water tank internal dimensions WxDxH (mm): 400 x 180 x 150 • Temperature range: 5 to 50 deg C • Heater and compressor assembly • PID temperature controller • RS-232 interface for control and data readout • Front viewing window, illuminated interior
Horizontal Glass Column : • Square stainless steel tube (40 x 40 x 200mm) with a front glass window to view the sensors’ position • Glass window marked with mm scale • Provision to insert 10 ICP sensors from top surface • 5 temp sensors (Pt1000) also placed to record the precise temp reading in the proximity of ICP sensors • 1 standard pressure sensor for benchmarking and 1 temp sensor (Pt1000) for temp control • Vertical Glass Column: • Acrylic; Internal dia 10 mm; Height 1500 mm • Detachable • Marked with mm scale • Zero coincides with the centre of the horizontal column • Two solenoid switches for attaching pressure generator and pulse generator, if required • Valve to drain out the water
What has been done so far… • Talks/discussions have been going on with a potential vendor regarding the development of such a setup. • Slight changes to the above model has been suggested by the vendor(For instance, building the cooling assembly and display behind the horizontal tank as opposed to the design in the image which suggests sideways) • Meanwhile, the operation of the ICP monitoring and signal conditioning device used by Kush Tripathi is being studied to see if it can be incorporated into the setup. • Status as of today: • Purchase order yet to be released as vendor needs more time to disclose new quotations.
Catheter(above) Dimensions: 1 mm x 1 mm Square membrane (400 um x 400 um) 200 um x 200 um Aluminium pads Plan for the Fabricated Sensor
Off-chip circuit for electronic interfacing(above). Pressure and Temperature values are extracted from the sensor by completing the Wheatstone’s bridge using this circuit. Signal conditioning circuit(left)