A new implantable pressure sensor for long-term monitoring of intracranial pressure is presented. The sensor is powered by telemetry and can be interrogated wirelessly. A capacitive pressure transducer, whose capacitance is converted to a frequency-encoded signal by an application-specific integrated circuit (ASIC), senses the absolute pressure. The pressure-encoded signal, the ASIC input voltage, and onboard calibration parameters are transmitted to an external reading unit. The proposed novel packaging solution is designed for long-term stability and reliability of the sensor. The accuracy of sensor at body temperature is better than 2 mbar across a pressure range of 600-1200 mbar. The sensor is 13 mm in diameter and 4.5 mm in height.

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Abstract-The goal of this study was to propose a general numerical analysis methodology to evaluate the magnetic resonance imaging (MRI)-safety of active implants. Numerical models based on the finite element (FE) technique were used to estimate if the normal operation of an active device was altered during MRI imaging. An active implanted pump was chosen to illustrate the method. A set of controlled experiments were proposed and performed to validate the numerical model. The calculated induced voltages in the important electronic components of the device showed dependence with the MRI field strength. For the MRI radiofrequency fields, significant induced voltages of up to 20 V were calculated for a 0.3T field-strength MRI. For the 1.5 and 3.0T MRIs, the calculated voltages were insignificant. On the other hand, induced voltages up to 11 V were calculated in the critical electronic components for the 3.0T MRI due to the gradient fields. Values obtained in this work reflect to the worst case situation which is virtually impossible to achieve in normal scanning situations. Since the calculated voltages may be removed by appropriate protection circuits, no critical problems affecting the normal operation of the pump were identified. This study showed that the proposed methodology helps the identification of the possible incompatibilities between active implants and MR imaging, and can be used to aid the design of critical electronic systems to ensure MRI-safety.Index Terms-Biomedical equipment safety, finite element methods, magnetic resonance imaging.

The MedStream Programmable Infusion Pump, an intrathecal pump indicated for the treatment of chronic intractable pain and severe spasticity (CE-mark) or severe spasticity (US), has a highly accurate medication delivery (within 10% of the programmed flow rate) and is certified for use in 3-Tesla magnetic resonance imaging systems (conditional). Performance of the telemetric link between external control-unit and implanted pump was assessed in sheep (in vivo) up to 26 weeks, resulting in 1040 communication sessions. The telemetric communication envelope (communication distance and maximum antenna tilt angles) and communication duration were characterized in an in vitro test. Capacitance measurements of the piezoelectric actuator of the valve, valve flow rates, and leak rates were measured in an in vitro cyclic accelerated aging test to assess reliability of the valve over 6,200 k cycles. The pump was well tolerated in vivo; all communication sessions between control-unit and pump were successful (P = 6.889 × 10(-14)). Mean communication distance between pump and control-unit was 3.8 cm, with the maximum antenna tilt angles being 40° (θy) and 50° (θx) for all test cases; the maximum communication duration was 5.5 s. Capacitance measurements, flow rates, and leak rates were within ±10 % range up to 6,200 k cycles corresponding to approximately 10 times the valve cycles over the specified service life of the pump (8 years), except for one flow-rate value, which can be explained by the measurement setup. These results demonstrate the reliability of the telemetry link and piezoelectric valve system of the MedStream Programmable Infusion Pump.