asscc 2010 21uw inductively powered implant ic

A 21.6 W Inductively Powered Implantable IC for Blood Flow Measurement Pradeep Basappa Khannur, Kok Lim Chan, Jia Hao Cheong, Kai Kang, Andreas Astuti Lee, Xin Liu, Huey Jen Lim, Kotlanka Ramakrishna and Minkyu Je Institute of Microelectronics, A*STAR (Agency for Science, Technology and Research) 11 Science Park Road, Singapore Science Park II, Singapore 117685 Email: [email protected] Abstract — This paper presents a fully integrated inductively powered implantable circuits for blood flow measurement, which are embedded within vascular prosthetic grafts for early detection of graft degradation or failure. The ASIC interfaces with micro-fabricated pressure sensors and uses a 13.56MHz carrier frequency for power transfer and command/data communication. A backscatter-modulated passive telemetry is used for transmitting sensor readout information to an external monitoring device. The chip has been fabricated in 0.18 µm CMOS process, occupies a total active area of 1.5 1.78mm 2 and consumes a total power of 21.6 µW. The rectifier achieves an efficiency of 66%. The sub- µW 10-bit SAR ADC achieves an ENOB of 8.5 bits at 106KS/s convers ion rate. I. I NTRODUCTION Hundreds of vascular prosthetic grafts are implanted eve- ryday for haemodialysis or bypass purposes all over the world. At least 20-30% of the existing renal haemodialysis popula- tion have a prosthetic vascular graft in-situ. In addition, thou- sands of lower limb bypasses are performed all over the world yearly, of which at least 20% require the use of prosthetic grafts. Prosthetic grafts are frequently used in vascular surgery in the context of bypass surgery for lower limb ischemia or as a conduit for haemodialysis in renal failure. In these settings, graft failure can result in deleterious outcomes for the patients i.e. worsening ischemia, inability to undergo haemodialysis. Insufficient blood flow rates in these grafts are predictive of subsequent graft thrombosis and failure. Underlying this is the presence of stenoses in the graft or downstream from the graft. Variations in flow rates can localize the position of significant stenosis that may result in graft thrombosis. Flow rate monitoring provides an indication for early intervention to prevent graft failure. As such, a large amount of resources are devoted to detecting failing grafts vis-a-vis decreasing flow rates. In par- ticular, significant amounts of time and financial resources are spent on using different modalities to monitor graft flow rate and detect early failures. These modalities include ultrasound, computer tomography (CT) scan and formal angiograms. Disadvantages of these modalities include the need for significant amounts of procedural time (ultrasound, angiogram), the use of nephrotoxic contrast (CT scan and angiograms) and invasiveness (angiograms). More importantly, these proce- dures are not entirely risk-free for patients and come with some procedural morbidity and monitoring of flow rates are done at regular intervals (i.e. once in 4-6 months). There are a few commercially available flow rate detection devices (in- travascular) but they are invasive in nature causing trauma to the patient for every measurement. An implantable system that can provide convenient monitoring of blood flow in vascular prosthetic grafts with a simple hand-held device is desired. With the sensor-embedded graft, the failing graft can be detected at its earlier stage thus implementing early intervention strategies. Similarly, this will reduce the number of graft surveillance scans (CTs, angiograms, etc.) per patient from a routine process to one done only when there are abnormalities detected in the flow rates. The ASIC presented in this paper is designed for a passive implantable microsystem, Sensor-Embedded Prosthetic Vas- cular Graft, which can be powered wirelessly (through induc- tive coupling) to sense the blood flow rate and transmit it through wireless interface to a hand-held device which can send the data to the medical practitioner. The highly sensitive nanowire-based pressure sensor is used in this microsystem, which is not the scope of this paper, as t he sensing element for detecting the blood flow rate. Figure 1. (a) Simplified block diagr am of the blo od flow measurement system, (b) Conceptual structure of the prosthetic graft with the sensor, IC and coil. This work is funded by A*STAR (Agency for Science, Technology and Research) SERC (Science and Engineering Research Council), Singapore nder the grant no. 0921480069 . Graft (a) (b) 9-5 IEEE Asi an Solid-State C ircui t s Con f eren ce N o vem b er 8-10, 2010 / Bei j i n g,Chin a 978-1-4244 - 829 8-6/ 10/$26.00 ®20 10 IEEE

asscc 2010 21uw inductively powered implant ic

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