Authors: Amit Ayer, MD; Siddharth Krishnan, PhD; Tyler Ray, PhD; Nikhil Murthy, MD; Zachary Abecassis, BS; Matthew Potts, MD; John Rogers, PhD (Chicago, IL)
Shunt-related complications are a major cause of morbidity with costs estimated at over 100 million dollars yearly. Shunts often malfunction and current diagnostic modalities are lacking, ranging from expensive and inconclusive imaging tests with potential radiation to inaccurate and invasive sampling or radionucleotide studies. Noninvasive, accurate interpretation of shunt function provides significant benefits and we thus propose a novel wireless solution reliant on thermal anisotropy and flexible sensor technology.
Metallic, resistance temperature detectors (RTD’s) are rendered in ultrathin formats (<100 nm) allowing millikelvin temperature measurements and simultaneous low-power Joule heating of mechanically coupled tissue. The combination of targeted heating and sensing allows for measurements of transient tissue thermal responses to directly yield k and α values with established algorithms. Thus, skin-mounted, ‘epidermal’ sensor can track hydration in outer skin layers. Addition of impedance electrodes allows multimodal sensing and advances in near-field communication (NFC) have allowed integration of a flexible antenna, miniaturized electronics, and soft, stretchable RTD elements into a wireless, smartphone-compatible platform for continuous monitoring. Strategic configurations sensing and actuating elements can generate heat maps tracking thermal anisotropy induced by blood vessels or fluid flowing through subdermal implants like catheters. Novel algorithms combine finite element analysis with analytical scaling laws to yield quantitative flow rates. This allows for over 100, individually addressable sensors to create detailed heat maps measuring flow in subdermal ventriculoperitoneal (VP) shunts in hydrocephalic patients.
4 shunted patients and 1 patient with an external ventricular drain were evaluated along with standard assessments including radionucleotide imaging and operative exploration. Obtained sensor readings appropriately correlated with clinical shunt diagnostic evaluations in both functional and nonfunctional shunts without any noted adverse events.
Noninvasive wireless sensors may provide a versatile and cost-reductive means of diagnosing shunt failure.