Francis Kralick

In-Vitro and In-Vivo Trans-Scalp Evaluation of an Intracranial Pressure Implant at 2.4 GHz

Elevation of intracranial pressure is one of the most important issues in neurosurgery and neurology in clinical practice. The prevalent techniques for measuring intracranial pressure require equipments that are wired, restricted to a hospital environment, and cause patient discomfort. A novel method for measuring the intracranial pressure is described. A wireless completely implantable device, operating at an industrial-scientific-medical band of 2.4 GHz, has been developed and tested. In-vitro and in-vivo evaluations are described to demonstrate the feasibility of microwave pressure monitoring through scalp, device integrity over a long period of time, and repeatability of pressure measurements. A distinction between an epidural and sub-dural pressure monitoring techniques is also described. Histo-pathological results obtained upon a long-term device implantation favor the utilization of the sub-dural pressure monitoring method. On the other hand, in-vivo studies illustrate a maximum pressure reading error of 0.8 mm middot Hg obtained for a sub-dural device with a capacitive microelectromechanical system sensor compared to 2 mm middot Hg obtained for an epidural device with a piezoresistive sensor.

Malignant Nerve Sheath Tumor of the Spinal Accessory Nerve: A Unique Presentation of a Rare Tumor

Background Malignant peripheral nerve sheath tumors (MPNSTs), sarcomas originating from tissues of mesenchymal origin, are rare in patients without a history of neurofibromatosis. Case Report We report a case of an MPNST of the spinal accessory nerve, unassociated with neurofibromatosis, which metastasized to the brain. The tumor, originating in the intrasternomastoid segment of the spinal accessory nerve, was removed. Two years later, the patient presented with focal neurological deficits. Radiographic findings revealed a well-defined 2.2×2.2×2.2 cm, homogeneously enhancing mass in the left parieto-occipital region of the brain surrounded by significant vasogenic edema and mass effect, culminating in a 1-cm midline shift to the right. The mass was surgically removed. The patient had nearly complete recovery of vision, speech, and memory. Conclusions To our knowledge, this is the first documented case of an MPNST arising from an extracranial segment of the spinal accessory nerve and metastasizing to the brain.

Issues in Wireless Intracranial Pressure Monitoring at Microwave Frequencies

Intracranial pressure (ICP) monitoring has a signiflcant role in the diagnosis and prognosis of various brain diseases. The most prevalent technique of monitoring ICP is using catheter based systems, which involve risks including infection, brain damage and patient dis- comfort. A novel wireless epidural pressure sensor unit which can be implanted in a burr hole drilled in the skull is proposed. The unit operates at an ISM band of 2.4GHz and radiates a microwave signal as a function of pressure. In-vitro and in-vivo tests were performed to study the e-ciency of this measurement technique. This paper presents the design issues and experimental results of the prototype devices developed so far.

Design and Fabrication of a PDMS/Parylene Microvalve for the Treatment of Hydrocephalus

We present a novel microvalve for the treatment of a pathological condition, i.e., hydrocephalus. This microvalve is made of polydimethylsiloxane/Parylene composite layer which has a 3-D dome petal shape. This geometry enables the microvalve to rectify fluid flow in the forward and backward directions. New microfabrication techniques such as dome-shaped SU-8 mold fabrication and excimer laser machining for valve opening have been investigated to build the proposed microvalve. The pressure drop versus flow rate characteristics of the fabricated microvalve was investigated through in vitro flow tests. The flow test results showed that a 10 × 10 microvalve array with a cross-cut opening shape (200 × 60 μm) was found to be optimal for the treatment of hydrocephalus.

Embedded microwave system for monitoring of intracranial pressure

Intracranial pressure is of increasing interest in the management of patients who are suffering from various neurological disorders such as hydrocephalus, traumatic brain injury, and blast injury. Long-term monitoring of intracranial pressure may be desirable in these conditions to aid in determining the outcome of any treatment. A completely implantable microwave device for monitoring of intracranial pressure has been designed and characterized. The application of an embedded Planar Inverted-F antenna in this implant is also investigated.

Micro-fabricated Shunt to Mimic Arachnoid Granulations for the Treatment of Communicating Hydrocephalus

Hydrocephalus is the abnormal accumulation of cerebrospinal fluid (CSF) within the confines of the skull that if left untreated results in significant morbidity and mortality. The treatment for hydrocephalus has remained essentially unchanged for over 50 years. It was a technological advance in materials that allowed John Holter, in conjunction with neurosurgeons Spitzer and Nulsen, to devise a valve and shunt system that diverted excess CSF from the ventricular space to the peritoneum. This ventriculo-peritoneal (VP) shunt is far from ideal, with problems associated with under/over shunting, mechanical mismatch, infection, high failure rates, disconnection and erosion. With the advances in the field of micro-fabrication and micro-machines we propose an innovative shunt system that would mimic the function of arachnoid granulations. This micro-fabricated shunting device, or micro-mechanical arachnoid granulation (MAG), consists of a multiplicity of micro-valves each 210 μm in diameter that each adhere to individual micro-needles. This work demonstrates the design and initial test results of the micro-valve with parameters for low cracking pressure, optimal flow rate, and reflux that would mimic the function of the native arachnoid granulations.