The vision of the Medical Electronic Device Research Center (MEDRC) is to transform the medical electronic device industry: to revolutionize medical diagnostics and treatments, bringing health care directly to the individual; and to create enabling technology for the future information-driven healthcare system. Specific areas that show promise are wearable or minimally invasive monitoring devices, medical imaging, laboratory instrumentation, and the data communication from these devices and instruments to healthcare providers and caregivers.

The MEDRC establishes a partnership between the microelectronics industry, the medical devices industry, medical professionals, and MIT to collaboratively achieve improvements in the cost and performance of medical electronic devices similar to those that have occurred in personal computers, communication devices and consumer electronics. The Medical Electronic Device Realization Center (MEDRC) was established to better connect industry, academia, and physicians.  In the MEDRC, research activities are jointly defined by faculty, physicians and clinicians, and industrial partners.  A visiting scientist from a project’s sponsoring company is present at MIT.  Ultimately this individual is the champion that helps translate the technology back to the company for commercialization and provide the industrial viewpoint in the realization of the technology.    We foster the creation of prototype devices and intellectual property in the field of medical electronic systems and serve as a catalyst for the successful deployment of innovative healthcare technology at an affordable price.

MEDRC projects have the advantage of insight from the technology arena, the medical arena, and the business arena, thus significantly increasing the chances that their devices will fulfill a real healthcare need as well as be profitable for companies to ensure a stable supply of the new devices.  With a new trend toward increased healthcare quality, disease prevention, and cost-effectiveness, such a comprehensive perspective is crucial.

The collective aim of the MEDRC is to revolutionize medical diagnostics and treatments, bringing health care directly to the individual, and creating technology for the future of information-driven healthcare.   We focus on areas of medical devices that are enabled and enhanced by electronics and computation – imaging, point-of-care devices, diagnostics and therapeutic instrumentation, ambulatory physiological monitors, etc.

The MEDRC serves as a focal point for large business, for venture-funded startups, and for the medical community. The Center fosters the creation of prototype devices and intellectual property and aims to serve as the catalyst for the deployment of innovative healthcare technology that will reduce the cost of healthcare in both the developed and developing world. Current members are Analog Devices, GE Global Research/Healthcare, and Maxim Integrated Products.

Most current ultrasound imaging systems use piezoelectric materials for the ultrasound transducer. The recent development of micro-electromechanical systems (MEMS) allowed fabrication of capacitive micromachined ultrasound transducers (CMUTs).  A CMUT is a micromachined capacitor whose value changes according to the DC bias voltage or external pressure due to the physical deformation of the top plate by electrostatic force or external pressure. The major advantages of this transducer technology are the potential for integration with supporting electronic circuits, ease of fabrication, higher resolution due to small transducer size, and improved bandwidth and sensitivity ^[1] .

This project focuses on the front-end design of portable ultrasound systems using CMUTs. Figure 1 presents a conceptual block diagram of the system. Implementing an ADC at each channel input makes possible digital beam-forming in the receive (Rx) path, which enhances ultrasound image quality. To implement as many ADCs as the number of transducer channels, each ADC must consume as little power as possible, and each should be implemented in a small area. Considering the required performance, zero-crossing-based (ZCB) pipelined ADC is a suitable architecture ^[2] .  For the first part of this project, a 50-MHz 12-bit ZCB pipelined ADC is designed. The highly digital implementation characteristic of the zero-crossing detection technique enables energy-efficient operation and voltage scaling. Supply voltage scaling based on the required sampling frequency and resolution provides constant energy efficiency over a wide range of sampling frequencies and resolutions.

Recently, a few 2D imaging systems using CMUT as ultrasound transducers have been reported, but they do not use real-time imaging ^[1] . We will consider the digital image processing block in the system level for real-time imaging.  After completing the 2D ultrasound image system using a 1D transducer, we will examine the feasibility of the 3D ultrasound image system using 2D transducers.

Figure 1: Conceptual block diagram of portable ultrasound system.

1. O. Oralkan, “Acoustical Imaging Using Capacitive Micromachined Ultrasonic Transducer Arrays: Devices, Circuits, and Systems,” Ph.D. thesis, Stanford University, Stanford, 2004.
2. L. Brooks and H.-S. Lee, “A zero- crossing-based 8b 200MS/s pipelined ADC,” IEEE International Solid-State Circuits Conference Digest of Technical Papers, 2007, pp. 460-615.

To achieve comfortable form factors for wireless medical devices, battery size, and thus power consumption, must be curtailed.  Often the largest power consumption for wireless medical devices is in storing or transmitting acquired data.  Body area networks (BAN) can alleviate power budgets by using low power transmitters to send data “locally” around the body to receivers that are around areas of the body that allow for larger form factors, like the wrist or the waist.  These receivers, which have larger power budgets, can then process and store the data or send it elsewhere using higher power transmitters.

Body-coupled communication (BCC) shows great potential in forming a BAN.  Traditional two-node BCC works by forming two capacitive links between a transmitter and a receiver, creating a circuit loop.  One of these links is created by both the transmitter and receiver capacitively coupling to the body, effectively using the body as a low-resistance channel between the respective capacitors.  The second link is created by coupling both the transmitter and receiver coupling to the environment, or “earth ground,” and using it as a return path.  Larger BANs can be made by coupling additional nodes to both the body and the environment.

An application for a BAN is for an implanted EEG recorder at the head, to communicate with a base station at the waist.  For implants, the traditional BCC will not work because capacitors E and F will short out capacitors A and D, reducing the transmission line between the transmitter and receiver to that shown in Figure 2. FSK data was sent across this channel in a variety of environments and activities including talking outdoors on a cell phone, exercising at a gym, and doing household chores.  There was no significant difference in the BER across these different environments.

1. T. G. Zimmerman, “Personal area networks (PAN): Near-field intrabody communication,” Master’s thesis, Massachusetts Institute of Technology, Cambridge, 1995.
2. S.-J. Song, N. Cho, S. Kim et al., “A 0.9V 2.6mW body-coupled scalable PHY transceiver for body sensor applications,” ISSCC Dig. Tech. Papers, pp. 366-367, Feb. 2007.
3. A. Fazzi et al., “A 2.75mW wideband correlation-based transceiver for body-coupled communication,” ISSCC Dig. Tech. Papers, pp. 204-205, Feb. 2009.

The Capacitive Micromachined Ultrasound Transducer (CMUT) is an alternative to traditional piezoelectric transducers. The CMUT technology provides an opportunity for highly integrated ultrasound-imaging system solutions because of its CMOS compatibility and ease of large array fabrication ^[1] .

This project aims to provide a highly flexible platform for 3D ultrasound imaging. Figure 1 presents the system architecture. The CMUT device is flip-chip bonded to the supporting electronic circuits, which eliminates the cables. As a result, the channel count of the imaging system is increased and the capacitive loading due to cables is greatly reduced. The transmitters in the system are reconfigurable to implement Tx Beamforming; the analog front-end receivers and the DSP perform various Rx Beamforming algorithms from the received echo waveforms. We successfully implemented a 2D ultrasound imaging system based on a 1D transducer and corresponding electronics as the first step. Currently a 3D ultrasound-imaging system using 2D transducers is investigated.

In the finished 1D IC fabricated in 0.18µm CMOS process, we implemented 4 channels of Tx and Rx analog front-end circuits. Each channel includes an LNA, a VGA and a high voltage pulser. Acoustic measurements are carried out to demonstrate the improved energy efficiency of the 3-level pulser in Tx. A mechanical 3D translation stage is set up, which mounts a hydrophone to probe ultrasound pressure in the medium. The pressure field measured is referred back to the surface of the CMUT transducer, so that the total emitted acoustic power can be calculated. The Tx efficiency is measured by dividing the acoustic power by the total transmission power. Different pulse shapes lead to different Tx efficiency results. The efficiency improvement of 3-level pulse shape over the traditional 2-level pulse shape is measured to be approximately 50%, which is in agreement with the theory (shown in Figure 2).

1. O. Oralkan, “Acoustical imaging using capacitive micromachined ultrasonic transducer arrays: Devices, circuits, and systems,” Ph.D. dissertation, Stanford, Palo Alto, 2004.

With the escalating costs of hospital visits, clinicians are opting to use at-home monitoring devices to diagnose patients.  Current ECG Holter monitoring devices typically have 24-48 hour memory and battery capacity ^[1] .  With many patients experiencing intermittent heart problems that can occur once every week or month, an event recorder or loop recorder is required ^[2] .  However, event recorders can save only up to a few minutes of ECG recordings.  This constraint leads to the loss of most of the data, which could be very important in alerting the user to the onset of future episodes.  Therefore, we have developed a Holter monitor prototype with the goal of battery and memory capacity of greater than one week.  Figure 1 shows a block diagram of the system.

We based the long-term monitor prototype around a Texas Instruments MSP430 low-power microcontroller that enables high computing power with very low power consumption.  The prototype monitor is mounted on standard 3M 2560 Red Dot electrodes. The central board is fabricated on a flexible PCB substrate.  Mounting the PCB directly on the electrodes improves the SNR by an estimated 40 dB compared to using wired leads ^[3] .  The monitor is “L”-shaped with rounded corners and placed on the patient’s chest (Figure 2).  The “L” shape enables several different ECG vectors to be recorded, depending on what the cardiologist wants to observe.  The monitor has a micro SD card on board, which is enough to store weeks of ECG data sampled at 250 Hz continuously, without compression.

1. D. Jabaudon, J. Sztajzel, K. Sievert, T. Landis, and R. Sztajzel, “Usefulness of ambulatory 7-day ECG monitoring for the detection of atrial fibrillation and flutter after acute stroke and transient ischemic attack,” Stroke, J. Amer. Heart Assoc., vol. 35, pp. 1647–1651, May 2004.
2. M. A. Rockx, J. S. Hoch, G. J. Klein, R. Yee, A. C. Skanes, L. J. Gula, and A. D. Krahn, “Is ambulatory monitoring for “Community-acquired” syncope economically attractive? A cost-effective analysis of a randomized trial of external loop recorders versus Holter monitoring,” AHJ vol. 150, no. 5, pp. 1065.e1-1065.e5, Nov. 2005.
3. A. Searle and L. Kirkup, “A direct comparison of wet, dry and insulating bioelectric recording electrodes,” Physiol. Meas., vol. 21, pp. 271-283, 2000.

Epilepsy is a common chronic neurological disorder that affects about 1% of the world population ^[1] . It is characterized by repeated seizures, which are caused by an abnormal neuronal firing rate of the affected brain area. Although EEG has been the chief modality in the diagnosis and treatment of epilepsy for more than half a century, the vast majority of tests are performed in the hospital setting and are of brief duration. Long-term recordings (from days to weeks) can be obtained, but these must occur in the hospital setting. Many patients, however, have intermittent seizures occurring far less often (once a month or even less frequently). Capturing a seizure on EEG is a prerequisite for making a definitive diagnosis, tailoring therapy, or moving toward certain solutions such as surgery. For patients with infrequent seizures, capturing a seizure on EEG might require being in the hospital for over a month, which might not be possible. Thus, there is a need for a wearable long-term outpatient EEG monitor.

Our first prototype consists of 1 EEG channel sampled at 512 Hz with a 12-bit resolution. Figure 1 shows the simplified system block diagram. The data is stored in a micro SDHC flash card similar to the ones found in digital cameras.

The system is housed in a hearing aid package as shown in Figure 2. One electrode is placed near the temporal lobe (close to T3), and the reference is placed on the mastoid.

1. W. C. Stacey and B. Litt, “Technology insight: neuroengineering and epilepsy – designing devices for seizure control,” Nature Clinical Practice Neurology, vol. 4, pp. 190-201, Apr 2008.

Traumatic brain injury (TBI) occurs in over 1.4 million persons annually in the United States ^[1] .  Monitoring of a patient’s cerebrovascular state following TBI is used in guiding therapy and mitigating secondary injury ^[2] .  Such monitoring, however, often relies on bulky capital equipment and a skilled operator, thus restricting its use to limited clinical environments (typically neurocritical care units).  This project seeks to develop a low-power, miniaturized transcranial Doppler (TCD) ultrasound system for measuring cerebral blood flow velocity (CBFV) in support of continuous cerebrovascular monitoring.

The system architecture, as illustrated in Figure 1, employs multi-channel transceiver electronics and a two-dimensional transducer array to permit electronic steering of the ultrasound beam.  A first-generation discrete eight-channel TCD prototype is shown in Figure 2.  Further revisions of the prototype system will increase channel count for improved beam steering functionality.  Advanced beam steering algorithms will allow for autonomous vessel location, thereby obviating the need for manual transducer alignment and operator expertise.  The wearable system will permit monitoring of cerebrovascular state in a wide variety of contexts that are currently unfeasible under standard measurement modalities.

1. J. A. Langlois, W. Rutland-Brown, and K. E. Thomas, “Traumatic brain injury in the United States: Emergency department visits, hospitalizations, and deaths,” Centers for Disease Control and Prevention, Atlanta, GA, 2004.
2. M. R. Bullock, J. T. Povlishock, Ed., “Guidelines for the management of severe traumatic brain injury,” Journal of Neurotrauma, vol. 24, Supplement 1, 2007.

Vital signs such as heart rate, blood pressure, blood oxygenation, cardiac output, and respiratory rate are necessary in determining the overall health of a patient.  Continuous monitoring of these vital signs can help healthcare workers assess the wearer’s overall state of health and identify risks for cardiovascular diseases ^[1] .

We propose the site behind the ear as a location for an integrated wearable vital signs monitor ^[2] . This location offers physiological signals such as the electrocardiogram (ECG), the photoplethysmogram (PPG), and the ballistocardiogram (BCG). The ECG measures the electrical activity from the heart and offers heart rate information. The PPG measures the blood volume and color under the skin using optical illumination. The PPG offers information such as continuous heart rate and blood oxygenation. The BCG measures the body’s mechanical reaction to the blood expelled by the heart and also provides the heart rate.

Using the peak timing data from ECG and BCG, the heart’s pre-ejection period (PEP) can be measured ^[3] . The PEP is a measure of heart contractility and heart muscle health. Figure 1 compares the measured RJ interval and PEP during a Valsalva breath-holding maneuver.

The device is designed to use the ear as a discreet and a natural anchor that reduces device visibility and the need for skin adhesives. A photo of our prototype device is shown in Figure 2. While the prototype currently uses off-the-shelf components, custom integrated circuits are being designed to replace those components to significantly decrease the device’s size and power consumption.

1. S. D. Pierdomenico, M. Di Nicola, A. L. Esposito, R. Di Mascio, E. Ballone, D. Lapenna and F. Cuccurullo, “Prognostic value of different indices of blood pressure variability in hypertensive patients,” American Journal of Hypertension, pp. 842-847, June 2009.
2. D. He, E. S. Winokur, T. Heldt, and C. G. Sodini, “The ear as a location for wearable vital signs monitoring,” IEEE Engineering in Medicine and Biology Conference, pp. 6389-6392, Sept. 2010.
3. D. He, E. S. Winokur, and C. G. Sodini, “A continuous, wearable, and wireless heart monitor using head ballistocardiogram (BCG) and head electrocardiogram (ECG),” IEEE Engineering in Medicine and Biology Conference, pp. 4729-4732, Aug. 2011.

Collaborators

• Brian Brandt, Maxim
• Dennis Buss, TI
• Tom O’Dwyer, Analog Devices
• Kai Thomenius, GE Global Research

Graduate Students

• G. Anderson, PhD, EECS
• K. Chen, PhD, EECS
• M. Delano, MEng, EECS
• D. He, PhD, EECS
• S. Petriangelo, MS, EECS
• B. do Valle , PhD, EECS
• E. Winokur, PhD, EECS

Support Staff

• C. Kinsella, Administrative Assistant II

Publications

Nausieda, I., Ryu, K.K., He, D., Akinwande, A.I., Bulovic, V., Sodini, C.G., “Mixed-Signal Organic Integrated Circuits in a Fully Photolithographic Dual Threshold Voltage Technology,” IEEE Transactions on Electron Devices, vol. 58, pp. 865-873, Feb., 2011.

Nguyen, K., Sodini, C.G.,  “Millimeter-Wave Imaging Using Silicon Technology,” International Symposium on VLSI Design, June, 2011.

He, D., Winokur, E.S., Sodini, C.G., “A Continuous, Wearable, and Wireless Heart Monitor Using Head Ballistocardiogram (BCG) and Head Electrocardiogram (ECG),” Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Sept. 2011.

Sodini, C.G., “Revolutionizing Medical Device Design”, DesignMED, Boston, Sept. 2011.