IEEE transactions on bio-medical engineering

Published by Institute of Electrical and Electronics Engineers
Online ISSN: 1558-2531
Publications
Article
One important feature of the baroreflex loop is its strong preference for oscillations around 0.1 Hz. In this study, we investigated heart rate intervals, arterial blood pressure (BP), and prefrontal oxyhemoglobin changes during 5 min rest and during brisk finger movements in 19 healthy subjects. We analyzed the phase coupling around 0.1 Hz between cardiovascular and (de)oxyhemoglobin oscillations, using the cross-spectral method. The analyses revealed phase shifts for slow oscillations in BP and heart rate intervals between -10° and -118° (BP always leading). These phase shifts increased significantly (p<0.01) in the movement session. The coupling between cardiovascular and oxyhemoglobin oscillations was less clear. Only 12 subjects demonstrated a phase coupling (COH(2) ≥ 0.5) between oxyhemoglobin and BP oscillations. This may be explained by an overwhelming proportion of nonlinearity in cardiovascular and hemodynamic systems. The phase shifts between slow cardiovascular and hemodynamic oscillations are relatively stable subject-specific biometric features and could be of interest for person identification in addition to other biometric data. Slow BP-coupled oscillations in prefrontal oxyhemoglobin changes can seriously impair the detection of mentally induced hemodynamic changes in an optical brain-computer interface, a novel nonmuscular communication system.
 
Article
A high-temperature superconductor (HTS) was used on magnetic resonance imaging (MRI) receiver coils to improve image quality because of its intrinsic low electrical resistivity. Typical HTS coils are surface coils made of HTS thin-film wafers. Their applications are severely limited by the field of view (FOV) of the surface coil configuration, and the improvement in image quality by HTS coil is also reduced as the ratio of sample noise to coil noise increases. Therefore, previous HTS coils are usually used to image small in vitro samples, small animals, or peripheral human anatomies. We used large-size HTS coils (2.5-, 3.5-, and 5.5-in mean diameter) to enhance the FOV and we evaluated their performance through phantom and human MR images. Comparisons were made among HTS surface coils, copper surface coils, and cool copper surface coils in terms of the signal-to-noise ratio (SNR) and sensitivity profile of the images. A theoretical model prediction was also used to compare against the experimental result. We then selected several human body parts, including the wrist, feet, and head, to illustrate the advantage of HTS coil over copper coil when used in human imaging. The results show an SNR gain of 200% for 5.5-in HTS coil versus same size copper coils, while for 2.5- and 3.5-in coils it is 250%. We also address the various factors that affect the performance of large size HTS coils, including the coil-to-sample spacing due to cryogenic probe and the coil-loading effect.
 
Article
A technique has been developed which allows for the optical measurement of the concentration-time relationship for a diffusion-limited material in indicator dilution studies. The material, 1-2 propanediol, is used as a probe of the permeability of capillaries in the lung. Comparisons between standard radioisotope measurements and the optical measurements are provided and show excellent agreement. The optical method represents an improvement over the standard radioisotope method in that it provides the same data at lower cost, lower risk, and without the delay required by the radiographic methods.
 
Article
This paper presents a low-phase-noise, hybrid LC-tank, analog frequency modulator for wireless biotelemetry employing on-chip NMOS varactors in the inversion region as the frequency tuning element. We demonstrate that a correct estimate for the destination signal-to-noise ratio, which quantifies the quality of the wirelessly received signal in a frequency-modulated biotelemetry system, is only achieved after taking into account the large-signal oscillation effect on the tank varactor. A prototype chip is fabricated using AMI 1.5-microm double-poly double-metal n-well CMOS process, and exhibits a measured gain factor of 1.21 MHz/V in the mid-range of the tuning voltage and a phase noise of -88.6 dBc/Hz at 10-kHz offset from the 95.1-MHz carrier while dissipating 1.48 mW from a 3 V power supply leading to a figure of merit (FOM) of -166.5 dBc/Hz. The VCO is successfully interfaced with a penetrating silicon microelectrode with 700 microm2 iridium recording sites for wireless in vitro recording of a 50 Hz simulated normal sinus rhythm signal from saline over a distance of approximately 0.25 m. Given a typical gain of approximately 40 dB for fully integrated front-end bioamplifiers, a wireless recording microsystem employing this VCO would be capable of detecting input biopotentials down to the submilivolt range.
 
Article
The purpose of this paper is to evaluate the capability of feature space analysis (FSA) for quantifying the relative volumes of principal components (thrombus, calcification, fibrous, normal intima, and lipid) of atherosclerotic plaque tissue in multicontrast magnetic resonance images (mc-MRI) acquired in a setup resembling clinical conditions ex vivo. Utilizing endogenous contrast, proton density, T1-weighted, and T2-weighted images were acquired for 13 carotid endarterectomy (CEA) tissues under near-clinical conditions (human 1.5 T GE Excite scanner with sequence parameters comparable to an in vivo acquisition). An FSA algorithm was utilized to segment and quantify the principal components of atherosclerotic plaques. Pilot in vivo mc-MRI images were analyzed in the same way as the ex vivo images for exploring the possible adaptation of this technique to in vivo imaging. Relative abundance of principal plaque components in CEA tissues as determined by mc-MRI/FSA were compared to those measured by histology. Mean differences +/- standard deviations were 5.8 +/- 4.1% for thrombus, 1.5 +/-1.4 % for calcification, 4.0 +/-2.8% for fibrous, 8.2 +/- 10% for normal intima, and 2.4 +/- 2.2% for lipid. Reasonable quantitative agreement between the classification results obtained with FSA and histological data was obtained for near-clinical imaging conditions. Combination of mc-MRI and FSA may have an application for determining atherosclerotic lesion composition and monitoring treatment in vivo.
 
Article
Our recent research has demonstrated that 11C-acetate could be a complementary tracer to 18F-fluorodeoxyglucose (FDG) in positron emission tomography (PET) imaging of hepatocellular carcinoma (HCC). In our previous modeling study, a three-compartment four-parameter model with a fixed contribution ratio of the liver's two blood supplies was proposed to characterize the kinetic behavior of 11C-acetate in liver. However, in real pathology, both tumor and nontumor liver tissue can be heterogeneous in the distribution and proportion of the two blood supplies. To further improve the accuracy of quantitative analysis, the actual proportion of the hepatic artery and portal vein (PV) in different regions of interest (ROIs) was investigated in this study. An extra parameter av was included in the model input function to describe the contribution of PV to the liver. Ten ROIs extracted from six patients were used to test the models with fixed/nonfixed weighted dual-input function. The weighted nonlinear least squares algorithm was used to estimate all of the parameters. Evaluation of the adequacy of the two models was conducted and the computer simulation was performed to test the estimation accuracy of the new model. The forward clearance K was also estimated by the linear Patlak method. The results show that the model with parameter av in the input function was more suitable for mapping the tracer time activity curves. Moreover, the estimated av value fits the practical physiological and pathological conditions well and could be a potential candidate to provide useful additional diagnostic information for the early detection of hepatic metastases.
 
Article
Hyperpolarized (HP) (13)C-labeled pyruvate studies with magnetic resonance (MR) have been used to observe the kinetics of metabolism in vivo. Kinetic modeling to measure metabolic rates in vivo is currently limited because of nonspecific hyperpolarized signals mixing between vascular, extravascular, and intracellular compartments. In this study, simultaneous acquisition of both (1)H and (13)C signals after contrast agent injection is used to resolve specific compartments to improve the accuracy of the modeling. We demonstrate a novel technique to provide contrast to the intracellular compartments by sequential injection of HP [1-(13)C] pyruvate followed by gadolinium-chelate to provide T(1)-shortening to extra-cellular compartments. A kinetic model that distinguishes the intracellular space and includes the T(1)-shortening effect of the gadolinium chelate can then be used to directly measure the intracellular (13)C kinetics.
 
Article
Electromagnetic absorption and subsequent heating of nanoparticle solutions and simple NaCl ionic solutions is examined for biomedical applications in the radiofrequency range at 13.56 MHz. It is shown via both theory and experiment that for in vitro measurements the shape of the solution container plays a major role in absorption and heating.
 
Article
Neurosurgical operations sometimes involve difficulties in finding out the real positions of small-size neoplasms shown on tomographical images. The articulated navigation system, with the aid of a computer, gives ongoing positional correspondence between the position in the patient's brain and the one in the tomographic images to assist neurosurgery.
 
Article
Cellular phones are used in the vicinity of the human head, resulting in localized exposure to this part of the body. To simulate exposure during cellular phone use, microwave energy absorption should be focused within the head region of laboratory animals. In this paper, we developed an exposure system using a figure-8 loop antenna to permit localized exposure of a rat head to 1500-MHz microwave fields, simulating human head exposure to cellular phones. We have numerically estimated the specific absorption rate (SAR) in a rat exposed to microwave fields via our new exposure system. The high ratio of SAR averaged over the target tissue (i.e., the brain) to that averaged over the whole body suggests that the figure-8 antenna can realize greater localized exposure than the previously used exposure system. We have also confirmed the effectiveness of our proposed system experimentally.
 
Article
We have developed a general-purpose electrotactile (electrocutaneous) stimulation system as a research tool for studying psychophysiological performance associated with various stimulation waveforms. An experimenter-defined command file specifies the stimulation current and waveform of each of the 16 channels. The system provides burst onset delay of 0-20 ms, phase current of 0-50 mA, interphase interval of 0-1000 microseconds, number of pulses per burst from 1-100, pulse repetition rate of 0.1-25 kHz, phase width of 2-1000 microseconds, and functionally-monophasic pulses (with zero dc current) or balanced-biphasic pulses (with equal positive and negative phases). The system automatically delivers the desired stimulation, prompts the subject for responses, and then logs subject responses. Key features of the system are 1) very flexible choice of bursts of pulsatile waveforms, 2) real-time control of all of the waveform parameters as mathematical functions of external analog inputs, and 3) high-performance electrode-driver circuitry.
 
Article
A 3-D application-specific microelectrode array has been developed for physiological studies in guinea pig cochlear nucleus (CN). The batch-fabricated silicon probes contain integrated parylene cables and use a boron etch-stop to define 15μm-thick shanks and limit tissue displacement. Targeting the ventral (three probes) and dorsal (two probes) subnuclei, the custom four-shank 32-site probes are combined in a slotted block platform having a 1.18-mm (2) footprint. The device has permitted, for the first time, high-density 3-D in vivo studies of ventral CN to dorsal CN connections, stimulating with 1000 μm (2) sites in one subnucleus while recording with 177 μm (2) sites in the other. Through these experiments, it has demonstrated the efficacy of bimodal silicon arrays to better understand the central nervous system at the circuit level. The 160 electrode sites also provide a high-density neural interface, which is an essential aspect of auditory prosthesis prototypes.
 
Article
In this paper, placement parameters for microstimulation electrodes in a visual prosthesis are evaluated based on retinotopic models of macaque and human lateral geniculate nucleus. Phosphene patterns were simulated for idealized microwire electrodes as well as for currently available clinical electrodes. For idealized microwire electrodes, spacing as large as 600 microm in three dimensions would allow for over 250 phosphenes per visual hemifield in macaques, and over 800 in humans.
 
Article
A new noninvasive estimation method for the plasma time-activity curve, i.e. input function (IF) of the tracer kinetic model in dynamic 18F-FDG microPET mouse studies, is proposed and validated. This estimation method comprises four steps. First, a novel constraint nonnegative matrix factorization (CNMF) segmentation algorithm was applied to extract the left ventricle (Lv) and myocardium (Myo) time activity curves (TACs). Second, we modeled the IF as a 7-parameter mathematic equation and constructed a dual-output model of the real TAC in Lv and Myo accounting for the partial volume and spillover effects. Then, we fit the image-derived Lv and Myo TACs to the dual-output model to estimate the parameters of the IF. Finally, the IF was validated by comparing it to the gold standard IF while considering the delay and dispersion effects. Our method was verified based on twenty mice datasets from the Mouse Quantitation Program database, provided by UCLA. The error of the areas under the curves between the delayed and dispersed estimated IF and the gold standard IF was 7.237% ¿ 6.742% (r ¿ 0.969), and the error of the 18F-FDG influx constant Ki of the Myo was 4.910% ¿ 6.810% (r ¿ 0.992). The results demonstrated the effectiveness of the proposed method.
 
Article
This study compared the potential for interference to medical devices from radio frequency (RF) fields radiated by GSM 900/1800-MHz, general packet radio service (GPRS) 900/1800-MHz, and wideband code division multiple access (WCDMA) 1900-MHz handsets. The study used a balanced half-wave dipole antenna, which was energized with a signal at the standard power level for each technology, and then brought towards the medical device while noting the distance at which interference became apparent. Additional testing was performed with signals that comply with the requirements of the international immunity standard to RF fields, IEC 61000-4-3. The testing provides a sense of the overall interference impact that GPRS and WCDMA (frequency division duplex) may have, relative to current mobile technologies, and to the internationally recognized standard for radiated RF immunity. Ten medical devices were tested: two pulse oximeters, a blood pressure monitor, a patient monitor, a humidifier, three models of cardiac defibrillator, and two models of infusion pump. Our conclusion from this and a related study on consumer devices is that WCDMA handsets are unlikely to be a significant interference threat to medical electronics at typical separation distances.
 
Article
Nonlinear energy operator (NEO) gives the estimate of energy content of a linear oscillator. This has been used to quantify the AM-FM modulating signals present in a sinusoid. In this paper, we give a new interpretation of NEO and extend its use in stochastic signals. We show that NEO accentuates the high-frequency content. This instantaneous nature of NEO and its very low computational burden make it an ideal tool for spike detection. The efficacy of the proposed method has been tested with simulated signals as well as with real electroencephalograms (EEG's).
 
Article
This paper investigates the internal electric and magnetic field distribution and the specific absorption rate (SAR) values in a magnetic resonance imaging-based model of the inner hearing system exposed to 900 and 1800 MHz. The internal fields distributions were calculated using the Finite Integration Technique. The estimation of the field values was evaluated along lines passing through that target organ, specifically from the vestibular to the cochlear region and from the apex to the base of the cochlea. The specific findings are: 1) higher internal fields strength and SAR value in the vestibular region rather than in the auditory region, especially for the inner ear closer to the external source; 2) higher internal fields strength in the basal and apical region of the cochlea than in the middle one; 3) local differences in the internal fields distribution and SAR value, comparing the head models including or not the inner auditory system model; 4) results' variability evaluated by changing the head-source mutual position and the dielectric properties of the inner hearing system.
 
Article
This paper proposes and evaluates the application of support vector machine (SVM) to classify upper limb motions using myoelectric signals. It explores the optimum configuration of SVM-based myoelectric control, by suggesting an advantageous data segmentation technique, feature set, model selection approach for SVM, and postprocessing methods. This work presents a method to adjust SVM parameters before classification, and examines overlapped segmentation and majority voting as two techniques to improve controller performance. A SVM, as the core of classification in myoelectric control, is compared with two commonly used classifiers: linear discriminant analysis (LDA) and multilayer perceptron (MLP) neural networks. It demonstrates exceptional accuracy, robust performance, and low computational load. The entropy of the output of the classifier is also examined as an online index to evaluate the correctness of classification; this can be used by online training for long-term myoelectric control operations.
 
Article
In the current international guidelines and standards for human exposure to microwaves (MWs), the basic restriction is determined by the whole-body average specific absorption rate (SAR). The basis for the guidelines is the adverse effect such as work stoppage in animals for whole-body average SARs above a certain level. Although it is known that absorbed MW energy causes the behavioral sign of thermal stress, the relationship of whole-body average SAR with temperature/temperature elevation has not been sufficiently investigated. In the present study, we performed experiments on rabbits exposed to 2.45-GHz MWs. A total of 24 measurements were conducted for power densities from approximately 100 to 1000 W/m(2). Our computational code for electromagnetic-thermal dosimetry was used to set the exposure time duration and incident power density. Our experimental results suggest that a core temperature elevation of 1 degrees C is an estimate of the threshold-inducing complex behavioral signs of MW-induced thermal stress in rabbits for different whole-body average SARs and exposure time durations. The whole-body average SAR required for MW-induced behavioral sign in rabbits was estimated as approximately 1.3 W/kg for 2.45-GHz MWs.
 
Article
Brain-computer interfaces require effective online processing of electroencephalogram (EEG) measurements, e.g., as a part of feedback systems. We present an algorithm for single-trial online classification of imaginary left and right hand movements, based on time-frequency information derived from filtering EEG wideband raw data with causal Morlet wavelets, which are adapted to individual EEG spectra. Since imaginary hand movements lead to perturbations of the ongoing pericentral mu rhythm, we estimate probabilistic models for amplitude modulation in lower (10 Hz) and upper (20 Hz) frequency bands over the sensorimotor hand cortices both contra- and ipsilaterally to the imagined movements (i.e., at EEG channels C3 and C4). We use an integrative approach to accumulate over time evidence for the subject's unknown motor intention. Disclosure of test data labels after the competition showed this approach to succeed with an error rate as low as 10.7%.
 
Article
In one type of brain-computer interface (BCI), users self-modulate brain activity as detected by electroencephalography (EEG). To infer user intent, EEG signals are classified by algorithms which typically use only one of the several types of information available in these signals. One such BCI uses slow cortical potential (SCP) measures to classify single trials. We complemented these measures with estimates of high-frequency (gamma-band) activity, which has been associated with attentional and intentional states. Using a simple linear classifier, we obtained significantly greater classification accuracy using both types of information from the same recording epochs compared to using SCPs alone.
 
Article
This paper describes a platform to achieve targeted drug delivery in next generation wireless capsule endoscopy. The platform consists of two highly novel sub-systems: one is a micro-positioning mechanism which can deliver 1 ml of targeted medication and the other is a holding mechanism which gives the functionality of resisting peristalsis. The micro-positioning mechanism allows a needle to be positioned within a 22.5o segment of a cylindrical capsule and be extendible by up to 1.5mm outside the capsule body. The mechanism achieves both these functions using only a single micro-motor and occupying a total volume of just 200mm3. The holding mechanism can be deployed diametrically opposite the needle in 1.8 s and occupies a volume of just 270mm3. An in-depth analysis of the mechanics is presented and an overview of the requirements necessary to realise a total system integration is discussed. It is envisaged that the targeted drug delivery platform will empower a new breed of capsule micro-robots for therapy in addition to diagnostics for pathologies such as ulcerative colitis and small intestinal Crohns disease.
 
Article
Evaluation of the influence of the autonomic nervous system on the ventricular repolarization duration was carried out using beat-to-beat analysis of the time intervals between the peaks of the R and T waves (RTm). After pre-processing of digitized Holter ECG's, auto and cross spectrum analyses were applied to heart rate and repolarization duration variability signals. Coherence analysis was used to assess the existence of common spectral contributions. The heart rate variability signal was used as reference of the sympatho-vagal balance at the sinus node. It was found that, in normal individuals, the autonomic nervous system directly influences the ventricular repolarization duration and that this influence is qualitatively very similar to the one that modulates the heart rate. Pathological alteration of these parallel autonomic activities to the heart (on the sinus node and on the ventricle) might cause uncoupling between depolarization and repolarization.
 
Article
A procedure for the 24 h tracking of the 0.25, 0.1, and 0.05 Hz oscillations in blood pressure (BP) and pulse interval (PI) in ambulant subjects has been developed. It includes: 1) sampling of a 24 h intra-arterial BP recording, extraction of the systolic (S) and diastolic (D) BP and PI from each heart beat followed by storage into separate series; 2) high-pass filtering and a splitting of each series into consecutive records of 256 values; 3) estimation of power spectral density (PSD) via FFT in each stationary record, and finally, computation of the power of each target oscillation. Using this procedure we analyzed data from ten hospitalized free-moving subjects in whom BP was recorded by the Oxford technique. The results revealed different patterns of the 0.25, 0.1, and 0.05 oscillations over the day-night cycle, showing a differentiated involvement during the 24 h of the mechanisms responsible for such rhythmic phenomena. Moreover, in order to reinforce the meaning of the obtained results and to exclude the possible negative effects due to the drawbacks typical of the FFT algorithm, we also performed a second spectral estimate based on the AR modeling. The obtained results validates the FFT approach.
 
Article
The objective monitoring of cough for extended periods of time has long been recognized as an important step towards a better understanding of this symptom, and a better management of chronic cough patients. In this paper, we present a system for the automatic analysis of 24-h, continuous, ambulatory recordings of cough. The system uses audio recordings from a miniature microphone and the detection algorithm is based on statistical models of the time-spectral characteristics of cough sounds. We validated the system against manual counts obtained by a trained observer on 40 ambulatory recordings and our results show a median sensitivity value of 85.7%, median positive predictive value of 94.7% and median false positive rate of 0.8 events/h. An analysis application was developed, with a graphical user interface, allowing the use of the system in clinical settings by technical or medical staff. The result of the analysis of a recording session is presented as a concise, graphical-based report. The modular nature of the system interface facilitates its enhancement with the integration of further modules.
 
Article
We have developed a three-channel ambulatory esophageal pressure monitor and tested it with a series of 24-h studies. The monitor is a battery-operated, microprocessor-based device that measures pressures from three transducers positioned in the esophagus, stores the data in its memory, and transfers the data to an IBM PC computer system at the end of the recording period. Programs on the PC then analyze the data and identify contractile events, categorizing them according to specific parameters. Other programs display the pressure waveforms on the PC and allow visual inspection of the entire recordings or, alternatively, of particular events of interest. The system detects contractile abnormalities in patients with intermittent, noncardiac chest pains. We tested the system on ten normal subjects and found a relatively high incidence of what are usually considered "abnormal" contractions.
 
Article
CT colonography (CTC) is one of the recommended methods for colorectal cancer screening. The subject's preparation is one of the most burdensome aspects of CTC with a cathartic bowel preparation. Tagging of the bowel content with an oral contrast medium facilitates CTC with limited bowel preparation. Unfortunately, such preparations adversely affect the 3D image quality. Thus far, data acquired after very limited bowel preparation were evaluated with a 2D reading strategy only. Existing cleansing algorithms do not work sufficiently well to allow a primary 3D reading strategy. We developed an electronic cleansing algorithm, aimed to realize optimal 3D image quality for low-dose CTC with 24-hour limited bowel preparation. The method employs a principal curvature flow algorithm to remove heterogeneities within poorly tagged fecal residue. In addition, a pattern recognition based approach is used to prevent polyp-like protrusions on the colon surface from being removed by the method. Two experts independently evaluated 40 CT colonography cases by means of a primary 2D approach without involvement of electronic cleansing as well as by a primary 3D method after electronic cleansing. The data contained four variations of 24-hour limited bowel preparation and was based on a low radiation dose scanning protocol. The sensitivity for lesions 6mm was significantly higher for the primary 3D reading strategy (84%) than for the primary 2D reading strategy (68%) (p = 0.031). The reading time was increased from 5:39min (2D) to 7:09min (3D) (p = 0.005); the readers' confidence was reduced from 2.3 (2D) to 2.1 (3D) (p = 0.013) on a 3-point Likert scale. Polyp conspicuity for cleansed submerged lesions was similar to not submerged lesions (p = 0.06). To our knowledge this study is the first to describe and clinically validate an electronic cleansing algorithm that facilitates low-dose CTC with 24-hour limited bowel preparation.
 
Article
Using pacemakers implanted in canines with surgically induced atrioventricular blocks, the effects of the microwave-oven frequencies (915 and 2450 MHz) and two radar frequencies (2810 and 3050 MHz) were evaluated. Quantitative evaluation of these fields with respect to complete inhibition of pacemakers can be made. A narrow zone of inhibition during some exposures-a ``window'' effect-not previously described is reported. The following field parameters would be regarded as potential situations for complete pacemaker inhibition: 1) 915-MHz-fields continuous- and sine-wave modulation at 120 Hz in field strengths over 75 V/m, and 2) fields at either 2810 or 3050 MHz pulsed at a rate of 40 pulses per second (pps) or less with a field strength greater than 250 V/m.
 
Article
A 27 MHz dual-device applicator of novel design, which is aimed to heat noninvasively with improved safety tumor masses at depth, is proposed. A substantially localized temperature gain is obtained by superimposing two delocalized low RF frequency and phase-coherent current distributions, which are launched to constructively interfere over a limited region emcompassing the tumor volume. An hybrid applicator (HA) has been developed, integrated one capacitive and one inductive heating device, and has been assessed on a 20 cm diameter cylindrical fat-muscle phantom. The interference pattern is characterized by a deep broad SAR maximum and by the disappearance of the central null SAR value typical of single inductive devices. An 80% SAR useful therapeutic volume (UTV) of a near-cylindrical shape of about 800 cm3 is obtained with a penetration of 6-8 cm for the phantom surface, with a noncritical axial length of approximately 21 cm. The UTV may be somehow controlled in size and penetration. These results are obtained with the tissue-like medium surrounding the UTV heated uniformly and safely to a temperature pedestal below the therapeutic temperature with about half RF power values to each of the heating devices.
 
Article
A family of 27 MHz heating devices has been developed and fundamental tests carried out. The devices consist in a pair of ring-like, flexible, capacitive electrodes, conformally wrapped round the tissue to be heated, for use in hyperthermia and rehabilitation treatment. These capacitive ring (CR) applicators produce an axial E-field which can uniformly heat the central portion of a 20 cm OD cylindrical phantom simulating fat and muscle tissues. This electrode-body configuration can be used to uniformly heat most human body segments with the highest symmetry congruence, the RF currents flowing parallel to the boundaries provided by the pseudo-axial symmetry of these segments. With respect to the rigid pads used in RF capacitive heating, the CR electrodes exhibit a larger working surface area. Moreover, they may be used with an interposed dielectric layer between the electrodes and the skin, to reduce edge effects. With respect to the axially symmetric radiators of higher frequency, they are applicable to larger cross-section body segments with increased penetration and without the need of an integral water bolus. The CR devices allow free access to most of the body surface for skin temperature measurement and conditioning, and for combined treatments. Moreover, the almost uniform heating pattern may represent a useful feature for standardizing treatment. The CR electrodes can easily be matched to the RF source even if they are low impedance devices, and they give rise to low-level stray fields, which can be taken care of by a local shield. These CR devices can be considered safe and practical and suitable for regional hyperthermic and rehabilitation treatment.
 
Article
In this paper, we address the problem of estimating the parameters of an electrophysiological model of the heart from a set of electrical recordings. The chosen model is the reaction-diffusion model on the transmembrane potential proposed by Aliev and Panfilov. For this model of the transmembrane, we estimate a local apparent two-dimensional conductivity from a measured depolarization time distribution. First, we perform an initial adjustment including the choice of initial conditions and of a set of global parameters. We then propose a local estimation by minimizing the quadratic error between the depolarization time computed by the model and the measures. As a first step we address the problem on the epicardial surface in the case of an isotropic version of the Aliev and Panfilov model. The minimization is performed using Brent method without computing the derivative of the error. The feasibility of the approach is demonstrated on synthetic electrophysiological measurements. A proof of concept is obtained on real electrophysiological measures of normal and infarcted canine hearts.
 
Article
The safe charge injection density for pulsing of 316LVM electrodes has been reported to be 40 microC/cm2. However, only 20 microC/cm2 is available for nonfaradic charge transfer and double layer charge injection. Therefore, we evaluated long term pulsing at 20 microC/cm2 with capacitor coupling.
 
Article
Goal: The purpose of this study was to develop, assess, and validate a custom 32-channel system to analyze the electrical properties of 3D artificial heart muscle (3D-AHM). Methods: In the present study, neonatal rat cardiac cells were cultured in a fibrin gel to drive the formation of 3D-AHM. Once the tissues were fully formed, the customized electrocardiogram (EKG) sensing system was used to obtain the different electrophysiological characteristics of the muscle constructs. Additionally, this system was used to evaluate the electrical properties of native rat hearts, for comparison to the fabricated tissues and native values found in literature. Results: Histological evaluation showed extensive cellularization and cardiac tissue formation. EKG data analysis yielded time delays between the signals ranging from 0 to 7ms. Optical maps exhibited slight trends in impulse propagation throughout the fabricated tissue. Conduction velocities were calculated longitudinally at 277.81cm/s, transversely at 300.79cm/s, and diagonally at 285.68cm/s for 3D-AHM. The QRS complex exhibited a R-wave amplitude of 438.42 ± 36.96μV and an average duration of 317.5 ± 16.5ms for the tissue constructs. Conclusion: The data collected in this study provides a clearer picture about the intrinsic properties of the 3D-AHM while proving our system's efficacy for EKG data procurement. Significance: To achieve a viable and permanent solution, the bioengineered heart muscle must physiologically resemble native heart tissue as well as mimic its electrical properties for proper contractile function. This study allows us to monitor such properties and assess the necessary changes that will improve construct development and function.
 
Article
A 32-electrode data collection system for Electrical Impedance Tomography (EIT) will be presented. In this system, the demodulator is a multiplexed sample and hold (S&H) circuit followed by a voltage difference stage. This configuration provides high CMRR due to the low (almost DC) operating frequency of the signals the difference stage is required to process.
 
The numerical set-up. The raw image (bottom layer), consisting of an impulsive stimulus, is analyzed by the image analysis scheme (middle layer) which inturn generates the phosphene image (upper layer). Thus, we are considering the response of a seven-phosphene array to a single spatial impulse somewhere in the field covered by their input sensitivity profiles. Note that phosphenes are arranged in a hexagonal mosaic, and the example shown involves a scheme of non-overlapping Gaussian kernels. 
Article
By way of extracellular, stimulating electrodes, a microelectronic retinal prosthesis aims to render discrete, luminous spots-so-called phosphenes-in the visual field, thereby providing a phosphene image (PI) as a rudimentary remediation of profound blindness. As part thereof, a digital camera, or some other photosensitive array, captures frames, frames are analyzed, and phosphenes are actuated accordingly by way of modulated charge injections. Here, we present a method that allows the assessment of image analysis schemes for integration with a prosthetic device, that is, the means of converting the captured image (high resolution) to modulated charge injections (low resolution). We use the mutual-information function to quantify the amount of information conveyed to the PI observer (device implantee), while accounting for the statistics of visual stimuli. We demonstrate an effective scheme involving overlapping, Gaussian kernels, and discuss extensions of the method to account for shortterm visual memory in observers, and their perceptual errors of omission and commission.
 
Article
A new system, which we call the frameless stereotaxic operating microscope, is discussed. Its purpose is to display CT or other image data in the operating microscope in the correct scale, orientation, and position without the use of a stereotaxic frame. A nonimaging ultrasonic rangefinder allows the position of the operating microscope and the position of the patient to be determined. Discrete fiducial points on the patient's external anatomy are located in both image space and operating room space, linking the image data and the operating room. Physician-selected image information, e.g., tumor contours or guidance to predetermined targets, is projected through the optics of the operating microscope using a miniature cathode ray tube and a beam splitter. Projected images superpose the surgical field, reconstructed from image data to match the focal plane of the operating microscope. The algorithms on which the system is based are described, and the sources and effects of errors are discussed. The system's performance is simulated, providing an estimate of accuracy. Two phantoms are used to measure accuracy experimentally. Clinical results and observations are given.
 
Article
Identifiability problem is a very important topic in the framework of model justification and not accounting for it during the modeling procedure can lead to meaningless results. While studying the receptor-ligand model parameter estimation from dynamic positron emission tomography data, each of the three possible conclusions to the identifiability problem (i.e., unidentifiable model, multiple solutions, or unique solution) are reached depending on the experimental protocol used. The identification of the model parameters from data obtained with a single tracer injection leads to disappointing numerical results since most of the parameters have to be considered as unidentifiable. A protocol including two injections, a first injection of the labeled ligand and a second injection of the cold ligand (displacement experiment) leads to two very different numerical solutions, which is surprising since such multiplicity of solutions was not indicated by a preliminary theoretical identifiability study. We show that a three-injections protocol, including both a displacement and coinjection experiment, allows to determine which of these two solutions is biologically valid.
 
Article
Potassium-39 ( (39)K) magnetic resonance imaging (MRI) is a noninvasive technique which could potentially allow for detecting intracellular physiological variations in common human pathologies such as stroke and cancer. However, the low signal-to-noise ratio (SNR) achieved in (39)K-MR images hampered data acquisition with sufficiently high spatial and temporal resolution in animal models so far. Full wave electromagnetic (EM) simulations were performed for a single-loop copper (Cu) radio frequency (RF) surface resonator with a diameter of 30 mm optimized for rat brain imaging at room temperature (RT) and at liquid nitrogen (LN 2) with a temperature of 77 K. A novel cryogenic Cu RF surface resonator with home-built LN 2 nonmagnetic G10 fiberglass cryostat system for small animal scanner at 9.4 T was designed, built and tested in phantom and in in vivo MR measurements. Aerogel was used for thermal insulation in the developed LN 2 cryostat. In this paper, we present the first in vivo (39)K-MR images at 9.4 T for both healthy and stroke-induced rats using the developed cryogenic coil at 77 K. In good agreement with EM-simulations and bench-top measurements, the developed cryogenic coil improved the SNR by factor of 2.7 ± 0.2 in both phantom and in in vivo MR imaging compared with the same coil at RT.
 
Article
This paper proposes a method for estimating three-dimensional (3-D) biocurrent distribution from spatio-temporal biomagnetic data. This method is based on the principle of generalized Wiener estimation, and it is formulated based on the assumption that current sources are uncorrelated. Computer simulation demonstrates that the proposed method can reconstruct a 3-D current distribution where the conventional least-squares minimum-norm method fails. The influence of noise is also simulated, and the results indicate that a signal-to-noise ratio of more than 20 for the uncorrelated sensor noise is needed to implement the proposed method. The calculated point spread function shows that the proposed method has very high spatial resolution compared to the conventional minimum norm method. The results of computer simulation of the distributed current sources are also presented, including cases where current sources are correlated. These results suggest that no serious errors arise if the source correlation is weak.
 
Aneurysm phantom flow pattern analysis of PC MRI data (top) and CFD data (bottom) in the aneurysm phantom. In the left figures the phantom surface is rendered. The arrows represent the vortex axes. The strength of the vortex is depicted by the length and color of the arrow. In the right figures the 2D visualizations of the velocity (arrows) and vorticity quantification (colored surfaces) are shown. The dark red colors of the surface visualization depict the center and magnitude of the vortex.
3D visualization of kernel deconvolution with Q -masking analysis applied for σ = 0.28 mm (top - left) and σ = 1.00 mm (top -right) for patient 1. 2D Slice detail for vortex pattern detected at different scale are shown in middle and bottom images with blue vectors representing velocity profiles. The dark red colors of the surface visualization depict the center and magnitude of the vortex. 
Kernel deconvolution with Q -masking results for patient 2 and 3 for σ=0.28 mm (left) and σ=1.00 mm (right). 
Kernel deconvolution with Q -masking analysis results at different time steps applied to patient 1 (top), 2 (middle) and 3 (bottom) at a scale of 0.28mm. 
Sm Criterion applied for different time steps (from left to right ) and for different patients ( top to bottom ) at σ=0.28mm
Article
Objective: Characteristics of vortices within intracranial aneurysmal flow patterns have been associated with increased risk of rupture. The classifications of these vortex characteristics are commonly based upon qualitative scores, and are, therefore, subjective to user interpretation. We present a quantitative method for automatic time-resolved characterization of 3-D flow patterns and vortex detection within aneurysms. Methods: Our approach is based upon the combination of kernel deconvolution and Jacobian analysis of the velocity field. The deconvolution approach is accurate in detecting vortex centers but cannot discriminate between vortices and high-shear regions. Therefore, this approach is combined with analysis of the Jacobian of the velocity field. Scale-space theory is used to evaluate aneurysmal flow velocity fields at various scales. Results: The proposed algorithm is applied to computational fluid dynamics and time-resolved 3-D phase-contrast magnetic resonance imaging of aneurysmal flow. Conclusion: Results show that the proposed algorithm efficiently detects, visualizes, and quantifies vortices in intracranial aneurysmal velocity patterns at multiple scales and follows the temporal evolution of these patterns. Significance: Quantitative analysis performed with this method has the potential to reduce interobserver variability in aneurysm classification.
 
Article
Traditional two-dimensional (2D) fusion framework usually suffers from the loss of the between-slice information of the third dimension. For example, the fusion of three-dimensional (3D) MRI slices must account for the information not only within the given slice but also the adjacent slices. In this work, a fusion method is developed in 3D shearlet space to overcome the drawback. On the other hand, the popularly used Average-Maximum fusion rule can capture only the local information but not any of the global information for it is implemented in a local window region. Thus, a global-to-local fusion rule is proposed. We firstly show the 3D shearlet coefficients of the high-pass subbands are highly non-Gaussian. Then, we show this heavy-tailed phenomenon can be modeled by the generalized Gaussian density (GGD) and the global information between two subbands can be described by the Kullback-Leibler distance (KLD) of two GGDs. The finally fused global information can be selected according to the asymmetry of the KLD. Experiments on synthetic data and real data demonstrate that better fusion results can be obtained by the proposed method.
 
Article
Magnetic resonance (MR) tagging is capable of accurate, noninvasive quantification of regional myocardial function. Routine clinical use, however, is hindered by cumbersome and time-consuming postprocessing procedures. We propose a fast, semiautomatic method for tracking three-dimensional (3-D) cardiac motion from a temporal sequence of short- and long-axis tagged MR images. The new method, called 3-D-HARmonic Phase (3D-HARP), extends the HARP approach, previously described for two-dimensional (2-D) tag analysis, to 3-D. A 3-D material mesh model is built to represent a collection of material points inside the left ventricle (LV) wall at a reference time. Harmonic phase, a material property that is time-invariant, is used to track the motion of the mesh through a cardiac cycle. Various motion-related functional properties of the myocardium, such as circumferential strain and left ventricular twist, are computed from the tracked mesh. The correlation analysis of 3D-HARP and FINDTAGS + Tag Strain(E) Analysis (TEA), which are well-established tag analysis techniques, shows that the regression coefficients of circumferential strain (E(CC)) and twist angle are r2 = 0.8605 and r2 = 0.8645, respectively. The total time required for tracking 3-D cardiac motion is approximately 10 min in a 9 timeframe tagged MRI dataset and has the potential to be much faster.
 
Article
Accurate assessment of mice cardiac function with magnetic resonance imaging is essential for longitudinal studies and for drug development related to cardiovascular diseases. Whereas dedicated small animal MR scanners are not readily available, it would be a great advantage to be able to perform cardiac assessment on clinical systems, in particular, in the context of translational research. However, mouse imaging remains challenging since it requires both high spatial and temporal resolutions, while gradient performances of clinical scanners often limit the reachable parameters. In this study, we propose a new cine sequence, named "interleaved cine," which combines two repetitions of a standard cine sequence shifted in time in order to reach resolution parameters compatible with mice imaging. More precisely, this sequence allows temporal resolution to be reduced to 6.8 ms instead of 13.5 ms initially imposed by the system's hardware. We also propose a two-step denoising algorithm to suppress some artifacts inherent to the new interleaved cine thus allowing an efficient enhancement of the image quality. In particular, we model and suppress the periodic intensity pattern and further denoise the sequence by soft thresholding of the temporal Fourier coefficients. This sequence was successfully validated with mass and function measurements on relevant mice models of cardiovascular diseases.
 
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This paper describes a method for matching high-temperature superconducting nuclear magnetic resonance (NMR) signal pickup coils to field-effect transistor (FET) preamplifiers using amplifier-specific noise figure and gain parameters to obtain a matching compromise that improves gain flatness for a given permissible noise figure. A technique for obtaining these parameters is also described in an appendix.
 
Article
This paper investigates adaptive digital notch filters for the elimination of powerline noise from biomedical signals. Since the distribution of the frequency variation of the powerline noise may or may not be centered at 60 Hz, three different adaptive digital notch filters are considered. For the first case, an adaptive FIR second-order digital notch filter is designed to track the center frequency variation. For the second case, the zeroes of an adaptive IIR second-order digital notch filter are fixed on the unit circle and the poles are adapted to find an optimum bandwidth to eliminate the noise to a pre-defined attenuation level. In the third case, both the poles and zeroes of the adaptive IIR second-order filter are adapted to track the center frequency variation within an optimum bandwidth. The adaptive process is considerably simplified by designing the notch filters by pole-zero placement on the unit circle using some suggested rules. A constrained least mean-squared (CLMS) algorithm is used for the adaptive process. To evaluate their performance, the three adaptive notch filters are applied to a powerline noise sample and to a noisy EEG as an illustration of a biomedical signal.
 
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The electrical and communication performance of a 0.8-microW UHF temperature telemeter designed for human vaginal placement is discussed; a solenoidal loop antenna was used, occupying a volume of 0.1 cm3. In situ, measured power absorption was between 19-25 dB, resulting in an effective operating range of 10 m. Capacitive loading lowered the antenna's resonant frequency by 1.4% and there was a significant polarization change in the radiated output.
 
Top-cited authors
Rosalind W Picard
  • Singapore-MIT Alliance
Patrick Mcsharry
  • University of Oxford
Bin He
  • Durban University of Technology
Daniel McDuff
  • Microsoft
Moncef Gabbouj
  • Tampere University