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Temporary cardiac pacemakers used in periods of need during surgical recovery involve percutaneous leads and externalized hardware that carry risks of infection, constrain patient mobility and may damage the heart during lead removal. Here we report a leadless, battery-free, fully implantable cardiac pacemaker for postoperative control of cardiac rate and rhythm that undergoes complete dissolution and clearance by natural biological processes after a defined operating timeframe. We show that these devices provide effective pacing of hearts of various sizes in mouse, rat, rabbit, canine and human cardiac models, with tailored geometries and operation timescales, powered by wireless energy transfer. This approach overcomes key disadvantages of traditional temporary pacing devices and may serve as the basis for the next generation of postoperative temporary pacing technology. A biodegradable pacemaker without external leads improves the safety of temporary cardiac pacing.

Radiofrequency ablation (RFA), a method of inducing thermal ablation (cell death), is often used to destroy tumours or potentially cancerous tissue. Current techniques for RFA estimation (electrical impedance tomography, Nakagami ultrasound, etc.) require long compute times (≥ 2 s) and measurement devices other than the RFA device. This study aims to determine if a neural network (NN) can estimate ablation lesion depth for control of bipolar RFA using complex electrical impedance - since tissue electrical conductivity varies as a function of tissue temperature - in real time using only the RFA therapy device's electrodes.Three-dimensional, cubic models comprised of beef liver, pork loin or pork belly represented target tissue. Temperature and complex electrical impedance from 72 data generation ablations in pork loin and belly were used for training the NN (403 s on Xeon processor). NN inputs were inquiry depth, starting complex impedance and current complex impedance. Training-validation-test splits were 70%-0%-30% and 80%-10%-10% (overfit test). Once the NN-estimated lesion depth for a margin reached the target lesion depth, RFA was stopped for that margin of tissue.The NN trained to 93% accuracy and an NN-integrated control ablated tissue to within 1.0 mm of the target lesion depth on average. Full 15-mm depth maps were calculated in 0.2 s on a single-core ARMv7 processor.The results show that a NN could make lesion depth estimations in real-time using less in situ devices than current techniques. With the NN-based technique, physicians could deliver quicker and more precise ablation therapy.

Radiofrequency ablation (RFA) is a popular modality for tumor treatment. However, inexpensive real-time monitoring of RFA within multiple tissue types is still an ongoing research topic. The objective of this study is to utilize multi-frequency electrical impedance data within real-time RFA depth estimation through data fusion schemes that include non-linear machine learning (ML) models. Multi-frequency tissue complex electrical impedance measurements are used to provide input data to the data fusion schemes. Our results show that the fusion schemes significantly decrease both the spread of residuals and the mean of the residuals for depth estimation. Thus, data fusion can be a significant tool for use in improving the performance of ML-based monitoring for RFA.

The modulation of current through an electrostatically formed nanowire (EFN) is controlled by the voltage on the four input gates. The behavior of this multi-gate transistor can be interpreted as a complex four-input switching process, enabling the computation of multiple-input threshold logic functions using a single device. We have therefore created a novel threshold logic family leveraging these unique capabilities that enables the efficient computation of complex logic functions. Experimental and simulation data are provided to demonstrate feasibility and evaluate behavior. This logic family overcomes the challenge posed by the input-output voltage mismatch inherent to EFNs and produces circuits with one-eighth the number of active logic devices and one-quarter the number of transistors required by CMOS.

Background While electromagnetic interference is widely recognized as a cause of noise detected by cardiac implanted electronic devices (CIEDs), we report on two cases of inappropriate activation of magnet response mode due to magnets in continuous positive airway pressure (CPAP) masks. Methods Two patients with St. Jude Medical dual-chamber pacemakers (Assurity DR 2240; St. Jude Medical, St. Paul, MN, USA) were discovered on routine outpatient device interrogation to have magnet response events that correlated with nightly use of their CPAP masks. A magnet response event was reproduced by positioning one CPAP mask over the patient's pulse generator site. The magnetic flux density was measured using a Gauss meter. Results It was found that their CPAP masks had magnetic clips that were used to secure the headgears. These appeared to be transiently positioned within sufficient proximity of the patients' CIEDs to activate magnet response events during sleep. The measured magnetic field density adjacent to a mask magnet was 136 Gauss. Conclusion Clinicians managing CPAPs and CIEDs should be aware of magnetic interference with the potential for inappropriate activation of magnet response mode. CPAP masks that are secured with magnetic clips should be avoided in patients with CIEDs, since this can result in inappropriate asynchronous pacing in pacemakers or potential failure to deliver life-saving tachytherapies in patients with implanted cardioverter-defibrillators.

The cascading of logic gates is a critical challenge for the development of spintronic logic circuits. Here we propose the first logic family exploiting magnetoresistive bipolar spin-transistors to achieve a complete spintronic logic family in which logic gates can be cascaded. This logic family, emitter-coupled spin-transistor logic (ECSTL), is an extension of emitter-coupled logic (ECL) that leverages the advanced features of spintronic devices. The current through the ECL differential amplifier is routed to create a magnetic field that modulates the magnetoamplification of the spin-transistors. This cascading mechanism supplements the voltage cascading available in conventional ECL, providing additional inputs to each logic stage. Each gate therefore has increased logical functionality, leading to logic minimization and compact circuits. No additional current is required to employ this added spintronic switching, resulting in improved speed, area, and power characteristics. This logic family achieves a power-delay product 10–25 times smaller than conventional ECL, inspiring a pathway for high-performance spintronic computing beyond 10 GHz.

This paper presents a platform combining an inverse electromagnetic design computational method with additive manufacturing to design and fabricate all-dielectric metadevices. As opposed to conventional flat metasurface-based devices that are composed of resonant building blocks resulting in narrow band operation, the proposed design approach creates non-resonant, broadband (Δλ/λ up to >50%) metadevices based on low-index dielectric materials. High-efficiency (transmission >60%), thin (≤2λ) metadevices capable of polarization splitting, beam bending, and focusing are proposed. Experimental demonstrations are performed at millimeter-wave frequencies using 3D-printed devices. The proposed platform can be readily applied to the design and fabrication of electromagnetic and photonic metadevices spanning microwave to optical frequencies.

In this paper we present an inverse-designed 3D-printed all-dielectric stretchable millimeter wave metalens with a tunable focal distance. Computational inverse-design method is used to design a flat metalens made of disconnected building polymer blocks with complex shapes, as opposed to conventional monolithic lenses. Proposed metalens provides better performance than a conventional Fresnel lens, using lesser amount of material and enabling larger focal distance tunability. The metalens is fabricated using a commercial 3D-printer and attached to a stretchable platform. Measurements and simulations show that focal distance can be tuned by a factor of 4 with a stretching factor of only 75%, a nearly diffraction-limited focal spot, and with a 70% focusing efficiency. The proposed platform can be extended for design and fabrication of multiple electromagnetic devices working from visible to microwave radiation depending on scaling of the devices., 11 pages, 4 figures

This brief proposes and analyzes a novel logic family composed solely of magnetic tunnel junctions (MTJs) to form complimentary pull-up and pull-down networks. This logic family solves the challenge of direct cascading in spintronic logic circuits while also providing non-volatile data storage. The increased logic density possible with complementary MTJs coupled with a charge pulse switching mechanism driven by ferromagnet polarization permits highly efficient logical computation. Furthermore, the presence of non-volatile memory within the logic structure provides a feasible hardware for non-von Neumann computer architectures.

HighlightsAutomatic, online calibration between a color camera and a depth camera.No special equipment; just a square, checkered target.Calibration occurs very quickly and with minimal user interaction.Online calibration allows user to see results immediately.Rigorous ground truth validation places this algorithm at leading edge. Automatic camera calibration has remained a hard topic in computer vision since its inception due to its reliance on the image correspondence problem. This problem becomes even more pronounced when calibrating a depth image with a color image due to a lack of simple correspondences between the two modalities. In this work, we develop a completely automatic, very fast, online algorithm that demonstrates how a consumer-grade depth camera can be calibrated with a color camera with minimal user interaction.

Using a 94-GHz millimeter-wave interferometer, we are able to calculate the relative displacement of an object. When aimed at the chest of a human subject, we measure the minute motions of the chest due to cardiac activity. After processing the data using a wavelet multiresolution decomposition, we are able to obtain a signal with peaks at heartbeat temporal locations. In order for these heartbeat temporal locations to be accurate, the reflected signal must not be very noisy. Since there is noise in all but the most ideal conditions, we created a statistical algorithm in order to compensate for unconfident temporal locations as computed by the wavelet transform. By analyzing the statistics of the peak locations, we fill in missing heartbeat temporal locations and eliminate superfluous ones. Along with this, we adapt the processing procedure to the current signal, as opposed to using the same method for all signals. With this method, we are able to find the heart rate of ambulatory subjects without any physical contact.

This paper presents a solution to an aiming problem in the remote sensing of vital signs using an integration of two systems. The problem is that to collect meaningful data with a millimeter-wave sensor, the antenna must be pointed very precisely at the subject's chest. Even small movements could make the data unreliable. To solve this problem, we attached a camera to the millimeter-wave antenna, and mounted this combined system on a pan/tilt base. Our algorithm initially finds a subject's face and then tracks him/her through subsequent frames, while calculating the position of the subject's chest. For each frame, the camera sends the location of the chest to the pan/tilt base, which rotates accordingly to make the antenna point at the subject's chest. This paper presents a system for concurrent tracking and data acquisition with results from some sample scenarios.

Obstructive sleep apnea (OSA) is a common sleep disorder that causes pauses of breathing due to repetitive obstruction of the upper airways of the respiratory system. The effect of this phenomenon can be observed in other physiological signals like the heart rate variability, oxygen saturation, and the respiratory effort signals. In this study, features from these signals were extracted from 50 control and 50 OSA patients from the Sleep Heart Health Study database and implemented for minute and subject classifications. A support vector machine (SVM) classifier was used with linear and second-order polynomial kernels. For the minute classification, the respiratory features had the highest sensitivity while the oxygen saturation gave the highest specificity. The polynomial kernel always had better performance and the highest accuracy of 82.4% (Sen: 69.9%, Spec: 91.4%) was achieved using the combined-feature classifier. For subject classification, the polynomial kernel had a clear improvement in the oxygen saturation accuracy as the highest accuracy of 95% was achieved by both the oxygen saturation (Sen: 100%, Spec: 90.2%) and the combined-feature (Sen: 91.8%, Spec: 98.0%). Further analysis of the SVM with other kernel types might be useful for optimizing the classifier with the appropriate features for an OSA automated detection algorithm.

A compact millimeter-wave (MMW) sensor has been developed for remote monitoring of human vital signs (heart and respiration rate). The low-power homodyne transceiver operating at 94 GHz was assembled by using solid-state active and passive block-type components and can be battery operated. A description of the MMW system front end and the back-end acquisition hardware and software is presented. Representative test case results on the application of various signal processing and data analysis algorithms developed to extract faint physiological signals of interest in presence of strong background interference are provided. Although the laboratory experiments so far have been limited to standoff distances of up to 15 m, the upper limit of the detection range is expected to be higher. In comparison with its microwave counterparts, the MMW system described here provides higher directivity, increased sensitivity, and longer detection range for measuring subtle mechanical displacements associated with heart and respiration functions. The system may be adapted for use in a wide range of standoff sensing applications including for patient health care, structural health monitoring, nondestructive testing, biometric sensing, and remote vibrometry in general.

Background Electronic pacemaker pulses are poorly reproduced in computerized electrocardiogram (ECG) tracings, impairing both automated and human interpretation. In this study, a high-bandwidth system is used to examine ECG and vectorcardiogram characteristics of pacemaker pulses. Methods In 69 subjects with artificial pacemakers, electrocardiograms were recorded at 75 000 samples per second with a high-bandwidth ECG system (GE Healthcare, Milwaukee, WI). Vectorcardiograms, as estimated with the Dower transform, were examined. Results Pulse loops in the vectorcardiogram consisted of distinct discharge and recharge waves, with an angle difference of 174° ± 10° (mean ± SD) in 3 dimensions. Atrial pulses were on average oriented anteriorly, superiorly, and to the left; right ventricular pulses were oriented posteriorly, superiorly, and to the right; and left ventricular pulses were oriented posteriorly, inferiorly, and to the right. Other details of pacemaker pulses could be readily observed. Conclusions The high-bandwidth ECG has the potential to improve interpretation of paced rhythms in computerized ECGs.

To evaluate the use of contrast material-enhanced magnetic resonance (MR) imaging with conventional T1-weighted gradient-recalled echo (GRE) and inversion-recovery (IR)-prepared GRE methods to quantitatively measure the size of irreversible electroporation (IRE) ablation zones in the liver in a rat model.All studies were approved by the institutional animal care and use committee and were performed in accordance with institutional guidelines. Seventeen adult male Sprague-Dawley rats were divided into four groups. Rats in groups 1-3 (n = 15 total) underwent IRE performed by using different IRE parameters after gadopentetate dimeglumine administration. Rats in group 4 (n = 2) underwent IRE ablation without prior gadopentetate dimeglumine injection to serve as control animals. MR imaging measurements (with conventional T1-weighted GRE and IR-prepared GRE methods) were performed 2 hours after IRE to predict the IRE ablation zones, which were correlated with pathology-confirmed necrosis areas 24 hours after IRE by using the Spearman correlation coefficient. Bland-Altman plots were also generated to investigate the agreement between MR imaging-measured ablation zones and reference standard histologic measurements of corresponding ablation zones.The necrotic areas measured on the pathology images were well correlated with the hyperintense regions measured on T1-weighted GRE images (r = 0.891, P.001) and normal tissue-nulled IR images (r = 0.874, P.001); pathology measurements were also well correlated with the smaller hyperintense regions measured on those IR images with inversion times specifically selected to null signal from the peripheral penumbra surrounding the ablation zone (r = 0.939, P.001). Bland-Altman plots indicated that these penumbra-nulled IR images provided more accurate predictions of IRE ablation zones, with T1-weighted GRE measurements tending to overestimate ablation zone sizes.Contrast-enhanced MR imaging permits accurate depiction of ablated tissue zones after IRE procedures. IR-prepared contrast-enhanced MR imaging can be used to quantitatively measure IRE ablation zones in the liver.http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100645/-/DC1.

To test the hypothesis that magnetic resonance (MR) imaging measurements can be used to immediately detect treated tissue regions after irreversible electroporation (IRE) ablation procedures in rodent liver tissues.All experiments received institutional animal care and use committee approval. In four rats for preliminary studies and 18 rats for formal assessment, MR imaging-compatible electrodes were inserted into the liver and MR imaging-monitored IRE procedures were performed at one of three electrode voltages (1000, 1500, or 2500 V), with T1- and T2-weighted images acquired before and immediately after application of the IRE pulses. MR imaging measurements were compared with both finite element modeling (FEM)-anticipated ablation zones and histologically confirmed ablation zones at necropsy. Intraclass and Spearman correlation coefficients were calculated for statistical comparisons.MR imaging measurements permitted immediate depiction of IRE ablation zones that were hypointense on T1-weighted images and hyperintense on T2-weighted images. MR imaging-based measurements demonstrated excellent consistency with FEM-anticipated ablation zones (r0.90 and P.001 for both T1- and T2-weighted images). MR imaging measurements were also highly correlated with histologically confirmed ablation zone measurements (rho0.90 and P.001 for both T1- and T2-weighted images).MR imaging permits immediate depiction of ablated tissue zones for monitoring of IRE ablation procedures. These measurements could potentially be used during treatment to elicit repeat application of IRE pulses or adjustments to electrode positions to ensure complete treatment of targeted lesions.

Irreversible electroporation (IRE) is an innovative local-regional therapy that involves delivery of intense electrical pulses to tissue to induce nanoscale cell membrane defects for tissue ablation. The purpose of this study was to investigate the feasibility of using IRE as a liver-directed ablation technique for the treatment of hepatocellular carcinoma (HCC). In the N1-S1 rodent model, hepatomas were grown in 30 Sprague-Dawley rats that were divided into treatment and control groups. For treatment groups, IRE electrodes were inserted and eight 100-μs 2,500-V pulses were applied to ablate the targeted tumor tissues. For both groups, magnetic resonance imaging scans were performed at baseline and 15-day follow-up intervals to determine tumor sizes (one-dimensional maximum diameter, Dmax; estimated two-dimensional cross-sectional area, Cmax) as a tactic to assess longitudinal outcomes. Additional groups of treated animals were sacrificed at 1-, 3-, and 7-day intervals posttherapy for pathology assessment of treatment response. Magnetic resonance images showed significant tumor size reductions within 15 days posttherapy (32 ± 31% Dmax and 52 ± 39% Cmax decreases compared with 110 ± 35% Dmax and 286 ± 125% Cmax increases for untreated tumors). Pathology correlation studies documented progression from poorly differentiated viable HCC tissues before treatment to extensive tumor necrosis and full regression in 9 of 10 treated rats 7 to 15 days after treatment. Our findings suggest that IRE can be an effective strategy for targeted ablation of liver tumors, prompting its further evaluation for HCC therapy. Cancer Res; 70(4); 1555–63

Background: In most patients, atrial fibrillation (AF) is initiated and maintained by pulmonary vein foci, but the relationship between left atrial (LA) events and the surface electrocardiogram (ECG) is largely unknown. We investigated whether LA events are reflected in the surface ECG and whether additional information can be obtained from recording posterior leads in patients with AF. Methods and Results: In 10 patients undergoing radiofrequency ablation of AF, we identified 103 5-second segments with a significant frequency gradient between right (RA) and left (LA) intraatrial electrograms, or with frequency changes from segment to segment in the same patient. QRS-T cancellation methods were used to isolate atrial activity in the surface ECG and peak frequencies were computed. Peak frequencies of different posterior leads were very similar (6.0 ± 1.3 Hz for V10, 6.0 ± 0.9 Hz for V9, 5.9 ± 1.4 Hz for V8, 6.0 ± 1.3 Hz for V7). We found a strong correlation between V1 and RA and between V9 and LA, 0.89 and 0.88, respectively, while the lowest correlation was found between lead V1 and LA, 0.62, P < 0.0001. Magnitude-squared coherence values were highest between V1 and RA and between V9 and LA. Conclusion: We have demonstrated that, by recording additional surface ECG leads from posterior locations, RA and LA electrical events and interatrial frequency gradients can be monitored noninvasively.

This concept paper provides a first quantitative analysis of complementary magnetic tunnel junction logic (CMAT), a novel cascaded logic family composed solely of magnetic tunnel junctions (MTJs). CMAT is a non-volatile logic family driven by field-induced spin-switching that was inspired by CMOS. A compact CMAT multiplexer is presented, and the impact of magnetoresistance on its behavior is analyzed. The efficiency of CMAT is shown to be a function of the MTJ magnetoresistance, providing impetus for further development of MTJs for computing applications.

Introduction: Fibrillatory waves on the surface ECG have been scrutinized to allow inferences about underlying mechanisms and pathophysiology, based on the premise that fibrillatory waves do not vary “randomly” but provide a consistent reflection of the underlying state of the atria in an individual patient. This premise is untested. Methods and Results: Ten standard ECGs were recorded over a 24-hour period in each of 20 clinically stable inpatients with atrial fibrillation. After QRS-T cancellation, the remainder fibrillatory waves were analyzed. Interpatient versus intrapatient differences in fibrillatory wave characteristics were evaluated by analysis of variance (ANOVA). The fibrillatory wave peak-to-peak amplitude of all the patients ranged from 0.06 to 0.35 mV, whereas 1 SD of the amplitude for each patient ranged from 0.004 to 0.053 mV. Short-term peak frequencies of all the patients ranged from 4.6 to 8.0 Hz, whereas 1 SD for each patient varied from 0.2 to 0.5 Hz. For these and all other parameters tested, interpatient differences were significantly greater compared to intrapatient differences (P < 0.0001). Conclusion: Fibrillatory wave characteristics are repeatable from ECG to ECG over 24 hours for clinically stable patients, whereas substantial differences are present between patients. Further study of the relationship of such characteristics to pathophysiology and management decisions is valid and warranted. (J Cardiovasc Electrophysiol, Vol. 15, pp. 911-917, August 2004)

QRS cancellation methods have been used to analyze atrial activity in the electrocardiogram for such rhythms as atrioventricular dissociated ventricular tachycardia and atrial fibrillation. However, how well the cancellation methods work has never been evaluated by some gold standard. In this study of patients undergoing radiofrequency ablation of the atrioventricular junction, the contribution of imperfect cancellation was evaluated by comparing the “pure” atrial fibrillation (the gold standard) during a brief ventricular asystole to data obtained by a cancellation method during pacing just before and after the asystole. The results were compared by linear regression. The peak frequencies were 4.8–7.3 (6.1 ± 0.8) Hz for the “pure” and 4.8–6.8 (5.9 ± 0.7) Hz for the cancelled electrocardiogram segments (R 2 = 0.89) (similar results for median frequency), and the mean short-time Fourier transform peak frequencies were 4.6–7.1 (5.9 ± 0.8) Hz for the “pure” and 4.7–6.8 (5.9 ± 0.7) Hz for the cancelled segments (R 2 = 0.96). Further comparison was accomplished using synthesized signals. Based on our study, the cancellation method is reliable for studying atrial fibrillatory wave characteristics. As reported previously, the peak frequency and most power for atrial fibrillation in humans are in the 4–9 Hz band.

The cascading of logic gates is one of the primary challenges for spintronic computing, as there is a need to dynamically create magnetic fields. Spin-diode logic provides this essential cascading, as the current through each spin-diode is modulated by a magnetic field created by the current through other spin-diodes. This logic family can potentially be applied to any device exhibiting strong positive or negative magnetoresistance, and allows for the creation of circuits with exceptionally high performance. These novel circuit structures provide an opportunity for spintronics to replace CMOS in general-purpose computing.

We demonstrate an all-optical scheme to multiply the repetition frequency of a high-rate optical pulse train by using a spectral filter to remove unwanted frequency components. A stable 58.5-GHz soliton pulse source at 1542 nm is filtered with a Fahry-Perot interferometer to achieve 117 and 175.5 GWz output pulse trains. This scheme is generally applicable to rate multiplication of mode-locked pulse trains using various types of spectral filters. All-optical rate conversion of continuous pulse trains may find applications in time division multiplexed optical networks at high bit rates, where electronic methods are cumbersome.

The objective of this article was to look for evidence of nonrandom behavior during atrial fibrillation hy examining long (> 15 minutes) recordings. We have previously reported transient “linking“ of atrial activation during atrial fibrillation, and showed that activation was not entirely randotn. Over the few episodes of linking seen during 1 minute, activation directions apparently repeated, indicating a possible anatomical or physiological constraint. In the present study, we examined atrial fibrillation over longer time periods to see if this constancy of direction was stable. Endocardial recordings were made from 12 patients with atrial fibrillation using a catheter with three orthogonal bipoies, aHowing measurements of local activation directions in three dimensions. The direction was calculated using Pipberger's half-area method, and episodes of transient linking were identified. An average direction for each episode of linking was calculated and plotted in two dimensions using spherical coordinates (altitude and azimuth). In addition, the nature of initiation and termination of linking was examined. Of the twelve patients, 611 episodes of linking (range 1 to 169 per patient, mean 51) were identified. The episodes for most patients clustered closely in direction. In contrast, directions measured for all activations (i.e., linked and not linked) filled up the entire available range. Linking in most cases subjectively appeared to initiate and terminate suddenly. The results indicate that the local anatomy, pathology, or physiology of the atrium has a strong constraining effect on the electrical activations occurring during atrial fibrillation, and revises our perception of activation during atrial fibrillation as “random.“ The demonstration that local properties greatly influence conduction during fibrillation has important implications for ablation or pacing therapy.

Two recently proposed spintronic logic families, spin-diode logic and emitter-coupled spin-transistor logic, provide an opportunity for high-performance cascaded logic circuits. These logic families make use of magnetoresistive semiconductor heterojunctions, in which the presence of a magnetic field causes a large increase in resistance. Spin-diode logic and emitter-coupled spin-transistor logic produce highly compact circuits with superior speed and power characteristics. In particular, circuits realized in these logic families use three to ten times fewer devices than conventional CMOS. Additionally, there is minimal dynamic power dissipation, presenting a pathway for low power high performance computing beyond 10 GHz.

This paper proposes an algorithm to synthesize combinational circuits based on spin diode logic technology. Spin diode is a magnetoresistive semiconductor heterojunction device which allows for a binary current based logic. The proposed algorithm takes the advantages of the functional composition (FC) approach to obtain fanout free network implementations with the minimum number of spin diodes. Experimental results have shown that the new proposal obtains better results when compared to the state-of-the-art algorithms that focus on traditional CMOS technology adapted to this new approach.

Using a 94-GHz homodyne interferometer employing a highly-directional quasi-optical lens antenna aimed at a human subject's chest, we can measure chest wall displacement from up to 10m away and through common clothing. Within the chest displacement signal are motions due to cardiac activity, respiration, and gross body movement. Our goal is to find the heart rate of the subject being monitored, which implies isolation of the minute movements due to cardiac activity from the much larger movements due to respiration and body movement. To accomplish this, we first find a subset of the true heartbeat temporal locations (called confident" heartbeats) in the displacement signal using a multi-resolution wavelet approach, utilizing Symlet wavelets. Although the chest displacement due to cardiac activity is orders of magnitude smaller than that due to respiration and body movement, wavelets find those heartbeat locations due to several useful properties, such as shape matching, high-pass filtering, and vanishing moments. Using the assumption that the confident" heartbeats are randomly selected from the set of all heartbeats, we are able to find the maximum a posteriori statistics of an inverse Gaussian probability distribution modeling the inter-heartbeat times. We then analyze the confident" heartbeats and decide which heartbeats are probabilistically correct and which are not, based on the inverse Gaussian distribution we calculated earlier. The union of the confident" set, after pruning, and the interpolated set forms a very close approximation to the true heartbeat temporal location set, and thus allows us to accurately calculate a heart rate.

Discusses measuring local activation direction variability using short segment lengths to quickly differentiate fibrillation from regular rhythms. It is concluded that the spatial precision of local activation direction shows promise as a potential discriminator of atrial fibrillation from regular atrial rhythms. For the authors' study set, excellent discrimination of atrial fibrillation from regular rhythms was achieved by spatial precision using segment lengths as short as 20 activations. The authors would expect that this method would be even more accurate using permanently implanted electrodes and could be implemented in real-time using four-electrode elements, and may be applicable in the ventricle as well.

The recent invention of magnetoresistive bipolar spin-transistors makes possible the creation of new spintronic logic families. Here we propose the first logic family exploiting these devices, extending emitter-coupled logic (ECL) to achieve a greater range of basis logic functions. By placing the wire from the output stage of ECL logic elements near spin-transistors in other logic stages throughout the circuit, additional basis logic elements can be realized. These new logic elements support greater logic minimization, resulting in enhanced speed, area, and power characteristics. A novel magnetic shielding structure provides this logic family with the crucial ability to cascade logic stages. This logic family potentially achieves a power-delay product 10–25 times smaller than conventional ECL, and can therefore be exploited to increase the performance of very high-speed logic circuits while broadening the range of design choices for a variety of electronic applications.

A continuous wave (CW) 94-GHz millimeter wave (mmW) standoff biosensor has been developed for remote biometric sensing applications. The sensor measures the demodulated in-phase (I) and quadrature-phase (Q) components of the received reflected mmW signal from a subject. Both amplitude and phase of the reflected signal are obtained from downconverted I and Q channels from the quadrature mixer. The mmW sensor can faithfully monitor human vital signs (heartbeat and respiration) at relatively long standoff distances. Principle Component Analysis (PCA) is used to extract the heartbeat, the respiration and the body motion signals. The approach allows one to deduce information about amplitude and beat-to-beat rate of the respiration and the heartbeat. Experimental results collected from a subject were analyzed and compared to the signal obtained with a three-electrode ECG monitoring instrument.

A modified polarized Monte Carlo code is developed that allows heterogeneous structure to be modeled. The code is validated with existent polarized Monte Carlo code. Heterogeneous structure simulating colon tissue is simulated to understand the difference between simulations of homogeneous vs heterogeneous tissue structure. Reflectance measurements from simulations containing increased blood vessel size and increased blood volume fraction, both markers for potential cancerous tissue, are studied in order to better interpret reflectance measurement from diagnostic probes.

BACKGROUND: The circulating wavelet hypothesis suggests that atrial fibrillation could terminate by either progressive fusion or simultaneous block of all wavelets. METHODS: Intraatrial recordings from the right atrial free wall were made during procainamide induced (n = 8) or spontaneous (n = 7) termination of electrically induced atrial fibrillation in 14 patients. Atrial rate, mean magnitude squared coherence, and direction of activation during sequential electrograms were measured. Rate and coherence were calculated from the earliest point within 5 minutes prior to termination as well as from the 4-second interval just prior to termination. RESULTS: Termination was directly to sinus rhythm (13 episodes) or to atrial flutter (2 episodes). For the eight procainamide induced terminations, rate decreased between the first measurement and the measurement just prior to termination, from 443 +/- 127 beats/min to 322 +/- 119 beats/min. For the seven spontaneous terminations, rate also decreased from 373 +/- 119 beats/min to 323 +/- 88 beats/min; however, a slight increase in atrial rate prior to termination was observed in three episodes. No specific patterns of atrial cycle lengths were seen during the final few seconds of fibrillation. No increase in coherence was observed. In seven episodes, recordings were made using orthogonal bipoles in the x, y, and z directions, allowing direction of activation of wavefronts to be measured. Three episodes showed multiple instances where direction of activation remained similar over several electrograms as we have previously reported for chronic fibrillation. However, no such instances precipitated termination in any of the seven episodes. CONCLUSIONS: Atrial fibrillation usually terminates directly to sinus rhythm and does so abruptly and without forewarning. While we and others have previously reported that the rate of atrial fibrillation decreases with procainamide infusion, a decrease in the rate of atrial fibrillation is not required for the rhythm to terminate and consequently may not be a part of the termination process at all. Coherence does not demonstrate a progressive increase in the organization of atrial fibrillation prior to termination. Lack of stabilization in the direction of activation of wavefronts in the final few seconds also fails to support fusion of wavefronts as the mechanism of termination of atrial fibrillation. Simultaneous block of all wavelets is consistent with, but not proven by, our observations.

Quantum noise in image sequences arises in a wide array of applications including medical and astronomical images and remote sensing. It is an undesirable artifact caused by the unavailability or intentional depletion of X-ray and/or light photons necessary for imaging. In this paper, we develop a recursive sliding window, locally linear minimum mean squared error motion-compensated temporal filter for the enhancement of image sequences corrupted by this type of noise. The filter is derived from the formulation of a noise model which describes the underlying physical processes of quantum noise. The recursive implementation of this filter will provide an intuitive manner for addressing subsequent image frames as new observations when acquired under quantum-limited conditions. Experimental results are provided which show the effectiveness of the proposed estimator on both sequences simulated with quantum noise and on real clinical sequences containing natural quantum mottle.

Clinical angiography requires hundreds of X-ray images, putting the patients and particularly the medical staff at risk. Dosage reduction involves an inevitable sacrifice in image quality. In this work, the latter problem is addressed by first modeling the signal-dependent, Poisson-distributed noise that arises as a result of this dosage reduction. The commonly utilized noise model for single images is shown to be obtainable from the new model. Stochastic temporal filtering techniques are proposed to enhance clinical fluoroscopy sequences corrupted by quantum mottle. The temporal versions of these filters as developed here are more suitable for filtering image sequences, as correlations along the time axis can be utilized. For these dynamic sequences, the problem of displacement field estimation is treated in conjunction with the filtering stage to ensure that the temporal correlations are taken along the direction of motion to prevent object blur. >

BACKGROUND Atrial fibrillation is usually thought of as a "random" pattern of circulating wavelets. However, local atrial activation should be influenced by the constant anatomy and receding tail of refractoriness from the previous activation. The general tendency for wave fronts to follow paths of previous excitation has been termed "linking." We examined intra-atrial electrograms recorded during atrial fibrillation for evidence of linking. METHODS AND RESULTS Two minutes of atrial fibrillation were recorded in 15 patients with an orthogonal catheter. We have previously demonstrated that this catheter can be used to detect changes in the direction of local atrial activation. A mean vector was calculated for each electrogram. The similarity of the direction of the vectors from two consecutive electrograms can be quantified on a scale of 1 to -1 by calculating the cosine (cos) of the smallest angle (theta) between them. Two vectors pointing in the same or opposite directions then have cos(theta) = 1 or -1, respectively. For the entire group of patients, mean cos(theta) was significantly greater than 0 (mean, 0.36; p less than 0.001). In nine of 15 patients, there were groups of six or more consecutive beats (total, 44 groups; range, six to 14 beats per group) in which the direction of activation of each beat was within 30 degrees of the previous beat. The likelihood of one group of six or 14 consecutive similar beats occurring by chance in any one patient in 1 minute is less than 0.05 and less than 0.0000001, respectively. There was a significant correlation (r = 0.90) between the amount of linking during the first and second minutes of atrial fibrillation in each patient. CONCLUSIONS Transient similarities in the direction of wavelet propagation in the majority of patients with atrial fibrillation is consistent with the presence of transient linking. To our knowledge, this is the first direct evidence that atrial activation during atrial fibrillation in humans is not entirely random.

Interference from gradient switching, radiofrequency pulses, and the magnetohydrodynamic effect distort ECG signals typically used for gating in cardiac MRI, potentially resulting in imprecise triggering. Furthermore, the use of a lead system during a MRI scan requires additional equipment and patient setup time. Self-gating (SG) is an alternative technique which directly utilizes MRI signals for cardiac gating; consequently, synchronization is related to the intrinsic motion of the heart instead of electrical activity. Previous work in SG used a simple first difference peak detection scheme to identify trigger times. We hypothesized that the SG trigger detection accuracy can be improved by using more advanced signal processing techniques.

Purpose To determine whether improved self-gating (SG) algorithms can provide superior synchronization accuracy for retrospectively gated cine MRI. Materials and Methods First difference, template matching, and polynomial fitting algorithms were implemented to improve the synchronization of MRI data using cardiac SG signals. Cine datasets were acquired during short-axis, two-, three-, and four-chamber cardiac MRI scans. The root-mean-square (RMS) error of SG synchronization positions compared to detected R-wave positions were calculated along with the mean square error (MSE) and peak signal-to-noise ratio (PSNR) comparing SG to electrocardiogram (ECG)-gated images. Overall image quality was also compared by two expert reviewers. Results RMS errors were highest for the first difference method for all orientations. Improvements for both template matching and cubic polynomial fitting methods were significant for two-, three-, and four-chamber scans. MSE values were lower and PSNR were significantly higher for the cubic method compared to the first difference method for all orientations. Reviewers scored the images to be of comparable quality. Conclusion Template matching and polynomial fitting improved the accuracy of cardiac cycle synchronization for two-, three-, and four-chamber scans; improvements in SG synchronization accuracy were reflected in improvements in analytical image quality. Implementation of robust postprocessing algorithms may bring SG approaches closer to clinical utilization. J. Magn. Reson. Imaging 2008;28:767–772. © 2008 Wiley-Liss, Inc.

We show that our recently reported microwave photonic jet technique for detection of deeply subwavelength pits in a metal substrate can be extended to optical wavelengths for purposes of high-density data storage. Three-dimensional finite-difference time-domain computational solutions of Maxwell's equations are used to optimize the photonic nanojet and pit configuration to account for the Drude dispersion of an aluminum substrate in the spectral range near lambda= 400 nm. Our results show that nanojet-illuminated pits having lateral dimensions of only 50 nm x 80 nm yield a contrast ratio 27 dB greater than previously reported using a lens system for pits of similar area. Such pits are much smaller than BluRay features. The high detection contrast afforded by the photonic nanojet could potentially yield significant increases in data density and throughput relative to current commercial optical data-storage systems while retaining the basic geometry of the storage medium.

T-wave alternans (TWA) manifests on the surface ECG as a pattern of alternating amplitude T-waves, typically in the microvolt range. Consequently, TWA is usually invisible at standard ECG display scales and must be detected using signal processing methods. There is a predictive relationship between TWA and sudden cardiac death, so proper detection and estimation may contribute to clinical decision-making. The objective of the 2008 Physionet/Computers in Cardiology Challenge was to estimate the magnitude of TWA in a dataset of 100 multi-lead ECGs. We used a modified moving average method (MMA) to detect and estimate TWA. We found that the TWA magnitude ranged from to 1.3 to 256.9 muV (43.9 plusmn 49.7 muV). The Kendall rank correlation coefficient obtained for the challenge was 0.451. In conclusion, the MMA method can be used for detection and estimation of TWA, though additional work could further improve the method.

Cardiac MR image data is typically acquired over multiple cardiac cycles, thus necessitating the use of a synchronization algorithm. Comparison of such algorithms is challenging, as the MR environment distorts the signals that might be used to derive the gating signal for synchronization. In this study, we evaluated three cardiac synchronization algorithms by means of two full-reference image quality metrics and two no-reference metrics; we compared the resulting values of these metrics with subjective analysis by expert reviewers. Both full-reference metrics indicated that there was a statistically significant difference between the cardiac synchronization algorithms. However, both no-reference metrics indicated that there was no statistically significant difference between any of the synchronization algorithms, which corresponded with the subjective analysis. In conclusion, no-reference image metrics correlated well with expert analysis of cardiac MR images, while the full-reference metrics were most likely oversimplified which provided misleading results.

Sample entropy, a nonlinear signal processing approach, was used as a measure of signal complexity to evaluate the cyclic behavior of heart rate variability (HRV) in obstructive sleep apnea syndrome (OSAS). In a group of 10 normal and 25 OSA subjects, the sample entropy measure showed that normal subjects have significantly more complex HRV pattern than the OSA subjects (p < 0.005). When compared with spectral analysis in a minute-by-minute classification, sample entropy had an accuracy of 70.3% (69.5% sensitivity, 70.8% specificity) while the spectral analysis had an accuracy of 70.4% (71.3% sensitivity, 69.9% specificity). The combination of the two methods improved the accuracy to 72.9% (72.2% sensitivity, 73.3% specificity). The sample entropy approach does not show major improvement over the existing methods. In fact, its accuracy in detecting sleep apnea is relatively low in the well classified data of the physionet. Its main achievement however, is the simplicity of computation. Sample entropy and other nonlinear methods might be useful tools to detect apnea episodes during sleep.

Self-gating (SG) is a cardiac MRI technique to synchronize data acquisition to the cardiac cycle based upon MR signal triggers as opposed to conventional ECG triggers. Fourteen healthy subjects underwent cardiac MRI scans in four different orientations: two chamber, three chamber, four chamber, and short axis. SG trigger times were computed using two methods, first difference and template matching, and ECG trigger times were also recorded for comparison. The root-mean-square (RMS) error was used to evaluate performance, defined as the variability relative to the mean difference between SG trigger times and ECG trigger times. The mean RMS error was lower for template matching than first difference approach for all scan orientations; the improvement in RMS error was statistically significant for all orientations except short axis. In conclusion, compared to the first difference approach, template matching improved the accuracy of trigger detection for two, three, and four chamber SG cardiac MRI scans.

Aims We investigated the process of spontaneous termination of atrial fibrillation (AF) to determine its time course from the surface ECG. Methods and results We studied fibrillatory waves in Holter recordings of paroxysmal and sustained AF. Following QRS-T cancellation dominant frequencies (DFs) were computed and the relationship of DF to termination was scrutinized. For 57 episodes of paroxysmal AF (PAF) in 24 patients, DF ranged from 4.4 to 6.5 Hz (5.2 ± 0.4 Hz) compared to 5.8 to 7.4 Hz (6.6 ± 0.6 Hz) for sustained AF recordings. Comparison of the atrial frequency of the ultimate to the penultimate second demonstrated a drop in frequency in 51 of 57 episodes, P < 0.00001. No comparable change was seen at longer time periods. Moments of comparably low frequency without termination were only occasionally seen in patients with PAF but not in patients with sustained AF. Conclusion Low frequency fibrillation was found to be much more likely to terminate. Frequency changes preceding spontaneous termination were abrupt, in contrast to the gradual frequency drop reported with drug-induced termination. The analysis of fibrillatory wave characteristics and their change over time might be used to target specific moments for pacing therapy in patients with AF.

Matched-filtering is applied to an algorithm similar to confocal microwave imaging of the breast in order to better detect tumors in a 3-D FDTD model. Strongly scattering objects detected by the imaging algorithm are examined for tumor existence through matched-filtering. Based on the matched-filtering examination, early-time clutter is well suppressed by this method. Also, an antenna-array with a spatial resolution of 8.3 mm is shown to be effective in reducing the clutter level for the successful detection of a 5-mm-diameter spherical tumor.

A novel spintronic computing paradigm is proposed and analyzed in which InSb p-n bilayer avalanche spin-diodes are cascaded to efficiently perform complex logic operations. This spin-diode logic family uses control wires to generate magnetic fields that modulate the resistance of the spin-diodes, and currents through these devices control the resistance of cascaded devices. Electromagnetic simulations are performed to demonstrate the cascading mechanism, and guidelines are provided for the development of this innovative computing technology. This cascading scheme permits compact logic circuits with switching speeds determined by electromagnetic wave propagation rather than electron motion, enabling high-performance spintronic computing.

The purpose of this study was to investigate the magnitude and time course of fibrillatory wave dynamics during spontaneous onset of paroxysmal atrial fibrillation (AF).We studied fibrillatory waves in Holter recordings of paroxysmal AF with regard to the fibrillation-free interval (FFI) preceding each episode.For 38 episodes of paroxysmal AF in 20 patients, dominant frequency (DF) ranged from 4.4 to 6.8 Hz (5.5 +/- 0.5 Hz). Long-FFI episodes showed a gradual increase in DF over the first 4 minutes (P.0001). Short-FFI episodes showed an increase only from the first to the second minute (P.003). For all 7 patients exhibiting both long-FFI and short-FFI episodes, short-FFI episodes had a higher initial DF (P.002).The dynamics during onset and their relation to the FFI are consistent with the influence of short-term electrophysiological changes and their reversal. These findings have implications for the timing of antifibrillatory interventions.

This study examined whether coherence measurements of cardiac rhythms could be estimated from a single lead with two electrode elements and whether such measurements could be used to differentiate fibrillatory and non-fibrillatory rhythms. Results indicate that magnitude-squared coherence (MSC) can be calculated from a single bipolar lead where MSC is determined between the bipole and one of the unipoles that constitutes the bipole. Furthermore, MSC calculated from a single lead can reliably discriminate atrial fibrillation from sinus rhythm.

Paroxysmal atrial fibrillation (AF) is self-terminating by definition, but the mechanisms by which this occurs are not wall understood. Holter recordings were used to develop and test algorithms for distinguishing between AF segments that are Non-terminating (N), Terminating within a second (T), and Soon terminating (within a minute, S). From rhe training set, the peak frequency ranges (mean±SD) were 4.8-6.0 (5.3±0.4) Hz for T 4.7- 6.4 (5.2±0.6) Hz for S, 4.8-7.3 (6.5±0.8) Hz for N. In 8 of IO T recordings there was a decrease in peak frequency from the penultimate to the ultimare second and in 8 of 10 T recordings there was a decrease in peak power. The last second had a lower peak frequency for T when compared to S of the same patient in 9 of IO patients. Between Nand T we correctly classified 20 of 20 from the training set and 29 of 30 from the test set. Bemeen S and T we correctly classified 20 of 20 from the training set and 20 of 20 from the test set.