Biomedical subjects

Douglas L Jones

Publications and source records attributed to Douglas L Jones.

13 recordsLinked to original sources

PubMed2006

Distant touch hydrodynamic imaging with an artificial lateral line.

Nearly all underwater vehicles and surface ships today use sonar and vision for imaging and navigation. However, sonar and vision systems face various limitations, e.g., sonar blind zones, dark or murky environments, etc. Evolved over millions of years, fish use the lateral line, a distributed linear array of flow sensing organs, for underwater hydrodynamic imaging and information extraction. We demonstrate here a proof-of-concept artificial lateral line system. It enables a distant touch hydrodynamic imaging capability to critically augment sonar and vision systems. We show that the artificial lateral line can successfully perform dipole source localization and hydrodynamic wake detection. The development of the artificial lateral line is aimed at fundamentally enhancing human ability to detect, navigate, and survive in the underwater environment.

Animals↗

PubMed2006

Somatic mutations in the connexin 40 gene (GJA5) in atrial fibrillation.

BACKGROUND: Atrial fibrillation is the most common type of cardiac arrhythmia and a leading cause of cardiovascular morbidity, particularly stroke. The cardiac gap-junction protein connexin 40 is expressed selectively in atrial myocytes and mediates the coordinated electrical activation of the atria. We hypothesized that idiopathic atrial fibrillation has a genetic basis and that tissue-specific mutations in GJA5, the gene encoding connexin 40, may predispose the atria to fibrillation. METHODS: We sequenced GJA5 from genomic DNA isolated from resected cardiac tissue and peripheral lymphocytes from 15 patients with idiopathic atrial fibrillation. Identified GJA5 mutations were transfected into a gap-junction-deficient cell line to assess their functional effects on protein transport and intercellular electrical coupling. RESULTS: Four novel heterozygous missense mutations were identified in 4 of the 15 patients. In three patients, the mutations were found in the cardiac-tissue specimens but not in the lymphocytes, indicating a somatic source of the genetic defects. In the fourth patient, the sequence variant was detected in both cardiac tissue and lymphocytes, suggesting a germ-line origin. Analysis of the expression of mutant proteins revealed impaired intracellular transport or reduced intercellular electrical coupling. CONCLUSIONS: Mutations in GJA5 may predispose patients to idiopathic atrial fibrillation by impairing gap-junction assembly or electrical coupling. Our data suggest that common diseases traditionally considered to be idiopathic may have a genetic basis, with mutations confined to the diseased tissue.

Adult↗

PubMed2006

Role of tumor necrosis factor-alpha in myocardial dysfunction and apoptosis during hindlimb ischemia and reperfusion.

OBJECTIVE: Peripheral vascular surgery involving limb ischemia/reperfusion is associated with tumor necrosis factor-alpha production and an increased risk of cardiac complications. The objective of this study was to investigate the role of tumor necrosis factor-alpha in myocardial apoptosis and dysfunction following hindlimb ischemia/reperfusion. DESIGN: Randomized perspective animal study. SETTING: Research laboratory. SUBJECTS: Adults male tumor necrosis factor-alpha(-/-) and littermate wild-type mice. INTERVENTIONS: Bilateral hindlimb ischemia/reperfusion was induced in wild-type and tumor necrosis factor-alpha(-/-) mice using tourniquet occlusion. After 2 hrs of hindlimb ischemia, the tourniquets were released, allowing reperfusion for 0.5-24 hrs. MEASUREMENTS AND MAIN RESULTS: In wild-type mice, hindlimb ischemia/reperfusion resulted in myocardial depression early during the reperfusion period (p < .05). These effects were temporally correlated with enhanced levels of myocardial and plasma tumor necrosis factor-alpha. All variables were restored to baseline levels by 24 hrs of reperfusion. Myocardial apoptosis, assessed by cell death enzyme-linked immunosorbent assay, terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling staining, and caspase-3 activity, was also significantly higher at 6 hrs of reperfusion (p < .05) but returned to baseline levels by 24 hrs. Interestingly, cardiac dysfunction and myocardial apoptosis were abolished in tumor necrosis factor-alpha mice subjected to the same degree of hindlimb ischemia/reperfusion as the wild-type mice. Treatment of etanercept restored cardiac function in wild-type mice. CONCLUSIONS: Tumor necrosis factor-alpha contributes significantly to myocardial dysfunction and apoptosis in hindlimb ischemia/reperfusion. Although a causal link between myocardial apoptosis and cardiac dysfunction is not established, our study does suggest that tumor necrosis factor-alpha may be a potential therapeutic target for cardiac injury in clinical situations involving prolonged remote ischemia/reperfusion.

Animals↗

PubMed2006

Asymptotically optimal blind estimation of multichannel images.

Optimal estimation of a two-dimensional (2-D) multichannel signal ideally decorrelates the data in both channel and space and weights the resulting coefficients according to their SNR. Many scenarios exist where the required second-order signal and noise statistics are not known in which the decorrelation is difficult or expensive to calculate. An asymptotically optimal estimation scheme proposed here uses a 2-D discrete wavelet transform to approximately decorrelate the signal in space and the discrete Fourier transform to decorrelate between channels. The coefficient weighting is replaced with a wavelet-domain thresholding operation to result in an efficient estimation scheme for both stationary and nonstationary signals. In contrast to optimal estimation, this new scheme does not require second-order signal statistics, making it well suited to many applications. In addition to providing vastly improved visual quality, the new estimator typically yields signal-to-noise ratio gains 12 dB or higher for hyperspectral imagery and functional magnetic resonance images.

Algorithms↗

PubMed2006

Beamformer performance with acoustic vector sensors in air.

For some time, compact acoustic vector sensors (AVSs) capable of sensing particle velocity in three orthogonal directions have been used in underwater acoustic sensing applications. Potential advantages of using AVSs in air include substantial noise reduction with a very small aperture and few channels. For this study, a four-microphone array approximating a small (1 cm3) AVS in air was constructed using three gradient microphones and one omnidirectional microphone. This study evaluates the signal extraction performance of one nonadaptive and four adaptive beamforming algorithms. Test signals, consisting of two to five speech sources, were processed with each algorithm, and the signal extraction performance was quantified by calculating the signal-to-noise ratio (SNR) of the output. For a three-microphone array, robust and nonrobust versions of a frequency-domain minimum-variance (FMV) distortionless-response beamformer produced SNR improvements of 11 to 14 dB, and a generalized sidelobe canceller (GSC) produced improvements of 5.5 to 8.5 dB. In comparison, a two-microphone omnidirectional array with a spacing of 15 cm yielded slightly lower SNR improvements for similar multi-interferer speech signals.

Air↗

PubMed2006

Classification of communication signals of the little brown bat.

Little brown bats, Myotis lucifugus, are known for their ability to echolocate and utilize their echolocation system to navigate, and locate and identify prey. Their echolocation signals have been characterized in detail but their communication signals are less well understood despite their widespread use during social interactions. The goal of this study was to develop an automatic classification algorithm for characterizing the communication signals of little brown bats. Sound recordings were made overnight on five individual male bats (housed separately from a large group of captive bats) for 7 nights, using a bat detector and a digital recorder. The spectral and temporal characteristics of recorded sounds were first analyzed and classified by visual observation of a call's temporal pattern and spectral composition. Sounds were later classified using an automatic classification scheme based on multivariate statistical parameters in MATLAB. Human- and machine-based analysis revealed five discrete classes of bat's communication signals: downward frequency-modulated calls, steep frequency-modulated calls, constant frequency calls, broadband noise bursts, and broadband click trains.

Algorithms↗

PubMed2005

En bloc exclusion of the pulmonary vein region in the pig using off pump, beating, intra-cardiac surgery: a pilot study of minimally invasive surgery for atrial fibrillation.

BACKGROUND: Off-pump, closed, beating heart, minimally-invasive surgery in patients with lone atrial fibrillation (AF) must be effective to become the preferred alternative to catheter ablation. Because of the inherent anatomical limitations of the epicardial access, we explored the feasibility of an intracardiac approach. METHODS: We report an acute study of en bloc, cryo-exclusion of the pulmonary vein region in 7 pigs. The left atrial appendage (LAA) was approached via a left thoracotomy. Electrodes were attached to the posterior wall of the left atrium (LPA) and right atrial appendage (RAA) for pacing and electrophysiological monitoring. A modified Surgifrost probe was introduced via the LAA and positioned using transesophageal (TEE) and intracardiac (ICE) echocardiographic guidance to generate encircling cryolesions (3 minutes, -105 degrees C) of the pulmonary vein region. RESULTS: A complete two-way block was achieved in 6 pigs and an incomplete block in 1. The excluded segment had very slow idiosyncratic rhythm or was electrically silent. In all pigs before isolation, sustained AF was inducible with the most rapid rhythms and fractionated electrograms recorded from the LA. While sustained AF was induced before exclusion, it was not after isolation in either the exclude or non-excluded segments. All tissue samples taken along the encircling cryolesions had transmural cryolesions on pathological examination. CONCLUSIONS: We conclude that off-pump, closed heart, beating, intracardiac AF surgery is feasible, reliable and can duplicate the accuracy and precision of the open-heart approach. However, further developments are needed to make this novel approach an alternative to current approaches for catheter ablation.

Animals↗

PubMed2004

Safety and feasibility of cryothermal ablation within the mid- and distal coronary sinus.

INTRODUCTION: The aim of this study was to assess the safety and feasibility of catheter-based cryothermal ablation lesions in the mid- and distal coronary sinus. METHODS AND RESULTS: Cryothermal ablation lesions were delivered using a 7-French catheter at the mid- (n = 13) and distal (n = 12) coronary sinus in 14 swine under general anesthesia. Lesions were delivered for 2 or 4 minutes in a 1:2 randomized ratio such that seven 2-minute lesions and eighteen 4-minute lesions were delivered to a maximum negative temperature of -70 degrees C. Integrity of the circumflex artery was assessed by angiography before and after each lesion application. In five animals, arterial Doppler flow velocity was continuously monitored and coronary flow reserve assessed. Histologic assessment of the left AV ring was made after a 48-hour survival period and lesions graded for depth and transmurality. Eighteen of 25 lesions were >3 mm deep: five of seven 2-minute lesions and thirteen of eighteen 4-minute lesions. Lesions were transmural in 18 of 25 cases. Two transmural lesions were limited in depth due to their epicardial position. One 2-minute mid-coronary sinus lesion was not found. Adherent thrombus was seen grossly in the coronary sinus at one site and only on microscopic examination in three other lesions. Angiography demonstrated no arterial spasm or thrombosis. Continuous-flow Doppler remained unchanged throughout lesion production. Coronary flow reserve was unchanged (1.7 +/- 0.8 preablation vs 1.7 +/- 1.0 postablation, P = 0.6). The media and intima were preserved in all cases. Necrosis of the adventitia was seen in one arterial segment. CONCLUSION: Catheter-based cryoablation can produce lesions in the musculature of the adjacent atrium and ventricle when accessed from the coronary sinus without significant injury to the coronary sinus or adjacent artery. This method has potential application as the ablation method of choice when such lesions are required.

Animals↗

PubMed2004

Overdetermined least-squares aberration estimates using common-midpoint signals.

As medical ultrasound imaging moves to larger apertures and higher frequencies, tissue sound-speed variations continue to limit resolution. In geophysical imaging, a standard approach for estimating near-surface aberrating delays is to analyze the time shifts between common-midpoint signals. This requires complete data-echoes from every source/receiver pair in the array. Unfocused common-midpoint signals remain highly correlated in the presence of delay aberrations; there is also tremendous redundancy in the data. In medical ultrasound, this technique has been impaired by the wide-angle, random-scattering nature of tissue. This has made it difficult to estimate azimuth-dependent aberration profiles or to harness the full redundancy in the complete data. Prefiltering the data with two-dimensional fan filters mitigates these problems, permitting highly overdetermined, least-squares solutions for the aberration profiles at many steering angles. In experiments with a tissue-mimicking phantom target and silicone rubber aberrators at nonzero stand-off distances from a one-dimensional phased array, this overdetermined, fan-filtering algorithm significantly outperformed other phase-screen algorithms based on nearest-neighbor cross-correlation, speckle brightness maximization, and common-midpoint signal analysis. Our results imply that there is still progress to be made in imaging with single-valued focusing operators. It also appears that the signal-to-noise penalty for using complete data sets is partially compensated by the overdetermined nature of the problem.

Algorithms↗

PubMed2004

Performance of time- and frequency-domain binaural beamformers based on recorded signals from real rooms.

Extraction of a target sound source amidst multiple interfering sound sources is difficult when there are fewer sensors than sources, as is the case for human listeners in the classic cocktail-party situation. This study compares the signal extraction performance of five algorithms using recordings of speech sources made with three different two-microphone arrays in three rooms of varying reverberation time. Test signals, consisting of two to five speech sources, were constructed for each room and array. The signals were processed with each algorithm, and the signal extraction performance was quantified by calculating the signal-to-noise ratio of the output. A frequency-domain minimum-variance distortionless-response beamformer outperformed the time-domain based Frost beamformer and generalized sidelobe canceler for all tests with two or more interfering sound sources, and performed comparably or better than the time-domain algorithms for tests with one interfering sound source. The frequency-domain minimum-variance algorithm offered performance comparable to that of the Peissig-Kollmeier binaural frequency-domain algorithm, but with much less distortion of the target signal. Comparisons were also made to a simple beamformer. In addition, computer simulations illustrate that, when processing speech signals, the chosen implementation of the frequency-domain minimum-variance technique adapts more quickly and accurately than time-domain techniques.

Algorithms↗

PubMed2003

Hybrid approach for minimally-invasive operative therapy of arrhythmias.

The failure of linear radiofrequency lesions to effectively replace operative therapy for atrial fibrillation (AF) is largely related to the inability to produce complete lines of conduction block. While pulmonary vein ablation enjoys success in patients with paroxysmal AF, patients with persistent AF and permanent AF fair less well. As such, a minimally-invasive, preferably "off pump" robotically-assisted procedure for complex arrhythmias like AF remains highly desirable. The shift to access from a mini-thoracotomy or port access will limit visualization and direct access to the ablation target. For the most part, the tools to overcome these limitations are not yet developed. As these develop, it is critical for the electrophysiologic effects of the delivered lesions to be assessed. With the development of non-fluoroscopic mapping systems and advances in imaging, a hybrid operative, electrophysiology (EP) suite can be equipped to provide full support for the surgeon and electrophysiologist. This will provide the opportunity to assess the efficacy and safety of ablation lesions, ideally with direct feedback to the surgeon. A hybrid approach will provide the opportunity to gain insights into the success and failure of specific ablation tools, approaches and lesions. This step will be crucial in understanding why specific procedures ultimately fail to cure AF and other complex arrhythmias.

Arrhythmias, Cardiac↗

PubMed2003

Blind estimation of reverberation time.

The reverberation time (RT) is an important parameter for characterizing the quality of an auditory space. Sounds in reverberant environments are subject to coloration. This affects speech intelligibility and sound localization. Many state-of-the-art audio signal processing algorithms, for example in hearing-aids and telephony, are expected to have the ability to characterize the listening environment, and turn on an appropriate processing strategy accordingly. Thus, a method for characterization of room RT based on passively received microphone signals represents an important enabling technology. Current RT estimators, such as Schroeder's method, depend on a controlled sound source, and thus cannot produce an online, blind RT estimate. Here, a method for estimating RT without prior knowledge of sound sources or room geometry is presented. The diffusive tail of reverberation was modeled as an exponentially damped Gaussian white noise process. The time-constant of the decay, which provided a measure of the RT, was estimated using a maximum-likelihood procedure. The estimates were obtained continuously, and an order-statistics filter was used to extract the most likely RT from the accumulated estimates. The procedure was illustrated for connected speech. Results obtained for simulated and real room data are in good agreement with the real RT values.

Acoustics↗

PubMed2002

Efficient three-dimensional imaging from a small cylindrical aperture.

Small-diameter cylindrical imaging platforms, such as those being considered in the development of in vivo ultrasonic microprobes, pose unique image formation challenges. The curved apertures they provide are incompatible with many of the commonly used frequency-domain synthetic aperture imaging algorithms. At the same time, their frequently small diameters place limits on the available aperture and the angular resolution that may be achieved. We obtain a three-dimensional, frequency-domain imaging algorithm for this geometry by making suitable approximations to the point spread function for wave propagation in cylindrical coordinates and obtaining its Fourier transform by analogy with the equivalent problem in Cartesian coordinates. For the most effective use of aperture, we propose using a focused transducer to place a virtual source a short distance from the probe. The focus is treated as a diverging source by the imaging algorithm, which then forms images on deeper cylindrical shells. This approach retains the simplicity and potential angular resolution of a single element, yet permits full use of the available probe aperture and a higher energy output. Computer simulations and experimental results using wire targets show that this imaging technique attains the resolution limit dictated by the operating wavelength and the transducer characteristics.

Computer Simulation↗