J.H. McClellan

Georgia Institute of Technology, Atlanta, Georgia, United States

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Publications (236)328.56 Total impact

  • Kyle R. Krueger, James H. McClellan, Waymond R. Scott
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    ABSTRACT: Ground-penetrating radar (GPR) is used to image and detect subterranean objects, for example, in landmine detection. Although full 3-D inversion of GPR measurements is possible for simple algorithms such as backprojection, it is impractical when using more advanced algorithms that involve $ell_1$-minimization. Many of the algorithms used for GPR imaging involve the storage, or online generation, of a huge dictionary matrix created from discretizing a high-dimensional nonlinear model. This parametric model includes all the target features that need to be extracted, including 3-D location, object orientation, and target type. As more parameters are added to the model, the dimensionality increases. If uniform sampling is done over high-dimensional parameter space, the size of the dictionary and the complexity of the inversion algorithms rapidly grow, exceeding the capability of real-time processors. This paper shows that strategic structuring of the dictionary, which takes advantage of translational invariance in the model, can reduce the dictionary storage by several orders of magnitude and exploit the fast Fourier transform for fast computation of previously highly impractical, bordering on impossible, 3-D GPR imaging problems.
    IEEE Transactions on Geoscience and Remote Sensing 06/2015; 53(7):1-12. DOI:10.1109/TGRS.2015.2388786 · 2.93 Impact Factor
  • Mu-Hsin Wei, Waymond R. Scott, James H. McClellan
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    ABSTRACT: Recent developments in the estimation of the discrete spectrum of relaxation frequencies (DSRFs) has opened doors to more robust subsurface target discrimination using electromagnetic induction measurements. In particular, a nonnegative least squares DSRF (NNLSQ-DSRF) estimation method has been shown to be robust and free from parameter tuning. In this letter, we propose an adaptive prefiltering process to complement the NNLSQ-DSRF where we attempt to linearly combine measurements and produce a filtered signal that is very likely to have a nonnegative DSRF, as well as an enhanced signal-to-noise ratio. Using synthetic and field data, we demonstrate that the proposed adaptive prefilter can effectively produce signals with nonnegative DSRFs.
    IEEE Geoscience and Remote Sensing Letters 05/2015; 12(5):1018-1022. DOI:10.1109/LGRS.2014.2374165 · 1.81 Impact Factor
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    ABSTRACT: Cardiac computed tomography angiography (CTA) is a minimally invasive imaging technology for characterizing coronary arteries. A fundamental limitation of CTA imaging is cardiac movement, which can cause artifacts and reduce the quality of the obtained images. To mitigate this problem, current approaches involve gating the image based on the electrocardiogram (ECG) to predict the timing of quiescent periods of the cardiac cycle. This paper focuses on developing a foundation for using a mechanical alternative to the ECG for finding these quiescent periods: the seismocardiogram (SCG). SCG was used to determine beat-by-beat systolic and diastolic quiescent periods of the cardiac cycle for nine healthy subjects, and 11 subjects with various cardiovascular diseases. To reduce noise in the SCG, and quantify these quiescent periods, a Kalman filter was designed to extract the velocity of chest wall movement from the recorded SCG signals. The average systolic and diastolic quiescent periods were centered at 29% and 76% for the healthy subjects, and 33% and 79% for subjects with cardiovascular disease. Both inter- and intra-subject variability in the quiescent phases were observed compared to ECG-predicted phases, suggesting that the ECG may be a suboptimal modality for predicting quiescence, and that the SCG provides complementary data to the ECG.
    IEEE transactions on bio-medical engineering 03/2015; DOI:10.1109/TBME.2015.2411155 · 2.23 Impact Factor
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    ABSTRACT: Accurate knowledge of cardiac quiescence is crucial to the performance of many cardiac imaging modalities, including computed tomography coronary angiography (CTCA). To accurately quantify quiescence, a method for detecting the quiescent periods of the heart from retrospective cardiac computed tomography (CT) using a correlation-based, phase-to-phase deviation measure was developed. Retrospective cardiac CT data were obtained from 20 patients (11 male, 9 female, 33-74 yr) and the left main, left anterior descending, left circumflex, right coronary artery (RCA), and interventricular septum (IVS) were segmented for each phase using a semiautomated technique. Cardiac motion of individual coronary vessels as well as the IVS was calculated using phase-to-phase deviation. As an easily identifiable feature, the IVS was analyzed to assess how well it predicts vessel quiescence. Finally, the diagnostic quality of the reconstructed volumes from the quiescent phases determined using the deviation measure from the vessels in aggregate and the IVS was compared to that from quiescent phases calculated by the CT scanner. Three board-certified radiologists, fellowship-trained in cardiothoracic imaging, graded the diagnostic quality of the reconstructions using a Likert response format: 1 = excellent, 2 = good, 3 = adequate, 4 = nondiagnostic. Systolic and diastolic quiescent periods were identified for each subject from the vessel motion calculated using the phase-to-phase deviation measure. The motion of the IVS was found to be similar to the aggregate vessel (AGG) motion. The diagnostic quality of the coronary vessels for the quiescent phases calculated from the aggregate vessel (PAGG) and IVS (PIV S) deviation signal using the proposed methods was comparable to the quiescent phases calculated by the CT scanner (PCT). The one exception was the RCA, which improved for PAGG for 18 of the 20 subjects when compared to PCT (PCT = 2.48; PAGG = 2.07, p = 0.001). A method for quantifying the motion of specific coronary vessels using a correlation-based, phase-to-phase deviation measure was developed and tested on 20 patients receiving cardiac CT exams. The IVS was found to be a suitable predictor of vessel quiescence. The diagnostic quality of the quiescent phases detected by the proposed methods was comparable to those calculated by the CT scanner. The ability to quantify coronary vessel quiescence from the motion of the IVS can be used to develop new CTCA gating techniques and quantify the resulting potential improvement in CTCA image quality.
    Medical Physics 02/2015; 42(2):983. DOI:10.1118/1.4906246 · 3.01 Impact Factor
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    ABSTRACT: Long baseline microphone arrays, where the distance between single microphones is large, is a cost-effective method to monitor activity in a large region of interest. The high range between source and sensors in a long baseline setup, generally leads to low signal-to-noise ratios (SNR). This affect the performance of localization. This paper investigates how energy based localization (EBL) can be used for localization and tracking of both single and multiple acoustic sources, within a long baseline array. Least-Squares (LS) optimization have been used for EBL-based localization, however the localization performance is sensitive to low SNR. We propose a tracking scheme based on a cost reference particle filter (CRPF) to increase performance during low SNR. The CRPF is a new class of particle filters which is able to estimate the system state from the available observations without a priori knowledge of any probability density function. We present a modified cost function, for EBL based localization, which is incorporated in the CRPF framework to increase tracking performance during simulated wind gusts and background noise. The proposed method outperforms LS based localization in the case of low SNR.
    Applied Acoustics 01/2015; 87:38-45. DOI:10.1016/j.apacoust.2014.06.002 · 1.07 Impact Factor
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    ABSTRACT: As a measure of chest wall acceleration caused by cardiac motion, the seismocardiogram (SCG) has the potential to supplement the electrocardiogram (ECG) to more accurately trigger cardiac computed tomography angiography (CTA) data acquisition during periods of cardiac quiescence. The SCG was used to identify the systolic and diastolic quiescent periods of the cardiac cycle on a beat-by-beat basis and from composite velocity signals for nine healthy subjects. The cardiac velocity transmitted to the chest wall was calculated using a Kalman filter. The average systolic and diastolic quiescent periods were centered at 30% and 76%, respectively. Inter- and intra-subject variability of the quiescent phases with respect to the ECG was observed, suggesting that the ECG may be a suboptimal modality for predicting cardiac quiescence.
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    ABSTRACT: Experimental data measured at a field test site with a broadband electromagnetic induction (EMI) sensor are presented. The system is an improved version of the Georgia Tech EMI system developed over the past several years. The system operates over a 300 to one bandwidth and is more sensitive while being more power efficient than earlier systems. Data measured with the system will be presented with an emphasis on features in the data that can be used to separate metallic targets from the soil response and to discriminate between certain classes of metallic targets.
    SPIE Defense + Security; 05/2014
  • Lingchen Zhu, Chenchi Luo, James H. McClellan
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    ABSTRACT: Cognitive radio (CR) systems offer higher spectrum utilization by opportunistically allocating the unused spectrum from primary users to secondary users. For CR it is vital to perform fast and accurate spectrum sensing in a wideband and noisy channel. Cyclic feature detection performs well in signal detection and is also highly robust to noise uncertainty. However, it requires a high sampling rate when operating over a wideband channel. Based on the sparsity of the cyclic spectrum, compressive sampling technique can extend sparse reconstruction to its case. This paper develops a simpler cyclic spectrum recovery method based on random sampling and demonstrates faster and better performance. Recent research on discrete random sampling provides a new connection between sub-Nyquist sampling and aliasing as a noise floor that can be dynamically shaped by different distributions of sampling times. Practical analog-to-digital converters can implement these random sampling schemes. Thus, a reduced hardware complexity cyclic feature detector based on the reconstructed cyclic spectrum is proposed to identify the spectrum occupancy within the entire wideband.
    2013 IEEE Global Conference on Signal and Information Processing (GlobalSIP); 12/2013
  • Kyle Krueger, Waymond R. Scott, James H. McClellan
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    ABSTRACT: Dictionary matching techniques have been an e ective way to detect the location and orientation of buried targets using electromagnetic induction (EMI) sensors. Two problems with dictionary detection are that they require a large amount of computer storage to enumerate nine dimensions, and fine discretization of the parameter space must be used to reduce modeling error. The proposed method shrinks the dictionary size by five orders of magnitude, and reduces modeling error by directly solving for the 3×3 tensor model of the target. A robust lowrank matrix approximation algorithm has been implemented which can also account for directional insensitivities in the measurements.
    Proceedings of SPIE - The International Society for Optical Engineering 06/2013; DOI:10.1117/12.2018019 · 0.20 Impact Factor
  • Chenchi Luo, Lingchen Zhu, J.H. Mcclellan
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    ABSTRACT: This paper proposes a general structure for FIR filters with adjustable magnitude and phase responses controlled by a few parameters. The Farrow structure which uses one parameter to control the fractional delay of an FIR filter can be viewed as special case. A filter bank structure consisting of different types of linear phase differentiators forms the basis of the structure. The filter bank outputs are combined with coefficients derived from a polynomial expansion of the desired frequency response. The magnitude and phase responses are controlled by synthesizing the polynomial coefficients from the small set of control parameters. A new optimal polynomial approximation strategy is also proposed to better approximate the family of target frequency responses.
    Acoustics, Speech and Signal Processing (ICASSP), 2013 IEEE International Conference on; 01/2013
  • G.A. Krudysz, J.H. Mcclellan
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    ABSTRACT: In this paper, we describe an on-line learning platform that enables students to develop conceptual knowledge, organize related concepts around supporting resources, and test their conceptual knowledge and its organization through numerous practice problems. We present these ideas in the context of our ongoing web-based educational platform ITS which we have deployed since 2010 for an introductory Signal Processing course at Georgia Tech. Specifically, we discuss the addition of two new features: the “Concept Browser” and the “Resource Selector”. These tools provide a user interface that explicitly fosters a concept oriented learning environment.
    Acoustics, Speech and Signal Processing (ICASSP), 2013 IEEE International Conference on; 01/2013
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    ABSTRACT: Two novel methods for detecting cardiac quiescent phases from B-mode echocardiography using a correlation-based frame-to-frame deviation measure were developed. Accurate knowledge of cardiac quiescence is crucial to the performance of many imaging modalities, including computed tomography coronary angiography (CTCA). Synchronous electrocardiography (ECG) and echocardiography data were obtained from 10 healthy human subjects (four male, six female, 23-45 years) and the interventricular septum (IVS) was observed using the apical four-chamber echocardiographic view. The velocity of the IVS was derived from active contour tracking and verified using tissue Doppler imaging echocardiography methods. In turn, the frame-to-frame deviation methods for identifying quiescence of the IVS were verified using active contour tracking. The timing of the diastolic quiescent phase was found to exhibit both inter- and intra-subject variability, suggesting that the current method of CTCA gating based on the ECG is suboptimal and that gating based on signals derived from cardiac motion are likely more accurate in predicting quiescence for cardiac imaging. Two robust and efficient methods for identifying cardiac quiescent phases from B-mode echocardiographic data were developed and verified. The methods presented in this paper will be used to develop new CTCA gating techniques and quantify the resulting potential improvement in CTCA image quality.
    01/2013; 1:1900211-1900211. DOI:10.1109/JTEHM.2013.2291555
  • Chenchi Luo, J.H. Mcclellan
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    ABSTRACT: This paper proposes a new perspective on the relationship between the sampling and aliasing. Unlike the uniform sampling case, where the aliases are simply periodic replicas of the original spectrum, random sampling theory shows that the randomization of sampling intervals shapes the aliases into a noise floor in the sampled spectrum. New insights into both the Fourier random sampling problem and Compressive Sensing theory can be obtained using the theoretical framework of random sampling. This paper extends the theory of continuous time random sampling to deal with random discrete intervals generated from a clock. A key result is established to relate the discrete probability distribution of the sampling intervals to the power spectrum of the aliasing noise. Based on the proposed theory, a generic discrete random sampling hardware architecture is also proposed for sampling and reconstructing a class of spectrally sparse signals at an average rate significantly below the Nyquist rate of the signal.
    Acoustics, Speech and Signal Processing (ICASSP), 2013 IEEE International Conference on; 01/2013
  • K.R. Krueger, J.H. Mcclellan, W.R. Scott
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    ABSTRACT: Sensor array measurements can be inverted to image a region containing targets. The resulting amplitude image is usually interpreted as target strength versus location, but often the imaged amplitude is a function of more parameters than just the location. Sparse target regions can be imaged with dictionary based modeling which relies on enumeration of each parameter with a dense grid. With many parameters, the dictionary becomes too large, which leads to computational complexity issues. This paper shows how additional parameters, such as target orientation and symmetry, can be represented by a tensor matrix instead of a simple amplitude. Furthermore, the tensor can be treated as a continuous variable just like amplitude, which enables extraction of multiple parameters, while reducing the storage requirements of the dictionary, and reducing off-grid modeling error.
    Acoustics, Speech and Signal Processing (ICASSP), 2013 IEEE International Conference on; 01/2013
  • Chenchi Luo, Lingchen Zhu, J.H. Mcclellan
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    ABSTRACT: This paper presents a novel digital blind calibration method for time interleaved analog to digital converters (TIADCs). A simple cost function based on the cross-correlation of channel statistics is used to derive a steepest descent algorithm for the compensation of timing mismatch errors. Instead of calibrating the timing mismatches independently for each channel, only one adaptation channel needs to be calibrated within a closed loop. The calibration of the rest of the channels can be coordinated according to a scaling relationship established during an initialization stage. As a result, both the computational complexity and convergence speed of the proposed algorithm can be improved significantly with little loss in calibration performance.
    Acoustics, Speech and Signal Processing (ICASSP), 2013 IEEE International Conference on; 01/2013
  • Source
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    ABSTRACT: Objective: We present a Matlab-based tool to convert electrocardiography (ECG) information from paper charts into digital ECG signals. The tool can be used for long-term retrospective studies of cardiac patients to study the evolving features with prognostic value. Methods and procedures: To perform the conversion, we: 1) detect the graphical grid on ECG charts using grayscale thresholding; 2) digitize the ECG signal based on its contour using a column-wise pixel scan; and 3) use template-based optical character recognition to extract patient demographic information from the paper ECG in order to interface the data with the patients' medical record. To validate the digitization technique: 1) correlation between the digital signals and signals digitized from paper ECG are performed and 2) clinically significant ECG parameters are measured and compared from both the paper-based ECG signals and the digitized ECG. Results: The validation demonstrates a correlation value of 0.85-0.9 between the digital ECG signal and the signal digitized from the paper ECG. There is a high correlation in the clinical parameters between the ECG information from the paper charts and digitized signal, with intra-observer and inter-observer correlations of 0.8-0.9 (p <; 0.05), and kappa statistics ranging from 0.85 (inter-observer) to 1.00 (intra-observer). Conclusion: The important features of the ECG signal, especially the QRST complex and the associated intervals, are preserved by obtaining the contour from the paper ECG. The differences between the measures of clinically important features extracted from the original signal and the reconstructed signal are insignificant, thus highlighting the accuracy of this technique. Clinical impact: Using this type of ECG digitization tool to carry out retrospective studies on large databases, which rely on paper ECG records, studies of emerging ECG features can be performed. In addition, this tool can be used to potentially integrate digitized- ECG information with digital ECG analysis programs and with the patient's electronic medical record.
    01/2013; 1:1800107-1800107. DOI:10.1109/JTEHM.2013.2262024
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    ABSTRACT: Capacitive touch screens are ubiquitous in today's electronic devices. Improved touch screen responsiveness and resolution can be achieved at the expense of the touch screen controller analog hardware complexity and power consumption. This paper proposes an alternative compressive sensing based approach to exploit the sparsity of simultaneous touches with respect to the number of sensor nodes to achieve similar levels of responsiveness. It is possible to reduce the analog data acquisition complexity at the cost of extra digital computations with less total power consumption. Using compressive sensing, in order to resolve the positions of the sparse touches, the number of measurements required is related to the number of touches rather than the number of nodes. Detailed measurement circuits and methodologies are presented along with the corresponding reconstruction algorithm.
    09/2012; 2(3):639-648. DOI:10.1109/JETCAS.2012.2217033
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    ABSTRACT: A semi-automated method for analyzing cardiac quiescence of anatomical cardiac features from two-dimensional echocardiographic cine data is presented. The method utilizes both active contour and optical flow techniques for feature identification and tracking. A curvature-based potential surface was used in the active contour calculations to attract the contour to regions of inflection on the image surface rather than the standard gradient-based surface that attracts the contour to strong edges. After identifying the feature in each frame, the frame-to-frame correlation matrix of the feature was calculated with correlation values corresponding to how well the feature matched between frames. Therefore prolonged regions of high correlation correspond to periods of cardiac quiescence. The location and duration of these periods were automatically identified from the correlation matrix by finding the largest region around each time index with a mean correlation above a specified threshold. In parallel, the position of the feature was calculated for each frame by finding the centroid of the pixel locations inside the contour. From this trajectory, the magnitude of the two-dimensional velocity was calculated. These methods were used to analyze the quiescence of the interventricular septum from an apical four-chamber echocardiogram performed on a human subject. Correlation-derived quiescent phases were observed to coincide with periods of the cardiac cycle with minimal velocity magnitude.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:4071-4. DOI:10.1109/EMBC.2012.6346861
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    ABSTRACT: Seismocardiography (SCG), a representation of mechanical heart motion, may more accurately determine periods of cardiac quiescence within a cardiac cycle than the electrically derived electrocardiogram (EKG) and, thus, may have implications for gating in cardiac computed tomography. We designed and implemented a system to synchronously acquire echocardiography, EKG, and SCG data. The device was used to study the variability between EKG and SCG and characterize the relationship between the mechanical and electrical activity of the heart. For each cardiac cycle, the feature of the SCG indicating Aortic Valve Closure was identified and its time position with respect to the EKG was observed. This position was found to vary for different heart rates and between two human subjects. A color map showing the magnitude of the SCG acceleration and computed velocity was derived, allowing for direct visualization of quiescent phases of the cardiac cycle with respect to heart rate.
    IEEE transactions on information technology in biomedicine: a publication of the IEEE Engineering in Medicine and Biology Society 05/2012; 16(5):869-77. DOI:10.1109/TITB.2012.2198071 · 2.07 Impact Factor
  • Kyle Krueger, James H. McClellan, Scott, Waymond R., Jr
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    ABSTRACT: Compressive sensing (CS) techniques have shown promise for subsurface imaging applications using wideband sensors such as stepped-frequency ground-penetrating radars (GPR). Excellent images can be computed using the CS techniques. However, the problem size is severely limited for 3-dimensional imaging problems which seem to require an explicit representation matrix that involves six dimensions. This paper shows how the underlying propagation model leads to a block-Toeplitz structure in two of the dimensions which can be exploited to reduce both the storage and computational complexity. The reduction by three orders of magnitude in computational resources for the CS problem will make 3-dimensional imaging applications feasible.
    Proceedings of SPIE - The International Society for Optical Engineering 05/2012; DOI:10.1117/12.919582 · 0.20 Impact Factor

Publication Stats

2k Citations
328.56 Total Impact Points

Institutions

  • 1989–2015
    • Georgia Institute of Technology
      • • School of Electrical & Computer Engineering
      • • Center for Signal & Image Processing
      Atlanta, Georgia, United States
  • 2011
    • Emory University
      • Department of Radiology and Imaging Sciences
      Atlanta, Georgia, United States
  • 2009
    • Rice University
      • Department of Electrical and Computer Engineering
      Houston, TX, United States
  • 2000–2004
    • Clark Atlanta University
      • Department of Engineering
      Atlanta, Georgia, United States
  • 1999–2001
    • Georgia Tech Research Institute
      Atlanta, Georgia, United States
  • 1998
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1995–1998
    • Rose Hulman Institute of Technology
      • Department of Electrical and Computer Engineering
      Terre Haute, IN, United States
    • Atlanta Technical College
      Atlanta, Georgia, United States
    • Washington State University
      • School of Electrical Engineering and Computer Science
      Pullman, WA, United States
  • 1996
    • University of Westminster
      Londinium, England, United Kingdom
  • 1994
    • University of California, Berkeley
      • Department of Electrical Engineering and Computer Sciences
      Berkeley, MO, United States