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Search Results: 1 - 10 of 468007 matches for " Alistair A Young "
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Evaluation of left ventricular torsion by cardiovascular magnetic resonance
Young Alistair A,Cowan Brett R
Journal of Cardiovascular Magnetic Resonance , 2012, DOI: 10.1186/1532-429x-14-49
Abstract: Recently there has been considerable interest in LV torsion and its relationship with symptomatic and pre-symptomatic disease processes. Torsion gives useful additional information about myocardial tissue performance in both systolic and diastolic function. CMR assessment of LV torsion is simply and efficiently performed. However, there is currently a wide variation in the reporting of torsional motion and the procedures used for its calculation. For example, torsion has been presented as twist (degrees), twist per length (degrees/mm), shear angle (degrees), and shear strain (dimensionless). This paper reviews current clinical applications and shows how torsion can give insights into LV mechanics and the influence of LV geometry and myocyte fiber architecture on cardiac function. Finally, it provides recommendations for CMR measurement protocols, attempts to stimulate standardization of torsion calculation, and suggests areas of useful future research.
Recovery of Myocardial Kinematic Function without the Time History of External Loads
Heye Zhang,Bo Li,Alistair A. Young,Peter J. Hunter
EURASIP Journal on Advances in Signal Processing , 2010, DOI: 10.1155/2010/310473
Abstract: A time-domain filtering algorithm is proposed to recover myocardial kinematic function using output-only measurements without the time history of external loads. The main contribution of this work is that the overall effect of all the external loads on the myocardium is treated as a random variable disturbed by the Gaussian white noise because the external loads of the myocardium are usually unknown in practical exercises. The kernel of our proposed algorithm is an iterative, multiframe, and sequential filtering procedure consisting of a Kalman filter and a least-squares filter. In our proposed implementation, the initial guess of myocardial kinematic function and residual innovation of all the state variables are first computed using a Kalman filter via state space equations only driven by the Gaussian white noise, and then the residual innovation is fed into a least-squares filter to estimate the total external loads of the myocardium. In the end, the initial guess of myocardial kinematic function is corrected using external loads provided by the least-squares filter. After the introduction of the whole structure of our algorithm, we demonstrate the ability of the framework on synthetic data and MR image sequences.
Applications and Comparisons of Four Time Series Models in Epidemiological Surveillance Data
Xingyu Zhang, Tao Zhang, Alistair A. Young, Xiaosong Li
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0088075
Abstract: Public health surveillance systems provide valuable data for reliable predication of future epidemic events. This paper describes a study that used nine types of infectious disease data collected through a national public health surveillance system in mainland China to evaluate and compare the performances of four time series methods, namely, two decomposition methods (regression and exponential smoothing), autoregressive integrated moving average (ARIMA) and support vector machine (SVM). The data obtained from 2005 to 2011 and in 2012 were used as modeling and forecasting samples, respectively. The performances were evaluated based on three metrics: mean absolute error (MAE), mean absolute percentage error (MAPE), and mean square error (MSE). The accuracy of the statistical models in forecasting future epidemic disease proved their effectiveness in epidemiological surveillance. Although the comparisons found that no single method is completely superior to the others, the present study indeed highlighted that the SVMs outperforms the ARIMA model and decomposition methods in most cases.
Accelerating global left-ventricular function assessment in mice using reduced slice acquisition and three-dimensional guide-point modelling
Alistair A Young, Debra J Medway, Craig A Lygate, Stefan Neubauer, Jürgen E Schneider
Journal of Cardiovascular Magnetic Resonance , 2011, DOI: 10.1186/1532-429x-13-49
Abstract: Five female C57Bl/6 mice 8 weeks post myocardial infarction induced by permanent occlusion of the left coronary artery, and six male control (un-operated) C57Bl/6 mice, were subject to CMR examination under isoflurane anaesthesia. Contiguous short axis (SAX) slices (1 mm thick 7-9 slices) were obtained together with two long axis (LAX) slices in two chamber and four chamber orientations. Using a mathematical model of the heart to interpolate information between the available slices, GPM LV mass and volumes were determined using full slice (all SAX and two LAX), six slice (four SAX and two LAX) and four slice (two SAX and two LAX) analysis protocols. All results were compared with standard manual volumetric analysis using all SAX slices.Infarct size was 39.1 ± 5.1% of LV myocardium. No significant differences were found in left ventricular mass and volumes between the standard and GPM full and six slice protocols in infarcted mice (113 ± 10, 116 ± 11, and 117 ± 11 mg respectively for mass), or between the standard and GPM full, six and four slice protocols in control mice, (105 ± 14, 106 ± 10, 104 ± 12, and 105 ± 7 mg respectively for mass). Significant differences were found in LV mass (135 ± 18 mg) and EF using the GPM four slice protocol in infarcted mice (p < 0.05).GPM enables accurate analysis of LV function in mice with relatively large infarcts using a reduced six slice acquisition protocol, and in mice with normal/symmetrical left-ventricular topology using a four slice protocol.Genetically manipulated mouse models are useful for studying the genetic determinants of cardiac disease. Surgical and pharmacological interventions are routinely performed to evaluate disease and treatment in these mouse models. Cardiovascular magnetic resonance (CMR) has been shown to provide accurate and precise non-invasive measures of cardiac function in control and chronically infarcted mice [1-4]. Typically, contiguous short axis (SAX) slices are acquired covering the left vent
Development of a method for the measurement of primary cilia length in 3D
Taryn Saggese, Alistair A Young, Chaobo Huang, Kevin Braeckmans, Susan R McGlashan
Cilia , 2012, DOI: 10.1186/2046-2530-1-11
Abstract: Point spread functions and experimental resolutions were calculated from subresolution microspheres embedded in 3D agarose gels for both wide-field fluorescence and confocal laser scanning microscopes. The degree of axial smearing and spherical aberration was calculated from xy:xz diameter ratios of 3D image data sets of 4 μm microspheres that had undergone deconvolution and/or Gaussian blurring. Custom-made 18 and 50 μm fluorescent microfibers were also used as calibration objects to test the suitability of processed image sets for 3D skeletonization. Microfiber length in 2D was first measured to establish an original population mean. Fibers were then embedded in 3D agarose gels to act as ciliary models. 3D image sets of microfibers underwent deconvolution and Gaussian blurring. Length measurements within 1 standard deviation of the original 2D population mean were deemed accurate. Finally, the combined method of deconvolution, Gaussian blurring and skeletonization was compared to previously published methods using images of immunofluorescently labeled renal and chondrocyte primary cilia.Deconvolution significantly improved contrast and resolution but did not restore the xy:xz diameter ratio (0.80). Only the additional step of Gaussian blurring equalized xy and xz resolutions and yielded a diameter ratio of 1.02. Following image processing, skeletonization successfully estimated microfiber boundaries and allowed reliable and repeatable measurement of fiber lengths in 3D. We also found that the previously published method of calculating length from 2D maximum projection images significantly underestimated ciliary length.This study used commercial and public domain image processing software to rectify a long-standing problem of 3D microscopy. We have shown that a combination of deconvolution and Gaussian blurring rectifies optical distortions inherent in 3D images and allows accurate skeletonization and length measurement of microfibers and primary cilia that are ben
Feasibility of single breath-hold left ventricular function with 3 Tesla TSENSE acquisition and 3D modeling analysis
Alistair A Young, Brett R Cowan, Stefan O Schoenberg, Bernd J Wintersperger
Journal of Cardiovascular Magnetic Resonance , 2008, DOI: 10.1186/1532-429x-10-24
Abstract: Differences (standard minus accelerated protocol mean ± s.d.) and coefficients of variation (s.d. of differences as a percentage of the average estimate) were 7.5 ± 9.6 mL and 6% for end-diastolic volume (p = 0.035), 0.4 ± 5.1 mL and 7% for end-systolic volume (p = NS), 7.1 ± 8.1 mL and 9% for stroke volume (p = 0.022), 2.2 ± 2.8% and 5% for ejection fraction (p = 0.035), and -7.1 ± 6.2 g and 4% for LV mass (p = 0.005), respectively. Intra- and inter-observer errors were similar for both protocols (p = NS for all measures).These results suggest that clinically useful estimates of LV function can be obtained in a TSENSE accelerated single breath-hold reduced slice acquisition at 3T using 3D modeling analysis techniques.Although Cardiovascular Magnetic Resonance (CMR) imaging provides accurate assessment of left ventricular (LV) mass and volumes [1], the data acquisition is relatively lengthy compared with computed tomography or echocardiography. The standard protocol for CMR LV volume and mass calculation is steady-state free precession (SSFP) image acquisition in contiguous (or with a small inter-slice gap) short axis slices, each slice being acquired in a separate breath-hold, so as to cover the entire LV [2] from the apex through the base into the left atrium. The endocardial and epicardial contours of the LV are then semi-automatically defined in each slice at end-diastole and end-systole, followed by manual editing where required, and the LV volume and mass calculated by slice summation [3]. However, this protocol typically requires 10–15 minutes for image acquisition.Evaluation of ventricular function from a single breath-hold acquisition would be advantageous in cases where scan time is at a premium, for example where patient tolerance is poor, or where ventricular function is not the primary clinical goal but a rapid estimate of ventricular function would add clinical value. Also, rapid evaluation of ventricular function is required where transient effects ar
Comparative Study of Four Time Series Methods in Forecasting Typhoid Fever Incidence in China
Xingyu Zhang, Yuanyuan Liu, Min Yang, Tao Zhang, Alistair A. Young, Xiaosong Li
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0063116
Abstract: Accurate incidence forecasting of infectious disease is critical for early prevention and for better government strategic planning. In this paper, we present a comprehensive study of different forecasting methods based on the monthly incidence of typhoid fever. The seasonal autoregressive integrated moving average (SARIMA) model and three different models inspired by neural networks, namely, back propagation neural networks (BPNN), radial basis function neural networks (RBFNN), and Elman recurrent neural networks (ERNN) were compared. The differences as well as the advantages and disadvantages, among the SARIMA model and the neural networks were summarized and discussed. The data obtained for 2005 to 2009 and for 2010 from the Chinese Center for Disease Control and Prevention were used as modeling and forecasting samples, respectively. The performances were evaluated based on three metrics: mean absolute error (MAE), mean absolute percentage error (MAPE), and mean square error (MSE). The results showed that RBFNN obtained the smallest MAE, MAPE and MSE in both the modeling and forecasting processes. The performances of the four models ranked in descending order were: RBFNN, ERNN, BPNN and the SARIMA model.
Regional Heterogeneity in 3D Myocardial Shortening in Hypertensive Left Ventricular Hypertrophy: A Cardiovascular CMR Tagging Substudy to the Life Study  [PDF]
Robert W. W. Biederman, Alistair A. Young, Mark Doyle, Richard B. Devereux, Eduardo Kortright, Gilbert Perry, Jonathan N. Bella, Suzanne Oparil, David Calhoun, Gerald M. Pohost, Louis J. Dell’Italia
Journal of Biomedical Science and Engineering (JBiSE) , 2015, DOI: 10.4236/jbise.2015.83021
Abstract: Background: Increased relative wall thickness in hypertensive left ventricular hypertrophy (LVH) has been shown by echocardiography to allow preserved shortening at the endocardium despite depressed LV midwall circumferential shortening (MWCS). Depressed MWCS is an adverse prognostic indicator, but whether this finding reflects reduced global or regional LV myocardial function, as assessed by three-dimensional (3D) myocardial strain, is unknown. Methods and Results: Cardiac Magnetic Resonance (CMR) tissue tagging permits direct evaluation of regional 3D intramyocardial strain, independent of LV geometry. We evaluated 21 hypertensive patients with electrocardiographic LVH in the LIFE study and 8 normal controls using 3D MR tagging and echocardiography. Patients had higher MR LV mass than normals (116 ± 40 versus 63 ± 6 g/m2, P = 0.002). Neither echocardiographic fractional shortening (32 ± 6 versus 33% ± 3%), LVEF (63% versus 64%) or mean end-systolic stress (175 ± 27 versus 146 ± 28 g/cm2) were significantly different, yet global MWCS was decreased by both echocardiography (13.4 ± 2.8 versus 18.2% ± 1.5%, P < 0.001) and MR (16.8 ± 3.6 versus 21.6% ± 3.0%, P < 0.005). 3D MR MWCS was lower at the base versus apex (P = 0.002) in LVH and greater in lateral and anterior regions versus septal and posterior regions ( P < 0.001), contributing to the higher mean global MWCS by MR than echo. MR longitudinal strain was severely depressed in LVH patients (11.0 ± 3.3 versus 16.5% ± 2.5%, P < 0.001) and apical twist was increased (17.5 ± 4.3 versus 13.7 ± 3.7, P < 0.05). Importantly, both circumferential and longitudinal shortening correlated with LV relative wall thickness (R > 0.60, P = 0.001 for both). Conclusions: In patients with hypertensive LVH, despite normal LV function via echocardiography or CMR, CMR intramyocardial tagging show depressed global MWCS while 3D MR strain revealed marked underlying regional heterogeneity of LV dysfunction.
Explict-scales projections of the partitioned non-linear term in direct numerical simulation of the Navier-Stokes equation
David McComb,Alistair Young
Physics , 1998,
Abstract: In this paper we consider the properties of the internal partitions of the nonlinear term, obtained when a filter with a sharp cutoff is introduced in wavenumber space. We see what appears to be some degree of independence of the choice of the position of the cutoff wavenumber for both instantaneous and time-integrated partitioned nonlinearities. We also investigate the basic idea of an eddy-viscosity model for subgrid terms and have found that while phase modelling will be very poor, amplitude modelling can be far more successful.
Aortic valve stenotic area calculation from phase contrast cardiovascular magnetic resonance: the importance of short echo time
Kieran R O'Brien, Ruvin S Gabriel, Andreas Greiser, Brett R Cowan, Alistair A Young, Andrew J Kerr
Journal of Cardiovascular Magnetic Resonance , 2009, DOI: 10.1186/1532-429x-11-49
Abstract: 15 patients with moderate or severe AS, were studied with three different TEs (2.8 ms/2.0 ms/1.5 ms), in the main pulmonary artery (MPA), left ventricular outflow tract (LVOT) and 0 cm/1 cm/2.5 cm above the aortic valve (AoV). PC estimates of stroke volume (SV) were compared with CMR left ventricular SV measurements and PC peak velocity, VTI and AVA were compared with Doppler echocardiography. CMR estimates of AVA obtained by direct planimetry from cine acquisitions were also compared with the echoAVA.With a TE of 2.8 ms, the mean PC SV was similar to the ventricular SV at the MPA, LVOT and AoV0 cm (by Bland-Altman analysis bias ± 1.96 SD, 1.3 ± 20.2 mL/-6.8 ± 21.9 mL/6.5 ± 50.7 mL respectively), but was significantly lower at AoV1 and AoV2.5 (-29.3 ± 31.2 mL/-21.1 ± 35.7 mL). PC peak velocity and VTI underestimated Doppler echo estimates by approximately 10% with only moderate agreement. Shortening the TE from 2.8 to 1.5 msec improved the agreement between ventricular SV and PC SV at AoV0 cm (6.5 ± 50.7 mL vs 1.5 ± 37.9 mL respectively) but did not satisfactorily improve the PC SV estimate at AoV1 cm and AoV2.5 cm. Agreement of CMR AVA with echoAVA was improved at TE 1.5 ms (0.00 ± 0.39 cm2) versus TE 2.8 (0.11 ± 0.81 cm2). The CMR method which agreed best with echoAVA was direct planimetry (-0.03 cm2 ± 0.24 cm2).Agreement of CMR AVA at the aortic valve level with echo AVA improves with a reduced TE of 1.5 ms. However, flow measurements in the aorta (AoV 1 and 2.5) are underestimated and 95% limits of agreement remain large. Further improvements or novel, more robust techniques are needed in the CMR PC technique in the assessment of AS severity in patients with moderate to severe aortic stenosis.Accurate assessment of lesion severity is central to surgical decision making for patients with aortic stenosis. Transthoracic echocardiographic assessment is typically used to make this assessment; however, poor image quality due to limited acoustic windows and the experie
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