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Date 8-11 Sept. 1996

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Displaying Results 1 - 25 of 185
  • Computers in Cardiology 1996

    Publication Year: 1996
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    Freely Available from IEEE
  • Separation of ventricular tachycardia from ventricular fibrillation using paired unipolar electrograms

    Publication Year: 1996 , Page(s): 1 - 4
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    In third-generation implantable antitachycardia devices, immediate defibrillation is necessary for ventricular fibrillation (VF) while lower-energy therapies convert many ventricular tachycardias (VTs). Precise distinction between true VF and VT is required if tiered-therapy is to be effectively utilized. To separate VF from VT, this study employed a measurement to quantify the coherence between two unipolar electrograms from the same catheter, where incoherence between signals indicates VF. A normalized cross correlation (CC) measured similarity, and standard deviation (STD) and interquartile range (IQR) of the CC measured consistency for sinus rhythm (SR), VT, and VF passages from 10 patients. Patient-independent STD thresholds of 0.15-0.25 and IQR thresholds of 0.3-0.6 provided 100% sensitivity and 100% specificity. This method was able to successfully separate VF from coherent rhythms (SR,VT). Proper distinction of VT would allow defibrillation to be deferred for consideration of lower energy therapies, providing significant energy savings. View full abstract»

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  • Fusion of intravascular ultrasound and biplane angiography for three-dimensional reconstruction of coronary arteries

    Publication Year: 1996 , Page(s): 5 - 8
    Cited by:  Papers (7)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (426 KB)  

    Typical three dimensional (3D) reconstruction techniques of coronary arteries from intravascular ultrasound (IVUS) have assumed that the artery was straight and disregarded the angular orientation of IVUS slices. The authors achieved accurate 3D reconstruction of coronary arteries by following the transducer in time with the aid of biplane angiograms. Simultaneously acquired IVUS images were then placed perpendicular to the transducer path. Angular orientation of the IVUS slices was determined by using the lumen outlines and the biplane contrast angiograms. Tracking the transducer eliminates the need for assisted pullback, making the procedure more accurate and suitable for clinical use. The reconstruction algorithm was evaluated for consistency using a self-validation scheme that created simulated angiograms, which were then compared with acquired angiograms. A good correlation (rep to 68% area overlap) was found between the two. View full abstract»

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  • Effect of long term physical training on heart rate variability

    Publication Year: 1996 , Page(s): 17 - 20
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    The purpose of this study was to investigate the influence of physical training on the autonomic nervous system in healthy subjects. The authors compared 28 trained athletes and 28 sedentary subjects and divided them into two age groups: 18 to 34 and 35 to 55 years of age. ECG was recorded during 2 minutes while the subjects were breathing periodically under metronome control. RR tachograms were obtained and heart rate variability (HRV) was calculated. In the younger subgroup (18-34 years of age) only the standard deviation of mean RR interval and the frequency content were significantly different. In the older subgroup (35-55 years of age), all measured parameters were significantly different. A clear peak around 0.083 Hz, in coherence with respiratory rate, was observed in athletes and was present to a much smaller amplitude in sedentary subjects. These results show that regular physical training enhances the synchronization between heart rate and respiratory frequency, with a more pronounced effect at a higher age. The fact that physical training has a distinct impact on HRV in healthy subjects, infers that exercising may be of value in the modification of cardiac autonomic activity in cardiac patients. View full abstract»

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  • Autonomic tone assessed by heart rate variability in uncomplicated coronary artery disease

    Publication Year: 1996 , Page(s): 21 - 24
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    Previous studies concerning heart rate variability (HRV) in uncomplicated coronary artery disease (CAD) show contradictory results. This is due in part to the inclusion of patients with previous infarction, poor left ventricular function, diabetes mellitus, hypertension or /spl beta/-blocker therapy in some of these studies. The authors performed HRV analysis in 44 consecutive patients with stable angina pectoris undergoing coronary angiography and classified them from single to three vessel disease. Patients with one of the features mentioned above were excluded. Twenty-three normal patients served as control group. No significant differences of the HRV parameters could be observed normals and CAD patients. It is concluded that HRV is not altered in uncomplicated CAD. View full abstract»

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  • Preprocessing heart rate variability data improves risk stratification in congestive heart failure

    Publication Year: 1996 , Page(s): 29 - 31
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    Ambulatory 24-hour heart rate variability (HRV) data were used to stratify thirty congestive heart failure (CHF) patients according to their risk of death. Eight of these patients subsequently died. A simple nonstationarity index (NSI) was used to sort the data from least to most stationary. Beginning with the most stationary segments, periodogram spectra were cumulatively estimated, and confidence intervals were also computed. Spectra were computed using only those segments which yielded narrower confidence intervals, and also using all the data segments. Spectral measures extracted included total spectral power and low to high frequency power ratio. A comparison between patients alive and deceased revealed that using the NSI improved the statistical significance of spectral measures. Thus preprocessing of HRV data prior to spectral analysis might provide better means of risk stratification among cardiac patients with subtle differences in spectral characteristics. View full abstract»

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  • Altered cardiorespiratory control in patients with severe congestive heart failure: a transfer function analysis approach

    Publication Year: 1996 , Page(s): 33 - 36
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (407 KB)  

    The role of respiration in controlling central venous return and cardiac output was investigated in 5 patients with congestive heart failure (CHF) before and after therapy and 7 controls. Transfer function analyses were performed to quantify respiratory sinus arrthymia (RSA), arterial baroreflex gain, and the mechanical influence of respiration, during spontaneous and random interval breathing. CHF patients had markedly reduced RSA and arterial baroreflex gain compared to controls, resulting in minimal HR variability at frequencies above 0.05 Hz. HR variability was preserved in 3/5 CHF patients at frequencies below 0.05 Hz, and was associated with periodic breathing and oscillations of systolic blood pressure (SBP) and central venous pressure (CVP), which improved with therapy. In addition, CHF subjects had alterations of the mechanical link between respiration and central venous pressure which were normalized in some patients by therapy. Transfer function analysis can provide insight into circulatory regulation and therapy effects in CHF patients. View full abstract»

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  • Lumen detection in human IVUS images using region-growing

    Publication Year: 1996 , Page(s): 37 - 40
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (515 KB)  

    To assess the health of arterial tissue in intravascular ultrasound (IVUS) images, detection of luminal borders is critical. The authors have enhanced two automated border detection schemes using region-growing based on inter-pixel gray-scale differences, components-labeling (CL) and dilation-erosion, and watershed segmentation (WS) to correct for leaked regions due to signal drop-out and strut artifacts. The two methods were evaluated using 8 IVUS images with and without calcium lesions. Shapes were quantitatively analyzed, and the cross-sectional lumen areas calculated from the two automated methods were compared with the areas from expert traced images. Algorithm execution times were also compared. Results: CL vs. expert traced had a mean area difference of 7 pixels (p>0.05), WS vs. expert traced had a mean area difference of 394 pixels (p<0.05), for the leaked images. Thus region-growing with CL accurately predicts luminal areas of the artery and corrects for luminal leaks better than WS. View full abstract»

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  • Nonlinear wavelet filter for intracoronary ultrasound images

    Publication Year: 1996 , Page(s): 41 - 44
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (395 KB)  

    The development of a noise reduction filter for intracoronary ultrasound (ICUS) images is very important for the accurate detection of both lumen-intima (LI) and media-adventitia (MA) boundaries. In this study, the authors apply a nonlinear wavelet soft thresholding algorithm to ICUS images in order to enhance the detection of these boundaries. Three significant benefits can be achieved from this filtering algorithm: (1) the reconstructed images from thresholded wavelet coefficients is noise-free in the sense that no spurious oscillations are introduced; (2) boundary information in the image is preserved; (3) the wavelet transform procedure, which carries the authors' low-pass filtering and decimation, forces the image statistics from Rayleigh toward Gaussian. To compare the performance of the soft-thresholding algorithm as a preprocessing filter with other commonly used filters including the median filter, a local statistic filter and a Gaussian smoothing filter, the authors applied a standard boundary detection algorithm to a common set of images after preprocessing with each of the filters. View full abstract»

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  • 3-D intracoronary ultrasound surface detection using the "thin-plate" model

    Publication Year: 1996 , Page(s): 49 - 52
    Cited by:  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (427 KB)  

    Reliable detection of the vessel and lumen surfaces in 3-D intracoronary ultrasound images (ICUS) could significantly enhance both the qualitative and quantitative assessment of coronary anatomy. The authors have developed and implemented a surface estimation method using the "thin-plate" model and compared these results to those obtained using a 2-D method in the individual frames of both synthetic and real image data sets. The 2-D and 3-D estimates in each image frame were compared to the known synthetic image contours using the mean square error (MSE). In these test cases, the MSE in 3-D was less than the MSE in the 2-D estimates indicating an improvement in accuracy over the individual 2-D estimates. This surface estimation strategy is accurate, efficient, and will facilitate the development of methods to more effectively visualize and assess coronary anatomy in three dimensions. View full abstract»

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  • ECG-gated ICUS image acquisition combined with a semi-automated contour detection provides accurate analysis of vessel dimensions

    Publication Year: 1996 , Page(s): 53 - 56
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (426 KB)  

    At present most systems used for three-dimensional (3D) reconstruction's of two-dimensional intracoronary ultrasound (ICUS) images are based on an image acquisition with a pull-back device which withdraws the catheter with a constant speed, not taking account of cardiac motion and coronary dynamics/pulsation. Cyclic changes of the vessel dimensions and the movement of the catheter inside the vessel result in artifacts and inaccuracies of quantitative analysis. Furthermore, most systems in use for this kind of analysis applications store the ICUS image data on video tape for off-line analysis, which results in quality loss. To overcome these limitations and to achieve a rapid on-line analysis without quality loss resulting from unnecessary A/D-conversions, ECG-gated acquisition and direct digitisation of ICUS images was performed on-line. View full abstract»

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  • Clinical testing of a dual chamber atrial tachyarrhythmia detection algorithm

    Publication Year: 1996 , Page(s): 57 - 60
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (429 KB)  

    Currently available implantable cardioverter-defibrillators (ICDs) treat ventricular tachyarrhythmias and bradyarrhythmias (VVI), and do not intentionally treat atrial tachyarrhythmias. The Medtronic AMD 7250 dual chamber ICD combines detection and therapy for atrial and ventricular tachyarrhythmias. The dual chamber sensing/pacing circuits and tachyarrhythmia detection algorithms in an external prototype of the AMD 7250 have been studied during human cardiac electrophysiologic (EP) studies and ICD implants at Mayo Clinic. No adverse interactions between sensing, pacing and tachyarrhythmia detection were observed. Atrial tachyarrhythmia detection was appropriate in 12/12 episodes of induced atrial fibrillation, 19/20 episodes of induced atrial flutter and 6/9 episodes of induced atrial tachycardia. Overall detection performance for non-1:1 atrial tachyarrhythmias was 97% (37/38 episodes). View full abstract»

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  • Samples above the median: a nonparametric method for intracardiac signal assessment

    Publication Year: 1996 , Page(s): 69 - 72
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    In this investigation, a nonparametric (distribution-free) detection scheme, Samples Above the Median (SAM), is devised as an arrhythmia discriminant for implantable cardioverter defibrillators which is highly sensitive and specific yet introduces no appreciable computational demand. No widely accepted probability density function (p.d.f.) for intracardiac electrogram signals has been determined. A nonparametric method does not utilize the p.d.f. SAM was tested on 30 patients each with documented episodes of normal sinus rhythm (NSR) and ventricular tachycardia (VT). SAM achieved an electrogram specificity of 0.992 (476/480) and an electrogram sensitivity of 0.981 (471/480). SAM achieved an arrhythmia sensitivity and specificity of 1 using a 12 of 16 (75%) electrograms per arrhythmia criterion. View full abstract»

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  • Detection of atrial activity from high voltage leads of implantable ventricular defibrillators

    Publication Year: 1996 , Page(s): 77 - 79
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    In this study, the authors examined the atrial activity content of high voltage (HV) lead signals of implantable cardioverter defibrillators (ICDs) during device implantation. They also attempted to detect atrial fibrillation (AFib) by analyzing these signals. They used a method that canceled ventricular and correlated atrial activity from the HV lead signals and measured frequency and amplitude distribution information to discriminate sinus rhythm and AFib segments. The results suggest that atrial activity is present in HV lead signals, and AFib detection can be achieved in many, but not all cases, using information currently available to ICDs. View full abstract»

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  • Bivariate spectral analysis of nonstationary cardiovascular variability series through cross Wigner distribution

    Publication Year: 1996 , Page(s): 81 - 84
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (391 KB)  

    The Wigner Ville distribution has many of the desirable features required for the spectral analysis of cardiovascular series during the transients of autonomic tests, but it is not able to obtain insight into the mutual relationships between the series, making power measurements from the spectra often unreliable. This work proposes the Cross Wigner Distribution (CWD) as a new time-variant bivariate spectral analysis method. The CWD is compared with an approach based on adaptive filtering in order to evaluate its reliability in detecting correlated components between cardiovascular series. View full abstract»

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  • Arterial pressure control during non-hypo/hypertensive changes in central venous volume: assessment with multivariate autoregressive modeling

    Publication Year: 1996 , Page(s): 85 - 88
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (423 KB)  

    To evaluate how small decreases and increases of central volume influence heart rate and arterial pressure control multivariate autoregressive techniques were used to quantify the interactions between respiration, RR interval and arterial blood pressure during random interval breathing, at 3 low levels of lower body negative pressure and 3 low levels of increased central volume. In addition to the classic spectral parameters for each signal, the algorithms were used to derive the closed-loop feedforward and feedback gains for the baroreflex and the effects of respiration on RR interval. With reductions of central volume below control, baroreflex and respiratory sinus arrhythmia gains were generally reduced, while with increases of volume above control, they increased only for the first two levels, and decreased at the highest volume. These findings indicate that reflex heart rate control is maximum with mild hypervolemia, and are consistent with the presence of the Bainbridge reflex in healthy humans. View full abstract»

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  • Do alpha-index and phenylephrine test provide similar measurements of baroreflex sensitivity in cardiac patients with chronic heart failure?

    Publication Year: 1996 , Page(s): 89 - 92
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (339 KB)  

    To verify whether the phenylephrine test (PHE) and spectral analysis (alpha-index) provide similar measures of baroreflex sensitivity in patients with chronic heart failure due to left ventricular dysfunction, the authors evaluated by both methods a group of 40 patients during rest and controlled breathing (CB). R-R interval (RR), blood pressure (BP) and respiration were recorded in both conditions (600 heart beats), and bivariate spectral analysis was carried out. The alpha-index was measured when the magnitude squared coherence (MSC) between RR variability and systolic BP variability was >0.5 in the low frequency (/spl alpha/LF) and high frequency (/spl alpha/HF) bands; the mean /spl alpha/ was also computed. PHE followed immediately, with at least 3 injections during rest and one during CB. /spl alpha/LF could not be measured during both rest and CB in 40% of patients. The PHE slope could not be found in 7% of patients during rest and in 10% during CB. Regression analysis of the PHE slope vs /spl alpha/LF (r=0.61), /spl alpha/ HF (r=0.63) and /spl alpha/(r=0.67) showed a weak correlation during rest. No correlation was found during CB. View full abstract»

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  • Effects of metronome breathing on the assessment of autonomic control using heart rate variability

    Publication Year: 1996 , Page(s): 97 - 100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (371 KB)  

    Analysis of Heart Rate Variability is a non-invasive quantitative tool to study the influence of the autonomic nervous system on the heart. Rapid variations in heart rate, related to breathing are primarily mediated by the vagal limb of the autonomic nervous system. The resulting variations in heart rate are usually referred to as respiratory sinus arrhythmia. Metronome breathing (MB) is often advocated to assess more accurately vagal control. However, the additional value of MB over SB has never been established. The authors studied the effect of MB (0.25 Hz) on HRV variables in 12 healthy male subjects under stable conditions using pharmacological autonomic blockade. During MB several variables showed a lower absolute value, however a strong correlation existed between variables computed during spontaneous breathing (SB) and MB. MB offers some, but no important advantages over spontaneous breathing. View full abstract»

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  • Heart rate variability system identification using different signal descriptors

    Publication Year: 1996 , Page(s): 101 - 104
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (375 KB)  

    Finding appropriate signal descriptors for identification of an unknown system linking spontaneous heart rate variability and other physiological signals is considered here. A new method is proposed and its results compared with other existing methods in frequency domain and by parametric analysis. It is also shown that nonlinear identification is not necessary if neurocardiovascular system modelling is required and the proposed method is employed. View full abstract»

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  • The accuracy and reproducibility of an algorithm to correct for geometric image distortion in quantitative coronary angiography

    Publication Year: 1996 , Page(s): 105 - 108
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (419 KB)  

    The authors have developed a method to correct for image distortion (so-called dewarp). The method models the distortion by a set of two-dimensional polynomials of which the degree is optimally adjusted. The model parameters are derived through imaging a cm-grid put against the image intensifier (II) input screen. The derived accuracy of the pixel size (scale factor) was better than 0.006% and the RMS length of the residuals was 0.03-0.05 mm for cine film and 0.04-0.09 mm for on-line video images. The reproducibility for a dewarped position was 0.01-0.04 mm for cine film and 0.04-0.07 mm for video images, depending on the II size (14/17/27 cm). The dewarped size of an object (vessel) reproduced between 0.04% and 0.11% for cine film and between 0.15% and 0.18% for video images, depending on the II size. The main source of variability turned out to be an unstable high-voltage of the electron optics in the II. View full abstract»

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  • Overestimation of stenosis severity by single plane geometric measurements

    Publication Year: 1996 , Page(s): 109 - 112
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    Degrees of stenosis (DS) obtained geometrically from the angiographic projection which shows the greatest apparent diameter reduction can be suspected of overestimating the lesion severity. In comparison, biplane measurements in more or less orthogonal projections should be more accurate. These points are, however, not quite trivial because the errors depend on the shapes of stenotic lumens and on the edge detection algorithms. To investigate these aspects, 29 lumens of different shapes were computer simulated. The results of the simulation were compared to data obtained in patients by measuring geometrically and densitometrically 25 stenoses in biplane coronary angiograms. The results of the simulation and the patient data agree with the initial expectations. View full abstract»

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  • Evaluation of the reliability of calculated 3D vascular trees and their alignment with other views

    Publication Year: 1996 , Page(s): 113 - 116
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (357 KB)  

    Accurate intra- and inter-patient quantitative analyses of the coronary vasculature will require accurate methods for determination of the 3D coronary tree as well as methods to relate these data to previously acquired vascular trees. The authors have developed methods for determination of the 3D coronary trees from biplane angiograms and for alignment of calculated 3D trees with previously acquired 2D projections. After alignment, the projected centerlines of the aligned 3D vasculature and those in the reference image were visually similar in shape and position. The variation in the average RMS difference between calculated and reference centerlines was 1.3 mm, indicating a high similarity between the shapes of the calculated and actual vessels. These results indicate that the 3D vascular structure reconstructed from two views is accurate and that previously calculated 3D trees can be aligned with previously acquired images. View full abstract»

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  • Computer assisted coronary intervention: 3D reconstruction and determination of optimal views

    Publication Year: 1996 , Page(s): 117 - 120
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (458 KB)  

    The authors propose a novel method for computer assisted coronary intervention. The 3D coronary arterial tree is first reconstructed based on a pair of angiograms acquired from single-plane or bi-plane systems at arbitrary orientations. With this 3D structure, the views of selected vessel segments with minimal vessel foreshortening and overlapping are determined in the form of a sequence of gantry angulations. A computer simulation confirmed the accuracy of 3D centerline reconstruction to within 2.5% error. To date 3D reconstruction have been completed in 20 RCA, 16 LCA, and 3 bypass grafts. With the proposed technique, coronary sizing can be optimized for lesion length. Practice interventions can be completed in this computer assisted process that should lead to more accurate, efficient, and safe coronary procedure. View full abstract»

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  • Electronic image archiving in the catheterization laboratory: multicenter comparison of enhanced optical storage with 1024/sup 2/ digital and 35 mm cine-film

    Publication Year: 1996 , Page(s): 121 - 124
    Cited by:  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (485 KB)  

    The authors developed a bi-directional 1249/625 lines converter, able to store and to replay high resolution (1249 lines) video images, from Component Record Video (CRV) Optical Laser (Analogue) Videodisks. Image quality was evaluated four ways: (1) The authors evaluated Quantitative Coronary Angiography (QCA) on standard coronary test phantoms using enhanced CRV storage images digitally processed and also compared 78 arterial measurements ranging 0.65 to 4.85 mm both front the digital hard disc (D) and the CRV optical disc (CRV), using the same QCA analytical package. No systematic over or underestimation occurred, the mean variability was inferior to 0.1 mm and results were similar to the results obtained in the literature from digitally stored images. (2) Outside experts compared 593 static images stored on CRV discs to the same images stored in 1024/sup 2/ digital format blinded to source of image. The four experts found no visual or medical difference in 98% of evaluated images and minor differences in the remainder. (3) 90 representatives from 63 institutions compared images from both a digital hard drive and the enhanced CRV optical (analogue) storage. During the test they were blinded as to the source of the images. The representatives found no difference in image resolution, quality diagnostic accuracy, and medical relevance. (4) Two of the experts also compared the enhanced CRV optically stored image to the image obtained on simultaneously recorded 35 mm cine film, and found the enhanced CRV stored image to be superior or similar, but never inferior to the film image. It is concluded that High-Resolution CRV storage represents a cost effective solution for excellent image quality equivalent to digitally stored images, permitting permanent electronic archiving inside the cath-lab, and allowing digital image processing and digital DICOM network and CD-ROM based image communication. View full abstract»

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  • Temporal and spatial summation of endocardial inverse solutions using a multielectrode probe

    Publication Year: 1996 , Page(s): 125 - 128
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (342 KB)  

    Localizing the sites of origin and identifying the mechanisms of arrhythmias are paramount to selecting appropriate pharmacological therapies or advancing nonpharmacological approaches for their management. The goal of the study was to develop and validate mathematical methods to reconstruct endocardial potentials (electrograms) and activation sequences from potential data measured with a noncontact multielectrode probe. A custom-made cylindrical probe was used to measure cavitary potentials in the canine intact left ventricle. The probe-cavity geometric model was determined using epicardial echocardiography. The boundary element method, combined with Tikhonov regularization, was used to compute the potentials at the endocardial surface. Endocardial electrograms were computed during paced rhythms and were in excellent agreement with directly-measured endocardial electrograms. View full abstract»

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