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PubMedDate not supplied

Effect of background correction on left ventricular ejection fraction calculation through analysis of a simple cardiac model.

The dependence of the left ventricular ejection fraction calculation on the background correction in gated cardiac blood pool studies is examined by analyzing a simple cardiac model. It is shown that the ejection fraction is relatively insensitive to the background correction when an accurately determined variable region of interest is used, but that with a fixed region of interest the background correction must be accurately estimated. A similar ejection fraction-background correction relationship is obtained in the analysis of clinical cardiac data. Based on the cardiac model, two methods are suggested which, with further investigation and refinement, may lead to a more accurate and consistent technique for determining ejection fraction and background.

Heart↗
PubMedDate not supplied

Absolute volumetric blood flow measurements using dual-energy digital subtraction angiography.

In recent years, as a solution to the well-documented problems associated with visual interpretation of coronary arteriograms, more physiologic means of assessing coronary artery stenosis are being investigated. Absolute arterial blood flow assessed as a function of time can be a valuable aid in the analysis of functional significance of arterial lesions and obstructions. An absolute volumetric blood flow measurement technique using a motion immune dual-energy subtraction technique is being investigated, where the kVp and filtration are switched at 30 Hz. The low- and high-energy images are corrected for scatter and veiling glare before subtraction. In this technique, the absolute arterial blood flow is calculated by combining the videodensitometric analysis of spatial and temporal aspects concerning the contrast propagation through the arterial bed using tissue suppressed energy subtracted images. The blood flow measurement technique was validated using a pulsatile pump and a flow chamber imaged over a Humanoid chest phantom. A 20-MHz Doppler flow probe was used to validate the measurement of phasic volumetric blood flow. The measured (M) and known (K) mean blood flow for the entrance vessel technique and the videodensitometric calibration technique were related by M = 1.14K - 0.12 ml/s (r2 = 0.98) and M = 1.12K - 0.23 ml/s (r2 = 0.90), respectively. The results indicate that phasic volumetric blood flow can be measured using a CCD camera in conjunction with real time dual-energy subtraction.

Angiography, Digital Subtraction↗
PubMed1995

Magnetic resonance imaging kappa-space segmentation using phase-encoding groups the accuracy of quantitative measurements of pulsatile flow.

The use of phase-encode grouping (PEG) allows acquisition of a complete cardiac cine in a single breath hold, eliminating respiratory artifacts and improving edge definition. One approach to quantitative magnetic resonance (MR) flow measurements in pulmonary, coronary, and renal arteries uses phase velocity mapping with a PEG, single breath-hold, cine technique. Phantom studies were designed to evaluate the accuracy of MR phase velocity mapping (MRV) with PEG in continuous and pulsatile flow measurements in small vessels. Experiments were performed on a 1.5-T MRI system and results were compared with those obtained by timed volume measurements and a transit-time ultrasound flowmeter. Flow velocity, pulsatile flow wave form, pulsing rate, and PEG size were varied. For continuous flow, MRV measured velocities correlated well with those calculated from timed volume measurements (r > 0.998) under mean spatial velocities ranging from 20-100 cm s-1. The temporal mean velocity difference between MRV and ultrasound flowmeter measurements was less than +/- 2.9 cms-1 under pulsatile flow conditions with PEG sizes of 5 or less, however, the mean velocity difference was > 7 cm s-1 for PEG sizes of 8 or more. Accurate MR velocity measurement with PEG in small vessels under conditions of pulsatile flow is possible if an appropriate PEG size is selected.

Artifacts↗
PubMed1999

Quantitative angiographic blood-flow measurement using pulsed intra-arterial injection.

A technique for quantitative blood-flow measurement using a novel pulsed injection of radiographic contrast agent is reported. A pressurized source of contrast agent is interrupted by a rotary valve at rates ranging from 1 to 30 Hz, producing well-defined boli at the end of a catheter. The position of these boli can be recorded by a digital radiographic system and analyzed by one of several previously reported techniques, to produce quantitative measurements of blood velocity and flow rate throughout the cardiac cycle. The contrast-agent flow wave form produced by the pulsed injector has been measured with an electromagnetic flow meter, for driving pressures ranging from 600 to 1500 kPa. Excellent modulation of the contrast agent is observed for injection frequencies up to 20 Hz, through catheters up to 100 cm in length. Preliminary in vitro angiographic flow measurements have been performed using an x-ray image intensifier, coupled to a linear photodiode array as the digital detector. Both constant flow and pulsatile human blood-flow wave forms were simulated within a 6.4-mm-diam straight tube and monitored with an electromagnetic flow meter. These experiments indicate that the pulsed injector can be used to provide estimates of arterial blood flow over the entire cardiac cycle (including reverse flow), to within about +/-11%, following injection of less than 10 ml of iodinated contrast agent.

Angiography, Digital Subtraction↗
PubMed2003

Noncontact ultrasound stimulated optical vibrometry study of coupled vibration of arterial tubes in fluids.

Coupled vibration of arterial tubes is analyzed with the wave propagation approach and first-order shear deformation theory. Both the interior and exterior fluids are considered as compressible so that acoustic waves can be generated and propagated in the fluids. Results obtained using the theory have been evaluated against those available in the literature and the agreement has been found to be good. The theory can be used for future research on the vibration and acoustics of arterial walls. Vibration experiments were carried out on a silicone rubber tube in a water tank with a novel ultrasound stimulated optical vibrometry system. This system uses the radiation force of ultrasound to vibrate the tube at low frequency and records the resulting response by a laser vibrometer. Both the excitation and measurement are remote and noncontact. The silicone rubber tube was chosen because it has mechanical properties close to those of arteries. The fundamental frequency is well excited by the radiation force and measured with the laser. The measured fundamental frequency is in good agreement with the present theory.

Arteries↗
PubMed2003

A physiologically based approach for the estimation of recirculatory parameters.

Indicator dilution studies are used to provide estimates for several physiological parameters such as cardiac output as well as intra- and extravascular volumes. This study introduces a novel technique for the estimation of recirculatory parameters. A mathematical model based on a dispersion-convection partial differential equation (PDE), derived from the fractal geometry of the vascular tree and the hydrodynamics of the blood flow, is used to describe the spatiotemporal profile of tracers in the circulatory system. Initially, the equation is fitted to concentration-time (C,t) data of a tracer to derive the parameter estimates of the model equation; in a subsequent step, these estimates along with appropriate changes of the parameters of the PDE are used to generate the early concentration-time profile of a hypothetical appropriate tracer without recirculation. Thus, the area under the concentration-time curve of the first passage of the tracer is calculated and used for the estimation of various physiological parameters, including cardiac output, miscellaneous partial blood volumes, and the corresponding mean transit times. The procedure was applied successfully to literature data of various tracers from humans and dogs.

Animals↗
PubMed1964

PHASE SEPARATION IN SUSPENSIONS FLOWING THROUGH BIFURCATIONS: A SIMPLIFIED HEMODYNAMIC MODEL.

In the laminar flow of a suspension of neutrally buoyant spheres through a bifurcation, intended as a simplified macroscopic model of the flow of blood, the concentration in the side branch is generally lower than in the main branch, and is affected primarily by the ratio of discharges in the two branches, the concentration up-stream, and by the branch size.

Blood Circulation↗
PubMed2001

Development and validation of a Bayesian index for predicting major adverse cardiac events with percutaneous transluminal coronary angioplasty.

OBJECTIVE: To create a risk model for predicting major adverse complicating events of percutaneous transluminal coronary angioplasty (PTCA), and to test the accuracy of the model on a prospective cohort of patients SETTING: Tertiary cardiac centre METHODS: Available software can predict probabilities of events using Bayes's theorem. To establish the accuracy of these predictive tools, a Bayes table was created to evaluate major adverse complicating events (MACE)-death, emergency coronary artery bypass grafting (CABG), or Q wave infarct occurring during the in-patient episode-on the first 1500 patients in the department PTCA database (development group); the predictive value of this model was then tested with the subsequent 1000 patients (evaluation group). The following probabilities were assessed to determine their association with MACE: age, sex, left ventricular function, American Heart Association lesion morphology classification, cardiogenic shock, previous CABG, diabetes, hypertension, multivessel PTCA. MAIN OUTCOME MEASURES: To establish the discriminatory ability of the predictive index, calibration plots and receiver operating characteristic (ROC) curves were obtained to compare the development and evaluation groups. RESULTS: The ROC curve plotted to determine the discriminatory value of the Bayesian table created from the development group (n = 1500) in predicting MACE in the evaluation group (n = 1000) showed a moderately predictive area under the curve of 0.76 (SEM 0.07). This predictive accuracy was confirmed with separately constructed calibration plots. CONCLUSIONS: Accurate predictions of MACE can be identified in populations undergoing percutaneous intervention. The database used allows operators to obtain consent from patients appropriately from their own experience rather than from other published data. If a national PTCA database existed along similar lines, individual operators and interventional centres could compare themselves with nationally available data.

Age Factors↗
PubMed1985

Left ventricular volume and ejection fraction determined by gated blood pool emission tomography.

Electrocardiogram gated single photon emission computed tomography of the intracardiac blood pools is a recent development that involves the acquisition of images in multiple projections after in vivo erythrocyte labelling with technetium-99m and reconstruction of these images into tomographic sections in any desired plane. The technique was used in 25 subjects to measure left ventricular volume, by summing the areas of the ventricle in each of the tomographic sections, and the results compared with those using a counts based (non-geometric) technique from planar radionuclide ventriculography. Endocardium was defined with the aid of a contour at 43% of maximum left ventricular counts, and this contour was validated for a left ventricular phantom. Correlation between tomographic and counts based left ventricular volume was close. Similarly, ejection fraction correlated well. The technique is therefore an accurate method for determining left ventricular volume and ejection fraction, avoiding the assumptions about shape made by other geometric methods.

Cardiac Output↗
PubMed1992

Reappraisal of the coupling interval of ventricular extrasystoles as an index of ectopic mechanisms.

OBJECTIVE: A mathematical model of modulated ventricular parasystole based on the relation between the coupling interval and the preceding RR interval was developed in an attempt to distinguish between parasystolic automaticity and other mechanisms. MATHEMATICAL MODEL: The relation between the coupling interval and the preceding RR interval was examined by plotting the coupling interval of each extrasystole against the preceding RR interval (coupling interval/RR diagram). The coupling interval/RR diagrams obtained from simulations with various modulation modes suggested that the parasystolic mechanism was likely when the dots representing extrasystoles appeared as discrete clusters. In contrast, a linear horizontal accumulation of dots indicated a non-parasystolic mechanism. CLINICAL OBSERVATION: To verify the validity of the simulations, 24 hour electrocardiographic recordings from 60 patients with frequent ventricular extrasystoles (> 1000/day) were analysed to determine whether the extrasystoles showed intrinsic periodicity. Intrinsic periodicity indicative of a parasystolic mechanism was seen in 14 (93%) of 15 patients in whom the coupling interval/RR diagram was characteristic of a parasystolic mechanism. When the coupling interval did not change (variability < 200 ms) over a wide range of RR intervals (> 700 ms) intrinsic periodicity was never identified (0/17). Parasystolic automaticity was the likely mechanism in 11 of the remaining 28 patients (39.3%) in whom coupling interval/RR diagrams were not definitive. CONCLUSION: These data indicate that definite patterns of coupling interval/RR diagrams can be used to distinguish between parasystolic and non-parasystolic mechanisms.

Adolescent↗
PubMed1993

Contribution of the 24 hour electrocardiogram to the prediction of sudden coronary death.

BACKGROUND: Sudden coronary death is a major public health issue. The identification of patients at high risk should therefore be as efficient as possible. This study compares simple and more elaborate risk stratification procedures. METHODS: Risk functions for the prediction of sudden death were determined in a population of 6693 consecutive patients who had 24 hour electrocardiography for various indications. The functions were based on the clinical and electrocardiographical data on 245 patients who died suddenly during 2 year follow up and 467 patients randomly drawn from the total study population. RESULTS: The model based on history (age, sex, myocardial infarction, congestive heart failure, palpitation, syncope, use of diuretics, and use of nitrates), 12 lead electrocardiography (major intraventricular conduction defect, T wave abnormality, and ST depression > or = 0.05 mV), and standard rhythm analysis of 24 hour electrocardiography (ventricular tachycardia, frequent premature atrial complexes, sinus tachycardia (> 150 min-1), and atrial fibrillation) was almost as efficient in the prediction of sudden death as extended models that also contained information from exercise testing, echocardiography, ventriculography, and computer-aided re-analysis of 24 hour electrocardiography (QT and RR interval variability). CONCLUSIONS: These results indicate that additional information from advanced function tests does little to increase the efficiency of prediction of sudden coronary death over that of tests based on history, the standard 12 lead electrocardiogram, and 24 hour electrocardiography.

Cohort Studies↗
PubMed2006

Wavelet-based estimation of hemodynamic response function from fMRI data.

We present a new algorithm to estimate hemodynamic response function (HRF) and drift components of fMRI data in wavelet domain. The HRF is modeled by both parametric and nonparametric models. The functional Magnetic resonance Image (fMRI) noise is modeled as a fractional brownian motion (fBm). The HRF parameters are estimated in wavelet domain by exploiting the property that wavelet transforms with a sufficient number of vanishing moments decorrelates a fBm process. Using this property, the noise covariance matrix in wavelet domain can be assumed to be diagonal whose entries are estimated using the sample variance estimator at each scale. We study the influence of the sampling rate of fMRI time series and shape assumption of HRF on the estimation performance. Results are presented by adding synthetic HRFs on simulated and null fMRI data. We also compare these methods with an existing method,(1) where correlated fMRI noise is modeled by a second order polynomial functions.

Bayes Theorem↗
PubMed2000

New currents in electrical stimulation of excitable tissues.

Electric fields can stimulate excitable tissue by a number of mechanisms. A uniform long, straight peripheral axon is activated by the gradient of the electric field that is oriented parallel to the fiber axis. Cortical neurons in the brain are excited when the electric field, which is applied along the axon-dendrite axis, reaches a particular threshold value. Cardiac tissue is thought to be depolarized in a uniform electric field by the curved trajectories of its fiber tracts. The bidomain model provides a coherent conceptual framework for analyzing and understanding these apparently disparate phenomena. Concepts such as the activating function and virtual anode and cathode, as well as anode and cathode break and make stimulation, are presented to help explain these excitation events in a unified manner. This modeling approach can also be used to describe the response of excitable tissues to electric fields that arise from charge redistribution (electrical stimulation) and from time-varying magnetic fields (magnetic stimulation) in a self-consistent manner. It has also proved useful to predict the behavior of excitable tissues, to test hypotheses about possible excitation mechanisms, to design novel electrophysiological experiments, and to interpret their findings.

Animals↗
PubMed2002

Biomechanical dynamics of the heart with MRI.

Magnetic resonance imaging (MRI) provides a noninvasive way to evaluate the biomechanical dynamics of the heart. MRI can provide spatially registered tomographic images of the heart in different phases of the cardiac cycle, which can be used to assess global cardiac function and regional endocardial surface motion. In addition, MRI can provide detailed information on the patterns of motion within the heart wall, permitting calculation of the evolution of regional strain and related motion variables within the wall. These show consistent patterns of spatial and temporal variation in normal subjects, which are affected by alterations of function due to disease. Although still an evolving technique, MRI shows promise as a new method for research and clinical evaluation of cardiac dynamics.

Heart↗
PubMed1988

Inferior vena cava filters: in vitro comparison of clot trapping and flow dynamics.

Using a flow model that simulated the inferior vena cava (IVC), the authors conducted an in vitro comparison of the Mobin-Uddin (MU), Kimray-Greenfield (KG), Amplatz spider (A), Günther basket (G), Simon nitinol (SN), and bird's nest (BN) filters. The following parameters were evaluated: clot-trapping capacity and flow dynamics, which included measurements of pressure gradients across filters and assessment of flow patterns. The MU, A, G, SN, and BN filters trapped an average of 80%-100% of small clots and 100% of large clots. The KG filter, in a central position, trapped 0%-10% of small clots and 60%-100% of larger clots. In the eccentric position, the KG filter trapped only 20% of all clots. The BN and SN filters showed the least flow turbulence. Moderate turbulence was observed with the G and KG filters, while the MU and A filters showed marked turbulence. The current standard KG filter allowed the passage of small and large clots. When specific parameters were considered--such as clot-trapping capacity and flow-dynamic performance--the BN, SN, and G IVC filters were superior to the other filters that were tested.

Filtration↗
PubMed1989

Hepatic artery model for evaluating the distribution of intraarterial chemotherapy infusion: nonpulsed versus pulsed infusions.

The effect of a commercially available pulsatile slow-infusion system on the degree of infusate mixing and distribution was assessed in a life-size glass model of the hepatic arterial system. The authors determined, both visually and quantitatively, the mixing homogeneity of a low-flow infusion (1.4 mL/min) of red dye through a side-hole catheter (2.5 F outer diameter) into pulsatile flow (300 mL/min) of a fluid with the same viscosity as blood. When comparing nonpulsed versus pulsed infusion techniques, the authors found that the pulsatile infusion system did not significantly improve the inhomogeneity of dye distribution in the 16 hepatic arterial branches. The results of this in vitro study suggest that a pulsatile infusion system that uses low pulse velocities without regard for cardiac cycle is less than optimal and does not significantly improve drug mixing at the standard slow infusion rates. Moreover, as potential new intraarterial delivery systems are developed to improve drug mixing, in vitro models may be the most useful means of initially evaluating their efficacy.

Hepatic Artery↗
PubMed1991

US-assisted aspiration thrombectomy: in vitro investigations.

The authors describe the use of a new ultrasound (US)-aspiration thrombectomy technique. An oscillating US probe was inserted into a thin-walled, large-bore aspiration catheter. Experiments tested the ability of the new device and other catheter combinations to remove clot material from a Petri dish, as well as from small and large vessel models made of silicone and glass tubes, respectively. Results of the experiments demonstrated that an oscillating 1.0-mm US probe inserted into an aspiration catheter (7-9 F in diameter) promoted clot fragmentation and allowed continuous aspiration of thrombi of any size. When compared with simple large-bore catheter aspiration and with mechanical fragmentation by means of a US probe within a catheter that was flushed to cool the probe, US-assisted aspiration thrombectomy demonstrated significantly better results for percutaneous transcatheter removal of fresh thrombi.

Equipment Design↗
PubMed1991

Quantification of vascular stenosis with color Doppler flow imaging: in vitro investigations.

The accuracy of quantifying the degree of vascular stenosis with color Doppler flow imaging (7.5-MHz, linear array system) was determined in an experimental study carried out on six concentric and five eccentric model stenoses (cross-sectional area reduction, 13.4%-93.8%). The measurements were made with use of pulsatile flow at four different flow rates (70.8-339.0 mL/min). The degree of stenosis was calculated from the ratio of prestenotic to intrastenotic flow velocity. The most exact measurement of the degree of stenosis could be achieved with Doppler spectral analysis by determining the maximum peak systolic velocity (r = .994, y = 0.98x - 3.2). With the velocity values derived only from the color-coded image, it was also possible to find the most exact degree of stenosis (r = .995, y = 0.99x - 2.9). For quantification of stenosis, pre- and intrastenotic Doppler spectral analysis is no longer necessary if the stenosis can be imaged sufficiently with color Doppler.

Blood Flow Velocity↗