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Cardiac Cycle (cardiac + cycle)
Selected AbstractsEffect of reduced total blood volume on left ventricular volumes and kinetics in type 2 diabetesACTA PHYSIOLOGICA, Issue 1 2010S. Lalande Abstract Aim:, Although impaired left ventricular (LV) diastolic function is commonly observed in patients with type 2 diabetes, it remains unclear whether the impairment is caused by altered LV relaxation or changes in LV preload. The purpose of this study was to examine the influence of LV function and LV loading conditions on stroke volume in men with type 2 diabetes. Methods:, Cardiac magnetic resonance imaging scans were performed in eight men with type 2 diabetes and 11 non-diabetic men matched for age, weight and physical activity level. Total blood volume was determined with the Evans blue dye dilution technique. Results:, End-diastolic volume (EDV), the ratio of peak early to late mitral inflow velocity (E/A) and stroke volume were lower in men with type 2 diabetes than in non-diabetic individuals. Peak filling rate and peak ejection rate were not different between diabetic and non-diabetic individuals; however, men with type 2 diabetes had proportionally longer systolic duration than non-diabetic individuals. Heart rate was higher and total blood volume was lower in men with type 2 diabetes. The lower total blood volume was correlated with a lower EDV in men with type 2 diabetes. Conclusions:, Men with type 2 diabetes have an altered cardiac cycle and lower end-diastolic and stroke volume. A lower total blood volume and higher heart rate in men with type 2 diabetes suggest that changes in LV preload, independent of changes in LV relaxation or contractility, influence LV diastolic filling and stroke volume in this population. [source] An evaluation of a visual biofeedback intervention in dyslexic adultsDYSLEXIA, Issue 1 2005Elizabeth Liddle Abstract A prototype of a biofeedback system designed to treat dyslexia by improving heart-rate variability was evaluated in a single blind study of dyslexic adults. Treatment consisted of four 15 minute exposures to a visual display synchronized with either the participant's own cardiac cycle (intervention condition), or of a synthesized cardiac cycle (placebo condition). Repeated measures were made of picture naming speed, single word reading speed and accuracy, copying speed, heart-rate variability and performance on a lateralized visual temporal order judgement task. Small but significant improvements were found in reading and naming speed in the treatment group relative to the placebo group. No significant improvements were found in unspeeded reading measures. Results from heart-rate measures indicated that treatment had effected a shift in the ratio between parameters reflecting the influence of the sympathetic and parasympathetic autonomic nervous systems (ANS), respectively, in favour of the parasympathetic. In the temporal order judgement task, participants who received treatment showed a reduced level of overall improvement relative to that seen in those who received placebo, coupled with evidence of a shift in visual attention from left to right hemifield in their pattern of performance. The results are interpreted as indicating that the treatment induces a shift in autonomic balance in favour of the parasympathetic ANS, and that this shift is also reflected in increased efficiency of left cerebral hemisphere circuits implicated in the perceptual-motor processes required for naming and reading fluency. Conversely, it is also reflected in lower spatial awareness of peripheral visual stimuli, particularly those presented to left hemifield. Copyright © 2004 John Wiley & Sons, Ltd. [source] Left Ventricular Apical Thin Point Viewed with Two-Dimensional EchocardiographyECHOCARDIOGRAPHY, Issue 8 2009Guo Baosheng M.D. The aim of this study was to evaluate the usefulness of two-dimensional echocardiography in observing the left ventricular apical thin point (LVATP) and to view the change in thickness and width of the LVATP during the cardiac cycle. Transthoracic echocardiography was performed in 32 healthy adult volunteers to observe the LVATP in an apical three-chamber view. The width and thickness of the LVATP were measured at the end-diastole as well as at the end-systole. With two-dimensional echocardiography, the LVATP could be clearly shown. The width of the LVATP at the end-diastole and end-systole was 3.3 mm ± 1.4 mm versus 0.9 mm±0.4 mm, P < 0.001; the thickness of the LVATP at the end-diastole and end-systole was 1.7 mm ± 0.6 mm versus 1.8 mm ± 0.8 mm, P > 0.05. The LVATP can be viewed with two-dimensional echocardiography; the LVATP changes significantly in width during the cardiac cycle, whereas the thickness of the LVATP changes insignificantly. [source] A Comparison of Echocardiographic Techniques in Determination of Arterial Elasticity in the Pediatric PopulationECHOCARDIOGRAPHY, Issue 5 2009Michael Fahey M.D. Background: Many methods are used to measure arterial elasticity in children using echocardiography. There is no data to support the equivalence of the different techniques. The goal of this study was to evaluate the reproducibility of several techniques used to measure arterial elasticity using echocardiography. Methods: Aortic distension in two different sites (arterial distension) through the cardiac cycle was measured by (four) two-dimensional (2D) and M-mode echocardiographic techniques in 20 children without significant structural heart disease. These measurements combined with noninvasive blood pressure measurements were used to calculate arterial elastic indices. Arterial elasticity was expressed in terms of distensibility and stiffness. Data were collected by two sonographers and interpreted by two reviewers. Paired Student's t-test and Pitman's test for equality of variance for correlated observations were used to detect differences between different sonographers, different reviewers, and different techniques. Results: No significant difference in the measured elasticity between sonographers or reviewers was observed. There was a somewhat increased variance in two of the four techniques evaluated. There was no significant difference in elasticity measured using different techniques to evaluate the same arterial site, although a significantly decreased elasticity was noted from measurements taken in the proximal ascending aorta as compared with the distal ascending aorta. Conclusions: Many echocardiographic techniques produce reproducible measurements of arterial elasticity. There may be intrinsic differences in arterial elasticity between different segments of the ascending aorta, which have not been previously described in children with normal cardiac anatomy. Comparisons of data from separate studies must take these differences into account. [source] Assessment of Carotid Compliance Using Real Time Vascular Ultrasound Image Analysis in Marfan SyndromeECHOCARDIOGRAPHY, Issue 4 2009Anatoli Kiotsekoglou M.D. Background: Fibrillin-1 deficiency, dysregulated cytokine transforming growth factor-,, and increased collagen deposition related to fibrillin-1 gene mutations could predispose to impaired carotid compliance (CC) in Marfan syndrome (MFS). We sought to detect any alterations in CC using the vascular image analysis system (VIA). Methods and Results: Thirty-two MFS patients, 20 men and 12 women (mean age 34.2 ± 12.05 years), and 29 controls matched for age, sex, and body surface area (BSA) were recruited. The entire length of each carotid system was initially scanned longitudinally using a 14 MHz linear transducer. Then, a stereotactic clamp held the transducer in contact with the carotid artery. Arterial diameter changes during the cardiac cycle were recorded for 1 minute from both right (RCCA) and left common carotid arteries (LCCA) separately using the VIA system. RCCA and LCCA compliance and distensibility measurements were significantly reduced in MFS patients when compared to controls, P < 0.05. RCCA and LCCA intima-media thickness did not differ between patients and controls, P > 0.05. MFS diagnosis and age were associated with reduced CC in both carotid arteries after adjusting for variables such as, sex, BSA, heart rate, beta-blockade, intima-media thickness, and aortic root size. Conclusions: Our findings showed a reduction in CC in adult patients with MFS. This could be attributed to fibrillin-1 deficiency resulting in structural abnormalities in the carotid arterial wall. [source] Real Time Three-Dimensional Echocardiography Evaluation of Mitral Annular Characteristics in Patients with Myocardial HypertrophyECHOCARDIOGRAPHY, Issue 4 2008Fatih Yalçin M.D. It has been shown that systolic excursion of the mitral annulus (MA) correlates well with left ventricular (LV) systolic function. Evaluation of the complicated shape and dynamics of the mitral annulus, however, may require rigorous methodology. The aim of this study was to investigate differences in MA motion between hypertrophic cardiomyopathy (HCM) and left ventricular hypertrophy (LVH) patients due to hypertension or aortic stenosis using real time three-dimensional echocardiography (RT3DE). We studied 10 HCM, 10 LVH, and 10 controls. Mean MA area changes between early and late systole were 9.5 ± 4.3% in HCM, 26 ± 15% in LVH and 19 ± 10% in normal controls. MA apicobasal motion was 5.8 ± 4 mm in HCM, 11 ± 4 mm in LVH, and 13.6 ± 6 mm in normal controls. RT3DE with digital reconstruction of MA accurately display complicated MA geometry and dynamics during a cardiac cycle. Annular function in LVH was similar to that of the normal group while annular apicobasal motion and area changes were reduced in HCM. [source] Active Vegetations Can Be Differentiated from Chronic Vegetations by Visual Inspection of Standardized Two-Dimensional EchocardiogramsECHOCARDIOGRAPHY, Issue 2 2000PH.D., TAHIR TAK M.D. The ability to differentiate active from chronic valvular vegetations (VEGs) by digital image processing and by visual observation was evaluated in 18 patients with a clinical diagnosis of infective endocarditis (IE). Two-dimensional echocardiographic (2-DE) examinations were performed on all patients at diagnosis and after a mean period of 52 days. Two comparable images (active and chronic) from the same patient and in the same phase of the cardiac cycle were digitized, magnified, and displayed on a high resolution monitor. The mean pixel intensity (MPI) was 72 ± 14 in the active stage and 143 ± 23 in the chronic stage (P < 0.0001). The VEG size was 0.64 ± 0.15 cm2 in the active stage and decreased to 0.46 ± 0.17 cm2 in the chronic stage (P < 0.001). Two experienced echocar-diographers, who were blinded to the age of the VEGs, identified each echocardiographic image as active or chronic based on visual observation of density of the VEGs. The VEGs were correctly identified as active or chronic in 17 out of the 18 patients. In summary, although digital image processing of 2-DE may be useful, the density of VEGs assessed by visual inspection will help differentiate between active and chronic VEGs of IE. The standardization procedure at the time of the initial study and use of identical gain settings in subsequent studies are key factors in making this distinction. [source] Ventricular Fibrillation Induced by Stretch Pulse: Implications for Sudden Death Due to Commotio CordisJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 9 2006FRANK BODE M.D. Introduction: Nonpenetrating chest wall impact (commotio cordis) may lead to sudden cardiac death due to the acute initiation of ventricular fibrillation (VF). VF may result from sudden stretch during a vulnerable window, which is determined by repolarization inhomogeneity. Methods: We examined action potential morphologies and VF inducibility in response to sudden myocardial stretch in the left ventricle (LV). In six Langendorff perfused rabbit hearts, the LV was instrumented with a fluid-filled balloon. Increasing volume and pressure pulses were applied at different times of the cardiac cycle. Monophasic action potentials (MAPs) were recorded simultaneously from five LV epicardial sites. Inter-site dispersion of repolarization was calculated in the time and voltage domains. Results: Sudden balloon inflation induced VF when pressure pulses of 208,289 mmHg were applied within a window of 35,88 msec after MAP upstroke, a period of intrinsic increase in repolarization dispersion. During the pressure pulse, MAPs revealed an additional increase in repolarization dispersion (time domain) by 9 ± 6 msec (P < 0.01). The maximal difference in repolarization levels (voltage domain) between sites increased from 19 ± 3% to 26 ± 3% (P < 0.05). Earliest stretch-induced activation was observed near a site with early repolarization, while sites with late repolarization showed delayed activation. Conclusions: Sudden myocardial stretch can elicit VF when it occurs during a vulnerable window that is based on repolarization inhomogeneity. Stretch pulses applied during this vulnerable window can lead to nonuniform activation. Repolarization dispersion might play a crucial role in the occurrence of fatal tachyarrhythmias during commotio cordis. [source] Prenatal diagnosis of atrial septal aneurysmJOURNAL OF CLINICAL ULTRASOUND, Issue 1 2008Jeng-Hsiu Hung MD Abstract We report the prenatal diagnosis of fetal atrial septal aneurysm based on the observation of a fluttering flap in the left atrium. The aneurysm was associated with an interatrial communication. In a 4-chamber view, separate arms of the aneurysm could be seen contracting in and extending out in response to the fetal cardiac cycle, giving the fluttering appearance of a jellyfish. The aneurysm disappeared 1 month after birth with no complications. The findings in this case indicate that isolated atrial septal aneurysm is a natural transient phase of spontaneous closure of the foramen ovale during normal fetal development. © 2007 Wiley Periodicals, Inc. J Clin Ultrasound, 2008 [source] Artifact-reduced two-dimensional cine steady state free precession for myocardial blood- oxygen-level-dependent imagingJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2010Xiangzhi Zhou PhD Abstract Purpose: To minimize image artifacts in long TR cardiac phase-resolved steady state free precession (SSFP) based blood-oxygen-level-dependent (BOLD) imaging. Materials and Methods: Nine healthy dogs (four male, five female, 20,25 kg) were studied in a clinical 1.5 Tesla MRI scanner to investigate the effect of temporal resolution, readout bandwidth, and motion compensation on long repetition time (TR) SSFP images. Breath-held 2D SSFP cine sequences with various temporal resolutions (10,204 ms), bandwidths (239,930 Hz/pixel), with and without first-order motion compensation were prescribed in the basal, mid-ventricular, and apical along the short axis. Preliminary myocardial BOLD studies in dogs with controllable coronary stenosis were performed to assess the benefits of artifact-reduction strategies. Results: Shortening the readout time by means of increasing readout bandwidth had no observable reduction in image artifacts. However, increasing the temporal resolution in the presence of first-order motion compensation led to significant reduction in image artifacts. Preliminary studies demonstrated that BOLD signal changes can be reliably detected throughout the cardiac cycle. Conclusion: Artifact-reduction methods used in this study provide significant improvement in image quality compared with conventional long TR SSFP BOLD MRI. It is envisioned that the methods proposed here may enable reliable detection of myocardial oxygenation changes throughout the cardiac cycle with long TR SSFP-based myocardial BOLD MRI. J. Magn. Reson. Imaging 2010;31:863,871. ©2010 Wiley-Liss, Inc. [source] Cine cardiac imaging using black-blood steady-state free precession (BB-SSFP) at 3TJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2009Tamer A. Basha MSE Abstract Purpose To propose a new black-blood (BB) pulse sequence that provides BB cine cardiac images with high blood-myocardium contrast. The proposed technique is based on the conventional steady-state free precession (SSFP) sequence. Materials and Methods Numerical simulations of the Bloch equation were conducted to compare the resulting signal-to-noise ratio (SNR) to that of conventional BB imaging, including the effects of changing the imaging flip angle and heart rates. Simulation results were verified using a gel phantom experiment and five normal volunteers were scanned using the proposed technique. Results The new sequence showed higher SNR and contrast-to-noise ratio (CNR) (,100%) compared to the conventional BB imaging. Also, the borders of the left ventricle (LV) and right ventricle (RV) appear more distinguishable than the conventional SSFP. We were also able to cover about 80% of the cardiac cycle with short breath-hold time (,10 cardiac cycles) and with reasonable SNR and CNR. Conclusion Based on an SSFP conventional sequence, the new sequence provides BB cines that cover most of the cardiac cycle and with higher SNR and CNR than the conventional BB sequences. J. Magn. Reson. Imaging 2009;30:94,103. © 2009 Wiley-Liss, Inc. [source] 3D diffusion tensor MRI with isotropic resolution using a steady-state radial acquisitionJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2009Youngkyoo Jung PhD Abstract Purpose To obtain diffusion tensor images (DTI) over a large image volume rapidly with 3D isotropic spatial resolution, minimal spatial distortions, and reduced motion artifacts, a diffusion-weighted steady-state 3D projection (SS 3DPR) pulse sequence was developed. Materials and Methods A diffusion gradient was inserted in a SS 3DPR pulse sequence. The acquisition was synchronized to the cardiac cycle, linear phase errors were corrected along the readout direction, and each projection was weighted by measures of consistency with other data. A new iterative parallel imaging reconstruction method was also implemented for removing off-resonance and undersampling artifacts simultaneously. Results The contrast and appearance of both the fractional anisotropy and eigenvector color maps were substantially improved after all correction techniques were applied. True 3D DTI datasets were obtained in vivo over the whole brain (240 mm field of view in all directions) with 1.87 mm isotropic spatial resolution, six diffusion encoding directions in under 19 minutes. Conclusion A true 3D DTI pulse sequence with high isotropic spatial resolution was developed for whole brain imaging in under 20 minutes. To minimize the effects of brain motion, a cardiac synchronized, multiecho, DW-SSFP pulse sequence was implemented. Motion artifacts were further reduced by a combination of linear phase correction, corrupt projection detection and rejection, sampling density reweighting, and parallel imaging reconstruction. The combination of these methods greatly improved the quality of 3D DTI in the brain. J. Magn. Reson. Imaging 2009;29:1175,1184. © 2009 Wiley-Liss, Inc. [source] Fast four-dimensional coronary MR angiography with k-t GRAPPAJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2008Peng Lai MS Abstract Purpose To investigate the effectiveness of k-t GRAPPA for accelerating four-dimensional (4D) coronary MRA in comparison with GRAPPA and the feasibility of combining variable density undersampling with conventional k-t GRAPPA (k-t2 GRAPPA) to alleviate the overhead of acquiring autocalibration signals. Materials and Methods The right coronary artery of nine healthy volunteers was scanned at 1.5 Tesla. The 4D k -space datasets were fully acquired and subsequently undersampled to simulate partially parallel acquisitions, namely, GRAPPA, k-t GRAPPA, and k-t2 GRAPPA. Comparisons were made between the images reconstructed from full k-space datasets and those reconstructed from undersampled k-space datasets. Results k-t GRAPPA significantly reduced artifacts compared with GRAPPA and high acceleration factors were achieved with only minimal sacrifices in vessel depiction. k-t2 GRAPPA could further increase imaging speed without significant losses in image quality. Conclusion By exploiting high-degree spatiotemporal correlations during the rest period of a cardiac cycle, k-t GRAPPA and k-t2 GRAPPA can greatly increase data acquisition efficiency and, therefore, are promising solutions for fast 4D coronary MRA. J. Magn. Reson. Imaging 2008. © 2008 Wiley-Liss, Inc. [source] Comparison between three-dimensional volume-selective turbo spin-echo imaging and two-dimensional ultrasound for assessing carotid artery structure and functionJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2005Lindsey A. Crowe PhD Abstract Purpose To compare a volume-selective three-dimensional turbo spin echo (TSE) technique with ultrasound (US) for assessing carotid artery wall structure and function. Materials and Methods A three-dimensional volume-selective TSE technique was used to image the carotid artery in 10 healthy subjects and five hypertensive subjects (each of whom were scanned three times while they received different hypertension treatments). Lumen and wall area were measured on MR images. Two-dimensional US measurements of the intima-media thickness (IMT) and lumen diameter were taken in three orientations through a single cross section. The lumen area change over the cardiac cycle was used to determine distension. For validation, a Bland-Altman analysis was used to compare the vessel wall and lumen areas measured by three-dimensional MRI volumes with those obtained by US scans. Results Agreement between the two methods was found. The mean difference in distension between US and MRI was 1.2% (±5.1%). For the wall area measurements, good agreement was shown, but there was a systematic difference due to the visualization of the adventitia by MRI. Both techniques offer an easy way to objectively measure lumen indices. MRI can provide the complete circumference over the length of a vessel, while US is flexible and relatively inexpensive. The application of US is limited, however, when subjects are poorly echogenic. A difference between hypertensive and healthy subjects was found. Conclusion There was a good agreement between MRI and the clinically established two-dimensional US method. The MRI method has the advantage of providing increased vessel coverage, which permits one to assess localized abnormalities without assuming vessel uniformity. J. Magn. Reson. Imaging 2005;21:282,289. © 2005 Wiley-Liss, Inc. [source] Divergent effects of ephedrine and phenylephrine on cardiovascular hemodynamics of near-term fetal sheep exposed to hypoxemia and maternal hypotensionACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 7 2007T. Erkinaro Background:, We hypothesized that the administration of ephedrine and phenylephrine for maternal hypotension modifies cardiovascular hemodynamics in near-term sheep fetuses. Methods:, At 115,136 days of gestation, chronically instrumented, anesthetized ewes with either normal placental function or increased placental vascular resistance after placental embolization were randomized to receive boluses of ephedrine (n = 12) or phenylephrine (n = 12) for epidural-induced hypotension after a short period of hypoxemia. Fetal cardiovascular hemodynamics were assessed by Doppler ultrasonography at baseline, during hypotension and after vasopressor treatment. Results:, During hypotension, fetal PO2 decreased and proximal branch pulmonary arterial and pulmonary venous vascular impedances increased. Additionally, in the embolized fetuses, the time-velocity integral ratio between the antegrade and retrograde blood flow components of the aortic isthmus decreased. These parameters were restored to baseline conditions by ephedrine but not by phenylephrine. With phenylephrine, weight-indexed left ventricular cardiac output and ejection force decreased in the non-embolized fetuses, and the proportion of isovolumetric contraction time of the total cardiac cycle was elevated in the embolized fetuses. Conclusions:, After exposure to hypoxemia and maternal hypotension, ephedrine restored all fetal cardiovascular hemodynamic parameters to baseline. Phenylephrine did not reverse fetal pulmonary vasoconstriction or the relative decrease in the net forward flow through the aortic isthmus observed in fetuses with increased placental vascular resistance. Moreover, fetal left ventricular function was impaired during phenylephrine administration. [source] 4D retrospective black blood trueFISP imaging of mouse heartMAGNETIC RESONANCE IN MEDICINE, Issue 5 2009Sylvain Miraux Abstract The purpose of this study was to demonstrate the feasibility of steady-state True fast imaging with steady precession (TrueFISP) four-dimensional imaging of mouse heart at high resolution and its efficiency for cardiac volumetry. Three-dimensional cine-imaging of control and hypoxic mice was carried out at 4.7 T without magnetization preparation or ECG-triggering. The k -space lines were acquired with the TrueFISP sequence (pulse repetition time/echo time = 4/2 ms) in a repeated sequential manner. Retrospective reordering of raw data allowed the reconstruction of 10 three-dimensional images per cardiac cycle. The acquisition scheme used an alternating radiofrequency phase and sum-of-square reconstruction method. Black-blood three-dimensional images at around 200 ,m resolution were produced without banding artifact throughout the cardiac cycle. High contrast to noise made it possible to estimate cavity volumes during diastole and systole. Right and left ventricular stroke volume was significantly higher in hypoxic mice vs controls (20.2 ± 2 vs 15.1 ± 2; P < 0.05, 24.9 ± 2 vs 20.4 ± 2; P < 0.05, respectively). In conclusion, four-dimensional black-blood TrueFISP imaging in living mice is a method of choice to investigate cardiac abnormalities in mouse models. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Myocardial perfusion MRI with sliding-window conjugate-gradient HYPRMAGNETIC RESONANCE IN MEDICINE, Issue 4 2009Lan Ge Abstract First-pass perfusion MRI is a promising technique for detecting ischemic heart disease. However, the diagnostic value of the method is limited by the low spatial coverage, resolution, signal-to-noise ratio (SNR), and cardiac motion-related image artifacts. In this study we investigated the feasibility of using a method that combines sliding window and CG-HYPR methods (SW-CG-HYPR) to reduce the acquisition window for each slice while maintaining the temporal resolution of one frame per heartbeat in myocardial perfusion MRI. This method allows an increased number of slices, reduced motion artifacts, and preserves the relatively high SNR and spatial resolution of the "composite images." Results from eight volunteers demonstrate the feasibility of SW-CG-HYPR for accelerated myocardial perfusion imaging with accurate signal intensity changes of left ventricle blood pool and myocardium. Using this method the acquisition time per cardiac cycle was reduced by a factor of 4 and the number of slices was increased from 3 to 8 as compared to the conventional technique. The SNR of the myocardium at peak enhancement with SW-CG-HYPR (13.83 ± 2.60) was significantly higher (P < 0.05) than the conventional turbo-FLASH protocol (8.40 ± 1.62). Also, the spatial resolution of the myocardial perfection images was significantly improved. SW-CG-HYPR is a promising technique for myocardial perfusion MRI. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Phase-sensitive cardiac tagging,REALTAGMAGNETIC RESONANCE IN MEDICINE, Issue 1 2007J. Andrew Derbyshire Abstract Fully inverting spins, instead of merely saturating them, provides superior contrast for tagging procedures. The resulting improvement in tag contrast-to-noise ratio (CNR) yields higher-precision tag detection. Also, thinner slices and hence reduced tag separations can be employed, providing displacement and strain measurements with better spatial resolution. Alternatively, the improved tag contrast can be used to obtain cine images covering a greater portion of the cardiac cycle. The use of standard magnitude reconstruction for images of these inversion tags causes rectification of the negative-valued signals from the tags, confounding the image interpretation. Therefore, a phase-sensitive reconstruction scheme of the inverted tags must be employed. Here we demonstrate the implementation of inverted tags with phase-sensitive reconstruction in a ramped-flip-angle, steady-state free precession (SSFP) sequence. Magn Reson Med 58:206,210, 2007. © 2007 Wiley-Liss, Inc. [source] Effects of cord motion on diffusion imaging of the spinal cordMAGNETIC RESONANCE IN MEDICINE, Issue 2 2006Hardave S. Kharbanda Abstract Measurement of diffusion and its dependence on direction has become an important tool for clinical and research studies of the brain. Diffusion imaging of the spinal cord may likewise prove useful as an indicator of tissue damage and axonal integrity; however, it is more challenging to perform diffusion imaging in the cord than in the brain. Here we report a study of the effects of motion on single-shot fast spin echo (FSE) diffusion tensor imaging (DTI) of the spinal cord. Diffusion imaging was performed at four different times in the cardiac cycle both without and with velocity compensation of the diffusion gradients. Uncompensated diffusion images demonstrated substantial signal loss artifacts in the cord that were strongly dependent on the delay after the pulse-oximeter trigger. Quantitative diffusion analysis was also strongly affected by this motion artifact. The use of flow-compensated gradients helped to restore normal signal in the cord, especially at particular trigger delays. Theoretical arguments suggest that improved spatial resolution may help eliminate this signal loss. Even with higher spatial resolution, motion-related signal attenuation may still occur in diffusion imaging of pathologies that alter the motion of the cord. However, this same cord motion may contain diagnostically valuable information when probed using appropriate diffusion imaging approaches. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Assessment of regional systolic and diastolic dysfunction in familial hypertrophic cardiomyopathy using MR tagging,MAGNETIC RESONANCE IN MEDICINE, Issue 3 2003Daniel B. Ennis Abstract Diastolic and systolic left ventricular (LV) dysfunction often significantly contribute to disabling symptoms in familial hypertrophic cardiomyopathy (FHC). This study compares regional LV function (midwall circumferential strain) during systole and diastole in eight FHC patients and six normal volunteers (NVs) using MR tagging. A prospectively-gated fast gradient-echo sequence with an echo-train readout was modified to support complementary spatial modulation of magnetization (CSPAMM) tagging and full cardiac cycle data acquisition using the cardiac phase to order reconstruction (CAPTOR), thus providing tag persistence and data acquisition during the entire cardiac cycle. Total systolic strains in FHC patients were significantly reduced in septal and inferior regions (both P < 0.01). Early-diastolic strain rates were reduced in all regions of the FHC group (all P < 0.03). The combination of CSPAMM and CAPTOR allows regional indices of myocardial function to be quantified throughout the cardiac cycle. This technique reveals regional differences in systolic and diastolic impairment in FHC patients. Magn Reson Med 50:638,642, 2003. Published 2003 Wiley-Liss, Inc. [source] Cardiac diffusion MRI without motion effectsMAGNETIC RESONANCE IN MEDICINE, Issue 1 2002Jiangang Dou Abstract We present a method for diffusion tensor MRI in the beating heart that is insensitive to cardiac motion and strain. Using a stimulated echo pulse sequence with two electrocardiogram (ECG) triggers, diffusion-encoding bipolar gradient pulses are applied at identical phases in consecutive cardiac cycles. In this experiment, diffusion is encoded at a single phase in the cardiac cycle of less than 30 ms in duration. This encoding produces no phase shifts for periodic motion and is independent of intervening strains. Studies in a gel phantom with cyclic deformation confirm that by using this sequence we can map the diffusion tensor free of effects of cyclic motion. In normal human subjects, myocardial diffusion eigenvalues measured with the present method showed no significant change between acquisitions encoded at maximum contractile velocity (peak) vs. at myocardial standstill (end-systole), demonstrating motion independence of in vivo diffusion measurements. Diffusion tensor images acquired with the present method agree with registered data acquired with a previous cardiac diffusion MRI method that was shown to be valid in the normal heart, strongly supporting the validity of MRI diffusion measurement in the beating heart. Myocardial sheet and fiber dynamics measured during systole showed that normal human myocardial sheet orientations tilt toward the radial during systole, and fiber orientations tilt toward the longitudinal, in qualitative agreement with previous invasive studies in canines. These results demonstrate the technique's ability to measure myocardial diffusion accurately at any point in the cardiac cycle free of measurable motion effect, as if the heart were frozen at the point of acquisition. Magn Reson Med 48:105,114, 2002. © 2002 Wiley-Liss, Inc. [source] Rapid measurement of aortic wave velocity: In vivo evaluationMAGNETIC RESONANCE IN MEDICINE, Issue 1 2001Kenneth A. Kraft Abstract A 1D MR sequence has been developed for determining aortic flow wave velocity (WV), a metric of arterial compliance, within a single cardiac cycle. Studies were carried out on the thoracic aortas of 10 normal volunteers. Correlative WV data were also acquired from each subject using a conventional phase-velocity 2D mapping technique. Aortic WV in this cohort was found to range from 411 to 714 cm/s and was highly correlated (R = 0.95) between the two methods. Peak blood velocity was also measured using both methods and found to agree closely. The reproducibility of WV measurements using the rapid 1D method averaged 7.6%, which is comparable or better than that achieved using existing noninvasive techniques. Magn Reson Med 46:95,102, 2001. © 2001 Wiley-Liss, Inc. [source] Fetal tricuspid valve Doppler at 11,13 weeks and 6 days: reference values and reproducibilityPRENATAL DIAGNOSIS, Issue 8 2010Milena Almeida Prado Ninno Abstract Objective To determine normal blood flow velocities across the fetal tricuspid valve (TV) at 11,13 weeks and 6 days of gestation and to examine the reproducibility of these measurements. Methods A prospective study involving 166 normal singleton pregnancies examined at 11,13 weeks and 6 days was carried out. Descriptive analysis of E- and A-waves' maximum velocities, E/A ratio, duration of the cardiac cycle (C) and diastole (D) and D/C ratio were calculated. Intraobserver and interobserver agreement analysis was performed in a subgroup of 12 cases. Results Average ( ± SD) flow velocities were: E-wave, 25.0 ( ± 4.6) cm/s; A-wave, 42.9 ( ± 5.9) cm/s; E/A, 0.58 ( ± 0.07); cardiac cycle, 390 ( ± 21.1) ms; diastole, 147 ( ± 18) ms and D/C, 0.38 ( ± 0.04). Significant correlation was observed between all parameters (except A-wave) and gestational age but not with nuchal translucency (NT). Intraclass correlation coefficients (interobserver, intraobsever examiner 1 and intraobserver examiner 2) were: E-wave, 0.53, 0.53 and 0.64; A-wave, 0.45, 0.46 and 0.49; cardiac cycle, 0.70, 0.79 and 0.84 and diastole, 0.63, 0.85 and 0.82, respectively. Conclusions The present study establishes normal Doppler parameters for blood flow across the TV at 11,13 weeks and 6 days and demonstrates that these parameters do not correlate with NT measurement and have good/moderate reproducibility. Copyright © 2010 John Wiley & Sons, Ltd. [source] Attenuation of positive and negative affect in men and women at increased risk for hypertension: A function of endogenous barostimulation?PSYCHOPHYSIOLOGY, Issue 1 2009Daniel Z. Wilkinson Abstract We hypothesized that activation of endogenous baroreflexes would be associated with reduced responsivity to affective stimuli and that this effect would be enhanced in individuals at risk for hypertension. Images from the International Affective Picture System were presented during systolic and diastolic phases of the cardiac cycle. Affective responsivity was measured using electromyographic activity, skin conductance, and ratings of arousal and valence. Compared to offspring of normotensives, individuals with a parental history of hypertension showed reduced responsivity to both positive and negative affective stimuli; however, responsivity did not differ as a function of cardiac cycle phase. Although these findings do not support a barostimulation mechanism of affective dampening, it is premature to discount the baroreflex inhibition hypothesis given the limited affective reactions elicited by visual stimuli presented in the laboratory. [source] Psychomotor speed in hypertension: Effects of reaction time components, stimulus modality, and phase of the cardiac cyclePSYCHOPHYSIOLOGY, Issue 3 2007Louisa Edwards Abstract Hypertension is characterized by cognitive deficits. As evidence for impaired psychomotor speed, including slower reaction times, is mixed, we aimed to provide a detailed investigation of simple reaction time in hypertension. Pre-motor and motor reaction times were measured across the cardiac cycle in 30 hypertensives and 29 normotensives to determine the effects of phasic and tonic blood pressure on performance. Auditory, visual, and tactile simple reaction time tasks were completed with stimuli presented 0, 300, and 600 ms after the R-wave of the electrocardiogram. Reaction times did not differ between hypertensives and normotensives. Although pre-motor reaction times were faster during the late phase than the early phase of the cardiac cycle whereas motor reaction times were unchanged, this effect was similar for hypertensives and normotensives. No sensory-motor deficits were evident in these hypertensives regardless of baroreceptor activity. [source] A Segmental Polynomial Model of Ventricular Electrograms as a Simple and Efficient Morphology Discriminator for Implantable DevicesANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2006Jeffrey L. Williams M.D. Background: The goal of this study is to construct a polynomial model of the ventricular electrogram (EGM) that faithfully reproduces the EGM and can be implemented in current, low computational power implantable devices. Such a model of ventricular EGMs is still lacking. Methods: New Zealand White rabbits underwent chronic implantation of pacemakers through a left thoracotomy approach. Unipolar ventricular EGMs sampled at a frequency of 1 kHz were stored digitally in 1-minute segments before and after intravenous injection of isoproterenol or procainamide. Each cardiac cycle was divided into a QR and an RQ segment which were modeled separately using a 6th order polynomial equation. Results: The 14 coefficients of each cardiac cycle were reproducible throughout the baseline recordings (r , 0.94, P < 0.002). Isoproterenol caused no changes in the coefficients of the QR segment but significantly altered all but one of the seven coefficients of the RQ segment (p6= 0.0039, p5= 0.017, p4= 0.00007, p3= 0.112, p2= 0.00016, p1= 0.0086, pa= 0.00003). Procainamide caused statistically significant changes in both QR segment (p6= 0.018, p5= 0.287, p4= 0.019, p3= 0.176, p2= 0.016, p1= 0.362, pa= 0.000044) and RQ segment (p6= 0.0028, p5= 0.036, p4= 0.002, p3= 0.058, p2= 0.022, p1= 0.718, pa= 0.0018) coefficients. Conclusion: Our data demonstrate the feasibility of a segmental polynomial equation that reproduces the phases of depolarization and repolarization of the rabbit EGM. This model is reproducible and demonstrates the expected changes with antiarrhythmic drug administration. If reproduced in humans, these findings can have wide applications in patients with implantable devices, ranging from morphologic discrimination of arrhythmias to early detection of metabolic derangements or drug effects. [source] The Importance of dQ/dt on the Flow Field in a Turbodynamic Pump With Pulsatile FlowARTIFICIAL ORGANS, Issue 9 2009Fangjun Shu Abstract Fluid dynamic analysis of turbodynamic blood pumps (TBPs) is often conducted under steady flow conditions. However, the preponderance of clinical applications for ventricular assistance involves unsteady, pulsatile flow,due to the residual contractility of the native heart. This study was undertaken to demonstrate the importance of pulsatility and the associated time derivative of the flow rate (dQ/dt) on hemodynamics within a clinical-scale TBP. This was accomplished by performing flow visualization studies on a transparent model of a centrifugal TBP interposed within a cardiovascular simulator with controllable heart rate and stroke volume. Particle image velocimetry triggered to both the rotation angle of the impeller and phase of the cardiac cycle was used to quantify the velocity field in the outlet volute and in between the impeller blades for 16 phases of the cardiac cycle. Comparison of the unsteady flow fields to corresponding steady conditions at the same (instantaneous) flow rates revealed marked differences. In particular, deceleration of flow was found to promote separation within the outlet diffuser, while acceleration served to stabilize the velocity field. The notable differences between the acceleration and deceleration phases illustrated the prominence of inertial fluid forces. These studies emphasize the importance of dQ/dt as an independent variable for thorough preclinical validation of TBPs intended for use as a ventricular assist device. [source] Left ventricular unloading and concomitant total cardiac output increase by the use of percutaneous impella recover LP 2.5 assist device during high-risk coronary interventionCATHETERIZATION AND CARDIOVASCULAR INTERVENTIONS, Issue 2 2005Marco Valgimigli Abstract A number of techniques have been proposed for circulatory support during high-risk percutaneous coronary interventions (PCI), but no single approach has achieved wide acceptance so far. We report on a patient with severe left ventricular (LV) impairment who underwent a PCI with the use of a new left ventricular assist device, the Impella Recover LP 2.5 system. The effects on global cardiac output were determined by thermodilution (TD) and LV pressure-volume loops obtained by conductance catheter. The activation of the pump resulted in a rapid and sustained unloading effect of the LV. At the same time, the continuous expulsion of blood into ascending aorta throughout the cardiac cycle produced by the pump resulted in an increase of systemic overall CO, measured by the TD technique, of 1.43 L/min. The procedure was uncomplicated and the patient remained uneventful at follow-up. Our single experience gives new input for future trials to assess the effect of the Impella Recover LP 2.5 assist device on outcome in this subset of patients. © 2005 Wiley-Liss, Inc. [source] LARGE-SCALE SIMULATION OF THE HUMAN ARTERIAL TREECLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 2 2009L Grinberg SUMMARY 1Full-scale simulations of the virtual physiological human (VPH) will require significant advances in modelling, multiscale mathematics, scientific computing and further advances in medical imaging. Herein, we review some of the main issues that need to be resolved in order to make three-dimensional (3D) simulations of blood flow in the human arterial tree feasible in the near future. 2A straightforward approach is computationally prohibitive even on the emerging petaflop supercomputers, so a three-level hierarchical approach based on vessel size is required, consisting of: (i) a macrovascular network (MaN); (ii) a mesovascular network (MeN); and (iii) a microvascular network (MiN). We present recent simulations of MaN obtained by solving the 3D Navier,Stokes equations on arterial networks with tens of arteries and bifurcations and accounting for the neglected dynamics through proper boundary conditions. 3A multiscale simulation coupling MaN,MeN,MiN and running on hundreds of thousands of processors on petaflop computers will require no more than a few CPU hours per cardiac cycle within the next 5 years. The rapidly growing capacity of supercomputing centres opens up the possibility of simulation studies of cardiovascular diseases, drug delivery, perfusion in the brain and other pathologies. [source] Quantification of left ventricular volumes and ejection fraction from gated 99mTc-MIBI SPECT: MRI validation of the exini heart software packageCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 2 2009Oliver H. Winz Summary The aim of the study was to validate the accuracy of the exini heart software (exini) package in assessing left ventricular end-diastolic/systolic volumes (EDV, ESV) and ejection fraction (LVEF) from gated 99mTc-MIBI single-photon emission tomography (SPECT). Cardiac magnetic resonance imaging (cMRI) was used as reference. Furthermore, effects of perfusion defects and image quality in SPECT on correlation between gated SPECT and magnetic resonance imaging were investigated. Methods:, Seventy patients were examined using gated SPECT (rest study, eight gates per cardiac cycle). EDV, ESV and LVEF were calculated from gated SPECT using exini. Directly before or after SPECT, cMRI (20 gates cardiac per cycle) was performed. EDV, ESV and LVEF were calculated using Simpson's rule. Perfusion defects were quantified using the summed-rest-score (SRS). Total number of myocardial counts were used to rate image quality. Results:, Correlation between results of gated SPECT and cMRI was high for EDV (R = 0·89) and ESV (R = 0·94) and good for LVEF (R = 0·78). ESV (exini 54 ± 31 ml versus cMRI 57 ± 34 ml) and LVEF (exini 62·9 ± 11·7% versus cMRI 60·6 ± 13·9%) did not differ significantly whereas exini overestimated EDV significantly compared with cMRI (exini 144 ± 41 ml versus cMRI 137 ± 36 ml; P<0·005). No correlation was found between absolute differences of the results given by gated SPECT and cMRI and SRS or total myocardial counts (R < 0·18). Conclusion:, End-diastolic volume, ESV and LVEF calculated from gated SPECT using exini agree with cMRI over a wide range of values. Correlation between both the methods was good for EDV and ESV, and acceptable for LVEF. No relevant influence of image quality or SRS on the accuracy of exini results was found. [source] | |||||||||||||||||||||||||||||||