[Research on calculation of the regional cerebral blood volume based on minimum mean square error method].

In this paper, the Fourier transform based minimum mean square error (FT-based MMSE) method is used to calculate the regional cerebral blood volume (rCBV) in magnetic resonance (MR) perfusion imaging, and the method is improved to handle the existing noise in the imaging process. In the experiments with signal-to-noise ratio (SNR) of 50 dB, the rCBV values were compared with the results using MMSE method. The effects of different SNRs on the estimation of rCBV were analyzed. The experimental results showed that MMSE was a simple way to filter the measurement noise, and could calculate rCBV accurately. Compared with other existing methods, the present method is not sensitive to environment, and furthermore, it is suitable to deal with the perfusion images acquired from the environment with larger SNR.

Assessment of left ventricular diastolic function by early diastolic mitral annulus peak acceleration rate: experimental studies and clinical application.

We sought to examine the hemodynamic determinants and clinical application of the peak acceleration rate of early (Ea) diastolic velocity of the mitral annulus by tissue Doppler. Simultaneous left atrial and left ventricular (LV) catheterization and Doppler echocardiography were performed in 10 dogs. Preload was altered using volume infusion and caval occlusion, whereas myocardial lusitropic state was altered with dobutamine and esmolol. The clinical application was examined in 190 consecutive patients (55 control, 41 impaired relaxation, 46 pseudonormal, and 48 restrictive LV filling). In addition, in 60 consecutive patients, we examined the relation between it and mean wedge pressure with simultaneous Doppler echocardiography and right heart catheterization. In canine studies, a significant positive relation was present between peak acceleration rate of Ea and transmitral pressure gradient only in the stages with normal or enhanced LV relaxation, but with no relation in the stages where the time constant of LV relaxation (tau) was > or =50 ms. Its hemodynamic determinants were tau, LV minimal pressure, and transmitral pressure gradient. In clinical studies, peak acceleration rate of Ea was significantly lower in patients with impaired LV relaxation irrespective of filling pressures (P < 0.001) and with similar accuracy to peak Ea velocity (area under the curve for septal and lateral peak acceleration rates: both 0.78) in identifying these patients. No significant relation was observed between peak acceleration rate and mean wedge pressure. Peak acceleration rate of Ea appears to be a useful index of LV relaxation but not of filling pressures and can be applied to identify patients with impaired LV relaxation irrespective of their filling pressures.

Time interval between onset of mitral inflow and onset of early diastolic velocity by tissue Doppler: a novel index of left ventricular relaxation: experimental studies and clinical application.

OBJECTIVES: The goal of this study was to examine the diagnostic utility of the time to onset of early (Ea) diastolic velocity of the mitral annulus by tissue Doppler (TD) in comparison with the time to onset of mitral inflow (T(Ea-E)) for the assessment of left ventricular (LV) relaxation. BACKGROUND: Tissue Doppler imaging of the mitral annulus provides useful information about myocardial function. So far, studies have focused on the measurement of peak Ea, but have not evaluated the diagnostic utility of the time to onset of Ea. METHODS: Simultaneous left heart catheterization and Doppler echocardiography (DE) were performed in 10 dogs. Left atrial pressures and LV volumes and pressures were measured before and after constriction of the circumflex (cx) coronary artery. The delay in Ea was next examined in 60 consecutive patients, undergoing simultaneous right heart catheterization and DE. Furthermore, (T(Ea-E)) was used to predict filling pressures in a prospective group of 33 patients. RESULTS: In canine studies, significant prolongation in the time interval (T(Ea-E)) was noted after cx constriction, which had a significant relation with tau (tau) (r = 0.93, p < 0.01). In human studies, Ea was significantly delayed in patients with impaired relaxation and pseudonormal LV filling in comparison with age-matched controls. In the prospective group, pulmonary capillary wedge pressure (PCWP) derived as: PCWP(Doppler) = LV(end-systolic pressure) x e(-IVRT/(T(Ea-E))), where IVRT is isovolumetric relaxation time; PCWP(Doppler) related well to PCWP(catheter) (r = 0.84, p < 0.001). CONCLUSIONS: T(Ea-E) is a useful novel index of LV relaxation. It can be used to identify patients with diastolic dysfunction and predict PCWP.

Dynamic three-dimensional visualization of the left ventricle by intracardiac echocardiography.

Cardiac function and hemodynamics are routinely evaluated during catheterization in patients with heart disease. Although intracardiac echocardiography (ICE) has been employed in guiding electrophysiology procedures, it has not been effectively used in assessing hemodynamics. We tested the utility of ICE in measuring left ventricular (LV) volume throughout the cardiac cycle. In four normal dogs (weight = 26 to 37 kg), a 10-F sheath was inserted through the femoral artery and placed inside the LV along its major axis. An ICE catheter (9 F, 9 MHz) was then inserted through the sheath into the LV. The ICE catheter was pulled back inside the sheath in 1-mm intervals starting from the apex, and 2-D tomographic images were continuously acquired while gating to respiration. Subsequently, the ICE catheter was replaced by a conductance catheter to measure single-beat volume signals. Stroke volume was determined by thermodilution for validation. All measurements were made in each dog while pacing the atrium at two different cycle lengths (range = 300 to 500 ms). The endocardial boundary was digitized from the ICE images throughout the cardiac cycle and LV volume was computed by integrating multiple segments along the major axis (range = 55 to 70 mm). We found that ICE accurately reconstructed LV 3-D anatomy. Stroke volume by ICE was in excellent agreement with thermodilution (error = 3.8 +/- 3.0%, r = 0.99, n = 8) and was highly reproducible. Morphology of LV volume signals correlated well with corresponding instantaneous volume signals derived by conductance (r = 0.93, n = 8). In conclusion, ICE accurately reconstructs LV anatomy and volume throughout the cardiac cycle in the normal heart. This approach could facilitate interventional diagnostic and therapeutic procedures.

Smoothness processing of infrared image based on AMSS.

The Infrared images have been applied in clinical diagnoses, but the images are noisy and blurred. Therefore the smooth processing that can keep edges is needed. Traditional smoothing methods have the common defect that they smooth not only the noise region but also the edges. AMSS (affine morphological scale space) algorithm can be used to better save the edge information, it has the Partial Differential Equation that is of morphological affine invariability and contrast invariability. The smooth processing method based on AMSS is introduced to handle the infrared image in this paper, and the better performance is obtained.

Retrograde ethanol infusion in the vein of Marshall: regional left atrial ablation, vagal denervation and feasibility in humans.

BACKGROUND: The vein of Marshall (VOM) is an attractive target during ablation of atrial fibrillation due to its autonomic innervation, its location anterior to the left pulmonary veins and drainage in the coronary sinus. METHODS AND RESULTS: We studied 17 dogs. A coronary sinus venogram showed a VOM in 13, which was successfully cannulated with an angioplasty wire and balloon. In 5 dogs, electroanatomical maps of the left atrium were performed at baseline and after ethanol infusion in the VOM, which demonstrated a new crescent-shaped scar, extending from the annular left atrium towards the posterior wall and left pulmonary veins. In 4 other dogs, effective refractory periods (ERP) were measured at 3 sites in the left atrium, before and after high-frequency bilateral vagal stimulation. The ERP decreased from 113.6+/-35.0 ms to 82.2+/-25.4 ms (p<0.05) after vagal stimulation. After VOM ethanol infusion, vagally-mediated ERP decrease was eliminated (from 108.6+/-24.1 ms to 96.4 +/-16.9ms, p=NS). The abolition of vagal effects was limited to sites near the VOM (ERP: 104+/-14 ms, vs 98.6+/-12.2 ms post vagal stimulation, p=ns), as opposed to sites remote to VOM (ERP: 107.2+/-14.9 ms, vs 78.6+/-14.7ms post vagal stimulation, p<0.05). To test feasibility in humans, 5 patients undergoing pulmonary vein antral isolation had successful VOM cannulation and ethanol infusion: left atrial voltage maps demonstrated new scar involving the infero-posterior left atrial wall extending towards the left pulmonary veins. CONCLUSIONS: Ethanol infusion in then VOM achieves significant left atrial tissue ablation, abolishes local vagal responses and is feasible in humans.

Model study of imaging myocardial infarction by intracardiac electrical impedance tomography.

Electrical impedance tomography (EIT) detects tissue composition inside a medium by determining its resistive properties, and uses various electrode configurations to pass a small electric current and measure corresponding potential. We investigated the feasibility of reconstructing scarred tissue inside the heart wall by employing EIT on the basis of a catheter carrying a plurality of electrodes and placed inside the blood-filled heart cavity. We built a computer model of the biological medium, and reconstructed the resistivity distribution using the finite element method and Tikhonov regularization. The results established the successful implementation of the numeric methods and the possibility of localizing and quantifying scarred myocardium. Novel application of EIT from inside the heart cavity could be useful during catheterization and may complement other diagnostic modalities. Further research is necessary to assess the impact of several factors on the accuracy of the reconstruction and include number of electrodes, catheter location, and scar size.

Retinex enhancement of infrared images.

With the ability of imaging the temperature distribution of body, infrared imaging is promising in diagnostication and prognostication of diseases. However the poor quality of the raw original infrared images prevented applications and one of the essential problems is the low contrast appearance of the imagined object. In this paper, the image enhancement technique based on the Retinex theory is studied, which is a process that automatically retrieve the visual realism to images. The algorithms, including Frackle-McCann algorithm, McCann99 algorithm, single-scale Retinex algorithm, multi-scale Retinex algorithm and multi-scale Retinex algorithm with color restoration, are experienced to the enhancement of infrared images. The entropy measurements along with the visual inspection were compared and results shown the algorithms based on Retinex theory have the ability in enhancing the infrared image. Out of the algorithms compared, MSRCR demonstrated the best performance.

Integrated multimodal-catheter imaging unveils principal relationships among ventricular electrical activity, anatomy, and function.

Multiple imaging modalities are employed independent of one another while managing complex cardiac arrhythmias. To combine electrical, anatomical, and functional imaging in a single catheter system, we developed a balloon catheter that carried 64 electrodes on its surface and an intracardiac echocardiography (ICE) catheter through a central lumen. The catheter system was inserted, and the balloon was inflated inside the left ventricle (LV) of eight dogs with 6-wk-old infarction, created by occlusion in the left anterior descending coronary artery. Anatomy was constructed by ICE imaging (9 MHz) through the balloon. Single-beat noncontact mapping (NCM) was performed via the multielectrode array to reconstruct unipolar endocardial electrograms during sinus rhythm. Standard contact mapping (CM) of the endocardium was also carried out for reference. Myocardial infarction in anterior LV extending from the middle to apical regions was localized both by ICE and NCM and validated by CM and pathology. The overall difference in the activation times between NCM and CM was 3 +/- 1 ms. Unipolar voltage in infarcted middle anterior LV was smaller than the voltage in normal middle inferior LV both by NCM (11 +/- 4 vs. 16 +/- 3 mV; P = 0.002) and CM (11 +/- 3 vs. 20 +/- 4 mV; P < 0.001). Unipolar voltage was also inversely related to infarct transmurality, both by NCM (r = -0.87; P = 0.005) and CM (r = -0.94; P < 0.001). The infarct area by ICE (7.7 +/- 2.9 cm(2)) was in agreement with CM (bipolar voltage, <1 mV; and area, 7.6 +/- 3.3 cm(2); r = 0.80; P = 0.016). Meanwhile, the voltage threshold that depicted the infarct area by NCM was directly related to the smallest unipolar voltage reconstructed within the infarct (r = 0.96; P < 0.001). In conclusion, combining NCM and ICE imaging in a single catheter system is feasible. The preclinical development of such an integrated system and its evaluation in experimental myocardial infarction demonstrate capabilities for single-beat mapping at multiple sites as well as the online assessment of anatomy and myocardial function.

A novel feature-tracking echocardiographic method for the quantitation of regional myocardial function: validation in an animal model of ischemia-reperfusion.

OBJECTIVES: The aim of this study was to validate a novel, angle-independent, feature-tracking method for the echocardiographic quantitation of regional function. BACKGROUND: A new echocardiographic method, Velocity Vector Imaging (VVI) (syngo Velocity Vector Imaging technology, Siemens Medical Solutions, Ultrasound Division, Mountain View, California), has been introduced, based on feature tracking-incorporating speckle and endocardial border tracking, that allows the quantitation of endocardial strain, strain rate (SR), and velocity. METHODS: Seven dogs were studied during baseline, and various interventions causing alterations in regional function: dobutamine, 5-min coronary occlusion with reperfusion up to 1 h, followed by dobutamine and esmolol infusions. Echocardiographic images were acquired from short- and long-axis views of the left ventricle. Segment-length sonomicrometry crystals were used as the reference method. RESULTS: Changes in systolic strain in ischemic segments were tracked well with VVI during the different states of regional function. There was a good correlation between circumferential and longitudinal systolic strain by VVI and sonomicrometry (r = 0.88 and r = 0.83, respectively, p < 0.001). Strain measurements in the nonischemic basal segments also demonstrated a significant correlation between the 2 methods (r = 0.65, p < 0.001). Similarly, a significant relation was observed for circumferential and longitudinal SR between the 2 methods (r = 0.94, p < 0.001 and r = 0.90, p < 0.001, respectively). The endocardial velocity relation to changes in strain by sonomicrometry was weaker owing to significant cardiac translation. CONCLUSIONS: Velocity Vector Imaging, a new feature-tracking method, can accurately assess regional myocardial function at the endocardial level and is a promising clinical tool for the simultaneous quantification of regional and global myocardial function.

Resistivity parameters estimation based on 2D real head model using improved differential evolution algorithm.

The improved Differential Evolution (DE)algorithm is proposed in this paper to solve the resistivity parameters estimation problem based on 2D real head model. Our simulations demonstrate that the improved DE algorithm is robust in obtaining high quality reconstruction, and the convergence is much faster than the usual DE algorithm.Furthermore, the selection of the amplification parameters is much easier.

Myocardial contrast echocardiography of radiofrequency ablation lesions.

INTRODUCTION: The study tested the feasibility of differentiating radiofrequency ablation lesions from normal myocardium and quantifying their dimensions by myocardial contrast echocardiography (MCE). METHODS AND RESULTS: In 11 normal dogs, we created 14 focal and 4 linear lesions at different left ventricular sites.MCE was performed both before and after ablation by using an intracardiac echocardiography catheter (9 MHz)and infusing contrast microbubbles through the left coronary artery. An independent observer examined the lesion pathology. We found that intracardiac echocardiography alone could not delineate lesion dimensions. However, after ablation, MCE localized the lesions as well-defined, low-contrast areas within the normally opacified myocardium. Lesion dimensions byMCE immediately after ablation and 30 minutes later were similar. In 12 focal lesions, the average maximum depth (5.55 +/- 1.38 mm) and average maximum diameter(10.38 +/- 2.09 mm) by MCE were in excellent agreement with the pathologic depth (5.20 +/- 1.45 mm) and diameter(10.61 +/- 1.67 mm). Two focal lesions could not be detected by MCE and later were found to be superficial. Three-dimensional MCE correctly reconstructed the extent and shape of linear lesions compared to pathology (length: 18.7+/- 5.7 vs 18.5 +/- 5.6 mm; maximum longitudinal cross-sectional area: 81.2 +/- 9.6 vs 76.0 +/-10.3 mm(2)). CONCLUSION: MCE accurately localized and quantified radiofrequency ablation lesions in the normal leftv entricle. This new application of MCE may advance'ablation for managing ventricular arrhythmias that involve intramural or epicardial regions by providing instantaneous anatomic feedback on the effects of ablation during catheterization.

MNR Method with Self-Determined Regularization Parameters for Solving Inverse Resistivity Problem.

The modified Newton-Raphson (MNR) method is used to solve the inverse resistivity problem in this paper. Using Tikhonov regularization method, comparisons among the L-curve method, the zero-crossing (ZC) method and the generalized cross validation (GCV) method are carried out for determining the regularization parameters of MNR method. By these criterions the appropriate regularization parameters are self-determined and adjusted with the reconstruction iterations. Our simulation experiments on 2D circle model showed that the GCV method can provide the best reconstruction quality with the fastest speed in inverse resistivity problem using MNR method.

Nonfluoroscopic localization of intracardiac electrode-catheters combined with noncontact electrical-anatomical imaging.

We recently combined noncontact mapping and intracardiac echocardiography (ICE) in a single catheter-system that permitted 3D electrical-anatomical imaging of the heart. The objective of the present study was to develop a nonfluoroscopic method to localize standard, navigational electrode-catheters, which also operated in conjunction with noncontact electrical-anatomical imaging. Accordingly, electrode-catheters were fixed at the endocardium in the LV of three dogs and in the RA of two other dogs. A catheter-system was placed inside the heart cavity, and consisted of a 9-F sheath carrying a coaxial noncontact 64-electrode lumen-probe on the outside (diameter = 7 mm), and a central ICE catheter on the inside (9 MHz). To reconstruct the endocardial anatomy, the ICE catheter was pulled back inside the sheath and multiple 2D tomographic images were acquired. The noncontact probe was then advanced over the sheath and into the heart cavity. Current pulses were injected into the endocardial contact electrodes and all probe electrodes sensed corresponding potentials. Measured probe potentials localized the endocardial electrodes based on the least squares numeric method, and was verified by ICE. We found that the 3D endocardial geometry reconstructed by ICE depicted important anatomical details. All endocardial electrodes were identified by ICE and were correctly matched with corresponding endocardial anatomy. The difference in computed electrode locations compared to ICE was 5.4 +/- 2.4 mm (n = 10). In conclusion, nonfluoroscopic localization of standard navigational electrode-catheters within true and detailed 3D images of cardiac anatomy is feasible. Integrating this approach with noncontact electrical-anatomical imaging could facilitate diagnosing arrhythmias and advancing their therapy.

Novel noncontact catheter system for endocardial electrical and anatomical imaging.

The study objective was to integrate noncontact mapping and intracardiac echocardiography (ICE) in a single catheter system that enables both electrical and anatomical imaging of the endocardium. We developed a catheter system on the basis of a 9-F sheath that carried a coaxial 64-electrode lumen-probe on the outside and a central ICE catheter (9 F, 9 MHz) on the inside. The sheath was placed in the right atrium (RA) of 3 dogs, and in the left ventricle (LV) of 3 other dogs. To construct cardiac anatomy, the ICE catheter was pulled back over several beats inside the sheath starting from the tip and two-dimensional tomographic images were continuously acquired. To recover endocardial electrograms, the probe was advanced over the sheath and single-beat noncontact electrograms were simultaneously recorded. Endocardial contact electrodes were placed at select sites for validation as well as for pacing. Three-dimensional electrical-anatomical images reconstructed during sinus and paced rhythms correctly associated RA and LV activation sequences with underlying endocardial anatomy (overall activation error = 3.4 +/- 3.2 ms; overall spatial error = 8.0 +/- 3.5 mm). Therefore, accurate fusion of electrical imaging with anatomical imaging during catheterization is feasible. Integrating single-beat noncontact mapping with ICE provides detailed, three-dimensional electrical-anatomical images of the endocardium, which may facilitate management of arrhythmias.

Haemodynamic insights into the effects of ischaemia and cycle length on tissue Doppler-derived mitral annulus diastolic velocities.

In the present study, we performed simultaneous epicardial echocardiography and left heart catheterization on ten adult dogs to investigate the effects of ischaemia and tachycardia on the mitral annulus early (E(a)) and late (A(a)) diastolic velocities and the haemodynamic mechanisms involved. Left atrial pressure and left ventricular (LV) volumes and pressures were measured with 5 French Millar catheters. In each dog, inferior vena cava occlusion was used to alter preload and circumflex coronary artery occlusion was applied to induce ischaemia at two different cycle lengths: 450 and 550 ms. At both cycle lengths, ischaemia resulted in a reduction in LV relaxation, LV global and ipsilateral systolic function, transmitral pressure gradient (TMG), E(a) and A(a) ( P <0.05). The shorter cycle length was associated with a shorter tau (time constant of LV relaxation), reduced TMG and reduced septal and lateral E(a) ( P <0.05 for all variables). Both septal and lateral A(a) were significantly increased ( P <0.05). Ischaemia influences E(a) through changes in LV relaxation, global and regional systolic function and TMG. An increase in heart rate reduces E(a), but increases A(a).

Localizing and quantifying ablation lesions in the left ventricle by myocardial contrast echocardiography.

INTRODUCTION: The inability to determine the extent and intramural depth of ablation lesions can hamper the success of catheter ablation. The study tested the feasibility of differentiating radiofrequency ablation lesions from normal myocardium and quantifying their dimensions by myocardial contrast echocardiography (MCE). METHODS AND RESULTS: In 11 normal dogs, we created 14 focal and 4 linear lesions at different left ventricular sites. MCE was performed both before and after ablation by using an intracardiac echocardiography catheter (9 MHz) and infusing contrast microbubbles through the left coronary artery. We initially used two-dimensional MCE to image focal lesions and subsequently three-dimensional MCE to image linear lesions. An independent observer examined the lesion pathology. We found that intracardiac echocardiography alone could not delineate lesion dimensions. However, after ablation, MCE localized the lesions as well-defined, low-contrast areas within the normally opacified myocardium. Lesion dimensions by MCE immediately after ablation and 30 minutes later were similar. In 12 focal lesions, the average maximum depth (5.55 +/- 1.38 mm) and average maximum diameter (10.38 +/- 2.09 mm) by MCE were in excellent agreement with the pathologic depth (5.20 +/- 1.45 mm) and diameter (10.61 +/- 1.67 mm). Two focal lesions could not be detected by MCE and later were found to be superficial. Three-dimensional MCE correctly reconstructed the extent and shape of linear lesions compared to pathology (length: 18.7 +/- 5.7 vs 18.5 +/- 5.6 mm; maximum longitudinal cross-sectional area: 81.2 +/- 9.6 vs 76.0 +/- 10.3 mm2). CONCLUSION: MCE accurately localized and quantified radiofrequency ablation lesions in the normal left ventricle. This new application of MCE may advance ablation for managing ventricular arrhythmias that involve intramural or epicardial regions by providing instantaneous anatomic feedback on the effects of ablation during catheterization.

Three EIT approaches for static imaging of head.

Three EIT approaches for static imaging of head are investigated in this paper. The modified Newton-Raphson (MNR) method and the differential evolution (DE) algorithm are applied to the impedance reconstruction of 2D section of head based on real head model. Comparisons are carried out on the results obtained using simulated data, and a DE-MNR combination method is proposed, which demonstrated high impedance reconstruction quality with fast convergence in the 2D EIT simulation for static imaging of head.

EEG source localization using differential evolution method.

Differential evolution (DE) method is used in This work to solve the EEG source localization problem based on equal current dipole model. The single dipole sources with four-shell concentric sphere model are reconstructed. Our simulations demonstrate that DE algorithm is robust in obtaining high quality reconstruction for EEG problems with single current dipole sources.