Biomedical subjects

Tino Ebbers

Publications and source records attributed to Tino Ebbers.

5 recordsLinked to original sources

PubMed2006

Quantification of intravoxel velocity standard deviation and turbulence intensity by generalizing phase-contrast MRI.

Turbulent flow, characterized by velocity fluctuations, is a contributing factor to the pathogenesis of several cardiovascular diseases. A clinical noninvasive tool for assessing turbulence is lacking, however. It is well known that the occurrence of multiple spin velocities within a voxel during the influence of a magnetic gradient moment causes signal loss in phase-contrast magnetic resonance imaging (PC-MRI). In this paper a mathematical derivation of an expression for computing the standard deviation (SD) of the blood flow velocity distribution within a voxel is presented. The SD is obtained from the magnitude of PC-MRI signals acquired with different first gradient moments. By exploiting the relation between the SD and turbulence intensity (TI), this method allows for quantitative studies of turbulence. For validation, the TI in an in vitro flow phantom was quantified, and the results compared favorably with previously published laser Doppler anemometry (LDA) results. This method has the potential to become an important tool for the noninvasive assessment of turbulence in the arterial tree.

Blood Flow Velocity↗

PubMed2004

Flow patterns in the aortic root and the aorta studied with time-resolved, 3-dimensional, phase-contrast magnetic resonance imaging: implications for aortic valve-sparing surgery.

OBJECTIVE: Sparing the aortic valve has become a surgical option for patients who require repair of aortic root ectasia and have normal valve leaflets. Surgical approaches to valve sparing differ with regard to preservation of the native sinuses of Valsalva. The role of the sinuses and the importance of maintaining them remain controversial. METHODS: By using a time-resolved, 3-dimensional, phase-contrast magnetic resonance imaging technique, aortic root and aortic blood velocity data were acquired from 2 patients with Marfan syndrome 6 months after aortic valve-sparing surgery with straight Dacron grafts and contrasted with data from 6 normal volunteers. RESULTS: In normal aortas vortical blood flow became apparent in the individual sinuses after peak systole. The vortices filled the available space behind the valve leaflets and persisted until diastole, expanding and moving inward during aortic valve closure. In contrast, no vortices were observed in the postoperative patients with Marfan syndrome with negligible sinuses. CONCLUSIONS: Changes in supravalvular flow accompany loss of sinus architecture. Whether the presence, size, and velocity of supravalvular vortices affects the function or durability of the preserved aortic valve remains to be studied.

Adult↗

PubMed2004

Three-directional myocardial motion assessed using 3D phase contrast MRI.

Regional myocardial function is a complex entity consisting of motion in three dimensions (3D). Besides magnetic resonance imaging (MRI), no other noninvasive technique can give a true 3D description of cardiac motion. Using a time-resolved 3D phase contrast technique, three-dimensional image volumes containing myocardial velocity data in six normal volunteers were acquired. Coordinates and velocity information were extracted from nine points placed in different myocardial segments in the left ventricle (LV), and decomposed into longitudinal (V(L)), radial (V(R)), and circumferential (V(C)) velocity components. Our findings confirm a longitudinal apex-to-base gradient for the LV, with only a small motion of the apex. The mean velocity for V(L) for all the basal segments was higher compared to the midsegments during systole [3.5+/-1.2 vs. 2.5+/-1.7 cm/s (p<0.01)], early filling [-6.9+/-1.8 vs. -4.9+/-1.8 cm/s (p<0.001)], and during atrial contraction [-2.2+/-1.4 vs. -1.6+/-1.3 cm/s (p<0.05)]. A similar pattern was observed when comparing velocities from the midsegments to the apex. Radial velocity was higher during early filling in the midportion of the lateral [-4.9+/-2.7 vs. -3.2+/-1.6 cm/s (p<0.05)] wall compared to the basal segments, no difference was observed for the septal [-2.0+/-1.5 vs. -0.3+/-2.5 cm/s (p=0.15)], anterior [-5.8+/-3.3 vs. -4.0+/-1.7 cm/s (p=0.17)], and posterior [-2.3+/-2.1 vs. -2.5+/-1.0 cm/s (p=0.78)] walls. When observing the myocardial velocity in a single point and visualizing the movement of the main direction of the velocities in this point as vectors in velocity vector plots like planes, it is clear that myocardial movement is by no means one dimensional. In conclusion, our time-resolved 3D, phase contrast MRI technique makes it feasible to extract myocardial velocities from anywhere in the myocardium, including all three velocity components without the need for positioning any slices at the time of acquisition.

Adult↗

PubMed2002

Correction for displacement artifacts in 3D phase contrast imaging.

PURPOSE: To correct for displacement artifacts in 3D phase contrast imaging. MATERIALS AND METHODS: A 3D phase contrast pulse sequence was modified so that displacements of velocity measurements were restricted to one direction. By applying a postprocessing method, displaced measurements could be traced back to their accurate positions. Flow studies were performed using a phantom that generated flow through a stenosis, directed oblique relative to the phase and frequency encoding directions. Velocity profiles and streamline visualization were used to compare displaced and corrected velocity data to a reference. RESULTS: Velocity profiles obtained from the original measurement showed skewed profiles due to the displacement artifact, both at close proximity to the orifice as well as further downstream. After correction, concordance with the reference improved considerably. CONCLUSION: The displacement artifact, which restricts the accuracy of phase contrast measurements, can be corrected for using the proposed method. Correction of the phase contrast velocity data may improve the accuracy of subsequent flow analysis and visualization.

Artifacts↗

PubMed2002

Kinematics of the heart: strain-rate imaging from time-resolved three-dimensional phase contrast MRI.

A four-dimensional mapping (three spatial dimensions + time) of myocardial strain-rate would help to describe the mechanical properties of the myocardium, which affect important physiological factors such as the pumping performance of the ventricles. Strain-rate represents the local instantaneous deformation of the myocardium and can be calculated from the spatial gradients of the velocity field. Strain-rate has previously been calculated using one-dimensional (ultrasound) or two-dimensional (2-D) magnetic resonance imaging) techniques. However, this assumes that myocardial motion only occurs in one direction or in one plane, respectively. This paper presents a method for calculation of the time-resolved three-dimensional (3-D) strain-rate tensor using velocity vector information in a 3-D spatial grid during the whole cardiac cycle. The strain-rate tensor provides full information of both magnitude and direction of the instantaneous deformation of the myocardium. A method for visualization of the full 3-D tensor is also suggested. The tensors are visualized using ellipsoids, which display the principal directions of strain-rate and the ratio between strain-rate magnitude in each direction. The presented method reveals the principal strain-rate directions without a priori knowledge of myocardial motion directions.

Biomechanical Phenomena↗