Purpose:To evaluate an improved image acquisition and data-processing strategy for assessing aortic vascular geometry and 3D blood flow at 3T. Materials and Methods:In a study with five normal volunteers and seven patients with known aortic pathology, prospectively ECG-gated cine three-dimensional (3D) MR velocity mapping with improved navigator gating, real-time adaptive k-space ordering and dynamic adjustment of the navigator acceptance criteria was performed. In addition to morphological information and three-directional blood flow velocities, phase-contrast (PC)-MRA images were derived from the same data set, which permitted 3D isosurface rendering of vascular boundaries in combination with visualization of blood-flow patterns.Results: Analysis of navigator performance and image quality revealed improved scan efficiencies of 63.6% Ϯ 10.5% and temporal resolution (Ͻ50 msec) compared to previous implementations. Semiquantitative evaluation of image quality by three independent observers demonstrated excellent general image appearance with moderate blurring and minor ghosting artifacts. Results from volunteer and patient examinations illustrate the potential of the improved image acquisition and data-processing strategy for identifying normal and pathological blood-flow characteristics. Conclusion:Navigator-gated time-resolved 3D MR velocity mapping at 3T in combination with advanced data processing is a powerful tool for performing detailed assessments of global and local blood-flow characteristics in the aorta to describe or exclude vascular alterations.

A three-dimensional computational fluid dynamics (CFD) method has been developed to simulate the flow in a pumping left ventricle. The proposed method uses magnetic resonance imaging (MRI) technology to provide a patient specific, time dependent geometry of the ventricle to be simulated. Standard clinical imaging procedures were used in this study. A two-dimensional time-dependent orifice representation of the heart valves was used. The location and size of the valves is estimated based on additional long axis images through the valves. A semi-automatic grid generator was created to generate the calculation grid. Since the time resolution of the MR scans does not fit the requirements of the CFD calculations a third order bezier approximation scheme was developed to realize a smooth wall boundary and grid movement. The calculation was performed by a Navier-Stokes solver using the arbitrary Lagrange-Euler (ALE) formulation. Results show that during diastole, blood flow through the mitral valve forms an asymmetric jet, leading to an asymmetric development of the initial vortex ring. These flow features are in reasonable agreement with in vivo measurements but also show an extremely high sensitivity to the boundary conditions imposed at the inflow. Changes in the atrial representation severely alter the resulting flow field. These shortcomings will have to be addressed in further studies, possibly by inclusion of the real atrial geometry, and imply additional requirements for the clinical imaging processes.

Purpose: To detect and investigate details in left ventricular (LV) motion patterns with a temporal resolution comparable to that of echocardiography. Material and Methods:To assess global and regional myocardial motion in high temporal detail, respiratory-gated MR phase-contrast measurements with three-directional velocity encoding (venc) were performed in 12 healthy volunteers and two patients with LV hypertrophy in basal, midventricular, and apical locations of the LV with a temporal resolution of 13.8 msec. Results:The volunteer data revealed details in LV motion patterns that were known only from echocardiography. For all volunteers, characteristic myocardial motion patterns, such as triphasic global diastolic expansion, could be detected with high accuracy. One volunteer underwent an additional echocardiographic measurement in order to corroborate the complex motion features as measured by MRI. Patient examinations revealed substantial changes in diastolic function compared to motion patterns in healthy volunteers. Conclusion:The proposed high-temporal-resolution velocitymapping technique provides previously undetectable information on LV performance, and is highly promising for the detection of local and global motion abnormalities in patients with disturbed LV performance, such as diastolic dysfunction.

The phase contrast MRI technique for high temporal resolution velocity mapping is therefore very promising for the investigation and better understanding of the myocardial motion in normal subjects and patients with disturbed left ventricular performance and may validate further testing of different models of cardiac structure.

4D flow-sensitive MRI permits the comprehensive evaluation of blood flow characteristics in patients after repair of TOF. Altered flow patterns for different surgical techniques in the small patient cohort may indicate its value for patient monitoring and potentially identifying optimal surgical strategies.

Cardiac MRI function measurements are typically based on multiple breathhold 2D sequences to acquire images of the entire heart. In the present study, the feasibility of a cine 3D TrueFISP technique in which several complete volumetric measurements may be obtained during a single breathhold is demonstrated. In contrast to 3D FLASH, the TrueFISP sequence offers an excellent contrast between the myocardium and the intraventricular cavity without the use of contrast agent. An ECG-gated 3D cine TrueFISP sequence was implemented with a repetition time of 2.4 -2.8 ms, which allows imaging of the complete heart within a single breathhold throughout 20 -46 heartbeats with a 3D frame rate of 8 -13 volumes per cardiac cycle and a spatial resolution of about 1.5 ؋ 3.5 ؋ 3.5 mm Cine magnetic resonance imaging represents a method for quantification the 3D functional geometry of the ventricles (1-3). The standard methods for the acquisition of 2D datasets during a single breathhold include turbo-gradient echo sequence (4,5), echo-planar imaging (EPI) (6), and spiral EPI (7). The drawback of these 2D methods is the reduced signal-to-noise ratio (SNR), the sensitivity to motion between scans, and a relatively poor contrast between the myocardium and the intraventricular blood volume. A multislice technique based on 2D TrueFISP acquisitions has proven to offer a superior contrast between myocardium and blood (8). For covering the complete heart, multiple breathholds are necessary to get the functional information in any desired plane of the ventricles. Multiple breathholds, however, require an increased acquisition time and lead to a possible mismatch of adjacent slices due to different breathhold positions.In addition, using multiple breathholds can lead to problems during stress examinations due to the prolonged scan time. The assessment of the complete left ventricle may not be possible because the duration of the imaging procedure may exceed the longest acceptable duration of the stress test. This may be important because stress MR imaging with dobutamine has been shown to be superior to dobutamine stress echocardiography for the noninvasive detection of myocardial ischemia (9).The recent development of high-performance gradient systems enables the acquisition of a single 3D cardiac dataset within a single breathhold. Previously proposed methods for volumetric imaging during a single breathhold are 3D FLASH techniques (10), EPI sequences (11), and segmented EPI techniques (12). Besides these single 3D acquisition techniques, a contrast-enhanced cine 3D projection technique with a temporal aperture of 60 ms within one breathhold has been developed (13). In the present study, we propose a cine 3D technique without the use of a contrast agent based on a balanced SSFP (steadystate free precession), or TrueFISP sequence. This imaging technique offers very high signal-to-noise ratio (SNR) and high contrast between myocardium and blood, which is necessary for the assessment of the left ventricular function. A further advantage as d...

Background-An exact understanding of normal age-and gender-matched regional myocardial performance is an essential perquisite for the diagnosis of heart disease. Magnetic resonance phase-contrast imaging (tissue phase mapping) enabling the analysis of segmental, 3-directional myocardial velocities with high temporal resolution (13.8 ms) was used to assess left ventricular motion. Methods and Results-Radial, long-axis, and rotational myocardial velocities were acquired in 58 healthy volunteers (3 age groups, 29 women) in left ventricular basal, midventricular, and apical short-axis locations. For increased age, reduced (PϽ0.003) and prolonged long-axis and radial velocities (PϽ0.05) during diastole and reduced long-axis velocities (PϽ0.001) and apical rotation (PϽ0.005) during systole were found for both genders. Women demonstrated a reduced systolic twist (Pϭ0.009), apical rotation (Pϭ0.01), and systolic radial velocities (PϽ0.02) compared with men. Segmental analysis of long-axis motion with aging revealed differences in regional reduction of systolic (lateral 52% versus 30%) and diastolic (lateral 57% versus 41%) velocities in women compared with men. In basal segments, young women demonstrated higher long-axis velocities (ϩ11% during diastole) than men, whereas this difference was reversed in older subjects (same segments, Ϫ20%). In addition, increased age resulted in a prolonged time to peak diastolic apical rotation (PϽ0.04) in women compared with men. Conclusions-Age and gender strongly influence regional myocardial motion. Tissue phase mapping provides a comprehensive quantitative analysis of all myocardial velocities with high temporal and spatial resolution. The knowledge of the detected ageand gender-related differences in myocardial motion is fundamental for further investigations of cardiac disease. Clinical Trial Registration-http://www.zks.uni-freiburg.de/uklreg/php/suchergebnis_all.php. Identifier: UKF001739(Circ Cardiovasc Imaging. 2010;3:54-64.)Key Words: magnetic resonance imaging Ⅲ myocardial contraction Ⅲ aging Ⅲ gender V olumetric analysis of the left ventricle based on MRI has been established as a reference standard for the determination of left ventricular (LV) performance. 1 However, early changes in LV motion and regional pathologies may be overlooked by these global parameters because they do not reflect diastolic function or segmental contractility, which are not uniform within the healthy LV. 2 Therefore, a complete segmental analysis of velocities is preferable to detect subtle changes in LV motion. 3 Quantitative noninvasive assessment of regional myocardial performance still remains challenging. 4 Myocardial velocities and derived parameters mainly based on tissue Doppler imaging were suggested as markers for LV contractility 5 and diastolic function. 4 However, because tissue Doppler velocity analyses do not allow assessing all myocardial velocity components, ie, radial, long-axis, and rotational motion for the different LV regions, MRI applications have been developed as alterna...

Purpose:To evaluate an optimized k-t-space related reconstruction method for dynamic magnetic resonance imaging (MRI), a method called PEAK-GRAPPA (Parallel MRI with Extended and Averaged GRAPPA Kernels) is presented which is based on an extended spatiotemporal GRAPPA kernel in combination with temporal averaging of coil weights. Materials and Methods:The PEAK-GRAPPA kernel consists of a uniform geometry with several spatial and temporal source points from acquired k-space lines and several target points from missing k-space lines. In order to improve the quality of coil weight estimation sets of coil weights are averaged over the temporal dimension. Results:The kernel geometry leads to strongly decreased reconstruction times compared to the recently introduced k-t-GRAPPA using different kernel geometries with only one target point per kernel to fit. Improved results were obtained in terms of the root mean square error and the signal-to-noise ratio as demonstrated by in vivo cardiac imaging. Conclusion:Using a uniform kernel geometry for weight estimation with the properties of uncorrelated noise of different acquired timeframes, optimized results were achieved in terms of error level, signal-to-noise ratio, and reconstruction time. DYNAMIC MRI is an important foundation for many clinical applications such as time-resolved (Cine) cardiac imaging for the assessment of left ventricular function. To achieve sufficient spatial and temporal resolution fast data acquisition is essential, particularly for applications that require breath-holding. In order to reduce total acquisition time or to increase spatiotemporal resolution, parallel imaging techniques such as SENSE or GRAPPA have been introduced. By decreasing the number of phase-encoding steps by a reduction factor R, imaging can be substantially accelerated (1,2). Based on varying sensitivity in multiple receiver coil arrays, parallel imaging reconstruction algorithms remove resulting aliasing artifacts either in the image domain (2) or regenerate the missing data in k-space (1). For parallel imaging reconstruction using the kspace related GRAPPA technique the image reconstruction and the combination of images from different receiver coils are decoupled. Therefore, the process of unaliasing of the uncombined coil images (generated from each coil) can be optimized separately.For conventional parallel dynamic MRI using GRAPPA, the central k-space for each timeframe is fully sampled, forming the autocalibration signal (ACS) lines, while the outer k-space is undersampled in the phase-encoding (ky) direction according to a user-defined reduction factor R. All timeframes are reconstructed independently using a kernel with a certain extension in kx-and ky-direction. The kernel is shifted across the ACS lines in order to estimate the coil weights needed for the reconstruction (or interpolation) of the missing lines in outer k-space. For the reconstruction process of the missing k-space lines, the kernel is shifted by an increment of R in ky-direction over the undersampl...