Accelerating cine phase-contrast flow measurements using k-t BLAST and k-t SENSE.

Conventional phase-contrast velocity mapping in the ascending aorta was combined with k-t BLAST and k-t SENSE. Up to 5.3-fold net acceleration was achieved, enabling single breath-hold acquisitions. A standard phase-contrast (PC) sequence with interleaved acquisition of the velocity-encoded segments was modified to collect data in 2 stages, a high-resolution under sampled and a low-resolution fully sampled training stage. In addition, a modification of the k-t reconstruction strategy was tested. This strategy, denoted as "plug-in," incorporates data acquired in the training stage into the final reconstruction for improved data consistency, similar to conventional keyhole. "k-t SENSE plug-in" was found to provide best image quality and most accurate flow quantification. For this strategy, at least 10 training profiles are required to yield accurate stroke volumes (relative deviation <5%) and good image quality. In vivo 2D cine velocity mapping was performed in 6 healthy volunteers with 30-32 cardiac phases (spatial resolution 1.3 x 1.3 x 8-10 mm(3), temporal resolution of 18-38 ms), yielding relative stroke volumes of 106 +/- 18% (mean +/- 2*SD) and 112 +/- 15% for 3.8 x and 5.3 x net accelerations, respectively. In summary, k-t BLAST and k-t SENSE are promising approaches that permit significant scan-time reduction in PC velocity mapping, thus making high-resolution breath-held flow quantification possible.     

Optimizing spatiotemporal sampling for k-t BLAST and k-t SENSE: application to high-resolution real-time cardiac steady-state free precession.

In k-t BLAST and k-t SENSE, data acquisition is accelerated by sparsely sampling k-space over time. This undersampling in k-t space causes the object signals to be convolved with a point spread function in x-f space (x = spatial position, f = temporal frequency). The resulting aliasing is resolved by exploiting spatiotemporal correlations within the data. In general, reconstruction accuracy can be improved by controlling the k-t sampling pattern to minimize signal overlap in x-f space. In this work, we describe an approach to obtain generally favorable patterns for typical image series without specific knowledge of the image series itself. These optimized sampling patterns were applied to free-breathing, untriggered (i.e., real-time) cardiac imaging with steady-state free precession (SSFP). Eddy-current artifacts, which are otherwise increased drastically in SSFP by the undersampling, were minimized using alternating k-space sweeps. With the synergistic combination of the k-t approach with optimized sampling and SSFP with alternating k-space sweeps, it was possible to achieve a high signal-to-noise ratio, high contrast, and high spatiotemporal resolutions, while achieving substantial immunity against eddy currents. Cardiac images are shown, demonstrating excellent image quality and an in-plane resolution of approximately 2.0 mm at >25 frames/s, using one or more receiver coils.     

k-t BLAST and k-t SENSE: dynamic MRI with high frame rate exploiting spatiotemporal correlations.

Dynamic images of natural objects exhibit significant correlations in k-space and time. Thus, it is feasible to acquire only a reduced amount of data and recover the missing portion afterwards. This leads to an improved temporal resolution, or an improved spatial resolution for a given amount of acquisition. Based on this approach, two methods were developed to significantly improve the performance of dynamic imaging, named k-t BLAST (Broad-use Linear Acquisition Speed-up Technique) and k-t SENSE (SENSitivity Encoding) for use with a single or multiple receiver coils, respectively. Signal correlations were learned from a small set of training data and the missing data were recovered using all available information in a consistent and integral manner. The general theory of k-t BLAST and k-t SENSE is applicable to arbitrary k-space trajectories, time-varying coil sensitivities, and under- and overdetermined reconstruction problems. Examples from ungated cardiac imaging demonstrate a 4-fold acceleration (voxel size 2.42 x 2.52 mm(2), 38.4 fps) with either one or six receiver coils. k-t BLAST and k-t SENSE are applicable to many areas, especially those exhibiting quasiperiodic motion, such as imaging of the heart, the lungs, the abdomen, and the brain under periodic stimulation.     

Accelerating cardiac cine 3D imaging using k-t BLAST.

By exploiting spatiotemporal correlations in cardiac acquisitions using k-t BLAST, gated cine 3D acquisitions of the heart were accelerated by a net factor of 4.3, making single breathhold acquisitions possible. Sparse sampling of k-t space along a sheared grid pattern was implemented into a cine 3D SSFP sequence. The acquisition of low-resolution training data, which was required to resolve aliasing in the k-t BLAST method, was either interleaved into the sampling process or obtained in a separate prescan to allow for shorter breathhold durations in patients with heart disease. Volumetric datasets covering the heart with 20 slices at a spatial resolution of 2 x 2 x 5 mm3 were recorded with 20 cardiac phases in a total breathhold duration of 25-27 sec, or 18 sec if partial Fourier sampling was additionally employed. The feasibility of the method was demonstrated on healthy volunteers and on patients. The comparison of endocardial area derived from single slices of the 3D dataset with values extracted from separate single-slice acquisitions showed no significant differences. By shortening the acquisition substantially, k-t BLAST may greatly facilitate volumetric imaging of the heart for evaluation of regional wall motion and the assessment of ventricular volume and ejection fraction.     

Fast dynamic contrast-enhanced lung MR imaging using k-t BLAST: a spatiotemporal perspective

Dynamic contrast-enhanced MR imaging has long been an attractive alternative to measure pulmonary perfusion as it offers simultaneous acquisition of high-resolution anatomical images and various functional information without exposing to ionizing radiation. As higher temporal resolution in addition to simultaneous acquisition of more slices from different positions favors more precise diagnosis, rapid acquisition of multiple images during bolus contrast administration remains essential to pulmonary perfusion imaging. Nevertheless, the branching morphology together with asynchronization of contrast-enhanced pulmonary perfusion scattered among distinct blood vessels imposes difficulties to faster imaging. This work demonstrates that k-t broad-use linear acquisition speed-up technique (k-t BLAST), having substantial performance on accelerating cardiac cine imaging, can be applied to accelerate dynamic contrast-enhanced lung imaging up to a factor of 5 with errors less than 6% on five healthy subjects and less than 10% on 13 patients, respectively, in the overall signal intensity. Perfusion parameter estimates show somewhat less errors than those in overall signal intensity. Results from healthy subjects and two groups of patients with various diseases show high consistency between fully sampled datasets and their accelerated counterparts. These suggest feasibility of accelerated contrast-enhanced lung images in clinical examinations and potential of extending k-t BLAST into related applications.     

Unaliasing by fourier-encoding the overlaps using the temporal dimension (UNFOLD), applied to cardiac imaging and fMRI.

In several applications, MRI is used to monitor the time behavior of the signal in an organ of interest; e.g., signal evolution because of physiological motion, activation, or contrast-agent accumulation. Dynamic applications involve acquiring data in a k-t space, which contains both temporal and spatial information. It is shown here that in some dynamic applications, the t axis of k-t space is not densely filled with information. A method is introduced that can transfer information from the k axes to the t axis, allowing a denser, smaller k-t space to be acquired, and leading to significant reductions in the acquisition time of the temporal frames. Results are presented for cardiac-triggered imaging and functional MRI (fMRI), and are compared with data obtained in a conventional way. The temporal resolution was increased by nearly a factor of two in the cardiac-triggered study, and by as much as a factor of eight in the fMRI study. This increase allowed the acquisition of fMRI activation maps, even when the acquisition time for a single full time frame was actually longer than the paradigm cycle period itself. The new method can be used to significantly reduce the acquisition time of the individual temporal frames in certain dynamic studies. This can be used, for example, to increase the temporal or spatial resolution, increase the spatial coverage, decrease the total imaging time, or alter sequence parameters e.g., repetition time (TR) and echo time (TE) and thereby alter contrast. Magn Reson Med 42:813-828, 1999.     

Improving k-t SENSE by adaptive regularization.

The recently proposed method known as k-t sensitivity encoding (SENSE) has emerged as an effective means of improving imaging speed for several dynamic imaging applications. However, k-t SENSE uses temporally averaged data as a regularization term for image reconstruction. This may not only compromise temporal resolution, it may also make some of the temporal frequency components irrecoverable. To address that issue, we present a new method called spatiotemporal domain-based unaliasing employing sensitivity encoding and adaptive regularization (SPEAR). Specifically, SPEAR provides an improvement over k-t SENSE by generating adaptive regularization images. It also uses a variable-density (VD), sequentially interleaved k-t space sampling pattern with reference frames for data acquisition. Simulations based on experimental data were performed to compare SPEAR, k-t SENSE, and several other related methods, and the results showed that SPEAR can provide higher temporal resolution with significantly reduced image artifacts. Ungated 3D cardiac imaging experiments were also carried out to test the effectiveness of SPEAR, and real-time 3D short-axis images of the human heart were produced at 5.5 frames/s temporal resolution and 2.4 x 1.2 x 8 mm3 spatial resolution with eight slices.     

Noquist: reduced field-of-view imaging by direct Fourier inversion.

A novel technique called "Noquist" is introduced for the acceleration of dynamic cardiac magnetic resonance imaging (CMRI). With the use of this technique, a more sparsely sampled dynamic image sequence is reconstructed correctly, without Nyquist foldover artifact. Unlike most other reduced field-of-view (rFOV) methods, Noquist does not rely on data substitution or temporal interpolation to reconstruct the dynamic image sequence. The proposed method reduces acquisition time in dynamic MRI scans by eliminating the data redundancy associated with static regions in the dynamic scene. A reduction of imaging time is achieved by a fraction asymptotically equal to the static fraction of the FOV, by omitting acquisition of an appropriate subset of phase-encoding views from a conventional equidistant Cartesian acquisition grid. The theory behind this method is presented along with sample reconstructions from real and simulated data. Noquist is compared with conventional cine imaging by retrospective selection of a reduced data set from a full-grid conventional image sequence. In addition, a comparison is presented, using real and simulated data, of our technique with an existing rFOV technique that uses temporal interpolation. The experimental results confirm the theory, and demonstrate that Noquist reduces scan time for cine MRI while fully preserving both spatial and temporal resolution, but at the cost of a reduced signal-to-noise ratio (SNR).     

k-t BLAST reconstruction from non-Cartesian k-t space sampling.

Current implementations of k-t Broad-use Linear Acqusition Speed-up Technique (BLAST) require the sampling in k-t space to conform to a lattice. To permit the use of k-t BLAST with non-Cartesian sampling, an iterative reconstruction approach is proposed in this work. This method, which is based on the conjugate gradient (CG) method and gridding reconstruction principles, can efficiently handle data that are sampled along non-Cartesian trajectories in k-t space. The approach is demonstrated on prospectively gated radial and retrospectively gated Cartesian imaging. Compared to a sliding window (SW) reconstruction, the resulting image series exhibit lower artifact levels and improved temporal fidelity. The proposed approach thus allows investigators to combine the specific advantages of non-Cartesian imaging or retrospective gating with the acceleration provided by k-t BLAST.     

Feasibility of k-t BLAST technique for measuring "seven-dimensional" fluid flow

PURPOSE: To investigate the feasibility of rapid MR measurement of "seven-dimensional" (three velocity components, three dimensions, and time) fluid flow using the k-t Broad-use Linear Acquisition Speed-Up Technique (BLAST). MATERIALS AND METHODS: Complete k-space data were acquired for pulsatile fluid flow in a model of a stenosed carotid bifurcation. The data was subsampled to simulate "training" and "accelerated acquisition" data for reconstruction using k-t BLAST. RESULTS: Flow waveforms estimated from k-t BLAST reconstructions were in good agreement with those measured from the full data set for overall speedup factors up to approximately four times when slice-by-slice undersampling in k(y) was used. Accuracy was better than 25 mm/second or 7% (root-mean-square error) for individual time frames under these conditions. Flow patterns in the plane of symmetry, near the bifurcation, and in the stenosis were also in good agreement with those reconstructed from the full data set. Improved performance was obtained from undersampling in both k(y) and k(z), when acceleration factors up to 12 times gave acceptable results. CONCLUSION: The k-t BLAST technique can be applied to flow quantification, and may make feasible the acquisition of time-resolved blood flow from extended arterial regions within acceptable examination times.     

Extension of the UNFOLD method to include free breathing.

Unaliasing by Fourier-encoding the overlaps using the temporal dimension (UNFOLD) is a method to reduce the data acquisition burden in dynamic MRI. The method works by forcing aliased signals to behave in specific ways through time, so that these unwanted signals can be detected and removed. Unexpected events in time, such as displacements caused by breathing, have the potential to disturb the temporal strategy and may affect UNFOLD's ability to suppress aliasing artifacts. This work presents an extension of the UNFOLD method to accommodate temporal encoding disruptions. While the main type of disruption considered here comes from respiratory motion, other types of disruption can be envisioned, such as departures from the usual UNFOLD k-space sampling scheme. This extended version of UNFOLD was incorporated into UNFOLD-sensitivity encoding (UNFOLD-SENSE), and should also be applicable to closely related methods such as temporal SENSE (TSENSE), k-t Broaduse Linear Acquisition Speed up Technique (k-t BLAST), and k-t SENSE. Five patients were imaged with a modified version of a myocardial-perfusion sequence, and UNFOLD was used either alone or in conjunction with SENSE to obtain an acceleration of 2.0 (in three patients) or 3.0 (in two patients). In both cases this extended version of UNFOLD was able to suppress artifacts caused by the presence of breathing motion.     

k-t GRAPPA: a k-space implementation for dynamic MRI with high reduction factor.

A novel technique called "k-t GRAPPA" is introduced for the acceleration of dynamic magnetic resonance imaging. Dynamic magnetic resonance images have significant signal correlations in k-space and time dimension. Hence, it is feasible to acquire only a reduced amount of data and recover the missing portion afterward. Generalized autocalibrating partially parallel acquisitions (GRAPPA), as an important parallel imaging technique, linearly interpolates the missing data in k-space. In this work, it is shown that the idea of GRAPPA can also be applied in k-t space to take advantage of the correlations and interpolate the missing data in k-t space. For this method, no training data, filters, additional parameters, or sensitivity maps are necessary, and it is applicable for either single or multiple receiver coils. The signal correlation is locally derived from the acquired data. In this work, the k-t GRAPPA technique is compared with our implementation of GRAPPA, TGRAPPA, and sliding window reconstructions, as described in Methods. The experimental results manifest that k-t GRAPPA generates high spatial resolution reconstruction without significant loss of temporal resolution when the reduction factor is as high as 4. When the reduction factor becomes higher, there might be a noticeable loss of temporal resolution since k-t GRAPPA uses temporal interpolation. Images reconstructed using k-t GRAPPA have less residue/folding artifacts than those reconstructed by sliding window, much less noise than those reconstructed by GRAPPA, and wider temporal bandwidth than those reconstructed by GRAPPA with residual k-space. k-t GRAPPA is applicable to a wide range of dynamic imaging applications and is not limited to imaging parts with quasi-periodic motion. Since only local information is used for reconstruction, k-t GRAPPA is also preferred for applications requiring real time reconstruction, such as monitoring interventional MRI.     

Accelerated aortic flow assessment with compressed sensing with and without use of the sparsity of the complex difference image

Phase contrast (PC) cardiac MR is widely used for the clinical assessment of blood flow in cardiovascular disease. One of the challenges of PC cardiac MR is the long scan time which limits both spatial and temporal resolution. Compressed sensing reconstruction with accelerated PC acquisitions is a promising technique to increase the scan efficiency. In this study, we sought to use the sparsity of the complex difference of the two flow‐encoded images as an additional constraint term to improve the compressed sensing reconstruction of the corresponding accelerated PC data acquisition. Using retrospectively under‐sampled data, the proposed reconstruction technique was optimized and validated in vivo on 15 healthy subjects. Then, prospectively under‐sampled data was acquired on 11 healthy subjects and reconstructed with the proposed technique. The results show that there is good agreement between the cardiac output measurements from the fully sampled data and the proposed compressed sensing reconstruction method using complex difference sparsity up to acceleration rate 5. In conclusion, we have developed and evaluated an improved reconstruction technique for accelerated PC cardiac MR that uses the sparsity of the complex difference of the two flow‐encoded images. Magn Reson Med 70:851–858, 2013. © 2012 Wiley Periodicals, Inc.     

Evaluation of global cardiac functional parameters using single-breath-hold three-dimensional cine steady-state free precession MR imaging with two types of speed-up techniques: comparison with two-dimensional cine imaging.

The purpose of this study was to demonstrate the feasibility of single-breath-hold three-dimensional (3D) cine cardiac magnetic resonance (MR) imaging using steady-state free precession (SSFP) and two types of speed-up techniques for evaluation of global cardiac function. Twenty-one patients with acquired cardiac diseases were enrolled and underwent two-dimensional (2D) and 3D cine cardiac SSFP MR imaging using a 1.5T unit. Sensitivity encoding (n=12) and k-t broad-use linear acquisition speed-up (BLAST; n=9) were employed for the 3D cine imaging. High correlations for cardiac functional parameters were observed between 2D and 3D cine images (P<0.0001, r>0.94). However, end-diastolic volume and ejection fraction of the left ventricle were significantly lower in the 3D cine imaging with k-t BLAST than in the 2D cine imaging (P<0.0025). On the other hand, k-t BLAST allowed for a shorter breath-holding time owing to the higher acceleration factor. In conclusion, the single-breath-hold 3D cine imaging combined with speed-up techniques provided global cardiac functional parameters comparable to 2D cine imaging.     

Assessment of left ventricular volumes and mass with fast 3D cine steady-state free precession k-t space broad-use linear acquisition speed-up technique (k-t BLAST)

PURPOSE: To compare left ventricular (LV) volume and mass assessment using two-dimensional (2D) cine steady-state free precession (SSFP) and k-t space broad-use linear acquisition speed-up technique (k-t BLAST) accelerated 3D magnetic resonance imaging (MRI). MATERIALS AND METHODS: On a commercially available 1.5T MR scanner, 2D cine SSFP, six- and eight-fold accelerated 3D k-t BLAST were performed to evaluate LV volumes and mass in 17 volunteers. After semiautomatic segmentation of the different MR data sets, the resulting volumes and mass were compared according to the mean difference, 95% confidence interval, standard deviation (SD), Pearson's correlation coefficient, Bland-Altman analysis, and the Pitman-Morgan test. RESULTS: Data acquisition was successful in all subjects. The number of required breathholds was reduced from a maximal of five for the 2D cine SSFP sequence to two for 3D k-t BLAST sequences. Comparing LV volumes, there was excellent agreement between 2D and 3D cine 8x k-t BLAST SSFP volumes (mean difference +/- 2SD end-diastolic volume [EDV] = 5 +/- 8 mL, end-systolic volume [ESV] = 1 +/-12 mL, and stroke volume [SV] = 3 +/- 8 mL), and mass (-1.8 +/- 9 g). CONCLUSION: k-t BLAST-accelerated 3D sequences allow accurate assessment of LV volumes and mass compared to 2D cine SSFP. This method may reduce costs and increase patient comfort due to shortened data acquisition time and reduced number of breathholds.     

Split‐acquisition real‐time CINE phase‐contrast MR flow measurements

The temporal and spatial resolution of real‐time phase‐contrast magnetic resonance (PCMR) is restricted by the need to acquire two interleaved phase images. In this article, we propose a split‐acquisition real‐time CINE PCMR technique, where the acquisition of flow‐encoded and flow‐compensated data is divided into separate blocks. By comparing magnitude images, automatic matching of data in cardio‐respiratory space allows subtraction of background phase offsets. Thus, the data is acquired in real‐time but with phase correction originating from a different heart beat. This effectively doubles the frame rate, allowing either higher temporal or spatial resolution. Two split‐acquisition sequences were tested: one with high‐temporal resolution and one with high‐spatial resolution. Both sequences showed excellent agreement in stroke volumes in 20 adults when validated against cardiac‐gated PCMR and interleaved real‐time PCMR (cardiac gated: 95.2 ± 20.0 mL, interleaved real‐time: 96.2 ± 20.7 mL, high‐temporal resolution: 95.6 ± 20.1 mL, high‐spatial resolution: 95.5 ± 20.4 mL). In six children, the high‐spatial resolution sequence provided more accurate flow measurements than interleaved real‐time PCMR, when compared with cardiac‐gated PCMR (cardiac gated: 20.6 ± 7.6 mL, interleaved real‐time: 24.3 ± 9.2 mL, high‐spatial resolution: 20.8 ± 7.8 mL), due to the increased spatial resolution. The matching technique is shown to be accurate (truth: 94.6 ± 21.8, split‐acquisition: 95.0 ± 21.9 mL) and quantitative image quality (signal‐to‐noise ratio, velocity‐to‐noise ratio and edge sharpness) is acceptable. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Compressed sensing in dynamic MRI.

Recent theoretical advances in the field of compressive sampling-also referred to as compressed sensing (CS)-hold considerable promise for practical applications in MRI, but the fundamental condition of sparsity required in the CS framework is usually not fulfilled in MR images. However, in dynamic imaging, data sparsity can readily be introduced by applying the Fourier transformation along the temporal dimension assuming that only parts of the field-of-view (FOV) change at a high temporal rate while other parts remain stationary or change slowly. The second condition for CS, random sampling, can easily be realized by randomly skipping phase-encoding lines in each dynamic frame. In this work, the feasibility of the CS framework for accelerated dynamic MRI is assessed. Simulated datasets are used to compare the reconstruction results for different reduction factors, noise, and sparsity levels. In vivo cardiac cine data and Fourier-encoded velocity data of the carotid artery are used to test the reconstruction performance relative to k-t broad-use linear acquisition speed-up technique (k-t BLAST) reconstructions. Given sufficient data sparsity and base signal-to-noise ratio (SNR), CS is demonstrated to result in improved temporal fidelity compared to k-t BLAST reconstructions for the example data sets used in this work.     

Accelerated time-resolved three-dimensional MR velocity mapping of blood flow patterns in the aorta using SENSE and k-t BLAST

Purpose

To assess the feasibility and potential limitations of the acceleration techniques SENSE and k-t BLAST for time-resolved three-dimensional (3D) velocity mapping of aortic blood flow. Furthermore, to quantify differences in peak velocity versus heart phase curves.

Materials and methods

Time-resolved 3D blood flow patterns were investigated in eleven volunteers and two patients suffering from aortic diseases with accelerated PC-MR sequences either in combination with SENSE (R = 2) or k-t BLAST (6-fold). Both sequences showed similar data acquisition times and hence acceleration efficiency. Flow-field streamlines were calculated and visualized using the GTFlow software tool in order to reconstruct 3D aortic blood flow patterns. Differences between the peak velocities from single-slice PC-MRI experiments using SENSE 2 and k-t BLAST 6 were calculated for the whole cardiac cycle and averaged for all volunteers.

Results

Reconstruction of 3D flow patterns in volunteers revealed attenuations in blood flow dynamics for k-t BLAST 6 compared to SENSE 2 in terms of 3D streamlines showing fewer and less distinct vortices and reduction in peak velocity, which is caused by temporal blurring. Solely by time-resolved 3D MR velocity mapping in combination with SENSE detected pathologic blood flow patterns in patients with aortic diseases. For volunteers, we found a broadening and flattering of the peak velocity versus heart phase diagram between the two acceleration techniques, which is an evidence for the temporal blurring of the k-t BLAST approach.

Conclusion

We demonstrated the feasibility of SENSE and detected potential limitations of k-t BLAST when used for time-resolved 3D velocity mapping. The effects of higher k-t BLAST acceleration factors have to be considered for application in 3D velocity mapping.     

Single-breathhold four-dimensional assessment of left ventricular volumes and function using k-t BLAST after application of extracellular contrast agent at 3 Tesla

PURPOSE: To prospectively determine the feasibility and accuracy of a four-dimensional (4D) k-space over time broad-use linear acquisition speed-up technique (k-t BLAST) for the evaluation of left ventricular (LV) volumes in comparison to standard multiple-breathhold cine imaging, using a 3.0 Tesla (3T) MR system. MATERIALS AND METHODS: In 23 subjects, short-axis cine loops completely covering the LV were acquired using conventional turbo gradient echo (GRE) imaging. Immediately after administration of gadobenate dimeglumine, a rapid single-breathhold k-t BLAST 4D dataset with the same coverage was acquired and reconstructed to short-axis views. Quantitative aortic flow measurement for LV stroke volume (LVSV) was used to calibrate both techniques. For GRE and k-t BLAST cine imaging: LV volumes, ejection fraction (EF), and blood-to-myocardium-contrast (BMC) were determined. RESULTS: k-t BLAST and GRE sequences showed a strong correlation for LV volumes and EF (r = 0.97-0.99; P < 0.001). Excellent agreement was also found between the LVSV determined by aortic flow measurements and LVSV assessed using GRE sequence and k-t BLAST sequence. BMC of GRE was similar to that of k-t BLAST cine imaging. CONCLUSION: The use of the single-breathhold 4D k-t BLAST technique for the assessment of LV volume is feasible and accurate in 3T MRI.     

Flow and peak velocity measurements in patients with aortic valve stenosis using phase contrast MR accelerated with k-t BLAST

Objective

To investigate the accuracy of velocity measurements in patients with aortic valve stenosis using phase contrast (PC) imaging accelerated with SENSE (Sensitivity Encoding) and k-t BLAST (Broad-use Linear Acquisition Speed-up Technique).

Methods

Accelerated quantitative breath hold PC measurements, using SENSE and k-t BLAST, were performed in twelve patients whose aortic valve stenosis had been initially diagnosed using echocardiography. Stroke volume (SV) and peak velocity measurements were performed on each subject in three adjacent slices using both accelerating methods.

Results

The peak velocities measured with PC MRI using SENSE were −8.0 ± 9.5% lower (p < 0.01) compared to the peak velocities measured with k-t BLAST and the correlation was r = 0.83. The stroke volumes when using SENSE were slightly higher 0.4 ± 17.1 ml compared to the SV obtained using k-t BLAST but the difference was not significant (p > 0.05).

Conclusions

In this study higher peak velocities were measured in patients with aortic stenosis when combining k-t BLAST with PC MRI compared to PC MRI using SENSE. A probable explanation of this difference is the higher temporal resolution achieved in the k-t BLAST measurement. There was, however, no significant difference between calculated SV based on PC MRI using SENSE and k-t BLAST, respectively.