Evaluation of intracranial stenoses and aneurysms with accelerated 4D flow

Department of Radiology, University of California San Francisco, San Francisco, CA 94143-0628, USA.
Magnetic Resonance Imaging (Impact Factor: 2.09). 08/2009; 28(1):41-6. DOI: 10.1016/j.mri.2009.05.042
Source: PubMed


The aim of this study was to evaluate intracranial arterial stenoses and aneurysms with accelerated time-resolved three-dimensional (3D) phase-contrast MRI or 4D flow. The 4D flow technique was utilized to image four normal volunteers, two patients with intracranial stenoses and two patients with intracranial aneurysms. In order to reduce scan time, parallel imaging was combined with an acquisition strategy that eliminates the corners of k-space. In the two patients with intracranial stenoses, 4D flow velocity measurements showed that one patient had normal velocity profiles in agreement with a previous magnetic resonance angiogram (MRA), while the second showed increased velocities that indicated a less significant narrowing than suspected on a previous MRA, as confirmed by catheter angiography. This result may have prevented an invasive angiogram. In the two patients with 4-mm intracranial aneurysm, one had a stable helical flow pattern with a large jet, while the other had a temporally unstable flow pattern with a more focal jet possibly indicating that the second aneurysm may have a higher likelihood of rupture. Accelerated 4D flow provides time-resolved 3D velocity data in an 8- to 10-min scan. In the stenosis patients, the addition of 4D flow to a traditional MRA adds the velocity data provided from transcranial Doppler ultrasound (TCD) possibly allowing for more accurate grading of stenoses. In the aneurysm patients, visualization of flow patterns may help to provide prognostic information about future risk of rupture.

Download full-text


Available from: Michael D Hope,
  • Source
    • "It should be noted that similar 4D velocity mapping techniques have been applied in different vascular territories such as peripheral vessels [99], carotid arteries [25,100], large intra-cranial arteries [27,28,101,102], and to the velocities of myocardial movements and deformation [32-34]. 4D velocity acquisitions can be used independent from the used MRI platform without major differences with respect to possible implementations of the MR pulse sequence. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Phase contrast cardiovascular magnetic resonance (CMR) is able to measure all three directional components of the velocities of blood flow relative to the three spatial dimensions and the time course of the heart cycle. In this article, methods used for the acquisition, visualization, and quantification of such datasets are reviewed and illustrated. Currently, the acquisition of 3D cine (4D) phase contrast velocity data, synchronized relative to both cardiac and respiratory movements takes about ten minutes or more, even when using parallel imaging and optimized pulse sequence design. The large resulting datasets need appropriate post processing for the visualization of multidirectional flow, for example as vector fields, pathlines or streamlines, or for retrospective volumetric quantification. Multidirectional velocity acquisitions have provided 3D visualization of large scale flow features of the healthy heart and great vessels, and have shown altered patterns of flow in abnormal chambers and vessels. Clinically relevant examples include retrograde streams in atheromatous descending aortas as potential thrombo-embolic pathways in patients with cryptogenic stroke and marked variations of flow visualized in common aortic pathologies. Compared to standard clinical tools, 4D velocity mapping offers the potential for retrospective quantification of flow and other hemodynamic parameters. Multidirectional, 3D cine velocity acquisitions are contributing to the understanding of normal and pathologically altered blood flow features. Although more rapid and user-friendly strategies for acquisition and analysis may be needed before 4D velocity acquisitions come to be adopted in routine clinical CMR, their capacity to measure multidirectional flows throughout a study volume has contributed novel insights into cardiovascular fluid dynamics in health and disease.
    Journal of Cardiovascular Magnetic Resonance 01/2011; 13(1):7. DOI:10.1186/1532-429X-13-7 · 4.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this paper is to discuss the use of linear phase adaptive filters in the tracking of time-varying sinusoids. Efficient algorithms for filters of this type have recently been proposed [1,2]. The filter of interest is an FIR operator consisting of 2M+1 coefficients. The center coefficient is constrained to be unity and the remaining coefficients have even symmetry about this point. Because of these constraints the filtering process may be viewed as one of symmetrically smoothing the input signal-hence the filter is termed the symmetric smoother. The filter coefficients are adapted so as to minimize a time weighted average of the square of the filter output. In this paper, two such algorithms considered: the exact least squares technique [2] and the LMS gradient algorithm [3]. Results illustrating the properties of the symmetric smoother in both a stationary and time-varying environment are presented. On the basis of these results, it is concluded that care must be exercised when interpreting the spectral estimates obtained from a linear phase filter.
    Acoustics, Speech, and Signal Processing, IEEE International Conference on ICASSP '83.; 05/1983
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have developed PC HYPRFlow, a comprehensive MRA technique that includes a whole-brain CE dynamic series followed by PC velocity-encoding, yielding a time series of high-resolution morphologic angiograms with associated velocity information. In this study, we present velocity data acquired by using the PC component of PC HYPRFlow (PC-VIPR). Ten healthy volunteers (6 women, 4 men) were scanned by using PC HYPRFlow and 2D-PC imaging, immediately followed by velocity measurements by using TCD. Velocity measurements were made in the M1 segments of the MCAs from the PC-VIPR, 2D-PC, and TCD examinations. PC-VIPR showed approximately 30% lower mean velocity compared with TCD, consistent with other comparisons of TCD with PC-MRA. The correlation with TCD was r = 0.793, and the correlation of PC-VIPR with 2D-PC was r = 0.723. PC-VIPR is a technique capable of acquiring high-resolution MRA of diagnostic quality with velocity data comparable with TCD and 2D-PC. The combination of velocity information and fast high-resolution whole-brain morphologic angiograms makes PC HYPRFlow an attractive alternative to current MRA methods.
    American Journal of Neuroradiology 01/2011; 32(1):54-9. DOI:10.3174/ajnr.A2240 · 3.59 Impact Factor
Show more