Article

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: 2.02). 08/2009; 28(1):41-6. DOI: 10.1016/j.mri.2009.05.042
Source: PubMed

ABSTRACT 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

Full-text

Available from: Michael D Hope, Jul 05, 2015
0 Followers
 · 
121 Views
  • [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 · 3.68 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The initiation, growth and rupture of intracranial aneurysms are intensively studied by computational fluid dynamics. To gain confidence in the results of numerical simulations, validation of the results is necessary. To this end the unsteady flow was measured in a silicone phantom of a realistic intracranial aneurysm. A flow circuit was built with a novel unsteady flow rate generating method, used to model the idealised shape of the heartbeat. This allowed the measurement of the complex three-dimensional velocity distribution by means of laser-optical methods such as laser doppler anemometry (LDA) and particle image velocimetry (PIV). The PIV measurements, available with high temporal and spatial distribution, were found to have good agreement with the control LDA measurements. Furthermore, excellent agreement was found with the numerical results.
    Experiments in Fluids 01/2011; 52(1):37-52. DOI:10.1007/s00348-011-1206-z · 1.91 Impact Factor