Intracranial 4D Flow MRI

The brain vasculature is a complex flow network with a large range of velocities and patient anatomy, and interest in quantitative brain imaging biomarkers is growing. 4D Flow is used in a variety of neurovascular applications to quantify the impact of the disease on local hemodynamics and flow distributions throughout the whole brain.

  1. Healthy hemodynamics of the brain
    4D Flow images of the brain are a rich and multi-dimensional data set. To simplify this data while retaining the most important features, we represent the neurovasculature as a flow distribution network graph (FDNG). Here we show (A) time-averaged pathlines derived from the 4D flow velocity information, (B) identification of vessels (yellow) and schematic representation as a FDNG (blue), and (C) a standardized FDNG containing mean and standard deviations of flow values over a group of healthy controls with the same Circle of Willis structure variant.

    Primary contact: Susanne Schnell (PhD)
    Investigators: Susanne Schnell (PhD), TBD
    Collaborations: Northwestern University (Michael Markl, Ann Ragin, Maria Aristova)

  2. Cerebral Aneurysms
    Cerebral aneurysms are a life-threatening condition and currently, too simplified models are used to decide on treatment or regular follow-up. The risk of aneurysm growth or rupture is difficult to assess and hemodynamic factors are considered as new imaging biomarkers. 4D-flow MRI is employed for the comprehensive in-vivo analysis of hemodynamics.
    We previously investigated the relationship of size and morphology with hemodynamics of different intracranial aneurysms (IA). 4D flow MRI demonstrated the influence of lesion size and morphology on aneurysm hemodynamics suggesting the potential of 4D-flow MRI to assist in the classification of individual aneurysms. Future longitudinal studies and correlation with aneurysm risk factors or aneurysm growth/rupture are required to evaluate the utility of hemodynamic markers for improved risk assessment and therapy planning

    Primary contact: Susanne Schnell (PhD)
    Investigators: Susanne Schnell (PhD), TBD
    Collaborations: Northwestern University (Ann Ragin, Maria Aristova, Sameer Ansari, Mike Hurley)
  3. CSF flow
    The purpose of this study is to establish CSF 4D flow MRI patterns in normal individuals and to assess the effect of spine positioning on these flow patterns. Once we establish CSF flow patterns in healthy controls, we will investigate whether patients with Chiari I Malformation (CIM) exhibit similar patterns or if they are particular to CIM, which may correlate with symptom severity and/or likelihood to improve following surgery.
    MR imaging protocols for CIM include sagittal images to assess the position of the cerebellar tonsils. Sometimes, 2D phase-contrast (PC) imaging is obtained to investigate whether structural abnormalities are resulting in abnormal CSF flow at the foramen magnum. Often, CSF flow improves after posterior fossa decompression when compared to a preoperative study. Unfortunately, interpretation of these studies is highly subjective and associated with poor interrater reliability.
    Better, more reliable imaging techniques could improve patient selection for surgery and outcomes. Compared to 2D PC MRI, volumetric flow evaluation with ECG-triggered 3D PC MRI using 3-directional velocity encoding (4D flow MRI) is ideally suited to quantify CSF flow dynamics due to the desired extent of flow coverage. However, due to the long T1 relaxation time of CSF and the typical repetition times (TR) of 7 ms for one-directional velocity encoding and 21 ms for 3-directional velocity encoding, the flip angle (FA) of such PC MRI acquisition has to be very low (about 3-6°) for maximum signal in CSF. This results in overall low signal intensity and thus high noise. We plan to investigate a new strategy that allows longitudinal signal recovery and thus acquisition with increased  FA < 15° to achieve improved signal intensities in the CSF.

    Primary contact: Susanne Schnell (PhD)
    Investigators: Susanne Schnell (PhD), TBD
    Collaborations: Northwestern University (Michael Markl, Tarek Hijaz, Alex Kurutz, Ali Shaibani)
  4. Age-related hemodynamic changes
    We are interested in examining changes in cardiac hemodynamics with age and the relationship to cerebral blood flow and distribution. Hemodynamic information from velocity encoded MR imaging can be combined with quantitative brain imaging to determine the prognostic significance for structural and microstructural brain changes, including atrophy and volume loss in specific regions of interest. This approach can be used to evaluate subtle, clinically silent changes that occur in the brain in association with factors such as hypertension and cerebral small vessel disease and to determine the impact on brain network organization. This approach has considerable potential to yield new insights concerning how vascular factors influence individual differences in neurological outcomes in older adults and the shared role in age-related neurological disorders.

    Primary contact: Susanne Schnell (PhD)
    Investigators: Susanne Schnell (PhD), Mark Höller (PhD), TBC
    Collaborations: Northwestern University (Ann Ragin, Maria Aristova)

Advanced MR Image Analysis

  1. Assessment of Stenosis and Flow Distribution in Intracranial Atherosclerotic Disease
    This study focuses on the assessment of hemodynamic impact of intracranial atherosclerotic disease (ICAD) using 4D flow MRI. ICAD is one of the main causes of ischemic stroke worldwide and is associated with a high risk of stroke recurrence in patients potentially due to hemodynamic failure. Therefore, the evaluation of hemodynamic influences of the lesion on the cerebral blood flow distribution and blood flow in stenotic vessels may be useful for ICAD characterization and risk stratification. Here, we used dual-venc 4D flow MRI for in-vivo measurement of time-resolved and 3D velocity of blood in major cerebral arteries.

    Primary contact: Susanne Schnell (PhD)
    Investigators: Susanne Schnell (PhD), TBD
    Collaborations: Northwestern University (Michael Markl, Sameer Ansari,Ann Ragin, Maria Aristova), UCSF (David Saloner, Jared Narvid)
  2. Individualized Assessment of Hemodynamics in Cerebral Arteriovenous Malformations
    Cerebral arteriovenous malformation (AVM) is a congenital, pathological vascular connection between the arterial and venous cerebral vasculature and has severe complications such as seizure or subarachnoid hemorrhage. An accurate, low-risk hemodynamic assessment across vessel sizes and flow velocities in the cerebral vasculature is needed to improve hemorrhage risk estimates at baseline and throughout staged treatment. We are working to address these needs by developing a non-invasive, non-contrast comprehensive 4D Flow imaging approach to characterize time-resolved 3D blood flow and pressure gradients in AVM. This includes characterizing the hemodynamics of AVMs with 4D flow to identify the most clinically relevant metrics and optimizing the 4D flow imaging process to provide that information, from sequence and scan parameters to data post-processing, presentation, and clinical correlation.

    Primary contact: Susanne Schnell (PhD)
    Investigators: Susanne Schnell (PhD), TBD
    Collaborations: Northwestern University (Michael Markl,Maria Aristova, Ali Shaibani), Purdue University (Vitaliy Rayz)