During the past decade our group has developed highly accelerated MR angiographic techniques based on undersampled radial acquisition, constrained reconstruction, and phase contrast imaging. Three basic modes of functional MRA (fMRA) will be implemented using 3D radial acquisition (VIPR). These are: 1. Contrast-enhanced (CE) time-resolved angiography with highly constrained reconstruction (HYPR) 2. Undersampled phase contrast imaging 3. HYPR processed CE-MRA using the phase contrast data for the composite image (HYPR FLOW) See Figure 1 in specific aims for an overview of the three modes. The first mode typically provides acceleration factors of 20 to 200 relative to non-accelerated, Nyquist- satisfying Cartesian acquisition with noise factors an order of magnitude less than for parallel imaging. The phase contrast mode provides a method for non-CE angiography with excellent isotropic spatial resolution. This information permits the measurement of flow and pressure gradients in small vessels, adding a new dimension to non-invasive angiography. In the third mode, which also provides flow derived information, undersampling factors of up to 1000 relative to the Nyquist requirements have been achieved, providing voxel volumes an order of magnitude smaller than competing techniques, with temporal resolution of about 0.75 seconds. We propose to optimize these acquisition and reconstruction methods and to begin preliminary investigations of the feasibility of new applications such as relative wall shear stress measurement and pressure gradients. We will use simulations, phantom studies, volunteers and patients to determine the range of spatial and temporal resolution required for various applications and the sampling and SNR requirements for accurate determination of flow-derived quantities. We will obtain pilot studies in patients with altered flow conditions related to intracranial arterial stenosis, aneurysm and arteriovenous malformations. The data will be processed to provide a temporal series, displays of velocity, volume flow, relative wall shear stress and pressure gradients.
Functional Magnetic Resonance Angiography (fMRA) is a method to visualize the vascular structures of the brain. The technique has benefits over current methods in that it covers the entire brain and provides temporal information, high spatial resolution and flow dynamics. It is of minimal risk compared to conventional catheter based angiography and is thus better suited for the evaluation of atherosclerotic disease in elderly patients. It is a major advance in the evaluation of patients with atherosclerotic disease, brain aneurysms and vascular malformations, which are the leading causes of stoke in the US.
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|Chang, W; Frydrychowicz, A; Kecskemeti, S et al. (2011) The effect of spatial resolution on wall shear stress measurements acquired using radial phase contrast magnetic resonance angiography in the middle cerebral arteries of healthy volunteers. Preliminary results. Neuroradiol J 24:115-20|
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|Frydrychowicz, Alex; François, Christopher J; Turski, Patrick A (2011) Four-dimensional phase contrast magnetic resonance angiography: potential clinical applications. Eur J Radiol 80:24-35|
|Wu, Yijing; Kecskemeti, Steven R; Johnson, Kevin et al. (2011) HYPR TOF: time-resolved contrast-enhanced intracranial MR angiography using time-of-flight as the spatial constraint. J Magn Reson Imaging 33:719-23|
|Wu, Yijing; Johnson, Kevin; Kecskemeti, Steven R et al. (2011) Time resolved contrast enhanced intracranial MRA using a single dose delivered as sequential injections and highly constrained projection reconstruction (HYPR CE). Magn Reson Med 65:956-63|
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