Radial sliding‐window magnetic resonance angiography (MRA) with highly‐constrained projection reconstruction (HYPR)

Abstract

Sufficient temporal resolution is required to image the dynamics of blood flow, which may be critical for accurate diagnosis and treatment of various intracranial vascular diseases, such as arteriovenous malformations (AVMs) and aneurysms. Highlyconstrained projection reconstruction (HYPR) has recently become a technique of interest for high-speed contrast-enhanced magnetic resonance angiography (CE-MRA). HYPR provides high frame rates by preferential weighting of radial projections while maintaining signal-to-noise ratio (SNR) by using a high SNR composite. An analysis was done to quantify the effects of HYPR on SNR, contrast-to-noise ratio (CNR), and temporal blur compared to the previously developed radial sliding-window technique using standard filtered backprojection or regridding methods. Computer simulations were performed to study the effects of HYPR processing on image error and the temporal information. Additionally, in vivo imaging was done on patients with angiographically confirmed AVMs to measure the effects of alteration of various HYPR parameters on SNR as well as the fidelity of the temporal information. The images were scored by an interventional radiologist in a blinded read and were compared with X-ray digital subtraction angiography (DSA). It was found that with the right choice of parameters, modest improvements in both SNR and dynamic information can be achieved as compared to radial sliding-window MRA. Magn

Recent advances in 3D time-resolved contrast-enhanced MR angiography

“…This is usually traded off with reduced SNR. These and other effects have been studied in detail previously .…”

“…However, if an image is ascribed to some time T because that is the time at which central k ‐space is measured, then the use of any data measured after that specific time in forming that image will cause artifactual nonzero signal in blood vessels in advance of the contrast material actually arriving there. This is called "anticipation artifact" and has been described in Cartesian as well as non‐Cartesian MRA acquisition. A tell‐tale sign is the premature appearance of slight but nonzero signal in venous structures several frame intervals prior to significant enhancement.…”

Accelerated Time-Resolved Contrast-Enhanced Magnetic Resonance Angiography of Dural Arteriovenous Fistulas Using Highly Constrained Reconstruction of Sparse Cerebrovascular Data Sets

“…(18, 19) HYPRFlow is well suited for characterizing AVMs and DAVFs because whole brain coverage allows the whole lesion to be characterized which is possible because the relative sparsity of vessels in 3D space allows for the use of undersampling techniques such as radial acquisition (VIPR). Previous work has demonstrated that use of the HYPR reconstruction method provides improved SNR compared to radially sampling k -space with a sliding window reconstruction method (33)…”

Fast Contrast-Enhanced 4D MRA and 4D Flow MRI Using Constrained Reconstruction (HYPRFlow): Potential Applications for Brain Arteriovenous Malformations

“…30 The advantage of combining radial encoding and constrained reconstructions to increase SNR has been previously demonstrated in healthy subjects 31 and patients with AVMs. 32 …”