Three‐dimensional reconstruction of limited‐view projections for contrast‐enhanced magnetic resonance angiography at high temporal and spatial resolution

Abstract

The feasibility of reconstructing three-dimensional (3D) MRI data sets from limited-view projections is investigated in phantom and in vivo animal studies to improve the temporal resolution of magnetic resonance angiography without sacrificing spatial resolution. Thirty-two pairs of orthogonal biplane projections are acquired in an interleaved manner during the first pass of a contrast agent. The full data set is reconstructed as a priori 3D information. Each pair of projections is then reconstructed into an individual 3D data set based on a correlation analysis with the a priori data set. In this way, time-resolved 3D data sets at 1-to 2-s time intervals are reconstructed with submillimeter spatial resolution. Three-dimensional (3D) contrast-enhanced magnetic resonance angiography (MRA) has been widely applied as a minimally invasive vascular imaging modality (1). To avoid venous enhancement and to improve arterial signalto-noise ratio (SNR) of the 3D data set, elliptical centricordered (EC) sequences are normally used to acquire central regions of k-space at the peak arterial enhancement (2). This requires accurate timing of the contrast arrival at the region of interest and also a good estimate of the contrast distribution time through the region on a patient-by-patient basis to optimize the acquisition parameters such as the injection rate, repetition time (TR), and data matrix size (3). Recessed EC sequences (4) were developed to minimize artifacts associated with timing errors and successfully improved the robustness of contrast-enhanced MRA in clinical applications. However, in some particular situations, such as among patients with arteriovenous fistula or arteriovenous malformations, the blood flow pattern may be significantly altered by irregular pathways and the time for artery-vein contrast passage may be shortened to only a few seconds (5). In such circumstances, venous contamination cannot be avoided even with an accurate timing of the contrast arrival.Time-resolved MRA has been developed for the applications where temporal resolution is of critical importance. Techniques such as time-resolved imaging of contrast kinetics (TRICKS) and projection-reconstruction TRICKS (6 -8) are able to produce 3D data sets at a high temporal rate (2-4 s/3D set) by undersampling data and using view-sharing reconstructions. Therefore, difficulties associated with contrast timing are avoided, and pathologic information can potentially be observed. However, these techniques are not without limitations. Due to the view-sharing (or sliding window) reconstructions, temporal information is smoothed. Therefore, rapid signal changes are not expected to be captured well. Furthermore, the undersampling of high-resolution data both spatially and temporally introduces concerns about the accuracy of the dynamic signals in small vessels.Alternatively, high temporal resolution can be achieved by trading off the spatial resolution in the through-plane dimension (9). This works well clinically when the signal overlapping in the throu...

Time‐resolved MR angiography with limited projections

“…Since HYPR is a noniterative algorithm, it is expected to be more applicable in clinical practice than iterative approaches, such as the assignment and update with correlation (AUCTION) algorithm (7). On the other hand, the iterative approaches are expected to be more flexible in terms of controlling artifacts.…”

“…The acceptable undersampling factors in PR are approximately six in two dimensions and 50 in three dimensions. Recent work with limited view projections (7) and highly constrained backprojection (HYPR) (8) incorporated a composite image as the prior knowledge of the object, thus further leveraging the undersampling factor. When combined with time‐resolved imaging of contrast kinetics (TRICKS) (9), HYPR achieved a 3D undersampling factor of 225.…”

Free-breathing pediatric MRI with nonrigid motion correction and acceleration

“…For data acquisition, radial imaging and radial‐Cartesian hybrid imaging exhibit advantageous motion properties while sampling in a variable‐density manner. Therefore, we modified the 3D Cartesian acquisition to include both variable‐density sampling and radial‐like phase‐encode ordering.…”

Whole‐heart imaging using undersampled radial phase encoding (RPE) and iterative sensitivity encoding (SENSE) reconstruction

“…A radial phase‐encoding (RPE) scheme where k ‐space data are radially acquired in the phase‐encoding plane while still using a fixed readout direction has been proposed (13). This sampling was used in MRA where the data is sparse and simply structured.…”