Combination of 2D sensitivity encoding and 2D partial fourier techniques for improved acceleration in 3D contrast‐enhanced MR angiography

Abstract

Sensitivity encoding (SENSE) and partial Fourier (PF) techniques both reduce MRI acquisition time. Two-dimensional SENSE uses coil sensitivities to unfold aliasing in the phase/ slice-encoding plane. One-dimensional PF and homodyne reconstruction are routinely applied in the frequency/phase-encoding plane to compensate for nonsampled k-space of the presumed real magnetization. Recently, a modified 3D elliptical centric acquisition was proposed to facilitate 2D-PF and homodyne reconstruction on an undersampled phase/slice-encoding plane. In this work we hypothesized that this 2D-PF technique can be combined with 2D-SENSE to achieve a greater acceleration factor than what each method can provide separately. Reconstruction of data whereby SENSE and PF are applied along the same axes is described. Contrast-enhanced MR angiography (CE-MRA) results from experiments using four receiver coils in phantom and volunteer studies are shown. In 11 volunteer studies, the SENSE-PF-homodyne technique using sevenfold acceleration (4؋ SENSE, 1.7؋ PF) consistently pro- Three-dimensional (3D) contrast-enhanced MR angiography (CE-MRA) has become a well accepted technique for clinical imaging of many vascular regions (1,2). Since it was first described over a decade ago (3,4), a number of methods have been developed to improve the attainable spatial resolution. These include shorter repetition times (TRs), faster and stronger encoding gradients, and specific k-space acquisition techniques. One example of the latter is the elliptical centric (EC) view order (5,6), which because of its intrinsic suppression of venous signal allows extensive acquisition times and potentially high spatial resolution. Another example is projection reconstruction (PR) (7,8), which provides high spatial resolution with robust insensitivity to undersampling artifacts. These methods continue to evolve.Simultaneously with these advances in CE-MRA has been the development of parallel imaging methods (9 -11), in which sparse sampling is implemented along the phaseencoding axes. These have been successfully applied in various ways to CE-MRA, resulting in reduced scan time, improved spatiotemporal resolution, and additional venous suppression (12-17). Partial Fourier (PF) imaging is an additional, older method for accelerating data acquisition (18,19). Under the assumption that the magnetization of the imaging object is purely real, the resultant conjugate symmetric property of k-space is exploited, allowing in principle a twofold reduction in the number of measured data points. In practice, the actual time savings is less than twofold, due to the need to collect additional samples near central k-space to account for a phase map across the imaging plane. Current PF techniques are typically implemented in one dimension, either along the frequency readout axis (partial echo) or the phase-encoding axis (partial number of excitations (NEX)). Even with these advances there continues to be a need for improved spatial resolution (near 1 mm isotropic) and shorter acquisiti...

Peripheral Vasculature: High-Temporal- and High-Spatial-Resolution Three-dimensional Contrast-enhanced MR Angiography

“…For the same approximate 20-second acquisition time per image, CAPR provides images at a three to four times higher frame rate versus those previously reported (15,41,42). For the same approximate 5-second frame time, the 20- (43,44).…”

“…brain (34)(35)(36) and the lower legs (15), with acceleration factors of four or higher. In the latter study (15), 3D images of both lower legs were obtained with spatial resolution of 1.5 ϫ 1.2 ϫ 1.3 mm in an acquisition time of 19 seconds.…”

“…In the latter study (15), 3D images of both lower legs were obtained with spatial resolution of 1.5 ϫ 1.2 ϫ 1.3 mm in an acquisition time of 19 seconds. The purpose of this study was to prospectively evaluate the feasibility of performing high-spatial-resolution (1-mm isotropic) time-resolved 3D contrast-enhanced MR angiography of the peripheral vasculature with Cartesian acquisition with projection-reconstruction-like sampling (CAPR) and eightfold accelerated 2D SENSE.…”

“…Methods were developed for time-resolved 3D acquisition (10), which in general involved a trade-off of temporal for spatial resolution (11). For MR angiography of the peripheral vasculature, a variety of methods have specifically been developed (12)(13)(14)(15)(16)(17), including some that allow imaging over an extended field of view (FOV) (18)(19)(20)(21)(22)(23)(24)(25)(26)(27).…”

Accelerated time-resolved 3D contrast-enhanced MR angiography at 3T: clinical experience in 31 patients

“…Higher magnetic fields and the associated gain in SNR as well as effects on T1-relaxation [8,9] are highly beneficial for CE-MRA. Also, recently developed state-of-the-art data acquisition techniques, such as parallel imaging with generalized auto-calibrating partially parallel acquisitions (GRAPPA) [10], view sharing such as time-resolved echo-shared angiography technique (TREAT) or time-resolved imaging of contrast kinetics (TRICKS) [7,11,12] and partial Fourier acquisition in phase and slice encoding directions [13] have improved current imaging modalities. In combination with modern multi-channel systems, whole-body CE-MRA has become feasible [14,15].…”