Anja C. S. Brau

Multiecho reconstruction for simultaneous water‐fat decomposition and T2* estimation

To describe and demonstrate the feasibility of a novel multiecho reconstruction technique that achieves simultaneous water‐fat decomposition and T2* estimation. The method removes interference of water‐fat separation with iron‐induced T2* effects and therefore has potential for the simultaneous characterization of hepatic steatosis (fatty infiltration) and iron overload.

Water–fat separation with IDEAL gradient‐echo imaging

To combine gradient‐echo (GRE) imaging with a multipoint water–fat separation method known as “iterative decomposition of water and fat with echo asymmetry and least squares estimation” (IDEAL) for uniform water–fat separation. Robust fat suppression is necessary for many GRE imaging applications; unfortunately, uniform fat suppression is challenging in the presence of B0 inhomogeneities. These challenges are addressed with the IDEAL technique.

Isotropic MRI of the knee with 3D fast spin-echo extended echo-train acquisition (XETA) : Initial experience

OBJECTIVE The purpose of our study was to prospectively compare a recently developed method of isotropic 3D fast spin-echo (FSE) with extended echo-train acquisition (XETA) with 2D FSE and 2D fast recovery FSE (FRFSE) for MRI of the knee. SUBJECTS AND METHODS Institutional review board approval, Health Insurance Portability and Accounting Act (HIPAA) compliance, and informed consent were obtained. We studied 10 healthy volunteers and one volunteer with knee pain using 3D FSE XETA, 2D FSE, and 2D FRFSE. Images were obtained both with and without fat suppression. Cartilage and muscle signal-to-noise ratio (SNR) and cartilage-fluid contrast-to-noise ratio (CNR) were compared using a Students t test. We also compared reformations of 3D FSE XETA with 2D FSE images directly acquired in the axial plane. RESULTS Cartilage SNR was higher with 3D FSE XETA (56.8 +/- 9 [SD]) compared with the 2D FSE (45.8 +/- 8, p < 0.01) and 2D FRFSE (32.5 +/- 5.3, p < 0.01). Muscle SNR was significantly higher with 3D FSE XETA (52.1 +/- 4.3) than 2D FSE (45.2 +/- 9, p < 0.01) and 2D FRFSE (23.6 +/- 6.2, p < 0.01). Fluid SNR was significantly higher for 2D FSE (144.9 +/- 33) than 3D FSE XETA (104.7 +/- 18, p < 0.01). Compared with 2D FSE and 2D FRFSE, 3D FSE XETA had lower cartilage-fluid CNR due to higher cartilage SNR (p < 0.01). Three-dimensional FSE XETA acquired volumetric data sets with isotropic resolution. Reformatted images in the axial plane were similar to axial 2D FSE acquisitions but with thinner slices. CONCLUSION Three-dimensional FSE XETA acquires high-resolution (approximately 0.7 mm) isotropic data with intermediate and T2-weighting that may be reformatted in arbitrary planes. Three-dimensional FSE XETA is a promising technique for MRI of the knee.

Effects of refocusing flip angle modulation and view ordering in 3D fast spin echo

Recent advances have reduced scan time in three‐dimensional fast spin echo (3D‐FSE) imaging, including very long echo trains through refocusing flip angle (FA) modulation and 2D‐accelerated parallel imaging. This work describes a method to modulate refocusing FAs that produces sharp point spread functions (PSFs) from very long echo trains while exercising direct control over minimum, center‐k‐space, and maximum FAs in order to accommodate the presence of flow and motion, SNR requirements, and RF power limits. Additionally, a new method for ordering views to map signal modulation from the echo train into ky‐kz space that enables nonrectangular k‐space grids and autocalibrating 2D‐accelerated parallel imaging is presented. With long echo trains and fewer echoes required to encode large matrices, large volumes with high in‐ and through‐plane resolution matrices may be acquired with scan times of 3–6 min, as demonstrated for volumetric brain, knee, and kidney imaging. Magn Reson Med 60:640–649, 2008.

Comparison of reconstruction accuracy and efficiency among autocalibrating data‐driven parallel imaging methods

The class of autocalibrating “data‐driven” parallel imaging (PI) methods has gained attention in recent years due to its ability to achieve high quality reconstructions even under challenging imaging conditions. The aim of this work was to perform a formal comparative study of various data‐driven reconstruction techniques to evaluate their relative merits for certain imaging applications. A total of five different reconstruction methods are presented within a consistent theoretical framework and experimentally compared in terms of the specific measures of reconstruction accuracy and efficiency using one‐dimensional (1D)‐accelerated Cartesian datasets. It is shown that by treating the reconstruction process as two discrete phases, a calibration phase and a synthesis phase, the reconstruction pathway can be tailored to exploit the computational advantages available in certain data domains. A new “split‐domain” reconstruction method is presented that performs the calibration phase in k‐space (kx, ky) and the synthesis phase in a hybrid (x, ky) space, enabling highly accurate 2D neighborhood reconstructions to be performed more efficiently than previously possible with conventional techniques. This analysis may help guide the selection of PI methods for a given imaging task to achieve high reconstruction accuracy at minimal computational expense. Magn Reson Med 59:382–395, 2008.

Imaging near metal with a MAVRIC-SEMAC hybrid.

The recently developed multi‐acquisition with variable resonance image combination (MAVRIC) and slice‐encoding metal artifact correction (SEMAC) techniques can significantly reduce image artifacts commonly encountered near embedded metal hardware. These artifact reductions are enabled by applying alternative spectral and spatial‐encoding schemes to conventional spin‐echo imaging techniques. Here, the MAVRIC and SEMAC concepts are connected and discussed. The development of a hybrid technique that utilizes strengths of both methods is then introduced. The presented technique is shown capable of producing minimal artifact, high‐resolution images near total joint replacements in a clinical setting. Magn Reson Med, 2010.

Ankle: Isotropic MR Imaging with 3D-FSE-Cube—Initial Experience in Healthy Volunteers

The purpose of this prospective study was to compare a new isotropic three-dimensional (3D) fast spin-echo (FSE) pulse sequence with parallel imaging and extended echo train acquisition (3D-FSE-Cube) with a conventional two-dimensional (2D) FSE sequence for magnetic resonance (MR) imaging of the ankle. After institutional review board approval and informed consent were obtained and in accordance with HIPAA privacy guidelines, MR imaging was performed in the ankles of 10 healthy volunteers (four men, six women; age range, 25-41 years). Imaging with the 3D-FSE-Cube sequence was performed at 3.0 T by using both one-dimensional- and 2D-accelerated autocalibrated parallel imaging to decrease imaging time. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) with 3D-FSE-Cube were compared with those of the standard 2D FSE sequence. Cartilage, muscle, and fluid SNRs were significantly higher with the 3D-FSE-Cube sequence (P < .01 for all). Fluid-cartilage CNR was similar for both techniques. The two sequences were also compared for overall image quality, blurring, and artifacts. No significant difference for overall image quality and artifacts was demonstrated between the 2D FSE and 3D-FSE-Cube sequences, although the section thickness in 3D-FSE-Cube imaging was much thinner (0.6 mm). However, blurring was significantly greater on the 3D-FSE-Cube images (P < .04). The 3D-FSE-Cube sequence with isotropic resolution is a promising new MR imaging sequence for viewing complex joint anatomy.

Generalized self-navigated motion detection technique: Preliminary investigation in abdominal imaging

Patient motion remains a primary obstacle to diagnostic image quality, especially in the abdomen, despite the existence of various motion artifact reduction techniques. This work presents a self‐navigated motion detection method that can be generalized for most pulse sequences and k‐space trajectories. Motion information is extracted directly from raw MR data, requiring no additional gradient or RF pulses, no physiologic monitoring equipment, and minimal—if any—impact on scan time. Initial feasibility results with a two‐dimensional gradient echo sequence are shown in phantom studies and in vivo volunteer abdominal studies, demonstrating the sensitivity of the method to both respiratory motion and cardiovascular pulsatility. Prospectively gated images were acquired using the self‐navigated data to synchronize image acquisition with motion. These preliminary results suggest that the self‐navigated method is a promising technique for reducing motion artifacts in clinical abdominal and cardiac applications. Magn Reson Med, 2006.

Accelerated Slice Encoding for Metal Artifact Correction

To demonstrate accelerated imaging with both artifact reduction and different contrast mechanisms near metallic implants.

New MR Imaging Methods for Metallic Implants in the Knee: Artifact Correction and Clinical Impact

To evaluate two magnetic resonance imaging (MRI) techniques, slice encoding for metal artifact correction (SEMAC) and multiacquisition variable‐resonance image combination (MAVRIC), for their ability to correct for artifacts in postoperative knees with metal.