Pilot study of improved lesion characterization in breast MRI using a 3D radial balanced SSFP technique with isotropic resolution and efficient fat-water separation

Diffusion-weighted double-echo steady-state with a three-dimensional cones trajectory for non-contrast-enhanced breast MRI

The image quality limitations of echo-planar diffusion-weighted imaging (DWI) are an obstacle to its widespread adoption in the breast. Steady-state DWI is an alternative DWI method with more robust image quality but its contrast for imaging breast cancer is not well-understood. The aim of this study was to develop and evaluate diffusion-weighted double-echo steady-state imaging with a three-dimensional cones trajectory (DW-DESS-Cones) as an alternative to conventional DWI for non-contrast-enhanced MRI in the breast. This prospective study included 28 women undergoing clinically indicated breast MRI and six asymptomatic volunteers. In vivo studies were performed at 3 T and included DW-DESS-Cones, DW-DESS-Cartesian, DWI, and CE-MRI acquisitions. Phantom experiments (diffusion phantom, High Precision Devices) and simulations were performed to establish framework for contrast of DW-DESS-Cones in comparison to DWI in the breast. Motion artifacts of DW-DESS-Cones were measured with artifact-to-noise ratio in volunteers and patients. Lesion-to-fibroglandular tissue signal ratios were measured, lesions were categorized as hyperintense or hypointense, and an image quality observer study was performed in DW-DESS-Cones and DWI in patients. Effect of DW-DESS-Cones method on motion artifacts was tested by mixed-effects generalized linear model. Effect of DW-DESS-Cones on signal in phantom was tested by quadratic regression. Correlation was calculated between DW-DESS-Cones and DWI lesion-to-fibroglandular tissue signal ratios. Inter-observer agreement was assessed with Gwet's AC. Simulations predicted hyperintensity of lesions with DW-DESS-Cones but at a 3% to 67% lower degree than with DWI. Motion artifacts were reduced with DW-DESS-Cones versus DW-DESS-Cartesian (p < 0.05). Lesion-to-fibroglandular tissue signal ratios were not correlated between DW-DESS-Cones and DWI (r = 0.25, p = 0.38). Concordant hyperintensity/hypointensity was observed between DW-DESS-Cones and DWI in 11/14 lesions. DW-DESS-Cones improved sharpness, distortion, and overall image quality versus DWI. DW-DESS-Cones may be able to eliminate motion artifacts in the breast allowing for investigation of higher degrees of steady-state diffusion weighting. Malignant breast lesions in DW-DESS-Cones demonstrated hyperintensity with respect to surrounding tissue without an injection of contrast. LEVEL OF EVIDENCE: 2. TECHNICAL EFFICACY STAGE: 1.

Interleaved, undersampled radial multiple-acquisition steady-state free precession for improved left atrial cine imaging

PURPOSE

Balanced steady-state free precession (bSSFP) left atrial (LA) cine suffers from off-resonance artifacts, particularly in the pulmonary veins (PVs). Linear combination or multiple-acquisition SSFP (MA-SSFP) effectively removes banding but greatly increases scan time. We hypothesized that MA-SSFP with interleaved radial undersampling, where each phase-cycling is acquired with an interleaved set of radial projections, would improve image quality of LA cine with a small increase of scan time and streak artefacts.

METHODS

Undersampled radial MA-SSFP with and without interleaving was compared with fully sampled radial bSSFP by means of simulations, phantoms, and in vivo imaging. Ten healthy subjects were imaged on a 3T scanner, with bSSFP and MA-SSFP cine of the left atrium, and B0-mapping. Images were assessed (1 = worst, 5 = best) by 2 independent readers, with respect to 5 qualitative criteria and apparent signal-to-noise ratio.

RESULTS

In healthy subjects, off-resonance differed from the right inferior PVs to the LA cavity by 163 Hz ± 73 Hz at 3T. Compared with fully sampled radial bSSFP, interleaved radial MA-SSFP significantly improved image quality with respect to off-resonance artifacts (3.8 ± 0.6 versus 2.3 ± 1.0; P = 0.005), PV conspicuity (2.8 ± 1.0 versus 4.3 ± 0.5; P = 0.005), and the number of visualized PVs (1.7 ± 0.4 versus 0.9 ± 0.7; P = 0.008), although with greater streak artifacts (3.4 ± 0.4 versus 4.9 ± 0.2; P = 0.004) and lower measured apparent signal-to-noise ratio (24 ± 9 versus 69 ± 36; P = 0.002). Flow artifacts were similar. Interleaved radial MA-SSFP reduced streaking artifacts and increased apparent signal-to-noise ratio versus noninterleaved radial.

CONCLUSIONS

Interleaved radial MA-SSFP cine reduces banding artifacts with an acceptable increase of scan time and streak artifacts. The proposed technique improves the LA and PV visualization in bSSFP cine imaging.

Balanced SSFP Dixon imaging with banding-artifact reduction at 3 Tesla

PURPOSE

To develop a three-dimensional (3D) balanced steady-state free-precession (bSSFP) two-point Dixon method with banding-artifact suppression to offer robust high-resolution 3D bright-fluid imaging.

METHODS

A complex sum reconstruction that combines phase-cycled bSSFP images acquired at specific echo times for robust fat/water separation without banding was investigated and compared with a magnitude-based method. Bloch simulations using both single-peak and multiple-peak fat models were performed to predict the performance of these methods for a wide range of echo times and repetition times. The quality and degree of fat/water separation was evaluated in both simulations and using in vivo imaging.

RESULTS

Simulations predicted that both effective banding-artifact suppression and substantial improvements in fat/water separation are possible at echo times that are different from conventional echo times, enabling improved spatial resolution. Comparisons between various echo times and repetition times in vivo validated the improved fat/water separation and effective banding-artifact removal predicted by the simulations.

CONCLUSION

The proposed complex sum Dixon 3D bSSFP method is able to effectively separate fat and water at different sets of echo times, while removing banding-artifacts, providing a fast, high-resolution, T2 -like sequence without blurring.

High-resolution 3D radial bSSFP with IDEAL

Radial trajectories facilitate high-resolution balanced steady state free precession (bSSFP) because the efficient gradients provide more time to extend the trajectory in k-space. A number of radial bSSFP methods that support fat-water separation have been developed; however, most of these methods require an environment with limited B0 inhomogeneity. In this work, high-resolution bSSFP with fat-water separation is achieved in more challenging B0 environments by combining a 3D radial trajectory with the IDEAL chemical species separation method. A method to maintain very high resolution within the timing constraints of bSSFP and IDEAL is described using a dual-pass pulse sequence. The sampling of a unique set of radial lines at each echo time is investigated as a means to circumvent the longer scan time that IDEAL incurs as a multiecho acquisition. The manifestation of undersampling artifacts in this trajectory and their effect on chemical species separation are investigated in comparison to the case in which each echo samples the same set of radial lines. This new bSSFP method achieves 0.63 mm isotropic resolution in a 5-min scan and is demonstrated in difficult in vivo imaging environments, including the breast and a knee with ACL reconstruction hardware at 1.5 T.