Clinically feasible NODDI characterization of glioma using multiband EPI at 7 T - PubMed (original) (raw)

Clinically feasible NODDI characterization of glioma using multiband EPI at 7 T

Qiuting Wen et al. Neuroimage Clin. 2015.

Abstract

Recent technological progress in the multiband echo planer imaging (MB EPI) technique enables accelerated MR diffusion weighted imaging (DWI) and allows whole brain, multi-b-value diffusion imaging to be acquired within a clinically feasible time. However, its applications at 7 T have been limited due to B1 field inhomogeneity and increased susceptibility artifact. It is an ongoing debate whether DWI at 7 T can be performed properly in patients, and a systematic SNR comparison for multiband spin-echo EPI between 3 T and 7 T has not been methodically studied. The goal of this study was to use MB EPI at 7 T in order to obtain 90-directional multi-shell DWI within a clinically feasible acquisition time for patients with glioma. This study included an SNR comparison between 3 T and 7 T, and the application of B1 mapping and distortion correction procedures for reducing the impact of variations in B0 and B1. The optimized multiband sequence was applied in 20 patients with glioma to generate both DTI and NODDI maps for comparison of values in tumor and normal appearing white matter (NAWM). Our SNR analysis showed that MB EPI at 7 T was comparable to that at 3 T, and the data quality acquired in patients was clinically acceptable. NODDI maps provided unique contrast within the T2 lesion that was not seen in anatomical images or DTI maps. Such contrast may reflect the complexity of tissue compositions associated with disease progression and treatment effects. The ability to consistently obtain high quality diffusion data at 7 T will contribute towards the implementation of a comprehensive brain MRI examination at ultra-high field.

Keywords: 7 Tesla; Glioma; Multiband EPI; NODDI; SNR.

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Figures

Fig. 1

Fig. 1

Reconstruction flowchart for a data set with MB = 3 and in-plane R = 3. A. Aliased image and its undersampled k-space in PE direction. B. Zero filled k-space in the non-accelerated direction for un-folding aliased slices. C. Reconstructed full k-space with GRAPPA/ARC. D. Single coil un-aliased images. E. K-space of un-aliased slices. F. Full k-space after partial k-space reconstruction with POCS. G. Single coil images after Fermi filtering in k-space. H. Reconstructed images with sum of square coil combination.

Fig. 2

Fig. 2

A. Center slice and the SNR map of a volunteer acquired with MB1 and MB3 at 3 T and 7 T. It can be noted that SNR is less homogeneous at 7 T due to B1 inhomogeneity, and the reduction in SNR from MB1 to MB3 is smaller at 7 T compared to 3 T. B. Scatter plot of median SNR values of all slices of 5 volunteers (V1–V5). Median SNR of each method was highlighted with a black line, with median SNR = 68.4 and 43.9 for 3 T MB1 and MB3, 50.2 and 46.1 for 7 T MB1 and MB3.

Fig. 3

Fig. 3

A. g-Factor maps at 3 T and 7 T when undersampling in one direction (MB1, in-plane, R = 3), or in two directions (MB3, in-plane R = 3). g-Factor maps were calculated from sensitivity maps estimated from a phantom data acquired at different field strengths with 32-channel coils. B. Scatter plot of median 1/g value of all slices. Median 1/g values of each method were shown in black line, with median 1/g = 0.97 and 0.57 for 3 T MB1 and MB3 and 0.98 and 0.71 for 7 T MB1 and MB3.

Fig. 4

Fig. 4

A. ADC and FA maps for patient data acquired with (1) 3 T standard DTI, b = 1000, 24dir; (2) 7 T multiband, b = 1000, 30dir; (3) 7 T multiband, b = 2000, 60dir and (4) 7 T multiband, double shell. B. Box plots of median ADC and FA within NAWM, GM of 14 patients. C. Susceptibility artifact correction with TOPUP for a patient data set that was acquired with multiband at 7 T.

Fig. 5

Fig. 5

NODDI maps of three patients with lesions of different grades, together with ADC and FA maps fitted from the same double-shell data, and 3 T T1-gad and FLAIR images. T2L was outlined, defined as the hyperintensity abnormality in the FLAIR image. Within in the T2L, variations were seen in viso, vic, and vec, reflecting different water mobility characteristics at different parts of the lesion. Contrast enhancing lesions were present in all patients (arrow) and all demonstrated elevated OD and vic. The white arrow indicated two interesting regions at the edge of T2L of the grade II and grade III patients, which could easily be easily missed on anatomical images and DTI maps, but was highlighted due to elevated vec.

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