All Publications

  • Deep Learning-Based Water-Fat Separation from Dual-Echo Chemical Shift-Encoded Imaging. Bioengineering (Basel, Switzerland) Wu, Y., Alley, M., Li, Z., Datta, K., Wen, Z., Sandino, C., Syed, A., Ren, H., Xing, L., Lustig, M., Pauly, J., Vasanawala, S. 2022; 9 (10)


    Conventional water-fat separation approaches suffer long computational times and are prone to water/fat swaps. To solve these problems, we propose a deep learning-based dual-echo water-fat separation method. With IRB approval, raw data from 68 pediatric clinically indicated dual echo scans were analyzed, corresponding to 19382 contrast-enhanced images. A densely connected hierarchical convolutional network was constructed, in which dual-echo images and corresponding echo times were used as input and water/fat images obtained using the projected power method were regarded as references. Models were trained and tested using knee images with 8-fold cross validation and validated on out-of-distribution data from the ankle, foot, and arm. Using the proposed method, the average computational time for a volumetric dataset with ~400 slices was reduced from 10 min to under one minute. High fidelity was achieved (correlation coefficient of 0.9969, l1 error of 0.0381, SSIM of 0.9740, pSNR of 58.6876) and water/fat swaps were mitigated. I is of particular interest that metal artifacts were substantially reduced, even when the training set contained no images with metallic implants. Using the models trained with only contrast-enhanced images, water/fat images were predicted from non-contrast-enhanced images with high fidelity. The proposed water-fat separation method has been demonstrated to be fast, robust, and has the added capability to compensate for metal artifacts.

    View details for DOI 10.3390/bioengineering9100579

    View details for PubMedID 36290546

  • Rapid fat-water separated T1 mapping using a single shot radial inversion-recovery spoiled gradient recalled pulse sequence. NMR in biomedicine Li, Z., Mathew, M., Syed, A. B., Feng, L., Brunsing, R., Pauly, J. M., Vasanawala, S. S. 2022


    T1 mapping is increasingly used in clinical practice and research studies. With limited scan time, existing techniques often have limited spatial resolution, contrast resolution, and slice coverage. High fat concentrations yield complex errors in Look-Locker T1 methods. In this study, a dual-echo 2D radial IR T1 (DEradIR-T1) technique was developed for fast fat/water-separated T1 mapping. The DEradIR-T1 technique was tested in phantoms, 5 volunteers and 28 patients using a 3T clinical MRI scanner. In our study, simulations were performed to analyze the composite (fat + water) and water-only T1 under different echo times (TEs). In standardized phantoms, an inversion-recovery spin echo (IR-SE) sequence with and without fat saturation pulses served as a T1 reference. Parameter mapping with DEradIR-T1 was also assessed in vivo and values were compared with modified Look-Locker inversion recovery (MOLLI). Bland-Altman analysis and two-tailed paired t-test were used to compare the parameter maps from DEradIR-T1 with the references. Simulations of the composite and water-only T1 under different TEs and levels of fat matched the in vivo studies. T1 maps from DEradIR-T1 on a NIST phantom (PComp =0.97) and a Calimetrix fat/water phantom (PWater = 0.56) matched with the references. In vivo T1 was compared with that of MOLLI: R Comp 2 = 0.77 ; R water 2 = 0.72 . In this work, intravoxel fat is found to have a variable, echo-time dependent effect on measured T1 values, and this effect may be mitigated using the proposed DRradIR-T1.

    View details for DOI 10.1002/nbm.4803

    View details for PubMedID 35891586

  • Repeatability and robustness of MP-GRASP T1 mapping. Magnetic resonance in medicine Li, Z., Xu, X., Yang, Y., Feng, L. 1800


    PURPOSE: To demonstrate the repeatability of fast 3D T1 mapping using Magnetization-Prepared Golden-angle RAdial Sparse Parallel (MP-GRASP) MRI and its robustness to variation of imaging parameters including flip angle and spatial resolution in phantoms and the brain.THEORY AND METHODS: Multiple imaging experiments were performed to (1) assess the robustness of MP-GRASP T1 mapping to B1 inhomogeneity using a single tube phantom filled with uniform MnCl2 liquid; (2) compare the repeatability of T1 mapping between MP-GRASP and inversion recovery-based spin-echo (IR-SE; over 12 scans), using a commercial T1MES phantom; (3) evaluate the longitudinal variation of T1 estimation using MP-GRASP with varying imaging parameters, including spatial resolution, flip angle, TR/TE, and acceleration rate, using the T1MES phantom (106 scans performed over a period of 12 months); and (4) evaluate the variation of T1 estimation using MP-GRASP with varying imaging parameters in the brain (24 scans in a single visit). In addition, the accuracy of MP-GRASP T1 mapping was also validated against IR-SE by performing linear correlation and calculating the Lin's concordance correlation coefficient (CCC).RESULTS: MP-GRASP demonstrates good robustness to B1 inhomogeneity, with intra-slice variability below 1% in the single tube phantom experiment. The longitudinal variability is good both in the phantom (below 2.5%) and in the brain (below 2%) with varying imaging parameters. The T1 values estimated from MP-GRASP are accurate compared to that from the IR-SE imaging (R2 = 0.997, Lin's CCC = 0.996).CONCLUSION: MP-GRASP shows excellent repeatability of T1 estimation over time, and it is also robust to variation of different imaging parameters evaluated in this study.

    View details for DOI 10.1002/mrm.29131

    View details for PubMedID 34971467

  • Rapid high-resolution volumetric T1 mapping using a highly accelerated stack-of-stars Look Locker technique MAGNETIC RESONANCE IMAGING Li, Z., Fu, Z., Keerthivasan, M., Bilgin, A., Johnson, K., Galons, J., Vedantham, S., Martin, D. R., Altbach, M. 2021; 79: 28-37


    To develop a fast volumetric T1 mapping technique.A stack-of-stars (SOS) Look Locker technique based on the acquisition of undersampled radial data (>30× relative to Nyquist) and an efficient multi-slab excitation scheme is presented. A principal-component based reconstruction is used to reconstruct T1 maps. Computer simulations were performed to determine the best choice of partitions per slab and degree of undersampling. The technique was validated in phantoms against reference T1 values measured with a 2D Cartesian inversion-recovery spin-echo technique. The SOS Look Locker technique was tested in brain (n = 4) and prostate (n = 5). Brain T1 mapping was carried out with and without kz acceleration and results between the two approaches were compared. Prostate T1 mapping was compared to standard techniques. A reproducibility study was conducted in brain and prostate. Statistical analyses were performed using linear regression and Bland Altman analysis.Phantom T1 values showed excellent correlations between SOS Look Locker and the inversion-recovery spin-echo reference (r2 = 0.9965; p < 0.0001) and between SOS Look Locker with slab-selective and non-slab selective inversion pulses (r2 = 0.9999; p < 0.0001). In vivo results showed that full brain T1 mapping (1 mm3) with kz acceleration is achieved in 4 min 21 s. Full prostate T1 mapping (0.9 × 0.9 × 4 mm3) is achieved in 2 min 43 s. T1 values for brain and prostate were in agreement with literature values. A reproducibility study showed coefficients of variation in the range of 0.18-0.2% (brain) and 0.15-0.18% (prostate).A rapid volumetric T1 mapping technique was developed. The technique enables high-resolution T1 mapping with adequate anatomical coverage in a clinically acceptable time.

    View details for DOI 10.1016/j.mri.2021.03.003

    View details for Web of Science ID 000648404700005

    View details for PubMedID 33722634

    View details for PubMedCentralID PMC8107135

  • A multi-scale residual network for accelerated radial MR parameter mapping Magnetic Resonance Imaging Fu, Z., Mandava, S., Keerthivasan, M. B., Li, Z., Johnson, K., Martin, D. R., Altbach, M. I., Bilgin, A. 2020; 73: 152-162
  • Rapid high-resolution T1 mapping using a highly accelerated radial steady-state free-precession technique Journal of Magnetic Resonance Imaging Li, Z., Bilgin, A., Johnson, K., Galons, J., Vedantham, S., Martin, D. R., Altbach, M. I. 2019; 49 (1): 239-252

    View details for DOI 10.1002/jmri.26170

  • Accelerated MR parameter mapping with a union of local subspaces constraint Magnetic Resonance in Medicine Mandava, S., Keerthivasan, M. B., Li, Z., Martin, D. R., Altbach, M. I., Bilgin, A. 2018; 80 (6): 2744-2758

    View details for DOI 10.1002/mrm.27344

  • Volumetric MRI of the lungs during forced expiration Magnetic Resonance in Medicine Berman, B. P., Pandey, A., Li, Z., Jeffries, L., Trouard, T. P., Oliva, I., Cortopassi, F., Martin, D. R., Altbach, M. I., Bilgin, A. 2016; 75 (6): 2295-2302

    View details for DOI 10.1002/mrm.25798