Berkin Bilgic¹, Luke Xie², Russell Dibb², Christian Langkammer¹, Aysegul Mutluay¹, Huihui Ye¹, Jonathan R Polimeni¹, Chunlei Liu², Lawrence L Wald¹, and Kawin Setsompop^1
1Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ²Radiology, Duke University Medical Center, Durham, NC, United States

Rapid 3D-GRE imaging with Wave-CAIPI attains high quality reconstruction at 15-fold acceleration to facilitate fast acquisition of extremely time consuming COSMOS and STI protocols at multiple head orientations. This technique revealed exquisite cortical contrast and detailed depiction of iron rich nuclei; it enabled detection of anisotropic structures such as white matter tracts. Wave-CAIPI permits a 5:35 min acquisition per orientation at 0.5 mm isotropic resolution for COSMOS, and a 90 sec acquisition per orientation at 1.1 mm isotropic resolution for STI. Furthermore, we deployed a novel EPI-FLEET sequence for rapid and low-distortion calibration acquisition, thus enabling coil sensitivity estimation of both head and body coils from a 10 sec scan.

PINAR SENAY ÖZBAY^1,2, Yolanda Dürst², Klaas Paul Prüssmann², and Daniel Nanz^1
1Department of Radiology, University Hospital Zürich, Zürich, Switzerland, ²Institute of Biomedical Engineering, ETH Zürich, Zürich, Switzerland

Field fluctuations due to breathing and limb motions can create artifacts, which might become severe at very high field. This study investigated to what degree the use of real-time high-order feedback-field control (FFC) with NMR-field-probes can avoid generation of artifacts that were deliberately attempted to be generated in quantitative susceptibility maps (QSM) by 1) deep breathing, and 2) arm movement, each case with and without FFC. Image quality in FFC scans was clearly improved with a better visualization of fine structures, reduced ghosting artifacts and correction of larger areas with unlikely alteration of susceptibility as compared with the standard scans.

Kyle S Decker^1,2 and Chunlei Liu^3,4
1Center for In Vivo Microscopy, Duke University, Durham, NC, United States, ²Biomedical Engineering, Duke University, Durham, NC, United States,³Brain Imaging and Analysis Center, Duke University, Durham, NC, United States, ⁴Radiology, Duke University, Durham, NC, United States

Through the use of improved processing methods, we are able to use a single-shift p-space image reconstruction to produce high fidelity multipole frequency maps using multi-echo data. The temporal-variance of higher-order multipole frequency distribution is dominant in the white matter (WM), thus allowing the use of temporal-variance to enhance multipole frequency maps of WM in the p-space. This method suppresses artifacts in isotropic regions including gray matter and allows isolated characterization of sub-voxel WM anisotropy. The resulting temporal-variance weighted p-space multipole frequency maps provide a new contrast mechanism with enhanced WM anisotropy and contrast.

Manisha Aggarwal¹, Xu Li², Susumu Mori^1,2, and Peter C. M. van Zijl^1,2
1Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²F.M. Kirby Research Center, Kennedy Krieger Institute, Baltimore, MD, United States

In this study, we investigate susceptibility-induced B₀-orientation dependence of the apparent relaxation rate (R₂*) and signal frequency measurements in the ex vivo fixed human brainstem. Gradient echo (GRE) data acquired at 11.7T showed distinct modulation of R₂* and frequency contrasts between the corticospinal and transverse pontine fibers in the brainstem, which closely approximated sin⁴θ and sin²θ dependencies on orientation relative to the static B₀ field. We further investigate the estimation of fiber orientation maps based on the modulated R₂* curves, and compare the results with primary eigenvector maps derived using diffusion MRI.

Wei Li^1,2, Nian Wang³, Bing Wu⁴, Timothy Q. Duong¹, and Chunlei Liu^3,5
1Research Imaging Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States, ²Ophthalmology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States, ³Brain Imaging and Analysis Center, Duke University, Durham, NC, United States, ⁴GE Healthcare, Beijing, China, ⁵Radiology, Duke University, Durham, NC, United States

A novel method, namely iLSQR, is developed for quantitative susceptibility mapping. This method uses the previously developed LSQR method to derive an initial mapping of magnetic susceptibility, a fast quantitative susceptibility mapping method to estimate the susceptibility boundaries, and an iterative approach to estimate and remove the susceptibility artifact using ill-conditioned k-space regions only. With a fixed set of parameters, this iLSQR method provides effective elimination of streaking artifacts, unbiased quantification of magnetic susceptibility as compared to COSMOS, and robustness over a range of spatial resolutions. This method is provided in the software package of STI Suite v2.12.

Ryota Sato¹, Toru Shirai¹, Yo Taniguchi¹, Takenori Murase², Yoshitaka Bito², and Hisaaki Ochi^1
1Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo, Japan, ²Hitachi Medical Corporation, Chiba, Japan

To improve estimation of small-vein susceptibility, a method is proposed for QSM using a pre-estimated as additional structural information instead of a magnitude image and the values in the high-frequency domain in k-space. The pre-estimated susceptibility map is calculated without regularization in order to preserve small-vein contrasts. The effects of using the pre-estimated susceptibility map as structural information and high-frequency values in k-space on the small-vein susceptibility were evaluated in experiments using healthy volunteer. According to the evaluation results, underestimation of small-vein susceptibility is reduced by using the pre-estimated susceptibility map as structural information and high-frequency values in k-space.

Tian Liu^1,2, Cynthia Wisnieff^2,3, Dong Zhou², Pascal Spincemaille², and Yi Wang^2,3
1MedImageMetric LLC, New York, NY, United States, ²Radiology, Weill Cornell Medical College, New York, NY, United States, ³Biomedical Engineering, Cornell University, Ithaca, NY, United States

A vector model for quantitative susceptibility mapping (vector QSM) is proposed, allowing the reconstruction of a susceptibility vector map from a single orientation. Compared to scalar QSM, the vector QSM models the magnetic field inhomogeneity better and improves image quality with reduced signal variation. Compared to susceptibility tensor imaging (STI), vector QSM drastically reduces the required number of scans and has improved signal to noise ratio. Vector QSM may be useful in studying multiple sclerosis lesions to investigate the molecular underpinning of longitudinal susceptibility changes.

Diana Khabipova¹, Rolf Gruetter^1,2, and José P. Marques^1
1CIBM, Lausanne, Vaud, Switzerland, ²Radiology, University of Lausanne and Geneva, Vaud, Switzerland

This study compares the ability of the different contrasts (R1, R2star and Susceptibility) to provide insights into the cortical brain structure. The cortical R1 and R*2 maps shown show similar contrast to that reported by other groups. The χ, as opposed to R1 maps and R*2, does not decrease monotonically from inner surfaces to outer surfaces, suggests that myelin and iron contributions are cancelling each other and might have distinguishable cortical distributions. Combination of information using different contrasts at different depths could provide useful information for cortical segmentation as is supported by the reproducibility of the single subject data.

Omer Faruk Oran¹, Necip Gurler¹, and Yusuf Ziya Ider^1
1Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey

In this study we investigate the feasibility of using slice-selection and readout gradient induced eddy currents for low frequency conductivity imaging

S. Mandija¹, P. Petrov², S.W.F. Neggers², A.D. de Weijer³, P.R. Luijten¹, and C.A.T. van den Berg^1
1Imaging Division, UMC Utrecht, Utrecht, Netherlands, ²Brain Center Rudolf Magnus, UMC Utrecht, Utrecht, Netherlands, ³FMRIB Center, University of Oxford, Oxford, United Kingdom

In this abstract we show a new combined TMS-MRI setup and a specific MR sequence that allow us to guide and provide dosimetry of TMS magnetic field with the MR scanner for a patient specific treatment. In fact, using precise MR based map of the TMS magnetic field, in combination with electromagnetic simulations and pre-acquired anatomical images, we can evaluate the behaviour of the induced TMS electric field and therefore precisely target a certain functional area by overlaying these maps.