Saifeng Liu¹, Jaladhar Neelavalli², Weili Zheng³, and Ewart Mark Haacke^2,4
1School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada, ²The Magnetic Resonance Imaging Institute for Biomedical Research, Detroit, Michigan, United States,³Biomedical Engineering, Wayne State University, Detroit, Michigan, United States, ⁴Academic Radiology, Wayne State University, Detroit, Michigan, United States

The forward calculation enables us to predict and remove the background field variation. However, it becomes insufficient when the eddy currents are considerable. We proposed to add an polynomial fitting to the forward calculation. With this new method, the background filed variation can be properly fitted and most of the phase artifacts were removed. This allows us to use a high-pass filter with smaller size to reduce the error in susceptibility mapping.

José P. Marques^1,2, Yves Wiaux^3,4, and Rolf Gruetter^1,5
1Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland, ²Department of Radiology, University of Lausanne, Lausanne, Vaud, Switzerland, ³Signal Processing Laboratory 5, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, ⁴Medical Image Processing Laboratory, University of Geneva, Geneva, Switzerland, ⁵Department of Radiology, University of Lausanne and Geneva, Switzerland

In this abstract a fast iterative method to filter the large background phase shifts of susceptibility origin in phase imaging is presented. The algorithm is based on the matching pursuit iterative methodology to solve the ill posed inverse problem of finding a susceptibility distribution outside that can explain the field inside the region of interest. The algorithm is demonstrated both in synthetic and in vivo brain data acquired at 7T.

Se Rim Park¹, Ung Jang^1,2, and Dosik Hwang^1,2
1School of Electrical and Electronic Engineering, Yonsei University, Seoul, Korea, Republic of, ²Yonsei University

IN SWI MR venography, long echo time might be desired for high contrast. However, longer echo time eventually introduces artifacts mainly caused because of unexpected macroscopic field inhomogeneity, especially around the orbito-frontal cortex. In order to correct the image, for the first step, local inhomogeneity is directly calculated after the signal acquisition, and Local Field Gradient (LFG) map is created. Then each signal is corrected to certain degree according to this LFG value so that the optimum image is restored.

Wei Feng¹, Jaladhar Neelavalli¹, and E.M. Haacke^1
1Wayne State University, Detroit, MI, United States

Susceptibility weighted imaging (SWI) utilizes phase information at long echo time (TE). However, due to long TE, phase aliasing inevitably occurs. For the purpose of SWI, phase wraps can be removed by conventional region growing methods or homodyne filtering. Region growing phase unwrapping methods are not always reliable and conventional homodyne highpass filtering induces undesired artifacts. We propose a new pixel-wise catalytic multiecho phase unwrapping scheme (CAMPUS) that is not based on region growing and does not require filtering. It is suited for multiecho gradient echo imaging with short inter-echo spacing, which is exploited to unwrap the multiecho phase data.

Ferdinand Schweser^1,2, Karsten Sommer^1,3, Marie Atterbury^1,4, Andreas Deistung¹, Berengar Wendel Lehr¹, and Jürgen R. Reichenbach^1
1Medical Physics Group, Dept. of Diagnostic and Interventional Radiology 1, Jena University Hospital, Jena, Germany, ²School of Medicine, Friedrich Schiller University of Jena, Jena, Germany,³School of Physics and Astronomy, Friedrich Schiller University of Jena, Jena, Germany, ⁴Dept. of Physics, Brown University, Providence, RI, United States

In this study we investigated the impact of regularization and kernel type used with the SHARP method based on a numerical brain model. Furthermore, we present the smallest possible kernel, which allows overcoming one of the major pitfalls of SHARP, i.e. the missing values at the edges of the brain.

Debra E. Horng^1,2, Ethan K. Brodsky^1,2, and Scott B. Reeder^1,2
1Radiology, University of Wisconsin-Madison, Madison, WI, United States, ²Medical Physics, University of Wisconsin-Madison, Madison, WI, United States

Quantitative perfusion imaging of liver tumors requires acquisitions that occur over alternating periods of breathing and breath-holding. Knowledge of the time range when the liver is not moving is necessary for accurate perfusion modeling. In this work, we describe the use of DC phase and DC magnitude signal measured every TR from a 3D-radial contrast enhanced acquisition to identify breath-holding periods. Results demonstrate excellent agreement with respiratory bellows, which were used as the reference standard.

Se Young Chun^1,2, Timothy G Reese^2,3, Bastien Guerin^1,2, Ciprian Catana^2,3, and Georges El Fakhri^1,2
1Division of Nuclear Medicine & Molecular Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, United States, ²Radiology, Harvard Medical School, Boston, MA, United States, ³Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, United States

Motion artifacts in PET becomes a key problem affecting image quality. Combined MR-PET provides a new opportunity to improve PET image quality with accurately estimated motion from simultaneously acquired tagged MR without increased radiation dose. Here we report progress in our in-vivo motion correction study, showing results from a free-breathing primate that demonstrates the feasibility of PET motion correction in simultaneous MR-PET. Our tagged MR based motion correction methods significantly reduced motion artifacts and noise as compared to no motion correction or gating. They achieved image qualities comparable to those of gating method with much longer (8x) acquisition.

Matthias Honal¹, and Tobias Baumann^2
1Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²Department of Radiology, University Medical Center Freiburg, Germany

The application of respiratory gating for MRI with continuously moving table is difficult. Due to the variability of the breathing motion over time the coverage of the complete k-space in the available measurement time which is fixed by the table motion cannot be guaranteed. In this study a variant of respiratory gating is proposed that acquires the required k-space data in a limited time as consistently as possible with respect to motion. Compared to acquisitions without motion correction blurring artifacts are reduced thereby significantly improving the diagnostic image quality.

Michael Hofer¹, Gernot Reishofer², Stephen Keeling³, Michael Riccabona⁴, Manuela Aschauer⁵, and Rudolf Stollberger^6
1Institute of Medical Engineering, University of Technology, Graz, Austria, ²Department of Radiology, Medical University, Graz, Austria, ³Institute for Mathematics and Scientific Computing, Karl Franzens University Graz, Austria, ⁴Department of Pediatric Radiology, Medical University Graz, Austria, ⁵Department of Radiology, Medical University Graz, Austria, ⁶Institute of Medical Engineering, University of Technology Graz, Austria

For the non-invasive assessment of renal perfusion and functional parameters it is important to get tissue specific data (e.g. renal cortex, renal medulla). To overcome the problem of intensity variations, an image registration procedure was implemented which derives a virtual template image series that keeps the underlying signal time course intact. The algorithm is evaluated for a synthetic kidney phantom and in vivo DCE-MRI data. It is seen that the algorithm is robust against signal changes due to the uptake of contrast media. Our results indicate that for pixel-by-pixel evaluation of the renal blood flow, registration is mandatory.

Robert Grimm¹, Kai Tobias Block², Berthold Kiefer², and Joachim Hornegger^1,3
1Pattern Recognition Lab, Department of Computer Science, University of Erlangen-Nuremberg, Erlangen, Germany, ²Siemens Healthcare MR, Erlangen, Germany, ³Erlangen Graduate School in Advanced Optical Technologies (SAOT)

Radial k-space sampling is a promising technique for abdominal imaging due to the high motion robustness and the embedded information on the respiration phase. However, these self-gating signals are often corrupted by high-frequency variations from an angle-dependent bias, caused by inaccurate gradient timings. Here, we present a novel filtering scheme to estimate and correct the bias without compromising temporal resolution. After correction, the variance of the signal can be used to assess the quality of the gating signal for different slices. The approach is evaluated with volunteer data acquired under irregular breathing patterns, and results from gated reconstructions are shown.

Alto Stemmer¹, and Berthold Kiefer^1
1Healthcare Sector, Siemens AG, Erlangen, Germany

Slices acquired at the beginning of the acquisition period of a respiratory triggered sequence may suffer from insufficient fat suppression, if a spectral selective saturation or inversion pulse is used for fat suppression. The proposed reason is the interruption of fat steady state during inspiration while the sequence waits on the next trigger. In this work the sequence of fat suppression modules is continued in the trigger pauses. This maintains the steady state and results in consistent fat suppression in all slices.

Raphaël Sablong¹, Adrian Rengle¹, Audrey Pouzin¹, and Olivier Beuf^1
1CREATIS, CNRS UMR 5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France

An optical-based device designed to synchronize MRI acquisition on small animals was developed using a transmit-receive pair of optical fibers. The suitability of the developed device was assessed on ten mice and compared with ECG-gated and a retrospective technique (IntraGate). MR images of mice heart depict low visible motion artifacts with all three investigated methods and no significant SNR differences were found on images acquired or processed with these different methods. However, depending on device used, the triggering point does not correspond to the same instant of the cardiac cycle inducing a time shift between image series acquired with the devices. Full fiber optical-based signal derived from heart and respiratory motion was suitable for prospective triggering for heart MR imaging. The fiber optic device performed as well as the ECG. The optical fiber-based device could be an attractive alternative to commercially available triggering devices for small animal MRI, when retrospective method is inappropriate, in difficult environments such as small volume available and fast gradients switching.

Slavisa Jovanovic^1,2, Laure Rousselet^1,2, Lucas Albouy^1,2, Pierre-André Vuissoz^1,2, Cédric Pasquier^3,4, and Jacques Felblinger^1,2
1Imagerie Adaptative Diagnostique et Interventionnelle, Nancy-Université, Nancy, France, ²U947, INSERM, Nancy, France, ³CIT801, INSERM, Nancy, France, ⁴CIC-IT,CHU-Nancy, Nancy, France

Physiological motions can impair MR image quality by generating artifacts. To overcome or decrease artifact generation in MR images, synchronization or image processing techniques taking into account these motions must be employed. In order to validate either new motion sensors or motion correction algorithms in MRI environment before their use in clinics, a reproducible motion generation system is needed. Most of the solutions we find in literature are limited to a small range of applications and basic motion types. Within this framework, we present a dynamic fully MRI-compatible motion generation platform which was developed to evaluate the influence of its generated motion on MR image quality of phantoms and to assess image processing algorithms used for motion artifacts removal. As an initial test, we evaluate a motion correction algorithm GRICS by imposing on its inputs a known 2D motion generated with the developed mobile platform.

Yusuf A Bhagat¹, Chamith S Rajapakse¹, Jeremy F Magland¹, Michael J Wald¹, Hee K Song¹, Mary B Leonard², and Felix W Wehrli^1
1Laboratory for Structural NMR Imaging, University of Pennsylvania, Philadelphia, PA, United States, ²Nephrology, The Children's Hospital of Philadelphia, United States

Subtle subject movement during high-resolution µMR scanning of trabecular bone (TB) causes blurring rendering the data unreliable for quantitative analysis. Images that were visually free of motion artifacts from two groups of 10 healthy individuals each differing in age were selected. We then applied retrospectively derived translational motion trajectories as phase shift to the k-space data of these 20 subjects. Motion induction affected all TB structural parameters. The significant difference in structural parameter group means of the motion-free images was lost upon motion degradation. The results underscore the importance of subject movement and its correction for TB structure analysis.

Thomas Lange¹, Daniel Nicolas Splitthoff¹, Maxim Zaitsev¹, and Julian Maclaren^1
1Department of Radiology, University Medical Center Freiburg, Freiburg, Germany

Prospective motion correction based on an optical tracking system in combination with retrospective phase correction has recently been proposed for spectroscopic imaging in the human brain and has been validated for in-plane motion. In this work, the method is assessed for through-plane motion, focussing on the characterisation of motion-induced field distortions in the VOI and evaluating the potential for real-time shimming. Through-plane motion causes stronger spectral degradation compared to in-plane motion, particularly in the frontal cortex close to the nasal cavities. For rotational motion, the field distortions may contain large second-order components, which are hard to correct in real time.

Michael Herbst¹, Julian Maclaren¹, Jan Gerrit Korvink^2,3, and Maxim Zaitsev^1
1Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²Dept. of Microsystems Engineering - IMTEK, University of Freiburg, Freiburg, Germany, ³Freiburg Institute of Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany

Monitoring head motion is becoming a popular way to prevent motion artifacts in brain imaging. However, previously-described systems all have major practical problems. We present a new method that uses ‘optical-tracking-tape’, consisting of bend-sensitive optical fibre. The tape is attached to the head of the subject and used to identify motion for real-time data rejection. In comparison with other systems a major advantage of the tape is the setup time (3minutes). No time consuming calibration step is necessary and no direct line of sight on the patients head is required, which makes the system usable even with a enclosed headcoils.

Yen-Wei Cheng¹, Ming-Choung Chou², Nai-Yu Cho³, Cheng-Yu Chen³, and Hsiao-Wen Chung^1
1Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, ²Department of Medical Imaging and Radiological Sciences, Kaohsiung Medical University, Kaohsiung, Taiwan,³Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan

Corrupted signals in diffusion-weighted images due to hardware instability and physiological-related fluctuations are observed in Q-ball imaging. We proposed two suitable methods to restore the lost signals in DWIs and reduce the ODF errors in this study. The corrupted signals were replaced by its repeated scan to get the gold standard. The mean ODF errors between damaged QBI and gold standard QBI before correction were 2.32%. However, the mean ODF errors were reduced to 0.51% and 0.45% after correction by symmetrical compensation method and neighboring interpolation method. Therefore, we concluded that neighboring interpolation was suitable adjunct for QBI data processing.

Gary Chiaray Lee^1,2, Caroline Jordan^3,4, Pamela Tiet², Carlos Ruiz², Brian Hargreaves³, and Steven Conolly^1,2
1Berkeley/UCSF Bioengineering Joint Graduate Group, Berkeley, CA, United States, ²Bioengineering, UC Berkeley, Berkeley, CA, United States, ³Radiology, Stanford University, ⁴Bioengineering, Stanford University

Magnetic susceptibility differences at air and tissue boundaries produce B0 field inhomogeneities near the skin and air cavities in the body, may cause significant imaging artifacts, including intravoxel dephasing, and distortion. These artifacts can result in unreliable chemically selective fat suppression, which exploit the 3.5 ppm chemical shift between fat and water. We have developed susceptibility matching pyrolytic graphite-embedded foams that are safe for patient use in MRI. Here we demonstrate significantly improved in vivo susceptibility matching in the hand and neck, improved frequency selective fat suppression in fat phantoms, and that the foams do not adversely affect SNR.

Pei-Hsin Wu¹, Nan-Kuei Chen², and Hsiao-Wen Chung^1,3
1Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, Taiwan, ²Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, United States,³Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan

We proposed an improved multi-TE approach for accurate B0 mapping with phase unwrapping along the TE dimension, using sparse TE spacing for shorter acquisition time. The k-space energy spectrum analysis method was used for an initial estimation of the phase evolution as a function of TE, following which the accurate phase values were derived on a pixel-by-pixel basis from the multi-TE data. Experimental results in the human brain using four TE values with 9 msec spacing suggested that our approach yielded accurate B0 maps in good agreement with those obtained from 37 TE values at 0.752 msec spacing.

Wei Lin¹, Feng Huang¹, George R Duensing¹, and Arne Reykowski^1
1Invivo Corporation, Philips Healthcare, Gainesville, FL, United States

A rapid off-resonance artifact correction method is proposed based on data convolution in k-space (ORACLE). The acquired k-space is divided into segments based on their readout time, and a convolution kernel is applied to each segment to render artifact-free data. ORACLE does not require a separate B0 mapping scan, therefore reducing the scan time and eliminating the need to align the B0 map with the actual imaging data. Phantom and in vivo brain scans demonstrate the successful application to radial, spiral and EPI datasets.

Daniel Nicolas Splitthoff¹, and Maxim Zaitsev^1
1Dept. of Radiology, Medical Physics, Unversity Medical Center Freiburg, Freiburg, Germany

Recently the generalised non-linear SENSE Shimming (SSH) method was introduced, which can be used for estimating B0 inhomogeneities. The approach uses a reference image and tries to explain the time curve of a Free Induction Decay (FID) based on a model including relaxation and inhomogeneities. Due to the usage of the FID the method was up to now restricted to axial slices. We here introduce the concept of frequency filtered FIDs which enables the method to be used with an arbitrary slice orientation. Results from an in vivo measurement are shown.

Dan Xu¹, Joe K. Maier², Kevin F. King¹, and Gaohong Wu^2
1Applied Science Laboratory, GE Healthcare, Waukesha, WI, United States, ²GE Healthcare, Waukesha, WI, United States

B0 inhomogeneity can lead to significant signal loss especially for slices far off isocenter and/or pulse sequences with spectral spatial fat suppression pulses. Collecting B0 map on a per-subject basis is impractical because of the prolonged scan time. In this paper, we propose a method to estimate and correct the per-slice B0 offset using the freely available echo planar imaging (EPI) reference data. Spin echo EPI results on a phantom show that the method can increase the signal for slices 15 cm away from isocenter from 37% to over 75% as compared to signal at the isocenter slice.

Iulius Dragonu¹, Daniel Nicolas Splitthoff¹, Nicoleta Baxan¹, Paul Freitag², Jürgen Hennig¹, and Maxim Zaitsev^1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freibug, Baden-Wuerttemberg, Germany, ²Bruker Biospin, Ettlingen, Baden-Wuerttemberg, Germany

The B0 magnetic field may change during the experiment for several reasons: physiological motion, such as breathing, subject motion and hardware imperfections, such as passive shim element heating. Changes in B0 homogeneities can lead to unwanted signal fluctuations in EPI time course acquisitions. As suggested previously, shim navigators may allow the detection of magnetic field evolution. It has been demonstrated that the phase of a projection is not necessarily proportional to the B0 field inhomogeneities along the direction of that projection. In this work, we propose a method for detection of zero- and first-order in plane shims (f0, A11 and B11) based on shim navigators and reference multi gradient echo images.

Diego Hernando¹, Catherine DG Hines¹, and Scott B Reeder^1,2
1Radiology, University of Wisconsin, Madison, WI, United States, ²Medical Physics, University of Wisconsin, Madison, WI, United States

Quantitative, non-invasive estimation of R2* is an important biomarker of hepatic iron overload. Unfortunately, estimates of R2* may be confounded by the presence of fat, as well as the signal dephasing that occurs from macroscopic magnetic field gradients caused by external susceptibility. In this work, we propose a method that uses the complex signal for estimation of R2*, correcting for the presence of fat and macroscopic field variations. Phantom and liver imaging results are shown to illustrate the proposed method.

Yoonho Nam¹, Hahnsung Kim¹, and Dong-Hyun Kim^1
1Electrical & Electronic Engineering, Yonsei University, Seoul, Korea, Republic of

Accurate measurement of T2* values, excluding the effects of macroscopic field inhomogeneity, is required in many applications. Macroscopic field inhomogeneity induces additional signal decay and leads to underestimated T2* values. Using compensation gradients in slice-selection direction, so called z-shim method, is an effective technique to restore additional signal loss due to macroscopic field inhomogeneity. Therefore, T2* measurements by using these compensation gradients raise the accuracy of T2* values. However, it requires additional scan time for different compensation gradients. In this study, we propose a post-processing technique with alternating compensation gradients in a single scan for accurate T2* measurement.

Jan Ole Blumhagen^1,2, Ralf Ladebeck¹, Matthias Fenchel¹, Jürgen Kampmeier¹, and Klaus Scheffler^2
1Magnetic Resonance, Siemens Healthcare, Erlangen, Bavaria, Germany, ²Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland

Recently, the potential impact of a limited MR-based field-of-view (FoV) in whole-body MR/PET attenuation correction has been shown. In MR/PET the tissue attenuation map can be calculated from the MR images. However, the FoV restriction may cause a truncation of the MR data for bigger patients and therefore can bias the PET data reconstruction. In this work, we will show exemplarily for 2DFT spin-echo sequences a method that offers an extended FoV in the transversal plane of up to 600mm using a gradient field that compensates B0 inhomogeneities.

Jan Ole Blumhagen^1,2, Ralf Ladebeck¹, Matthias Fenchel¹, Jürgen Kampmeier¹, and Klaus Scheffler^2
1Magnetic Resonance, Siemens Healthcare, Erlangen, Bavaria, Germany, ²Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland

Several studies demonstrated rectification of static-field inhomogeneities inside a field-of-view (FoV) of less than 500mm using phantom-based or patient-based post-processing methods. However, in whole-body MR/PET a distortion-free MR image using an axial FoV up to 600mm would improve the human attenuation correction. Furthermore, an extended FoV can be useful in image-guided radio-surgery and biopsy. In this work we will show exemplarily for 2D spin-echo that significant distortion reduction using post-processed B0 correction can be achieved for an axial FoV up to 600mm.

Hao Lv¹, and Yong Chuan Lai^1
1MR Engineering, GE Healthcare, Beijing, Beijing, China, People's Republic of

In this study, a novel method using signal Magnitude Difference map (MD map) is proposed to correct EPI distortion. Compared with existing methods, it gives more robust & effective correction while only minimal sequence modification is needed.

Eelke Visser^1,2, Benedikt A. Poser³, Markus Barth^1,4, and Marcel P. Zwiers^1,2
1Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, Netherlands, ²Department of Cognitive Neuroscience, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands, ³Department of Medicine, Queen's Medical Center, Honolulu, Hawaii, United States, ⁴Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany

Inhomogeneities of the main magnetic field are known to cause considerable geometric distortion of EPI-acquired data. Accelerated acquisition reduces the problem, but does not eliminate it. We calculate field maps directly from the phase maps of the first two echoes in a multi echo EPI acquisition and use these to correct the residual distortions. The resulting geometrical fidelity yields a significant improvement in the co-registration to undistorted data.

Daniel Nicolas Splitthoff¹, and Maxim Zaitsev^1
1Dept. of Radiology, Medical Physics, Unversity Medical Center Freiburg, Freiburg, Germany

It is well known that Echo Planar Imaging (EPI) suffers strongly from geometric distortions caused by B0 inhomogeneities. As a remedy it has for example been suggested to correct for the distortions in the image processing, based on prescans. Nevertheless such approaches relay on the assumption that the field inhomogeneities due not change during the measurement, which is not necessarily the case. We here present an improved version of projection based real time linear shim detection and correction, that takes into account the cross talk between axes, when the orthogonality is broken due to inhomogeneous magnetisation distributions. The applicability of the method is shown in in vivo correction of motion induced shim changes.

Se-Hong Oh¹, Jun-Young Chung¹, Myung-Ho In², Maxim Zaitsev³, Oliver Speck², Young-Bo Kim¹, and Zang-Hee Cho^1
1Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Korea, Republic of, ²Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany, ³Department of Radiologic Research, Medical Physics, University Hospital of Freiburg, Freiburg, Germany

Echo-planar imaging (EPI) is one of the fastest and most widely used MRI pulse sequences in the field of MRI. Compared to conventional imaging sequence, EPI is more prone to a variety of artifacts. A prominent EPI artifact is geometric distortion due to strong magnetic field inhomogeneity and susceptibility. Recently, a number of different approaches have been proposed for correcting the distortion in EPI, one of them is the point spread function (PSF) mapping method. PSF distortion correction techniques are now extensively used and are successful in the low field strength MRI such as 1.5T or 3.0T. These techniques, however, are still unable to correct distortions in UHF MRI. Especially in UHF MR, EPI image has both compressed and stretched geometric distortions depending on the B1 field inhomogeneity and local susceptibility. The shift map obtained in the non-distortion (x-s) has more information over compressed area. However, the ¡°PSF shift map¡± obtained in the distortion plane or direction (x-y) has more information in stretched area. Therefore, to correct both compressed and stretched region, shift map with more information is selectively applied method is needed. To combine both method we propose a PSF mapping method, which takes into account both the distortion and the non-distortion dimensional correction schemes, instead of previously employed singular method where either non-distortion or distortion dimensional correction are used. By combining the distortion and non-distortion dimensional correction scheme, we can correct more accurately the geometric distortion

Sinyeob Ahn¹, and Xiaoping Hu^1
1Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States

Distortion caused by field inhomogeneity is prominent along the phase-encode (PE) direction in echo planar imaging (EPI). This work describes a method for correcting image distortion along the PE direction using a view angle tilting (VAT) technique in spin-echo EPI (SE-EPI). SE-EPI-VAT utilizes the addition of gradient blips along the slice-select direction, concurrently applied with the PE gradient blips, producing an additional phase. This phase offsets an unwanted phase by field inhomogeneity, resulting in the correction of distortion. The proposed method is simple and requires no post-processing. It was validated by a phantom and human brain imaging.