SSFP & Non-Cartesian
Monday 3 May 2010
Room A9 11:00-13:00 Moderators: Jin Hyung Lee and Krishna S. Nayak

11:00 73.

An Analytical Description of Balanced SSFP with Finite RF Excitation - not available
Oliver Bieri1
University of Basel Hospital, Basel, Switzerland

Conceptually, the only flaw in the common SSFP signal theory is the assumption of quasi-instantaneous radio-frequency (RF) pulses. An exact analytical solution for finite RF balanced SSFP will be derived and it will be shown that finite RF effects can be quite significant even for moderate RF pulse durations. Thus care should be taken when interpreting SSFP signal based on the common Freeman-Hill formulae since only recently it was realized that besides finite RF pulses also magnetization transfer effects may induce a significant modulation in the steady state amplitude.

11:12   74.

Simple Cross-Solution for Banding Artifact Removal in BSSFP Imaging
Qing-San Xiang1,2, Michael N. Hoff2
1Radiology, University of British Columbia, Vancouver, BC, Canada; 2Physics & Astronomy, University of British Columbia, Vancouver, BC, Canada

Balanced SSFP imaging (or TrueFISP, FIESTA) has broad clinical applications for its high time efficiency and desirable contrast. Unfortunately, banding artifacts are often seen in bSSFP images as signal modulation due to B0 inhomogeneity.  To reduce banding, phase-cycled bSSFP acquisitions have been used with various reconstruction algorithms, such as Maximum Intensity Projection (MIP), Sum of Squares (SOS), Nonlinear Averaging (NLA), and Complex Sum (CS).  However, none of these techniques remove banding completely. In this work, a novel elliptical signal model and a simple analytical “Cross-Solution (XS)” are presented. The latter is able to remove banding artifacts completely.

11:24 75. 

Spectral Profile Design for Multiple Repetition Time Balanced SSFP
R. Reeve Ingle1, Tolga Çukur1, Dwight G. Nishimura1
1Electrical Engineering, Stanford University, Stanford, CA, United States

A method for optimizing the spectral profile of a given multiple repetition time balanced SSFP (multi-TR bSSFP) sequence is proposed and analyzed via Bloch simulation and phantom imaging.  In this method, a linear model of transverse magnetization versus flip angle is constructed by perturbing pairs of flip angles and simulating the resulting change in transverse magnetization.  Least-squares analysis is used to compute flip angles that minimize the squared error between the linear model and a desired magnetization profile.  The method is demonstrated on a reference multi-TR bSSFP sequence, resulting in a 6 dB improvement in the passband-to-stopband ratio.

11:36 76. 

Extended Chimera SSFP - not available
Oliver Bieri1, Klaus Scheffler1
1Radiological Physics, University of Basel Hospital, Basel, Switzerland

Only recently, a new type of steady-state free precession (SSFP) sequence was introduced, termed chimera SSFP. The chimera sequence consists of two alternating SSFP kernels: odd TR-intervals feature a balanced SSFP (bSSFP) type of protocol, whereas even TR-intervals undergo gradient dephasing (non-balanced SSFP) and hence the name. In contrast to the recently proposed sequence, the non-balanced SSFP kernel is played out with minimal TR → 0 and the constraint of identical flip angles for both kernels is discarded. Frequency response profile modifications achievable with the extended chimera sequence are discussed.

11:48 77.  

Suppression of Banding and Transient Signal Oscillations in Balanced SSFP Using a Spoiled RF Pre-Phasing Approach
Jon Fredrik Nielsen1, Daehyun Yoon2, Douglas C. Noll1
1Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States; 2Electrical Engineering and Computer Sciences, University of Michigan, Ann Arbor, MI, United States

Balanced steady state free precession (bSSFP) offers high SNR efficiency and unique contrast mechanisms, but is prone to banding artifacts and transient signal oscillations. We present an RF “pre-phasing” approach for suppression of banding and transient oscillations in bSSFP.

12:00 78. 

Dual-Projection Cardiac and Respiratory Self-Navigated Cine Imaging Using SSFP
Liheng Guo1, Elliot R. McVeigh1, Robert J. Lederman2, J Andrew Derbyshire2, Daniel A. Herzka1
Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States; 2Translational Medicine Branch, National Heart, Lung, and Blood Institute, National Institute of Health, Bethesda, MD, United States

A dual-projection self-navigated SSFP sequence is implemented to acquire navigation projections at two alternating angles during all TRs; it offers projections of high spatiotemporal resolution at two different orientations, thus providing a platform for 2D motion tracking and robust self-navigation, which can replace the standard ECG gating and patient breath hold. Preliminary post-processing of the projection data has shown that cardiac and respiratory motions can be automatically extracted and separated, and that free-breathing cardiac cine images can be automatically reconstructed to comparable quality as standard breath-hold images.

12:12  79. 

Optimized 3D Single Shot Trajectories by Radial Arrangement of Individual Petals (RIP)
Benjamin Zahneisen1, Thimo Grotz1, Kuan J. Lee1, Marco Reisert1, Juergen Hennig1
1University Hospital Freiburg, Freiburg, Germany

With the use of multiple localized, small receive coil arrays, single shot whole brain coverage becomes feasible for fMRI applications using undersampled reconstruction. Using a 3D-rosette trajectory and iterative, regularized reconstruction a 64³ volume can be acquired in 23ms with acceptable PSF-broadening. However, the analytical rosette offers only limited degrees of freedom for optimization. In this work we present an optimized 3D single-shot trajectory based on a radial arrangement of individual petals (RIP-trajectory). Compared to the “conventional” rosette trajectory it has a narrower PSF, no visible sidelobes and is faster (19.3ms) and therefore less sensitive to field inhomogeneities.

12:24   80. 

Image Domain Propeller FSE (IProp-FSE)
Stefan Skare1,2, Samantha Holdsworth1, Roland Bammer1
1Radiology, Stanford University, Stanford, CA, United States; 2Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden

In PROPELLER imaging, multiple blades are acquired in k-space and rotated around the center to cover all of k-space. This has proven useful to mitigate motion artifacts in Cartesian FSE. In this work, a new pulse sequence called Image domain Propeller FSE (iProp-FSE) is proposed as an alternative for T2-w imaging, having propeller blades in the image domain instead of k-space. Similar to PROPELLER, motion correction can be performed between the blades. Moreover, the averaging effect of all blades in the center of the image FOV increases the SNR locally, which is especially useful for multi-channel head coils.

12:36 81.

Steer-PROP: A GRASE-PROPELLER Sequence with Inter-Echo Steering Gradient Pulses
Girish Srinivasan1,2, Novena Rangwala1,2, Xiaohong Joe Zhou1,3
1Center for Magnetic Resonance Research, University of Illinois Medical Center, Chicago, IL, United States; 2Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, United States; 3Departments of Radiology, Neurosurgery and Bioengineering, University of Illinois Medical Center, Chicago, IL, United States

PROPELLER imaging has increasingly been used in motion-sensitive applications such as long anatomic scans and diffusion imaging. EPI-PROPELLER provides short scan times but is susceptible to off-resonance artifacts, producing distorted images. FSE-based PROPELLER, on the other hand, offers excellent immunity against off-resonance artifacts at the expense of acquisition efficiency. We propose a new PROPELLER sequence - Steer-PROP - which mediates the problems in EPI- and FSE-PROPELLER. This sequence has reduced the scan time by at least 3 times as compared to FSE-PROPELLER and avoided the off-resonance artifacts in EPI sequences.  Steer-PROP also provides a natural mechanism to effectively address a long-standing phase correction problem.

12:48 82.

Image Reconstruction from Radially Acquired Data Using Multipolar Encoding Fields
Gerrit Schultz1, Hans Weber1, Daniel Gallichan1, Jürgen Hennig1, Maxim Zaitsev1
1Diagnostic Radiology - Medical Physics, University Hospital Freiburg, Freiburg, BW, Germany

In this contribution a radial imaging technique is presented in the context of nonlinear and non-bijective encoding fields. Efficient image reconstruction methods are described and analyzed. For multipolar encoding fields, the reconstruction can be performed in a particularly simple and useful way: The inverse Radon Transform to polar coordinates leads to undistorted images represented in polar coordinates. In the angular direction pixels are aliased equidistantly. Therefore a standard Cartesian SENSE algorithm is applicable for the unfolding process. The developed reconstruction method is applied to simulated as well as measured data to demonstrate each reconstruction step separately.



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