TRADITIONAL POSTER - ismrm

Poster Sessions
technique was found to decrease the Nyquist ghost by at least 75%, yielding images comparable to those obtained by using time-consuming, blade-specific
reference scans.
3101. Anisotropic Gradient Time Delay Correction for Oblique Radial Readouts Used in Ultrashort
TE (UTE) Imaging
Atsushi M. Takahashi 1
1 Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States
Gradient delays in MRI system are typically anisotropic and yield artifacts that are especially noticable in ramp sampled, center-out, radial k-space
trajectories. We have developed a calibration procedure and a mathematical formulation for correcting artifacts from anisotropic gradient delays.
3102. Correcting for Gradient Imperfections in Ultra-Short Echo Time Imaging
Jeremy F. Magland 1 , Hamidreza Saligheh-Rad 1 , Felix W. Wehrli 1
1 Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA, United States
Imperfections in readout gradients can cause scanner-specific problems in ultra-short echo time (UTE) imaging sequences. In addition to slight gradient
delays, the shape of the readout gradient waveform may not be trapezoidal. Here we describe a simple technique for mapping the k-space trajectory of the
initial readout ramp in a UTE pulse sequence. The method uses data from a short calibration scan in which two dimensions of spatial encoding is applied
prior to readout. After correcting for B0 inhomogeneity, the method provides a very accurate measurement of the k-space trajectory during the ramp, which
can be used as input to a gridding-based reconstruction algorithm.
3103. Scaling in Readout Direction: A Vibration-Induced Distortion of Diffusion-Weighted Images and Its
Retrospective Correction by Affine Registration
Siawoosh Mohammadi 1 , Michael Deppe 1 , Harald E. Moller 2
1 Department of Neurology, University of Muenster, Muenster, NRW, Germany; 2 Magnetic Resonance Unit, Max Planck Institute for
Human Cognitive and Brain Sciences, Leipzig, Sachsen, Germany
The strong lobes of the diffusion gradients cause different kinds of MR artifacts, like eddy-current (EC) and vibration effects. While EC effects could
significantly be reduced using a twice-refocused spin-echo (TRSE) sequence for DTI acquisition, the vibration effects become more evident when the TRSE
sequence is used. We showed that the vibration-induced motion leads to an affine scaling effect in x and y-direction that could be retrospectively corrected.
While the y scaling is also subject to EC effects, the x scaling seems to correct solely vibration effects and might thus be usable for comparing vibration
effects of different data sets.
3104. Rapid Concomitant Field Correction for 2D Spiral Imaging
Ajit Devaraj 1 , Payal Bhavsar 1 , James G. Pipe 1
1 Keller Center for Imaging Innovation, Barrow Neurological Institute, Phoenix, AZ, United States
Concomitant fields are a source of artifact for non-axial spiral images. The resulting artifacts are similar to Bo in-homogeneity blurring, hence challenging to
account for. This work presents a rapid approach based on separable de-blur kernels. The efficacy of the proposed approach is demonstrated on both
simulated and phantom sagittal images.
3105. Efficient Off-Resonance Corrected Reconstruction of Rosette Trajectories by Deformed Interpolation
Kernels
Marco Reisert 1 , Jürgen Hennig 1 , Thimo Grotz 1 , Benjamin Zahneisen 1
1 Medical Physics, University Hospital Freiburg, Freiburg, Baden-Wuerttemberg, Germany
Using a 3D rosette trajectory and iterative, regularized reconstruction a 64 3 volume can be acquired in less than 30ms. Single shot trajectories suffer from
off-resonance effects because of their long readout times. Common off-resonance correction methods approximate the phase map by a time segmentation to
correct for these effects but slow down the reconstruction. We therefore have developed an off-resonance correction, which uses an approximation in space
rather than in time by deforming k-space interpolation kernels leading to a speed up of a factor of 10 at comparable reconstruction quality.
3106. MR Gradient Estimation Using a Linear Time Invariant Model
Nii Okai Addy 1 , Holden H. Wu 1,2 , Dwight G. Nishimura 1
1 Electrical Engineering, Stanford University, Stanford, CA, United States; 2 Cardiovascular Medicine, Stanford University, Stanford,
CA, United States
MR system imperfections limit the accuracy with which gradient waveforms of fast imaging trajectories such as spirals and 3D cones, are generated on the
scanner. This mainly results in a delay of achieved k-space trajectories from the theoretical case. It is possible to measure the system delays for each axis and
manually adjust the timing of the gradients to improve image reconstruction. However, a range of delay values can be observed on a single axis. This work
models the gradient system with a linear time invariant model for accurate estimation of a range of gradient waveforms generated on the scanner.
3107. Reference Coils Signal Combinations Removes Gradient Switching Artefacts in Physiological
Recordings During MRI
Roki Viidik 1,2 , Simon Bergstrand 3 , Tomas Karlsson 3 , Göran Starck 2,4
1 Department of Signals and Systems, Chalmers University of Technology, Göteborg, Sweden; 2 Department of Medical Physics and
Biomedical Engineering, Sahlgrenska University Hospital, Göteborg, Sweden; 3 Institute of Neuroscience and Physiology, Sahlgrenska
University Hospital, Göteborg, Sweden; 4 Department for Radiation Physics, University of Gothenburg, Göteborg, Sweden
Physiological registrations simultaneously with MR scanning usually require the removal of a huge gradient switching artefact from the weak physiological
signal. We investigated a concept with pickup coils for simultaneous gradient switching registration for artefact removal. Adapted combinations of three
reference signals recorded at the rear of the magnet could minimize the gradient artefact in all signal recordings at different positions in front of the magnet.
The presented method works with any pulse sequence and any position and geometry of electrode leads loop.