Traditional Posters: Diffusion & Perfusion - ismrm

Center Utrecht, Netherlands; 4 Department of Clinical Neurology, University of Oxford, Oxford, United
Kingdom
Diffusion Tensor Imaging data acquired at increased field strength shows increased Signal to Noise Ratio. This work compares the
uncertainties of DTI-based metrics when scanning at 1.5 3 and 7T. By scanning the same nine volunteers at each field strength, and
applying a wild bootstrap method to calculate the uncertainty of the fitted tensors, it is shown that with increasing SNR, the
uncertainties for FA and the primary eigenvector decrease.
1642. Validation of Diffusion Tensor Imaging in the Presence of Metal Implants
Felix Schwab 1 , Bram Stieltjes 2 , Frederik Bernd Laun 3
1 Medical Physics in Radiology, Deutsches Krebsforschungszentrum , Heidelberg, Baden Württemberg,
Germany; 2 Radiology, Deutsches Krebsforschungszentrum, Heidelberg, Germany; 3 Medical Physics in
Radiology, Deutsches Krebsforschungszentrum, Heidelberg, Baden Württemberg, Germany
The diffusion weighted imaging of the spinal chord is often impeded by metal implants. A quantitative analysis of these effects is
performed on a standard titanium implant using phase maps acquired from FLASH sequences and ADC maps acquired from diffusion
weighted EPI sequences. The shift δb/b is calculated as a measure of the error. Artefacts caused by the separate parts of the implant
are mostly benign and thus diffusion measurements should be feasible if a small distance to the implant is observed.
1643. Within Subject Averaging of Diffusion Tensor MRI Data Sets: A Test-Retest
Reproducibility Evaluation
Nico Dario Papinutto 1 , Jorge Jovicich 1
1 Center for Mind/Brain Sciences, University of Trento, Mattarello, Trento, Italy
The accuracy and precision of a Diffusion tensor imaging (DTI) acquisition of in-vivo human brains depends on both the acquisition
protocol and post-processing used for data analysis. In many cases multiple acquisitions from the same session are averaged to
increase signal-to-noise ratio and reduce sensitivity to motion during the acquisition. The complexity of DTI datasets allows for
several processing paths to complete eddy current correction, co-registration, averaging and tensor fitting. Here we assess the
sensitivity of fractional anisotropy (FA) test-retest reproducibility to different methods for merging multiple within-subject DTI
acquisitions.
1644. The Signal Intensity MUST Be Modulated by the Determinant of the Jacobian
When Correcting for Eddy Currents in Diffusion MRI
Derek K. Jones 1
1 CUBRIC, Cardiff University , Cardiff, Wales, United Kingdom
Eddy currents plague diffusion MRI. When they produce a stretch / compression of the image along the phase encode direction, the
resultant change in voxel volume leads to a reduction/ increase in signal intensity. Many eddy current correction packages fail to
account for this signal change. Here we show that the consequences can be drastic for diffusion tensor MRI, with biases in fibre
orientation being as big as 5 degrees in regions of low anisotropy. We conclude that the signal intensity must be modulated by the
volumetric change, in order to obtain meaningful and robust results from diffusion MRI.
1645. Dimensional Comparisons of Diffusion Tensor Metrics in Monte Carlo Simulations
and Secondary Progressive Multiple Sclerosis
Lingchih Lin 1 , Xiaoxu Liu 2 , Jianhui Zhong 3
1 Department of Physics and Astronomy , University of Rochester, Rochester, NY, United States; 2 Department
of Electrical and Computer Engineering, University of Rochester, Rochester, NY, United States; 3 Department of
Imaging Sciences, University of Rochester, Rochester, NY, United States
The analytical relationships of diffusion tensor (DT) derived parameters were compared to quantify the subtle dependent variation
between these metrics. This sensitivity evaluation includes the estimation from Monte Carlo simulations and the implementation in a
study of five healthy controls and five patients of secondary progressive multiple sclerosis (SPMS). The fractional anisotropy (FA)
was simulated as one-dimensional, two-dimensional, and three-dimensional function and reveal distinct properties in different tissue
categories. Both white matter (WM) and gray matter (GM) deterioration were observed with decreasing and increasing FA and
changes in radial and axial diffusivities in SPMS.
1646. DTI in the Clinic: Evaluating the Effects of Smoothing
Marta Moraschi 1 , Gisela E. Hagberg 2 , Giovanni Giulietti 1 , Margherita Di Paola 2 ,
Gianfranco Spalletta 2 , Bruno Maraviglia 3 , Federico Giove 3
1 MARBILAb, Enrico Fermi Center, Rome, Italy; 2 Santa Lucia Foundation, Rome, Italy; 3 Department of
Physics, 'Sapienza' University of Rome, Rome, Italy
We evaluated the effects of smoothing on the outcomes of a Diffusion Tensor Imaging (DTI) voxel-based analyses trying to separate
differential effects between patients and controls. Gaussian smoothing introduced a high variability of results in clinical analysis,
greatly dependent on the kernel size. On the contrary, anisotropic smoothing proved itself capable of maintaining boundary structures,
with only moderate dependence of results on smoothing parameters. Our study suggests that anisotropic smoothing is more suitable in
voxel based DTI studies; however, regardless of technique, a moderate level of smoothing seems to be preferable considering the
artifacts introduced by this manipulation.