Simultaneous Short T2 Excitation and Long T2 Suppression RF Pulses
Michael Carl¹, Mark Bydder², Eric Han¹, Graeme Bydder^2
1GE Healthcare, Waukesha, WI, United States; ²University of California, San Diego, CA, United States

We present a specialized RF technique based on applying a 180° RF excitation pulse that can achieve short T2 tissue excitation and long T2 tissue suppression simultaneously, which may open the possibility for direct excitation of only short T2 tissues, in place of additional separate long T2 suppression techniques. We optimized the RF pulse parameters and experimentally tested the sequence.

MRI with Zero Echo Time: Hard Versus Sweep Pulse Excitation
Markus Weiger^1,2, Klaas Paul Pruessmann², Franciszek Hennel^3
1Bruker BioSpin AG, Faellanden, Switzerland; ²Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; ³Bruker BioSpin MRI GmbH, Ettlingen, Germany

Zero echo time (TE) is achieved in an MRI sequence when the readout gradient is already on during the excitation. 3D radial techniques designed in this way have been proposed using either a hard pulse excitation or a pulse with a frequency sweep, as in the SWIFT technique. The two versions are compared in this work. It is demonstrated that they are equivalent with respect to T2 sensitivity but that the SNR of zero ZE MRI with hard pulse excitation is superior to its sweep pulse counterpart due to the periodical acquisition gapping required in a practical implementation of the latter.

Optimization of Iron Oxide Nanoparticles Detection Using Ultrashort TE Imaging
Olivier Maciej Girard¹, Kazuki N. Sugahara², Lilach Agemy², Erkki Ruoslahti², Graeme M. Bydder³, Robert F. Mattrey^3
1Department of Radiology , University of California, San Diego, CA, United States; ²Vascular Mapping Center, Burham Institute for Medical Research at UCSB, Santa Barbara, CA, United States; ³Department of Radiology, University of California, San Diego, CA, United States

Iron oxide nanoparticles (IONPs) are used in various MRI applications. They are usually considered to be negative contrast agents due to their strong T2* effect, but they also have intrinsic T1 shortening properties that can produce positive contrast using appropriate pulse sequences. Here we show that a multiecho ultrashort TE sequence can be used very efficiently to generate three different contrasts (T1, T2* and hybrid T1-T2*) in a single acquisition, providing increased detection sensitivity and specificity while benefiting from positive contrast Contrary to conventional wisdom, T1-contrast can be superior to the T2*-contrast when imaging with IONPs.

Highly Localized Positive Contrast of Small Paramagnetic Objects Using 3D Center-Out RAdial Sampling with Off-Resonance Reception (RASOR)
Peter Roland Seevinck¹, Hendrik De Leeuw¹, Clemens Bos², Chris JG Bakker^1
1Radiology, University Medical Center Utrecht, Utrecht, Netherlands; ²Philips Healthcare, Best, Netherlands

We present a 3D imaging technique, applying RAdial Sampling with Off-resonance Reception (RASOR), to accurately depict and localize small paramagnetic objects with high positive contrast. The RASOR imaging technique is a fully frequency encoded 3D ultrashort TE (UTE) center-out acquisition method, which utilizes a large excitation bandwidth and off-resonance reception. By manually introducing an offset, Äf0, to the central reception frequency (f0), the magnetic field disturbance causing the typical radial signal pile in 3D center-out sampling can be compensated for, resulting in a hyperintense signal at the exact location of the small paramagnetic object. This was demonstrated by 1D simulations and experiments of gel phantoms containing three paramagnetic objects with very different geometry, viz., subvoxel stainless steel spheres, paramagnetic brachytherapy seeds and a puncture needle. In all cases, RASOR is shown to generate high positive contrast exactly at the location of the paramagnetic object, as confirmed by X-ray computed tomography (CT).

In Vivo Demonstration of Enhancing Gas-Filled Microbubble Magnetic Susceptibility with Iron Oxide Nanoparticles
April M. Chow^1,2, Kannie W.Y. Chan^1,2, Ed X. Wu^1,2
1Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong SAR, China; ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR, China

Gas-filled microbubbles have been shown as an MR susceptibility contrast agent; however, microbubble susceptibility effect is relatively weak when compared with other contrast agents. Studies have indicated that, by embedding magnetic nanoparticles, the magnetic susceptibility of the shell can be increased, thus enhancing the microbubble susceptibility effect. In this study, we further demonstrated the synergistic effect of gas core with iron oxide nanoparticles in achieving the overall microbubble susceptibility effect and characterized in vivo enhancements of microbubble susceptibility effects by entrapping iron oxide nanoparticles at 7 T, leading to the practical use of microbubbles as an intravascular MRI contrast agent.

A Novel Approach to Positive Contrast Using SPIOs in the Motional Averaging Regime
Jon Furuyama¹, Yung-Ya Lin^2
1Radiology, University of California, Los Angeles, CA, United States; ²Chemistry and Biochemistry, University of California, Los Angeles, CA, United States

Currently, positive contrast with superparamagnetic iron oxide nanoparticles (SPIOs) is limited to large particles within the static dephasing regime. We present a novel approach to generating positive contrast from SPIOs within the motional averaging regime. By simply adding a T2-weighted sequence prior to an inversion recovery sequence, we show a 30-fold improvement in contrast-to-noise ratio (CNR) over ordinary inversion recovery sequences. By taking advantage of the latest advances in nanotechnology, we expect an even greater improvement by making use of nanoparticles that have both T1 and T2 enhancement.

Susceptibility Tensor Imaging
Chunlei Liu^1,2
1Brain Imaging and Analysis Center, Duke University, Durham, NC, United States; ²Radiology, Duke University, Durham, NC, United States

We propose a susceptibility tensor imaging (STI) technique to measure and quantify anisotropy of magnetic susceptibility. This technique relies on the measurement of resonance frequency offset at different orientations. We propose to characterize the orientation variation of susceptibility using an apparent susceptibility tensor. The susceptibility tensor can be decomposed into three eigenvalues (principle susceptibilities) and associated eigenvectors that are coordinate-system independent. We show that the principle susceptibilities offer strong contrast between gray and white matter while the eigenvectors provide orientation information of an underlying magnetic network. We believe that this network may further offer information of white matter fiber orientation.

Midbrain Nuclei Visualization Improved by Susceptibility-Enhanced 3D Multi-Echo SSFP for Deep Brain Stimulation Guidance
Ming-Long Wu¹, Geoffrey S. Young², Nan-Kuei Chen^1
1Brain Imaging and Analysis Center, Department of Radiology, Duke University Medical Center, Durham, NC, United States; ²Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States

MRI is routinely used for stereotactic guidance and surgical preparation for deep brain stimulation implantation. In preoperative MRI, a high contrast between midbrain nuclei and surrounding white matter is needed for more accurate electrode placement. Although conventional T2- and T2*-weighted imaging can be used for visualization of midbrain nuclei, a long TE value is needed and thus the scan time cannot be shortened. In this study, a 3D multi-echo steady-state free precession method is used to provide superior contrast at TE < 10ms. By further integrating SWI reconstruction and multi-echo SSFP, a direct and highly robust visualization of midbrain nuclei can be achieved.

Brain Iron: Comparison of Postmortem SWI with Chemical Tissue Analysis
Nikolaus Krebs¹, Christian Langkammer, ¹², Walter Goessler³, Franz Fazekas², Kathrin Yen¹, Stefan Ropele², Eva Scheurer^1
1Ludwig Boltzmann Institute for Clinical-Forensic Imaging, Graz, Austria; ²Department of Neurology, Medical University of Graz, Graz, Austria; ³Institute of Chemistry - Analytical Chemistry, University of Graz, Graz, Austria

Certain neurodegenerative diseases are associated with increased iron concentration in specified brain regions. To provide an up to date basis for validation of MR-based assessment of brain iron content, iron concentrations in selected grey and white matter regions of postmortem human brains were determined using inductively coupled plasma mass spectrometry (ICPMS) and compared to corresponding susceptibility weighted images (SWI). Measured iron concentrations were in good agreement in most brain regions with values published before. Visual comparison of the measured results with contrast in SWI showed that areas with high iron content correlate well with hypointense regions.

Microscopic Susceptibility Variation and Transverse Relaxation for the De Facto Brain Tumor Microvasculature - not available
David Bonekamp¹, Eugene Kim², Barney Douglas Ward³, Jiangyang Zhang¹, Arvind P. Pathak^1
1Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States; ²Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States; ³Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States

Development of new susceptibility-based contrast MR imaging biomarkers of angiogenesis (e.g. susceptibility-based blood volume and vessel size index) requires biophysical models that incorporate accurate representations of the brain tumor vasculature to establish an accurate relationship to the molecular basis of angiogenesis. We investigate the relationship between brain tumor angiogenesis and susceptibility-based contrast MRI by incorporating the de facto brain vasculature in a state-of-the-art computational model of MR image contrast called the finite perturber method (FPM). Our simulations show substantial signal differences between regions of tumor vascularity and normal brain while enabling to study the entire vascular network of a mouse brain at the same time.