R. Reeve Ingle¹, and Dwight G. Nishimura^1
1Electrical Engineering, Stanford University, Stanford, California, United States

We investigate a phenomenon whereby small, alternating perturbations of parameters (such as RF flip angles or phases) in a balanced SSFP sequence can cause large, localized deviations in the steady-state magnetization profile. These deviations can be very severe (e.g., sharp notches or spikes in the magnetization profile) but localized to a narrow range of off-resonant frequencies, with the rest of the profile being essentially identical to the unperturbed bSSFP profile. We develop mathematical and physical explanations of this phenomenon, demonstrate via Bloch simulations, present phantom results, and describe potential applications for positive-contrast imaging and fMRI.

Oliver Bieri¹, Carl Ganter², and Klaus Scheffler^1
1Department of Medical Radiology, Radiological Physics, University of Basel Hospital, Basel, Switzerland, ²Institut für Radiologie, Klinikum rechts der Isar, Technische Universität München

Musculoskeletal (MSK) imaging benefits from increased resolution at higher fields, as this may improve diagnostic accuracy and confidence. Especially 3D double echo steady state (DESS) sequences, offering a high contrast between cartilage and joint fluid, have gained increased interest for high resolution MSK imaging. Here, we resolve the reason for a prominent loss of contrast between fluid and tissues, as observed with high resolution DESS imaging, but being inherent in all non-balanced SSFP sequences. We will show that for anisotropic scans the contrast between fluids and tissues can be almost completely restored using an alternative dephasing concept for non-balanced SSFP.

Oliver Bieri¹, Carl Ganter², and Klaus Scheffler^1
1Department of Medical Radiology, Radiological Physics, University of Basel Hospital, Basel, Switzerland, ²Institut für Radiologie, Klinikum rechts der Isar, Technische Universität München, Munich, Germany

In this work, a new and truly diffusion-weighted (i.e., relaxation time independent) SSFP technique is introduced using a double-echo steady state approach (true-dwDESS). As a result, quantitative SSFP DWI can be performed in the very-rapid-pulsing regime which offers substantially increased SNR and scanning efficiency. Finally, high-resolution quantitative DWI is demonstrated for human articular cartilage in the knee joint at 3.0T.

Tony Stoecker¹, Kaveh Vahedipour¹, Eberhard Pracht¹, Daniel Brenner¹, and N. Jon Shah^1,2
1Institute of Neuroscience and Medicine - 4, Forschungszentrum Juelich, Juelich, Germany, ²Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

Mapping of relaxation times and proton density with high isotropic resolution is best performed with a 3D acquisition and, thus, short TR. As refocusing of transverse magnetization is unavoidable in such approaches, accurate quantification needs a signal equation accounting for T₂. Here, the DESS sequence was chosen, where every Nth pulse was replaced by a 180° magnetization preparation pulse (MP-DESS). The echoes between two MP-pulses are segmented into several images along the recovery. A proper signal equation is given by the extended phase graph. The resulting least-squares fit yields accurate T₁, T₂, and M₀ maps in vivo.

Djaudat Idiyatullin¹, Steven Suddarth², Curt Corum¹, Gregor Adriany¹, and Michael Garwood^1
1CMRR, Radiology, University of Minnesota, Minneapolis, MN, United States, ²Agilent Technologies, Santa Clara, CA, United States

This work describes the first attempt to implement SWIFT (SWeep Imaging with Fourier Transform) in a continuous mode for imaging and spectroscopy. We connected a standard quadrature hybrid with quad coils and acquired NMR signal during continuous radiofrequency excitation. We utilized a chirped radiofrequency to minimize the radiofrequency field for excitation of the spin system for the target flip angle and bandwidth. Due to the complete absence of “dead time” continuous SWIFT extends the application of MRI and spectroscopy to studying spin systems having extremely fast relaxation or broad chemical shift distribution beyond that of the gapped SWIFT sequence.

Kenneth Otho Johnson¹, and Craig H Meyer^1
1Biomedical Engineering, University of Virginia, Charlottesville, VA, United States

Interferometric techniques are developed for MR imaging. Cross correlation of spectroscopic readouts provides enhanced resolution to CSI, and may require fewer readouts. A preliminary study illustrates the enhanced resolution. The application of interferometric techniques may have a broader impact on the MRI community.

Liheng Guo¹, Antonio J Machado Segundo², John A Derbyshire³, John A Carrino², and Daniel A Herzka^4
1Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States, ²Department of Radiology and Radiological Science, Johns Hopkins School of Medicine,³Translational Medicine Branch, DIR, NHLBI, National Institutes of Health, Bethesda, MD, ⁴1Department of Biomedical Engineering, Johns Hopkins School of Medicine

We propose a self-gated imaging method using navigator projections acquired at high spatiotemporal resolution and gated retrospective reconstruction, with the aim to provide high-quality kinematic joint imaging with minimal patient setup and no mechanical apparatus. Preliminary 2D imaging results of the knee in 3T have shown that the joint in motion can be clearly visualized from the automatically reconstructed cine.

Christoph Juchem¹, Terence W Nixon¹, Peter B Brown¹, Scott McIntyre¹, Douglas L Rothman¹, and Robin A de Graaf^1
1MR Research Center, Yale University, New Haven, CT, United States

Magnetic field modeling with the multi-coil approach has been used to generate anatomy-matched magnetic field shapes that are spatially specific enough for the selective excitation of individual regions in 2-dimensional slices with single frequency-selective RF pulses. The low SAR method is demonstrated for brain extraction and outer-volume-suppression (i.e. excitation of everything but the brain) in the mouse at 9.4 Tesla.

Hyunyeol Lee¹, Jin-Seok Seo^1,2, and Jaeseok Park^2
1Department of Medical Science, Yonsei University, Seoul, Korea, Republic of, ²Department of Radiology, Yonsei University, Seoul, Korea, Republic of

The proposed SNR optimized, accelerated, phase-sensitive, dual-acquisition, single-slab, 3D, turbo/fast spin echo imaging method simultaneously enhances SNR and imaging efficiency by an optimal design of variable refocusing flip angles in the second acquisition period and elliptical incoherent sampling patterns, while simultaneously generating high resolution, isotropic, T2-weighted and CSF-suppressed images within clinically acceptable imaging time (~7mins).

Clemens Diwoky¹, and Rudolf Stollberger^1
1Institute of Medical Engineering, Graz University of Technology, Graz, Austria

Fully balanced steady state free precession (bSSFP) acquisitions are known as the most efficient pulse sequences in the perspective of SNR per time. For high-field systems with higher resonance offsets and for imaging parameters resulting in longer repetition times the applicability of bSSFP is limited by banding artefacts. To overcome or improve this limitation we propose a balanced 3D-radial UTE sequence. The power of this new approach could be shown with in-vivo high resolution 3D imaging with 0.2 mm isotropic voxels on a clinical 3T system in 7min.