Short symmetric and highly selective asymmetric first and second order gradient modulated offset independent adiabaticity (GOIA) pulses for applications in clinical MRS and MRSI.

Gradient modulated RF pulses, especially gradient offset independent adiabaticity (GOIA) pulses, are increasingly gaining attention for high field clinical magnetic resonance spectroscopy and spectroscopic imaging (MRS/MRSI) due to the lower peak B amplitude and associated power demands achievable relative to its non-modulated adiabatic full passage counterparts. In this work we describe the development of two GOIA RF pulses: 1) A power efficient, 3.0 ms wideband uniform rate with smooth truncation (WURST) modulated RF pulse with 15 kHz bandwidth compatible with a clinically feasible peak B amplitude of 0.

Dynamic multicoil technique (DYNAMITE) MRI on human brain.

Purpose: Spatial encoding for MRI is generally based on linear x, y, and z magnetic field gradients generated by a set of dedicated gradient coils. We recently introduced the dynamic multicoil technique (DYNAMITE) for B field control and demonstrated DYNAMITE MRI in a preclinical MR environment. In this study, we report the first realization of DYNAMITE MRI of the in vivo human head.

On the magnetic field dependence of deuterium metabolic imaging.

Deuterium metabolic imaging (DMI) is a novel MR-based method to spatially map metabolism of deuterated substrates such as [6,6'- H ]-glucose in vivo. Compared with traditional C-MR-based metabolic studies, the MR sensitivity of DMI is high due to the larger H magnetic moment and favorable T and T relaxation times. Here, the magnetic field dependence of DMI sensitivity and transmit efficiency is studied on phantoms and rat brain postmortem at 4, 9.

Deuterium metabolic imaging (DMI) for MRI-based 3D mapping of metabolism in vivo.

Currently, the only widely available metabolic imaging technique in the clinic is positron emission tomography (PET) detection of the radioactive glucose analog 2-F-fluoro-2-deoxy-d-glucose (FDG). However, FDG-PET does not inform on metabolism downstream of glucose uptake and often provides ambiguous results in organs with intrinsic high glucose uptake, such as the brain. Deuterium metabolic imaging (DMI) is a novel, noninvasive approach that combines deuterium magnetic resonance spectroscopic imaging with oral intake or intravenous infusion of nonradioactive H-labeled substrates to generate three-dimensional metabolic maps.

Elliptical localization with pulsed second-order fields (ECLIPSE) for robust lipid suppression in proton MRSI.

Proton MRSI has great clinical potential for metabolic mapping of the healthy and pathological human brain. Unfortunately, the promise has not yet been fully achieved due to numerous technical challenges related to insufficient spectral quality caused by magnetic field inhomogeneity, insufficient RF transmit power and incomplete lipid suppression. Here a robust, novel method for lipid suppression in H MRSI is presented.

Selective proton-observed, carbon-edited (selPOCE) MRS method for measurement of glutamate and glutamine C-labeling in the human frontal cortex.

Purpose: C magnetic resonance spectroscopy (MRS) in combination with infusion of C-labeled substrates has led to unique insights into human brain metabolism and neurotransmitter cycling. However, the low sensitivity of direct C MRS and high radiofrequency power requirements has limited C MRS studies to predominantly data acquisition in large volumes of the occipital cortex. The purpose of this study is to develop an MRS technique for localized detection of C-labeling of glutamate and glutamine in the human frontal lobe.

Comparison of direct C and indirect H-[C] MR detection methods for the study of dynamic metabolic turnover in the human brain.

A wide range of direct C and indirect H-[C] MR detection methods exist to probe dynamic metabolic pathways in the human brain. Choosing an optimal detection method is difficult as sequence-specific features regarding spatial localization, broadband decoupling, spectral resolution, power requirements and sensitivity complicate a straightforward comparison. Here we combine density matrix simulations with experimentally determined values for intrinsic H and C sensitivity, T and T relaxation and transmit efficiency to allow selection of an optimal C MR detection method for a given application and magnetic field.

Detection of cerebral NAD in humans at 7T.

Purpose: To develop H-based MR detection of nicotinamide adenine dinucleotide (NAD ) in the human brain at 7T and validate the H results with NAD detection based on P-MRS.

Methods: H-MR detection of NAD was achieved with a one-dimensional double-spin-echo method on a slice parallel to the surface coil transceiver. Perturbation of the water resonance was avoided through the use of frequency-selective excitation.

DYNAmic Multi-coIl TEchnique (DYNAMITE) shimming of the rat brain at 11.7 T.

The in vivo rat model is a workhorse in neuroscience research, preclinical studies and drug development. A repertoire of MR tools has been developed for its investigation; however, high levels of B0 magnetic field homogeneity are required for meaningful results. The homogenization of magnetic fields in the rat brain, i.

Assessment of early diastolic strain-velocity temporal relationships using spatial modulation of magnetization with polarity alternating velocity encoding (SPAMM-PAV).

A novel MR imaging technique, spatial modulation of magnetization with polarity alternating velocity encoding (SPAMM-PAV), is presented to simultaneously examine the left ventricular early diastolic temporal relationships between myocardial deformation and intra-cavity hemodynamics with a high temporal resolution of 14 ms. This approach is initially evaluated in a dynamic flow and tissue mimicking phantom. A comparison of regional longitudinal strains and intra-cavity pressure differences (integration of computed in-plane pressure gradients within a selected region) in relation to mitral valve inflow velocities is performed in eight normal volunteers.

Multicoil shimming of the mouse brain.

MR imaging and spectroscopy allow the noninvasive measurement of brain function and physiology, but excellent magnetic field homogeneity is required for meaningful results. The homogenization of the magnetic field distribution in the mouse brain (i.e.

Surgically implantable magnetic resonance angiography coils improve resolution to allow visualization of blood flow dynamics.

Background: Magnetic resonance angiography (MRA) is clinically useful but of limited applicability to small animal models due to poor signal resolution, with typical voxel sizes of 1 mm(3) that are insufficient to analyze vessels of diameter <1 mm. We determined whether surgically implantable, extravascular MRA coils increase signal resolution adequately to examine blood flow dynamics

Methods: A custom MRA coil was surgically implanted near the carotid artery of a New Zealand White rabbit. A stenosis was created in the carotid artery to induce complicated, non-laminar flow.

In situ 3D magnetic resonance metabolic imaging of microwave-irradiated rodent brain: a new tool for metabolomics research.

The rapid elevation in rat brain temperature achieveable with focused beam microwave irradiation (FBMI) leads to a permanent inactivation of enzymes, thereby minimizing enzyme-dependent post-mortem metabolic changes. An additional characteristic of FBMI is that the NMR properties of the tissue are close to those of the in vivo condition and remain so for at least 12 h. These features create an opportunity to develop magnetic resonance spectroscopy and imaging on microwave-irradiated samples into a technique with a resolution, coverage and sensitivity superior to any experiment performed directly in vivo.

Natural abundance (17)O NMR spectroscopy of rat brain in vivo.

Oxygen is an abundant element that is present in almost all biologically relevant molecules. NMR observation of oxygen has been relatively limited since the NMR-active isotope, oxygen-17, is only present at a 0.037% natural abundance.

Sample-specific diamagnetic and paramagnetic passive shimming.

When homogenizing the static magnetic field over extended in vivo volumes, significant residual inhomogeneity can remain after spherical harmonic shim optimization. This is due to the low spatial orders of shims available on in vivo MR systems and the presence of higher-order inhomogeneity in the vicinity of anatomic air cavities. Mediation of this problem through the development of higher-order spherical harmonic shims is severely impeded by bore space limitations.

High magnetic field water and metabolite proton T1 and T2 relaxation in rat brain in vivo.

Comprehensive and quantitative measurements of T1 and T2 relaxation times of water, metabolites, and macromolecules in rat brain under similar experimental conditions at three high magnetic field strengths (4.0 T, 9.4 T, and 11.

Dynamic shim updating (DSU) for multislice signal acquisition.

Dynamic shim updating (DSU) is a technique for achieving optimal magnetic field homogeneity over extended volumes by dynamically updating an optimal shim setting for each individual slice in a multislice acquisition protocol. Here the practical implementation of DSU using all first- and second-order shims is described. In particular, the hardware modifications and software requirements are demonstrated.

Detection of [1,6-13C2]-glucose metabolism in rat brain by in vivo 1H-[13C]-NMR spectroscopy.

Localized, water-suppressed (1)H-[(13)C]-NMR spectroscopy was used to detect (13)C-label accumulation in cerebral metabolites following the intravenous infusion of [1,6-(13)C(2)]-glucose (Glc). The (1)H-[(13)C]-NMR method, based on adiabatic RF pulses, 3D image-selected in vivo spectroscopy (ISIS) localization, and optimal shimming, yielded high-quality (1)H-[(13)C]-NMR spectra with optimal NMR sensitivity. As a result, the (13)C labeling of [4-(13)C]-glutamate (Glu) and [4-(13)C]-glutamine (Gln) could be detected from relatively small volumes (100 microL) with a high temporal resolution.