Magnetic resonance angiography: physical principles and applications.

Magnetic resonance angiography (MRA) is the visualization of hemodynamic flow using imaging techniques that discriminate flowing spins in blood from those in stationary tissue. There are two classes of MRA methods based on whether the magnetic resonance imaging signal in flowing blood is derived from the amplitude of the moving spins, the time-of-flight methods, or is based on the phase accumulated by these flowing spins, as in phase contrast methods. Each method has particular advantages and limitations as an angiographic imaging technique, as evidenced in their application space.

MR imaging: deconstructing timing diagrams and demystifying k-space.

Magnetic resonance imaging (MRI) works on the principle that hydrogen molecules, which are abundant in organic tissue, have a magnetic moment arising from the spin of the protons in the nucleus. All atoms consist of a nucleus made of protons and neutrons. When a sample is put in a large magnet field, the hydrogen atoms become magnetized resulting in a bulk magnetization of the sample.

Time-resolved contrast-enhanced magnetic resonance angiography in the investigation of suspected intracranial dural arteriovenous fistula.

Cerebral angiography is widely regarded as the gold standard for the evaluation and diagnosis of neurovascular abnormalities. However, recent improvements in the spatial and temporal resolution of time-resolved magnetic resonance angiography (MRA) offer clinicians a non-invasive alternative to cerebral angiography. We explored the utility of this technique in an elderly female patient with a suspected intracranial dural arteriovenous fistula (dAVF).

3D coronary motion tracking in swine models with MR tracking catheters.

Purpose: To develop MR-tracked catheters to delineate the three-dimensional motion of coronary arteries at high spatial and temporal resolution.

Materials And Methods: Catheters with three tracking microcoils were placed into nine swine. During breath-holds, electrocardiographic (ECG)-synchronized 3D motion was measured at varying vessel depths.

Probing restrictive diffusion dynamics at short time scales.

Diffusion imaging gradients serve to spectrally filter the temporally evolving diffusion tensor. In this framework, the design of diffusion sensitizing gradients is reduced to the problem of adequately sampling q-space in the spectral domain. The practical limitations imposed by the requirement for delta-function type diffusion-sensitizing gradients to adequately sample q-space, can be relaxed if these impulse gradients are replaced with chirped oscillatory gradients.

Field propagation phenomena in ultra high field NMR: a Maxwell-Bloch formulation.

The principal advantage of NMR at high field is the concomitant increase in signal-to-noise ratio (SNR). This can be traded for improved spatial resolution and combined with parallel imaging to achieve higher temporal resolution. At high field strength, the RF-wavelength and the dimension of the human body complicate the development of NMR coils.

Chemical shift anisotropic mapping of a coherent optical absorber using magnetic field induced quantum beats.

A new method for mapping the spatial structure of optical coherent materials which relies on imposing a set of linear orthogonal gradient magnetic fields for a controlled hyperfine splitting of energy levels to create characteristic quantum beats when illuminated with a laser pulse with sufficient bandwidth to excite these levels is proposed. In this approach, a spectroscopic fingerprint of the dopant sites due to concentration and field susceptibilities in the sample is achieved through a Fourier decomposition of the radiative relaxation decay in an approach analogous to nuclear magnetic resonance spectroscopy due to the imposition of a controlled spatial-spectral encoding scheme. A three pulse sequence necessary to interrogate a gradient resolved voxel is also discussed.

Multidimensional spatial-spectral holographic interpretation of NMR photography.

A spectral holographic interpretation arises naturally in nuclear magnetic resonance (NMR) photography from either the intrinsic chemical shift anisotropy of the spin system or the field inhomogeneity due to the applied spatial encoding gradients. We can thus think of NMR photography as arising from a "diffraction" off a spatial-spectral holographic grating. The spatial holographic component arises from a high dielectric constant (>50) of the NMR medium at high field strength (>4 T) when the excitation wavelength is commensurate with the size of the NMR sample; otherwise, it is a volume spectral holographic grating.

Time-domain frequency-selective processing in nuclear magnetic resonance: a spatial-spectral holographic perspective.

The fundamental nuclear magnetic resonance (NMR) imaging equation can be derived from a spatial-spectral holographic wavefront reconstruction formulation similar to that in quantum optics. A spatial-spectral holographic interpretation arises naturally in NMR from the inhomogeneous linewidth broadening due to either an imposed set of linear orthogonal gradient fields or from the intrinsic chemical anisotropy of the spin system. We can thus think of NMR k-space as a spatial-spectral holographic grating.