Lower than low: Perspectives on zero- to ultralow-field nuclear magnetic resonance.

The less-traveled low road in nuclear magnetic resonance is discussed, honoring the contributions of Prof. Bernhard Blümich, aspiring towards reaching 'a new low.' A history of the subject and its current status are briefly reviewed, followed by an effort to prophesy possible directions for future developments.

Calculated signal-to-noise ratio of MRI detected with SQUIDs and Faraday detectors in fields from 10 microT to 1.5 T.

We examine the calculated signal-to-noise ratio (SNR) achievable with different MRI detection modalities in precession fields ranging from 10 microT to 1.5 T. In particular, we compare traditional Faraday detectors with both tuned and untuned detectors based on superconducting quantum interference devices (SQUIDs).

Prostate spectroscopy at 3 Tesla using two-dimensional S-PRESS.

Two-dimensional (2D) strong-coupling point-resolved spectroscopy (S-PRESS) is introduced as a novel approach to (1)H MR spectroscopy (MRS) in the prostate. The technique provides full spectral information and allows for an accurate characterization of the citrate (Cit) signal. The method is based on acquiring a series of PRESS spectra with constant total echo time (TE).

Optimizing PRESS localized citrate detection at 3 Tesla.

Analytical methods are used to characterize the response of the strongly coupled two-spin system of citrate to point-resolved spectroscopy (PRESS)-based sequences at 3 T. The signal output is analyzed line by line, as well as in the Cartesian product operator basis. Patterns with a periodicity of 80.

SQUID-detected MRI at 132 microT with T1-weighted contrast established at 10 microT--300 mT.

T(1)-weighted contrast MRI with prepolarization was detected with a superconducting quantum interference device (SQUID). A spin evolution period in a variable field between prepolarization and detection enabled the measurement of T(1) in fields between 1.7 microT and 300 mT; T(1) dispersion curves of agarose gel samples over five decades in frequency were obtained.

Chemical-shift-selective filter for the in vivo detection of J-coupled metabolites at 3T.

A chemical-shift-selective filter (CSSF) was applied to the detection of J-coupled metabolites in the human brain. This filter is an acquisition-based technique that requires the chemical shifts (CS's) of different metabolites, but not their whole multiplet structures, to be resolved. The sequence is based on the 2D constant-time spin-echo experiment, which yields pure CS spectra in the indirect dimension.

Zero- to low-field MRI with averaging of concomitant gradient fields.

Magnetic resonance imaging (MRI) encounters fundamental limits in circumstances in which the static magnetic field is not sufficiently strong to truncate unwanted, so-called concomitant components of the gradient field. This limitation affects the attainable optimal image fidelity and resolution most prominently in low-field imaging. In this article, we introduce the use of pulsed magnetic-field averaging toward relaxing these constraints.

Microtesla MRI with a superconducting quantum interference device.

MRI scanners enable fast, noninvasive, and high-resolution imaging of organs and soft tissue. The images are reconstructed from NMR signals generated by nuclear spins that precess in a static magnetic field B0 in the presence of magnetic field gradients. Most clinical MRI scanners operate at a magnetic field B0 = 1.

In vivo 1H NMR spectroscopy of individual human brain metabolites at moderate field strengths.

This article reviews spectral editing techniques for in vivo 1H NMR spectroscopy of human brain tissue at moderate field strengths of 1.5-3 Tesla. Various aspects of 1H NMR spectroscopy are discussed with regard to in vivo applications.

Liquid-state NMR and scalar couplings in microtesla magnetic fields.

We obtained nuclear magnetic resonance (NMR) spectra of liquids in fields of a few microtesla, using prepolarization in fields of a few millitesla and detection with a dc superconducting quantum interference device (SQUID). Because the sensitivity of the SQUID is frequency independent, we enhanced both signal-to-noise ratio and spectral resolution by detecting the NMR signal in extremely low magnetic fields, where the NMR lines become very narrow even for grossly inhomogeneous measurement fields. In the absence of chemical shifts, proton-phosphorous scalar (J) couplings have been detected, indicating the presence of specific covalent bonds.