9 Basic principles and medical/biological applications of nuclear magnetic resonance (NMR) Flashcards
Which nuclei are able to give an NMR signal?
Whose resultant nuclear spin is different from zero; i.e. those nuclei which contain odd number of protons and/or odd number of neutrons.
List at least three nuclei which can be used in biological applications of nuclear magnetic resonance!
1H, 13C, 15N, 23Na, 31P
What happens to the elementary magnetic moments in an external magnetic field?
The interaction of magnetic moments with the external magnetic field causes their alignment as well as their precession about the magnetic field.
What are the possible states of the magnetic moment of a 1H nucleus in an external magnetic field?
The nuclear spin of 1H is 1⁄2, therefore its magnetic moment has two possible alignments with respect to the magnetic field: it can be aligned either with (parallel alignment – lower energy level or ground state) or against (antiparallel alignment – higher energy level or excited state) the magnetic field.
Give the equation describing the NMR resonance frequency of a nucleus as a function of the external magnetic field neglecting chemical shift?
𝑓=𝛾𝑁/2𝜋 𝐵𝑒𝑥𝑡
f: resonance frequency
𝛾𝑁: gyromagnetic ratio of the nucleus Bext: external magnetic field
Define the gyromagnetic ratio of a nucleus!
It is the ratio of the magnetic moment (MN) to the intrinsic angular momentum (spin; LN) of the given nucleus:
𝛾𝑁 = Mn/Ln = uNgn/h
gn is the nuclear g-factor, u n is the nuclear magneton and h = h/2pi
What region of the electromagnetic spectrum can be used to excite nuclear spins placed in a magnetic field?
Radiowaves ( aprox10 8 Hz): NMR
What factors influence the resonance frequency in NMR?
Quality of the absorbing nucleus, its chemical environment and the strength of the external magnetic field.
How can the relative concentration of absorbing nuclei be determined from an NMR spectrum?
From the area under the absorption lines corresponding to different nuclei.
What is chemical shift in NMR?
The local magnetic field experienced by a given nucleus is altered by the chemical environment resulting in a change in its original resonance frequency.
What is chemical shift in NMR?
The local magnetic field experienced by a given nucleus is altered by the chemical environment resulting in a change in its original resonance frequency.
What is the macroscopic consequence of the alignment of nuclear magnetic moments by the external magnetic field?
A macroscopic magnetization (equilibrium or longitudinal magnetization) is formed in the direction of the external magnetic field.
What provides the signal in pulse NMR techniques?
The precession of transverse magnetization (i.e. the xy component of the net magnetization vector at right angles to the main magnetic field) generated by a short, intense radiofrequency pulse. Precession takes place at the resonance frequency of the nucleus in the given magnetic field.
What provides the signal in pulse NMR techniques?
The precession of transverse magnetization (i.e. the xy component of the net magnetization vector at right angles to the main magnetic field) generated by a short, intense radiofrequency pulse. Precession takes place at the resonance frequency of the nucleus in the given magnetic field.
What is spin-spin and spin-lattice relaxation?
Spin–spin relaxation is the mechanism responsible for the decay of transverse magnetization generated by the radiofrequency pulse. Spin–lattice relaxation is responsible for the recovery of the original longitudinal magnetization vector.
