There are certain metal ions which are well known for T1 relaxation (eg. Mn2+) and there are some which show T2 relaxation more efficiently (eg. Cobalt ions). Metals like Gadolinium can show both the relaxations in good amount. What is the factor which determines whether a magnetic metal ion will show T1 or T2 relaxation?
At the first place, it depends on their magnetic properties and concentrations.
Hi Kashmiri,
It depends what magnetic properties of the element are.
If it is paramagnetic as Gd or Mn it influences more T1 relaxation by shortening T1 relaxation time and increasing (positive contrast agents) signal on T1 weighted images.
The ferromagnetic sobstances as ferrum oxides influences more T2 relaxation time causing its shortenig and decrasing the signal (negative contrast agent) on T2 weighted images.
Best wishes,
Rafal
Relaxation is a complicated process and it is difficult to calculate relaxivities of metal ions quantitatively. As written above, the decisive property is the magnetic dipole moment of an atom or ion, which depends mostly on the number of unpaired electrons.
However, the magnetic dipole moment generally influences both longitudinal (T1) and transverse (T2) relaxation (i. e., ions with greater dipole moment show higher relaxivities r1and r2). The exact quantitative values of r1 and r2 depend also on the microscopic molecular dynamics and the microenvironment around the ion, e. g.,. on the average molecular distance, the number of coordinated water molecules, the molecular tumbling rate, and the (dipolar) correlation time.
For details, see e.g. the attached references (and the classical article by Bloembergen, Purcell, and Pound "Relaxation Effects in Nuclear Magnetic Resonance Absorption" Phys. Rev. 1948; 73: 679).
Article Proton Relaxation Times in Paramagnetic Solutions
Article Relaxation of solvent protons by paramagnetic ions and its d...
Article Influence of Paramagnetic Ions and pH on Proton NMR Relaxati...
Hallo, I've just read your question, and even if time went by, I would like to say something about: 1) every paramagnetic substance has got an effect on both T1 and T2; 2) the effect is proportional to the contrast agent total magnetic moment ; 3) the effect (should I say impact, or influence? my English is not so good as I would like) is proportional to the concentration of the contrast agent: at low concentrations prevails the T1 effect over the T2 effect; at high concentrations prevails T2 effects; 4)relaxation speeds up if the contrast agent had got a high molecular weigh, or asymmetric shape ( higher correlation time ) 5) relaxation efficiency is better at low intensity field
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