Estimation of the magnitude of quadrupole relaxation enhancement in the context of magnetic resonance imaging contrast

Abstract

Magnetic Resonance Imaging (MRI) is one of the most powerful diagnostic tools providing maps of 1 H relaxation times of human body. The method needs, however, a contrast mechanism to enlarge the difference in the relaxation times between healthy and pathological tissues. In this work we discuss the potential of a novel contrast mechanism for MRI, based on Quadrupole Relaxation Enhancement (QRE) and estimate the achievable value of QRE under the most favorable conditions. It has turned out that the theoreticaly possible enhancement factors are smaller than those of typical paramagnetic contrast agents but in turn the field-selectivity of QRE-based agents makes them extremely sensitive to subtle changes of the electric field gradient in the tissue. So far QRE has been observed for solids (in most cases for 14 N) as a result of very slow dynamics and anisotropic spin interactions, believed to be necessary for QRE to appear. We show the first evidence that QRE can be achieved in solutions of compounds containing a high spin nucleus (209 Bi) as the quadrupole element. The finding of QRE in liquid state is explained in terms of spin relaxation theory based on the stochastic Liouville equation. The results confirm the relaxation theory and motivate further exploration of the potential of QRE for MRI.

Dynamics of Solid Proteins by Means of Nuclear Magnetic Resonance Relaxometry

“…As the spin and spatial variables cannot be separated in the stochastic Liouville approach, one constructs a basis being an outer product of the spin and rotational variables: |Oα)=|sans-serifΣ,σ)⊗|L,K,M), where Σ ranges from 1 to (2S+1), i.e., 3 for 14 N, σ=−sans-serifΣ,…,sans-serifΣ while the quantum numbers L , K , M correspond to the indices of Wigner rotation matrices; for practical calculations it is sufficient to set L = 1, …, 8, K = − L , …, L , M = − L , …, L . Then the relaxation rate, R1HN, is given as [22,49,50,51,52]: R1HN=Re{[T11]+[M]−1[T11]}where the matrix [ M ] is defined in the {|Oα)(Oβ|}…”

“…Then the relaxation rate, R1HN, is given as [22,49,50,51,52]: R1HN=Re{[T11]+[M]−1[T11]}where the matrix [ M ] is defined in the {|Oα)(Oβ|} basis constructed from pairs of the |Oα) vectors. The matrix elements are given as [21,22,25,51,52]: [M]α,β=304aQ(−1)σ′F|K−K′|2[(…”

A Novel Class of 1H‐MRI Contrast Agents Based on the Relaxation Enhancement Induced on Water Protons by 14N‐Containing Imidazole Moieties

“…The idea of developing MRI contrast agents based on the detection of QPs has also been recently tackled by Scharfetter et al [35–37] . They investigated 209 Bi (I=9/2) containing organometallic compounds reporting interesting results that, however, appeared difficult to translate into living systems.…”

Design of a fast field-cycling magnetic resonance imaging system, characterization and methods for relaxation dispersion measurements around 1.5 T

“…For the contrast agents and samples studied here, the NMRD profiles (directly for R1, and indirectly for R2 as it can be extracted from echo attenuation) appeared linearly varying with B0. The slopes and corresponding to the first order derivative of, respectively, the longitudinal and transverse relaxation rates with respect to the magnetic field at 1.5 T, and the NMRD profiles could be summarized by a first order polynomial around 1.5 T. This linear behaviour is expected for these types of contrast agents and samples [13][14][15]46 , but that may not be the case in specific situations such as when using specific contrasts agents exploiting quadrupole relaxation enhancement 47 . The obtained values both for R1 and R2 dispersion are consistent with previously published data (see appendix)…”