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MRI thermometry based on PARACEST agents.

ABSTRACT: A novel magnetic resonance imaging (MRI) thermometry technique is demonstrated in vitro based upon the use of a PARACEST (PARAmagnetic Chemical Exchange Saturation Transfer) agent. This new method takes advantage of the high concentration of bulk water (the readout signal for imaging) and the hyperfine frequency shift properties of PARACEST agents. For two prototypes, Dy(1)3+ and Eu(2)-, the chemical shifts (delta, in ppm) of the Ln3+-bound water molecules are linearly dependent on temperature (T, in degrees C) over the range of 20-50 degrees C (delta = 6.9 x T - 944.7 and delta = -0.4 x T + 64.6, respectively). This offers the exciting possibility of improving the temperature dependencies approximately 690- and approximately 40-fold over the most widely used water PRF thermometry (Proton Resonance Frequency: -0.01 ppm/ degrees C).

SUBMITTER: Zhang S

PROVIDER: S-EPMC2570850 | biostudies-literature | 2005 Dec

REPOSITORIES: biostudies-literature

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MRI thermometry based on PARACEST agents.

Zhang Shanrong S Malloy Craig R CR Sherry A Dean AD

Journal of the American Chemical Society 20051201 50

A novel magnetic resonance imaging (MRI) thermometry technique is demonstrated in vitro based upon the use of a PARACEST (PARAmagnetic Chemical Exchange Saturation Transfer) agent. This new method takes advantage of the high concentration of bulk water (the readout signal for imaging) and the hyperfine frequency shift properties of PARACEST agents. For two prototypes, Dy(1)3+ and Eu(2)-, the chemical shifts (delta, in ppm) of the Ln3+-bound water molecules are linearly dependent on temperature ( ...[more]

PMID: 16351064

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Project description:BackgroundProton resonance frequency shift (PRFS) magnetic resonance (MR) thermometry exploits the local magnetic field changes induced by the temperature dependence of the electron screening constant of water protons. Any other local magnetic field changes will therefore translate into incorrect temperature readings and need to be considered accordingly. Here, we investigated the susceptibility changes induced by the inflow and presence of a paramagnetic MR contrast agent and their implications on PRFS thermometry.MethodsPhantom measurements were performed to demonstrate the effect of sudden gadopentetate dimeglumine (Gd-DTPA) inflow on the phase shift measured using a PRFS thermometry sequence on a clinical 3 T magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) system. By proton nuclear magnetic resonance spectroscopy, the temperature dependence of the Gd-DTPA susceptibility was measured, as well as the effect of liposomal encapsulation and release on the bulk magnetic susceptibility of Gd-DTPA. In vivo studies were carried out to measure the temperature error induced in a rat hind leg muscle upon intravenous Gd-DTPA injection.ResultsThe phantom study showed a significant phase shift inside the phantom of 0.6 ± 0.2 radians (mean ± standard deviation) upon Gd-DTPA injection (1.0 mM, clinically relevant amount). A Gd-DTPA-induced magnetic susceptibility shift of ΔχGd-DTPA = 0.109 ppm/mM was measured in a cylinder parallel to the main magnetic field at 37°C. The temperature dependence of the susceptibility shift showed dΔχGd-DTPA/dT = -0.00038 ± 0.00008 ppm/mM/°C. No additional susceptibility effect was measured upon Gd release from paramagnetic liposomes. In vivo, intravenous Gd-DTPA injection resulted in a perceived temperature change of 2.0°C ± 0.1°C at the center of the hind leg muscle.ConclusionsThe use of a paramagnetic MR contrast agent prior to MR-HIFU treatment may influence the accuracy of the PRFS MR thermometry. Depending on the treatment workflow, Gd-induced temperature errors ranging between -4°C and +3°C can be expected. Longer waiting time between contrast agent injection and treatment, as well as shortening the ablation duration by increasing the sonication power, will minimize the Gd influence. Compensation for the phase changes induced by the changing Gd presence is difficult as the magnetic field changes are arising nonlocally in the surroundings of the susceptibility change.

Dataset Information

MRI thermometry based on PARACEST agents.

Publications

MRI thermometry based on PARACEST agents.

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