Relaxation Rate Dispersion of Blood due to Paramagnetic Ions: An Implications for Magnetic Resonance Relaxation Dispersion Imaging
The Field cycling approach was used to investigate the proton relaxation rate dispersion of paramagnetic ions in blood samples over a frequency range of 10 kHz to 10 MHz. We used a relatively high magnetic field to magnetise the samples first (0.5 T). This field was swiftly (1 ms) lowered to a lower value in the range 0.1 mT – 0.5 T, where the excited proton spin may relax over a time period of roughly 3T1max, using electronic means. The magnetic field is then swiftly increased to a greater level in order to detect the NMR signal. The relaxation characteristics were investigated using a three-compartment water proton-spin exchange model. We calculated a correlation frequency for each compartment by fitting the dispersion curves to a sum of Lorentz distributions. Low concentrations of paramagnetic ions have a significant impact on relaxation rate dispersion in the low frequency area of 10 MHz, according to our findings. This effect could be utilised to map inorganic paramagnetic or organic free-radical chemicals employed as contrast agents in medical applications, as well as to trace cellular activity by subtracting MR pictures acquired at high (>100 mT) and low (10 mT) relaxation fields. Such picture sequences could be utilised to investigate the brain’s oxygen status and metabolism, as well as the production and distribution of reactive oxygen species. This approach, known as “Magnetic Resonance Relaxation Dispersion Imaging” (MARDI), could be used to study the evolution of numerous neurological illnesses such as stroke, MS, Alzheimer’s disease, and brain tumours. It may also be appropriate for visualising tumour oxygenation and in vivo ROS distributions in radiation therapy, which might be useful in dose planning as well as assessing and optimising the effects of different radiation therapy regimes. The utilisation of an Overhauser-enhanced pre-polarized MRI system for imaging studies of tumour hypoxia and red-ox state as radiotherapy prognostic variables has been proven.
Author (s) Details
Bertil R. R. Persson
Medical Radiation Physics, Lund University, Lund, Sweden
Medical Radiation Physics, Lund University, Lund, Sweden and MAX Laboratory, Lund University, Lund, Sweden.
Leif G. Salford
Department of Neurosurgery, Lund University, Lund, Sweden
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