Temperature dependence of relaxation times and temperature mapping in ultra-low-field MRI.
Ultra-low-field MRI is an emerging technology that allows MRI and NMR measurements in microtesla-range fields. In this work, the possibilities of relaxation-based temperature measurements with ultra-low-field MRI were investigated by measuring T1 and T2 relaxation times of agarose gel at 50 μT-52 mT and at temperatures 5-45°C. Measurements with a 3T scanner were made for comparison. The Bloembergen-Purcell-Pound relaxation theory was combined with a two-state model to explain the field-strength and temperature dependence of the data. The results show that the temperature dependencies of agarose gel T1 and T2 in the microtesla range differ drastically from those at 3T; the effect of temperature on T1 is reversed at approximately 5 mT. The obtained results were used to reconstruct temperature maps from ultra-low-field scans. These time-dependent temperature maps measured from an agarose gel phantom at 50 μT reproduced the temperature gradient with good contrast.
Department of Biomedical Engineering and Computational Science, Aalto University School of Science, P.O. Box 12200, FI-00076 AALTO, Finland; AMI Centre, Aalto University School of Science, P.O. Box 13000, FI-00076 AALTO, Finland. Electronic address: panu.t.vesanen@gmail.com.
Panu T
PT
Vesanen
Koos C J
KC
Zevenhoven
Jaakko O
JO
Nieminen
Juhani
J
Dabek
Lauri T
LT
Parkkonen
Risto J
RJ
Ilmoniemi
Relaxation theory; Temperature mapping; Ultra-low-field MRI