Absolute temperature MR imaging with thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethyl-1,4,7,10-tetraacetic acid (TmDOTMA⁻)

Abstract

MR thermometry based on the water ¹H signal provides high temporal and spatial resolution, but it has low temperature sensitivity (∼0.01 ppm/°C) and requires monitoring of another weaker signal for absolute temperature measurements. The use of the paramagnetic lanthanide complex, thulium 1,4,7,10- tetraazacyclo-dodecane-1,4,7,10-tetramethyl-1,4,7,10-tetraac- etate (TmDOTMA⁻), which is ∼60 times more sensitive to temperature than the water ¹H signal, is advanced to image absolute temperatures in vivo using water signal as a reference. The temperature imaging technique was developed using gradient echo and asymmetric spin echo imaging sequences on 9.4 Tesla (T) horizontal and vertical MR scanners. A comparison of regional temperatures measured with TmDOTMA⁻ and fiber-optic probes showed that the accuracy of imaging temperature is <0.3°C. The temperature imaging technique was found to be insensitive to inhomogeneities in the main magnetic field. The feasibility of imaging temperature of intact rats at ∼1.4 mmol/kg dose with ∼1-mm spatial resolution in only 3 min is demonstrated. TmDOTMA⁻ should prove useful for imaging absolute temperatures in deep-seated organs in numerous biomedical applications. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.