MRI thermometry in phantoms by use of the proton resonance frequency shift method: application to interstitial laser thermotherapy.
In this work the temperature dependence of the proton resonance frequency was assessed in agarose gel with a high melting temperature (95 degrees C) and in porcine liver in vitro at temperatures relevant to thermotherapy (25-80 degrees C). Furthermore, an optically tissue-like agarose gel phantom was developed and evaluated for use in MRI. The phantom was used to visualize temperature distributions from a diffusing laser fibre by means of the proton resonance frequency shift method. An approximately linear relationship (0.0085 ppm degrees C(-1)) between proton resonance frequency shift and temperature change was found for agarose gel, whereas deviations from a linear relationship were observed for porcine liver. The optically tissue-like agarose gel allowed reliable MRI temperature monitoring, and the MR relaxation times (T1 and T2) and the optical properties were found to be independently alterable. Temperature distributions around a diffusing laser fibre, during irradiation and subsequent cooling, were assessed with high spatial resolution (voxel size = 4.3 mm3) and with random uncertainties ranging from 0.3 degrees C to 1.4 degrees C (1 SD) with a 40 s scan time.
Department of Radiation Physics, Lund University Hospital, Sweden.
J
J
Olsrud
R
R
Wirestam
S
S
Brockstedt
A M
AM
Nilsson
K G
KG
Tranberg
F
F
Ståhlberg
B R
BR
Persson
D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D005782:Gels; D006979:Hyperthermia, Induced / Q000379:methods*; D066298:In Vitro Techniques; D053685:Laser Therapy; D008099:Liver; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D008962:Models, Theoretical; D055095:Optics and Photonics; D019047:Phantoms, Imaging; D012685:Sepharose; D013552:Swine; D013696:Temperature; D013821:Thermometers
D005782:Gels; D012685:Sepharose