MRI thermodosimetry in laser-induced interstitial thermotherapy.
OBJECTIVE
The aim of this study was to establish a correlation between a thermal measurement and a magnetic resonance imaging (MRI) signal during laser-induced interstitial thermotherapy (LITT) in liver.


METHODS
Pig liver was irradiated for 15 minutes with a diode laser at two different powers, 0.5 W (450 J) and 1.5 W (1,350 J). Tissue temperature was monitored every 20 seconds using thermocouples. Thermosensitive MRI sequences (T(1)-weighted Turbo-Flash) were acquired with the same irradiation parameters. Correlation between MRI signals (SI) and temperature measures was defined at two different distances from the fiber (5 and 10 mm).


RESULTS
At 0.5 W, temperatures rose progressively up to a maximum increase of 9.5 degrees C at 5 mm and 4 degrees C at 10 mm after 15 minutes. The corresponding MRI signal decreased progressively to -27.6 SI at 5 mm and -18.5 SI at 10 mm. At 1.5 W, temperatures rose dramatically at 5 mm, reaching a plateau. The temperature elevation measured at the end of the irradiation was of 30 degrees C whereas at 10 mm it was only 14.5 degrees C. The MRI signal varied accordingly, remaining inversely proportional to temperature (-76 SI at 5 mm and -35.5 SI at 10 mm).


CONCLUSIONS
An inversely proportional relationship was observed between MRI signal in sequential Turbo-Flash and temperature. MRI should allow to analyze heat diffusion in the liver, and thus to monitor real-time LITT treatments.
Prudhomme
Michel
M
Département de Chirurgie Digestive et de Cancérologie Digestive, rue du Pr R. Debré F30900 Nîmes, France. michel.prudhomme@chu-nimes.fr
Mattéi-Gazagnes
Martine
M
Fabbro-Peray
Pascale
P
Puche
Pierre
P
Chabalier
Jean-Paul
JP
Delacrétaz
G
G
François-Michel
Lopez F M
LF
Godlewski
Guilhem
G
D000818:Animals; D004058:Diffusion / Q000528:radiation effects; D004195:Disease Models, Animal; D005110:Extracellular Space / Q000502:physiology / Q000528:radiation effects*; D006979:Hyperthermia, Induced; D066298:In Vitro Techniques; D008099:Liver / Q000473:pathology* / Q000503:physiopathology / Q000528:radiation effects*; D008113:Liver Neoplasms / Q000473:pathology* / Q000503:physiopathology / Q000532:radiotherapy*; D028022:Low-Level Light Therapy; D008279:Magnetic Resonance Imaging; D011874:Radiometry; D013552:Swine