In situ temperature measurements with thermocouple probes during laser interstitial thermotherapy (LITT): quantification and correction of a measurement artifact.
OBJECTIVE
The purpose of this work was to quantify the magnitude of an artifact induced by stainless steel thermocouple probes in temperature measurements made in situ during experimental laser interstitial thermo-therapy (LITT). A procedure for correction of this observational error is outlined.


METHODS
A CW Nd:YAG laser system emitting 20W for 25-30 s delivered through a fiber-optic probe was used to create localized heating. The temperature field around the fiber-optic probe during laser irradiation was measured every 0.3 s in air, water, 0.4% intralipid solution, and fatty cadaver pig tissue, with a field of up to fifteen needle thermocouple probes.


RESULTS
Direct absorption of Nd:YAG laser radiation by the thermocouple probes induced an overestimation of the temperature, ranging from 1.8 degrees C to 118.6 degrees C in air, 2.2 degrees C to 9.9 degrees C in water, 0.7 C to 4.7 C in intralipid and 0.3 C to 17.9 C in porcine tissue after irradiation at 20W for 30 s and depending on the thermocouple location. The artifact in porcine tissue was removed by applying exponential and linear fits to the measured temperature curves.


CONCLUSIONS
Light absorption by thermocouple probes can induce a significant artifact in the measurement of laser-induced temperature increases. When the time constant of the thermocouple effect is much smaller than the thermal relaxation time of the surrounding tissue, the artifact can be accurately quantified. During LITT experiments where temperature differences of a few degrees are significant, the thermocouple artifact must be removed in order to be able accurately to predict the treatment outcome.
Manns
F
F
Department of Biomedical Engineering, University of Miami College of Engineering, Coral Gables, Florida 33146, USA.
Milne
P J
PJ
Gonzalez-Cirre
X
X
Denham
D B
DB
Parel
J M
JM
Robinson
D S
DS
D000818:Animals; D016477:Artifacts; D055592:Biophysical Phenomena; D001703:Biophysics; D005336:Fiber Optic Technology; D006979:Hyperthermia, Induced / Q000295:instrumentation / Q000379:methods*; D053685:Laser Therapy; D008954:Models, Biological; D055100:Optical Fibers; D013193:Stainless Steel; D013552:Swine; D013696:Temperature; D014867:Water
D014867:Water; D013193:Stainless Steel