Magnetic resonance imaging of interstitial laser photocoagulation of normal rat liver: Imaging-histopathological correlation

Aim - To correlate the magnetic resonance imaging signal changes observed during interstitial laser photocoagulation (ILP) therapy with histopathological analysis of tissue necrosis. A 1.5T MR system was used. Lesions were produced with a diode laser (805 nm) in the liver of normal Wistar rats at laparotomy under general anaesthesia and imaged during treatment. Seventeen lesions were monitored with a T1-weighted spin echo (T1WSE) sequence, and 15 with a FLASH sequence. Treated tissue was removed and stained for NADPH-diaphorase to determine the extent of devitalization. Per-procedural T1WSE showed an expanding area of low signal which developed a high signal rim as ILP progressed. FLASH imaging showed an expanding area of low intensity which was replaced by a complex region of signal change as treatment progressed. Good imaging-histopathological correlation was shown: for T1WSE, r(2)=0.88 (P<0.001) and for FLASH, r(2)=0.95 (P<0.001). MR imaging during hepatic ILP accurately shows the extent of tissue necrosis and therefore may become clinically useful in the control of interstitial thermal treatments to liver lesions.