Computer-controlled production of intracranial lesions using magnetic resonance thermometry

Fiber optically delivered laser energy may be ideal in treating small intracerebral lesions with minimal invasiveness. We have continued development of a laser-computer system for automated magnetic resonance thermal imaging (MRTI) guidance and control of intracerebral laser interstitial thermal therapy (LITT). The system consists of a workstation which is interfaced to a clinical MR scanner via Ethernet and to a compact high power diode laser via hardware interface. The system analyzes MRTI data to compute temperature changes based on the proton resonance frequency (PRF) shift, and constructs two-dimensional maps of temperature and estimated chronic thermal damage during therapy. Images are obtained approximately every 4.5 seconds allowing near-real-time tracking of LITT progress. A graphical user interface allows specification of temperature constraints on the image which regulate delivery of thermal energy. We have tested the ability of the system to create small focal intracranial lesions of specified dimension in both normal canine brain (n = 6 animals, 15 lesions) and in an intracerebral tumor model grown from inoculum (n = 11 animals, 15 lesions). Histological analysis was used to assess the accuracy of MRTI-derived predictions of lesion size and to assess effectiveness of reaching prescribed tumor boundaries.