**4. Technical aspects and commercially available components of LITT**

#### **4.1. MR thermometry**

After numerous attempts of measuring the thermal energy delivery to the target tissue during LITT, including the use of skin thermometers, subcutaneous and interstitial probes, infrared detectors and thermographic cameras [28, 29, 52–56], it was the addition of MR thermometer that played the most significant role in allowing real-time monitoring and quantification of thermal energy delivery leading to thermal ablation [27]. MR thermography based on the temperature-dependent water proton resonance frequency (PRF) is capable of providing visual imaging together with a quantification model of thermal deposition with accurate temporal and spatial resolution. The theory behind PRF is based on the fact that as tempera‐ ture increases during LITT, the number of free H2O molecules also increases due to break‐ age of hydrogen bonds between H2O molecules. The hydrogen nuclei (proton) are mobilized more efficiently within the gradient field when in the free H2O molecule state, producing realtime imaging that can be interpreted and visualized using the proper computer software in the treatment workstation [57, 58].
