A pilot study for clinical feasibility of the near-harmonic 2D referenceless PRFS thermometry in liver under free...

The conventional implementations of proton resonance frequency shift (PRFS) magnetic resonance thermometry (MRT) require the subtraction of single or multiple temporal references, a motion sensitive critical feature. A pilot study was conducted here to investigate the clinical feasibility of near-harmonic two-dimensional (2D) referenceless PRFS MRT, using patient data from MR-guided laser ablation of liver malignancies.

PRFS MRT with respiratory-triggered multi-slice gradient-recalled (GRE) acquisition was performed under free breathing in six patients. The precision of the novel referenceless MRT was compared with the reference phase subtraction. Coupling the referenceless MRT with a model-based, real-time compatible regularisation algorithm was also investigated.

The precision of MRT was improved by a factor of 3.3 when using the referenceless method as compared to the reference phase subtraction. The approach combining referenceless PRFS MRT and model-based regularisation yielded an estimated precision of 0.7° to 2.1°C, resulting in millimetre-range agreement between the calculated thermal dose and the 24 h post-treatment unperfused regions in liver.

The application of the near-harmonic 2D referenceless MRT method was feasible in a clinical scenario of MR-guided laser-induced thermal therapy (LITT) ablation in liver and permitted accurate prediction of the thermal lesion under free breathing in conscious patients, obviating the need for a controlled breathing under general anaesthesia.