# Quantitative ex vivo assessment of target temperature and ablation duration for protocol optimization of microwave ablation procedures with mr thermometry

## TL;DR

This study evaluates how target temperature and ablation duration affect MRI thermometry quality during microwave ablation in bovine livers, finding that lower temperatures improve image quality but reduce ablation volume.

## Contribution

The study introduces a controlled ex vivo framework to optimize microwave ablation protocols using MR thermometry and identifies temperature-duration combinations that balance image quality and lesion size.

## Key findings

- Lower target temperatures (60°C) with moderate ablation durations (7:30 min) yield the highest MRI thermometry quality.
- Ablation areas correlate strongly with macroscopic necrosis, but lesion volumes decrease at lower temperatures.
- A staged two-level approach is suggested to balance thermometry quality and ablation volume in clinical workflows.

## Abstract

To quantitatively assess the influence of target temperature and ablation duration on the quality of proton resonance frequency shift (PRFS)-based MR thermometry during microwave ablation (MWA) in a controlled ex vivo model, and to identify parameter ranges associated with improved thermometry performance. Thirty-two MWAs were performed in 10 ex vivo bovine livers in a 1.5-tesla MRI system with multi-slice volumetric real-time thermometry yielding temperature and thermal dose maps. The experiments were conducted twice using all combinations of four target temperatures (60; 80; 100; 120 °C) and four ablation times (5:00; 7:30; 10:00; 15:00 min). Thermometry quality was rated on a 5‑point Likert scale. Ablation areas were compared with histopathology (hematoxylin and eosin, H&E; and nicotinamide adenine dinucleotide, NADH‑diaphorase) and correlated using Spearman coefficients. Likert scores were compared across temperatures using Kruskal-Wallis and Mann-Whitney U tests. All evaluations were performed independently by two readers. Lesion areas varied from 2.6 to 12.9 cm², increasing primarily with target temperature. Ablation areas from temperature and thermal dose maps correlated strongly with macroscopically visual necrosis (p < 0.01). Likert scores differed significantly across temperatures (p < 0.05). The highest image quality was achieved at 60 °C for 7:30 min, showing comparable scores as at 80° for 15:00 min, but significantly differing from 100 °C to 120 °C. In this controlled ex vivo setting, lower target temperatures were associated with improved MRI thermometry quality, providing more reliable visualization of ablation zones; however, ablation volumes decreased at lower temperatures. Furthermore, these empirical ex vivo observations suggest that a staged two-level approach may support a clinical workflow strategy aimed at balancing thermometry image quality and ablation volume. Given the absence of perfusion and motion effects, these findings require further validation before clinical translation.

The online version contains supplementary material available at 10.1038/s41598-026-41656-3.