MR-guided laser-induced thermotherapy in ex vivo porcine kidney: comparison of four different imaging sequences

Purpose: To evaluate the clinical value of different magnetic resonance imaging (MRI) sequences for a real-time thermo-monitoring during laser-induced thermotherapy (LITT) in kidneys.

Methods: Twenty-eight ex vivo pig kidneys were treated with laser ablation under MR guidance in a high-field MR scanner (Magnetom Espree or Avanto Fit, Siemens, Germany). For the thermal ablation of the kidney, a neodymium yttrium-aluminum-garnet (Nd:YAG) laser was used in combination with a special protective catheter (length 43 cm, 4 French) which is sealed at the distal end. First, ablation was performed for 7, 10, and 13 minutes using FLASH sequences for investigation of time-dependent growth of lesion size. In the second step, we evaluated the optimal imaging sequence during a 7 minutes ablation of the kidney and after cooling using four different MR sequences (Haste, FLASH, radial VIBE, and Caipirinha DIXON).

Results: Macroscopic lesion volume increased from 3,784 ± 1,525 mm(3) to 7,683 ± 5,756 mm(3) after the ablation from 7 to 13 minutes and MR volume ranged from 2,107 ± 1,674 mm(3) to 2,934 ± 1,549 mm(3) after the ablation from 7 to 13 minutes. During ablation, FLASH (132 ± 34%) and radial VIBE (120 ± 43%) sequences displayed lesion volumes most efficiently with a trend to overestimation. The Caipirinha DIXON (323 ± 24%) sequence overestimated the volumes significantly during real-time monitoring. The volumes measured by MRI with FLASH (61 ± 30%), Haste (67 ± 28%), or radial VIBE (48 ± 14%) sequences after cooling of the kidney after ablation were always underestimated. The Caipirinha DIXON (142 ± 2%) sequence still overestimated the lesion volume after cooling of the kidney.

Conclusion: LITT is a feasible ablation modality in kidney tissue. Moreover, macroscopic and MR lesion volume increases time-dependently. For online monitoring, radial VIBE and FLASH sequences seem to be most efficient.