Navigator respiratory‐triggered diffusion‐weighted imaging in the follow‐up after hepatic radiofrequency ablation—initial results

Abstract

Purpose:To evaluate diffusion alterations after hepatic radiofrequency (RF) ablation using a navigator respiratorytriggered diffusion-weighted imaging (NRT-DWI) sequence with regard to potential diagnostic information for detection of local tumor progression (LTP). Materials and Methods:One hundred forty-eight consecutive follow-up magnetic resonance (MR) examinations of 54 patients after hepatic RF ablation were reviewed. Apparent diffusion coefficient (ADC) values of ablation zones and liver parenchyma were assessed using a single-shot echoplanar imaging sequence with the NRT technique. ADC values of ablation zones and adjacent signal alterations identified in NRT-DWI were analyzed with regard to LTP. Conclusion:NRT-DWI is useful in the follow-up imaging after RF ablation. ADC-based evaluation of signal alterations adjacent to the ablation zone may contribute to the identification of LTP and nontumoral posttreatment tissue changes.

Added value of diffusion weighted MRI in evaluation of treatment response: post radiofrequency ablation for hepatocellular carcinoma

“…This is due to the fact that therapeutically induced nontumoral tissue changes (e.g., edema, inflammation, fibrosis, and necrosis) usually show low cellularity and therefore present with less signal in DWI (and high ADC, respectively), and can thereby be distinguished from tumoral tissue that presents with high signal in DWI (and low ADC value, respectively) (15). This is in accordance with Schraml et al (23) and Kim et al (24) who in their studies regarding the DW-MRI and ADC values for follow-up after RF ablation, found that ADC maps could be helpful for analyzing unclear hyperintense areas adjacent to the ablation zone Its margin presents bright signal on DWI (D) and dark in the corresponding ADC (E) images, and the ADC value of the entire area revealed a relatively high value (1.25 · 10 À3 mm 2 /s); however studying the peripheral margin alone revealed significant low ADC values (1.07 · 10 À3 mm 2 /s). In long term follow-up it showed evidence of LTP.…”

Therapy Monitoring of Magnetic Resonance–Guided Radiofrequency Ablation Using T1- and T2-Weighted Sequences at 1.5 T

“…It should be mentioned as another nonenhanced technique that potentially allows for therapy guidance and can be used complementary to the standard examination in clinical aftercare. 28 During ablation, the destruction of the cell structure leads to an increase in diffusivity in the ablation zone, which is surrounded by a diffusion restricted rim corresponding to the local hyperemic reaction. This phenomenon can be used to characterize the ablation zone during the therapy.…”

Perivascular parenchymal extension of the ablation zone following liver microwave ablation

“…Unexpected extension of the ablation zone along major intrahepatic vessels (figure 2) may lead to non-target ablation, hence a comprehensive understanding of factors influencing the ablation zone is vital for safe planning and delivery of treatment. MRI offers better soft tissue resolution than CT and techniques such as DWI have an increasing role in the follow-up of liver thermal ablation 7. The increased use of these techniques may help detect unexpected complications.…”