Unenhanced T1-Weighted MRI Useful for Assessment of Radio Frequency Ablation for Early-Stage Hepatocellular Carcinoma

The objective of a recent study was to determine if unenhanced T1-weighted spoiled gradient recalled echo (SPGR) images are useful in the early evaluation of treatment efficacy following RFA of HCC.

The study has concluded that unenhanced T1-weighted SPGR recalled echo images can be useful for evaluating early treatment efficacy following radio frequency ablation (RFA) of hepatocellular carcinoma (HCC).

Participants/Methodology
Twenty-three patients who had undergone percutaneous RFA of 28 HCC nodules were evaluated in this retrospective analysis. Baseline CT and MRI examinations were performed prior to the procedure. Multidetector CT protocol consisted of unenhanced, as well as dynamic enhanced, images. MRI examinations were performed with a 1.5-Tesla system.

Prior to RFA, unenhanced and dynamic contrast-enhanced MR images were obtained. Within two days following RFA, unenhanced images were obtained utilizing the T1-weighted SPGR recalled echo sequence. Three radiologists reviewed the images.

The ablation was considered complete when a hyperintense area completely surrounded the tumor on the unenhanced T1-weighted SPGR recalled echo sequence. The ablation was considered incomplete if any of the following criteria were met:

1. a central high signal intensity zone did not cover the entire target tumor although within a peripheral hypointense band;
2. the target tumor was outside the high signal intensity area as well as the peripheral hypointense band; or
3. there was no signal change identified at the treated area.

On follow-up contrast enhanced CT, the RFA was considered complete if there was a hypodense nonenhancing area covering the entire target tumor.

Results of the Study
Eighteen of 28 HCC nodules treated demonstrated a central high signal intensity zone on MRI and nonenhancing area on CT covering the entire tumor.

Nine of the remaining 10 treated lesions demonstrated a central high signal intensity area on MRI, which did not cover the entire tumor. Three of these nine lesions demonstrated local recurrence at six-month follow-up. The last lesion did not demonstrate a hyperintense zone and therefore was considered incompletely ablated.

MRI was able to detect incomplete ablation with 100% sensitivity and 75% specificity. On the other hand, contrast enhanced CT had a sensitivity of 25% and specificity of 100% for detecting incomplete ablation.

Conclusions
Unenhanced T1-weighted MRI was considered useful for early assessment of the efficacy of RFA for HCC.

Reviewer’s Comments
These results are useful in demonstrating the potential role of unenhanced MRI in the early evaluation of patients following RFA therapy. In this patient population, where repeat imaging is essential to assess treatment efficacy, as well as for continued surveillance, the strengths of MRI would include lack of ionizing radiation and no need for contrast administration, as shown in this study.

One of the study limitations was the spatial resolution of the MR images, in that evaluation for residual tumor may be difficult when the border of the ablated area is in close proximity to the border of the tumor.

Author: John C. Sabatino, MD, MSD

Reference
Khankan AA, Murakami T, et al. Hepatocellular Carcinoma Treated With Radio Frequency Ablation: An Early Evaluation With Magnetic Resonance Imaging.
J Magn Reson Imaging 2008; 27 (March): 546-551: