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ORIGINAL ARTICLE
Year : 2021  |  Volume : 34  |  Issue : 1  |  Page : 264-268

Diffusion-weighted MRI after radiofrequency ablation for hepatocellular carcinoma


1 Department of Radiodiagnosis, Faculty of Medicine, National Liver Institute, Menoufia University, Egypt
2 Department of Radiodiagnosis, National Liver Institute, Menoufia University, Egypt
3 Diagnostic and Interventional Radiology Department, National Liver Institute, Menofia University, Egypt

Date of Submission09-Sep-2019
Date of Acceptance14-Sep-2019
Date of Web Publication27-Mar-2021

Correspondence Address:
Heba A El-Balshy
Berket El-Sabae, Menoufia
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_236_19

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  Abstract 


Objective
This paper aims to evaluate the role of diffusion-weighted (DW) MRI in patients with hepatocellular carcinoma (HCC) treated by radiofrequency ablation (RFA).
Background
HCC is the most common primary cancer of the liver. RFA has become a widely used treatment for HCC, with some studies reporting significant long-term survival results. DW MRI had been investigated for assessment of treatment response to RFA.
Patients and methods
From October 2016 to May 2017, 30 patients with 30 lesions diagnosed as HCC had undergone DW MRI after RFA. The results were compared with the abdominal triphasic spiral computed tomography, which was used as the reference standard.
Results
The study included 30 patients with 30 HCC lesions. After RFA, there were 12 (40%) lesions with residual HCC activity and 18 (60%) adequately managed lesions. The mean apparent diffusion coefficient value in residual lesions was significantly lower than the mean apparent diffusion coefficient value in ablated lesions (P < 0.001). DW MRI had a sensitivity of 92%, a specificity of 100%, and an accuracy of 97%.
Conclusion
DW MRI was complementary for abdominal triphasic spiral computed tomography in the assessment of tumor response after RFA. Diffusion-weighted MRI is considered to be capable of evaluating the response to therapy of HCC.

Keywords: diffusion, dynamic, hepatocellular carcinoma, magnetic resonance, radiofrequency


How to cite this article:
El-Kholy MR, Al Warraky MS, Hassanien SA, El-Balshy HA. Diffusion-weighted MRI after radiofrequency ablation for hepatocellular carcinoma. Menoufia Med J 2021;34:264-8

How to cite this URL:
El-Kholy MR, Al Warraky MS, Hassanien SA, El-Balshy HA. Diffusion-weighted MRI after radiofrequency ablation for hepatocellular carcinoma. Menoufia Med J [serial online] 2021 [cited 2021 Dec 4];34:264-8. Available from: http://www.mmj.eg.net/text.asp?2021/34/1/264/312025




  Introduction Top


Hepatocellular carcinoma (HCC) is the most common primary hepatic malignancy in adults. It is the sixth most common cancer worldwide and the third most common cause of cancer death [1].

Radiofrequency ablation (RFA) is accepted as an established local treatment of malignant hepatic tumors improving the survival rates of patients with unresectable liver metastases or being curative for patients with HCC [2].

The rationale for the use of percutaneous ablation techniques is based on some relevant advantages: it destroys the tumor, avoiding the loss or the damage of nontumoral liver parenchyma, as occurs with resection and arterial chemoembolization; there is a low risk of complications associated with the procedure; it is possible to easily repeat the treatment in case of recurrent lesions; and finally, it is easily available and relatively inexpensive [3].

Although dynamic contrast-enhanced examinations have become a routine component of abdominal imaging, the high cost/benefit ratio and risk of contrast media side effects remain an issue [4].

Diffusion-weighted MRI (DWI) has then been introduced into abdominal imaging, representing a supplementary tool for detecting and characterizing hepatic lesions [5].

DWI is now increasingly being used to evaluate tumors' response to various treatments. It provides a unique insight into tissue cellularity, tissue organization, integrity of cells and membranes, as well as the tortuosity of the extracellular space, which can be helpful for detecting malignant diseases, and for distinguishing tumor tissues from nontumor tissues [6].

The diffusion-weighted (DW) technique should be used as an additional sequence to supplement conventional MRI protocol studies for proper characterization of focal liver lesions [7].

This study aimed to assess the value of DWI and analysis of the apparent diffusion coefficient (ADC) value in the evaluation of treatment response after RFA in HCC.


  Patients and methods Top


This prospective study was carried out on 30 patients with HCC who presented to the National Liver Institute, Menoufia University, from October 2016 to May 2017. The primary diagnosis of cases was made on the basis of the typical enhancement pattern on triphasic computed tomography (CT) scan. The decision to perform RFA was made by the HCC committee at the National Liver Institute. The results of DW MRI were compared with the triphasic CT results, which are considered the standard reference. The triphasic CT was performed using the SOMATOM Definition Flash CT Scanner (20-slice) (Siemens Healthineers Global, Erlangen, Germany).

The study was approved by the Ethical Committee of Menoufia Faculty of Medicine and an informed consent was obtained from each patient included in the study.

The procedure was carried out using a percutaneous approach under real-time ultrasound guidance (Philips iu 22, Philips Ultrasound Bothell, WA, USA). RFA is performed by RITA model x1500 and RF 3000. Multiple overlapping ablations will be applied where needed to achieve an adequate ablative margin of at least 0.5 cm.

MRI was performed using a 1.5-T MRI scanner, Optima MR450w (GE Healthcare, Chicago, Illinois, USA), equipped with a phased-array surface coil.

An MRI follow-up scan was performed 2 weeks after RFA. Both included in-phase/out-phase sequences, T2-weighted imaging (WI), and DWI. The parameters of diffusion sequence were as follows: repetition time/echo time: 1.2 s/61 ms; matrix: 124 × 124; field of view: 369 mm; section thickness: 10 mm; flip angle: 90°; and number of averages: 4.

Analysis was carried out through Advantage Workstation 4.6 (GE Healthcare).

The images were analyzed for the size and the enhancement pattern of the treated lesions confirmed on subtraction images, followed by calculation of the maximum transverse dimension of the enhancing tumor tissue after RFA.

Also, analysis of the signal intensities in DWI and the ADC map was carried out.

DW MRI in this study was obtained by applying four different b values (0, 50, 600, and 1000s/mm2). The images of the four b values were compared and the residual HCC activity in diffusion series was identified by sustained hyperintensity with increasing b values combined with hypointesnsity in the generated ADC map.

The mean ADC of the focal lesion was calculated by positioning multiple regions of interest over the tumor in consecutive image sections. The regions of interests may be placed directly into the ADC map or copied into the map from those drawn on DW images.

Data were fed into the computer using IBM (SPSS Inc., Chicago, Illinois, USA) software package, version 20.0. The results were expressed by applying ranges, mean ± SD, Wilcoxon sign test, Kruskal–Wallis test, and P (probability) values.


  Results Top


Abdominal triphasic spiral CT, as the reference standard test for the 30 patients, showed post-treatment adequately managed lesions in 18 (60%) patients and residual lesions (not adequately manages lesions) in 12 (40%) patients [Table 1].
Table 1: Computed tomography finding of the hepatocellular carcinoma lesions of the included 30 patients in terms of the size of the managed lesions and enhancement component diameter after radiofrequency ablation in 12 residual lesions and 18 adequately managed lesions

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On comparing the DWI findings with abdomial spiral triphasic CT findings after RFA treatment, there were 11 (91.7%) true residual lesions and 18 (100%) true adequately managed lesions [Table 2].
Table 2: Diagnostic accuracy measures of diffusion-weighted MRI in 18 adequately managed lesions and 12 residual lesions after radiofrequency ablation

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According to DW MRI, the mean ADC value in residual lesions was significantly lower than the mean ADC value in ablated lesions (P < 0.001). The mean ADC value in patients with residual lesions was 0.98 ± 0.09 × 103 mm2/s, ranging from 0.82 to 1.11, whereas the mean ADC value in patients with adequately managed lesions was 1.33 ± 0.16 × 103 mm2/s, ranging from 0.95 × 103 to 1.61 × 103 mm2/s [Table 3].
Table 3: Diagnostic accuracy measures of diffusion-weighted MRI in 18 adequately managed lesions and 12 residual lesions after radiofrequency ablation

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By evaluation of the managed lesions by DWI using the size of the restricted component and the ADC value, 18 Residual lesions (confirmed by post RFA spiral CT) showed cut-off point of the restricted component less than 0.5 cm and 16 of them with ADC mean value greater than 1.15 × 10−3 mm2/s and 12 adequate managed lesions (confirmed by post-RFA spiral CT) all of them showed mean ADC value less than or equal to 1.15 × 10−3 mm2/s while 11 of them showed cut-off point of restricted component size up to 0.5 cm [Table 4].
Table 4: Comparison between residual lesions and adequately managed lesions after radiofrequency ablation in hepatocellular carcinoma patients

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Imaging after radiofrequency ablation

The 2-week triphasic CT examination after RFA showed no enhancement at the arterial phase neither washout at the delayed phase, denoting no residual HCC. The 2-week MRI study after RFA showed adequate management to the target lesion, showing no enhancement in the arterial phase of DCE MRI study. Also, there was sustained hyperintensity in the DWI as well as the corresponding ADC map [Figure 1].
Figure 1: (a) Noncontrast CT study of the liver post radiofrequency ablation. (b) Arterial phase of tirphasic CT: arterial enhancement of the managed right hepatic lobe focal lesion at segment VII. (c) and (d) portovenous and delayed phases of tirphasic CT washout at the previous hepatic focal lesion denoting residual tumoral tissue. (e) and (f) Postradiofrequency ablation MRI axial in-phases and out-phases showing predominantly low-signal intensity of the right hepatic lobe HCC. (g) MRI axial T2 FS PROP showing low-signal intensity of the lesion. (h) and (i) Diffusion-weighted imaging and the corresponding ADC showing facilitated diffusion of the managed lesion. (j) and (k) Colored map ADC with an average ADC value of 1.14 × 10-3. ADC, apparent diffusion coefficient; CT, computed tomography; HCC, hepatocellular carcinoma.

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  Discussion Top


MRI provides detailed anatomical, functional, and molecular characterizations for the assessed tissue [8].

The current study showed DWI sensitivity of 92% and specificity of 100% in assessing viable tumor after RFA. The high sensitivity and specificity was not in agreement with the results of DWI performed after transarterial chemoembolization as reported by Kamel et al. [9] and Chen et al. [10], who showed high senstivity and low specificity of DWI.

Our study results showed that ablation zones can be differentiated visually from the surroundying parenchyma of the liver in the DW images and also by means of ADC maps in all patients and this is in agreement with the results of Hamid et al. [11]. However, analysis of ablation zones measured at different time points after RF ablation indicated no significant changes in the ADC values, which is is in agreement with Lu et al. [12], who asessed liver tumor post-treatment response in the ablation zones afterRFA.

By measuring the ADC of the hepatic parenchyma (background) within segment VI if possible, otherwise within segment V, the mean ADC value in our results was 1.11 ± 0.16 × 10−3 mm2/s. Mostafa [13] found that the mean ADC value of liver parenchyma was 1.18 × 10−3 mm2/s, whereas Scharml et al. [14] found that the mean ADC value of the liver parenchyma was 1.06 ± 0.21 × 10−3 mm2/s.

In our study, the well-ablated lesions showed a hypointense signal in DWI and the mean ADC value was 1.33 ± 0.16 × 10-3 mm2/s, whereas the residual lesions showed a hyperintense signal in DWI, with a lower mean ADC value of 0.98 ± 0.09 × 10-3 mm2/s, with a statistically significant difference between the residual tumor and the well-ablated lesions. This is not in agreement with the results of Scharml et al. [14], who found that the mean ADC value of the ablated lesions of 1.22 ± 0.30 × 10-3 mm2/s did not show a significant difference from the mean ADC value of the residual lesions of 1.19 ± 0.30 × 10-3 mm2/s. This is also not in agreement with the results of Hamid et al. [11], who obtained a higher mean ADC value of the ablated lesion of 1.4 × 10-3 mm2/s and a lower mean ADC value in the residual lesion of 0.8 × 10-3 mm2/s.

However, this is in agreement with Minami et al. [15] and Koda et al. [16], who showed lower mean ADC values of the residual lesions than the well-ablated lesions, which showed higher mean ADC values.

In our study, false-positive cases showed hyperintense areas in high b value DW images and did not correspond to residual lesions. This is in agreement with the Park et al. [17] study, in which it was observed that tumor necrosis intermingled with the fibrotic component and also inflammatory granulation tissues that mimic viable tumor.

In our study the b values used were 0, 50, 600, and 1000 to avoid intravoxel perfusion resulting from low b values less than 50 s/mm2 and imaging degradation resulting from high P values greater than 1000 s/mm2. In the study of Chen et al. [10], the P values used were 0 and 500 s/mm2, in the study of Sahin et al. [18], the P values used were 0, 50, 400, and 800 s/mm2, and in the study of Hamid et al. [11], P values used were 0, 300, and 600 s/mm2.

Moreover, it has been shown in our study that the level of ADC may help us to recommend a cut-off value of less than or equal to 1.15 × 10−3 mm2/s. Values below this level indicate viability of the malignancy. After RFA, the ADC values increase above this limit. Gourtsoyianni et al. [19] recommended a cut-off value of 1.47 × 10−3 mm2/s.

In our study, it was found that ADC maps are a helpful tool in the analysis of the hyperintense areas close to the ablation zone and they can differentiate between tumoral tissue and the peripheral postablation changes. The peripheral signal alteration of the ablation zone showed lower ADC values in patients with residual lesions. This is in agreement with Scharml et al. [14] and Kim et al. [20] in terms of the DWI and ADC values after RF ablation, in which lower mean ADC values were found in patients with residual lesions.

As a part of self-criticism of our study, the present study had some limitations. The most important limitation is that despite using the breath-hold examination technique, which provided a short acquisition time, some patients had to be excluded because of motion artifacts.


  Conclusion Top


DWI is a promising tool in the evaluation of the post-RFA HCC and can provide information about molecular tissue characteristics; thus, it have an additional value in the evaluation and follow-up of local ablative therapy in patients with HCC.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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