Hepatocellular carcinoma is the most common hepatic primary malignant tumors and is the third leading cause of cancer deaths worldwide. It claims the lives of around 500,000 people every year [9]. Functional MRI techniques as diffusion-weighted imaging detect early MR signal changes in tissues within several weeks after RFA, based on the degree of cell membrane integrity [10].
The purpose of this study was to evaluate the clinical utility of DWI compared to the dynamic contrast-enhanced MRI using a 3 T MRI unit in detecting remaining viable tissue in HCC following radiofrequency ablation.
The current study, like other studies [11,12,13], found overlap in the T1 WI and T2 WI signal intensity between the non-viable well-ablated bed and the viable lesion where the T2 WI hyperintensity was noted in 80% of the viable lesion and 36% of the non-viable ablated bed. Coagulation necrosis, hemorrhage, and the residual viable lesion are responsible for this considerable heterogeneity in the signal intensities which may complicate the assessment of HFL after RFA [11]. On the other hand, the hyperintense signal was the most detected T1 signal in the non-viable ablated bed and the hypointense signal was the most frequently noted signal in the viable lesion, yet 40% of both viable and non-viable ablated bed exhibited isointense signal. When evaluating the post-treatment response to RFA utilizing abbreviated MRI procedures, this overlap in signal intensity raises debate, and future research may emphasize the advantage of the non-contrast MRI sequence.
In this study, a DWI with satisfactory imaging quality and reasonable acquisition duration was achieved utilizing parallel imaging and the breath-hold methods on a 3-T scanner with b values of 0, 500, and 800 s/mm. Saleh et al. [13] utilized 3 T MRI equipment with similar b values, while Ebeed et al. [12] used a 1.5 T MRI unit with b values of 50, 400, and 800 s/mm2.
In the present study, 15 patients had lesion enhancement that was classified as a viable lesion following RFA, and Chernyak et al. [14] state that the presence of either arterial phase hyperenhancement or washout, independent of lesion size, is sufficient to define a treated lesion as viable.
In the current study, the sensitivity and specificity of DWI were 80% and 88%, respectively, and a similar result was also obtained in a study done by Ludwig et al. [15] who revealed that the sensitivity and specificity of DWI for diagnosing viable HCC after loco-regional therapy were 78.6% and 88.4%, respectively, yet Youssef et al. [16] revealed lower specificity after loco-regional treatment for HCC with a specificity value of 64.3%. The DWI falsely diagnosed three non-viable ablated beds as viable with diffusion restriction noted, which was related to the post-ablation tumoral necrosis and hemorrhage. Hypercellularity mixed with a fibrotic component in the peri-lesion parenchymal inflammatory granulation would limit water diffusion [17].
The mean ADC value of the viable lesions in our study was statistically significantly lower than that of the non-viable lesion (P < 0.001), and the best ADC cutoff value for discrimination between viable and non-viable ablated bed post-RFA was 1.01 × 103 mm2/s with sensitivity of 80% and specificity of 100%, and other studies which evaluated the ADC after RFA showed higher cutoff values with a range from 1.05 to 1.19 × 10−3 mm2/s [18,19,20]. These studies were conducted in a 1.5 T MRI unit, yet in the current study, a 3 T MRI unit was used which provide a higher signal-to-noise ratio and better DWI resolution.
The normalized ADC liver and normalized ADC spleen were used to differentiate between non-viable and viable lesions in the current study, and to our knowledge, no previous study had used these normalized ADC values. However, a study was done on the pancreas to differentiate between benign and malignant lesions, which revealed a statistically significant difference in the mean normalized ADC values between the benign and malignant lesions [21].
In our study, we reported that the normalized ADC liver cutoff value was 0.81 with a sensitivity of 73.3% and specificity of 96%, while the normalized ADC spleen cutoff value was 1.22 with a sensitivity of 80% and specificity of 92%. Although the sensitivity and specificity of ADC were greater than that of normalized value, both were comparable and further research may reveal the added usefulness of this new measurement.
The standardized reporting technique must be a dynamic process that is subject to clinical and radiological reassessment as well as data validation in order to be evaluated and developed further [22,23,24]. The DWI was regarded as one of the minor characteristics in the LI-RADS v2018 for categorization of the non-treated hepatic focal lesion, while the LI-RADS treatment response is based solely on the enhanced pattern of the treated HCC, and it does not include the DWI and ADC. Many previous trials, including this study, have shown the usefulness of DWI and ADC in detecting residual HCC following loco-regional treatment. The DWI acquired the benefit of eliminating contrast injection, which may be a significant issue in patients with renal impairment.
DWI has some benefits over DCE-MRI, including a shorter examination time. The procedure is also simple to repeat, allowing for close monitoring throughout the loco-regional treatment. DWI images also require less post-processing time than DCE-MRI images. Finally, in cases of tumor inhomogeneity, DWI is useful because it allows for a quick assessment of the entire tumor.
Limitation
In this study, some constraints were met. First, this prospective study had a small number of patients included; nevertheless, several other studies had a similar number of patients [1, 12, 13]. Second, technical issues with the DWI technique, such as respiratory and pulsation motion artifacts, particularly for peripherally placed lesions near the diaphragmatic copula, resulting in a low signal-to-noise ratio and a loss of spatial resolution. Partial volume averaging issues were also encountered, which resulted in calculation mistakes, and we attempted to overcome these challenges by using the lowest ROI feasible and taking numerous measurements.