RF ablation appears to be a safe and promising procedure for the treatment of inoperable NSCLC and metastases.

Objective: To determine the ability of MR imaging to detect the pathological changes occurring in radiofrequency (RF) thermal lesions and to assess its accuracy in revealing the extent of tissue necrosis. Materials and Methods:Using an RF electrode, thermal lesions were created in the livers of 18 rabbits. The procedure involved three phases. In the acute phase, six animals were killed the day after performing thermal ablation with RF energy, and two on day 3. In the subacute and chronic phases, eight rabbits underwent percutaneous hepatic RF ablation. After performing MR imaging, two animals were sacrificed at 1, 2, 4, and 7 weeks after the procedure, and MRpathologic correlation was performed. Results:In the acute phase, the thermal ablation lesions appeared at gross examination as well-circumscribed, necrotic areas, representing early change in the coagulative necrosis seen at microscopic examination. They were hypointense on T2-weighted images, and hyperintense on T1-weighted images. Gadolinium-enhanced MR imaging showed that a thin hyperemic rim surrounded the central coagulative necrosis. In the subacute phase, ablated lesions also showed extensive coagulative necrosis and marked inflammation at microscopic examination. Beyond two weeks, the lesions showed gradual resorption of the necrotic area, with a peripheral fibrovascular rim. The size of lesions measured by MR imaging correlated well with the findings at gross pathologic examination. Conclusion:MR imaging effectively demonstrates the histopathological tissue change occurring after thermal ablation, and accurately determines the extent of the target area.mage-guided, percutaneous ablative therapies using thermal energy sources such as radiofrequency (RF) (1 3), microwave (4) and laser (5) are rapidly evolving as minimally invasive techniques for the treatment of primary and metastatic hepatic tumors. The potential benefits of these techniques over conventional surgical options include tumor ablation in nonsurgical candidates, reduced morbidity compared with surgery, and use of the procedure on an outpatient basis (6). Preliminary clinical reports have demonstrated that hepatic RF ablation produces effective local disease control in a significant proportion of patients with nonresectable liver tumors (7 9). However, according to even the most optimistic longterm report of percutaneous RF thermal therapy in colorectal metastases, local tumors recurred in 35% of cases (10). In addition, recent studies have shown that a significant proportion of patients with hepatocellular carcinomas greater than 3 5 cm in diameter experienced local recurrence after the use of current thermal ablation strategies (11 12).

The aim of this study was to determine the value of delayed-phase imaging (DPI) of gadobenate dimeglumine (Gd-BOPTA)-enhanced MR imaging for the evaluation of focal hepatic tumors compared with precontrast imaging and early dynamic phase imaging. The MR images were obtained in 48 patients with 98 focal hepatic tumors. Three-dimensional gradient-echo (GRE) imaging obtained before and 30, 60, and 1 h after administration of 0.1 mmol/kg of gadobenate dimeglumine. Each image set was analyzed qualitatively (lesion detection, conspicuity, delineation, and enhancement pattern on DPI) and quantitatively [signal-to-noise ratio (SNR), tumor-liver contrast-to-noise ratio (CNR)]. Improved lesion-to-liver contrast during the dynamic phase imaging was observed compared with precontrast images. The DPI showed a homogeneous enhancement of liver parenchyma and distinctive enhancement features of focal liver lesions: metastases (85%) showed a target shaped enhancement, and hepatocellular carcinomas (HCCs) showed an inhomogeneous (58%) or homogeneous enhancement (21%). The DPI showed better performance for the detection of metastases than other images by increasing lesion delineation ( p<0.05). The absolute CNR of metastasis measured from periphery of the tumors on DPI was greater than precontrast and arterial phase imaging ( p<0.05). The Gd-BOPTA during both dynamic and delayed phases provides valuable information for the characterization of focal liver lesions, and furthermore, Gd-BOPTA-enhanced DPI contributed to the improved detection of liver metastasis compared to precontrast and early dynamic imaging.

SPIO-enhanced MR imaging and multiphasic CT show similar diagnostic accuracy, sensitivity, and positive predictive value for the detection of HCC in patients with relatively mild hepatitis B-induced cirrhosis.

Gadobenate dimeglumine-enhanced MRI has a higher sensitivity for small hepatocellular carcinomas (