Flash-echo gray-scale imaging in the subtraction mode for assessing perfusion of small hepatocellular carcinoma

Focal liver lesions: role of contrast-enhanced ultrasound

The introduction of microbubble contrast agents and the development of contrast-specific techniques have opened new possibilities in liver imaging. Initially, only intermittent imaging with Doppler detection was available. Second-generation contrast agents and low mechanical index real-time scanning techniques are decisive advances that enable convenient liver examinations with high sensitivity and specificity. Hepatic lesions usually show typical perfusion and enhancement patterns through the various contrast phases, which help their characterization. Several published studies and the daily clinical routine show that, as opposed to conventional ultrasound (US), contrast-enhanced US can substantially improve detection and differentiation of focal liver lesions. Today, contrast-enhanced US is the dynamic imaging modality of choice for differentiation of focal liver lesions. Contrast uptake patterns of the most relevant liver lesions, as well as important clinical indications are presented and discussed.

Small hepatic nodules (< or =2 cm) in cirrhosis patients: characterization with contrast-enhanced ultrasonography

AIM

We evaluated the efficacy of contrast-enhanced ultrasonography (CEUS) for the characterization of small hepatic nodules (< or =2 cm) in cirrhosis patients.

PATIENTS AND METHODS

Thirty cirrhosis patients with 30 hepatic nodules (1-2 cm) were enrolled in this study. Eighteen hepatic nodules were hepatocellular carcinomas (HCC) and 12 were benign lesions. CEUS was performed using microbubble contrast (Levovist). With surrounding hepatic parenchyma as a reference, two characteristics of hepatic nodules, including arterial phase enhancement (AE) and the absence of delayed phase enhancement (ADE), were evaluated as criteria for the diagnosis of HCC. A radiologist independently reviewed the dynamic computed tomographies (CT) of 26 hepatic nodules.

RESULTS

CEUS showed AE in 15 nodules (13 HCC and two benign) and ADE in 17 lesions (14 HCC and three benign). For HCC, the coincidental AE of both CEUS and dynamic CT was 40%. Using both AE and ADE for HCC diagnosis, the sensitivity, specificity, accuracy, positive predictive value and negative predictive values were 55.6%, 91.7%, 70%, 90.9% and 57.9%, respectively. When using either AE or ADE for HCC diagnosis, the same parameters were 94.4%, 66.7%, 83.3%, 81% and 88.9%, respectively. One benign hepatic nodule with both AE and ADE was diagnosed as HCC 29 months after the CEUS study.

CONCLUSIONS

A combination of characteristics of AE and ADE as determined by CEUS was highly specific for small HCCs in cirrhosis patients. Concurrent delayed phase imaging is useful in the diagnosis of small hypovascular HCCs.

Flash-echo contrast sonography in the evaluation of response of small hepatocellular carcinoma to percutaneous ablation

PURPOSE

To evaluate the use of flash-echo contrast sonography (FECS) in subtraction mode in assessing small hepatocellular carcinoma (HCC) after percutaneous local ablation therapy.

METHODS

Between March 2000 and February 2002, we prospectively assessed small HCCs after percutaneous local ablation therapy using FECS in subtraction mode. Thirty-three patients (22 men, 11 women) with 35 tumors ranging in size from 1.1 to 3.0 cm (mean +/- SD, 2.0 +/- 0.5) were enrolled. Twenty-one tumors received percutaneous ethanol injection only, 13 tumors received percutaneous microwave ablation therapy only, and the remaining tumor received both treatments. CT, hepatic angiography, and follow-up were used as gold standards in analyzing the accuracy of FECS in detecting residual tumors.

RESULTS

The agreements between FECS and CT, FECS and hepatic angiography, and all 3 imaging modalities were 80% (28/35), 85.7% (30/35), and 77.1% (27/35), respectively. Twenty-one patients with 23 completely ablated tumors were followed up for 5 to 39 months (mean +/- SD, 20.2 +/- 11.2). Recurrent disease was detected in 11 (52.4%) patients; local tumor recurrence occurred in 4 (17.4%) patients. The sensitivity, specificity, accuracy, and positive and negative predictive value of FECS in detecting viable tumors were 53.8% (7/13), 90.9% (20/22), 77.1% (27/35), 77.8% (7/9), and 76.9% (20/26), respectively.

CONCLUSIONS

FECS in subtraction mode shows good agreement with hepatic angiography and CT in the assessment of small HCC after percutaneous local ablation therapy. The sensitivity of FECS in detecting residual tumors is suboptimal.

Real-time harmonic contrast material-specific US of focal liver lesions

Recent advances in contrast material-enhanced ultrasonography (US) mainly include (a) development of low-acoustic-pressure (low-mechanical-index) harmonic software, capable of obtaining real-time images without disrupting contrast material microbubbles, and (b) commercialization of new contrast media ("second-generation" contrast media), capable of producing intense echo signals in this low-mechanical-index setting. With use of low-mechanical-index continuous-mode contrast-enhanced US, the circulatory kinetic models of various focal liver lesions can be displayed dynamically. Hepatic lesions usually have typical perfusion characteristics and enhancement patterns through the various phases of parenchymal enhancement, which helps characterize lesions and, in most cases, allows definitive diagnosis, even among lesions that exhibit very similar baseline appearances. Because of the use of harmonic technologies at low emission frequencies, there is some loss of spatial resolution and overall image quality, typically resulting in a grainy appearance. In addition, lesion depth affects the detectability of vascularity to some degree in that poor signal arises from deep-seated lesions. Moreover, liver attenuation (eg, in patients with steatosis or chronic liver disease) further reduces the sensitivity of contrast-enhanced US. Nevertheless, with its unique capacity to provide images in real time, low-mechanical-index contrast-enhanced US is the dynamic imaging modality of choice in the differential diagnosis of focal liver lesions.