Contrast media in liver sonography: correlation with enhanced dynamic magnetic resonance imaging

Detection of intratumoral vascularity in small hepatocellular carcinoma by coded phase inversion harmonics

OBJECTIVE

To investigate the value of contrast-enhanced coded phase inversion harmonic imaging (PIHI) in the depiction of intratumoral vascularity in small hepatocellular carcinoma (HCC).

METHODS

Eighty-five patients with 106 HCCs < or =3 cm in diameter were evaluated with coded harmonic angio (CHA), a coded PIHI, with use of an intravenous contrast medium, Levovist. Intratumoral vessels were detected in the early arterial phase, and tumor parenchymal stain was demonstrated in the late vascular phase. The detectability of intratumoral vascularity on contrast-enhanced CHA was compared with that on dynamic computed tomography (CT) and digital subtraction angiography (DSA).

RESULTS

With a combination of both vessel images and parenchymal flow images demonstrated by contrast-enhanced CHA, 98 of 106 small HCCs were evaluated as being hypervascular or isovascular. Using the results on dynamic CT as a gold standard, the sensitivity, specificity and accuracy were 95.1, 100 and 95.3%, respectively. The detection rate of intratumoral vascularity by contrast-enhanced CHA was 92.5% (98/ 106), compared with 97.2% (103/106) on dynamic CT (p = 0.14) and 88.9% (40/45) on DSA (p = 0.53).

CONCLUSIONS

Contrast-enhanced coded PIHI is a sensitive tool for depicting intratumoral vascularity of small HCC.

A review of nonconventional ultrasound techniques and contrast-enhanced ultrasonography of noncardiac canine disorders

Modern ultrasound contrast media are gas-containing stabilized microbubbles that remain intact in the circulating blood for several minutes after intravenous injection and increase the intensity of the backscattered ultrasound. When the microbubbles disappear from the blood, they can be detected in the parenchyma of the liver and the spleen for about 30 more minutes (late liver- and spleen-specific phase). The insonated microbubbles produce second harmonic ultrasound frequencies, whose detection requires nonconventional ultrasound modalities such as pulsed inversion imaging. Nonconventional ultrasound techniques can also be used without microbubbles because second harmonics can be generated by ultrasound in tissues as well. The physical principles and advantages of nonconventional ultrasound techniques are described. The circulating microbubbles can be used not only to enhance weak Doppler signals, but also to perform dynamic contrast studies. Contrast-enhanced dynamic ultrasound studies--similar to contrast-enhanced CT and MRI examinations--have been used in humans to characterize lesions noninvasively (i.e., without biopsies) found during conventional ultrasound examinations. To map the distribution of contrast medium in a nodule or in an organ, specific scanning techniques such as stimulated acoustic emission have been developed. Stimulated acoustic emission occurs when high acoustic pressure ultrasonic waves disrupt the stationary or slowly moving microbubbles. This results in the release of a large amount of harmonic ultrasound frequencies. When the stimulated acoustic emission technique is used for dynamic studies, scanning must be interrupted several times to allow the microvasculature of the lesion to refill with microbubbles (interval delay imaging). The contrast patterns of malignant and benign hepatic nodules in humans have been the most intensively studied. Another type of dynamic study in humans measures the transit time of the contrast medium; that is, how fast the peripherally injected microbubbles reach the hepatic veins. Hepatic cirrhosis can be differentiated from other diffuse parenchymal liver diseases by a shorter transit time. Introducing nonconventional ultrasound techniques and ultrasound contrast media in veterinary diagnostic imaging may have potential value; however, intensive research should be carried out before ultrasound contrast agents can routinely be used in clinical practice.

Assessment of arterial tumor vascularity in small hepatocellular carcinoma. Comparison between color doppler ultrasonography and radiographic imagings with contrast medium: dynamic CT, angiography, and CT hepatic arteriography

Hepatocellular carcinoma (HCC) is characterized by tumor vascularization from the hepatic artery. The objective of our work was to compare color Doppler ultrasonography (CDU), including power Doppler ultrasonography (PDU) with radiographic imagings with contrast medium in regard to the detection of the arterial tumor vascularity of small hepatocellular carcinomas (HCC). We examined 42 small HCC lesions 2 cm or less in diameter in 37 patients for arterial tumor vascularity by conventional CDU, PDU, dynamic computed tomography (dCT), digital subtraction angiography (DSA), and CT hepatic arteriography (CTA). Color images were detected in 25 (59.5%) and 28 (66.7%) of the 42 lesions with conventional CDU and PDU, respectively, and tumor vascularity was detected in 26 (61.9%) by dCT, 23 (54.8%) by DSA, and 29 (69.0%) by CTA. Tumor vascularity could be detected in 51.9% by PDU and CTA, more than by conventional CDU, dCT, and DSA (44.4, 44.4, and 33.3%, respectively) in well-differentiated HCC, whereas the detection rates by these techniques were almost equal (86.7% by CDU, 93.3% by PDU, dCT, and DSA, 100% by CTA, respectively) in moderately and poorly differentiated HCC. PDU is superior to CDU, dCT and DSA and equal to CTA for the detection of tumor vascularity in small HCC, particularly in well-differentiated HCC.