Development of Microbubble Contrast Agents for High Frequency Ultrasound Microscopy

PURPOSE: To develop optimal microbubble contrast agents (MBCAs) for performing ultrasound microscopy when examining small animals. MATERIALS AND METHODS: We prepared three types of MBCAs. First, a mixture of three parts of 40% dextran and one part of 5% human serum albumin were sonicated with perfluorocarbon (PFC) (MB1-D40A5P). Second, three parts of 40% dextran and one part of 1% human serum albumin were sonicated with PFC (MB2-D40A1P). Third, all parts of 1% bovine serum albumin were sonicated with PFC (MB3-A1P). We measured the microbubbles' sizes and concentrations with using image analysis software. The acoustic properties of the microbubbles were assessed both in vitro and in vivo. RESULTS: The majority of the MB1-D40A5Ps had a diameter of 2-5 um, the mean diameter of the MB2-D40A1Ps was 2.5 um, and the mean diameter of the MB3-A1Ps was less than 2.0 um. Among the microbubbles, the MB1-D40A5Ps and MB2-D40A1Ps showed increased echogenicity in the abdominal vessels, but the duration of their contrast effect was less than 30 sec. On the contrary, the MB3-A1Ps exhibited strong enhancement in the vessels and their duration was greater than 120 sec. CONCLUSION: A microbubble contrast agent consisting of all parts of 1% serum albumin sonicated with PFC is an effective contrast agent for ultrasound microscopy.

Radiofrequency Ablation of Liver Cancer: Early Evaluation of Therapeutic Response with Contrast-Enhanced Ultrasonography

The early assessment of the therapeutic response after percutaneous radiofrequency (RF) ablation is important, in order to correctly decide whether further treatment is necessary. The residual unablated tumor is usually depicted on contrast-enhanced multiphase helical computed tomography (CT) as a focal enhancing structure during the arterial and portal venous phases. Contrast-enhanced color Doppler and power Doppler ultrasonography (US) have also been used to detect residual tumors. Contrast-enhanced gray-scale US, using a harmonic technology which has recently been introduced, allows for the detection of residual tumors after ablation, without any of the blooming or motion artifacts usually seen on contrast-enhanced color or power Doppler US. Based on our experience and reports in the literature, we consider that contrast-enhanced gray-scale harmonic US constitutes a reliable alternative to contrast-enhanced multiphase CT for the early evaluation of the therapeutic response to RF ablation for liver cancer. This technique was also useful in targeting any residual unablated tumors encountered during additional ablation.

Focal Hepatic Lesions: Evaluation with Contrast-Enhanced Gray-Scale Harmonic US

OBJECTIVE: To determine the findings of various focal hepatic lesions at contrast-enhanced gray-scale ultrasound (US) using a coded harmonic angio (CHA) technique and emphasizing lesion characterization. MATERIALS AND METHODS: The study involved 95 patients with 105 focal hepatic lesions, namely 51 hepatocellular carcinomas (HCCs), 22 metastases, 22 hemangiomas, four cases of focal nodular hyperplasia (FNH), and six nontumorous nodules. After the injection of a microbubble contrast agent (SH U 508A), gray-scale harmonic US studies using a CHA technique were performed with a combination of continuous scanning to assess the intratumoral vasculature (vascular imaging) and interval-delay scanning to determine the sequential enhancement pattern (acoustic emission imaging). Each imaging pattern was categorized and analyzed. RESULTS: At vascular imaging, 69% of HCCs (35/51) showed irregular branching vessels, while in 91% of metastases (20/22) a peripherally stippled pattern was observed. Intratumoral vessels were absent in 95% of hemangiomas (21/22) and all nontumorous lesions (6/6), while in 75% of FNHs (3/4) a spoke-wheel pattern was evident. At acoustic emission imaging, 71% of HCCs (36/51) showed heterogeneous enhancement and 86% (19/22) of metastases showed rim- or flame-like peripheral enhancement during the early phase, with washout occurring in all HCCs and metastases (100%, 73/73) during the late phase. In hemangiomas, enhancement was either peripheral and nodular (19/22, 86%) or persistent and homogeneous (3/22, 14%), and 75% of FNHs (3/4) became isoechoic during the late phase. CONCLUSION: At contrast-enhanced gray-scale US using a CHA technique, a period of continuous scanning depicted the intratumoral vasculature, and interval-delay scanning demonstrated the sequential enhancement pattern. The characteristic findings of various focal hepatic lesions were thus determined.

Detection of Hepatic VX2 Tumors in Rabbits: Comparison of Conventional US and Phase-Inversion Harmonic US During the Liver-Specific Late Phase of Contrast Enhancement

OBJECTIVE: To compare phase-inversion sonography during the liver-specific phase of contrast enhancement using a microbubble contrast agent with conventional B-mode sonography for the detection of VX2 liver tumors. MATERIALS AND METHODS: Twenty-three rabbits, 18 of which had VX2 liver tumor implants, received a bolus injection of 0.6 g of Levovist (200 mg/ml). During the liver-specific phase of this agent, they were evaluated using both conventional sonography and contrast-enhanced phase-inversion harmonic imaging (CE-PIHI). Following sacrifice of the animals, pathologic analysis was performed and the reference standard thus obtained. The conspicuity, size and number of the tumors before and after contrast administration, as determined by a sonographer, were compared between the two modes and with the pathologic findings. RESULTS: CE-PIHI demonstrated marked hepatic parenchymal enhancement in all rabbits. For VX2 tumors detected at both conventional US and CE- PIHI, conspicuity was improved by contrast-enhanced PIHI. On examination of gross specimens, 52 VX2 tumors were identified. Conventional US correctly detected 18 of the 52 (34.6%), while PIHI detected 35 (67.3%) (p < 0.05). In particular, conventional US detected only three (8.3%) of the 36 tumors less than 10 mm in diameter, but CE-PIHI detected 19 such tumors (52.8%) (p < 0.05). CONCLUSION: Compared to conventional sonography, PIHI performed during the liver-specific phase after intravenous injection of Levovist is markedly better at detecting VX2 liver tumors.

The Study of Renal Perfusion Image in Rabbit by Harmonic Ultrasound with Microbble Contrast Agent in Comparison with 99mTc-DTPA: Focusing on US Scan Technique and Concentration of Contrast Agent

PURPOSE: To compare the results of harmonic ultrasound (US) renal perfusion imaging using 99mTc-DTPA as contrast agent with those obtained when a microbubble contrast medium was used. MATERIALS AND METHODS: Twenty rabbits underwent harmonic US renal perfusion imaging using 99mTc-DTPA as contrast agent, and the imaging procedure was then repeated using a microbubble contrast medium. Three different concentrations of contrast media (200, 300 and 400 mg/ml) and two different scanning techniques (intermittent and continuous) were used, and the images obtained were assessed using six different methods. By means of a computer program, the images were converted to a renal perfusion curve and Tpeak values were calculated. Images obtained after use of the two different contrast media were compared. RESULTS: Tpeak at renal perfusion imaging using 99mTc-DTPA was 6.3+/-0.9 sec, and where microbubble contrast agent was used, the findings were was as follows: 13.8+/-1.6 sec (method 1), 6.5+/-1.1 sec (method 2), 14.8+/-1.7 sec (method 3), 6.6+/-1.0 sec (method 4), 15.2+/-2.0 sec (method 5), 6.4+/-0.7 sec (method 6). Method 6 had the highest correlation coefficients. CONCLUSION: In conclusion, the harmonic ultrasound renal perfusion images acquired using 99mTc-DTPA were similar to those obtained using microbubble contrast agent. Continuous scanning techniques showed correlation.

Focal Hepatic Lesions: Contrast-Enhancement Patterns at Pulse-Inversion Harmonic US using a Microbubble Contrast Agent

OBJECTIVE: To analyze the contrast-enhancement patterns obtained at pulseinversion harmonic imaging (PIHI) of focal hepatic lesions, and to thus determine tumor vascularity and the acoustic emission effect. MATERIALS AND METHODS: We reviewed pulse-inversion images in 90 consecutive patients with focal hepatic lesions, namely hepatocellular carcinoma (HCC) (n=43), metastases (n=30), and hemangioma (n=17). Vascular and delayed phase images were obtained immediately and five minutes following the injection of a microbubble contrast agent. Tumoral vascularity at vascular phase imaging and the acoustic emission effect at delayed phase imaging were each classified as one of four patterns. RESULTS: Vascular phase images depicted internal vessels in 93% of HCCs, marginal vessels in 83% of metastases, and peripheral nodular enhancement in 71% of hemangiomas. Delayed phase images showed inhomogeneous enhancement in 86% of HCCs; hypoechoic, decreased enhancement in 93% of metastases; and hypoechoic and reversed echogenicity in 65% of hemangiomas. Vascular and delayed phase enhancement patterns were associated with a specificity of 91% or greater, and 92% or greater, respectively, and with positive predictive values of 71% or greater, and 85% or greater, respectively. CONCLUSION: Contrast-enhancement patterns depicting tumoral vascularity and the acoustic emission effect at PIHI can help differentiate focal hepatic lesions.

The Diagnostic Value of Contrast Enhanced Power Doppler US on Small Breast Lesions

PURPOSE: To evaluate the usefulness of contrast-enhanced power Doppler ultrasonography (PDUS) in differentiating small benign from small malignant breast lesions. MATERIALS AND METHODS: Thirty-one solid breast lesions (<2 cm in size; 17 benign and 14 malignant) prospectively underwent US and PDUS before and after the injection of contrast agent (SH U 508A). Morphologic analysis involved independent assessment of the findings of US and the patterns of Doppler signals before and after contrast enhancement at PDUS, and sensitivity and specificity were thus evaluated. The diagnostic accuracy of US accompanied by PDUS was also determined before and after contrast enhancement. Hemodynamic analysis involved measurement of the time lapse between contrast injection at PDUS and observed change in Doppler signals. For this, a sonic VIOR computer-assisted program was used and the results were correlated with the pathologic findings. RESULTS: The sensitivities of US before and after contrast enhanced PDUS were 100%, 35.7%, and 57%, with specificities of 47%, 88.2% and 76%, respectively. The diagnostic accuracy of US was 35% with noncontrast PDUS, and 77% before and after contrast enhanced PDUS. The recorded time lapse between contrast injection at PDUS and observed change in Doppler signals did not correlate closely with the pathologic findings. CONCLUSION: In that it improved visualization of the morphology of vascular Doppler signals, microbubble contrast-enhanced PDUS complemented US and PDUS in differentiating between small benign and small malignant breast lesions.

Gray-Scale Stimulated Acoustic Emission: Differential Diagnosis between Hepatocellular Carcinoma and Metastastic Adenocarcinoma

PURPOSE: To assess the value of gray-scale stimulated acoustic emission in differential diagnosis between hepatocellular carcinoma and metastatic adenocarcinoma. MATERIALS AND METHODS: Twenty-four cases of epatocellular carcinoma (HCC) in 23 patients and 26 cases of metastatic adenocarcinoma in 14 patients were prospectively examined using the pulse-inversion harmonic technique after intravenous SH U 508A administration. Gray-scale stimulated acoustic emission (SAE) was measured 5 mins after bolus injection of a contrast agent (4g, 400 mg/ml). The presence or absence of SAE signals at internal and marginal areas of the tumor and the appearance (smooth or irregular) of its border were compared. In addition, the SAE index [SAE (parenchyma) - SAE (tumor)/ SAE (parenchyma)] was histographically determined using a computerized program (PiView TM ; Mediface, Seoul, Korea). The statistics were analysed using student'st test. RESULT: Of the 24 HCC cases, 20 (83%) showed internal SAE signals, while 23 (96%) marginal signals were emitted. Of the 26 cases of metastatic adenocarcinoma, one (4%) showed internal SAE signals, while in five (19%), these signals were marginal. The tumoral border was irregular in 19 HCC lesions (79%) and smooth in 23 metastatic lesions (88%). For HCC and metastatic tumors, the mean SAE index was 0.38 +/-0.15 and 0.60 +/- 0.08, respectively (p < 0.001). CONCLUSION: Gray-scale stimulated acoustic emission can be a useful tool in differential diagnosis between heatocellular carcinoma and metastatic adenocarcinoma.

Vesicoureteral Reflux in Children: Comparison of Contrast - Enhanced Voiding Ultrasonography with Radiographic Voiding Cystourethrography: Preliminary Report

PURPOSE: To compare the usefulness of contrast-enhanced voiding ultrasonography(US) with that of radiographic voiding cystourethrography(VCUG) for the diagnosis of vesicoureteral reflux(VUR) in children. MATERIALS AND METHODS: Ninety-five kidney-ureter units of 47 patients referred for investigation of VUR underwent contrast-enhanced voiding US followed by radiographic VCUG. After baseline US examination of the urinary tract, residual urine in the bladder was drained through an inserted Foley catheter and the bladder was gravity filled at a height of 1 m with normal saline. A galactose-based, microbubble-containing echo-enhancing agent (Levovist; Schering, Berlin, Germany) was then administered. The amount of this was approximately 10% of bladder capacity, and VUR was diagnosed when microbubbles appeared in the ureter or pelvo-calyceal system. Using radiographic VCUG as a reference point, the accuracy with which contrast-enhanced voiding US detected VUR was calculated. RESULTS: In 87 of 95 kidney-ureter units (91.6%), the two methods showed similar results regarding the diagnosis or exclusion of VUR, which was detected by both in 12 units, but by neither in 75. VUR was shown to occur in a total of 20 units, but in eight of these by one method only. In two units, VUR detected by contrast-enhanced voiding US was not demonstrated by radiographic VCUG; in six units, the reverse was true. In the detection of VUR, contrast-enhanced voiding US showed a sensitivity of 66.7%, a specificity of 97.4%, a positive predictive value of 85.7%, and a negative predictive value of 92.6%. CONCLUSION: Contrast-enhanced voiding US is highly specific and has high positive and negative predictive values; its sensitivity, however, is not sufficiently high. The modality appears to be a useful diagnostic tool for the detection of VUR without exposure to ionizing radiation, though to be certain of its value, more experience of its use is first required.

The Use of Contrast-Enhanced Color Doppler Ultrasound in the Differentiation of Retinal Detachment from Vitreous Membrane

OBJECTIVE: To compare the clinical utility of contrast-enhanced color Doppler US in the differentiation of retinal detachment (RD) from vitreous membrane (VM) with that of various conventional US modalities, and to analyze the enhancement patterns in cases showing an enhancement effect. MATERIALS AND METHODS: In 32 eyes examined over a recent two-year period, RD (n=14) and VM (n=18) were confirmed by surgery (n=28) or clinical follow-up (n=4). In all cases, gray-scale, color Doppler, and power Doppler US were performed prior to contrast injection, and after the intravenous injection of Levovist (Schering, Berlin) by hand for 30 seconds at a dose of 2.5 g and a concentration of 300 mg/mL via an antecubital vein, contrast-enhanced color Doppler US was performed. At Doppler US, the diagnostic criterion for RD and VM was whether or not color signals were visualized in membranous structures. RESULTS: Diagnostic accuracy was 78% at gray-scale US, 81% at color Doppler US, 59% at power Doppler US, and 97% at contrast-enhanced color Doppler US. The sensitivity of color Doppler US to color signals in RD increased from 57% to 93% after contrast enhancement. The enhancement patterns observed were signal accentuation (n=3), signal extension (n=2), signal addition (n=3), and new signal visualization (n=5). CONCLUSION: Contrast-enhanced color Doppler US was the most accurate US modality for differentiating RD from VM, showing a significantly increased signal detection rate in RD.

The Use Contrast-Enhanced Color Doppler Ultrasonography in the Detection of Hepatocellular Carcinoma-Related Vessels

PURPOSE: To assess the value of contrast-enhanced color Doppler ultrasonography(US) in the detection of ves-sels related to hepatocellular carcinoma(HCC). MATERIALS AND METHODS: Between July 1997 and April 2000, 76 HCCs in 70 patients (50 men and 20 women; mean age, 57.8 years) were confirmed histologically or clinically. Tumor site and size at gray scale US, and afferent, intratumoral and efferent color signals at precontrast and postcontrast color Doppler US were deter-mined. Afferent signals were classified as basket or penetrating type, and intratumoral signals as spotty, linear or mixed. Efferent signals were categorized as signal to portal vein or signal to hepatic vein, and postcontrast color signal changes as focal, general or marginal spotty type. We also measured the color percentage of intra-tumoral signals as seen during precontrast and postcontrast study. RESULTS: The detection rate changed from 41(53.9%) to 60(78.9%) in cases with afferent signals, from 50(65.8%) to 64(84.2%) in those with intratumoral signals, and from 6(7.9%) to 9(11.8%) in those with efferent signals. Overall, 74(97.4%) cases showed positive findings at postcontrast color Doppler US. The most common enhancing pattern was general, occurring in 33(43.4%) cases. The color percentage of intratumoral signals increased from an average of 8.2% to 34.9%. The detection rate of intratumoral signals from tumors less than 3 cm in diameter increased from 56.8% to 100%, and that of deeply-located tumor-related signals (17 cas-es) increased from 47.1% to 94.1%. CONCLUSION: The use of contrast enhanced color Doppler US increased the detection rate of afferent, intratumoral, and efferent signals, especially that of intratumoral signals from tumors less than 3 cm in diameter and signals from deeply located tumors. In addition, the modality can aid the diagnosis of HCC by evaluating tumor dynamics.

Evaluation of Residual Hepatocellular Carcinoma after Transcatheter Arterial Chemoembolization: Usefulness ofContrast Enhanced Power Doppler Ultrasonography - Preliminary Report

PURPOSE: To determine the usefulness of microbubble contrast enhanced power Doppler ultrasonography (PDUS)for the detection of residual tumor in hepatocellular carcinomas (HCCs) treated by transcatheter arterialchemoembolization (TACE). MATERIALS AND METHODS: Fourteen nodular HCCs (size range: 1 - 7.3 cm, mean: 3.5) intwelve patients treated by TACE, and on the basis of follow-up liver CT, thought to have a residual tumor, wereincluded in this study. Between July 1997 and April 1998, PDUS examinations were performed with a 2-4 MHz convextransducer before and after intravenous injection of a microbubble contrast agent (Levovist(, Schering AG, Berlin,Germany). Real-time power Doppler ultrasonographic images were recorded on videotape and representative imageswere color-printed. Tumor vascularity was analyzed on real-time images with regard to its presence or absence, andchanges, and two observers reached a consensus. The results were compared with those of other diagnostic tests(three-phase helical CT, conventional angiography, percutaneous biopsy, and/or surgical pathology). RESULTS: Contrast-enhanced PDUS revealed intratumoral vascularity in ten of 14 tumors, none of which showed vascularity onunenhanced PDUS. In the remaining four tumors, both unenhanced and enhanced PDUS showed intratumoral tumorvascularity, which in all cases was more pronounced on enhanced than on unenhanced PDUS. Other diagnostic testsrevealed residual tumors in eleven lesions. CONCLUSION: Microbubble contrast-enhanced PDUS was more sensitivethan non-enhanced PDUS in depicting vascularity within a residual tumor and could be a useful method for thedetection of residual tumor in HCCs treated by TACE.