Liver vascular transit time analyzed with dynamic hepatic venography with bolus injections of an US contrast agent: early experience in seven patients with metastases

Effects of ulinastatin on renal perfusion evaluated by Doppler ultrasonography in a porcine model of septic shock

The present study aimed to evaluate the effect of ulinastatin (UTI) on renal perfusion using Doppler ultrasonography in a porcine model of septic shock induced by smoking inhalation and live methicillin-resistant Staphylococcus aureus instillation. A total of 32 healthy Landrace pigs were randomly assigned into the following four groups: Sham group (SH; n=5), septic shock group (SS; n=9), septic shock treated with vancomycin (15 mg/kg) group (VAN; n=9) and septic shock treated with UTI (50,000 U/kg) + vancomycin (UTI; n=9) group. Renal perfusion was evaluated by contrast-enhanced ultrasound (CEUS) at baseline and at the end of the protocol (24 h). The spectrum of interlobar or arcuate artery was selected to calculate the corrected resistive index (cRI). Sulphur hexafluoride microbubbles were bolus injected via a venous catheter. The peak intensity (Pi) and area under curve (AUC) were calculated using a time-intensity curve. Compared with the baseline group, cRI was increased significantly at the end of the protocol, except for that in the SH group, whereas Pi decreased significantly after injury in all experimental groups but was higher in the UTI group compared with that in the SS and VAN groups (both P<0.001). Linear correlation was found between the cardiac output (CO) and Pi (R²=0.752; P<0.001). The AUC was significantly decreased after injury in the SS and VAN groups compared with the baseline group. All parameters detected by CEUS were improved in the UTI group, and significant differences were found between the UTI and SS or VAN group (all P<0.05). In conclusion, acute renal injury, which occasionally occurs during septic shock, is accompanied with a significantly lower perfusion rate in the renal microcirculation. By contrast, UTI can significantly improve renal perfusion, which can be reliably evaluated using CEUS.

Contrast-enhanced computed tomography findings of canine primary renal tumors including renal cell carcinoma, lymphoma, and hemangiosarcoma

In veterinary medicine, abdominal ultrasonography is used to rank the differential diagnosis of renal lesions. However, a conventional sonographic examination may show nonspecific findings. The purpose of this study was to assess the computed tomography (CT) findings of canine renal tumors, including renal cell carcinoma (RCC), lymphoma, and hemangiosarcoma (HSA). In this retrospective study, the following CT parameters were recorded for each dog: 1) extent of renal involvement of tumors, 2) enhancement pattern, 3) number of renal tumors, 4) renal tumor vessel enhancement in the corticomedullary phase, 5) presence of lymphadenopathy and lung metastasis, and 6) attenuation values of the renal tumors on the pre- and post-contrast corticomedullary, nephrographic, and excretory phase images. Fifteen dogs met the inclusion criteria, of which nine had RCCs, four had lymphomas, and two had HSAs. RCCs tended to show heterogeneous enhancement and unilateral renal involvement, and vessel enhancement was detected in the corticomedullary phase in dogs with RCC. Conversely, renal lymphomas showed homogeneous enhancement, bilateral renal involvement, and multiple masses; in these dogs, no vessel enhancement was detected in the corticomedullary phase, and the incidence of lymphadenopathy was low. However, in dogs with lymphadenopathy, the renal lymphoma was associated with regionally severe lymphadenopathy. Finally, renal HSAs tended to show heterogeneous enhancement with a non-enhanced area and unilateral renal involvement; in these dogs, vessel enhancement was detected in the nephrographic phase, with the enhancement expanding around the vessel. These findings had no significant differences. Further studies with a larger sample size are required to examine the association between CT and histopathological findings.

Measuring Intrahepatic Vascular Changes Using Contrast-Enhanced Ultrasonography to Predict the Prognosis of Alcoholic Hepatitis Combined with Cirrhosis: A Prospective Pilot Study

Background/Aims

Acute hepatic dysfunction combined with alcoholic hepatitis (AH) in alcoholic cirrhosis is related to hepatic hypo-perfusion secondary to intrahepatic necroinflammation, neoangiogenesis, and shunt. The hepatic vein arrival time (HVAT) assessed by microbubble contrast-enhanced ultrasonography (CEUS) is closely correlated with the severity of intrahepatic changes. We investigated the usefulness of HVAT to predict short-term mortality of AH in cirrhosis.

Methods

Thirty-nine patients with alcoholic cirrhosis (27 males) and AH were prospectively enrolled. HVAT study was performed within 3 days after admission using ultrasonic contrast (SonoVue^®). The primary outcome was 12-week mortality.

Results

Twelve-week mortality developed in nine patients. HVAT was significantly different between the mortality and survival groups (9.3±2.0 seconds vs 12.6±3.5 seconds, p=0.002). The odds ratio of a shortened HVAT for 12-week mortality was 1.481 (95% confidence interval, 1.050–2.090; p=0.025). The area under the receiver operating characteristic curve of HVAT for 12-week mortality was 0.787 (p=0.010). The combination of MDF and HVAT ≥11.0 seconds resulted in an 87.5% survival rate even if the MDF score ≥32; however, HVAT <11.0 seconds was related with mortality despite a MDF score<32.

Conclusions

HVAT using microbubble CEUS could be a useful additional index to predict short-term mortality in patients with AH and cirrhosis.

Assessment of contrast-enhanced ultrasonography of the hepatic vein for detection of hemodynamic changes associated with experimentally induced portal hypertension in dogs

OBJECTIVE To assess the use of contrast-enhanced ultrasonography (CEUS) of the hepatic vein for the detection of hemodynamic changes associated with experimentally induced portal hypertension in dogs. ANIMALS 6 healthy Beagles. PROCEDURES A prospective study was conducted. A catheter was surgically placed in the portal vein of each dog. Hypertension was induced by intraportal injection of microspheres (10 to 15 mg/kg) at 5-day intervals via the catheter. Microsphere injections were continued until multiple acquired portosystemic shunts were created. Portal vein pressure (PVP) was measured through the catheter. Contrast-enhanced ultrasonography was performed before and after establishment of hypertension. Time-intensity curves were generated from the region of interest in the hepatic vein. Perfusion variables measured for statistical analysis were hepatic vein arrival time, time to peak, time to peak phase (TTPP), and washout ratio. The correlation between CEUS variables and PVP was assessed by use of simple regression analysis. RESULTS Time to peak and TTPP were significantly less after induction of portal hypertension. Simple regression analysis revealed a significant negative correlation between TTPP and PVP. CONCLUSIONS AND CLINICAL RELEVANCE CEUS was useful for detecting hemodynamic changes associated with experimentally induced portal hypertension in dogs, which was characterized by a rapid increase in the intensity of the hepatic vein. Furthermore, TTPP, a time-dependent variable, provided useful complementary information for predicting portal hypertension. IMPACT FOR HUMAN MEDICINE Because the method described here induced presinusoidal portal hypertension, these results can be applied to idiopathic portal hypertension in humans.

Hepatic Vein Arrival Time for Diagnosis of Liver Cirrhosis: A 10-Year Single-Center Experience With Contrast-Enhanced Sonography

OBJECTIVES

To evaluate the performance of contrast-enhanced sonography with a second-generation contrast agent in assessing the severity of chronic diffuse liver disease and differentiating cirrhotic from noncirrhotic liver disease.

METHODS

Contrast-enhanced sonography was performed after intravenous bolus injection of a second-generation contrast agent in 14 healthy control participants and 160 consecutive patients with cirrhotic and noncirrhotic liver disease (n = 78 and 82, respectively) enrolled between March 2004 and April 2014. The intensity of enhancement in a main hepatic vein was used to determine hepatic vein arrival time, time to peak intensity, and peak contrast enhancement.

RESULTS

The hepatic vein arrival time was lower in cirrhotic patients compared with both noncirrhotic patients and controls (mean ± SD, 15.0 ± 2.8, 21.5 ± 3.4, and 25.6 ± 4.7 seconds, respectively; P < .05). The hepatic vein arrival time in noncirrhotic patients was also significantly lower than that in controls (P < .05). The time to peak intensity was significantly lower in cirrhotic patients compared with noncirrhotic patients and controls (40.7 ± 13.7, 49.4 ± 12.8, and 51.2 ± 13.7 seconds; P < .05). A receiver operating characteristic curve analysis revealed that the hepatic vein arrival time more accurately excluded a diagnosis of liver cirrhosis than the time to peak intensity (area under the receiver operating characteristic curve, 0.953 versus 0.694). Specifically, a hepatic vein arrival time cutoff value of 17 seconds excluded liver cirrhosis with 91.1% sensitivity and 93.6% specificity.

CONCLUSIONS

Contrast-enhanced sonography is a valid alternative method for noninvasive staging of liver diseases. The hepatic vein arrival time could be used to exclude liver cirrhosis in a clinical setting.

Exploring Targeted Contrast-Enhanced Ultrasound to Detect Neural Inflammation

Targeted contrast-enhanced ultrasound (TCEUS) is an innovative method of molecular imaging used for detection of inflammatory biomarkers in vivo. By targeting ultrasound contrast to cell adhesion molecules (CAMs), which are known inflammatory markers within neural tissue, a more direct evaluation of neural inflammation can be made. Due to the novel nature of TCEUS, standardized methods of image analysis do not yet exist. Time intensity curve (TIC) shape analysis is currently used in magnetic resonance contrast imaging to determine temporal behavior of perfusion. Therefore, the presented research attempts to determine TIC shape analysis utility in TCEUS imaging by applying it to TCEUS scans targeted to CAMs present in neural inflammation. This was done in an animal model that underwent a traumatic spinal cord injury to induce inflammation ( n = 31). Subjects were divided into four groups, each receiving a TCEUS targeted to a different CAM seven days after surgery (P-selectin, intracellular adhesion molecule 1 [ICAM-1], vascular cell adhesion molecule 1 [VCAM-1], and control). TICs were generated using average pixel intensity within the injured region of the spinal cord. TIC shape analysis found similar curves were produced while targeting P-selectin and VCAM-1, both demonstrating rapid and sustained enhancement. Control injections demonstrated no enhancement. ICAM-1 injections demonstrated limited enhancement and a shape similar to the control.

Targeted microbubbles in the experimental and clinical setting

BACKGROUND

Microbubbles have improved ultrasonography imaging techniques over the past 2 decades. Their safety, versatility, and easiness of use have rendered them equal or even superior in some instances to other imaging modalities such as computed tomography and magnetic resonance imaging. Herein, we conducted a literature review to present their types, general behavior in tissues, and current and potential use in clinical practice.

METHODS

A literature search was conducted for all preclinical and clinical studies involving microbubbles and ultrasonography.

RESULTS

Different types of microbubbles are available. These generally improve the enhancement of tissues during ultrasonography imaging. They also can be attached to ligands for the target of several conditions such as inflammation, angiogenesis, thrombosis, apoptosis, and might have the potential of carrying toxic drugs to diseased sites, thereby limiting the systemic adverse effects.

CONCLUSIONS

The use of microbubbles is evolving rapidly and can have a significant impact on the management of various conditions. The potential for their use as targeting agents and gene and drug delivery vehicles looks promising.

Hepatic vein arrival time as assessed by contrast-enhanced ultrasonography is useful for the assessment of portal hypertension in compensated cirrhosis

The measurement of the hepatic venous pressure gradient (HVPG) for the estimation of portal hypertension (PH) in cirrhosis has some limitations, including its invasiveness. Hepatic vein arrival time (HVAT), as assessed by microbubble contrast-enhanced ultrasonography (CEUS), is negatively correlated with the histological grade of liver fibrosis because of the associated hemodynamic abnormalities. Anatomical and pathophysiological changes in liver microcirculation are the initial events leading to PH. However, the direct relationship between HVAT and PH has not been evaluated. The present study measured both HVPG and HVAT in 71 consecutive patients with compensated cirrhosis and analyzed the relationship between the two parameters (i.e., the derivation set). Results were validated in 35 compensated patients with cirrhosis at another medical center (i.e., the validation set). The derivation set had HVPG and HVAT values of 11.4 ± 5.0 mmHg (mean ± standard deviation; range, 2-23) and 14.1 ± 3.4 seconds (range, 8.4-24.2), respectively; there was a statistically significant negative correlation between HVPG and HVAT (r(2) = 0.545; P < 0.001). The area under the receiver operating characteristic curve (AUROC) was 0.973 for clinically significant PH (CSPH; HVPG, ≥ 10 mmHg), and the sensitivity, specificity, positive predictive value, negative predictive value, and positive and negative likelihood ratios for CSPH for an HVAT cut-off value of 14 seconds were 92.7%, 86.7%, 90.5%, 89.7%, 6.95, and 0.08, respectively. In addition, a shorter HVAT was associated with worse Child-Pugh score (P < 0.001) and esophageal varices (P = 0.018). In the validation set, there was also a significant negative correlation between HVAT and HVPG (r(2) = 0.538; P < 0.001), and AUROC = 0.953 for CSPH. HVAT was significantly correlated with PH. These results indicate that measuring HVAT is useful for the noninvasive prediction of CSPH in patients with compensated cirrhosis.

Contrast-enhanced ultrasound in oncology

In patients with known malignant disease, 51% of liver lesions less than 1.5 cm turn out to be benign. Whether the probability of malignancy is high or low, further investigations are often necessary to definitely exclude malignancy. Contrast-enhanced ultrasonography has a prominent role in lesion characterization with a diagnostic accuracy comparable with computed tomography and magnetic resonance imaging. Anti-angiogenic treatment is common in most oncological institutions and the response evaluation is a new challenge with a research focus on the change in tumour vasculature and perfusion. In planning biopsies, CEUS can identify necrotic and viable areas of tumours and improve the diagnostic accuracy.

Imaging of perfusion using ultrasound

Ultrasound can be used to image perfusion in two ways: the traditional one using Doppler and the more recent using microbubble contrast agents. Doppler is simple to use and inexpensive but is limited to larger vessels with faster flow rates. It cannot interrogate the microvasculature because bulk tissue movement is faster than capillary flow. It has been used for liver and tumour flow. Contrast studies are much richer and can assess both the macro- and microcirculation. One approach analyses the time-intensity curves in a region of interest, e.g. a tumour, myocardium, brain, following bolus i.v. injection. Another approach measures the time taken for the microbubbles to cross a vascular bed of interest. These arrival times can be useful for the liver in both diffuse and focal diseases and for the kidney. Features derived from time-intensity curves following bolus i.v. injections of microbubbles form sensitive early indicators of the vascular response of tumours to antivascular drugs. This approach, known as dynamic contrast-enhanced ultrasound (DCE-US), has been accepted as a valid technique for monitoring tumour response by several authorities.

Assessment of tissue perfusion by contrast-enhanced ultrasound

Contrast-enhanced ultrasound (CEUS) with microbubble contrast agents is a new imaging technique for quantifying tissue perfusion. CEUS presents several advantages over other imaging techniques in assessing tissue perfusion, including the use of microbubbles as blood-pool agents, portability, availability and absence of exposure to radiation or nuclear tracers. Dedicated software packages are necessary to quantify the echo-signal intensity and allow the calculation of the degree of tissue contrast enhancement based on the accurate distinction between microbubble backscatter signals and native tissue background. The measurement of organ transit time after microbubble injection and the analysis of tissue reperfusion kinetics represent the two fundamental methods for the assessment of tissue perfusion by CEUS. Transit time measurement has been shown to be feasible and has started to become accepted as a clinical tool, especially in the liver. The loudness of audio signals from spectral Doppler analysis is used to generate time-intensity curves to follow the wash-in and wash-out of the microbubble bolus. Tissue perfusion may be quantified also by analysing the replenishment kinetics of the volume of microbubbles after their destruction in the imaged slice. This allows to obtain semiquantitative parameters related to local tissue perfusion, especially in the heart, brain, and kidneys.

Indicator dilution models for the quantification of microvascular blood flow with bolus administration of ultrasound contrast agents

Indicator dilution methods have a long history in the quantification of both macro- and microvascular blood flow in many clinical applications. Various models have been employed in the past to isolate the primary pass of an indicator after an intravenous bolus injection. The use of indicator dilution techniques allows for the estimation of hemodynamic parameters of a tumor or organ and thus may lead to useful diagnostic and therapy monitoring information. In this paper, we review and discuss the properties of the lognormal function, the gamma variate function, the diffusion with drift models, and the lagged normal function, which have been used to model indicator dilution curves in different fields of medicine. We fit these models to contrast-enhanced ultrasound time-intensity curves from liver metastases and the ovine corpora lutea. We evaluate the models' performance on the image data and compare their predictions for hemodynamic-related parameters such as the area under the curve, the mean transit time, the full-width at half-maximum, the time to the peak intensity, and wash-in time. The models that best fit the experimental data are the lognormal function and the diffusion with drift.

Diagnosis of liver cirrhosis with contrast-enhanced ultrasound

The assessment of the extent of liver fibrosis is very important for the prognosis and clinical management of chronic liver diseases. Although liver biopsy is the gold standard for the assessment of liver fibrosis, new non-invasive diagnostic methods are urgently needed in clinical work due to certain limitations and complications of biopsy. Noninvasive imaging studies play an important role in the diagnosis of focal liver disease and diffuse liver diseases. Among them, ultrasonography is the first choice for study of the liver in clinical work. With the development of ultrasound contrast agents and contrast specific imaging techniques, contrast-enhanced ultrasound (CEUS) shows good performance and great potential in the evaluation of liver fibrosis. Researchers have tried different kinds of contrast agent and imaging method, such as arrival time of contrast agent in the hepatic vein, and quantitative analysis of the enhancement level of liver parenchyma, to evaluate the degree of liver fibrosis during the past 10 years. This review mainly summarizes the clinical studies concerning the assessment of liver fibrosis using CEUS.

Hepatic transit time analysis using contrast-enhanced ultrasound with BR1: A prospective study comparing patients with liver metastases from colorectal cancer with healthy volunteers

We prospectively compared hepatic transit time (HTT) measurements in subjects with liver metastases from colorectal cancer (group a) and healthy volunteers (group b) using contrast-enhanced ultrasound with BR1. The purpose of this study was to verify our hypothesis that the hemodynamic changes of the liver, which occur during metastasis seeding, would shorten the HTT, and we expect that such changes could be used for the detection of occult liver metastases from colorectal cancer in the future. The study had institutional review board approval and all subjects gave informed written consent. Group a and group b consisted of 22 subjects each. Baseline and post contrast images were acquired starting 10 s before and ending 40 s after administration of BR1, using nonlinear imaging at a frame rate of 5/s. The baseline images were used to determine the signal intensity without contrast enhancement as the reference signal. Arrival times (AT) of the contrast agent for the hepatic artery, the portal vein and one hepatic vein were determined using (i) quantitative analysis and (ii) subjective analysis by two blinded readers. HTT was calculated based on arrival time measurements. Quantitative and subjective analysis showed significantly shorter arterial to venous and portal to venous HTT in group a compared with group b (p < 0.001). Arterial to venous HTT (quantitative analysis) was < or = 9 s in 19 of 22 subjects of group a and >9 s in 18 of 22 subjects of group b (sensitivity 86%, specificity 82%, positive predictive value 83%, negative predictive value 86%, area under the curve [AUC] 0.87). Portal to venous HTT (quantitative analysis) was < 7 s in 21 of 22 subjects of group a and > 7s in 15 of 22 subjects of group b (sensitivity 95%, specificity 68%, PPV 75%, NPV 94%, AUC 0.85). There was an inverse relation with number of liver segments involved for arterial to venous and portal to venous HTT in group a (p < 0.05), but no correlation between HTT and overall volume of metastases (group a) or subject age (group b). From the results of our study, we conclude that HTT measurements using contrast-enhanced ultrasound with BR1 can detect hemodynamic changes caused by metastatic liver disease from colorectal cancer. However, comparison with the literature suggests that the use of other contrast agents might provide better results. Comparison of different contrast agents for the purpose of transit time analysis would therefore be useful before embarking on a prospective trial looking at the detection of occult liver metastases in patients with colorectal cancer. (E-mail: jhohmann@uhbs.ch).

Contrast-enhanced ultrasound to evaluate the severity of chronic hepatitis C

BACKGROUND

Non-invasive techniques are being developed to assess the severity of liver disease. Haemodynamic changes in the hepatic circulation during the development of liver disease can be evaluated with contrast-enhanced ultrasound.

AIM

To evaluate the possible correlation between ultrasound contrast-agent transit times and different stages of chronic hepatitis C.

PATIENTS

Sixteen patients with clinically evident hepatitis C virus-related cirrhosis, 22 non-cirrhotic patients with chronic hepatitis C and 14 controls with no clinical evidence of liver disease were studied.

METHODS

Contrast-enhanced hepatic ultrasonography was performed with a sulphur hexafluoride-filled microbubble contrast agent, and time curves of hepatic vein signal intensity were analysed to determine the time of enhancement onset (hepatic vein arrival time) and peak enhancement (hepatic vein peak enhancement).

RESULTS

Hepatic vein arrival time in cirrhotic patients was significantly shorter (p<0.001) than in non-cirrhotic patients and controls. Within the group with chronic hepatitis C, METAVIR scores of fibrosis and necro-inflammatory changes had no significant effect on hepatic vein arrival times.

CONCLUSION

Analysis of the time of onset of ultrasound contrast enhancement of the hepatic vein appears to be a simple, non-invasive method for reliably excluding cirrhosis with signs of portal hypertension, but not for assessing the severity of either chronic hepatitis C or cirrhosis.

Quantitative contrast ultrasound analysis of renal perfusion in normal dogs

Eight normal dogs with no evidence of renal disease, weighing between 8 and 25 kg were imaged using contrast harmonic ultrasound after injection of a microbubble contrast medium. All dogs received three separate bolus injections of 0.05 ml of commercial contrast medium (Definity). Time/mean pixel value (MPV) curves were generated for selected regions in the cortex and medulla of the left kidney in each dog. Upslope, downslope, baseline, peak intensity, and time to peak were calculated for each zone. For a bolus injection, within the renal cortex (averaging all subjects) the upslope was 7.4 +/- 1.5 MPV/s, downslope was -0.4 +/- .2 MPV/s, baseline was 66.8 +/- 9.3 MPV, peak was 103.6 +/- 8.2 MPV, time to peak (from injection) was 12.8 +/- 5.3 s and from time of contrast medium reaching the kidney was 5.1 +/- 2.0 s. Within the renal medulla (averaging all subjects), upslope was 2.8 +/- 1.7 MPV/s, downslope was -0.3 +/- .2 MPV/s, baseline was 39.3 +/- 6.0 MPV, peak was 65.2 +/- 14.3 MPV, time to peak from injection was 20.9 +/- 6.4 s and from time of contrast reaching the kidney was 11.6 +/- 4.1 s. These baseline data may prove useful in the evaluation of dogs with diffuse disease or vascular compromise.

Technology Insight: advances in liver imaging

The role of diagnostic imaging in the assessment of liver disease continues to gain in importance. The classic techniques used for liver imaging are ultrasonography, CT and MRI. In the past decade, there have been significant advances in all three techniques. In this article, we discuss the advances in ultrasonography, CT and MRI that have improved assessment of focal and diffuse liver disease, including the development of hardware, software, processing algorithms and procedural innovations.

Recent applications of ultrasound: diagnosis and treatment of hepatocellular carcinoma

Ultrasound (US) has the advantages of real-time observation, simple technique, and a noninvasive procedure compared to other imaging modalities. The recent development of digital technologies has enabled the observation of sonograms with improved signal-to-noise ratio, penetration, and spatial and contrast resolutions. Furthermore, microbubble contrast agents have increased the diagnostic ability of US examination, and the use of three-dimensional sonograms is now not unusual. These advances have furthered the usefulness of US for liver tumors in clinical practice. This article reviews the recent applications of US in the diagnosis and treatment of hepatocellular carcinoma.

Dynamic US contrast study of the liver: Vascular and delayed parenchymal phase

We evaluated the time-intensity curves of the ultrasound contrast agent, Levovist, in the aorta, portal vein and liver parenchyma in order to define distribution of the agent when it is administered by an intravenous bolus injection. Twelve healthy volunteers were studied. All 12 subjects were examined for the study of vascular phase and five of the subjects were examined for the study of delayed parenchymal phase. To evaluate vascular enhancement, transverse abdominal scanning was performed. To evaluate parenchymal enhancement, liver scanning was done just once at 14 time points up to 60 min after injection. The time-intensity curves in the aorta and the portal vein indicated the conventional curves of blood pool agents such as iodine CT agents and gadolinium MRI agents. They showed steep initial rises and peaks at 20 s and 30 s after injection, respectively. Parenchymal enhancement reached a peak five minutes after injection, with a plateau for 20 min subsequently. It has been proved that there are two phases of Levovist contrast ultrasonography, the vascular phase and the delayed parenchymal phase.

Ultrasound contrast agents: an overview

With the introduction of microbubble contrast agents, diagnostic ultrasound has entered a new era that allows the dynamic detection of tissue flow of both the macro and microvasculature. Underpinning this development is the fact that gases are compressible, and thus the microbubbles expand and contract in the alternating pressure waves of the ultrasound beam, while tissue is almost incompressible. Special software using multiple pulse sequences separates these signals from those of tissue and displays them as an overlay or on a split screen. This can be done at low acoustic pressures (MI<0.3) so that the microbubbles are not destroyed and scanning can continue in real time. The clinical roles of contrast enhanced ultrasound scanning are expanding rapidly. They are established in echocardiography to improve endocardial border detection and are being developed for myocardial perfusion. In radiology, the most important application is the liver, especially for focal disease. The approach parallels that of dynamic CT or MRI but ultrasound has the advantages of high spatial and temporal resolution. Thus, small lesions that can be indeterminate on CT can often be studied with ultrasound, and situations where the flow is very rapid (e.g., focal nodular hyperplasia where the first few seconds of arterial perfusion may be critical to making the diagnosis) are readily studied. Microbubbles linger in the extensive sinusoidal space of normal liver for several minutes whereas they wash out rapidly from metastases, which have a low vascular volume and thus appear as filling defects. The method has been shown to be as sensitive as three-phase CT. Microbubbles have clinical uses in many other applications where knowledge of the microcirculation is important (the macrocirculation can usually be assessed adequately using conventional Doppler though there are a few important situations where the signal boost given by microbubbles is useful, e.g., transcranial Doppler for evaluating vasospasm after subarachnoid haemorrhage). An important situation where demonstrating tissue devitalisation is important is in interstitial ablation of focal liver lesions: using microbubble contrast agents at the end of a procedure allows immediate evaluation of the adequacy of the ablation which can be extended if needed; this is much more convenient and cost-saving than moving the patient to CT and perhaps needing an additional ablation session at a later date. Similar considerations suggest that contrast-enhanced ultrasound might have a role in abdominal trauma: injury to the liver, spleen and kidneys can be assessed rapidly and repeatedly if necessary. Its role here alongside dynamic CT remains to be evaluated. Infarcts or ischaemia and regions of abnormal vascularity, especially in malignancies, in the kidneys and spleen seem to be useful and improved detection of the neovascularisation of ovarian carcinomas is promising. Similar benefits in the head-and-neck and in the skin while the demonstration of the neovascularisation of atheromatous plaques and of aggressive joint inflammation offer interesting potentials.

Hepatic vein transit time of SonoVue: a comparative study with Levovist

PURPOSE

To prospectively compare transit times of Levovist and SonoVue in healthy volunteers and patients with biopsy-proved hepatitis C-related liver disease.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Forty patients and 25 healthy volunteers were examined. Subjects fasted, a bolus of SonoVue (0.6 mL) was injected into a cubital fossa vein, and hepatic venous time-intensity profiles were measured with spectral Doppler tracing. This was repeated with two injections of Levovist (2 g) and another injection of SonoVue. Time-intensity curves of spectral Doppler signals of right and middle hepatic veins were analyzed. A sustained signal intensity increase of 10% above baseline levels indicated hepatic vein transit time (HVTT). Carotid artery audio intensity was measured in volunteers. Analysis of variance and t tests were used for statistical analysis.

RESULTS

Twelve patients had mild hepatitis; 18, moderate or severe hepatitis; and 10, cirrhosis. Mean HVTTs in control, mild hepatitis, moderate or severe hepatitis, and cirrhosis groups were 38.3 seconds +/- 2.4 (standard error), 47.5 seconds +/- 6.5, 29.5 seconds +/- 10.8, and 17.6 seconds +/- 5.0, respectively, with Levovist (P < .001) and 29.4 seconds +/- 6.9, 27.4 seconds +/- 9.3, 22.9 seconds +/- 4.7, and 16.4 seconds +/- 4.9, respectively, with SonoVue (P < .001). HVTT decreased as severity increased at imaging with both contrast agents. There was no significant difference in HVTT between mild and moderate hepatitis groups with SonoVue; however, there were significant differences in HVTT between all patient groups with Levovist. HVTT of SonoVue was shorter than that of Levovist in all groups (P < .001) except the cirrhosis group; in this group, HVTT of the two contrast agents was similar (P = .05). No difference was observed in mean cardiopulmonary transit time for SonoVue or Levovist (9.1 seconds +/- 2.4 [standard error] and 8.4 seconds +/- 2.5, respectively, P = .18).

CONCLUSION

HVTT was significantly shorter with SonoVue than with Levovist; there was no significant difference in cardiopulmonary transit time.

Gray scale contrast enhancement and quantification in different positions of rabbit liver

OBJECTIVE

The purpose of this study was to evaluate the difference between central and ventral peripheral positions and the difference between left and right lobes in rabbit liver with gray scale contrast enhancement.

METHODS

An in vivo model of perfusion was studied with a sulfur hexafluoride contrast agent and low-mechanical-index, real-time, gray scale harmonic imaging. The contrast agent (0.1 mL/kg body weight) was applied respectively in 10 rabbits by intravenous bolus injection. The time-intensity curve was used to obtain flow-related parameters such as time to enhancement (ET), time to peak intensity (PIT), peak signal intensity (PSI), enhancement duration (ED), and area under the curve (AUC).

RESULTS

There was a significant difference in parameters of the time-intensity curve between central and peripheral ventral positions of liver parenchyma (P < .05), except for the ED in the left liver. The ET and PIT were earlier, the PSI higher, the ED longer, and the AUC larger in the central position of parenchyma than in the peripheral position. In addition, the ET and PIT were earlier, the PSI higher, the ED longer, and the AUC larger in the right lobe of liver parenchyma than in the left lobe. There was a significant difference in parameters of the time-intensity curve between the left and right lobes of liver parenchyma (P < .05), except for the ET of the peripheral position.

CONCLUSIONS

Flow parameters are different between central and ventral peripheral positions and between left and right lobes of hepatic parenchyma.

Hepatic transit time of ultrasound contrast in biopsy characterized liver disease

PURPOSE

To study the hepatic transit time of an ultrasound contrast agent in patients with liver disease, and to evaluate the mechanism(s) of the well-established shorter cubital vein to hepatic vein transit time in cirrhosis.

MATERIAL AND METHODS

Thirty-four patients scheduled for Menghini liver biopsy were studied by ultrasound after injection of 2.5 g Levovist (Schering, Berlin, Germany) into an arm vein. The time from injection until the first appearance of contrast echoes in the hepatic artery and hepatic veins was registered. Hepatic transit time was the difference between the two.

RESULTS

Biopsy showed cirrhosis in 9 patients, other diffuse hepatic pathology in 23 patients, and normal liver in 2 patients. Mean hepatic vein arrival time was earlier in cirrhosis than in other liver disease (19.4 s versus 26.0 s; P = 0.013), and hepatic transit time was shorter (6.6 s versus 11.6 s; P = 0.024). A hepatic transit time <10 s was found in all patients with cirrhosis, but also in 10 of 23 patients with other liver pathology.

CONCLUSION

Hepatic transit time measurement could not be used to distinguish between cirrhosis and other hepatic pathology, but a transit time = 10 s excluded cirrhosis. The earlier hepatic vein arrival time in cirrhosis is apparently mainly caused by intrahepatic shunting rather than by early arrival of contrast to the liver.

Contrast-enhanced ultrasonography in normal canine liver. Evaluation of imaging and safety parameters

Contrast-enhanced ultrasonography, a new imaging modality in veterinary medicine, can provide data on tissue perfusion. The objective of this study was to use the ultrasonographic contrast agent SonoVue to evaluate various transit time indices in the normal canine liver, to examine the effect of anesthesia on these parameters, and to evaluate the safety of this agent in dogs. The liver of 11 healthy dogs was studied by ultrasound during an intravenous bolus injection of SonoVue. Each dog underwent the examination twice, first with and later without the use of anesthesia. A time-intensity curve was generated from a selected region of interest within the liver from each scanning session. Ratios derived from peak enhancement, time to peak enhancement, up-slope and full-width half-maximum (FWHM) of the curve were calculated from the time-intensity curves, and are reported. There were no statistically significant differences (P > 0.05) in peak enhancement, up-slope and FWHM between dogs that were anesthetized and dogs that were not. Time to peak enhancement, however, was significantly shorter when the dogs were anesthetized than when they were nonanesthetized (P < 0.05). There were no biologically significant changes in clinical laboratory findings. This study indicates that contrast-enhanced ultrasound using SonoVue gives reproducible liver perfusion data, and appears to be a safe and well-tolerated agent for use in dogs. When considering normal values, the use of anesthetic drugs has to be considered.

Time-intensity-based quantification of vascularity with single-level dynamic contrast-enhanced ultrasonography: a pilot animal study

OBJECTIVE

The purpose of this study was to delineate the hemodynamic features of VX2 tumor and perineoplastic liver parenchyma and to evaluate the potential usefulness of single-level dynamic ultrasonography in the diagnosis of tumors by the analysis of time-intensity curves.

METHODS

An in vivo animal model was studied using a low mechanical index in conjunction with single-level dynamic contrast-enhanced ultrasonography. A sulfur hexafluoride contrast agent (SonoVue; Bracco SpA, Milan, Italy) was applied in 8 rabbits by intravenous bolus injection. Data were acquired before and after VX2 tumor induction. Corresponding parameters of the time-intensity curve were measured using wash-in/wash-out curve software.

RESULTS

No significant difference was found in the time to enhancement, time to peak intensity, peak signal intensity, and enhancement duration between liver parenchyma before and after VX2 tumor induction (P > .05). The typical enhancement pattern of VX2 tumors was hyperechoic relative to liver parenchyma during the early phase and hypoechoic during the later phase. The curves obtained in carcinomas revealed an early arrival time and time to peak intensity with an irregular and sharp decrease of the intensity signal and a very early return to baseline, presenting a much more rapid wash-in and wash-out of ultrasonographic contrast agents. There was a significant difference in the time to enhancement, time to peak intensity, peak signal intensity, and enhancement duration between the VX2 tumors and perineoplastic liver parenchyma (P < .001).

CONCLUSIONS

Single-level dynamic contrast-enhanced ultrasonography with a low mechanical index level could provide real-time and continuous enhanced images and fully delineate the typical enhancement pattern of liver tumors. The analysis of time-intensity curves may provide useful, complementary, and quantitative information. This technique may be useful for the diagnosis of liver tumors, especially those showing an atypical enhancement pattern on biphasic helical computed tomographic scanning.

Hepatic transit time: indicator of the therapeutic response to radiofrequency ablation of liver tumours

The aim of this study was to evaluate changes of hepatic transit time (HTT) in patients treated by radiofrequency ablation (RFA). Five consecutive patients (2 females, 3 males; mean age 66 years) referred for treatment of liver neoplasm with percutaneous application of RFA were included in this study. The HTT of contrast agent (Sonovue(R); Bracco International B.V., Amsterdam, The Netherlands) was measured in patients with liver metastases on the basis of time intensity curve (TIC(R)) before and after RFA, respectively. Changes of HTT before vs after RFA were compared with therapeutic response based on three-phase dynamic CT or MRI. Before RFA HTT in all 5 patients was less than 10 s (mean 6.2+/-1.5 s). After RFA HTT in patients with complete therapeutic response was 11.3+/-1.2 s, whereas two patients with incomplete treatment showed unchanged HTT below 10 s (mean 6.3+/-1.8 s). Successful RFA leads to a normalization in HTT. HTT using ultrasound contrast agent appears to provide a new and alternative approach in assessing the therapeutic effect of RFA in liver metastases.

Cyclosporine A Does Not Alter Ultrasonic Indices of Renal Blood Flow: A Potential Tool for Differentiating Toxicity from Acute Rejection?

The narrow therapeutic window of cyclosporine A (CsA) means its use is controlled by pharmacokinetic monitoring. However, pharmacokinetics do not always reflect the functional effects of a drug--its pharmacodynamics, such as vasoconstriction. We developed a technique for measuring renal blood flow and used a pig model to determine whether CsA-induced renal vasoconstriction could be detected, thus offering a tool for pharmacodynamic therapeutic drug monitoring. This has been shown to differentiate acute rejection from acute tubular necrosis. Power Doppler intensitometry was used to assess relative vascular volume, and the renal arteriovenous transit time was determined with an intravenous microbubble bolus. Measurements were taken before and at intervals after an intravenous bolus of CsA (10 mg/kg). There was no correlation between index and CsA concentration. Lack of detectable effect after CsA administration to high concentrations suggests that this technique may be able to differentiate CsA toxicity from acute rejection.

Grey-scale contrast enhancement in rabbit liver with SonoVue at different doses

To evaluate the dose of ultrasound (US) contrast agent (UCA) in relation to the contrast-enhancement effect, an in vivo model of perfusion was studied using SonoVue, a second-generation UCA, and low mechanical index (MI) grey-scale harmonic imaging. SonoVue, at eight different doses (0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14 and 0.16 mL/kg BW), was applied in five normal rabbits. Flow-related parameters obtained from time-intensity curves were calculated and plotted over the contrast agent doses, and nonlinear curve fitting was performed. Results showed that, along with an increase of the administrated contrast agent dose, the enhancement duration (ED) and the area under the curve (AUC) increased logarithmically, and the time to enhancement (ET) decreased logarithmically. There was a progressive increase of the peak signal intensity (PSI) following an increase of SonoVue dose only in the dose range of 0.02 up to 0.10 mL/kg body weight (BW) in the portal vein and in the dose range of 0.02 up to 0.12 mL/kg BW in the liver parenchyma. Moreover, a good correlation was observed between the parameters obtained from liver parenchyma and those obtained from the portal vein. The results indicated that SonoVue in conjunction with continuous harmonic low-MI grey-scale imaging has the capability of flow quantification on both vessels and parenchyma. The parameters of time-intensity curve were influenced intensely by different contrast agent doses.

A Novel Technique to Measure Splanchnic Transit Time Using Microbubble Ultrasound

OBJECTIVE

The objective of this study was to measure splanchnic transit time by intravenous injection of a microbubble.

MATERIALS AND METHODS

Ten volunteers were examined before and after eating. After Doppler indices of splanchnic circulation were obtained, the superior mesenteric artery (SMA) and vein (SMV) were simultaneously interrogated using power Doppler ultrasound after intravenous injection of a microbubble. Contrast arrival in the SMA and subsequently the SMV was recorded and splanchnic transit time calculated from differences in the time-intensity curves.

RESULTS

Splanchnic transit time decreased significantly after eating (mean 11 vs. 6.9 seconds; P = 0.007), reflecting splanchnic hemodynamics. Between-subject variability attributable to repeated measurements was least for the SMA resistive index (17%) but 56% for the new index, suggesting poor reproducibility.

CONCLUSION

Splanchnic transit time may be measured by microbubble injection but is subject to considerable measurement error. Newer microbubbles and imaging methods may allow more reproducible measurements.

A review of the sonographic assessment of tumor metastases in liver and superficial lymph nodes

Diagnostic imaging techniques are an important part of the diagnostic workup and staging of cancer patients. Ultrasound is of particular interest in this respect. In so far as tumor metastases are concerned, ultrasonography of regional lymph nodes and of the liver can provide valuable information. In humans many criteria, some of them objective, have been evaluated as indicators of malignancy. The most diagnostically helpful of these include the short/long axis ratio of the lymph node, the pattern of distribution of the blood vessels within the lymph node, and to some extent the calculated values for resistive and pulsatility indices. Putative objective criteria to improve the specificity of ultrasound for metastases detection in the liver have also been evaluated. These include perfusion indices, primarily using analysis of Doppler frequencies (Doppler perfusion index) and hepatic venography using an ultrasound contrast agent. Contrast-enhanced ultrasonography is a new and promising area to help the initial diagnosis and characterization of malignancy, particularly for focal lesions in the liver. This review discusses the use of ultrasound for detection of metastases and presents material from four veterinary cases.

Contrast enhanced ultrasound in liver imaging

Ultrasound contrast agents were originally introduced to enhance the Doppler signals when detecting vessels with low velocity flow or when imaging conditions were sub-optimal. Contrast agents showed additional properties, it was discovered that a parenchymal enhancement phase in the liver followed the enhancement of the blood pool. Contrast agents have made ultrasound scanning more accurate in detection and characterization of focal hepatic lesions and the sensitivity is now comparable with CT and MRI scanning. Further, analysis of the transit time of contrast agent through the liver seems to give information on possible hepatic involvement, not only from focal lesions but also from diffuse benign parenchymal disease. The first ultrasound contrast agents were easily destroyed by the energy from the sound waves but newer agents have proved to last for longer time and hereby enable real-time scanning and make contrast enhancement suitable for interventional procedures such as biopsies and tissue ablation. Also, in monitoring the effect of tumour treatment contrast agents have been useful. A brief overview is given on some possible applications and on different techniques using ultrasound contrast agents in liver imaging. At present, the use of an ultrasound contrast agent that allows real-time scanning with low mechanical index is to be preferred.

Usefulness of contrast-enhanced wide-band Doppler ultrasonograpy to diagnose alveolar echinococcosis of the liver and evaluate the effect of the treatment

Alveolar echinococcosis is a rare parasitic disease caused by Echinococcus multicularis and most commonly involves the liver. Early diagnosis and accurate evaluation of the effect of the treatment are essential to improve the prognosis of patients with alveolar echinococcosis of the liver (AEL). The aim of this study was to demonstrate the characteristic imaging of AEL by contrast-enhanced Dynamic Flow (CE-DF) employing a wide-band Doppler technique for the diagnosis and the accurate evaluation of the effect of the treatment. Four patients with five AEL lesions before treatment or during medication were examined by CE-DF. All of the five AEL lesions examined by CE-DF revealed a defect with an irregular and distinct margin like a worm-eaten defect appearance, which was never observed on other hepatic lesions, in liver perfusion image during post-vascular phase. In addition, CE-DF made it possible to measure the size of AEL lesions accurately because the margin was detected distinctly. These data suggest that CE-DF is clinically useful for the diagnosis of AEL and the evaluation of the effect of the treatment.

Liver metastases in cancer: detection with contrast-enhanced ultrasonography

In patients with known or suspected malignancy, ultrasonography (US) is often the first choice for liver imaging because of its widespread availability and low cost. Compared with contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI), the sensitivity of conventional US for detecting hepatic metastases is relatively poor. The advent of microbubble contrast agents changed this situation. Sensitivity and specificity increased substantially with the use of these contrast agents and contrast-specific imaging modes in recent years. Currently, numerous US imaging methods exist, based on Doppler techniques or harmonic imaging. They exploit the complex nonlinear behavior of microbubbles in a sound field to achieve marked augmentation of the US signal. Although microbubble contrast agents are essentially blood pool agents, some have a hepatosplenic specific late phase. Imaging during this late phase is particularly useful for improving the detection of malignant liver lesions and allows US to perform similarly to spiral CT as shown by recent studies. In addition, this late phase imaging is very helpful for lesion characterization. Low mechanical index imaging with the newer perfluor agents permits real-time imaging of the dynamic contrast behavior during the arterial, portal venous, and late phases and is particularly helpful for lesion characterization. The use of US for hemodynamic studies of the liver transit time may detect blood flow changes induced by micrometastases even before they become visible on imaging. In this field of functional imaging, further research is required to achieve conclusive results, which are not yet available.

[Ultrasound contrast agents]

Ultrasound contrast agents consist of tiny gas bubbles encapsulated by a stabilising membrane or shell. When combined with recent contrast-specific ultrasound techniques, they provide substantial enhancement of vessels and solid organs. The clinical use and the diagnostic value of ultrasound contrast agents are in principle comparable to those of contrast agents for CT and MRI. They add an additional dimension of information to sonography, which results in considerable improvement of diagnostic accuracy in many cases. This paper reviews the physicochemical properties of various microbubble contrast agents, discusses non-linear bubble behaviour and contrast-specific imaging techniques. An overview of the most important radiological clinical applications in the liver, kidney and spleen is given.

The role of ultrasound in molecular imaging

Ultrasound has received less attention than other imaging modalities for molecular imaging, but has a number of potential advantages. It is cheap, widely available and portable. Using Doppler methods, flow information can be obtained easily and non-invasively. It is arguably the most physiological modality, able to image structure and function with less sedation than other modalities. This means that function is minimally disturbed, and multiple repeat studies or the effect of interventions can easily be assessed. High frame rates of over 200 frames a second are achievable on current commercial systems, allowing for convenient cardiac studies in small animals. It can be used to guide interventional or invasive studies, such as needle placement. Ultrasound is also unique in being both an imaging and therapeutic tool and its value in gene therapy has received much recent interest. Ultrasound biomicroscopy has been used for in utero imaging and can guide injection of virus and cells. Ultrahigh frequency ultrasound can be used to determine cell mechanical properties. The development of microbubble contrast agents has opened many new opportunities, including new functional imaging methods, the ability to image capillary flow and the possibility of molecular targeting using labelled microbubbles.

Characterization of focal hepatic lesions with contrast-enhanced C-cube gray scale ultrasonography

AIM: To characterize enhancement patterns of focal hepatic lesions using C-cube gray scale sonography with a microbubble contrast agent and to evaluate its usefulness in differential diagnosis of hepatic lesions.

METHODS: Fifty-four patients with 58 focal hepatic lesions were examined with Levovist-enhanced C-cube gray scale sonography. The final diagnosis of hepatic lesions was 29 primary liver cancers, 4 metastases, 8 hemangiomas, 12 focal nodular hyperplasias, 2 inflammatory pseudotumors of the liver and 3 angiomyolipomas. The initiation time of enhancement in various lesions and enhancement duration after administration of contrast agent were compared. Vascular findings in lesions were classified as peripheral enhancement, homogenous enhancement, mosaic enhancement and no enhancement depending on microbubble signals in the lesion relative to the liver parenchyma.

RESULTS: The initiation time of enhancement in hemangioma (48 ± 12 s) was significantly later compared to other lesions (P < 0.05). The enhancement duration of malignancies (69 ± 33 s in primary liver cancer, 61 ± 23 s in metastasis) was significantly shorter compared to benign lesions (P < 0.05). Intranodular enhancement appearing at arterial phase and decreasing at portal venous phase was considered characteristic for malignancy. Intranodular enhancement did not appear earlier than the liver parenchyma, and peripheral enhancement pattern was regarded as positive findings for hemangioma. Intranodular enhancement appeared in the arterial phase, and homogenous enhancement pattern sustained in the whole portal venous phase were regarded as positive findings for focal nodular hyperplasia. No microbubble signals appeared in two inflammatory pseudotumors of the liver.

CONCLUSION: C-cube gray scale sonography can demonstrate dynamic intranodular enhancement in various focal hepatic lesions. The information provided by this methodology may be useful in the differential diagnosis of hepatic lesions.

Evaluation of liver parenchymal blood flow with contrast-enhanced US: preliminary results in healthy and cirrhotic patients

RATIONALE AND OBJECTIVES

To determine whether changes in hepatic parenchymal blood flow in cirrhotic patients can be evaluated with contrast-enhanced ultrasound (US) after Levovist administration.

MATERIALS AND METHODS

Ten normal volunteers, 16 Child A and 16 Child C cirrhotic patients were evaluated with contrast-enhanced US. Frames obtained at progressively increasing pulse intervals of 2, 4, 7, and 10 seconds in the same scan plane during infusion of Levovist (300 mg/mL, 150 mL/h) have been digitally recorded. Pulse intervals versus signal intensity (PI-SI) plots were fitted to a straight line whose slope is proportional to the speed of blood in the liver parenchyma. Enhancement differences in late phase have been evaluated measuring the SI after 7 minutes from the beginning of the infusion.

RESULTS

The slope of the PI-SI plot of the Child A cirrhotic patients was significantly lower than the slope of the normal controls (P < 0.05); conversely, no significant differences were found between the slope of the patients with Child C cirrhosis and that of the normal controls. In comparison with the normal subjects, the average SI at late phase decreased significantly both in patients with Child A (P < 0.05) and Child C (P < 0.001) cirrhosis.

CONCLUSION

Microbubble contrast agents could provide a noninvasive tool to detect and monitor hemodynamic changes that occur in the cirrhotic liver. Changes in the hepatospecific properties at late phase have also been demonstrated.

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.

Ultrasonographic detection of focal liver lesions: increased sensitivity and specificity with microbubble contrast agents

Ultrasonography (US) is the first choice for screening patients with suspected liver lesions. However, due to a lack of contrast agents, US used to be less sensitive and specific compared with computed tomography (CT) and magnet resonance imaging (MRI). The advent of microbubble contrast agents increased both sensitivity and specificity dramatically. Rapid developments of the contrast agents as well as of special imaging techniques were made in recent years. Today numerous different US imaging methods exist which based either on Doppler or on harmonic imaging. They are using the particular behaviour of microbubbles in a sound field which varies depending on the energy of insonation (low/high mechanical index, MI) as well as on the properties of the agent themselves. Apart from just blood pool enhancement some agents have a hepatosplenic specific late phase. US imaging during this late phase using relatively high MI in phase inversion mode (harmonic imaging) or stimulated acoustic emission (SAE; Doppler method) markedly improves the detection of focal liver lesions and is also very helpful for lesion characterisation. With regards to detection, contrast enhanced US performs similarly to CT as shown by recent studies. Early results of studies using low MI imaging and the newer perfluor agents are also showing promising results for lesion detection. Low MI imaging with these agents has the advantage of real time imaging and is particularly helpful for characterisation of focal lesions based on their dynamic contrast behaviour. Apart from the techniques which based on the morphology of liver lesions there were some attempts for the detection of occult metastases or micrometastases by means of liver blood flow changes. Also in this field the use of US contrast agents appears to have advantages over formerly used non contrast-enhanced methods although no conclusive results are available yet.

Vascularity of hepatic VX2 tumors of rabbits: Assessment with conventional power Doppler US and contrast enhanced harmonic power Doppler US

AIM: To investigate the characteristics of the vascularity of hepatic metastasis.

METHODS: Six New Zealand rabbits, weighing averagely 2.7 ± 0.4 kg, were selected and operated to establish hepatic VX2 tumor carrier model. Hepatic VX2 tumors were then imaged with conventional B mode US, second harmonic imaging (SHI), color Doppler flow imaging (CDFI), power Doppler imaging (PDI) and harmonic PDI by a transducer S8 connected to HP-5500 ultrasound system. A kind of self made echo contrast agent was intravenously injected at a dose of 0.01 mL/kg through ear vein, and then the venous passage was cleaned with sterilized saline.

RESULTS: Totally, 6 hypoechoic lesions and 3 hyperechoic lesions were found in the six carrier rabbits with a mean size about 2.1 ± 0.4 cm under conventional B mode ultrasound, they were oval or round in shape with a clear outline or a hypoechoic halo at the margin of the lesions. Contrast agent could not change the echogenicity of the lesions under conventional B mode and SHI, however, it could greatly increase the flow sensitivity of the lesions under PDI and harmonic PDI. Nutrient artery of these metastatic lesions might also be well depicted under contrast enhanced PDI and harmonic PDI.

CONCLUSION: Our result suggested that contrast enhanced PDI, especially harmonic PDI, was a promised method in the detection of vascularity of hepatic tumor nodules.

Earlier hepatic vein transit-time measured by contrast ultrasonography reflects intrahepatic hemodynamic changes accompanying cirrhosis

BACKGROUND/AIMS

Non-invasive diagnosis of cirrhosis by transit-time analysis of an ultrasound contrast agent has been reported, even though the mechanism by which contrast arrives to the hepatic vein earlier in cirrhosis than in normal controls is unknown. The aim of this study is to assess whether the earlier appearance of contrast in the hepatic vein depends on intrahepatic or extrahepatic causes.

METHODS

There were 15 participants: six volunteers, three patients with hepatitis, and six with cirrhosis. The contrast agent was given intravenously, and transit-time analysis of the hepatic artery, portal vein and hepatic vein was performed. The time-acoustic intensity curves in the three vessels were analyzed by an image and cineloop display and quantification software package.

RESULTS

The hepatic artery and portal vein arrival times were not significantly different among the three groups. On the other hand, hepatic vein arrival times were significantly earlier in cirrhosis (median 18 seconds) compared with arrival times in hepatitis patients (median 30 seconds, P < 0.001) and in healthy volunteers (median 31 seconds, P < 0.001). These results give support to a previous pilot study and indicate that most of the time delay in hepatic vein arrival time between cirrhosis and the other groups originated from intrahepatic circulation abnormalities.

CONCLUSIONS

This study confirms that the earlier appearance of contrast in the hepatic vein observed in cirrhosis is due to intrahepatic, and not extrahepatic, hemodynamic changes.

Functional ultrasound methods in oncological imaging

The real time nature of ultrasound and functional methods such as Doppler ultrasound mean that ultrasound can claim to have always been a functional imaging method, but recent developments in quantitation, dramatic improvement in Doppler performance and now microbubbles have created many exciting new applications. These include methods for assessing the neovascularity of tumours, for following the effects of therapy and for predicting the likelihood of development of metastatic disease at the staging of primary tumours.

Quantitative microbubble enhanced transrectal ultrasound as a tool for monitoring hormonal treatment of prostate carcinoma

BACKGROUND

We quantified changes in prostate carcinoma vascularity treated with anti-androgens using color Doppler and power transrectal ultrasound in combination with microbubble contrast agent Levovist.

METHODS

Thirty-six men with prostate carcinoma were studied at baseline and at intervals during treatment. At each attendance, Levovist((R)) (10 ml, 300 mg/ml) was given as an iv bolus. Using quantitative analysis, we calculated the pre-enhancement scores, arrival time, time to peak, peak value, and area under the time-enhancement curve (AUC). These were compared to pre-treatment values and serial PSA measurements.

RESULTS

The pre-enhancement, peak value, and AUC each showed a marked response with reductions within one week. The average AUC declined to 68% +/- 9% (mean +/- standard error) by week 1, 56% +/- 9% by week 3, and 20% +/- 4% by week 6. A strong correlation with changes in the mean PSA (r = 0.95, P < 0.001) was also measured. In four patients, Doppler indices did not fall with PSA: two patients with the most marked discrepancy relapsed at 6 months.

CONCLUSION

The vascular enhancement declined with therapy, similar to PSA. Microbubble enhanced ultrasound can show early response to treatment.