Comparison of contrast-enhanced fundamental imaging, second-harmonic imaging, and pulse-inversion harmonic imaging

Acoustic Angiography: Superharmonic Contrast-Enhanced Ultrasound Imaging for Noninvasive Visualization of Microvasculature

Acoustic angiography is a contrast-enhanced ultrasound technique that relies on superharmonic imaging to form high-resolution, three-dimensional maps of the microvasculature. In order to obtain signal separation between tissue and contrast, acoustic angiography has been performed with dual-frequency transducers with nonoverlapping bandwidths. This enables a high contrast-to-tissue ratio, and the choice of a high frequency receiving element provides high resolution. In this chapter, we describe the technology behind acoustic angiography as well as the step-by-step implementation of this contrast enhanced microvascular imaging technique.

Post-processing radio-frequency signal based on deep learning method for ultrasonic microbubble imaging

Background

Improving imaging quality is a fundamental problem in ultrasound contrast agent imaging (UCAI) research. Plane wave imaging (PWI) has been deemed as a potential method for UCAI due to its’ high frame rate and low mechanical index. High frame rate can improve the temporal resolution of UCAI. Meanwhile, low mechanical index is essential to UCAI since microbubbles can be easily broken under high mechanical index conditions. However, the clinical practice of ultrasound contrast agent plane wave imaging (UCPWI) is still limited by poor imaging quality for lack of transmit focus. The purpose of this study was to propose and validate a new post-processing method that combined with deep learning to improve the imaging quality of UCPWI. The proposed method consists of three stages: (1) first, a deep learning approach based on U-net was trained to differentiate the microbubble and tissue radio frequency (RF) signals; (2) then, to eliminate the remaining tissue RF signals, the bubble approximated wavelet transform (BAWT) combined with maximum eigenvalue threshold was employed. BAWT can enhance the UCA area brightness, and eigenvalue threshold can be set to eliminate the interference areas due to the large difference of maximum eigenvalue between UCA and tissue areas; (3) finally, the accurate microbubble imaging were obtained through eigenspace-based minimum variance (ESBMV).

Results

The proposed method was validated by both phantom and in vivo rabbit experiment results. Compared with UCPWI based on delay and sum (DAS), the imaging contrast-to-tissue ratio (CTR) and contrast-to-noise ratio (CNR) was improved by 21.3 dB and 10.4 dB in the phantom experiment, and the corresponding improvements were 22.3 dB and 42.8 dB in the rabbit experiment.

Conclusions

Our method illustrates superior imaging performance and high reproducibility, and thus is promising in improving the contrast image quality and the clinical value of UCPWI.

Value of contrast-enhanced ultrasonography for the detection and quantification of enthesitis vascularization in patients with spondyloarthritis

OBJECTIVE

To evaluate if contrast-enhanced ultrasound (CEUS) can improve the detection and quantification of the vascularization of mild enthesitis in spondyloarthritis (SpA) and to evaluate the influence of nonsteroidal antiinflammatory drugs (NSAIDs) on such detection.

METHODS

Fourteen patients with mildly active SpA were evaluated at 3 consecutive visits: at baseline while undergoing NSAID treatment (V1), after 1 week of stopping NSAIDs (V2), and after 1 week of resuming NSAIDs (V3). At each visit, enthesitis was evaluated clinically and by power Doppler US (PDUS). A selected enthesis with a doubtful PDUS vascularization signal was studied by CEUS in 2 steps: (1) using a dedicated technology that preserves microbubbles (Contrast Tuned Imaging technology [CEUS-CnTI]) and (2) using high PD (CEUS-PD) to destroy microbubbles. A linear mixed model statistical analysis, taking visits and contrast agent as fixed factors and the patient as a random factor, was used.

RESULTS

Disease activity and PDUS findings increased between V1 and V2 and then decreased between V2 and V3. As compared with PDUS alone, CEUS-PD and CEUS-CnTI each detected 1 supplementary vascularized enthesis at V1, CEUS-PD detected 1 vascularized enthesis and CEUS-CnTI detected 3 vascularized entheses at V2, and CEUS-PD and CEUS-CnTI each detected 2 vascularized entheses at V3. The mean inflammation score was increased by the use of CEUS (P = 0.04). This score increased between V1 and V2 (P = 0.03 by CEUS-PD and P = 0.01 by CEUS-CnTI) and decreased between V2 and V3.

CONCLUSION

CEUS improved the detection of enthesitis in SpA patients by confirming all doubtful enthesitis signals and confirming the absence of enthesis vascularization. The use of NSAIDs influenced the detection of vascularization.

Computer-aided diagnosis for contrast-enhanced ultrasound in the liver

Computer-aided diagnosis (CAD) has become one of the major research subjects in medical imaging and diagnostic radiology. The basic concept of CAD is to provide computer output as a second opinion to assist radiologists’ image interpretations by improving the accuracy and consistency of radiologic diagnosis and also by reducing the image-reading time. To date, research on CAD in ultrasound (US)-based diagnosis has been carried out mostly for breast lesions and has been limited in the fields of gastroenterology and hepatology, with most studies being conducted using B-mode US images. Two CAD schemes with contrast-enhanced US (CEUS) that are used in classifying focal liver lesions (FLLs) as liver metastasis, hemangioma, or three histologically differentiated types of hepatocellular carcinoma (HCC) are introduced in this article: one is based on physicians’ subjective pattern classifications (subjective analysis) and the other is a computerized scheme for classification of FLLs (quantitative analysis). Classification accuracies for FLLs for each CAD scheme were 84.8% and 88.5% for metastasis, 93.3% and 93.8% for hemangioma, and 98.6% and 86.9% for all HCCs, respectively. In addition, the classification accuracies for histologic differentiation of HCCs were 65.2% and 79.2% for well-differentiated HCCs, 41.7% and 50.0% for moderately differentiated HCCs, and 80.0% and 77.8% for poorly differentiated HCCs, respectively. There are a number of issues concerning the clinical application of CAD for CEUS, however, it is likely that CAD for CEUS of the liver will make great progress in the future.

Determination of breast cancer response to bevacizumab therapy using contrast-enhanced ultrasound and artificial neural networks

OBJECTIVE

The purpose of this study was to evaluate contrast-enhanced ultrasound and neural network data classification for determining the breast cancer response to bevacizumab therapy in a murine model.

METHODS

An ultrasound scanner operating in the harmonic mode was used to measure ultrasound contrast agent (UCA) time-intensity curves in vivo. Twenty-five nude athymic mice with orthotopic breast cancers received a 30-microL tail vein bolus of a perflutren microsphere UCA, and baseline tumor imaging was performed using microbubble destruction-replenishment techniques. Subsequently, 15 animals received a 0.2-mg injection of bevacizumab, whereas 10 control animals received an equivalent dose of saline. Animals were reimaged on days 1, 2, 3, and 6 before euthanasia. Histologic assessment of excised tumor sections was performed. Time-intensity curve analysis for a given region of interest was conducted using customized software. Tumor perfusion metrics on days 1, 2, 3, and 6 were modeled using neural network data classification schemes (60% learning and 40% testing) to predict the breast cancer response to therapy.

RESULTS

The breast cancer response to a single dose of bevacizumab in a murine model was immediate and transient. Permutations of input to the neural network data classification scheme revealed that tumor perfusion data within 3 days of bevacizumab dosing was sufficient to minimize the prediction error to 10%, whereas measurements of physical tumor size alone did not appear adequate to assess the therapeutic response.

CONCLUSIONS

Contrast-enhanced ultrasound may be a useful tool for determining the response to bevacizumab therapy and monitoring the subsequent restoration of blood flow to breast cancer.

Quantification of synovial and erosive changes in rheumatoid arthritis with ultrasound--revisited

Synovitis is a predictive factor of irreversible changes in the joints, tendons, and ligaments in patients with rheumatoid arthritis (RA). Therefore, the early demonstration of reversible, pre-erosive inflammatory features to diagnose RA, the monitoring of disease activity, and the response to therapy are of great importance. Technical developments in ultrasound now allow the quantification of synovitis and erosions, and enable the assessment and follow-up of disease activity. However, both the subjective and objective quantification techniques are associated with different problems. This review article highlights the advantages and disadvantages of sonographic quantification, and revisits the somewhat controversial positions apparent in the current literature. Familiarity with the imaging findings and the scoring systems used to characterize erosive changes are prerequisites for considerably improving the detection and monitoring of synovitis and erosions. The role of ultrasound in the diagnostic approach to RA, particularly in the quantification of synovial and erosive changes, will be explored and the current literature will be reviewed.

Nonlinear pulse compression in pulse-inversion fundamental imaging

Coded excitation can be applied in ultrasound contrast agent imaging to enhance the signal-to-noise ratio with minimal destruction of the microbubbles. Although the axial resolution is usually compromised by the requirement for a long coded transmit waveforms, this can be restored by using a compression filter to compress the received echo. However, nonlinear responses from microbubbles may cause difficulties in pulse compression and result in severe range side-lobe artifacts, particularly in pulse-inversion-based (PI) fundamental imaging. The efficacy of pulse compression in nonlinear contrast imaging was evaluated by investigating several factors relevant to PI fundamental generation using both in-vitro experiments and simulations. The results indicate that the acoustic pressure and the bubble size can alter the nonlinear characteristics of microbubbles and change the performance of the compression filter. When nonlinear responses from contrast agents are enhanced by using a higher acoustic pressure or when more microbubbles are near the resonance size of the transmit frequency, higher range side lobes are produced in both linear imaging and PI fundamental imaging. On the other hand, contrast detection in PI fundamental imaging significantly depends on the magnitude of the nonlinear responses of the bubbles and thus the resultant contrast-to-tissue ratio (CTR) still increases with acoustic pressure and the nonlinear resonance of microbubbles. It should be noted, however, that the CTR in PI fundamental imaging after compression is consistently lower than that before compression due to obvious side-lobe artifacts. Therefore, the use of coded excitation is not beneficial in PI fundamental contrast detection.

Power Doppler sonography and pulse-inversion harmonic imaging in evaluation of rheumatoid arthritis synovitis

OBJECTIVE

This study evaluates the value of contrast-enhanced pulse-inversion harmonic imaging (PIHI) to detect synovial vascularization and thus the therapeutic effects of prednisolone treatment on the inflammation in finger joints in rheumatoid arthritis (RA).

MATERIALS AND METHODS

Before and after 7 days of mid- to high-dose steroid therapy, blood tests and clinical and sonographic examinations were assessed in 14 patients. Two hundred eighty finger joints (metacarpophalangeal [MCP] I-V, interphalangeal [IP], and proximal interphalangeal [PIP] II-V) were investigated on power Doppler sonography to determine, in each patient, the finger joint with the strongest hypervascularization and to score the synovial vascularization. Further dynamic examination of the selected joint was performed on PIHI after i.v. administration of a second-generation sonographic contrast medium. Vascularization was quantified by calculating the area under the time-intensity curves. The changes in signal intensities before and after therapy were correlated with clinical examinations (disease activity score [DAS]).

RESULTS

The score of the joint with the strongest hypervascularization assessed by power Doppler sonography decreased significantly from 1.7 to 1.3 (p < 0.01); however, in six patients, no change was assessed after steroid therapy. In all patients, a significant reduction in PIHI signals was observed after therapy (p < 0.05). The baseline and follow-up median values of the area under the time-intensity curves were 8.56 +/- 1.28 and 7.65 +/- 0.66, respectively. The median values of the DAS decreased significantly from 4.90 +/- 0.86 to 3.6 +/- 1.0 (p < 0.01) 7 days after the steroid therapy.

CONCLUSION

PIHI and power Doppler sonography enable the detection of synovial perfusion alterations after steroid therapy and, therefore, may be useful tools for the evaluation of active inflammation in RA and for the assessment of therapeutic response. However, minor changes of synovial vascularization can be better detected on PIHI than on power Doppler sonography.

Echo-enhanced ultrasound with pulse inversion imaging: A new imaging modality for the differentiation of cystic pancreatic tumours

AIM: To describe and discuss echo-enhanced sonography in the differential diagnosis of cystic pancreatic lesions.

METHODS: The pulse inversion technique (with intravenous injection of 2.4 mL SonoVue^®) or the power-Doppler mode under the conditions of the 2^nd harmonic imaging (with intravenous injection of 4 g Levovist^®) was used for echo-enhanced sonography.

RESULTS: Cystadenomas frequently showed many vessels along fibrotic strands. On the other hand, cystadenocarcinomas were poorly and chaotically vascularized. ”Young pseudocysts” were frequently found to have a highly vascularised wall. However, the wall of the ”old pseudocysts” was poorly vascularized. Data from prospective studies demonstrated that based on these imaging criteria the sensitivities and specificities of echo-enhanced sonography in the differentiation of cystic pancreatic masses were > 90%.

CONCLUSION: Cystic pancreatic masses have a different vascularization pattern at echo-enhanced sonography. These characteristics are useful for their differential diagnosis, but histology is still the gold standard.

Echo-enhanced ultrasound--a new imaging modality for the differentiation of pancreatic lesions

INTRODUCTION

Echo-enhanced ultrasound is a newly available mode of imaging for differential diagnosis of pancreatic tumours. Ductal carcinomas are often hypovascularised compared with the surrounding tissue. Neuroendocrine tumours, on the other hand, are hypervascularised lesions. Tumours associated with pancreatitis have a different vascularisation pattern depending on inflammation and necrosis. Cystadenomas frequently have many vessels along the fibrotic strands.

RESULTS

Data from prospective studies have demonstrated, on the basis of these imaging criteria, that the sensitivity and specificity of echo-enhanced sonography for differentiation of pancreatic masses are >or=85 and >or=90%, respectively.

CONCLUSIONS

Pancreatic tumours have a different vascularisation pattern in echo-enhanced ultrasound. These characteristics can be used with high diagnostic accuracy for differential diagnosis.

Differentiation of cystic pancreatic neoplasms and pseudocysts by conventional and echo-enhanced ultrasound

BACKGROUND AND AIMS

Echo-enhanced sonography is a non-invasive and increasingly used procedure for the differentiation of pancreatic tumors. However, the diagnostic accuracy of this procedure compared to conventional ultrasound for the differential diagnosis of cystic pancreatic neoplasms from pseudocysts has never been investigated in a prospective study.

METHODS

Thirty-one patients with a cystic pancreatic lesion at the conventional ultrasound (mean age 57 years, range 36-82 years) were included in the study. Sonography was performed by an experienced examiner who was unaware of the patients' clinical diagnosis. The exact diagnosis was based on histological evidence from biopsy examination (surgical or transabdominal fine needle biopsy for all cystic neoplasms and five pseudocysts), or a follow-up of at least 18 months (four pseudocysts).

RESULTS

Of the 31 patients, 19 had cystadenomas, three had cystadenocarcinomas, and nine had pseudocysts. Only 27% of the cystadenomas and 67% of the pseudocysts could be correctly classified by conventional ultrasound. Conversely, 95% of the cystadenomas (P = 0.0001) and all pseudocysts were diagnosed correctly by echo-enhanced sonography. The sensitivity of echo-enhanced sonography with respect to diagnosing cystadenoma was 95% and its specificity was 92%. The corresponding values for pseudocysts were both 100%.

CONCLUSION

Echo-enhanced sonography has a high sensitivity and specificity in the differential diagnosis of cystic pancreatic tumors. With this procedure the differentiation of cystadenomas and pseudocysts can be improved. However, histology is the standard of reference.

Low mechanical index contrast-enhanced ultrasound better reflects high arterial perfusion of liver metastases than arterial phase computed tomography

RATIONALE AND OBJECTIVES

We investigated whether observing the arterial vascularization of liver metastases by contrast-enhanced ultrasound with low mechanical index (low-MI) imaging offers additional diagnostic information for the characterization of the liver lesions.

METHODS

Twenty nine patients with untreated liver metastases of different primaries were examined. Measurements were performed using a low frame rate, low-MI pulse inversion technique after injection of 2.4 mL SonoVue. The relative maximum signal intensity of the liver lesions related to the normal liver tissue was quantified. Ultrasound findings were compared with contrast-enhanced, dual-phase computed tomography (CT) using a pattern-based classification scheme.

RESULTS

Compared with contrast-enhanced CT, this modality better detects arterial perfusion. Metastases, even those usually considered hypovascularized, often showed homogeneous enhancement (66%) and higher arterial vascularization than normal liver tissue. CT did not show a comparable vascularization pattern (P < 0.001) or any similarly early signal intensity (P < 0.001).

CONCLUSIONS

Contrast-enhanced CT may not be able to visualize short-lasting but large differences of the arterial perfusion of liver metastases, as does contrast-enhanced low-MI ultrasound. This offers new methods for their characterization and for monitoring of therapeutic effects.

Evaluation of diagnostic criteria for liver metastases of adenocarcinomas and neuroendocrine tumours at conventional ultrasound, unenhanced power Doppler sonography and echo-enhanced ultrasound

PURPOSE

In order to improve the differential diagnosis between liver metastases of neuroendocrine tumours and adenocarcinomas, criteria for the masses at conventional ultrasound, unenhanced power Doppler sonography and echo-enhanced ultrasound were evaluated.

METHODS

Seventy-three patients with histologically proven liver metastases of a neuroendocrine tumour (n = 26) or an adenocarcinoma (n = 47) were investigated by conventional ultrasound as well as unenhanced power Doppler sonography and echo-enhanced ultrasound focusing on specific properties of the lesions.

RESULTS

Liver metastases of neuroendocrine tumours and adenocarcinomas showed a different contrast behaviour with echo-enhanced sonography. A hypervascularisation at the arterial and capillary phase were found in 85% of the neuroendocrine metastases, and in 17% of the masses of adenocarcinomas, respectively (p < 0.05).

CONCLUSIONS

The successful treatment of liver metastases requires a highly sensitive and specific diagnostic procedure for their differentiation. A hypervascularisation of the lesions during the arterial and capillary phase at echo-enhanced ultrasound may point to a neuroendocrine primary tumour. However, histology is the only standard of reference for the differentiation of liver metastases, and is necessary for optimal therapy.

Echo-enhanced sonography--an increasingly used procedure for the differentiation of pancreatic tumors

Echo-enhanced sonography is increasingly being used for differential diagnosis of pancreatic tumors. Ductal carcinomas are often hypovascularized compared with the surrounding tissue. On the other hand, neuroendocrine tumors are hypervascularized lesions. Tumors associated with pancreatitis have a different vascularization pattern depending on inflammation and necrosis. Cystadenomas frequently show many vessels along the fibrotic strands. Pancreatic tumors have a different vascularization pattern in echo-enhanced sonography. These characteristics can be used for differential diagnosis. However, histology is the standard of reference.

Differential diagnosis of focal liver lesions in signal-enhanced ultrasound using BR 1, a second-generation ultrasound signal enhancer

AIM

The aim was to evaluate the diagnostic value of contrast-enhanced ultrasound in the differential diagnosis of focal liver lesions, in a blinded experiment. In clinical routine the examiner can generally be influenced by the patient's history.

METHOD

62 patients with focal liver lesions, which could not be clearly differentiated and diagnosed by conventional ultrasound, were examined with contrast-enhanced (BR1, SonoVue, Bracco) ultrasound and included in a blinded prospective and randomized study. The examinations performed on a Sequoia 512 (Acuson) in a coherent contrast imaging method were recorded by an S-VHS recorder and afterwards analyzed by an examiner who did not know the patient's history. The basis of the diagnosis was the dynamic appearance and enhancement of the ultrasound contrast enhancer in different phases of liver perfusion. The conformation of the diagnoses was made by corresponding reference methods, as computer tomography, magnetic resonance imaging, biopsy and clinical follow-up.

RESULTS

The following diagnoses were confirmed by reference methods: 18 patients with metastases, 4 hepatocellular carcinomas, 19 haemangiomas, 6 focal nodular hyperplasias, 13 patients with focal fatty infiltration and 2 patients with focal fatty sparing. 59 out of 62 patients with one or more liver lesions were correctly diagnosed by contrast-enhanced ultrasound.

CONCLUSION

Second-generation ultrasound contrast enhancers improve the differential diagnosis of benign and malignant liver lesions considerably, especially in a blinded study.

Therapeutic response evaluation of malignant hepatic masses treated by interventional procedures with contrast-enhanced agent detection imaging

OBJECTIVE

To assess the usefulness of microbubble contrast-enhanced agent detection imaging in evaluating the therapeutic response of malignant hepatic masses to treatment with interventional procedures.

METHODS

Fifty-eight patients with 68 hepatocellular carcinomas and 6 metastases who were treated with interventional procedures were evaluated with SH U 508A-enhanced agent detection imaging and helical computed tomography. Helical computed tomography was also performed to help establish the outcome of therapy with unenhanced computed tomography 2 weeks after transcatheter arterial chemoembolization and with dynamic contrast-enhanced computed tomography 1 day after radio frequency ablation or percutaneous ethanol injection. The studies were reviewed separately and randomly, and the sensitivity and specificity of agent detection imaging for detection of viable tumor residue were determined by follow-up imaging performed at least 3 months later.

RESULTS

Follow-up computed tomography or magnetic resonance imaging revealed complete tumor responses in 44 (59.5%) of 74 cases after the therapeutic procedures. The sensitivity of agent detection imaging was 94.7% after transcatheter arterial chemoembolization and 72.7% after radio frequency ablation and percutaneous ethanol injection. The specificity of agent detection imaging for the detection of residual tumors was 80% after transcatheter arterial chemoembolization and 79.2% after radio frequency ablation and percutaneous ethanol injection. The false-positive rate for agent detection imaging in cases of radio frequency ablation or percutaneous ethanol injection was 20.8% (5 of 24), resulting from reactive hyperemia or vascularity within the safety margin. In the assessment of the therapeutic effects, the concordance of contrast-enhanced agent detection imaging with helical computed tomography was statistically significant after transcatheter arterial chemoembolization (P < .00001) and radio frequency ablation or percutaneous ethanol injection (P < .02).

CONCLUSIONS

Contrast-enhanced agent detection imaging proved useful and as effective as helical computed tomography for evaluating the therapeutic effects of interventional therapeutic procedures for malignant hepatic masses.

Contrast-enhanced ultrasound imaging for aortic stent-graft surveillance

PURPOSE

To compare unenhanced and enhanced ultrasound imaging to computed tomographic angiography (CTA) or magnetic resonance angiography (MRA) for surveillance of aortic endografts.

METHODS

Thirty consecutive patients (29 men; mean age 69 years, range 50-82) who underwent endovascular aortic aneurysm repair agreed to participate in a follow-up program. Patients underwent CTA (26/30) or MRA (4/30), plain abdominal radiography, and unenhanced and enhanced ultrasound examinations at 3, 12, and 24 months to evaluate aneurysm diameter, endoleaks, and graft patency. The accuracy of ultrasound was compared with CTA or MRA as the reference standards.

RESULTS

Twenty-six patients reached the 24-month assessment (mean follow-up 30 months, range 6-60). All endoleaks detected by CTA or MRA were confirmed by enhanced ultrasound; the aneurysm diameter in these patients remained unchanged or increased. In patients without endoleaks on any imaging method, the sac diameter remained unchanged or decreased. Endoleaks disclosed by enhanced ultrasound alone, all type II, numbered 16 at 3 months, 6 at 12 months, and 3 at 24 months. In this group, the aneurysm diameter remained unchanged or increased. Enhanced ultrasound yielded 100% sensitivity in detecting endoleaks, but compared with CTA and MRA, all endoleaks detected by enhanced ultrasound alone were false positives (mean specificity 65%). Nevertheless, because changes in the postoperative aneurysm diameter were similar in patients with endoleaks detectable on CTA/MRA and on enhanced ultrasound ("true positives") and in those with endoleaks detectable only on enhanced ultrasound ("false positives"), some endoleaks were possibly "true positive" results.

CONCLUSIONS

Enhanced ultrasound is a useful method in the long-term surveillance of endovascular aortic aneurysm repairs, possibly in association with CTA or MRA. Enhanced ultrasound also seems able to identify endoleaks missed by other imaging techniques, but this conclusion awaits further investigation.

Pulse-inversion harmonic imaging improves lesion conspicuity during US-guided biopsy

PURPOSE

To assess the feasibility of percutaneous biopsy of low-conspicuity focal liver lesions with use of pulse-inversion harmonic imaging (PIHI) guidance in the late phase after injection of microbubble contrast agent.

MATERIALS AND METHODS

Twelve patients referred for ultrasound (US)-guided biopsy had liver lesions lacking adequate conspicuity to undergo biopsy under conventional ultrasound (US) guidance. They underwent biopsy procedures performed with the use of PIHI guidance in the late phase after injection of Levovist. The conspicuity of lesions, procedure time, number of passes, and success and complication rates were documented and compared to a control group. The control group consisted of retrospective analysis of 19 patients who had undergone conventional US-guided biopsy procedures performed by the same radiologist.

RESULTS

After contrast material injection, all lesions had sufficient increases in conspicuity to be targeted under PIHI guidance. Procedure time was prolonged in the PIHI group (66 minutes; range, 30-120 min; vs control, 33 min; range, 15-77 min; P <.01, Wilcoxon signed-rank test). The number of passes was greater in the PIHI group (1.9 +/- 0.3; vs control, 1.4 +/- 0.6; P <.01, chi(2) test). No statistically significant difference was observed when comparing success and complication rates.

CONCLUSION

PIHI in the late phase after injection of Levovist generated clear delineation of focal liver lesions in all cases, allowing an accurate and safe sampling. This technique broadens the scope of US-guided biopsy to lesions lacking adequate conspicuity on conventional US.