An Innovative Ultrasound Technique for Evaluation of Tumor Vascularity in Breast Cancers: Superb Micro-Vascular Imaging

Clinical Applications of Superb Microvascular Imaging in the Liver, Breast, Thyroid, Skeletal Muscle, and Carotid Plaques

This article reviews the clinical applications of Superb Microvascular Imaging (SMI; Canon Medical Systems, Otawara, Japan) in the liver, breast, thyroid, skeletal muscle, and carotid plaques. Diseases that are closely associated with angiogenesis can be diagnosed by SMI in a relatively early phase, and using SMI can prevent adverse reactions associated with the contrast agents used in contrast-enhanced ultrasound. Super Microvascular Imaging also shows particular value in grading disease activities and monitoring therapeutic responses. Although SMI has some limitations, such as a lack of clinical standards, it can add information to conventional ultrasound examinations and may become a noninvasive alternative to invasive diagnostic procedures for many clinical conditions.

Evaluation of Ovarian Vascularity in Children by Using the "Superb Microvascular Imaging" Ultrasound Technique in Comparison With Conventional Doppler Ultrasound Techniques

OBJECTIVES

The aim of this study was to assess the feasibility of the novel "superb microvascular imaging" (SMI) Doppler ultrasound technique to detect ovarian vascularity in healthy children and to compare it with the conventional Doppler ultrasound techniques.

METHODS

This prospective study included 140 girls, aged 3 to 18 years, for which an abdominal ultrasound study was requested in the pediatrics outpatient clinics for suspicion of nonovarian pathologies. Nineteen individuals were excluded from the study due to incomplete ultrasound scanning. For the remaining 121 cases, gray scale ultrasound evaluation was performed followed by color Doppler imaging, power Doppler imaging, advanced dynamic flow, color SMI, and monochrome SMI to detect the presence and degree of vascularity in the ovaries. Ultrasound scanning was performed for all participants by the same doctor by using curvilinear probe via the suprapubic approach, and the images were independently evaluated by 3 different observers. The images were assessed with regard to the degree of vascularity and the presence of artifacts.

RESULTS

A total of 146 ovaries (42 right, 54 left, and 25 bilateral) were examined by sonography. The mean interrater agreement regarding the detection of vascularity was moderate for the color Doppler imaging, power Doppler imaging, advanced dynamic flow, and monochrome SMI techniques (κ = 0.514-0.551) and substantial for the color SMI technique (κ = 0.636) (P < .001). The techniques were found to be statistically significant for detecting vascularity: monochrome SMI > color SMI > power Doppler imaging > color Doppler imaging > advanced dynamic flow (P < .001).

CONCLUSION

SMI is a promising tool that can detect ovarian vascularity more effectively than the conventional Doppler ultrasound techniques.

Ultrasensitive Ultrasound Microvessel Imaging for Characterizing Benign and Malignant Breast Tumors

Tumor angiogenesis plays an important role during breast tumor growth. However, conventional Doppler has limited sensitivity to detect small blood vessels, resulting in a large overlap of Doppler features between benign and malignant tumors. An ultrasensitive ultrasound microvessel imaging (UMI) technique was recently developed. To evaluate the performance of UMI, we studied 44 patients with 51 breast masses. Tumor pathology served as the gold standard: 28 malignancies and 23 benignities. UMI provided a significant improvement in depicting smaller vessels compared with conventional Doppler. The microvessel morphologies observed on UMI were associated with tumor benign/malignant classification. The diagnostic accuracy of correct Breast Imaging Reporting and Data System (BI-RADS) classification rate (BI-RADS ≥4a: test positive; BI-RADS ≤3: test negative) as a fraction of total mass population was improved by 16% after combining conventional ultrasound with UMI compared with using conventional ultrasound alone. This improvement indicates the potential of UMI in reducing unnecessary benign biopsies and avoiding missed malignant biopsies.

Seeing the Unseen: Evaluating Testicular Vascularity in Neonates by Using the Superb Microvascular Imaging Ultrasound Technique

OBJECTIVES

To evaluate testicular vascularity in neonates by using the novel Superb Microvascular Imaging (SMI; Toshiba Medical Systems Corporation, Tokyo, Japan) ultrasound (US) technique and to compare this technique to conventional Doppler US techniques.

METHODS

A total of 140 healthy neonates between 2 and 60 days old who were admitted for routine screening were included in the study. However, in 9 cases, the Doppler study could not be completed. In the remaining 131 cases, color Doppler imaging (CDI), power Doppler imaging (PDI), Advanced Dynamic Flow (ADF; Toshiba Medical Systems), and monochrome SMI (mSMI) techniques were performed on a single representative testicle. Real-time cine images were captured for 5 to 10 seconds for each technique by using a high-frequency (7.2-14-MHz) linear transducer. The images were evaluated by 3 observers using a grading system to quantify the degree of vascularity and artifact interference.

RESULTS

A total of 131 testicles (74 right and 57 left) were evaluated, and vascularity was shown in 110 (84%) testicles with CDI, 109 (83%) with PDI, 94 (72%) with ADF, and 128 (98%) with mSMI by the consensus of all observers. The Doppler techniques were ranked from highest to lowest in the following order based on the degree of vascularity detected: mSMI > PDI > CDI > ADF (P < .001). Based on the presence of artifacts, the Doppler techniques were ranked as follows from high to low: ADF > CDI > PDI > mSMI (P < .001).

CONCLUSIONS

Superb Microvascular Imaging is a promising US technique that appears to detect testis vascularity better than conventional Doppler US techniques; however, further research is needed to support the results of this study.

Characterization of Breast Microcalcifications Using a New Ultrasound Image-Processing Technique

OBJECTIVES

To evaluate a new commercial image-processing technique (MicroPure; Toshiba America Medical Systems, Tustin, CA) for detection and characterization of breast microcalcifications in patients undergoing stereotactic or ultrasound-guided biopsies using mammography as the reference standard.

METHODS

One hundred female patients, with a total of 104 lesions, scheduled for an image-guided biopsy of an area with breast microcalcifications (identified on a prior mammogram) underwent MicroPure examinations of the breast using an Aplio XG scanner (Toshiba America Medical Systems) with a broad-bandwidth linear array. MicroPure combines nonlinear imaging and speckle suppression to mark suspected calcifications as white spots in a blue overlay image. Four independent and blinded readers (2 radiologists and 2 physicists) analyzed 208 digital clips consisting of dual grayscale ultrasound and MicroPure imaging, counting the number of microcalcifications seen with MicroPure. The observers also assessed the level of suspicion on a qualitative, visual analog, 6-point scale from 0 (no findings) over 1 (benign) to 5 (malignant).

RESULTS

The mean number of microcalcifications ± SD seen was 6.3 ± 3.5, whereas mammography saw 28.9 ± 24.6 (P = .66). When the MicroPure level of suspicion scores were compared with pathologic results using a receiver operating characteristic curve analysis, the areas under the curve ranged from 0.54 to 0.59. Nonetheless, malignant cases were seen to have significantly more microcalcifications than benign cases (mean number of microcalcifications, 6.9 ± 5.1 versus 5.3 ± 3.7; P = .02).

CONCLUSIONS

MicroPure can be used to identify areas with breast microcalcifications but cannot effectively characterize such areas. Instead, MicroPure may represent a new imaging method for guiding a biopsy to areas of microcalcifications.

Vascular index measured by smart 3-D superb microvascular imaging can help to differentiate malignant and benign breast lesion

Purpose: The purpose of our study was to prospectively evaluate the diagnostic performance of the vascular index (VI, defined as the ratio of Doppler signal pixels to pixels in the total lesion) measured via Smart 3-D superb microvascular imaging (SMI) for breast lesions.

Patients and methods: Two hundred and thirty-two consecutive patients with 236 breast lesions referred for biopsy at Peking Union Medical College Hospital were enrolled in the study from December 2016 to November 2017. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of VI were calculated with histopathologic results as the reference standard.

Results: Of the 236 breast lesions, 121 were malignant and 115 were benign. The mean VI was significantly higher in malignant lesions (9.7±8.2) than that in benign ones (3.4±3.3) (P<0.0001). Sensitivity, specificity, PPV, NPV and accuracy of VI (4.0 as the threshold) were respectively: 76.0%, 66.1%, 70.2%, 72.4% and 71.2% (P<0.05).

Conclusion: Smart three-dimensional (3-D) SMI is a noninvasive tool using two-dimensional (2-D) scanning to generate 3-D vascular architecture with a high-resolution image of micro-vessels. This can be used as a qualitative guide to identify the optimal 2-D SMI plane with the most abundant vasculature to guide VI quantitative measurements of breast lesions. Smart 3-D SMI may potentially serve as a noninvasive tool to accurately characterize benign versus malignant breast lesions.

Primary Application of Micro-Flow Imaging Technology in the Diagnosis of Hepatic Tumors

The purpose of the study was to evaluate the vascular architecture of focal liver lesions with the newly released non-contrast micro-flow imaging (MFI) technique. Eighty patients with 80 hepatic tumors were enrolled in this study. The richness of displayed blood flow was first compared with color Doppler flow imaging using grades according to Adler's method. The results indicated that MFI outperformed color Doppler flow imaging with a statistically significant difference (p <0.0001). With the enhanced position in arterial phase of contrast-enhanced ultrasound imaging as the ground truth, the displayed blood flow distribution within tumors in MFI was further evaluated. The coincidence rate between MFI and contrast-enhanced ultrasound was 73.75% (59/80), which was higher than that of color Doppler flow imaging (52.5%, 42/80) (p < 0.0001). Moreover, for the five cases of focal nodular hyperplasia, MFI clearly revealed the spoke-wheel or radiating intra-tumoral vasculature, a finding specific to the diagnosis of focal nodular hyperplasia.

Ultrasound Microvascular Blood Flow Evaluation: A New Tool for the Management of Thyroid Nodule?

BACKGROUND

Toshiba Medical System has developed a new Doppler technique [Superb Microvascular Imaging (SMI)] that has improved microvascular flow imaging. SMI depicts perinodular and intranodular thyroid microvascular flow in higher detail compared to standard colour Doppler (CD) and power Doppler (PD) imaging.

OBJECTIVE

Assess the nodular microvascular architecture by SMI compared to CD and PD features in a series of thyroid nodules submitted to fine needle aspiration cytology, in order to evaluate the potential of SMI in detecting thyroid cancer.

MATERIALS AND METHODS

From April 2016 to July 2017, 254 patients with thyroid nodules, evaluated as at high risk for malignancy in agreement with AACE/ACE/AME guidelines, were submitted to cytology. All nodules were previously submitted to ultrasound grayscale, CD, PD, and SMI evaluation. Benign and malignant nodules were stratified in accordance to the number of vessels visualised by SMI: score 1 with a maximum of two blood vessels and score 2 with three or more vessels.

RESULTS

Score 1 was found in 59.6% of benign nodules and in 17.9% of malignant nodules, whereas score 2 was found in 40.4% and in 82.1%, respectively (sensitivity 81.7%; specificity 60.5%, p < 0.001). Variables significantly associated with malignancy in the univariate analysis were gender (OR, 0.18; 95% CI, 0.08-0.37; p < 0.001), vascularity (OR, 1.91; 95% CI, 1.65-3.89; p < 0.001), and SMI (OR, 6.72; 95% CI, 3.89-11.59; p < 0.001); multivariate logistic model confirmed SMI score 2 as an independent risk factor for malignancy (OR, 6.99; 95% CI, 3.46-12.09; p < 0.001).

CONCLUSIONS

This prospective pilot study showed that SMI can depict intranodular flow in higher detail compared to CDI and PDI, thus improving thyroid cancer detection.

New Doppler imaging technique for assessing angiogenesis in breast tumors: correlation with immunohistochemically analyzed microvessels density

BACKGROUND

Microvessel density (MVD) is associated with grade and prognosis in breast tumors. However, conventional color Doppler flow (CDF) imaging has been limited to represent MVD of breast tumors.

PURPOSE

To evaluate whether a new Doppler imaging technique (AngioPLUS) can represent MVD of breast tumors.

MATERIAL AND METHODS

The institutional review board approved this retrospective study, and patients' informed consent was waived. CDF and AngioPLUS were available in pathologically confirmed 55 breast tumors of 53 women. For each lesion, vascular flow patterns (distribution and amount) of both Doppler images were retrospectively reviewed, and MVD was measured using immunohistochemical analysis of the biopsied tissue sections. MVD was subcategorized as low or high group with reference to the median. The associations between the Doppler features and MVD were evaluated using Fisher's exact test and Student's t test.

RESULTS

Of the 55 masses, 28 (50.9%) were benign and 27 (49.1%) were malignant. Vascular flow distribution and amount of both Doppler imaging were different between the benign and malignant lesions (CDF, P = 0.020 and P = 0.010; AngioPLUS, P = 0.002 and P = 0.005). MVD had no significant relationships with CDF features, but vascular flow distribution on AngioPLUS showed significant differences between the lesions with low and high MVD ( P = 0.020); Combined distribution was more frequent in the high MVD lesions than in the low MVD lesions (17/28, 60.7% vs. 6/27, 22.2%).

CONCLUSION

Our data confirmed the correlation between a new Doppler imaging technique, AngioPLUS, and MVD. We suggest that AngioPLUS can be used for assessing MVD in breast tumors.

Comparison of the Diagnostic Performance of Power Doppler Ultrasound and a New Microvascular Doppler Ultrasound Technique (AngioPLUS) for Differentiating Benign and Malignant Breast Masses

This study was performed to compare the diagnostic performance of power Doppler ultrasound (US) and a new microvascular Doppler US technique (AngioPLUS; SuperSonic Imagine, Aix-en-Provence, France) for differentiating benign and malignant breast masses. Power Doppler US and AngioPLUS findings were available in 124 breast masses with confirmed pathologic results (benign, 80 [64.5%]; malignant, 44 [35.5%]). The diagnostic performance of each tool was calculated to distinguish benign from malignant masses using a receiver operating characteristic curve analysis and compared. The area under the curve showed that AngioPLUS was superior to power Doppler US in differentiating benign from malignant breast masses, but the difference was not statistically significant.

Microvessel ultrasound of neonatal brain parenchyma: feasibility, reproducibility, and normal imaging features by superb microvascular imaging (SMI)

Objectives

To evaluate the feasibility and reproducibility of superb microvascular imaging (SMI) of the neonatal brain and to describe normal imaging features.

Methods

We performed transcranial ultrasound with SMI in 19 healthy term-born neonates. SMI was done according to a structured examination protocol, using two linear 18 MHz and 14 MHz transducers. Superficial and deep scans were acquired in the coronal and sagittal planes, using the left and right superior frontal gyri as anatomical landmarks. All SMI views were imaged by monochrome and colour SMI and evaluated with respect to visibility of extrastriatal (i.e. cortical and medullary) and striatal microvessels.

Results

We have described normal morphologic features of intraparenchymal brain microvasculature as “short parallel” cortical vessels, “smoothly curved” medullary vessels, and deep striatal vessels. In general, SMI performance was better on coronal views than on sagittal views. On superficial coronal scans, cortical microvessels were identifiable in 90–100%, medullary microvessels in 95–100%. On deep scans, cortical and medullary microvessels were visible in all cases, while striatal microvessels were identifiable in 71% of cases.

Conclusions

Cerebral SMI ultrasound is feasible and well-reproducible and provides a novel non-invasive imaging tool for the assessment of intraparenchymal brain microvasculature (extrastriatal and striatal microvessels) in neonates without the use of contrast.

Key Points

• Superb microvascular imaging (SMI) of the neonatal brain is feasible and reproducible.

• SMI depicts extrastriatal and striatal microvessels.

• SMI detects two types of extrastriatal microvessels: cortical and medullary.

Electronic supplementary material

The online version of this article (10.1007/s00330-018-5743-1) contains supplementary material, which is available to authorized users.

Significance of microvascular evaluation of ductal lesions on breast ultrasonography: Influence on diagnostic performance

We aim to investigate the significance of microvascular ultrasonography in breast ductal lesions for distinguishing benign from malignant lesions. Sixty-two ductal lesions were evaluated with gray-scale and three Doppler techniques before biopsy, Superb Microvascular Imaging (SMI), color Doppler (CDI), and power Doppler imaging (PDI). We evaluated number, distribution, and morphology of vessels. The area under the ROC curve of combined use of Doppler imaging was greater than that of gray-scale only and SMI had higher value than CDI and PDI (p < 0.05). Microvascular ultrasonography improves diagnostic performance that distinguishes benign from malignant breast ductal lesions, and SMI is superior to CDI and PDI.

Evaluation of Intraplaque Neovascularization Using Superb Microvascular Imaging and Contrast-Enhanced Ultrasonography

BACKGROUND

Several studies have shown a linkage between intraplaque neovascularization (IPN) and plaque instability. Although contrast-enhanced ultrasonography (CEUS) may help visualize IPN in the carotid artery, its benefits are limited in Japan, where there is no health insurance coverage for contrast agents in medical imaging. Superb microvascular imaging (SMI), however, enables the depiction of low-velocity blood flow. The current study compares the diagnostic accuracy of SMI and CEUS in the evaluation of IPN.

METHODS

The SMI and CEUS video images were transferred to a workstation and then analyzed to determine whether intraplaque blood flow signals were detected with SMI and whether plaques were contrast-enhanced with carotid artery CEUS. The images generated were independently interpreted by 2 radiologic technologists and 1 neurologist.

RESULTS

Intraplaque enhancement was observed in 19 patients using CEUS while intraplaque blood flow signals were observed in 12 patients using SMI. A 100% specificity was recorded for SMI (all 12 patients with SMI-detected intraplaque blood flow showed contrast-enhanced plaques), while its sensitivity was 63% (8 of the 15 patients with no SMI-detected intraplaque blood flow showed contrast-enhanced plaques on CEUS).

CONCLUSIONS

The results of this study show that patients with SMI-detected blood flow will tend to have plaque enhancement using CEUS. This suggests that SMI, as a simpler, safer, and noninvasive technique, can facilitate the visualization of carotid artery IPN without the use of a contrast agent, as well as in the clinical evaluation of plaque instability.

Application of superb microvascular imaging in focal liver lesions

AIM

To explore the ability of superb microvascular imaging (SMI) in differential diagnosis of focal liver lesions (FLLs) and to compare SMI morphology findings to those of color Doppler ultrasound and enhanced imaging.

METHODS

Twenty-four patients with 31 FLLs were included in our study, with diagnoses of hemangioma (HE) (n = 17), hepatocellular carcinoma (HCC) (n = 5), metastatic lesions (n = 5), primary hepatic lymphoma (n = 1), focal nodular hyperplasia (FNH) (n = 2), and adenoma (n = 1). Nine lesions were pathologically diagnosed, and 22 lesions were radiologically confirmed, all of which were evaluated by at least two types of enhanced imaging techniques. All patients had undergone SMI. Patients were divided into subgroups based on pathological and radiological diagnoses to analyze SMI manifestations. We also compared the SMI manifestations of the most common malignant FLLs (HCCs and metastatic lesions) with those of the most common benign FLLs (HEs).

RESULTS

HEs were classified into three SMI subgroups: diffuse dot-like type (n = 6), strip rim type (n = 8), and nodular rim type (n = 3). The sizes of the three types of HEs were significantly different (P = 0.00, < 0.05). HCCs were classified into two subgroups: diffuse honeycomb type (n = 2) and non-specific type (n = 3). Four of the metastatic lesions were the strip rim type, and the other metastatic lesion was the thick rim type, which is the same as that of lymphoma. FNH was described as a spoke-wheel type, and adenoma as a diffuse honeycomb type. The SMI types of HCCs and metastatic lesions were significantly different from those of HEs (P = 0.048, < 0.05).

CONCLUSION

SMI technology enables microvascular evaluation of FLLs without using any contrast agent. For HEs, lesion size may affect SMI performance. SMI is able to provide useful information for differential diagnosis of HCCs and metastatic lesions from HEs.

Microflow imaging: New Doppler technology to detect low-grade inflammation in patients with arthritis

Aim

To assess the efficacy of microvascular imaging in detecting low-grade inflammation in arthritis compared with Power Doppler ultrasound (PDUS).

Method and materials

Patients presenting for ultrasound with arthralgia were assessed with grey-scale, PDUS and Superb Microvascular Imaging (SMI). Videoclips were stored for analysis at a later date. Three musculoskeletal radiologists scored grey-scale changes, signal on PDUS and/or SMI within these joints. If a signal was detected on both PDUS and SMI, the readers graded the conspicuity of vascular signal from the two Doppler techniques using a visual analogue scale.

Results

Eighty-three patients were recruited with 134 small joints assessed. Eighty-nine of these demonstrated vascular flow with both PD and SMI, whilst in five no flow was detected. In 40 joints, vascularity was detected with SMI but not with PDUS (p = 0.007). Out of the 89 joints with vascularity on both SMI and PDUS, 23 were rated as being equal; while SMI scored moderately or markedly better in 45 cases (p <0.001).

Conclusion

SMI is a new Doppler technique that increases conspicuity of Doppler vascularity in symptomatic joints when compared to PDUS. This allows detection of low grade inflammation not visualised with Power Doppler in patients with arthritis.

Key Points

• SMI detects vascularity with improved resolution and sensitivity compared to Power Doppler.

• SMI can detect low-grade inflammation not seen with Power Doppler.

• Earlier detection of active inflammation could have significant impact on treatment paradigms.

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-017-5016-4) contains supplementary material, which is available to authorized users.

Ultrasonographic findings can identify 'pseudoprogression' under nivolumab therapy

'Pseudoprogression' is often seen in patients with melanomas who are treated with immune checkpoint inhibitors such as nivolumab or ipilimumab. We sometimes evaluate metastatic lesions by imaging tests such as computed tomography (CT) or positron emission tomography-CT. 'Pseudoprogression' usually occurs upon the initial administration, which may make it difficult for the physician to determine the disease condition. In our two cases of metastatic melanoma treated with nivolumab (antiprogrammed cell death-1 antibody), we examined the ultrasonography (US) of target lesions that could be accessed from the body surface, such as those of the regional lymph node or subcutaneous metastasis. In both cases, the US revealed a lesion approximately 10% greater in size after 40-50 days of nivolumab administration, even though the blood flow inside the tumour was reduced by about 20% within 50 days. From about 100 days after blood flow reduction was detected by US, the tumours began to decrease in size. However, contrast CT was unable to detect the association between tumour size and tumour blood flow. The present cases suggest that US could be a powerful tool for differentiating between 'pseudoprogression' and real progressive disease in patients treated with cancer immunotherapies such as those involving immune checkpoint inhibitors. The misdiagnosis of progressive disease can lead to unnecessary alterations to the current treatment. Therefore, the US findings in our study could be clinically useful and educational for physicians.

Up-to-date Doppler techniques for breast tumor vascularity: superb microvascular imaging and contrast-enhanced ultrasound

Ultrasonographic Doppler techniques have improved greatly over the years, allowing more sophisticated evaluation of breast tumor vascularity. Superb microvascular imaging (SMI) and contrast-enhanced ultrasound (CEUS) with second-generation contrast agents are two representative up-to-date techniques. SMI is a sensitive Doppler technique that adopts an intelligent filter system to separate low-flow signals from artifacts. With the development of second-generation contrast agents, CEUS has also emerged as a useful Doppler technique for evaluating tumor microcirculation. Both techniques can improve the diagnostic performance of gray-scale ultrasonography by providing vascular information useful not only for the morphologic assessment of microvessels, but also for the quantitative analysis of perfusion. In this review, we explain the imaging principles and previous research underlying these two vascular techniques, and describe our clinical experiences.