Hybrid ultrasound imaging techniques (fusion imaging)

Ultrasound Fusion: Applications in Musculoskeletal Imaging

Ultrasound fusion is an established technique that pairs real time B-scan ultrasound (US) with other forms of cross-sectional imaging, including computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET). Each of these imaging modalities has distinct advantages. CT provides superior anatomic resolution, with improved imaging of bone and calcified structures; MRI has superior contrast resolution; and PET provides physiologic information, identifying processes that are metabolically active (i.e., tumor, inflammatory conditions). However, these modalities are static. A key highlight of ultrasound is its capability of dynamic, real-time scanning. The ability to pair CT, MRI or PET with ultrasound can have significant advantages, both in diagnostic evaluation and when performing difficult or challenging image-guided interventions. Percutaneous interventions using ultrasound fusion have been described in the abdominal imaging literature; however, there have been very few musculoskeletal applications detailed in the literature. The purpose of this article is to review the basic concepts of real-time ultrasound fusion, and to detail, through the use of multiple case examples, its potential use as a safe and effective method for performing image-guided musculoskeletal interventions.

Image Fusion Involving Real-Time Transabdominal or Endoscopic Ultrasound for Gastrointestinal Malignancies: Review of Current and Future Applications

Image fusion of CT, MRI, and PET with endoscopic ultrasound and transabdominal ultrasound can be promising for GI malignancies as it has the potential to allow for a more precise lesion characterization with higher accuracy in tumor detection, staging, and interventional/image guidance. We conducted a literature review to identify the current possibilities of real-time image fusion involving US with a focus on clinical applications in the management of GI malignancies. Liver applications have been the most extensively investigated, either in experimental or commercially available systems. Real-time US fusion imaging of the liver is gaining more acceptance as it enables further diagnosis and interventional therapy of focal liver lesions that are difficult to visualize using conventional B-mode ultrasound. Clinical studies on EUS guided image fusion, to date, are limited. EUS-CT image fusion allowed for easier navigation and profiling of the target tumor and/or surrounding anatomical structure. Image fusion techniques encompassing multiple imaging modalities appear to be feasible and have been observed to increase visualization accuracy during interventional and diagnostic applications.

A Review on Data Fusion of Multidimensional Medical and Biomedical Data

Data fusion aims to provide a more accurate description of a sample than any one source of data alone. At the same time, data fusion minimizes the uncertainty of the results by combining data from multiple sources. Both aim to improve the characterization of samples and might improve clinical diagnosis and prognosis. In this paper, we present an overview of the advances achieved over the last decades in data fusion approaches in the context of the medical and biomedical fields. We collected approaches for interpreting multiple sources of data in different combinations: image to image, image to biomarker, spectra to image, spectra to spectra, spectra to biomarker, and others. We found that the most prevalent combination is the image-to-image fusion and that most data fusion approaches were applied together with deep learning or machine learning methods.

Application of ultrasound fusion imaging technique for unilateral percutaneous vertebroplasty in treatment of osteoporotic thoracolumbar compression fracture

OBJECTIVE

To evaluate application of a computed tomography (CT)-ultrasound fusion imaging technique to unilateral percutaneous vertebroplasty (PVP) for treating patients with osteoporotic thoracolumbar compression fracture.

METHODS

Fourteen patients with osteoporotic thoracolumbar compression fractures were included, randomly divided into CT-ultrasound fusion imaging (n = 7) and traditional X-ray fluoroscopy groups (n = 7). Patients in the first group underwent unilateral PVP using real-time CT-ultrasound fusion imaging. A body surface locator was placed on the side contralateral to the scheduled puncture site (2-3 cm from the spinous process). Patient CT image information was recorded in the ultrasound system for registration during real-time ultrasound and CT fusion imaging, and one-click automatic registration was then performed. The puncture point and target point at which the puncture needle arrived were determined on CT images, with the puncture being performed under ultrasound guidance. Patients in the second group underwent X-ray fluoroscopy-guided PVP. Bone cement injection was injected under monitoring using a C-arm X-ray system. Patients' X-ray exposure and puncture times were recorded and compared between the two groups.

RESULTS

The average puncture times in the CT-ultrasound fusion imaging and traditional X-ray fluoroscopy groups were 2.50±0.31 min (without exposing patients and operators to radiation) and 5.00±0.65 min (with the same duration of radiation exposure), respectively. The average times for bone cement injection were 3.29±0.81 min and 3.50±0.86 min, respectively. The mean visual analog scale (VAS) scores were 2.10±0.11 and 2.20±0.21, respectively. The bone cement was evenly distributed without cement leakage in patients in the CT-ultrasound fusion imaging group, but a poor distribution of bone cement and bone cement leakage were found in one patient in the traditional X-ray fluoroscopy group.

CONCLUSIONS

Real-time CT-ultrasound fusion imaging is easy to perform, and provides precise localization of the puncture point, path, and target point. The selected puncture path was reasonable, and the needle had reached the target point accurately, which increased the success rate of puncture without radiation exposure.

Application of imaging fusion combining contrast-enhanced ultrasound and magnetic resonance imaging in detection of hepatic cellular carcinomas undetectable by conventional ultrasound

BACKGROUND AND AIM

The aim of this study is to explore the value of volume navigation image fusion-assisted contrast-enhanced ultrasound (CEUS) in detection for radiofrequency ablation guidance of hepatocellular carcinomas (HCCs), which were undetectable on conventional ultrasound.

METHODS

From May 2012 to May 2014, 41 patients with 49 HCCs were included in this study. All lesions were detected by dynamic magnetic resonance imaging (MRI) and planned for radiofrequency ablation but were undetectable on conventional ultrasound. After a bolus injection of 2.4 ml SonoVue® (Bracco, Italy), LOGIQ E9 ultrasound system with volume navigation system (version R1.0.5, GE Healthcare, Milwaukee, WI, USA) was used to fuse CEUS and MRI images. The fusion time, fusion success rate, lesion enhancement pattern, and detection rate were analyzed.

RESULTS

Image fusions were conducted successfully in 49 HCCs, the technical success rate was 100%. The average fusion time was (9.2 ± 2.1) min (6-12 min). The mean diameter of HCCs was 25.2 ± 5.3 mm (mean ± SD), and mean depth was 41.8 ± 17.2 mm. The detection rate of HCCs using CEUS/MRI imaging fusion (95.9%, 47/49) was significantly higher than CEUS (42.9%, 21/49) (P < 0.05). For small HCCs (diameter, 1-2 cm), the detection rate using imaging fusion (96.9%, 32/33) was also significantly higher than CEUS (18.2%, 6/33) (P < 0.01). All HCCs displayed a rapid wash-in pattern in the arterial phase of CEUS.

CONCLUSIONS

Imaging fusion combining CEUS and MRI is a promising technique to improve the detection, precise localization, and accurate diagnosis of undetectable HCCs on conventional ultrasound, especially small and atypical HCCs.

The role of contrast-enhanced ultrasound imaging in the follow-up of patients post-endovascular aneurysm repair

Endovascular aneurysm repair is a minimally invasive technique for the treatment of abdominal aortic aneurysms. Patients who undergo endovascular aneurysm repair are potentially at risk of developing problems related to the graft such as the development of endoleaks. Endoleaks can cause expansion of the aneurysmal sac, which can potentially lead to rupture. It is for this reason that lifelong surveillance of patients is required to assess the graft and the aneurysmal sac. This article discusses the role of contrast-enhanced ultrasound in the follow-up of patients post-endovascular aneurysm repair. Contrast-enhanced ultrasound is rapidly becoming a powerful, accurate and cost-effective tool to complement computed tomography in the follow-up of endovascular aneurysm repair patients. Real-time imaging of contrast filling into the arterial system means that contrast-enhanced ultrasound is an excellent problem-solving tool, particularly when assessing for the type and anatomy of endoleaks. In some instances, contrast-enhanced ultrasound can detect endoleaks when other modalities are equivocal.

Virtual navigator real-time ultrasound fusion imaging with positron emission tomography for liver interventions

Real-time fusion imaging technologies are increasingly being used among interventional radiologists, mostly Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) dataset, fused with Ultrasound (US) imaging. In addition, fusion of Positron Emission Tomography (PET) and CT is increasingly diffused in clinical practice, due to the wide availability of PET scanners and the capability to make either a direct (acquisitions performed within the same system) or an indirect (procedure performed on an external workstation, merging the two different sets of acquired data) fusion with CT data. The present work describes the feasibility of real-time fusion imaging directly between PET data and US imaging, with CT scans being used only for PET-US fusion registration. Data on multimodality registration precision and clinical applications are presented as well.

Evaluation of MRI-US Fusion Technology in Sports-Related Musculoskeletal Injuries

INTRODUCTION

A combination of magnetic resonance imaging (MRI) with real-time high-resolution ultrasound (US) known as fusion imaging may improve visualization of musculoskeletal (MSK) sports medicine injuries. The aim of this study was to evaluate the applicability of MRI-US fusion technology in MSK sports medicine.

METHODS

This study was conducted by the medical services of the FC Barcelona. The participants included volunteers and referred athletes with symptomatic and asymptomatic MSK injuries. All cases underwent MRI which was loaded into the US system for manual registration on the live US image and fusion imaging examination. After every test, an evaluation form was completed in terms of advantages, disadvantages, and anatomic fusion landmarks.

RESULTS

From November 2014 to March 2015, we evaluated 20 subjects who underwent fusion imaging, 5 non-injured volunteers and 15 injured athletes, 11 symptomatic and 4 asymptomatic, age range 16-50 years, mean 22. We describe some of the anatomic landmarks used to guide fusion in different regions. This technology allowed us to examine muscle and tendon injuries simultaneously in US and MRI, and the correlation of both techniques, especially low-grade muscular injuries. This has also helped compensate for the limited field of view with US. It improves spatial orientation of cartilage, labrum and meniscal injuries. However, a high-quality MRI image is essential in achieving an adequate fusion image, and 3D sequences need to be added in MRI protocols to improve navigation.

CONCLUSION

The combination of real-time MRI and US image fusion and navigation is relatively easy to perform and is helping to improve understanding of MSK injuries. However, it requires specific skills in MSK imaging and still needs further research in sports-related injuries.

FUNDING

Toshiba Medical Systems Corporation.

Percutaneous radiofrequency ablation of malignant liver tumors with ultrasound and CT fusion imaging guidance

BACKGROUND

To evaluate the feasibility, accuracy, and utility of sonography (US) and CT fusion imaging guidance for radiofrequency ablation (RFA) of malignant liver tumors not visualized on conventional US.

METHODS

Seventy-seven patients with hepatocellular carcinoma and 15 patients with metastatic liver cancer with a total of 136 lesions underwent RFA with US and CT fusion imaging guidance. The mean number of punctures, success rate of a single ablation session, local tumor progression rates, and long-term outcome were evaluated. Treatment efficacy was evaluated by dynamic CT and contrast-enhanced US 1 month after RFA.

RESULTS

RFA was technically feasible in all patients, and no major complications occurred. The mean ± SD time needed to synchronize US and CT images was 13.9 ± 11.9 minutes (range, 5-55 minutes). The success rate of a single ablation session was 83.8% (114/136), and tumor residue was present in 7.4% of lesions (10/136). The mean number of treatment sessions was 1.2 ± 0.5 sessions. During follow-up, local tumor progression was observed for 15 (11.9%) lesions. Distant tumor recurrence was found in 51 (55.4%) patients.

CONCLUSIONS

US and CT fusion-assisted RFA is a safe and efficacious treatment for patients with hepatocellular carcinoma and metastatic liver cancer.

Real-time US-CT/MRI image fusion for guidance of thermal ablation of liver tumors undetectable with US: results in 295 cases

PURPOSE

This study was designed to assess feasibility of US-CT/MRI fusion-guided ablation in liver tumors undetectable with US.

METHODS

From 2002 to 2012, 295 tumors (162 HCCs and 133 metastases; mean diameter 1.3 ± 0.6 cm, range 0.5-2.5 cm) detectable on contrast-enhanced CT/MRI, but completely undetectable with unenhanced US and either totally undetectable or incompletely conspicuous with contrast-enhanced US (CEUS), were treated in 215 sessions using either internally cooled radiofrequency or microwave with standard ablation protocols, guided by an image fusion system (Virtual Navigation System, Esaote S.p.A., Genova, Italy) that combines US with CT/ MRI images. Correct targeting and successful ablation of tumor were verified after 24 hours with CT or MRI.

RESULTS

A total of 282 of 295 (95.6 %) tumors were correctly targeted with successful ablation achieved in 266 of 295 (90.2 %). Sixteen of 295 (5.4 %) tumors were correctly targeted, but unsuccessfully ablated, and 13 of 295 (4.4 %) tumors were unsuccessfully ablated due to inaccurate targeting. There were no perioperative deaths. Major complications were observed in 2 of the 215 treatments sessions (0.9 %).

CONCLUSIONS

Real-time virtual navigation system with US-CT/MRI fusion imaging is precise for targeting and achieving successful ablation of target tumors undetectable with US alone. Therefore, a larger population could benefit from ultrasound guided ablation procedures.

Virtual navigator automatic registration technology in abdominal application

Real-time Ultrasound (US) image fusion with a pre-acquired second imaging dataset - Computed Tomography (CT), Magnetic Resonance Imaging (MRI) and/or CT/PET - has become widely used in recent years for both diagnosis and image-guided interventional procedures. Liver and kidneys are the main focused anatomical districts, related to abdominal application. There are still nowadays some drawbacks, regarding the adoption of the fusion imaging technique in everyday practice especially regarding its ease of use and the time needed in order to obtain a precise real-time fusion between US and the second imaging modality. The present work is a preliminary study on the feasibility and practical use of an Automatic registration algorithm for CT-US real-time fusion imaging. Data obtained by tests performed on a Doppler phantom, for the assessment of the precision of the registration procedure and in-vivo Automatic registration tests, are presented.

Real-time virtual sonography visualization and its clinical application in biliopancreatic disease

AIM: To evaluate the usefulness of real-time virtual sonography (RVS) in biliary and pancreatic diseases.

METHODS: This study included 15 patients with biliary and pancreatic diseases. RVS can be used to observe an ultrasound image in real time by merging the ultrasound image with a multiplanar reconstruction computed tomography (CT) image, using pre-scanned CT volume data. The ultrasound used was EUB-8500 with a convex probe EUP-C514. The RVS images were evaluated based on 3 levels, namely, excellent, good and poor, by the displacement in position.

RESULTS: By combining the objectivity of CT with free scanning using RVS, it was possible to easily interpret the relationship between lesions and the surrounding organs as well as the position of vascular structures. The resulting evaluation levels of the RVS images were 12 excellent (pancreatic cancer, bile duct cancer, cholecystolithiasis and cholangiocellular carcinoma) and 3 good (pancreatic cancer and gallbladder cancer). Compared with conventional B-mode ultrasonography and CT, RVS images achieved a rate of 80% superior visualization and 20% better visualization.

CONCLUSION: RVS has potential usefulness in objective visualization and diagnosis in the field of biliary and pancreatic diseases.

Creation and characterization of an ultrasound and CT phantom for noninvasive ultrasound thermometry calibration

Ultrasound thermometry provides noninvasive 2-D temperature monitoring, and in this paper, we have investigated the use of computed tomography (CT) radiodensity to characterize tissues to improve the accuracy of ultrasound thermometry. Agarose-based tissue-mimicking phantoms were created with glyceryl trioleate (a fat-mimicking material) concentration of 0%, 10%, 20%, 30%, 40%, and 50%. The speed of sound (SOS) of the phantoms was measured over a temperature range of 22.1-41.1 °C. CT images of the phantoms were acquired by a clinical dedicated breast CT scanner, followed by calculation of the Hounsfield units (HU). The phantom was heated with a therapeutic acoustic pulse (1.54 MHz), while RF data were acquired with a 10-MHz linear-array transducer. Two-dimensional speckle tracking was used to calculate the thermal strain offline. The tissue-dependent thermal strain parameter required for ultrasound thermometry was analyzed and correlated with CT radiodensity, followed by the validation of the temperature prediction. Results showed that the change in SOS with the temperature increase was opposite in sign between the 0%-10% and 20%-50% trioleate phantoms. The inverse of the tissue-dependent thermal strain parameter of the phantoms was correlated with the CT radiodensity (R(2) = 0.99). A blinded ultrasound thermometry study on phantoms with a trioleate range of 5%-35% demonstrated the capability to estimate the tissue-dependent thermal strain parameter and estimate temperature with error less than ~1 °C. In conclusion, CT radiodensity may provide a method for improving ultrasound thermometry in heterogeneous tissues.

Percutaneous transhepatic biliary drainage assisted by real-time virtual sonography: a retrospective study

Background

Real-time virtual sonography (RVS) is a diagnostic imaging support system that can synchronize with ultrasound images in conjunction with computed tomography or magnetic resonance images using magnetic navigation system. RVS has been applied in clinical practice to perform such procedures as radiofrequency ablation and biopsy; however, the application of RVS for percutaneous transhepatic biliary drainage (PTBD) is rare.

Methods

Between 2007 and 2012, RVS-assisted PTBD was performed for 30 patients (19 males and 11 females; age range, 41 to 89 years; mean age, 66.9 years) with obstructive jaundice. The targeted bile duct was determined using the RVS system before the procedure. The intervention was considered to be successful when the targeted bile duct was punctured and the drainage catheter was placed in the bile duct. Complications were evaluated according to the Society of Interventional Radiology Clinical Practice Guidelines.

Results

A total of 37 interventions were performed for 30 patients. The interventions were successful in 35 (95%) of 37 interventions. The targeted bile ducts were: B3 (n = 24), B5 (n = 7), B8 (n = 3), B6 (n = 1), and the anterior (n = 1) and posterior (n = 1) branches of the right bile duct. The mean targeted bile duct diameter was 4.9 mm (1.9 to 8.2 mm). PTBD was able to be accomplished in all patients because the non-targeted bile ducts were successfully punctured alternatively. No major complications were observed in relation to the interventional procedure.

Conclusions

RVS-assisted PTBD is a feasible and safe procedure. Accurate puncture of targeted bile ducts can be achieved using this method.

Ultrasound thermal mapping based on a hybrid method combining cross-correlation and zero-crossing tracking

A hybrid method for estimating temperature with spatial mapping using diagnostic ultrasound, based on detection of echo shifts from tissue undergoing thermal treatment, is proposed. Cross-correlation and zero-crossing tracking are two conventional algorithms used for detecting echo shifts, but their practical applications are limited. The proposed hybrid method combines the advantages of both algorithms with improved accuracy in temperature estimation. In vitro experiments were performed on porcine muscle for preliminary validation and temperature calibration. In addition, thermal mapping of rabbit thigh muscle in vivo during high-intensity focused ultrasound heating was conducted. Results from the in vitro experiments indicated that the difference between the estimated temperature change by the proposed hybrid method and the actual temperature change measured by the thermocouple was generally less than 1 °C when the increase in temperature due to heating was less than 10 °C. For the in vivo study, the area predicted to experience the highest temperature coincided well with the focal point of the high-intensity focused ultrasound transducer. The computational efficiency of the hybrid algorithm was similar to that of the fast cross-correlation algorithm, but with an improved accuracy. The proposed hybrid method could provide an alternative means for non-invasive monitoring of limited temperature changes during hyperthermia therapy.

New paradigm for management of hepatocellular carcinoma by imaging

Based on recent clinical practice guidelines, imaging is largely replacing pathology as the preferred diagnostic method for determination of hepatocellular carcinoma (HCC). A variety of imaging modalities, including ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), nuclear medicine, and angiography, are currently used to examine patients with chronic liver disease and suspected HCC. Advancements in imaging techniques such as perfusion imaging, diffusion imaging, and elastography along with the development of new contrast media will further improve the ability to detect and characterize HCC. Early diagnosis of HCC is essential for prompt treatment, which may in turn improve prognosis. Considering the process of hepatocarcinogenesis, it is important to evaluate sequential changes via imaging which would help to differentiate HCC from premalignant or benign lesions. Recent innovations including multiphasic examinations, high-resolution imaging, and the increased functional capabilities available with contrast-enhanced US, multidetector row CT, and MRI have raised the standards for HCC diagnosis. Although hemodynamic features of nodules in the cirrhotic liver remain the main diagnostic criterion, newly developed cellspecific contrast agents have shown great possibilities for improved HCC diagnosis and may overcome the diagnostic dilemma associated with small or borderline hepatocellular lesions. In the 20th century paradigm of medical imaging, radiological diagnosis was based on morphological characteristics, but in the 21st century, a paradigm shift to include biomedical, physiological, functional, and genetic imaging is needed. A multidisciplinary team approach is necessary to foster an integrated approach to HCC imaging. By developing and combining new imaging modalities, all phases of HCC patient care, including screening, diagnosis, treatment, and therapy, can be dramatically improved.

Imaging techniques used for the real-time assessment of angiogenesis in digestive cancers

Angiogenesis has a critical role in primary tumor growth and the development of metastases. Several angiogenesis inhibitors were recently developed, being a very attractive target for digestive tumor therapy. However, individualized therapy should not only be based on the pre-treatment imaging evaluation, but also on sensitive monitoring of microvascular changes during treatment. State-of-the-art imaging techniques have the potential to visualize and characterize angiogenesis, although the technology and methodologies employed are recent and need further validation. The aim of this series of reviews was to analyze and enhance current knowledge and future perspectives about the real-time assessment of angiogenesis in digestive cancers, used for the longitudinal monitoring of the effects of chemo-radiotherapy (including anti-angiogenic therapies), as well as for the precise targeting of drugs through molecular-based drug-delivery systems.