Caroline Ewertsen

Real-Time Image Fusion Involving Diagnostic Ultrasound

OBJECTIVE The aim of our article is to give an overview of the current and future possibilities of real-time image fusion involving ultrasound. We present a review of the existing English-language peer-reviewed literature assessing this technique, which covers technical solutions (for ultrasound and endoscopic ultrasound), image fusion in several anatomic regions, and electromagnetic needle tracking. CONCLUSION The recent progress of real-time ultrasound in image fusion may provide several new possibilities, including diagnosis, treatment, and follow-up of oncologic patients.

A Comparative Study of Strain and Shear-Wave Elastography in an Elasticity Phantom

OBJECTIVE. The purpose of this study was to assess the diagnostic accuracy of strain and shear-wave elastography for determining targets of varying stiffness in a phantom. The effect of target diameter on elastographic assessments and the effect of depth on shear-wave velocity were also investigated. MATERIALS AND METHODS. We examined 20 targets of varying diameters (2.5-16.7 mm) and stiffnesses (8, 14, 45, and 80 kPa) with a 4-9-MHz linear-array transducer. Targets were evaluated 10 times with three different methods-shear-wave elastography, strain ratio, and strain histogram analysis-yielding 600 evaluations. AUCs were calculated for data divided between different stiffnesses. A 1.5-6-MHz curved-array transducer was used to assess the effect of depth (3.5 vs 6 cm) on shear-wave elastography in 80 scans. Mixed model analysis was performed to assess the effect of target diameter and depth. RESULTS. Strain ratio and strain histogram AUCs were higher than the shear-wave velocity AUC (p < 0.001) in data divided as 80 versus 45, 14, and 8 kPa. In data divided as 80 and 45 versus 14 and 8 kPa, the methods were equal (p = 0.959 and p = 1.000, respectively). Strain ratios were superior (p = 0.030), whereas strain histograms were not significantly better (p = 0.083) than shear-wave elastography in data divided as 80, 45, and 14 versus 8 kPa. Target diameter had an effect on all three methods (p = 0.001). Depth had an effect on shear-wave velocity (p = 0.001). CONCLUSION. The ability to discern different target stiffnesses varies between shear-wave and strain elastography. Target diameter affected all methods. Shear-wave elastography is affected by target depth.

EFSUMB Guidelines on Interventional Ultrasound (INVUS), Part I. General Aspects (Short Version).

This is the first part of the Guidelines on Interventional Ultrasound of the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) and covers all general aspects of ultrasound-guided procedures (short version; the long version is published online).

Evaluation of healthy muscle tissue by strain and shear wave elastography – Dependency on depth and ROI position in relation to underlying bone

PURPOSE The aim of this study was to evaluate the influence of depth and underlying bone on strain ratios and shear wave speeds for three different muscles in healthy volunteers. For strain ratios the influence from different reference region-of-interest positions was also evaluated. MATERIAL AND METHODS Ten healthy volunteers (five males and five females) had their biceps brachii, gastrocnemius, and quadriceps muscle examined with strain- and shear wave elastography at three different depths and in regions located above bone and beside bone. Strain ratios were averaged from cine-loops of 10s length, and shear wave speeds were measured 10 times at each target point. The distance from the skin surface to the centre of each region-of-interest was measured. Measurements were evaluated with descriptive statistics and linear regression. RESULTS Linear regression showed a significant influence on strain ratio measurements from the reference region-of-interest position, i.e. being above the same structures as the target region-of-interest or not (means: 1.65 and 0.78; (P<0.001)). For shear wave speeds, there was a significant influence from depth and location above or beside bone (P=0.011 and P=0.031). CONCLUSION Strain ratio values depend significantly on reference and target region-of-interest being above the same tissue, for instance bone. Strain ratios were not influenced by depth in this study. Shear wave speeds decreased with increasing scanning depth and if there was bone below the region-of-interest.

Strain Elastography Ultrasound: An Overview with Emphasis on Breast Cancer Diagnosis.

Strain elastography (SE), which estimates tissue strain, is an adjunct to the conventional ultrasound B-mode examination. We present a short introduction to SE and its clinical use. Furthermore, we present an overview of the 10 largest studies performed on the diagnostic accuracy of SE in breast cancer diagnostics. Eight of 10 studies presented data for both SE and B-mode imaging. Seven studies showed better specificity and accuracy for SE than for B-mode imaging in breast cancer diagnosis. Four studies showed an increase in specificity and accuracy when combining B-mode imaging with SE. The ways of combining B-mode imaging with SE in the diagnosis of breast cancer differed between the five studies. We believe that further studies are needed to establish an optimal algorithm for the combination of B-mode ultrasound and SE in breast cancer.

Biopsy Guided by Real-Time Sonography Fused with MRI : A Phantom Study

OBJECTIVE The purpose of our study was to test the accuracy of sonographically guided biopsies in a phantom of structures not visible on sonography but shown on MRI by using commercially available sonography systems with image fusion software. MATERIALS AND METHODS A previously recorded MRI examination from a custom-made phantom was loaded into the sonography system. The phantom contained spheres that were invisible to sonography and contained red dye. The red dye was visible in the biopsy if it was successful. The images were coregistered using structures visible on both sonography and MRI, and biopsies were taken. The biopsy procedure was continued until a biopsy was successful, and the number of needle passes and time spent were registered. RESULTS A total of 130 targets were hit. Ten minutes was used for loading the MRI data set and the coregistration; 94 of the 130 biopsies (72.3%) were successful at the first needle pass. The median number of needle passes until a successful biopsy was obtained was one (range, 1-7). CONCLUSION The described method was successful in obtaining an adequate sample in a phantom.

Imaging of the major salivary glands

The major salivary glands, submandibular, parotid and sublingual glands play an important role in preserving the oral cavity and dental health. Patients with problems of the major salivary glands may present with symptoms such as dry mouth, dysphagia and obstruction of duct, inflammation, severe dental caries or swelling. Imaging plays an important role in visualization of morphology and function, to establish a diagnosis, for treatment, and for surgical planning. There are several options for diagnostic imaging: plain radiography, sialography, ultrasound (US), magnetic resonance imaging (MRI), computed tomography (CT), salivary gland scintigraphy and 18F‐FDG positron emission tomography (PET). We present an overview of the modalities in relation to common salivary gland disease.

Freehand Biopsy Guided by Electromagnetic Needle Tracking: A Phantom Study

PURPOSE To evaluate the overall accuracy and time spent on biopsy guided by electromagnetic needle tracking in a phantom compared with the standard technique of US-guided biopsy with an attached steering device. Furthermore, to evaluate off-plane biopsy guided by needle tracking. MATERIALS AND METHODS Three different series of biopsy were performed in a phantom: one with a steering device attached to the transducer without needle tracking, simulating the standard ultrasound-guided biopsy procedure (series 1), one freehand in the scan plane using electromagnetic needle tracking (series 2), and one freehand off-the-scan plane using electromagnetic needle tracking (series 3). The phantom contained spheres of 1  cm in diameter filled with red dye. Each time of the phantom surface was perforated counted as an attempt. RESULTS 180 biopsies were performed. The mean time spent on each biopsy in series one was 19.9 seconds (SD: 9.1), in series two 34.1 seconds (SD: 17.9) and in series three 34.4 seconds (SD: 14.0). The overall rate of success was: 88 % for in-plane needle-guided biopsy, 87 % for in-plane needle tracking, and 92 % for off-plane needle tracking. No statistically significant difference between the methods was shown. CONCLUSION Needle navigation is a potentially valuable tool for image-guided biopsy with an equal rate of success compared with conventional image-guided biopsy. Furthermore, it enables off-plane image-guided biopsy.

Accuracy of visual scoring and semi-quantification of ultrasound strain elastography--a phantom study.

Purpose The aim of this study was to evaluate the performance of strain elastography in an elasticity phantom and to assess which factors influenced visual scoring, strain histograms and strain ratios. Furthermore this study aimed to evaluate the effect of observer experience on visual scorings. Materials and Methods Two operators examined 20 targets of various stiffness and size (16.7 to 2.5 mm) in an elasticity phantom at a depth of 3.5 cm with a 5–18 MHz transducer. Two pre-settings were used yielding 80 scans. Eight evaluators, four experienced, four inexperienced, performed visual scorings. Cut-offs for semi-quantitative methods were established for prediction of target stiffness. Data was pooled in two categories allowing calculations of sensitivity and specificity. Statistical tests chi-square test and linear regression as relevant. Results Strain ratios and strain histograms were superior to visual scorings of both experienced and inexperienced observers (p = 0.025, strain histograms vs. experienced observers, p<0.001, strain histograms vs. inexperienced observers, p = 0.044 strain ratios vs. experienced observers and p = 0.002 strain ratios vs. inexperienced observers). No significant difference in predicting target stiffness between strain ratios and strain histograms (p = 0.83) nor between experienced and inexperienced observers (p = 0.054) was shown when using four categories. When pooling data in two groups (80 kPa/45 kPa vs. 14/8 kPa) the difference between the observers became significant (p<0.001). Target size had a significant influence on strain ratios measurements (p = 0.017) and on visual scorings (p<0.001) but not on the strain histograms(p = 0.358). Observer experience had significant effect on visual scorings(p = 0.003). Conclusion Strain ratios and strain histograms are superior to visual scoring in assessing target stiffness in a phantom. Target size had a significant impact on strain ratios and visual scoring, but not on strain histograms. Experience influenced visual scorings but the difference between experienced and inexperienced observers was only significant when looking at two classes of target stiffness.

Ultrasound Elastography in Breast Cancer Diagnosis.

Ultrasound elastography is an established method for characterization of focal lesions in the breast. Different techniques and analyses of the images may be used for the characterization. This article addresses the use of ultrasound elastography in breast cancer diagnosis. In the first part of the article the techniques behind both strain- and shear-wave-elastography are explained and followed by a section on how to obtain adequate elastography images and measurements. In the second part of the article the application of elastography as an adjunct to B-mode ultrasound in clinical practice is described, and the potential diagnostic gains and limitations of elastography are discussed.