Fernando Mitsuyama Cardoso

Edge-Preserving Speckle Texture Removal by Interference-Based Speckle Filtering Followed by Anisotropic Diffusion

Ultrasonography has an inherent noise pattern, called speckle, which is known to hamper object recognition for both humans and computers. Speckle noise is produced by the mutual interference of a set of scattered wavefronts. Depending on the phase of the wavefronts, the interference may be constructive or destructive, which results in brighter or darker pixels, respectively. We propose a filter that minimizes noise fluctuation while simultaneously preserving local gray level information. It is based on steps to attenuate the destructive and constructive interference present in ultrasound images. This filter, called interference-based speckle filter followed by anisotropic diffusion (ISFAD), was developed to remove speckle texture from B-mode ultrasound images, while preserving the edges and the gray level of the region. The ISFAD performance was compared with 10 other filters. The evaluation was based on their application to images simulated by Field II (developed by Jensen et al.) and the proposed filter presented the greatest structural similarity, 0.95. Functional improvement of the segmentation task was also measured, comparing rates of true positive, false positive and accuracy. Using three different segmentation techniques, ISFAD also presented the best accuracy rate (greater than 90% for structures with well-defined borders).

Realistic IVUS Image Generation in Different Intraluminal Pressures

Intravascular ultrasound (IVUS) phantoms are important to calibrate and evaluate many IVUS imaging processing tasks. However, phantom generation is never the primary focus of related works; hence, it cannot be well covered, and is usually based on more than one platform, which may not be accessible to investigators. Therefore, we present a framework for creating representative IVUS phantoms, for different intraluminal pressures, based on the finite element method and Field II. First, a coronary cross-section model is selected. Second, the coronary regions are identified to apply the properties. Third, the corresponding mesh is generated. Fourth, the intraluminal force is applied and the deformation computed. Finally, the speckle noise is incorporated. The framework was tested taking into account IVUS contrast, noise and strains. The outcomes are in line with related studies and expected values. Moreover, the framework toolbox is freely accessible and fully implemented in a single platform.

Guidewire path determination for intravascular applications

Vascular diseases are among the major causes of death in developed countries and the treatment of those pathologies may require endovascular interventions, in which the physician utilizes guidewires and catheters through the vascular system to reach the injured vessel region. Several computational studies related to endovascular procedures are in constant development. Thus, predicting the guidewire path may be of great value for both physicians and researchers. However, attaining good accuracy and precision is still an important issue. We propose a method to simulate and predict the guidewire and catheter path inside a blood vessel based on equilibrium of a new set of forces, which leads, iteratively, to the minimum energy configuration. This technique was validated with phantoms using a ∅0.33 mm stainless steel guidewire and compared to other relevant methods in the literature. This method presented RMS error 0.30 mm and 0.97 mm, which represents less than 2% and 20% of the lumen diameter of the phantom, in 2D and 3D cases, respectively. The proposed technique presented better results than other methods from the literature, which were included in this work for comparison. Moreover, the algorithm presented low variation () due to the variation of the input parameters. Therefore, even for a wide range of different parameters configuration, similar results are presented for the proposed approach, which is an important feature and makes this technique easier to work with. Since this method is based on basic physics, it is simple, intuitive, easy to learn and easy to adapt.

Guidewire path simulation using equilibrium of forces

Vascular diseases are among the major causes of death in developed countries and the treatment of those pathologies may require endovascular interventions, in which the physician utilizes guidewires and catheters through the vascular system to reach the injured vessel region. Several computational studies related to endovascular procedures are in constant development. So, predicting the guidewire path may be of great value for both physicians and researchers. We propose a method to simulate and predict the guidewire and catheter path inside a blood vessel based on equilibrium of forces, which leads, iteratively, to the minimum energy configuration. This technique was validated with physical models using a Ø0.33mm stainless steel guidewire. This method presented RMS error, in average, less than 1 mm. Moreover, the algorithm presented low variation (in average, σ=0.03mm) due to the variation of the input parameters. Therefore, even for a wide range of different parameters configuration, similar results are presented, which makes this technique easier to work with. Since this method is based on basic physics, it is simple, intuitive, easy to learn and easy to adapt.

Interference based speckle filter

Speckle noise is a random granular texture produced by mutual interference of a set of scattered wavefronts, so it is inherent to ultrasonic imaging. Depending on the phase of the wavefronts, the interference may be constructive or destructive. In this work, we developed an interference based speckle filter (ISF), whose first step is to attenuate the destructive interference, because it carries little information about the imaged structures. In order to do that, we considered, for each pixel, the maximum between the median and the original value. To eliminate the remaining bright speckles, we applied a median filter. The resulting image had minimized speckle effects. We have created two basic numeric phantoms, a linear array ultrasound and an intravascular ultrasound phantoms, and we have simulated 20 random initializations of speckle noise for each phantom. Then, we filtered the noisy images using several filters: ISF, median, Wiener, anisotropic diffusion and speckle reducing anisotropic diffusion (SRAD). To evaluate and compare their performances, we have calculated mean and standard deviation of a homogeneous region, square root mean error and structural similarity (SSIM) for each one. ISF presented an overall 0.91 rate for SSIM, while SRAD and Wiener filter performed SSIM 0.87 and 0.85 rates, respectively. This filter is easy to implement, because it requires only a sequence of three basic operations (Median, MaxValue and Median) and it is also easy to set the input parameters (the two radii of the median filters). Mostly important, it is able to smooth speckle effects without blurring edges.

Realistic deformable 3D numeric phantom for transcutaneous ultrasound

Introduction Numerical phantoms are important tools to design, calibrate and evaluate several methods in various image-processing applications, such as echocardiography and mammography. We present a framework for creating ultrasound numerical deformable phantoms based on Finite Element Method (FEM), Linear Isomorphism and Field II. The proposed method considers that the scatterers map is a property of the tissue; therefore, the scatterers should move according to the tissue strain. Methods First, a volume representing the target tissue is loaded. Second, parameter values, such as Young’s Modulus, scatterers density, attenuation and scattering amplitudes are inserted for each different regions of the phantom. Then, other parameters related to the ultrasound equipment, such as ultrasound frequency and number of transducer elements, are also defined in order to perform the ultrasound acquisition using Field II. Third, the size and position of the transducer and the pressures that are applied against the tissue are defined. Subsequently, FEM is executed and deformation is computed. Next, 3D linear isomorphism is performed to displace the scatterers according to the deformation. Finally, Field II is carried out to generate the non-deformed and deformed ultrasound data. Results The framework is evaluated by comparing strain values obtained the numerical simulation and from the physical phantom from CIRS. The mean difference between both phantoms is lesser than 10%. Conclusion The acoustic and deformation outcomes are similar to those obtained using a physical phantom. This framework led to a tool, which is available online and free of charges for educational and research purposes.

An improved implementation of block matching for motion estimation in ultrasound imaging

Ultrasound elastography has become an important procedure that provides information about the tissue dynamics and may help on the detection of tissue abnormalities. Therefore, motion estimation in a sequence of ultrasound acquisition is crucial to the quality of this information. We propose a novel algorithm to perform speckle tracking, which consists in an implementation of 2D Block Matching with two enhancements: sub-pixel linear interpolation and displacement propagation, which are able to increase resolution, reduce computation time and prevent kernel mismatching errors. This method does not require any additional hardware and provide real-time information. The proposed technique was evaluated using four different numerical phantoms and its results were compared with the results from standard 2D block matching and optical flow. The proposed method outperformed the other two methods, providing an average error of 0.98 pixels, while standard 2D block matching and optical flow presented an average error of 2.50 and 10.03 pixels, respectively. The proposed algorithm was also assessed with four different physical phantoms and a qualitative comparison showed that the proposed technique presented results that were compatible to the results from the built-in elastography mode of the ultrasound equipment (Ultrasonix Touch).

Automatic Window Size Estimation for Speckle Noise Filters

Speckle noise is a random granular texture that is inherent to ultrasonic imaging. It makes object recognition more difficult for both humans and computers. There are several speckle filters in the literature which aim to mitigate the speckle noise while trying to preserve the borders of the objects. However, the choice of the filter parameters makes them hard to work with and, sometimes, may be arbitrary. Especially in window-based filters, the users have to select the window size. An excessively large window may deform or even erase the object of interest. On the other hand, a small window may leave the speckle noise unchanged. We propose a method that automatically determines the window size based on the speckle noise pattern. This technique calculates the average distance between the local maxima and the nearest local minimum, and vice-versa. This method provides a reliable parameter to characterize the speckle noise. We applied this technique using median filter, whose only parameter is the window size. The proposed method was validated numerically with root mean squared error and structural similarity and it presented better results than the direct application of median filter. Through visual assessment, it is possible to see that the proposed method is able to remove the speckle texture and preserve the object edges, while the direct application of the filter generated blurred borders.

Estimation of deformations in ultrasound images using dynamic programming

Dynamic medical images may provide valuable information such as contraction rate, deformation and elasticity. For this purpose, it is fundamental to estimate the displacement of each point of interest. However, in ultrasound this task is hampered by speckle noise. The objective is the estimation of structure deformation and contraction using robust tracking of a set of representative points in a sequence of ultrasound images. The proposed approach is based on discrete optimization of joint displacement estimation via dynamic programming where the criteria involved joint intensity and morphology similarity. We also investigated the effect of initialization of the graph by maximization of Bhattacharyya coefficient. We evaluated in realistic numerical phantoms with speckle noise and compared with traditional approaches. Ten points were considered in the phantom and we applied several affine transformations to generate the deformed images as well as finite element based deformations. The average displacement error has decreased from 4.4 ± 6.6 pixels to 1.9 ± 2.5 pixels for the approach with proposed initialization with statistical significant difference at 5% level. In conclusion, we have shown that robust estimation of first point of contour provides a major improvement in the mapping of the contour points by dynamic programming.