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Real-time volumetric ultrasound imaging using free hand scanning
Abstract
Fusion-based ultrasound (US)-guided biopsy in a breast is challenging due to the high deformability of the tissue
combined with the fact that the breast is usually differently deformed in CT, MR, and US acquisition which makes
registration difficult.
With this phantom study, we demonstrate the feasibility of a fusion-based ultrasound-guided method for breast biopsy.
3D US and 3D CT data were acquired using dedicated imaging setups of a breast phantom freely hanging in prone
position with lesions. The 3D breast CT set up was provided by Koning (Koning Corp., West Henrietta, NY). For US
imaging, a dedicated breast scanning set up was developed consisting of a cone-shaped revolving water tank with a 152-
mm-sized US transducer mounted in its wall and an aperture for needle insertion. With this setup, volumetric breast US
data (0.5x0.5x0.5 mm3 voxel size) can be collected and reconstructed within 3 minutes. The position of the lesion as
detected with breast CT was localized in the US data by rigid registration. After lesion localization, the tank rotates the
transducer until the lesion is in the US plane. Since the lesion was visible on ultrasound, the performance of the
registration was validated.
To facilitate guided biopsy, the lesion motion, induced by needle insertion, is estimated using cross-correlation-based
speckle tracking and the tracked lesion visualized in the US image at an update frequency of 10 Hz.
Thus, in conclusion a fusion-based ultrasound-guided method was introduced which enables ultrasound-guided biopsy in
breast that is applicable also for ultrasound occult lesions.
Adding volumetric ultrasound (3DUS) to MRI improves cancer detection rate in a breast. However, the fusion of 3DUS and MRI is challenging due to the different position (supine versus prone, respectively) and high deformation of a breast in the existing 3DUS scanners. In this study, we present and quantitatively evaluate a novel robot-assisted breast scanning system for 3D US acquisitions. Since the breast is scanned in a prone position with minimal and measurable deformation, this can facilitate MRI - 3DUS fusion. For quantitative evaluation, a breast-shaped rigid polyvinyl-alcohol phantom was constructed containing spherical lesions (15 mm diameter) with different echogenicity (−22 dB, −5 dB, −4 dB, 3 dB, 7 dB). First, the phantom was scanned with a Siemens Skyra 3T MRI (Siemens Healthcare, Erlangen, Germany). Next, the phantom was scanned by a robotic arm (KUKA, Augsburg, Germany) (Fig. 1a.) following a pre-planned spiral trajectory, determined from the MRI volume. The flange of the robot was equipped with an L10-5v US transducer attached to a P500 system (Siemens, Mountain View, CA, US). 2D B-mode US data were acquired for 3 minutes at 12 fps. The imaging depth was 5 cm, and the focal depth was set at 2 cm. A volume of 77 × 77 × 69 mm3 was reconstructed with an isotropic sampling distance of 0.2 mm utilizing a voxel nearest neighbor method with a subsequent “hole filling” step, i.e. interpolation. The contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were calculated per lesion and compared to reference values from the originally acquired 2D B-mode images. The 3D US volume was registered to the MRI volume by using 4 lesions as landmark, using rigid registration. The distance between the centers of the remaining lesion in MRI and 3DUS after the registration was calculated. The measurement was repeated for 5 combinations between lesions and landmarks. The average distance was used as a measure of registration accuracy. For the reconstructed volume only 24 % of the data were obtained by interpolation. On average, the CNR and SNR were 24% and 6% higher, respectively, for the 3DUS compared to the reference. The registration accuracy was 3.4 mm; hence, the presented scanning approach enables ultrasound breast 3D imaging in prone position facilitating MRI - 3D US fusion.
The developmental goal of 3D ultrasound imaging (3DUS) is to engineer a modality to perform 3D morphological ultrasound analysis of human muscles. 3DUS images are constructed from calibrated freehand 2D B-mode ultrasound images, which are positioned into a voxel array. Ultrasound (US) imaging allows quantification of muscle size, fascicle length, and angle of pennation. These morphological variables are important determinants of muscle force and length range of force exertion. The presented protocol describes an approach to determine volume and fascicle length of m. vastus lateralis and m. gastrocnemius medialis. 3DUS facilitates standardization using 3D anatomical references. This approach provides a fast and cost-effective approach for quantifying 3D morphology in skeletal muscles. In healthcare and sports, information on the morphometry of muscles is very valuable in diagnostics and/or follow-up evaluations after treatment or training. © 2017, Journal of Visualized Experiments. All rights reserved.
Visualized freehand 3-D ultrasound reconstruction offers to image incremental reconstruction during acquisition and guide users to scan interactively for high-quality volumes. We originally used the graphics processing unit (GPU) to develop a visualized reconstruction algorithm that achieves real-time level. Each newly acquired image was transferred to the memory of the GPU and inserted into the reconstruction volume on the GPU. The partially reconstructed volume was then rendered using GPU-based incremental ray casting. After visualized reconstruction, hole-filling was performed on the GPU to fill remaining empty voxels in the reconstruction volume. We examine the real-time nature of the algorithm using in vitro and in vivo datasets. The algorithm can image incremental reconstruction at speed of 26-58 frames/s and complete 3-D imaging in the acquisition time for the conventional freehand 3-D ultrasound.
Supersonic shear imaging (SSI) is a new ultrasound-based technique for real-time visualization of soft tissue viscoelastic properties. Using ultrasonic focused beams, it is possible to remotely generate mechanical vibration sources radiating low-frequency, shear waves inside tissues. Relying on this concept, SSI proposes to create such a source and make it move at a supersonic speed. In analogy with the "sonic boom" created by a supersonic aircraft, the resulting shear waves will interfere constructively along a Mach cone, creating two intense plane shear waves. These waves propagate through the medium and are progressively distorted by tissue heterogeneities. An ultrafast scanner prototype is able to both generate this supersonic source and image (5000 frames/s) the propagation of the resulting shear waves. Using inversion algorithms, the shear elasticity of medium can be mapped quantitatively from this propagation movie. The SSI enables tissue elasticity mapping in less than 20 ms, even in strongly viscous medium like breast. Modalities such as shear compounding are implementable by tilting shear waves in different directions and improving the elasticity estimation. Results validating SSI in heterogeneous phantoms are presented. The first in vivo investigations made on healthy volunteers emphasize the potential clinical applicability of SSI for breast cancer detection.
Medical ultrasound has become more indispensable in providing high quality real time images of the anatomy and blood flow. Three dimensional ultrasonic imaging has recently been developed which overcomes the limitations of two-dimensional ultrasound by reducing the variability and allowing the diagnostician to view the anatomy in 3D. This technique also provides tomographic images at a high rate, and the orientation of the images is flexible because they are not necessarily acquired as a stack of planes. The acquisition, reconstruction, and rendering techniques for 3D imaging are discussed, including their various applications and limitations.
Two-dimensional ultrasound (US) imaging has been successfully used in clinical applications as a low-cost, portable and non-invasive image modality for more than three decades. Recent advances in computer science and technology illustrate the promise of the 3-D US modality as a medical imaging technique that is comparable to other prevalent modalities and that overcomes certain drawbacks of 2-D US. This systematic review covers freehand 3-D US imaging between 1970 and 2017, highlighting the current trends in research fields, the research methods, the main limitations, the leading researchers, standard assessment criteria and clinical applications. Freehand 3-D US systems are more prevalent in the academic environment, whereas in clinical applications and industrial research, most studies have focused on 3-D US transducers and improvement of hardware performance. This topic is still an interesting active area for researchers, and there remain many unsolved problems to be addressed.
Volume reconstruction method plays an important role in improving reconstructed volumetric image quality for freehand three-dimensional (3D) ultrasound imaging. By utilizing the capability of programmable graphics processing unit (GPU), we can achieve a real-time incremental volume reconstruction at a speed of 25-50 frames per second (fps). After incremental reconstruction and visualization, hole-filling is performed on GPU to fill remaining empty voxels. However, traditional pixel nearest neighbor–based hole-filling fails to reconstruct volume with high image quality. On the contrary, the kernel regression provides an accurate volume reconstruction method for 3D ultrasound imaging but with the cost of heavy computational complexity. In this paper, a GPU-based fast kernel regression method is proposed for high-quality volume after the incremental reconstruction of freehand ultrasound. The experimental results show that improved image quality for speckle reduction and details preservation can be obtained with the parameter setting of kernel window size of 5×5×5 and kernel bandwidth of 1.0. The computational performance of the proposed GPU-based method can be over 200 times faster than that on central processing unit (CPU), and the volume with size of 50 million voxels in our experiment can be reconstructed within 10 seconds.
The user interface is critical to the clinical acceptance of free-hand D ultrasound imaging. In the system described here, the acquisition of scans from a conventional 2D probe is synchronized to probe movement. Motion-gated acquisition reduces the dependency of scan quality on the operator and can detect poor scanning technique. Automatic annotation is facilitated by recording the orientation of the patient. A 'virtual probe' enables a clinician to reslice the acquired data as if the patient were being rescanned. A 'thick reslice' enables spatial compounding to be implemented in the visualization process. The critical scale parameter, which is difficult to automatically determine, is intuitively interpreted as the slice thickness and interactively controlled by the clinician. Real-time volume rendering without prior segmentation of the data is possible using this technique. Shape-based interpolation assists manual segmentation of the data. The distance field from the segmentation process is used to mask the raw data and the result is volume rendered. A 3D scalpel enables efficient refinement of the segmentation by directly editing the volume- rendered view. The 3D scalpel prunes a set of user-defined contours to which a surface is fitted and the enclosed volume computed. A compact set of contours is retained by the system which allows the actions of the user to be undone. Three clinicians have tested the system, acquiring over 100 3D fetal scans, in a hospital environment.
Three-dimensional ultrasound (3DUS) offers a valuable approach to many diagnostic imaging problems and provides a relatively low cost alternative to D imaging modalities such as MRI and CT. To obtain a 3DUS image, a clinical ultrasound scanner is used to produce a sequence of adjacent 'slices' of the region of interest, which are recorded and used to reconstruct a volume. The required location of each slice may be found either by a priori knowledge of the scan path (mechanized scanning) or by tracking the path of the transducer at scan time (freehand scanning). For some imaging applications the scan path is irregular, making mechanized scanning difficult or impossible. Some examples are: imaging vascular disease in the carotid arteries, joint imaging and obstetrics. We have developed a freehand 3DUS system that is capable of such imaging tasks. We used phantoms containing a wire and a 50% stenosed cylinder phantom to test our system for vascular applications. We found the mean error in locating any image plane to be less than 0.1 mm ((sigma) equals 0.05 mm), with minimal geometric distortion. The degree of stenosis of the phantom was measured from a reconstructed volume to be 52.6% ((sigma) equals 2%). We have started a clinical stenosis study and a pilot joint imaging study. Our clinical results indicate that measurement of stenosis in patients should be possible.
Skeletal muscle volume is an important indicator of muscle function. Three-dimensional (3D) freehand ultrasound provides a noninvasive method for determining muscle volume and is acquired using a standard clinical ultrasound machine and an external tracking system to monitor transducer position. Eleven healthy volunteers were scanned with a 3D freehand system that uses an optical tracking device. Interest was concentrated on one of the muscles of the quadriceps group, rectus femoris and volume measurements performed on 30 mm cross-sections were compared with measurements derived from magnetic resonance imaging. Measured muscle volumes ranged from 5 cm3 to 28 cm3. The mean difference between measurements from 3D freehand ultrasound and magnetic resonance was 0.53 cm3 with 95% limits of agreement of ±2.14 cm3. Muscle volume measurements obtained using 3D ultrasound were within ±16% of the corresponding value from magnetic resonance imaging. We have shown for the first time that 3D freehand ultrasound can be used to determine human skeletal muscle volume accurately in vivo. (E-mail: [email protected]
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Three-dimensional (3-D) ultrasound (US) is an emerging new technology with numerous clinical applications. Ultrasound probe calibration is an obligatory step to build 3-D volumes from 2-D images acquired in a freehand US system. The role of calibration is to find the mathematical transformation that converts the 2-D coordinates of pixels in the US image into 3-D coordinates in the frame of reference of a position sensor attached to the US probe. This article is a comprehensive review of what has been published in the field of US probe calibration for 3-D US. The article covers the topics of tracking technologies, US image acquisition, phantom design, speed of sound issues, feature extraction, least-squares minimization, temporal calibration, calibration evaluation techniques and phantom comparisons. The calibration phantoms and methods have also been classified in tables to give a better overview of the existing methods.
There is an urgent need for a measurement protocol and software analysis for objective testing of the imaging performance of medical ultrasound equipment from a user's point of view. Methods for testing of imaging performance were developed. Simple test objects were used, which have a long life expectancy. First, the elevational focus (slice thickness) of the transducer was estimated and the in-plane transmit focus was positioned at the same depth. Next, the postprocessing look-up-table (LUT) was measured and linearized. The tests performed were echo level dynamic range (dB), contrast resolution (i.e., gamma of display, number of gray levels/dB) and sensitivity, overall system sensitivity, lateral sensitivity profile, dead zone, spatial resolution and geometric conformity of display. The concept of a computational observer was used to define the lesion signal-to-noise ratio, SNRL (or Mahalanobis distance), as a measure for contrast sensitivity. All the measurements were made using digitized images and quantified by objective means, i.e., by image analysis. The whole performance measurement protocol, as well as the quantitative measurements, have been implemented in software. An extensive data-base browser was implemented from which analysis of the images can be started and reports generated. These reports contain all the information about the measurements, such as graphs, images and numbers. The approach of calibrating the gamma by using a linearized LUT was validated by processing simultaneously acquired rf data. The contrast resolution and echo level of the rf data had to be compressed by a factor of two and amplified by a gain factor corresponding to 12 dB. This resulted in contrast curves that were practically identical to those obtained from DICOM image data. The effects of changing the transducer center frequency on the spatial resolution and contrast sensitivity were estimated to illustrate the practical usefulness of the developed approach of quality assurance by measuring objective performance characteristics. The developed methods might be considered as a minimum set of objective quality assurance measures. This set might be used to predict clinical performance of medical ultrasound equipment, taking into account the performance at a unique point in space i.e., the coinciding depths of the elevation and in-plane (azimuth) foci. Furthermore, it should be investigated whether the approach might be used to compare objectively various brands of equipment and to evaluate the performance specifications given by the manufacturer. Last but not least, the developed approach can be used to monitor, in a hospital environment, the medical ultrasound equipment during its life cycle. The software package may be viewed and downloaded at the website http://www.qa4us.eu. (E-mail: [email protected]
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Three-dimensional (3D) ultrasound (US) is increasingly being introduced in the clinic, both for diagnostics and image guidance. Although dedicated 3D US probes exist, 3D US can also be acquired with the still frequently used two-dimensional (2D) US probes. Obtaining 3D volumes with 2D US probes is a two-step process. First, a positioning sensor must be attached to the probe; second, a reconstruction of a 3D volume can be performed into a regular voxel grid. Various algorithms have been used for performing 3D reconstruction based on 2D images. Up till now, a complete overview of the algorithms, the way they work and their benefits and drawbacks due to various applications has been missing. The lack of an overview is made clear by confusions about algorithm and group names in the existing literature. This article is a review aimed at explaining and categorizing the various algorithms into groups, according to algorithm implementation. The algorithms are compared based on published data and our own laboratory results. Positive and practical uses of the various algorithms for different applications are discussed, with a focus on image guidance. (E-mail: [email protected]
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Freehand three-dimensional ultrasound: implementation and applications
- S Sherebin
- A Fenster
- R Rakin
- D Spence
S. Sherebin, A. Fenster, R. Rakin and D. Spence, "Freehand three-dimensional ultrasound: implementation
and applications.," Newport Beach, CA, USA, 1996.