Ultrasound Artifacts Research Articles

A wavelet thresholding method to reduce ultrasound artifacts

Abstract Artifacts due to enhancement, reverberation, and multi-path reflection are commonly encountered in medical ultrasound imaging. These artifacts can adversely affect an automated image quantification algorithm or interfere with a physician’s assessment of a radiological image. This paper proposes a soft wavelet thresholding method to replace regions adversely affected by these artifacts with the texture due to the underlying tissue(s), which were originally obscured. Our proposed method soft thresholds the wavelet coefficients of affected regions to estimate the reflectivity values caused by these artifacts. By subtracting the estimated reflectivity values of the artifacts from the original reflectivity values, estimates of artifact reduced reflectivity values are attained. The improvements of our proposed method are substantiated by an evaluation of Field II simulated, in vivo mouse and human heart B mode images.

Fast‐marching segmentation of three‐dimensional intravascular ultrasound images: A pre‐ and post‐intervention study

Intravascular ultrasound (IVUS) is a vascular imaging technique that is used to study atherosclerosis since it has the ability to show the lumen and the vessel wall. Cross-sectional images of blood vessels are produced and they provide quantitative assessment of the vascular wall, information about the nature of atherosclerotic lesions, as well as the plaque shape and size. Due to the ultrasound speckle, catheter artifacts, or calcification shadows, the automated analysis of large IVUS data sets represents an important challenge. A multiple interface 3D fast-marching method is presented for the detection of the lumen and external vessel wall boundaries. The segmentation is based on a combination of region and contour information, namely, the gray level probability density functions of the vessel structures and the intensity gradient. The detection of the lumen boundary is fully automatic. The segmentation method includes an interactive initialization procedure of the external vessel wall border. The segmentation method was applied to 20 in vivo IVUS data sets acquired from femoral arteries. This database contained three subgroups: Pullbacks acquired before balloon angioplasty (n=7), after the intervention (n=7), and at a 1 yr follow-up examination (n=6). Results were compared to validation contours that were manually traced by two experts on more than 1500 individual frames. For all subgroups, no significant difference was found between the area measurements of the segmentation and validation contours for the lumen and external vessel wall. Moreover, high intraclass correlation coefficients (> 0.96) between the area of the manually traced contours and detected boundaries with the fast-marching method were obtained for both vessel layers over the whole database. The segmentation performance was also evaluated with point-to-point contour distances between segmentation results and manually traced contours. A good overall accuracy was obtained with average distances < 0.13 mm and maximum distances < 0.46 mm, indicating a good performance in regions lacking information or containing artifacts. Only small differences of less than a pixel (0.02 mm) were observed between the average distance metrics of each subgroup, which prove the segmentation consistency. This new IVUS segmentation method provides accurate results that correspond well to the experts' manually traced contours, but requires much less manual interactions and is faster.

Probabilistic framework for tracking in artifact-prone 3D echocardiograms

The analysis of echocardiograms, whether visual or automated, is often hampered by ultrasound artifacts which obscure the moving myocardial wall. In this study, a probabilistic framework for tracking the endocardial surface in 3D ultrasound images is proposed, which distinguishes between visible and artifact-obscured myocardium. Motion estimation of visible myocardium relies more on a local, data-driven tracker, whereas tracking of obscured myocardium is assisted by a global, statistical model of cardiac motion. To make this distinction, the expectation-maximization algorithm is applied in a stationary and dynamic frame-of-reference. Evaluation on 35 three-dimensional echocardiographic sequences shows that this artifact-aware tracker gives better results than when no distinction is made. In conclusion, the proposed tracker is able to reduce the influence of artifacts, potentially improving quantitative analysis of clinical quality echocardiograms.

SU‐GG‐I‐131: Assessment of Transducer Artifacts Using a Novel, Low Cost Ultrasound Phantom

Purpose: Ultrasound artifacts are often identified by scanning a uniform region of a rigid tissue‐mimicking phantom while moving the transducer across the scan surface, and identifying any deviations from the expected smooth echotexture. Due to the rigid nature of commercial phantoms it is difficult to simultaneously couple the entire face of curved array transducers. We have proposed a novel low cost liquid phantom with a flexible scan surface. The purpose of this work is to demonstrate the proof of concept of this unique phantom. Method and Materials: The phantom consisted of a water/cornstarch solution enclosed in a thin latex balloon (thickness 0.24 mm). When shaken, the cornstarch provides a dynamic speckle pattern. Initial experiments were conducted to establish the basic effectiveness of this innovative phantom to demonstrate artifacts, to assess reproducibility of image acquisition, and inter‐operator variability. The phantom was imaged using an Acuson Sequoia US scanner and 4 transducer models (9L4, 6C2, 4V1 and EC‐10C5), and dynamic clips of the changing speckle field were recorded. Two transducers with independently‐confirmed artifacts were also tested. Results: The flexible scanning surface allowed excellent acoustic coupling of the entire face of all transducer models with the phantom, including tightly curved arrays. Little manual transducer motion was required with the liquid phantom as a result of the dynamic speckle field. Artifacts due to inactive elements were detected, including a single crystal dropout. Using a defined scan protocol, reproducible clips exhibiting low inter‐ and intra‐ operator dependency were obtained by 5 operators with minimal training, for transducers with and without artifacts. Conclusion: Due to its ease of operation, low cost, and sensitivity, this phantom may be superior to current methods of detecting ultrasound artifacts, and has the potential to promote better acceptance and compliance of ultrasound quality control.

US Artifacts

Image artifacts are commonly encountered in clinical ultrasonography (US) and may be a source of confusion for the interpreting physician. Some artifacts may be avoidable and arise secondary to improper scanning technique. Other artifacts are generated by the physical limitations of the modality. US artifacts can be understood with a basic appreciation of the physical properties of the ultrasound beam, the propagation of sound in matter, and the assumptions of image processing. US artifacts arise secondary to errors inherent to the ultrasound beam characteristics, the presence of multiple echo paths, velocity errors, and attenuation errors. The beam width, side lobe, reverberation, comet tail, ring-down, mirror image, speed displacement, refraction, attenuation, shadowing, and increased through-transmission artifacts are encountered routinely in clinical practice. Recognition of these artifacts is important because they may be clues to tissue composition and aid in diagnosis. The ability to recognize and remedy potentially correctable US artifacts is important for image quality improvement and optimal patient care.

Investigation of gain optimization technique in Doppler ultrasound system

In this paper the author describes a high sensitivity Doppler ultrasound system based on the principle of ensemble mean processing utilizing automatic gain optimization through system parameters. This technique allows a reduction of the physical size of the hardware and simplifies gain adjustment by reducing the gain range substantially. Such a system is not subject to Doppler ultrasound system artifacts such as the mirror effect and quantization.

Hilft das Ultraschallbiomikroskop (UBM) in der Diagnostik von intraskleralen Fremdkörpern?

Small intrascleral foreign bodies of different materials, especially plastic or organic, can sometimes not easily--or not at all--be detected by routine X-ray examination or computed tomography scan. The aim of our study was to evaluate the usefulness of ultrasound biomicroscopy (UBM) with regard to the detection and localisation of such foreign bodies. An in vitro study with the preparation of a scleral tunnel on 12 porcine eyes was performed. Small foreign bodies of different types of material were placed in the tunnel. The UBM was performed with a Humphrey Ultrasound Biomicroscope, Model 840, to evaluate its diagnostic value in detecting and specifying these sclera-covered foreign bodies. Even small foreign bodies of the anterior ocular segment of only 200 microm in size can be detected with the UBM due to the typical ultrasound patterns and artifacts. However, there is no diagnostic specificity for the corresponding material. The UBM is a high-frequency ultrasonic device with an imaging depth of 5 mm and a spatial resolution of 100 microm. Therefore it is a useful alternative or, respectively, additional diagnostic tool to common imaging techniques like routine X-ray imaging or CT scans, especially in the detection of non-metallic objects. It can provide important information for the ophthalmic surgeon with regard to pre-operative evaluation of the eye. Furthermore, the UBM might even substitute operative exploration of foreign bodies if they are located in the anterior segment of the eye.

Detecting stripe artifacts in ultrasound images.

Brain perfusion diseases such as acute ischemic stroke are detectable through computed tomography (CT)-/magnetic resonance imaging (MRI)-based methods. An alternative approach makes use of ultrasound imaging. In this low-cost bedside method, noise and artifacts degrade the imaging process. Especially stripe artifacts show a similar signal behavior compared to acute stroke or brain perfusion diseases. This document describes how stripe artifacts can be detected and eliminated in ultrasound images obtained through harmonic imaging (HI). On the basis of this new method, both proper identification of areas with critically reduced brain tissue perfusion and classification between brain perfusion defects and ultrasound stripe artifacts are made possible.

The use of Speckle Reduction Imaging (SRI) Ultrasound in the characterization of carotid artery plaques

Background and purpose Speckle Reduction Imaging is a new algorithm that improves the image quality of B-mode scanning by reducing the reverberation artifacts. In the present study the value of this method for the characterization of atherosclerotic plaques in the internal carotid artery was investigated. Methods Two hundred and twenty two patients (161 men, 61 women; mean age 73 years) referred for carotid ultrasound evaluation were included in the study. Patients with plaques of the internal carotid artery as identified by conventional B-mode scanning were investigated also with the addition of Speckle Reduction Imaging (SRI) with the use of a 4–11-MHz wide band linear transducer. Plaque morphology was rated according to a standardized protocol by two independent observers. Results For the determination of plaque echogenicity, the reproducibility of SRI ( κ = 0.83) was higher than that of conventional B-mode ultrasound ( κ = 0.68). The interobserver agreement for plaque surface characterization was also higher for SRI ( κ = 0.8) than for conventional B-mode ( κ = 0.61). At the evaluation of the image quality through a semiquantitative analysis, SRI was rated superior in the plaque texture resolution, plaque borders determination, vessel wall demarcation and fibrous cap depiction. In addition, the level of “speckle” was reduced with the use of SRI. Conclusions SRI is a technique that shows good general agreement with high-resolution B-mode and can be used for the characterization of atherosclerotic plaques in the carotid artery. Furthermore, because this advanced technique allows reduction of ultrasound artifacts, it improves the image quality allowing more precise visualization of plaque morphological details.

WE‐C‐330A‐09: Dynamic, MultiModality Imaging: Temporal Precision and US Artifact Reduction

Purpose: Herein we describe the development of a dynamic fusion technology for ultrasound (US) and other static 3D data sets. We tested whether the high US frame rate is sufficient to accurately track objects subject to respiratory motion. In addition, we used the spatial registration functions of the system to test whether aggressive compounding of US images would be efficacious in terms of artifact reduction and boundary detection. Materials/Methods: The system's dynamic spatial accuracy was tested using a phantom translated at a velocity of either 4 or 16 mm/s. To test inaccuracies due to video processing we offset the arm and video frame data in single frame increments. Static 3D US data sets were acquired incorporating an acoustic obstruction. Data sets were reconstructed using images from multiple angles of interrogation. Similar experiments were performed to assess the system's ability to reduce reverberation artifacts and tested on a human subject. Results: By correcting for video processing latency, the system was able to track object motion to 0.2 and 0.5 mm for speeds of 4 and 16 mm/s, respectively. Aggressive image compounding was able to reveal objects that were otherwise obstructed from a single view. Reverberation artifacts were reduced, in addition to enhancing certain object boundaries . These results were present although less obvious in early human testing. Conclusions: Our imaging system is spatially accurate over a range that permits interrogation of an adult abdomen from a wide range of angles. The system's ability to track respiratory motion has been demonstrated. Aggressive compounding demonstrated that obstructed test objects could be visualized by non‐intelligently summing images from varying angles. Soft tissue boundaries and other US artifacts may also benefit from application of the technology.Supported by NIH R01EB002899.

Intravascular ultrasound image segmentation: a three-dimensional fast-marching method based on gray level distributions

Intravascular ultrasound (IVUS) is a catheter based medical imaging technique particularly useful for studying atherosclerotic disease. It produces cross-sectional images of blood vessels that provide quantitative assessment of the vascular wall, information about the nature of atherosclerotic lesions as well as plaque shape and size. Automatic processing of large IVUS data sets represents an important challenge due to ultrasound speckle, catheter artifacts or calcification shadows. A new three-dimensional (3-D) IVUS segmentation model, that is based on the fast-marching method and uses gray level probability density functions (PDFs) of the vessel wall structures, was developed. The gray level distribution of the whole IVUS pullback was modeled with a mixture of Rayleigh PDFs. With multiple interface fast-marching segmentation, the lumen, intima plus plaque structure, and media layers of the vessel wall were computed simultaneously. The PDF-based fast-marching was applied to 9 in vivo IVUS pullbacks of superficial femoral arteries and to a simulated IVUS pullback. Accurate results were obtained on simulated data with average point to point distances between detected vessel wall borders and ground truth <0.072 mm. On in vivo IVUS, a good overall performance was obtained with average distance between segmentation results and manually traced contours <0.16 mm. Moreover, the worst point to point variation between detected and manually traced contours stayed low with Hausdorff distances <0.40 mm, indicating a good performance in regions lacking information or containing artifacts. In conclusion, segmentation results demonstrated the potential of gray level PDF and fast-marching methods in 3-D IVUS image processing.

3619: Ultrasound of shoulder instability: Correlation with ultrasonography and MR and US arthrography

The ultrasonography to diagnose rotator cuff injuries is well known, but that for the abnormalities of glenoid labrum is performed relatively a little. It may be the reason that (1) adjacent bony structures (coracoid process, acromion and humeral head) interfere with the sonic window, (2) the joint is located relatively deeply to use high-frequency transducer and (3) because of variable ultrasound artifacts it is difficult that small labral abnormality is revealed. However, ultrasonography is an inexpensive, dynamic, fast and easily accessible method.

A useful ultrasound artifact and its application - the 'twinkling sign'

The SA Journal of Radiology is the official journal of the Radiological Society of South Africa and the Professional Association of Radiologists in South Africa and Namibia. The SA Journal of Radiology is a general diagnostic radiological journal which carries original research and review articles, pictorial essays, case reports, letters, editorials, radiological practice and other radiological articles.

“Bayonet Artifact” during Ultrasound-guided Transarterial Axillary Block

Ultrasound-guided regional anesthesia is an emerging field that potentially provides better block efficacy than other current techniques.1–3In particular, ultrasound-guided axillary block had been described as an excellent technique for brachial plexus anesthesia.4,5With this method, a short axis (transverse cross-sectional) view of the axillary artery and surrounding nerves is obtained with the block needle approaching from the lateral aspect of the arm in the plane of imaging. Although V-shaped redirection of the block needle can be used to place local anesthetic on the superficial and deep sides of the axillary artery, transarterial placement of the needle may occur during the procedure.During an ultrasound-guided axillary block, we observed a bent echo of the 25-gauge 3.8-cm Quincke tip needle (Becton Dickinson and Company, Franklin Lakes, NJ). The needle shaft echo was bent toward the skin surface when the needle crossed the axillary artery (fig. 1). When examined after the procedure, the injection needle was perfectly straight.Described as a “bayonet artifact,” this ultrasound artifact causes apparent needle deformity and has been reported during breast biopsy in which a needle traverses a tumor surrounded by fat tissue.6Bayonet artifact occurs when the ultrasound beam passes through tissues with different speeds of sound. Similar speed of sound artifacts have been described in the soft tissues of the kidney.7–9Because all commercial ultrasound machines assume a uniform speed of sound of 1,540 m/s,10actual differences among speeds of sound in tissue change the apparent depth of received echoes. The speeds of sound among soft tissues may actually range from 1,450 m/s in fat to more than 1,600 m/s in muscle.10Thus, clinical scanning can routinely produce speed of sound errors of approximately 5%.This letter describes a bayonet artifact observed during regional anesthesia. The artifact occurred when the block needle passed through the axillary artery with the ultrasound beam nearly perpendicular to the needle. The speed of sound in whole blood (1,580 m/s) is higher than the average speed of sound in soft tissue (1,540 m/s).11Therefore, bending of the needle echo toward the transducer was seen when the needle passed through the axillary artery.Ultrasound guidance likely reduces the incidence of vascular puncture during regional block.12However, inadvertent vascular puncture has been reported during peripheral nerve blocks despite use of ultrasound guidance.13,14Therefore, bayonet artifacts from transarterial needle placement may occur during regional block even if vascular puncture was not intended.The basic premise of the in-plane approach for ultrasound-guided regional blockade is that precise placement of the block needle tip near nerves is possible in real time. However, there are circumstances under which the actual needle position and perceived image do not agree. Here, we describe one of those circumstances that occurred during transarterial axillary block.* San Francisco General Hospital, University of California, San Francisco, California. graya@anesthesia.ucsf.edu

Atypical Color Doppler Findings Related to Remote Lower-Extremity Traumatic Injury

Introduction Ultrasound artifacts can be misleading. This case demonstrates an unusual color Doppler artifact encountered while performing a lower-extremity venous evaluation. This color Doppler artifact was so unique that initially it was thought to be an incidental vascular finding. Case Study A 46-yr-old military veteran was seen in our noninvasive vascular laboratory for a lower-extremity venous evaluation because of left lower-extremity edema. He gave a history of chronic left lower-extremity pain from a war injury to his anterior left calf. An abscess developed 1.5 yr ago after he received whirlpool therapy. When the transducer was placed on the injury site, a large portion of the abscess filled with mosaic color that appeared to originate from the anterior portion. This color occurred without transducer movement. The appearance was similar to an arteriovenous fistula, which was suspected because of varicosities in the vicinity. However, pulsed Doppler revealed artifactual noise. Conclusion It was suspected that this was an impressive, atypical color Doppler reverberation artifact. The patient's tibiofibula radiographs showed pieces of shrapnel throughout the abscess. We hypothesize that the artifact was created by acceleration of the sound waves through the fluid in the large abscess with resonation between fragments of shrapnel. This is an example of a color Doppler artifact making it appear that there is flow in a location where there is none.

Ocular Ultrasonography in Horses

Ocular ultrasonography is a practical and valuable examination tool for horse eyes with anterior opacities that preclude ophthalmoscopy of deeper structures. Ultrasonography is indicated in cases of periocular trauma, exophthalmos, corneal masses, corneal edema and/or infiltrates, cataracts, and anterior uveitis. Transducers of 7 to 10 MHz may be used to identify and characterize cataracts, lens luxation, lens rupture, vitreal opacities, retinal detachment, endophthalmitis, microphthalmos, buphthalmos, and periorbital masses. High-resolution ultrasonography, using frequencies of 20 MHz and greater, provides improved detail of anterior segment structures. Ultrasound image artifacts are common, requiring knowledge of ocular anatomy and basic ultrasonographic principles for accurate interpretation.

Ultrasound artifacts as differential diagnostic problems in ultrasound of the upper abdomen

The word artifact stands for any visible result of imaging procedures which is caused by the procedure itself and not the entity being analyzed. Recognition of artifacts in everyday work is of great significance for final diagnosis, since their wrong interpretation not only compromises the value of ultrasound finding, but may also lead to a wrong therapeutic approach. Artifacts appear as the result of physical properties of an ultrasound beam, technical aspects of ultrasound apparatus and immobility in creation of ultrasound image. Artifacts in the form of acoustic shadows, acoustic enhancements and reverberation most commonly appear and lead to changed appearance of certain structures. That is why great experience and knowledge of radiologists-ultrasonographists is necessary, since diagnostic accuracy of the method itself is under their immediate control. Incorrect interpretation of artifacts and failure to recognize them reduces the value of ultrasound imaging which has, during the past 25 years, confirmed its exceptional diagnostic value.

Real-time compound ultrasonography: pictorial review of technology and the preliminary experience in clinical application of the abdomen.

The purposes of this essay are to illustrate the technology overview and theoretical benefits of real-time compound ultrasonography (US) and to present our preliminary clinical experience in the evaluation of normal and diseased abdomens. The application of compounding principles to real-time US and its recent reintroduction into mainstream commercial systems have offered new opportunities for its clinical application to the routine examination of the abdomen. In our early preliminary experience, this technique effectively suppressed many of the US artifacts, better depicted the margin or boundary of the lesion, and increased contrast resolution or lesion conspicuity. Therefore, we believe that real-time compound US is a promising technique that may enhance the diagnostic confidence of the examination in the evaluation of normal and diseased abdomens.

Diagnostic ultrasound artifacts during imaging of two-body interfaces: Part 1––Wavelength resonance

A diagnostic ultrasound technique is to be developed for measuring surface contact areas at the tibio-femoral interface of a total knee replacement in an in vitro industrial engineering setting as a design tool. As a first step, a previous study mathematically characterized the ultrasound behaviour expected at a two-body circular-on-flat interface of known geometry. In the current investigation, a series of test objects was constructed and imaged to experimentally validate the theoretical contact models. Specifically, several unique metal-on-polymer test objects, whose interfaces were point, non-point, and circular contact areas, were ultrasonically imaged. The effects of interface geometry, ultrasound resonance wavelength, λ/2, and compressive load were studied.

Diagnostic ultrasound artifacts during imaging of two-body interfaces: Part 2––beam thickness artifact

A diagnostic ultrasound method is being developed for measuring surface contact areas at the tibio–femoral interface of a total knee replacement in a non-clinical industrial setting as an engineering design tool. As an initial step towards this, a previous study mathematically predicted the effect of ultrasound beam thickness on contact area measurements at a two-body interface. In the current study, a novel metal-on-polymer acoustic test object was constructed to create circular two-body interfaces of known geometry. The object was ultrasonically imaged, contact areas measured, and the results compared with the theoretical model previously developed.