A pseudolesion of the liver caused by rib cartilage in B-mode ultrasonography

An artifactual protuberance at the surface of the liver in connection with an incomplete acoustic shadow is described. The reproduction of these phenomena in vitro was possible, providing an explanation of their origin. Rib cartilage, with its convex shape, and with the higher sound wave velocity and the higher attenuation compared with the surrounding tissue, causes these artifacts. The identification of a pseudolesion composed of these artifacts is simple if one considers its origin.     

Late Gadolinium Enhancement of the right ventricular myocardium: Is it really different from the left ?

It has been suggested that, in late gadolinium enhancement, the signal of right ventricular myocardium is nulled at a shorter inversion time than the left. While we initially made the same observation, we believe that the difference is not real, but results from artifacts.We present 7 cases as well as computer simulations to describe the nature of these artifacts and explain how they can create the impression of different inversion times for the right and left ventricle. At inversion times that are shorter than ideal for the myocardium a black rim can be seen at the border of the myocardium with blood on the inside and with fat on the outside. This is most likely a partial volume effect. The thin myocardium of the right ventricle is sandwiched between these black rims and, at a low spatial resolution, is no longer visible. In this case, the adjacent black rims may then be misinterpreted as myocardium. While black rims also occur on the left side, the myocardium is thicker and remains discernable as a separate layer. As a consequence, the optimal inversion time for the right ventricle only appears different from that for the left. In fact, in the presence of hypertrophy of the right ventricle or during systolic wall thickening we did not find a difference in inversion times between the left and right ventricle. We conclude that sufficient spatial resolution is important for adequate late gadolinium enhancement of the right ventricle.     

Review of artifacts associated with transrectal ultrasound: Understanding,recognition, and prevention of misinterpretation

Artifacts are inadequate representations of the structures being imaged. Transrectal ultrasound (TRUS) used for evaluating rectal tumors has its own, unique spectrum of artifacts such as (1) pseudomasses (beam thickness: imaging of rectal folds; mirror image: reflection at an intraluminal fluid level); (2) inadequate size of the lesion (mirror image or grating lobes); (3) simulation of malignant infiltration (beam thickness, attenuation or refraction); (4) incomplete field of view (shadowing; reverberation or mirror-image); (5) confusing echo patterns (side lobe artifacts or mirror image: reflection at the balloon surface). The understanding of the physical properties of ultrasound is the basis for the recognition of these artifacts and prevention of misinterpretation. We present a review of these artifacts and their causes. © 1995 John Wiley & Sons, Inc.     

Suppression of Grating Lobe Artifacts in Ultrasound Images Formed from Diverging Transmitting Beams by Modulation of Receiving Beams

In linear array transducers, owing to regular spacing of the array elements, grating lobes exist in transmission and reception. In ultrasonic imaging involving the use of diverging (unfocused) transmitting beams and steered receiving beams by linear transducer arrays, aperture apodization and spatial combination of steered receiving beams from multiple transmissions are not sufficient to suppress receive-grating lobe artifacts. To further suppress receive-grating lobe artifacts in reconstructed B-mode images, we propose a technique of modulating the receiving beams by a factor that is governed by the envelope of a corresponding signal, which is formed by filtering the receiving beam with a zero-phase low-pass filter with a cut-off frequency that is determined by the receiving beam steering angle. This technique suppressed receive-grating lobe artifacts without significant loss in spatial resolution in offline reconstructed B-mode images from simulation, phantom and in vivo imaging of the carotid artery. In a simulation of point scatterers, a relative reduction in grating lobe artifacts of 40 dB was realized in images from diverging beam scanning.     

Monitoring imaging of lesions induced by high intensity focused ultrasound based on differential ultrasonic attenuation and integrated backscatter estimation

We investigated the feasibility of two monitoring imaging methods to visualize and evaluate the high intensity focused ultrasound (HIFU) induced lesions in vitro during and after their formation, which were based on differential ultrasonic parameter estimation. Firstly, ultrasonic attenuation slope of tissue sample was estimated based on the spectral analysis of ultrasound RF backscattered signals. The differential attenuation slope maps were acquired, which were interpreted as the differences between the pretreatment image and those obtained in different stages during HIFU therapy. Secondly, ultrasonic integrated backscatter (IBS), defined as the frequency average of the backscatter transfer function over the useful bandwidth, was proposed quantitatively to evaluate the extent of lesions with the same RF signals as the first method. Differential IBS maps were also acquired to visualize temporal evolution of lesion formation. It was found in pig liver in vitro that more precise definition of the treated area was obtained from the differential IBS images than from differential attenuation slope images. Dramatic increase in both attenuation and IBS value was observed during the therapy, which may be related to dramatic enhancement of cavitation due to boiling and accompanying tissue damage. Two methods to obtain one differential image were compared and the cumulative differential image was found to be able to eliminate noises and artifacts to some extent, which was the cumulation of a series of differential images acquired from the differences between the temporally adjacent RF data frames. Moreover, we presented a bidirectional color code for identification of the artifacts due to tissue movements caused by HIFU radiation force. We conclude that cumulative differential IBS images have the potential to monitor the formation of HIFU-induced lesions.     

FMRI-adaptation to highly-rendered color photographs of animals and manipulable artifacts during a classification task

We used fMRI to identify brain areas that adapted to either animals or manipulable artifacts while participants classified highly-rendered color photographs into subcategories. Several key brain areas adapted more strongly to one class of objects compared to the other. Namely, we observed stronger adaptation for animals in the lingual gyrus bilaterally, which are known to analyze the color of objects, and in the right frontal operculum and in the anterior insular cortex bilaterally, which are known to process emotional content. In contrast, the left anterior intraparietal sulcus, which is important for configuring the hand to match the three-dimensional structure of objects during grasping, adapted more strongly to manipulable artifacts. Contrary to what a previous study has found using gray-scale photographs, we did not replicate categorical-specific adaptation in the lateral fusiform gyrus for animals and categorical-specific adaptation in the medial fusiform gyrus for manipulable artifacts. Both categories of objects adapted strongly in the fusiform gyrus without any clear preference in location along its medial-lateral axis. We think that this is because the fusiform gyrus has an important role to play in color processing and hence its responsiveness to color stimuli could be very different than its responsiveness to gray-scale photographs. Nevertheless, on the basis of what we found, we propose that the recognition and subsequent classification of animals may depend primarily on perceptual properties, such as their color, and on their emotional content whereas other factors, such as their function, may play a greater role for classifying manipulable artifacts.     

左右肘静脉注射对比剂对胸部CT血管成像的影响

目的：探讨左右肘静脉注射对比剂对胸部CT血管成像（CTA）的影响。方法将60例胸部CTA检查患者随机分为2组,每组30例,分别进行左右肘静脉注射对比剂,其他参数相同。扫描完成后,测量并比较降主动脉、肺动脉主干、右下肺动脉、左上肺动脉、左下肺动脉、右下肺静脉、左上肺静脉、左下肺静脉的CT强化值,并对胸部血管成像质量进行评价。结果2组患者的降主动脉、肺动脉主干、右下肺动脉、左上肺动脉、左下肺动脉、右下肺静脉、左上肺静脉、左下肺静脉的CT强化值分别为：（342.42±52.63）Hu和（369.04±88.87）Hu、（389.72±126.36）Hu和（411.46±110.98）Hu、（366.63±124.84）Hu和（392.67±115.59）Hu、（389.19±128.99）Hu和（390.24±114.47）Hu、（388.64±127.37）Hu和（404.64±124.47）Hu、（361.84±73.87）Hu和（370.40±91.42）Hu、（384.19±78.50）Hu和（401.68±96.32）Hu、（377.10±81.07）Hu和（388.59±74.89）Hu,差异均无统计学意义（P均＞0.05）。结论胸部CTA成像时,采用左右肘静脉注射对比剂,对血管的强化程度无明显影响。     

Nonlinear acoustics in diagnostic ultrasound

The propagation of ultrasonic waves is nonlinear. Phenomena associated with the propagation of diagnostic ultrasound pulses cannot be predicted using linear assumptions alone. These include a progressive distortion in waveform, the generation of frequency harmonics and acoustic shocks, excess deposition of energy and acoustic saturation. These effects occur most strongly when ultrasound propagates within liquids with comparatively low acoustic attenuation, such as water, amniotic fluid or urine. Within soft tissues, similar effects occur, although they are limited by absorption and scattering. Nonlinear effects are of considerable importance during acoustic measurements, especially when these are used to predict in situ exposure. Harmonic generation may be used to create images. These offer improvements over conventional B-mode images in spatial resolution and, more significantly, in the suppression of acoustic clutter and side-lobe artifacts. B/A has promise as a parameter for tissue characterisation, but methods for imaging B/A have shown limited success.     

Wavelet-based motion artifact removal for functional near-infrared spectroscopy

Functional near-infrared spectroscopy (fNIRS) is a powerful tool for monitoring brain functional activities. Due to its non-invasive and non-restraining nature, fNIRS has found broad applications in brain functional studies. However, for fNIRS to work well, it is important to reduce its sensitivity to motion artifacts. We propose a new wavelet-based method for removing motion artifacts from fNIRS signals. The method relies on differences between artifacts and fNIRS signal in terms of duration and amplitude and is specifically designed for spike artifacts. We assume a gaussian distribution for the wavelet coefficients corresponding to the underlying hemodynamic signal in detail levels and identify the artifact coefficients using this distribution. An input parameter controls the intensity of artifact attenuation in trade-off with the level of distortion introduced in the signal. The method only modifies wavelet coefficients in levels adaptively selected based on the degree of contamination with motion artifact. To demonstrate the feasibility of the method, we tested it on experimental fNIRS data collected from three infant subjects. Normalized mean-square error and artifact energy attenuation were used as criteria for performance evaluation. The results show 18.29 and 16.42 dB attenuation in motion artifacts energy for 700 and 830 nm wavelength signals in a total of 29 motion events with no more than -16.7 dB distortion in terms of normalized mean-square error in the artifact-free regions of the signal.     

ECG myogenic artifacts during clonic seizures: a disturbing (and interesting) finding

During motor seizures myogenic artifacts may appear on ECG. We report a patient with recurring convulsive seizures involving left side of his body in whom ECG served as a surrogate of electromyography (EMG), showing myogenic artifacts strongly correlated with clonic jerks. The possibility of standard ECG of recording myogenic potentials when clonic seizures occur is something intriguing, being at the same time both disturbing and informative. In such cases standard ECG works as an EMG, although ECG filter, sensitivity and paper speed is different from EMG currently used in neurophysiological laboratory. However, using standard ECG acquisition parameters, muscular activity may be recorded without excessive attenuation of high-frequency myogenic potentials, permitting to indicate the frequency of clonic movements. On the other hand, whenever possible, positioning of ECG surface electrodes on limbs not (or less) involved in clonic epileptic movements may permit to obtain a sufficiently informative ECG recording with less amount of myogenic artifacts, thus providing essential information on heart rate and rhythm.     

A comparison of theoretical and experimental ultrasound field distributions in canine muscle tissue in vivo.

Relative ultrasound field distributions were measured using thermal techniques in canine thighs in vivo and in water. The experimental results were compared with distributions obtained from a numerical model based on the one-dimensional integration of the Rayleigh-Sommerfeld diffraction integral. The comparisons showed that the theoretical model is a good approximation to the distributions measured in water, with the agreement decreasing for regions in front of the acoustic focus. The main lobe profiles obtained in the muscle tissue also agreed well with both theoretical results and results measured in water (focussing was not lost). However, these in vivo distributions showed enlargement of the side lobes indicating scattering of the waves. It was also found that the interfaces between muscle groups produced considerable beam distortions as well as increased side lobe levels. Scattering of energy from the main lobe to the side lobes was verified by measurements of the peak intensity and the total acoustic power attenuation coefficients for passage of the beams through the thighs which showed that the former was about 40% higher than the latter. Also, absolute intensity values at the acoustic focus were measured in water using a hydrophone (0.5 mm active diameter) for 11 transducers ranging in frequency from 0.246 to 3.54 MHz. When these absolute values were compared with the model predictions, it was found that the model consistently overestimated the experimental data by a factor of less than 2. That is, the model can also be used to obtain upper bounds for absolute intensity values. Consequences of these results on ultrasound hyperthermia treatments are discussed.     

Artifacts that may be present on a blood film

Many artifacts or pseudoartifacts may be noted during the examination of a blood film. Artifactual results also may be generated by automated hematology analyzers, which in turn may be investigated by blood film examination. Some artifacts are misdiagnosed, and this in turn leads to inappropriate investigations or treatment. An awareness of the spectrum of spurious or artifactual results may help to prevent such an unfortunate occurrence.     

Lateral inverse filtering of ultrasonic B-scan images

The formation of ultrasonic B-scan images using parallel beams may be modelled as a lateral, one-dimensional convolution of the beam profile and an unknown but wanted reflection coefficient. Lateral inverse filtering, or deconvolution, might therefore be used to improve the image quality. Two different deconvolution techniques are applied to both an image of a tissue mimicking phantom and a human liver. An enhancement of the resolution (defined as the reciprocal of the half-width of the image of a point reflector) of about 1.4 is achieved. This is in good agreement with the previously derived formula R = square root 1n SNR, which relates the signal-to-noise ratio, SNR, to the resolution enhancement, R. However, each method also creates artifacts, and despite the slight resolution enhancement, the deconvoluted liver images do not exhibit more information nor are they more appealing. So it is felt that the computational effort is wasted. This failure is not a fault of the special deconvolution techniques tried here, but rather caused by the logarithmic dependence of R on SNR and by the noise level, which is largely due to macro- and microscopic inhomogeneities of the tissue and cannot be made arbitrarily small.     

Impaired myocardial SPECT imaging secondary to silicon- and saline-containing breast implants

Early detection of coronary artery disease (CAD) in women has been challenging. Women are more likely to present with atypical symptoms, and non-invasive evaluation for CAD has been less accurate. Myocardial SPECT imaging is a well-established technique that provides important physiologic, anatomic, and prognostic information in women. Attenuation artifacts secondary to breast tissue are a common problem in women and can lead to decreased specificity of gated SPECT imaging. Cosmetic breast implants are increasing in popularity. The presence of a foreign object overlying the anterior wall of the heart in addition to native breast tissue can significantly increase attenuation artifacts. There is only one report to date describing attenuation artifact due to silicon breast implants in comparison to control, and there are no reports regarding saline breast implants. Here we report three cases of impaired myocardial SPECT imaging in women with breast implants: one patient with silicone implants, and two with saline-containing implants. Clinicians should be aware of this problem and women should be educated regarding the potential future diagnostic problems that may occur with breast implants before considering this cosmetic surgery.     

Digital path-dependent recompensation of contrast-enhanced echocardiographic images

The regional video intensity of two-dimensional (2D) ultrasonographic images is directly affected by energy losses from the ultrasonic beam propagating between the transducer and the specific region of interest (ROI). These losses are mainly dependent on the scattering and absorption properties of the more proximal tissues. The commonly utilized automatic time-gain compensation (TGC) procedures, based on the assumption of uniform scattering and energy conversion throughout the investigated tissues and organs, seem to be largely inadequate in the contrast echocardiographic studies which attempt to quantitate the contrast enhancement of myocardial tissue. We hereby present an algorithm for the non-linear adaptive path-dependent recompensation of the ultrasonographic video intensity for the non-uniform scattering and absorption in images obtained using automatic TGC. The variable energy losses are estimated in our technique according to the reflections from the different points along the acoustic beam. The proposed algorithm is a post-processing function. It was developed considering beam attenuation by scattering and absorption and comparing correction procedures necessary with and without the assumption of uniform attenuation. We hereby present the results obtained by applying this algorithm to contrast enhanced echocardiographic images of canine hearts. The artifacts produced by the inadequate automatic TGC are essentially reduced by the recompensation procedure. The recompensation allows the observation of the changes in video intensity induced in the myocardial tissue by contrast-enhancing media, which are otherwise severely obscured by contrast transit altering the propagation effects.     

"Synthetic" comets: a new look at lung sonography

Ultrasound interstitial syndrome is an echographic pattern of the lung characterized by the presence of multiple acoustic artifacts called "comets" or B-lines. It correlates to increase in extravascular lung water and to interstitial lung disease. From the physical and genetic point of view, the characteristics and the entity of this correlation have not yet been studied. The purpose of this study was to extrapolate past observations and demonstrate how comets or B-lines are artifactual images whose formation is linked to ultrasound interactions on discretely aerated tissues of variable density. Echographic comets were studied by scanning a wet synthetic, partially aerated polyurethane sponge (phantom). Density of the phantom in different drying phases was measured and correlated to the presence of echographic artifacts. Artifacts (comets) showed a different concentration from a completely white artifactual field to presence of rare comets. Their density correlates with porosity and geometry of the phantom. In our opinion, comets represent superficial, artifactual, density and geometry correlated phenomenon due to the acoustic permeability of a broken (collapsed) specular reflector, normally present when the phantom is dry.     

Distance resolution with the FM-CW ultrasonic echo-ranging system.

The ability of a frequency-modulated continous-wave system to resolve returns from closely spaced multiple stationary targets is examined. Because the output consists of discrete harmonics of the sweep repetition frequency, a range corresponding to an anharmonic beat frequency results in a spectrum of harmonics. The shape of the spectrum depends on the range and the nature of the target reflection. Unwanted harmonic spectral output results from the periodic sweep discontinuities and from amplitude modulation of the returns, which is caused by the inevitably limited transducer bandwidth and the frequency dependence of attenuation in tissue. Although pulse-echo systems are also subject to frequency dispersion and the transducer bandpass limit, the experimentally verified result is that both range measurement precision and multiple target resolution are inferior to those obtainable from the same transducer with conventional pulse-echo signal processing.     

Paired-angle multiplicative compounding

Ultrasound compounding is a method of combining multiple images from different angles in order to create a single image with improved resolution and reduced angular-dependent artifactual detail. Compounding methods traditionally calculate each pixel in the compound image as a simple functional relationship between pixel elements in the component image set. In order to achieve an even better resolution and further reduce angular-dependent artifacts, this paper investigates a new type of compounding we call paired angle multiplicative compounding (PAMC), in which compound images are produced by a summation of multiplied pairs of component images acquired at different angles. A PAMC image of a breast phantom demonstrates improved delineation ofmicrocalcifications in comparison to the mean operation. Images of the forearm are used to investigate larger angles of paired multiplication, the best improving contrast ratio (28%) and signal to noise ratio (24%) when compared to the mean method. The PAMC method is found to be similar to the MEM and median compounding operations, the largest difference being that it is better preserving contributions from normal incidence but at the expense of needing a larger angular range.     

Duplication Images in Vascular Sonography

Objective. The purpose of this study was to determine the characteristics and phenomena of duplication (or mirror) images in vascular sonography. Methods. We retrospectively reviewed 5 cases of vascular sonography that produced duplication images performed between June 30, 2009, and January 10, 2010. The 5 vascular studies included the subclavian artery (2), subclavian vein (1), carotid artery (1), and abdominal aorta (1). The characteristics of the color flow images and spectral Doppler waveforms in the artifactual vessels and in the true vessels were analyzed. Sources and mechanisms of producing duplication images were assessed. Results. We were able to generate color flows in the artifactual vessels that were the same as in the true vessels in 2 cases. However, we were able to generate images in which the apparent flow directions in the artifactual vessels differed from the actual flow observed in the true vessels in all 5 cases by changing the orientation of the ultrasound beam relative to the true flow and the reflecting surface. Conclusions. Duplication images result from mirror reflections producing multipath artifacts. The appearance of the flow in an artifactual vessel on color Doppler imaging strongly depends on the angle of the incident sound beam and the surface structure of the strong reflector relative to the flow in the true vessel. Alternating the scanning plane and the angle of the incident sound beam to the reflector may help distinguish a duplication artifact from a true vessel in ambiguous cases.     

Ultimate limits in ultrasonic imaging resolution

According to elementary theory, the resolution of an ultrasonic imaging system increases with the ultrasonic frequency. However, frequency is limited by frequency-dependent attenuation. For imaging at any required depth, resolution improvement beyond the limit imposed by ultrasonic frequency can be obtained by increasing the ultrasonic intensity. This is itself, however, dependent on safety considerations and the effects of nonlinearity. In homogeneous media, image resolution increases with decreasing f-number. Particularly at low f-numbers, however, tissue inhomogeneity leads to a deterioration in image quality. Inhomogeneity may also be considered in terms of phase aberration. It has been found that for a given aperture, image degradation due to phase aberration is worse at higher frequencies. Schemes have been proposed for correction of this problem, but so far model systems do not lend themselves to clinical application. Deconvolution is unsatisfactory, speed correction is impracticable and synthetic aperture scanning and holography are virtually useless in biological tissues. Ultrasound-computed tomography has had only limited success. Speckle reduction can improve target detectability, but at the expense of resolution. Time-frequency control provides a useful partial solution to the problem of resolution reduction resulting from attenuation. It is clear that improved resolution would result in significant clinical benefits. An optimisation system for aperture size and ultrasonic frequency is proposed with signal averaging for resolution enhancement of a defined object area. This would have a compact ultrasonic beam and would allow frame rate to be traded for resolution, by means of signal averaging.