Contrast Media in Ultrasonography: Basic Principles and Clinical Applications (Medical Radiology)

Contrast Media in Ultrasonography. Basic Principles and Clinical Applications. Editors; (view Part of the Medical Radiology book series (MEDRAD). Download .
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Technically, this involves a constraint on the second derivative along the resulting snakes contour. In the case of a noisy ultrasound image, this parameter is particularly important. This is most frequently derived from the image gradient i. Since the purpose is to find the underlying feature gradient, uncontaminated by ultrasound image speckle, snake processing on ultrasound data frequency involves a speckle reducing pre-processing step [ 31 , 32 ]. There are a number of frequently encountered speckle reducing algorithms [ 33 — 38 ].

Several examples of the use of snakes in ultrasound feature segmentation exist for both 2D [ 40 ] and 3D [ 41 , 42 ]. Fortunately, evolving processing speed enables the clinical realization of progressively more complex algorithms. Except in the case of tissue harmonic imaging, in which the nonlinear second harmonic of the transmitted fundamental is isolated i.

Frequently, the contrast qualities of an image can be improved by spatial compounding in which a common tissue region is viewed from independently oriented transmit beam angles [ 43 ]. Spatial compounding has been shown to reduce speckle, clutter and improve image qualities and the ability to differentiate tissues [ 43 ]. In particular, it has proven successful in breast ultrasound: A limitation, however, of transmit beam spatial compounding is that the aperture must be divided to yield independent apertures and this results in reduced resolution on a per aperture basis.

In the case of moving tissue one can, in principle, differentiate the desired moving signal from an overlying static haze artifact [ 45 — 47 ]. While most of these algorithms are computationally intensive, they have the potential for widespread incorporation into the future generation of clinical scanners. This class of artifact reduction has more utility in cardiology than in radiology. Although most applications of speckle tracking are in cardiology [ 48 — 50 ], there are a number of radiology applications. Golemati et al [ 51 ] discussed the utility of speckle tracking for assessing elastic properties of the arterial wall and plaque in carotid arteries.

Traditional Color Doppler processing is limited to detecting the 1D component of motion aligned with the ultrasound beam axis. It is also possible to estimate velocities using time domain cross-correlation [ 54 ] but this method is less frequently encountered in clinical implementations. However, all these early methods extract only the Doppler component aligned with the ultrasound beam axis. Given that vessels are frequently parallel to the skin surface e. In principle, this problem can be addressed using speckle tracking [ 55 ] but this typically requires high signal to noise ratio and, thus, is limited to shallow vessels like the carotid artery.

Speckle tracking is also a relatively computationally intensive process. Another solution for enabling Doppler detection of transverse motion is to introduce oscillation into the transverse direction [ 56 — 58 ]. Synthetic aperture-based approaches have also been proposed that transmit across all directions simultaneously and consequently can form images across the entire field of view at once [ 59 ]. By stepping the aperture source element across the array aperture, and combining the results from multiple transmit events, a high resolution wide-field Doppler image is acquired.

More recently, there has been growth in the area of plane wave Doppler processing [ 60 , 61 ]. Multiple acquisitions are obtained from multiple angles and these are combined. Significantly, Bercoff notes that real-time implementation of this Doppler processing places very high demands on processor speed and data bandwidth [ 61 ]. Since kHz Color Doppler has only recently become available, we are only now learning about its value in diagnoses. It is also noteworthy that these frame rates place them well beyond the foreseeable capabilities of competing imaging modalities even as frame improvements in competing modalities are enabled by significant technical advances.

Selected frames from a cardiac cycle obtained with using ultrafast compound Doppler. Although the majority of IVUS applications are in cardiology, there are a number of uses within interventional radiology. IVUS technology generally divides into those based on mechanically scanned single transducer element and those comprising a solid-state circumferential array [ 62 ].

IVUS provides cross-sectional vessel anatomic structural information that is not obtained using only X-Ray angiography — which gathers information from a projection across the vessel lumen. IVUS can provide a range of functional information about the vessel wall health and function [ 63 ], yet OCT is frequently presented as a technology that may potentially supplant IVUS based on its superior spatial resolution. Recently, there has been significant progress in the area of pairing IVUS and photoacoustic imaging [ 65 — 68 ].

IVUS can provide excellent anatomic information and some functional information. Photoacoustic imaging provides superior information on vessel wall composition [ 66 , 67 ] and can perform molecular imaging using appropriately targeted light absorbing nanoparticles [ 69 ] see below. Early versions of elastography primarily relied upon an external application of force during which tissue motion was tracked in using phase sensitive approaches applied to the beamformed radio frequency RF line data [ 70 , 71 ].

Over the years, many improvements have been proposed to the underlying algorithms to improve precision and accuracy [ 72 — 74 ][ 75 — 77 ]. The method has found application in a range of settings that include: The approach has been scaled down and performed using IVUS to assess vessel wall elasticity [ 82 — 84 ]. A major contribution in the field of elasticity involved the realization that acoustic radiation force could be used to project the force from within the body at a precise location instead of relying on an external force that rapidly decays with depth and is susceptible to artifacts due to intervening inhomogeneities [ 85 — 87 ].

This version of elasticity imaging is now in clinical usage [ 88 ]. More recently, considerable interest has arisen in shear wave elasticity imaging. Since a shear wave propagates slowly in tissue, the wavelength is low, which improves spatial resolution. Among the various implementations, supersonic shear imaging [ 89 ] appears to be the most promising and has yielded very encouraging early results. The method also relies on an ultrasfast scanner capable of full field imaging in response to a single transmit burst — i.

Promising results involving characterizing breast lesions have been reported using this approach [ 90 ]. It is also probable that a number of signal processing techniques, yet to be invented, will be enabled by this versatile high performance architecture. Photoacoustic or optoacoustic imaging involves the use of short duration laser pulses to induce transient thermal expansions giving rise to emitted ultrasound pulses emanating from the point of light absorption.

The received ultrasound pulses are processed in a manner analogous to conventional ultrasound receive signal processing. The receive path may involve either a mechanically scanned single element ultrasound transducer or a phased ultrasound array. Photoacoustic imaging has experienced an extraordinarily rapid rate of technical development in the past decade. Consequently, it should be viewed as a completely new imaging modality as opposed to a subset of ultrasound imaging.


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Photoacoustic imaging is discussed only briefly in this review. The reader is referred to the review article by Xu and Wang [ 91 ] for a more extensive discussion. Anatomic ultrasound image contrast is a function of tissue mechanical properties, tissue interfaces and backscatter density. Image contrast in photoacoustic imaging is determined by local light absorption conditions and this will typically also vary with optical wavelength.

Thus, it is feasible to image and differentiate between oxygenated and deoxygenated blood [ 91 ], differentiate lipid-dominant versus water-dominant tissue signals and detect other light-absorbing chomophores endogenous and exogenous. Traditional optical imaging is sensitive to these parameters but possesses extremely limited penetration due to light scattering at any significant depth. Photoacoustic imaging is projected to contribute across a wide range of clinical areas that include: Photoacoustic tomography, using reconstruction principles similar to those used in Computed Tomography, has extended the technical frontier in terms of very high resolution photoacoustic imaging [ 93 — 95 ].

Using these approaches, small animal whole body photoacoustic imaging systems have become developed [ 96 ] and are available commercially [ 97 ]. Photoacoustic imaging divides broadly into two modes of operation. In acoustic resolution photoacoustics, it is not necessary for the input light to be focused to a single point. Because of rapid light scattering in tissue, in any event the light signal becomes defocused beyond approximately 1 mm of depth.

In this scenario, photoacoustic imaging resolution is determined by the focusing performance of the receive ultrasound beamformation process. It is a common misperception to believe that light cannot penetrate deep into tissue. By choosing the correct light wavelength i. Additionally, photoacoustics has extensive applications in catheter-based applications where it can be paired with conventional IVUS [ 65 , 66 , 98 ]. Photoacoustics can also be paired with. Figure 3 , from Hu et al, [ ] illustrates a range of resolutions and sources of contrast that include optical resolution photoacoustic microscopy of sO2 in a mouse ear, acoustic resolution photoacoustic microscopy of hemoglobin concentration in a human palm, photoacoustic CT of Methylene Blue concentration in a rat sentinel lymph node, photoacoustic CT of cerebral hemodynamic changes in response to whisker stimulation in a rat and Photoacoustic endoscopy of a rabbit esophagus and adjacent tissue.

Components of Photoacoustic Tomography, with representative in vivo images across multiple resolution scales A Optical Resolution Photoacoustic Microscopy of sO2 in a mouse ear. B Acoustic Resolution Photoacoustic Microscopy of normalized total hemoglobin concentration, [hemoglobin], in a human palm. E Photoacoustic endoscopy of a rabbit esophagus and adjacent internal organs, including the trachea and lung.

Ultrasound contrast agents: basic principles.

Reprinted with permission from [ ]; Copyright, , American Association for the Advancement of Science. Contrast materials are applied in all imaging modalities, and ultrasound is not an exception. Early ideas of blood pool contrast ultrasound imaging first discovered by serendipity [ ] come from the use of air bubbles generated in saline, serum albumin solutions or viscous X-ray contrast media.

Unlike water or most of biological tissues , gas bubbles are very compressible; thus, in response to the passage of the ultrasound wave as the cycles of positive and negative pressure, microbubbles rapidly compress and expand about their equilibrium ambient pressure setting, with the particle diameter variation reaching several fold [ ]; movement of gas-liquid interface creates secondary pressure waves, i. Luckily for this field, relatively small bubbles, with the diameter somewhat less than of a red blood cell, can scatter MHz ultrasound very efficiently, and can be detected by ultrasound imaging, with excellent sensitivity.

Thus, the dose of the administered ultrasound contrast material can be in the single milligram or sub-milligram range, of which most material is either fully natural e.


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    • Non-microbubble ultrasound contrast agents were tested widely at the preclinical stage, but have not yet made it to the clinical application level, perhaps due to the larger required dose and lower acoustic backscatter. Ultrasound contrast is used as a general radiology intravascular agent worldwide so far the USA is an exception, where only cardiac ultrasound contrast imaging is approved in the clinic.

    Worldwide, several million ultrasound contrast exams take place every year; due to the low dose of the contrast material, serious side effects are infrequent; for the patients with kidney impairment, where X-ray contrast or Gd-based MRI contrast agents are undesirable, microbubble contrast exam may become the preferred option [ ].

    In order to observe microbubble particles in the bloodstream, contrast-specific detection schemes and pulse sequences have been implemented, with multi-pulse detection schemes being the most efficient. A combination of phase inversion i. Contrast mode is often used in combination with regular grayscale B-mode imaging for anatomy positioning see Figure 4. It is important that microbubble detection in the tissues can be achieved at low acoustic power levels, i.

    Ultrasound imaging of subcutaneneous tumor in a murine model. B-mode grayscale imaging anatomy. Imaging performed with Sequoia scanner equipped with 15L8 probe. Real-time ultrasound contrast imaging capability is often used for characterization of cancerous nodules: Modern imaging equipment has a color-coded arrival time routine, which allows a distinct presentation of the contrast arrival time differential between the tumor and surrounding tissues.

    In the s, at the time when microbubble detection was not as sensitive, the most efficient way to monitor microbubble contrast in the bloodstream was to destroy them by higher acoustic pressure of ultrasound. Typically, with mechanical index MI in excess of 0. Therefore, taking advantage of this targeted microbubble destruction in the interrogated volume with intermittent timed frame collection, Kaul et al [ ] devised a tool to monitor myocardial perfusion, with the aim to observe perfusion defects in heart muscle following myocardial infarction.

    Intermittent imaging was performed in synchrony with heart pulses, triggered by EKG, typically at end-systole. Following microbubble infusion, when microbubbles concentration in the vasculature reached a constant level, ultrasound imaging was initiated and performed at every heart beat, then at every other heartbeat, then every third, fourth and fifth heartbeat. It has been suggested that by timing the interval of ultrasound pulses, the fraction of the blood in the particular portion of the vasculature e.

    Lately, with the advent of high-sensitivity multipulse detection schemes, ultrasound contrast imaging does not require microbubble destruction anymore. Therefore, after a single destructive pulse, replenishment of microbubbles into the interrogated volume can be monitored in real time, with the traditional clinical imaging equipment at 20—50 frames per second [ ], see Figure 5 and accompanying video and with the most modern equipment at 10 3 Hz or even faster [ , ].

    Contrast ultrasound imaging of tumor vasculature perfusion in destruction-replenishment mode in a subcutaneous murine tumor model. Overall, perfusion studies with microbubble contrast are now routinely used in the clinical setting worldwide except USA as of now ; they can provide blood flux information in the settings where Doppler imaging is not useful due to smallest size of the vessels in the tissue e. An unfortunate limitation of this technique is in the inability of ultrasound at imaging frequencies to transit through the human skull without attenuation; thus, brain perfusion studies that are routinely performed with functional MRI cannot be performed with contrast ultrasound unless there is a burr hole present [ ].

    Expanding the ability of ultrasound imaging to collect information on the biological processes at the molecular and cellular level requires the use of a specialized contrast agents, targeted microbubbles [ ]. The general idea is traditional for targeted contrast imaging: The particles are administered in vivo e. As the typical mean size of microbubble contrast agents is several micrometers, these agents are unable to probe the receptors located outside of the vascular bed. Although nanobubble studies have been repeatedly reported in the literature over the past decade [ , ] , the acoustic backscatter and particle lifetime are both rather low and these agents have not approached practical application; therefore, ultrasound contrast imaging of leaky neovasculature e.

    Current progress of molecular imaging with micrometer-sized targeted bubbles has been significant. It started with a model ultrasound imaging study in vitro, in petri dishes, avidin-biotin targeting [ ], and progressed rapidly towards the use of cell cultures and antibody-mediated targeting [ ], followed by in vivo studies. Several targets were investigated with significant detail: The simplest targeted contrast agent is already in clinical use: Sonazoid perflubutane formulation is approved for liver imaging in Japan and South Korea [ ].

    Targeting specificity of this agent is based on its lipid shell composition, phosphatidylserine.

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    This phospholipid is a natural marker of apoptosis and a powerful driver for the phagocytic uptake of apoptotic cells [ , ], cell fragments and other particles [ ] by the cells of reticuloendothelial system RES and any other phagocytic cells, e. The latter cell is the first to adhere to vascular endothelium in the acute inflammatory response to ischemia-reperfusion injury, e. More specific endothelial markers of interest to microbubble targeting include selectins P- and E- and integrins, such as VCAM-1 and ICAM-1, which are expressed on the surface of vascular endothelium in response to inflammatory stimuli.

    Microbubble targeting of these molecules is achieved either via antibody placement on the bubble shell [ ] or the use of smaller molecules, such as peptides [ ], nanobodies [ ] or carbohydrates [ ]. Another significant application area for microbubble targeting is tumor vasculature: VEGF Receptor 2 is another important biomarker of the malignant tumor vasculature; this molecule is already a popular target for tumor detection with other imaging modalities [ ] as well as with ultrasound molecular imaging, via microbubbles decorated with anti-VEGFR2 antibodies, [ ], or single-chain VEGF [ ], which has been shown to achieve selective accumulation of microbubbles in the tumor neovasculature in a murine model see Figure 6.

    A synthetic heterodimeric peptide combination was discovered as a smaller molecule combination tool for VEGFR2 targeting [ ]. Prior to this, an early-phase BR55 clinical trial for prostate cancer patients with scheduled radical prostatectomy compared VEGFR2 histology with targeted ultrasound imaging. This early study suggested co-location of the tumor nodules by both methods [ ]. Molecular ultrasound imaging may be used to assist with image-guided biopsy e.

    Ultrasound imaging of subcutaneous colon adenocarcinoma. A, B-mode US image of tumor tissue marked by dotted line. Copyright, , Lippincott, Williams and Wilkins, reprinted with permission from reference [ ]. Overall, a combination of targeted contrast ultrasound agents with the wide availability of contrast imaging modalities on the ultrasound imaging equipment may result in the use of ultrasound molecular imaging for targeted diagnostics, image-guided biopsy and therapy. Focused ultrasound has been suggested as a therapeutic modality decades ago [ ], although wider clinical use of this approach started much later [ ].

    Induction of local hyperthermia by focused ultrasound is based on localized energy deposition. MRI can serve as a tool for precise temperature monitoring in the target tissue, although ultrasound imaging is used for ultrasound therapy guidance in the clinic widely outside of US. KW power of the therapeutic apparatus can achieve the desired temperature in the focal zone within seconds. Multi-element arrays optimally, with thousands of elements allow rapid electronic steering of the focal spot to accelerate the procedure and completely cover the desired treatment zone [ ]. Approved indications include uterine fibroid therapy [ ] and palliative treatment of bone metastases [ ].

    Lower frequency ultrasound KHz, necessary for penetrating human skull without heating it significantly is now being investigated as a tool for ultrasound therapy in the brain [ ]. We can hope that tumor therapy will be successful in clinical trials in the bone metastasis setting beyond palliation , as well as for treatment of brain tumors e.

    Success of this non-invasive therapeutic modality is supported by the ability to focus ultrasound tightly and rapidly deep within the body even through the skull. Limitations are also based on physical constraints: Ultrasound cannot efficiently travel through the gas phase, so lung treatment can only be performed for liquid-filled lungs [ ].

    In some instances, ribcage obscures access to the target e. There have been reports that ribs in the way of ultrasound beam had been resected prior to the treatment with a large aperture single element transducer [ ]. However, more appropriate would be to use multi-element array and adjust the transmit power for the elements which are obscured by the ribs [ ].

    Histotripsy implies high-power pulverization of the tissues: Following this treatment, a void in the biological tissue is created: Enhancing the rate of thrombolysis with ultrasound has been suggested more than a decade ago [ , ]. The idea is quite similar to tissue ablation, as described in the previous section; the acoustic energy applied for thrombolysis may be significantly lower, often within the limits of diagnostic ultrasound imaging.

    Ultrasound pressure wave provides mechanical action on the biological tissues including the clot and surrounding blood. Liquid media streaming improves convection of the participants of the thrombolytic cascade in proximity and within the clot structure, resulting in thrombolysis acceleration. We can hope that ultrasound-assisted thrombolysis, if applied quickly e. Ultrasound can be applied non-invasively [ ], or via a catheter [ ]. Ultrasound has been investigated as a tool for microbubble-assisted drug delivery for almost two decades. Initially [ ] model drugs were incorporated into the bubble shell.

    Later, tumor therapy in response to insonation was achieved in animal models [ , ] - but that was feasible mostly for rather hydrophobic drugs, e. Plasmid DNA could be attached onto the bubble shell electrostatically, and ultrasound-assisted transfection enhancement was observed with such constructs [ ].

    Attachment of drug-loaded liposomes onto the surface of microbubbles allows ultrasound-triggered drug delivery capability: This has been shown to work with widely used anticancer drugs, e. A combination approach, where existing drug is simply co-administered along with clinical grade approved microbubbles and focused ultrasound, will obviously get to clinical trials faster. In this approach, stable cavitation of microbubbles within the vasculature is used to transiently alter permeability of blood-brain barrier [ ].

    The disruption of the barrier is mild and transient permeability enhancement ceases within hours. However, large items, such as liposomes [ ] and other nanoparticles [ ] can be delivered into the brain tissue as efficiently as smaller items, such as antibodies [ ], other drugs [ ], or even Gd-based MRI contrast agents [ ] See Figure 7 as an example of penetration enhancement of Gd-DTPA across blood-brain barrier in a rat model.

    This approach has already led to an exciting demonstration of glioma treatment in a rodent model curative in a significant fraction of animals with a simple combination of long-circulating doxorubicin liposomes doxil and clinical perflutren microbubbles [ ].

    Success of therapy can be explained by the ability of PEG-coated liposomes to stay in the bloodstream for many hours, recirculate through the insonated area vasculature and extravasate for many hours, as long as the drug remains in the bloodstream and the barrier remains open. Expansion of this technique towards clinical applications could be predicted, ranging from tumor therapy [ ] to Alzheimer treatment [ , ]. Ultrasound-induced opening of blood brain barrier in a rat model. MRI contrast extravasation and accumulation white focal spots in the center of the image observed minutes after ultrasound treatment and Gd-DTPA administration.

    Copyright, Max Wintermark, , reprinted with permission.

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    Similar therapeutic approach can be applied in the situations other than the blood-brain barrier, to any endothelial lining in the vasculature that precludes entry of the drug into the diseased tissue. This approach has been applied to deliver particles of adeno-associated virus to the insonated myocardium [ ], as well as for the treatment of pancreatic cancer in an orthotopic xenograft mouse model, by a combination of anticancer drug gemcitabine and Sonovue microbubbles [ ].

    The latter combination has demonstrated interesting data in a clinical trial setting, initially showing the suppression of tumor growth in response to intravenous administration of gemcitabine, immediately followed by injections of Sonovue microbubbles every 3. Therapeutic applications of ultrasound may span beyond thermal or mechanical disruption of the tissues or drug delivery.

    Action of ultrasound on the tissues, possibly in combination with microbubbles, may lead to manifestation of a variety of therapeutic bioeffects, spanning from therapeutic angiogenesis [ ] to inhibiting blood flow in the tumors [ — ], to targeting therapeutic stem cells following intravenous administration [ ], bone fracture healing [ ], and, surprisingly, ultrasound action on splenic nerve to mitigate acute kidney injury [ , ]. Non-invasive brain stimulation by ultrasound is also quite intriguing [ ]. All these techniques are based on the ability of ultrasound as a pressure wave to provide guided energy deposition in the treatment area; in some instances the ultrasound action is further enhanced by the presence of vibrating microbubbles.

    Physiological effects demonstrated by ultrasound application are quite diverse and will definitely lead to the development of new therapeutic approaches and modalities. Ultrasound has become an indispensable tool of modern medicine that helps expand the borders of radiology. Hardware improvements, based on continuous acceleration of data processing rate, lower cost and smaller size of the electronic devices, are combined with smart transducer design, pulse sequences and novel data processing and analysis schemes.

    Hand-held and laptop ultrasound is already in wide use, soon to replace cart-based systems. Ultrasound contrast agents bring the ability to monitor tissue perfusion, and targeted agents enable molecular ultrasound imaging of the vascular biomarkers of angiogenesis or inflammation. The ability to direct ultrasound to the desired areas of the body opens up direct therapeutic applications of this modality, including targeted drug and gene delivery, and thrombolytic therapy enhancement.

    Overall, ultrasound is rapidly developing both as an imaging and a therapeutic modality. National Center for Biotechnology Information , U. Author manuscript; available in PMC Sep 1. Klibanov 1 Cardiovascular Division; Robert M. The publisher's final edited version of this article is available at Invest Radiol. See other articles in PMC that cite the published article.

    Open in a separate window. Phase aberration correction Phase aberration has been extensively studied since the late s [ 13 ]. Model-based segmentation and imaging Frequently, in radiology it is desirable to assess the shape or volume of a particular tissue region. Advances in Doppler Traditional Color Doppler processing is limited to detecting the 1D component of motion aligned with the ultrasound beam axis. Elastography Early versions of elastography primarily relied upon an external application of force during which tissue motion was tracked in using phase sensitive approaches applied to the beamformed radio frequency RF line data [ 70 , 71 ].

    Photoacoustic imaging Photoacoustic or optoacoustic imaging involves the use of short duration laser pulses to induce transient thermal expansions giving rise to emitted ultrasound pulses emanating from the point of light absorption. Contrast agents in ultrasound imaging Contrast materials are applied in all imaging modalities, and ultrasound is not an exception. Destruction-replenishment as a tool for perfusion contrast imaging In the s, at the time when microbubble detection was not as sensitive, the most efficient way to monitor microbubble contrast in the bloodstream was to destroy them by higher acoustic pressure of ultrasound.

    Molecular Targeted Contrast Ultrasound Imaging Expanding the ability of ultrasound imaging to collect information on the biological processes at the molecular and cellular level requires the use of a specialized contrast agents, targeted microbubbles [ ]. Thrombolysis with ultrasound Enhancing the rate of thrombolysis with ultrasound has been suggested more than a decade ago [ , ].

    Ultrasound-microbubble combination as a tool for targeted drug and gene delivery Ultrasound has been investigated as a tool for microbubble-assisted drug delivery for almost two decades. Bioeffects of ultrasound in therapeutic applications Therapeutic applications of ultrasound may span beyond thermal or mechanical disruption of the tissues or drug delivery. Conclusion Ultrasound has become an indispensable tool of modern medicine that helps expand the borders of radiology.

    Cramming More Components onto Integrated Circuits. Tanter M, Fink M. Ultrafast Imaging in Biomedical Ultrasound. Ieee Transactions on Information Technology in Biomedicine. Ultrasound image quality comparison between an inexpensive handheld emergency department ED ultrasound machine and a large mobile ED ultrasound system. International evidence-based recommendations on ultrasound-guided vascular access. Utility and diagnostic accuracy of hand-carried ultrasound for emergency room evaluation of chest pain.

    American Journal of Cardiology.

    Ultrasound contrast agents: basic principles. - PubMed - NCBI

    Ultrasound-guided removal of foreign bodies: The Journal of trauma. Battlefield applications for handheld ultrasound. Simulation of ultrasonic pulse propagation through the abdominal wall. The Journal of the Acoustical Society of America. Phase-aberration correction using signals from point reflectors and diffuse scatterers: IEEE transactions on ultrasonics, ferroelectrics, and frequency control.

    Elevation performance of 1. J Acoust Soc Am. Time-Reversal of Ultrasonic Fields. Adaptive imaging using the generalized coherence factor. Clement GT, Hynynen K. Micro-receiver guided transcranial beam steering. Experimental demonstration of noninvasive transskull adaptive focusing based on prior computed tomography scans.

    Towards aberration correction of transcranial ultrasound using acoustic droplet vaporization. Finite amplitude distortion-based inhomogeneous pulse echo ultrasonic imaging. Harmonic Spatial Coherence Imaging: Use of harmonic imaging without echocardiographic contrast to improve two-dimensional image quality. The American journal of cardiology. Clinical use of ultrasound tissue harmonic imaging. Int J Comput Vision.

    Supplemental Content

    Snakes based segmentation of the common carotid artery intima media. Segmentation of the prostate from suprapubic ultrasound images. Real-time speckle reduction and coherence enhancement in ultrasound imaging via nonlinear anisotropic diffusion. Ieee Transactions on Biomedical Engineering. Bamber JC, Daft C. Adaptive filtering for reduction of speckle in ultrasonic pulse-echo images. Dutt V, Greenleaf JF. Adaptive speckle reduction filter for log-compressed B-scan images.

    Michailovich OV, Tannenbaum A. Despeckling of medical ultrasound images. Speckle reducing anisotropic diffusion. Speckle reduction and contrast enhancement of echocardiograms via multiscale nonlinear processing. Speckle reducing anisotropic diffusion for 3D ultrasound images.

    Computerized Medical Imaging and Graphics. An early vision-based snake model for ultrasound image segmentation. Real-time spatial compound imaging: The significant improvements in the capabilities of ultrasound contrast agents and the greater number of contrast agents thoroughly under investigation as well as those already available on the market, mean the clinician and researcher must keep abreast of all developments in this revolutionary field.

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