Physics
Ultrasound Imaging
Ultrasound imaging uses high-frequency sound waves to create images of internal body structures. It is non-invasive and widely used for medical diagnosis and monitoring during pregnancy. The technique relies on the reflection and scattering of sound waves to generate detailed images of organs, tissues, and blood flow, making it a valuable tool in medical imaging.
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11 Key excerpts on "Ultrasound Imaging"
eBook - PDF- Paul Suetens(Author)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
Chapter 6 Ultrasound Imaging 6.1 Introduction Ultrasound Imaging or ultrasonography has been used in clinical practice for more than half a century. It is noninvasive, relatively inexpensive, portable, and has an excellent temporal resolution. Imaging by means of acoustic waves is not restricted to medical imaging. It is used in several other applications such as in the field of nondestructive testing of materials to check for microscopic cracks in, for example, airplane wings or bridges, in sound navigation ranging (SONAR) to locate fish, in the study of the seabed or to detect submarines, and in seismology to locate gas fields. The basic principle of Ultrasound Imaging is sim- ple. A propagating wave partially reflects at the inter- face between different tissues. If these reflections are measured as a function of time, information is obtained on the position of the tissue if the veloc- ity of the wave in the medium is known. However, besides reflection, other phenomena such as diffrac- tion, refraction, attenuation, dispersion, and scat- tering appear when ultrasound propagates through matter. All these effects are discussed below. Ultrasound Imaging is used not only to visualize morphology or anatomy but also to visualize func- tion by means of blood and myocardial velocities. The principle of velocity imaging was originally based on the Doppler effect and is therefore often referred to as Doppler imaging. A well-known example of the Doppler effect is the sudden pitch change of a whistling train when passing a static observer. Based on the observed pitch change, the velocity of the train can be calculated. Historically, the first practical realization of Ultrasound Imaging was born during World War I in the quest for detecting submarines. Relatively soon these attempts were followed by echographic techniques adapted to industrial applications for non- destructive testing of metals.
eBook - PDF- Andrew Webb(Author)
- 2022(Publication Date)
- Wiley-IEEE Press(Publisher)
135 4 Ultrasound Imaging 4.1 General Principles of Ultrasound Imaging Ultrasound Imaging produces a spatial map of the boundaries between tissues, and structures within tissues, by transmitting pulses of mechanical energy into the body and detecting the signals backscattered to the receiver. It operates at fre- quencies between ∼1 and ∼15 MHz, with lower frequencies being used to image deeper lying tissues and higher frequencies for better spatial resolution close to the surface. The intensity of the backscattered signals depends upon the difference in acoustic impedance between tissues. In addition to obtaining anatomical images, ultrasound is also used widely to measure blood flow in vessels via a Doppler shift in the frequency of the backscattered signal from red blood cells. The main uses of ultrasound are in obstetrics and gynecology, cardiovascular anatomy and function, musculoskeletal injuries, and assessment of blood flow in various vessels. The main strengths of ultrasound include: (i) It is nonionizing, portable, and inexpensive compared to the other imaging techniques, (ii) It is patient-friendly, with minimal patient preparation necessary and requir- ing only water-based gel to be placed on the patient to couple to the trans- ducer, (iii) It is a real-time technique with frame rates of tens to hundreds per second allowing visualization of moving organs, (iv) It can be easily integrated into surgical procedures, and (v) Doppler-based flow measurements can be interlaced with anatomical scans on a real-time basis to integrate morphology and function. The main challenges of ultrasound include: (i) Soft-tissue contrast is limited compared to the other imaging techniques, (ii) Ultrasound waves cannot penetrate through gas or bone, meaning that certain organs such as the brain cannot be imaged, Introduction to Biomedical Imaging, Second Edition. Andrew Webb. © 2023 The Institute of Electrical and Electronics Engineers, Inc.
- Adem Ozcelik, Ryan Becker, Tony Jun Huang(Authors)
- 2023(Publication Date)
- Wiley-VCH(Publisher)
99 4 Ultrasound and Ultrasonic Imaging in Medicine: Recent Advances Tu˘gba Ö. Onur Zonguldak Bülent Ecevit University, Department of Electrical-Electronics Engineering, Zonguldak 67100, Türkiye 4.1 Introduction In the 1940s, infrasonic technology, which was first used in radars during World War II, started to see use in research as a new method for medical imaging, and by the 1970s, it had been adopted for use in diagnostic medicine. In the last 20 years, ultra- sound imaging has become one of the most widely used imaging modalities due to its high biocompatibility, high tissue penetration depth, and portability. Because acous- tic waves are nonionizing, ultrasound is an attractive alternative to other methods as there is a lower risk of harm to the patient. Thanks to the rapid development of ultrasonic imaging technology, new meth- ods have evolved to further improve imaging quality. For example, tissue harmonic imaging (THI) has been adapted along with conventional Ultrasound Imaging to fur- ther improve imaging quality. The purpose of THI is to send sound waves with a lower frequency value into the body to obtain higher-quality images by detecting higher frequency sound waves by making use of intra-body vibrations. 4.2 Ultrasound Waves Ultrasound is a type of acoustic wave that is generated via mechanical vibrations and whose frequency is above the limit of human hearing (the human ear can hear sounds between 20 Hz and 20 kHz). In general, sounds with a frequency greater than 20 kHz are defined as ultrasound. Although there are various types of waves, “longitudinal compressional waves” are the most common acoustic waves that are used for diagnostic imaging. The particles that vibrate within the medium alternate between states of compression and rarefaction as the wave travels through the medium. In this way, energy is transported to the medium in a direction parallel Acoustic Technologies in Biology and Medicine, First Edition.
eBook - PDF- Robert Splinter(Author)
- 2010(Publication Date)
- CRC Press(Publisher)
32-13 Additional Reading ......................................................................................................................... 32-13 Robert Splinter 32.1 Introduction and Overview Ultrasound Imaging uses sound waves to determine the mechan-ical characteristics of tissue. Sound waves are longitudinal waves that travel through matter using the medium as a carrier for the wave energy . Th is means that sound cannot travel in a vacuum. In lo ngitudinal w aves, t he d irection o f w ave p ropagation i s parallel to t he mot ion of t he me chanism t hat forms t he w ave: particles, mole cules, a nd s o o n. I n c ontrast, ele ctromagnetic waves ( e.g., l ight, x -ray, a nd r adiowaves) a re t ransverse w aves where the electr ic fi eld and the magnet ic fi eld are perpendicular to each other, and the direction of propagation is perpendicular to the wave mechanism itself. Ultrasound waves are represented by medium compression a nd expansion, which form t he crests and valleys, respectively, in t he w ave description, t hat is, pres-sure waves. Figure 32.1 illustrates the compression at the crest of the wave and the expansion at the valley. Sound waves are generally classi fi ed based on the frequency of the waves. Infrasound waves are less than 20 Hz and cannot be heard b y h umans. A udible s ound f alls i n t he r ange b etween 20 Hz and 20,000 Hz. Any sound wave frequency above the limit of human hearing is technically considered ultrasound. However, diagnostic ultrasound generally uses f requencies ranging f rom 1 MHz up to 100 MHz. 32.2 Advantages of Ultrasonic Imaging One of the advantages of Ultrasound Imaging is that it is rela-tively inexpensive, mainly due to the relatively basic technologi-cal basis of this imaging modality. Ultrasound Imaging produces high-resolution i mages t hat r ival a nother rel atively c ommon imaging modality: x-ray imaging, plus it can produce real-time images .
eBook - PDF- Anthony Wolbarst(Author)
- 2005(Publication Date)
- Medical Physics Publishing(Publisher)
Ultrasound Imaging I: Reflections of Acoustic Waves in Elastic Tissues 1. Of Bats and Boats: Getting Around in the Dark 2. Creating Images from Echoes: Medical Ultrasound Is Much like SONAR 3. Sound Is a Mechanical Vibration Propagating through a Medium 4. The Frequency Spectrum of Pulsed Ultrasound Is Continuous 5. The Velocity of Sound in a Medium Is Nearly Independent of the Frequency and Wavelength 6. Intensity of Sound: The W/m 2 and the Decibel 7. Exponential Attenuation of Ultrasound with Depth in a Homogeneous Medium 8. Refraction of Ultrasound at an Interface between Media with Different Acoustic Properties 9. Reflection of Ultrasound at an Interface between Media with Different Acoustic Properties 10. Physical/Biologic Sources of Medically Relevant Ultrasound Information 11. Case Study: Echoes from a Bone Embedded in Tissue 12. Back Down to Earth 114 Chapter 11 For all the other technologies described in this book, the radiation that interacts with body tissues is either ionizing (x- and gamma ray) or r.f. (MRI) electromagnetic energy. Ultrasound (US) radiation consists of something quite dif- ferent: high-frequency sound waves, typically in the 1 to 10 MHz range. Some kinds of vibrations, such as those of a piano string or a piezoelectric element in an ultrasound transducer, form standing waves. Sound and ultrasound passing through air, water, or tissue, however, are in the form of traveling waves. Like light, ultrasound energy is absorbed by any medium through which it passes, and it undergoes refraction and reflection at interfaces between different media. A sharp ultrasound echo, in particular, will be produced at a sizable and relatively flat boundary between two materials with dif- ferent physical characteristics. It is the production of such echoes at organs, vessels, and other structures that underlies ultra- sound image formation.
eBook - PDFIntroductory Biomedical Imaging
Principles and Practice from Microscopy to MRI
- Bethe A. Scalettar, James R. Abney(Authors)
- 2022(Publication Date)
- CRC Press(Publisher)
Section II Medical Imaging 183 DOI: 10.1201/b22076-12 10 Ultrasound We turn now to medical imaging, which comprises the last four chapters in the text. Unlike our discus- sion of optical microscopy, which was organized thematically into physical phenomena like resolu- tion and contrast enhancement, the chapters on medical imaging are organized based on technique, and issues like resolution and contrast are addressed separately for each approach. Applications are dis- cussed at the start and the end of each chapter; they also are sprinkled throughout each chapter as appropriate. We begin with ultrasound (US), which is the only approach not founded on the use of EM radiation. 10.1 Essence of the Technique We present a detailed discussion of US imaging in future sections, but it is useful to start with a brief synopsis of its key features. US is a technique that maps body structures based on echo detection, similar to sound navigation and ranging (SONAR – Fig. 10.1 ). In brief, a device known as a transducer is used to generate and direct US into the body and to detect US that is reflected or scattered back by tissues and other anatomic structures. Several attributes of US make it useful for medi- cal imaging. These include a good balance between penetration of the body and interaction with body structures. US transit times within the body also are readily measurable. In particular, echo transit time is used to calculate tissue depth, and echo amplitude is used to generate contrast (Fig. 10.1b ). Large amplitude echoes arise from reflections at interfaces with big “mismatches,” like soft tissue/bone interfaces, and these appear as very bright areas in US images. Much weaker echoes are generated by reflections at inter- faces between “similar” structures, such as different soft tissues, which appear as lighter, variable shades of gray.
eBook - PDF- Liwu Lin(Author)
- 1997(Publication Date)
- World Scientific(Publisher)
Sound wave imaging differs from optic imaging in many aspects. Sound frequency and wavelength are in the magnitude of tens of centimeters, even one or two metres. If the wavelength of a matter is shorter than that of sound, it will not act as a barrier to the transmission of the sound. The wavelength of the medical ultrasonic wave is about 10 11 m. It behaves like radiation, exhibiting directivity, reflection, refraction, transmission, and scattering. Many comparatively small objects can block the transmission of ultrasounds. Objects with wavelengths longer than that of ultrasound reflect the ultrasounds, while objects with shorter wavelengths allow it to pass through. Objects with a similar wavelength can scatter ultrasonic waves. Medical ultrasonic tomography works on the interaction between ultrasounds and biological tissues. In principle, medical ultrasonic imaging can be reflection imaging or sonolranslucent and scattering imaging. Currently, common medical ultrasonic imaging apparatus arc based on the principle of pulsed echo technology, namely reflection imaging. Ultrasonic imaging by utilizing a pulsed echo reflected wave is associated with special sound impedance of the medium. Specific sound impedance in norma! tissues and pathologically changed tissues is different, so an abnormal boundary sound reflection may result. This phenomenon allows us to recognize an abnormality. Any ultrasonic medium will produce an image if there is internal mutation of the specific sound impedance. Therefore the ultrasound will form an image in the interior of a nontransluccnt tissue. The parameter used for examination is sound pressure (sound amplitude). Therefore all ultrasonic transducers are sensitive to sound pressure. This is different from optic or X-ray imaging by using high intensity examination. Their S/N ratio is much higher. This is also one of the advantages of ultrasonic imaging.
eBook - PDFTransesophageal Echocardiography Multimedia Manual
A Perioperative Transdisciplinary Approach
- André Denault, Pierre Couture, Annette Vegas, Jean Buithieu, Jean-Claude Tardif, André Y. Denault, André Y. Denault, Pierre Couture, Annette Vegas, Jean Buithieu, Jean-Claude Tardif(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
1 Principles of Ultrasound Alain Gauvin and Guy Cloutier Universite´ de Montre´al, Montreal, Quebec, Canada Michel Germain McGill University, Montreal, Quebec, Canada COMPRESSION AND RAREFACTION Ultrasound consists of mechanical sound waves whose frequencies are above the audible range, that is, 20,000 Hz (Hz stands for the number of wave cycles per second). Sound is defined as a mechanical wave that propagates in a medium due to molecular interaction. The mode of propagation of ultrasound is related to successive molecular compressions and rarefactions occurring in that medium (Fig. 1.1). When individual molecular motion is in the same direction as the wave propagation, it forms a longitu- dinal wave. When molecular motion is perpendicular to wave direction, it is a transverse (or shear) wave. Solids, such as biological tissues, can experience both transverse (or shear) and longitudinal waves. Ultra- sound in fluids and gases mostly experiences longitu- dinal propagation because of the lack of strong coupling between the molecules. Recent research sug- gests that shear waves may become clinically useful to characterize the viscoelastic properties of biological tissues and be used in sonoelasticity imaging and dynamic elastography. To understand ultrasound production, one can imagine a small transducer driving an oscillating surface in contact with gas molecules, as illustrated in Figure 1.2. As the surface moves forward, it pushes gas molecules in front of it, creating a zone of compression (Fig. 1.2A). The oscillating surface then retracts, during which time the newly created zone of compression moves forward. However, this backward motion of the surface also causes a rarefaction of local gas molecules (Fig. 1.2B). In the time elapsed between Figure 1.2A and B, the zone of increased density initially created moves forward at propagation speed denoted as c.
eBook - PDF- C. R. Hill, J. C. Bamber, G. R. ter Haar, C. R. Hill, J. C. Bamber, G. R. ter Haar(Authors)
- 2005(Publication Date)
- Wiley(Publisher)
Phys. Med. Biol. 45, 1521–1540. Duck, F.A., Baker, A.C. and Starrit, H.C. (1998). Ultrasound in Medicine. IoP Publishing, Bristol. Dunn, F., Tanaka, M., Ohtsuki, S. and Saijo, Y. (1996). Ultrasonic Tissue Characterisation. Springer, Tokyo. Dussik, K.T., Dussik, F. and Wyt, L. (1947). Auf dem Wege zur Hyperphonographie des Gehirnes. Wien Med. Ochenschr. 97, 425–429. Edelstein, W.A., Bottomley, P.A., Hart, H.R. and Smith, L.S. (1983). Signal, noise and contrast in nuclear magnetic resonance (NMR) imaging. J. Comput. Assist. Tomogr. 7, 391–401. Erikson, K., Hairston, A., Nicoli, A., Stockwell, J. and White, T. (1997). A 128 128 (16k) ultrasonic transducer hybrid array. In Acoustical Imaging, Vol. 23, S. Lees and L. Ferrari (eds). Plenum Press, New York, pp. 485–494. Espinola-Zavaleta, N., Vargas-Baron, J., Keirns, C., et al. (2002). Three-dimensional echocardiography in congenital malformations of the mitral valve. J. Am. Soc. Echocardiogr. 15, 468–472. Fatemi, M. and Greenleaf, J.F. (1996). Real-time assessment of the parameter of nonlinearity in tissue using ‘nonlinear shadowing’. Ultrasound Med. Biol. 22, 1215–1228. Fink, M. and Dorme, C. (1997). Aberration correction in ultrasonic medical imaging with time-reversal techniques. Int. J. Imag. Syst. Technol. 8, 110–125. Fitzgerald, P.J., Magnuson, J.A. James, D.H. and Strahbehn, D.W. (1987). Ultrasonic texture analysis to discriminate between normal, ischemic and infarcted myocardium. Ultrason. Imag. 9, 52. Forsberg, F. (1991). Assessment of hybrid speckle reduction algorithms. Phys. Med. Biol. 36, 1539–1549. Foster, F.S. and Hunt, J.W. (1979). Transmission of ultrasound beams through human tissue – focusing and attenuation studies. Ultrasound Med. Biol. 3, 257–268. Foster, F.S., Patterson, M.S., Arditi, M. and Hunt, J.W. (1981). The conical scanner: a two-transducer ultrasound scatter imaging technique. Ultrason. Imag. 3, 62–82. Foster, F.S., Pavlin, C.J., Harasiewicz, K.A., Christopher, D.A.
- Haim Azhari(Author)
- 2010(Publication Date)
- Wiley-IEEE Press(Publisher)
Schematic depiction of the “time-reversal” procedure. (Left) An ultrasonic pulse is transmitted from a point source within the target. The through- transmitted waves are detected and digitized by a transducer array. (Right) The detected signals are time-reversed and transmitted back toward the medium. As a result, the energy is focused at the target despite the distortions induced by the medium. 254 10 SPECIAL IMAGING TECHNIQUES distorted to provide useful focusing. One suggested solution is to utilize time reversal. A needle transducer can be inserted into the target location within the brain, and an ultrasonic pulse is transmitted. The waves traveling though the brain and the skull bones are naturally distorted substantially. An array positioned outside the head is used for wave reception and time- reversed transmission, as explained. The resulting effect is a good-quality focusing at and around the region of the needle (which can of course be removed). 10.7 ULTRASONIC COMPUTED TOMOGRAPHY Ultrasonic computed tomography (UCT) is an imaging procedure with which through-transmitted acoustic waves replace X rays in a CT scanner. The idea was first suggested (to the best of my knowledge) by James F Greenleaf [23]. Initial works have mapped the attenuation coefficients, and later works (e.g., reference 24) have also mapped the speed of sound. The main suggested application of UCT is breast imaging for tumor detection [25, 26]. In this section the basic principles of UCT in 2D and 3D are presented. 10.7.1 Basic Computed Tomography Principles As was explained in the previous sections, projection images of certain acous- tic properties of tissues can be obtained. For example, in Eq. (10.21) it was shown that by measuring the time of flight (TOF), the obtained signal is in fact an integral of the refractive index along the beam path.
eBook - PDFIntroduction to Medical Imaging
Physics, Engineering and Clinical Applications
- Nadine Barrie Smith, Andrew Webb(Authors)
- 2010(Publication Date)
- Cambridge University Press(Publisher)
Ultrasound is the only modality able to provide very high frame-rate real-time imaging over significant periods. It has almost no contraindications, unlike MRI which cannot be used for patients with many types of implant, and uses no ionizing radiation. It is also the only modality that is routinely used during pregnancy. As examples, applications to obstetrics, breast imaging, musculoskeletal damage and cardiac studies are outlined briefly below. 4.13.1 Obstetrics and gynaecology Parameters such as the size of the foetal head and extent of the developing brain ventricles (for diagnosis of hydrocephalus), and the condition of the spine are measured to assess the health of the foetus. If amniocentesis is necessary to detect disorders such as Down’s syndrome, then ultrasound is used for needle guidance. Doppler ultrasound is also used to measure foetal cardiac parameters such as blood velocity. Three-dimensional ultrasound provides high resolution images of the developing foetus, although such images tend to be more for show than for actual clinical diagnosis. The high spatial resolution and excellent image contrast possi-ble are shown in Figure 4.35 . 193 4.13 Clinical applications of ultrasound 4.13.2 Breast imaging Ultrasound Imaging is used to differentiate between solid and cystic lesions, and for the evaluations of lesions in young women with dense breast tissue or who are pregnant, since X-rays are not effective or not allowed, respectively [ 8 ]. Five different categories of lesion are defined by the American College of Radiography based on well-defined morphometric measures and image characteristics. High frequency ultrasound, between 9 and 12 MHz, is used for optimal image contrast, as well as for the highest axial and lateral resolution. The standard procedure is to use two-dimensional B-mode scanning. Breast lesions are generally hypoechoic, appearing darker than the surrounding tissue.
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