The Physics of Ultrasound - Research Paper Example

?Ipek Batca Prof. Eastwick College The Physics of Ultrasound Ultrasound is a form of imaging method, or imaging modality that enables medical practitioners to visualize the internal organs of the body through the use of high frequency sound waves directed at certain portions of the body sans the invasive procedures (Tole and Ostensen 1). It has been much widely known to the public due to its ease of use as well as being able to generate rapid image analyses (Gill 1). The beginnings of ultrasound imaging can be traced to the pursuits of the mining industry, wherein certain metals can be detected due to the differences between the densities of the layers that the sound waves pass through, and these differences were able to identify if the ground being scanned is pure rock or not (Hoskins 1). This same, simple principle of analyzing the different internal organs of the body based on the various densities of each tissue, as well as the ease of use of the sonogram machine in performing scans are able to contribute to the success of the ultrasound and its continued use until now (Gibbs 1). While the underlying physics of how ultrasound works can be simplified into a few simple steps, to understand fully how this kind of imaging modality works is essential, especially among medical practitioners and imaging specialists and technicians, so that they would be able to properly perform the imaging, assess the images and interpret them as accurately as possible, and in turn they could make the correct diagnosis for their patients, as well as give them the prescriptions that they need. The basic principle of ultrasound imaging is mostly based on how echoes work. Sound waves usually travel outward, from a point of origin. This is similar to how a stone creates a disturbance when dropped into a still body of water, and while the water itself does not move, the waves on the surface of the water create ripples that move away from where the stone was originally dropped (Hoskins 4). Because the waves travel only on the water’s surface, the energy that the stone released in the water gets transported outward, which may eventually reach the shore or some floating particles if the energy released is strong. However, if the energy is weak, the waves would dissipate quickly. In a way, the force used in throwing the stone into the water increases, the distance that the ripples could travel also increases relatively. Thus, the stronger the waves are from the beginning, the longer and the further they could travel from the point of origin (Gill 7). Sound waves have other characteristics, aside from strength or energy which could dictate the distance that can be traveled, as well as the strength of the wave. The height of the wave or amplitude is able to dictate whether the wave has a large amount of strength, or if it is weak (Gibbs 7). Waves that have high amplitudes are said to be loud, while those with low amplitudes are said to be higher in pitch. While ultrasound is barely audible, it does not necessarily mean that it is weak, as another factor called frequency also dictates the strength of the wave. Frequency is a property of waves, also known as cycles, which dictates how many waves are produced at any given second. Thus, the higher the frequency of the waves, the greater is the capacity to penetrate objects, and in turn the greater the energy of the waves (Gill 7). In the case of ultrasound waves, the range of the frequencies is between 2 MHz to 15 MHz, which has a thousand times more cycles than the normal audible levels of humans, thus having much more penetrating power than normal sound waves (7). Waves are capable of moving repeatedly, or oscillating from one place to another in a singular direction, and back again, or if the waves are rather weak, could get smaller and smaller as the distance they travel becomes longer, also called attenuation (Gill 8). Waves can also become compressed, depending on what surfaces that are present in the surrounding areas. When particles within adjoining locations started to move toward each other, the region is said to be undergoing compression, thus the pressure in the region increases, and in a similar manner, if the particles move apart within the same region, there is said to have a decrease in pressure, thus the region undergoes a phenomenon called rarefaction (Hoskins 4). At each point in the region or the medium, the sound waves become either compressed or expanded, depending on whether When sound waves travel, disturbances such as different forms of matter (solid, liquid or gas) could impede these waves from traveling in a linear fashion (Hoskins 4). Depending on what medium the sound waves would be passing through, these can either pass through without much interference (gas), pass through but with distortions of some degree (liquid), or possibly absorbed by the medium altogether (solid) (Gill). However, this is not absolute, as everything would still be dependent on the density of each material, thus some solids may be able to let some sound waves through much better than other solids, some may pass through some kinds of liquids better, and so on (Gibbs 2). Also, the spaces in between the molecules of the medium where the sound waves travel could also determine as to whether the waves would become much scattered, losing their energy in the process, or if they could pass through without losing much of the original penetrating power (Hoskins 6). If the sound waves are strong enough and the medium that the waves passed through contain closely-packed molecules, thus allowing them to bounce back, these waves could still travel back from their point of origin in a near frequency as they first traveled, but if the medium is loosely-packed or if the molecules have rather larger spaces between each other, this would ultimately absorb the waves or scatter them until such time that nothing returns to the point of origin (Gibbs 2). In this case, the medium where these waves passed through were able to determine as to whether the medium is conducive to letting sound pass through, or not (Hoskins 7). This is the same principle that is applied to the human body when using any kind of imaging modalities, but is most especially applicable when using ultrasound since it uses sound waves itself to create the images of internal organs or to show fetuses inside the mother’s womb. In the case of the generation of ultrasound for diagnostic purposes, it was previously mentioned that high frequency sound waves are used for this purpose. Since sound itself is a form of energy that uses vibrations, the principle of sound waves are also applicable to ultrasound, including the density of the medium as well as the strength of the generated waves. The difference is that ultrasounds vibrate much faster that regular sound waves, and this is achieved when certain particles or materials are electrically-excited, thus allowing the generation of waves are able to vibrate millions of times per second, and in turn are generating stronger and much more powerful waves (Tole and Ostensen 1). The ultrasound waves can be further harnessed to be aimed at a very specific area, so as to prevent further scattering of the waves and letting most reflect back into the transducer. This is done by adjusting the settings of transmitting the sound waves and narrowing the wave down, which creates a better resolution of the image (Gibbs 9). The rate at which the strength of the returning or echoing waves are detected by another part of the sonogram equipment called the transducer, and this picks up the echo of waves sent back or reflected by the tissues from which the ultrasound waves were beamed at (Gill 7). The reduction of the strength of sound waves or attenuation is able to directly affect the intensity of the ultrasound that reflects back to the transducer as it passes through tissues or objects (Tole and Ostensen 2). This is because the intensity becomes variable as it passes from one medium to another, from one kind of density to another kind of density. Also, the distances between the molecules may not reflect the waves back, but rather redirect them into another direction. If the waves are not reflected back properly, or if there is none detected by the transducer, the image produced in the sonogram would look dark and hollow, or would look very blurry, thereby preventing the clear transmission of the image where the ultrasound was performed. Thus, it can be possible that blurry or darkened images would appear in the sonogram imaging if the intensity of the sound waves become too low to be detected by the transducer, the waves may have not reflected properly back, or may have been scattered too much by the surrounding particles, some may have been refracted or bent and may not return to the point of origin, or the medium has ultimately absorbed the waves altogether (Gill 11). The implications of the properties of sound waves to the capacity of ultrasound to produce images through the reflection of waves back to the transducer are numerous. For one thing, the sound waves would be interacting with the different tissues as it passes through the body, or the targeted regions where the imaging would be done, and that some of the particles in the tissues could become resistant to the passing of the waves, making them resistant to mechanical disturbance (Tole and Ostensen 21). If the particles are highly-resistant, it is implied that the medium where the ultrasound waves are traveling through has high density, and if the medium does not resist much, it is said to have a low density, as in the case of bone tissues (dense) compared to muscle tissues (less dense). This kind of differences between the densities of the tissues is called the acoustic impedance of the target region (measured in Rayls), and that this is dependent on the compactness or the looseness of the cells or tissues that are undergoing the ultrasound scan (Gill 11). It is also possible that the medium where the sound waves pass through may have different densities due to the difference between the tissue barrier (e.g. stomach lining) and the cells inside this tissue barrier, thus making an acoustic boundary or tissue interfaces within the area that undergoes ultrasound scanning (Tole and Ostensen 22). The idea of the presence of acoustic impedance as well as an acoustic boundary could affect the appearance of the scan in the sonogram machine, and that darker areas could be interpreted as hollow or deep areas, while the lighter ones can be the bones or any denser vital organs, such as the intestines or the heart (Hoskins 8). The transducer, or the probe of the machine could detect these areas based on how the sound waves are reflected or not reflected back, thus bone has the highest acoustic impedance, which is around 7.8 Rayl, while the lowest is fat, which is why the bones appear lighter and have a much clearer shape, as opposed to fatty deposits in the body (Tole and Ostensen 24). Some of the basic physics of sound waves are easily utilized by ultrasound imaging this way, as well as to delineate each tissue or organ based on their density and penetrability alone. It is thus important that the technician that uses the ultrasound or the sonogram machine be fully aware of how the machine works, as well as to how the properties of the sound waves could affect the image that can be produced by the machine, so that the radiologist or other medical practitioners would be able to read and interpret the images correctly and properly. Likewise, the medical practitioners that would be reading the resulting image must be qualified and properly trained in order to prevent misdiagnosing patients. Ultrasound is basically a non-invasive procedure that is the imaging modality choice of most medical personnel, due to the simplicity of its use and the ease of getting images, and that these are high-frequency waves are able to penetrate human tissues, including bones, which allow for the creation of images of the internal organs or tissues inside patients. Successful ultrasound imaging lies on understanding the basic foundation of the properties of sound waves. Thus, by being aware of the properties of sound waves, medical personnel could easily harness the diagnostic potential of ultrasound imaging, as well as being able to perform scans and interpretations easily and with higher degrees of accuracy. Works Cited Gibbs, Vivien, David Cole and Antonio Sassano. Ultrasound Physics and Technology: How, Why and When. London: Elsevier, 2009. Print. Gill, Robert. The Physics and Technology of Diagnostic Ultrasound: A Practitioner's Guide. Sydney: High Frequency Publishing, 2012. Print. Hoskins, Peter R., Kevin Martin and Abigail Thrush. Diagnostic Ultrasound: Physics and Equipment. Cambridge: Cambridge University Press, 2010. Print. Tole, Nimrod M. and Harald Ostensen. Basic Physics of Ultrasonographic Imaging. Geneva: World Health Organization, 2005. Print. Read More