Physics-Based Ultrasound - Essay Example

Running Head: Physics-Based Ultrasound Physics-Based Ultrasound Table of Contents Table of Contents Introduction 2 Mechanics of Ultrasound Imaging 3 The Physics of Ultrasound Technology 3 How to Develop Quality Images 5 Obtaining Quality Superficial Images: Thyroid Gland 5 Obtaining Quality Deep Images: Fetal Heart 6 Conclusion 7 References 7 Introduction The following essay will provide a descriptive account of the general mechanics of ultrasound imaging. This overview will prelude the additional specifications that are required in imaging the fetal heart in a pregnant patient and the thyroid gland of an adult to lend further differentiation to The following essay will provide a descriptive account of ultrasound imaging in general before the complexities of the fetal heart and the thyroid gland of an adult lend further specificities to the process of precise imaging of these vastly different structures. Mechanics of Ultrasound Imaging The Physics of Ultrasound Technology Ultrasound imaging utilizes piezoelectric crystals which create sound when stimulated by alternating currents, concurrently using the charge accruement derived from sound waves exerting pressure on the piezoelectric crystals (Rubin 2005, p775). These crystals are located in the transducer probe. Periodic movement creates the waves of pressure necessary to move the pistons to different lengths along the medium (776). Faster movement of the pistons indicates closer compressions between each piston. The sound waves are created by the varying levels of pressure pulsations throughout the medium. High pressure indicates compression and low pressure indicates rarefaction (Rubin, p778). The transducer probe sends sounds and receives the echoes through the piezoelectric effect. When an electrical current reaches the piezoelectric crystals, sound waves travel emanate and the crystals change shape (Keogh, p344). The rapid shape fluctuations are responsible for the vibrations. The reverse also occurs: When the waves of sound reach the crystals, electric currents are released. The Central Processing Unit (CPU) of the ultrasound equipment contains the amplifiers and memory along with the necessary supply of power for the transducer probe (Keogh 2004, p333). Controlling when the transducer emits currents and computing the reception of the electrical pulses that are stimulated by the sound current, the CPU is able to calculate and create the image derived from the data. With the manipulation of the ultrasound pulses and the scan mode, the ultrasound technician is able to focus in on the images and search for any abnormalities. Time Gain Compensation (TGC) uses the differences between the reflection amplitudes and the reflector depth and with both values the TGC equalizes them. Reflectors exist with equal reflector coefficients which creates a differing amplitude reflections. This is dependent on the varying distances of the transducers. With the use of the TGC, amplitudes can be adjusted to allow for various path differences. When the path is lengthier, the corresponding amplitude is greater. Conversely, a shorter path has a smaller corresponding amplitude. Manufacturer presets must also be factored into decision-making by the ultrasonographer. The ultrasound machine automatically collects data of frequently-used settings. The operator optimizes the various settings for the best imaging and the ultrasound machine adopts these settings as standard. The operator of the ultrasound machine is given the option of accepting the modifications that have been made to the preset standards or maintaining the original settings provided by the manufacturing company. A report on modifications can be sent wirelessly to the manufacturer so that presets can be altered to more accommodating settings. In the use of tissue harmonic imaging, an ultrasonographer can take detailed images of various tissues in the body as well as the abnormalities that are crucial to diagnostic medicine (Henrickson 1999, p778). Lateral resolution is gained through the transmission of frequency and reception of harmonics. There is a deeper focal range possible in the use of tissue harmonic imaging as well. The apodization decreases the 3-D volume of interaction with the scanned tissues (Miller 2005, p233). In the use of harmonics, abnormalities are most prominent; the absence of these differences is a good sign there is nothing diagnostically problematic. When the ultrasonographer wants to take images to examine improvements in tumor growths, twice the frequency needs to be used with a shallower focal depth (Miller 2005, p243). The dynamic range in ultrasonography is the range of echoes that are interpreted in the order of strongest to weakest (Ibid). The strongest echo is conjured by the main bang which is nearly equivalent to the transducer-to-skin surface. In addition to the dynamic range, the ultrasonographer should be aware of the focal zones which will convey the appropriate depth. The use of multiple focal zones optimizes the lateral resolution, which should be used when viewing stationary objects like the thyroid gland. Conversely, focal zones should be lessened when imaging moving tissues, such as those of the fetal heart. The depth of the image is controlled with the zoom control. The number of pixels and the spatial resolution potential are changed along with the zooming feature. A large F.O.V. will produce a poor resolution spatially, and a narrow F.O.V. will show poor relative size amongst imaged structures. Therefore, it is essential that the ultrasonographer chooses the right medium for optimal imaging. How to Develop Quality Images Obtaining Quality Superficial Images: Thyroid Gland The thyroid gland is a stationary, superficial structure – a distinction which is particularly import in obtaining a quality image. An image is best attained with the delineation of the features of the thyroid through the use of ultrasound technology. The physical examination involves external radiation therapy. A neck ultrasound should be used in all patients with thyroid carcinoma to supplement palpation. It is prudent to perform a thyroid/neck ultrasound in all patients with thyroid cancer preoperatively, three months postoperatively. Ultrasound is best usedto determine the size and location of any malignancy. Obtaining Quality Deep Images: Fetal Heart Obtaining a clear, quality image of a fetal heart is very difficult for a few reasons. The first reason is the comparable depth of the image that needs to be obtained. The fetal heart is also a deep, non-stationary structure. Sometimes the position of the fetus makes obscures the heart, and it is actually common for pregnant mothers to be asked to come back at another time altogether due to the inability of the sonographer to scan an high-quality image. The purpose of procuring a scan of the fetal heart is to determine the cardiac rhythm of the fetus. A normal heartbeat (taken at 6 weeks) is 90-113 bpms and at 9 weeks, the ultrasound of a healthy fetus will show a cardiac rhythm between144-170 bpms. Anything below this heart rate is indicative of bradycardia, which is dangerous. Anything above the range of normalcy is tachycardia. Transducer probes have many different types. In the imaging of a heart, the use of multiple-element probes is recommended. Multiple element probes have various crystals, each with its own circuit. This enables the technician to use the pulse on differing elements at different times. The use of a large footprint in the acquisition of a quality fetal heart image. It is also essential to have a low-frequency bandwidth of 3-5 curvilinear array, which is the opportunity cost of low penetration and resultant low resolution. In moving structures such as the fetal heart, the increase of temporal resolution through increasing the creation of vital imagery. One factor that may prove difficult to the acquisition of good-quality images is fetal heart is the girth of the mother. Depth has to be adjusted according to the BMI of the mother. If the ultrasonographer decides to increase the number of focal zones, he will sacrifice the expedience of the image processing but gain the improve the resolution overall with poor temporal resolution. Conclusion The use of ultrasound technology is essential to the diagnostic medicine of such maladies as cancer (Olney 2006, p1116). References Hendrickson, J. Modern Physics 7th Edition. New York: Scholastic. 1999, p676 -697 Miller, J 2005. Instant Physics. New York: Harper Perennial Kuchel, P W. and G B Ralston, 2008. Schaum’s Outline Series: Theory and Problems of Radiology. New York: McGraw-Hill: 244-265 Olney, J W., NB. Farber, E Spitznagel and L N. Robins 2006. “Tumor”. J Neuropath Exp Neuro;55(11):1115-1123 McPhee, S J and M A Papadakis 2008. 2008 Current Medical Diagnosis and Treatment. New York: McGraw Hill Companies Inc.: 543-576 Rubin, E 2005. Rubin’s Pathology: Clinicopathologic Foundations of Medicine. Philadelphia, PA: Lippincott Williams & Wilkins Read More