Medical imaging technology plays an important role of creating internal images of the human body for clinical or medical purposes. Historically, this technology was born in November 1895 when Wilhelm Roentgen discovered electromagnetic radiation (x-ray) (Levine, 2010). Medical imaging technique can be defined as a technique which each modality could provide unique details of the human body function. The discovery of x-ray was a motivation reason for others to improve various technologies in medical imaging over the past years such as computed tomography (CT), ultrasound and magnetic resonance imaging (MRI) (Bradley, 2008). Ultrasound is one of the medical imaging technologies that are known as sound waves with a frequency above 20 KHz that excess the human hearing range using non-ionizing radiation. Ultrasound is a diagnostic modality technique that has been in clinical use over the past 40 years when Theodore Dussik and his brother Friederich in 1940s attempted to diagnose brain tumours using ultrasound waves, although their incredible work achieved success in 1970s (Newman & Rozycki, 1998). The aim of this study is to test the hypothesis that the minimum ultrasound transit time above noise (derived from the transit time spectrum) through cancellous bone may predict the velocity measurement. Therefore, deconvolution method has been used to predict ultrasound transit time through cancellous bone and then compare it to the reported transit time from clinical ultrasound bone densitometer (CUBA).
Ultrasound is a technique that involves creating an image from the returning waves after entering sound waves to the human body. The advantage of using ultrasound waves that are safe and not able to change cell structure is because; it has low energy which is used to visualize different areas of the body. This procedure does not cause damage to the structure of the cell, unlike x-ray which is a kind of ionization radiation that can change or damage the cell structure (Bradley, 2008).
Ultrasound image can be obtained by using a device called a transducer which works as an energy converter. This device converts electrical energy into mechanical energy, and there are techniques to measure ultrasound waves by using transducer device which known as pulse-eco and transmission techniques (Rizzatto, 1998).
The produced ultrasound image can describe many features of the artefacts and objects such as reflection, refraction, scattering and absorption due to the physical properties of the ultrasonic beam when interacts with tissue. Also, there are important quantities that can be used to define the produced ultrasound image such as the propagation speed, frequency, angle of incident, pulsed ultrasound and attenuation (Aldrich, 2007).
Ultrasound has been used widely over the past years for the assessment of bone due to the results of the speed of sound and attenuation of the sound wave that provide information of elasticity, density and structure of bone. Cancellous bone is one of the bones in the human body that have been used in this project for the assessment of osteoporosis (Rho, 1996). Osteoporosis can be defined as a disease which is manifested by a decrease of bone mass and density that lead to an increased risk of fracture (Sugerman, 2014). Different methods have been used to determine bone mineral density (BMD) including the dual energy x-ray absorptiometry (DEXA), quantitative x-ray computed tomography (QCT) and quantitative ultrasound (QUS) in the process of diagnosing osteoporosis (Shan et al., 2013).
There are different kinds of machines that are used to determine ultrasound waves such as Achilles (GE Medical Lunar), Quidel QUS-2 (Biomedx) and McCue CUBA Clinical. In this project, CUBA clinical system has been used to determine ultrasound waves. Some of the most significant properties of using CUBA clinical system are that the portable device has automatic transducers to be in direct contact to the sample, calf support and area to insert sample for positioning improvement (Langton et al., 1990).
CUBA clinical system is designed to measure time of flight (TOF), also called ultrasound transit time (UTT) and broadband ultrasound attenuation (BUA) can be used for the assessment of the fracture risk. Time of flight (TOF) is defined as the travelled time for ultrasound wave that propagates through a medium. However, velocity and BUA measurements are important to determine osteoporosis where the known information of the sample thickness and transit time is used to estimate the velocity of ultrasound. This helps in predicting the density and elasticity of bone, whereas the known information of broadband ultrasound attenuation helps in predicting the density and structure of the cancellous bone (Langton, Wille & Flegg, 2014).
The Nature of Ultrasound
Ultrasound is a sound or pressure wave that has a frequency of more than 20 KHz; this frequency is higher than the one detected by the human ear (Bertora, 2007). Ordinarily, ultrasound propagates as longitude waves through fluid, air and human tissue due to the changes in pressure with slow speed of propagating in all materials such as soft tissue; about 1540 m/s. The number of cycles or pressure changes in 1 second, known as the frequency of ultrasound, can be determined by the sound source only. It cannot be determined by the medium of the travelling sound, and the range of frequencies used in clinical procedures is between 2 to 10 MHz. The speed of sound waves that travel through a medium can be determined by the density and stiffness of that medium as it is demonstrated in figure 1. The changes in either density or stiffness will affect the pulse transit time where pulsed beams are used in clinical procedures to achieve the required resolution (Aldrich, 2007).
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Figure 1: Speed of ultrasound in different materials (Aldrich, 2007 p. S132)
Production of Ultrasound
Transducer is a small device that is responsible for producing ultrasound waves by receiving electrical energy from the source and converts it to mechanical vibrations (transit mode). The mechanical vibrations are, in turn, converted into electrical energy (receive mode) that works on a piezoelectric effect (Rizzatto, 1998). Piezoelectric materials have the ability to produce an electrical field when they are mechanically deformed, but in terms of applying an electrical field as a voltage pulse to piezoelectric materials, then the deformation will occur to the materials. Ceramic materials such as Lead titanate, Lead zirconate titanate (PZT) and Barium titanate are the standard piezoelectric materials that have been used for medical imaging processes (Whittingham, 2007).
- Quote paper
- Patrick Kimuyu (Author), 2018, Comparison of Velocity and Ultrasound Transit Time Spectroscopy in Cancellous Bone Phantom, Munich, GRIN Verlag, https://www.grin.com/document/388407