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Medical Physics - HANDWRITTEN!!!  

Prior Learning:

Define key verbs:

Describe: Give a detailed account in words.

Explain: Make (an idea or situation) clear to someone by describing it in more detail or revealing relevant facts.

Identify: Establish or indicate who or what (someone or something) is.

Evaluate: Form an idea of the amount, number, or value of; assess.

Assess: Evaluate or estimate the nature, ability, or quality of.

How would you answer a “why” question?

You can answer a why question by giving reason or purpose.

How would you answer a “how” question?  

You can answer a “how” question methodically in a clearly defined process.

Define accuracy, reliability and validity in the context of secondary source research.

To determine accuracy in the context of secondary source research, you must consider or evaluate the following:

Wether the information can be substantiated in more than one valid source.

To determine reliability in the context of secondary source research, you must consider or evaluate the following:

Wether the information can be substantiated in more than one valid source (is the information consistent with information from other reputable sources?). This means if you can find similar information in at least two valid sources, then your information could be considered reliable.

To determine validity in the context of secondary source research, you must consider or evaluate the following:

The author of the article’s credentials (whether the author is qualified in that particular area).

Wether it is current or old (check the date published).

Wether the site of publication is reputable (.gov, .edu, physics textbook.).

Whether the information relates to the problem or hypothesis being investigated.

Ultrasound:

Define ultrasound and identify the differences between ultrasound and sound in normal hearing range. Indicate the range of ultrasound used in medical imaging.

Ultrasounds are sound waves with high frequency, particularly used in medical imaging (Dux College, 2018). Ultrasound is safe, non-invasive, and does not use ionising radiation, it is applied in various ways in medical imaging, including: Abdominal ultrasound, bone sonometry, breast ultrasound, doppler fetal heart rate monitors, doppler ultrasound, echocardiogram, fetal ultrasound, ultrasound-guided biopsies, ophthalmic ultrasound and ultrasound-guided needle placement.

The range of human hearing is about 20 Hz to 20,000 Hz, comparatively, ultrasound waves have frequencies greater then 20,000 Hz (Ross & Bryskin, 2011). Ultrasound are sound waves, greater than the range of human hearing, however, they have shorter wavelengths than sound normal hearing range and are also inaudible to humans.

Describe the piezoelectric materials.

Piezoelectric materials are materials that produce an electric current when subjected under mechanical stress, they are usually found in solid materials such as crystals, ceramics and bones (Woodford, 2017). The piezoelectric process is also reversible, generating a strain by the application of an electric field, their shape will also change slightly. There is a large array of applications for piezoelectric materials, one of the most common applications of piezoelectricity is in the electric cigarette lighter and loudspeakers (Braybury, 2017).

Give two examples of piezoelectric materials.

The piezoelectric effect is found in a number of natural and man-made materials. Commonly used naturally-occurring crystals include quartz and it is also evident in dry bone (Pye, 2015).

What are the roles of the piezoelectric materials used when in ultrasound scanners?

The piezoelectric effect is utilised by an ultrasound transducer, capable of detecting the reflected ultrasound produced. (Wilson, 2016). Ultrasound transducers are capable of sending an ultrasound and can also detect the sound and convert it to an electrical signal to be analysed. When producing ultrasound waves, the piezoelectric crystal converts electrical signals to mechanical vibrations, depending on the voltage run through the crystal, it all either shrink or grow in size. A computer can produce images, calculate depths and calculate speeds by measuring the time between when the sound was sent and received, the amplitude of the sound and the pitch of the sound.

Define acoustic impedance.

Acoustic impedance (Z) of a material measures the extent in which sound waves are able to pass through a material, and is defined by the formula (Doenau, 2018):

    Z = pv

Where:   Z = acoustic impedance (kgm-2s-1)
 p = density of the medium (kgm-3)
 v = velocity of sound in a material (ms-1)

Different materials have different acoustic impedances based on their density and the velocity of sound in the material.

Describe how the principles of acoustic impedance, reflection and refraction are applied to ultrasound imaging.

Acoustic impedance, reflection and refraction of ultrasound frequencies will occur just as often as normal sound waves. Ultrasound frequencies are required be used rather than normal sound, so that penetration of certain tissues and organs in the human body are allowed (Wu & Farr, 2009). When ultrasound waves are emitted into the human body, some waves will be reflected back off tissue and others will pass through or refract, eventually reflecting off the dense human bone. The refracted pulse of ultrasound further continues through the patient’s body until it reaches the boundary of another medium. The same principles apply and some of the ultrasound is reflected back to the transducer and some is refracted. The time between each pulse and its ‘echo’ is recorded and the distance/depth of each boundary from the transducer can be determined. A computer interprets this information, and a scan of an ultrasound image is created.

Identify and describe the four different types of ultrasound scans. State a reason for the use of each of the ultrasound scans.

The four different types of ultrasound scans included; A-scans, B-scans, sector scans and phase scans.

An A-scan (amplitude scan) is a range-measuring system that records the time for an ultrasonic pulse to travel to an interface in the body and be reflected back, it also requires less complex equipment (Andriessen, 2008). An A-scan provides one-dimensional information about the location of the reflecting boundaries, the intensity of the reflected beams is plotted on a graph as a function of time. The size of the peaks provides information about the nature of the target organ. A-scans are used in ophthalmology for the diagnosis of eye diseases, measurements of distances in the eye, where images of the interior of the eye is needed and it provides data on the length of the eye and masses in the eye, which is a major determinant in common sight disorders.

B-scans (brightness scan) offers two-dimensional cross-sectional view of the eye as well as the orbit (Andriessen, 2008). A B-scan is used on the outside of the closed eyelid to view the eye, it can help accurately view other eye structures like the lens, choroid, sclera, vitreous and retina. In a B-scan the intensities of the reflected ultrasound are represented as spots of varying brightness, the brightest spot corresponding to the most intense reflected ultrasound. By moving the transducer probe, the body is viewed from a range of angles. A series of spots are obtained, each series corresponding to a different line through the body. B-scans are helpful diagnosing retinal detachment and is often combined with A-scans to help determine various eye abnormalities.

Sector scans are scans of a fan-shaped section of the body that produced clear, real-time images. They are made of a number of B-scans, the transducer is swept back and forth across the area, which builds up an image of the sector in the body through a series of dots of varying intensities (Doenau, 2018). Sector scans are much harder to produce than phase scans and are much less common. Its advantage is that it only requires a small entry ‘window’ into the body and is still valuable in imaging through a small space.

A phase scan is when a transducer emits ultrasound from at a stationary point and is able to view around bends in the body. Phase scans have hundreds of transducers in the same probe in order to take a high resolution real-time scan. The angle of the wavefront can be altered by firing the transducers one after another, when this happens they are out of phase (Simmons, 2015). By changing the angle of the wavefront, a three-dimensional image can be built up over a large area. Ultrasound scanning using phase scans is the most common scanning technique used today.

Collect three ultrasound images (from the web) and give a brief description of the image and what it is showing in terms of properties and features of ultrasound as a medical imaging tool.

This image is obtained by using a sector scan to observe the infants’s skull. A sector scan is advantageous in this situation as only a small ‘window’ is required to enter through the small space (Andriessen, 2008).

(Andriessen, 2008)

This image is of some tissue and demonstrates how ultrasound can image blood flow using the Doppler effect. A Doppler ultrasound is a non-invasive test that can be used to estimate the blood flow through your blood vessels by bouncing high-frequency sound waves off circulating red blood cells (Sheps, 2016). A Doppler ultrasound may help diagnose many conditions, including: blood clots, poorly functioning valves in your leg veins, heart valve defects, congenital heart disease, a blocked artery, bulging arteries etc.

("Innovating Meaningful Healthcare | Philips Healthcare", 2014)

An echocardiogram, this is an image obtained of the heart's left ventricle, used to diagnose, manage and follow-up of patients with any suspected or known heart diseases (Engine, 2017). Assessment of the left ventricular function is extremely important as it correlates with symptoms, prognosis and complications in a large number of conditions. Echocardiography is one of the most widely used diagnostic tests in cardiology. Echocardiography uses standard two-dimensional, three-dimensional, and Doppler ultrasound to create images of the heart.

("Innovating Meaningful Healthcare | Philips Healthcare", 2014)

Jane was six months into her pregnancy. Her obstetrician performed an ultrasound scan of her uterus to examine the position of the foetus. Why is ultrasound the investigation of choice for examining a foetus during pregnancy?

Ultrasound scan is currently considered to be a safe, non-invasive, accurate indispensable obstetric tool and cost-effective investigation for the foetus (O'Brien, 2013). An ultrasound is safe and doesn’t cause any harm to either the mother or developing baby as it does not use ionising radiation. There are many different medical uses for an ultrasound scan during pregnancy including: to check the baby's growth and physical development, to determine viability of pregnancy, to work out the age of baby in a dating scan and to monitor the pregnancy if there have been complications (bleeding, fluid loss, hypertension etc).

Lisa presented to her GP with a lump in her neck. After examining her, the GP decided that such a lump was likely to be related to the thyroid gland. Explain why thyroid problems are best shown using ultrasound and why?

Thyroid ultrasound uses sound waves to produce pictures of the thyroid gland within the neck. It is commonly used to evaluate lumps or nodules found during a routine physical or other imaging exam. Ultrasound is very sensitive and shows many nodules that cannot be felt, an ultrasound can also check if the thyroid gland is underactive or overactive (Stang & Jewell, 2016). An ultrasound for a thyroid gland can give your doctor a lot of valuable information, such as: if a growth is fluid-filled or solid, the number of growths, the location of the growth, whether a growth has distinct boundaries and blood flow to the growth.

List two other clinical uses of ultrasound.

Renal: Pulsed ultrasound phase scans are used to determine the size of the kidneys or the ureters, detect kidney tumours, kidney stones or blockages of the renal tubes (Wu & Farr, 2009).

Cardiology: A real-time ultrasound phase scan which allows inside observation of the heart to identify abnormal structures or functions, measuring blood flow through the heart and major blood vessels (Freudenrich, 2001).

Using this statement, assess the impact of particular advances in physics on the development of technologies’. (1 page minimum response)

“Knowledge of the behaviour of waves, particularly with reference to reflected waves from moving objects, has been essential to the development of Doppler ultrasound techniques.”

The Doppler effect is defined as the apparent change in the frequency of sound when the source of the sound is moving relative to its receiver (Wu & Farr, 2009, 331). Doppler ultrasound is a technique that combines the established ultrasound procedures with the Doppler effect when a wave is reflected off a moving target. It is a special ultrasound technique that allows the observation and evaluation of blood flow through arteries and veins in the abdomen, arms, legs, neck, brain (in infants and children) or within various body organs such as the liver or kidneys.

Simple continuous wave Doppler, (which provided a sensitive method to measure blood velocity but with the limitation of range ambiguity) progressed to pulse wave Doppler, (which overcame the range ambiguity limitation with range gating), to colour flow imaging (CFI) techniques (this development represented a major advance in medical ultrasound and greatly extended its use in vascular and cardiac imaging) (Carson & Fenster, 2009, 414).

Due to the advances in physics, many modern Doppler instruments have been able to produce an image of the anatomy of the body and blood flow to be recorded in real time, by using high computing speed and power, enabling it to interpret the data. This is called real-time, two-dimensional colour flow imaging which plays a critical role in medical technology. Another important advance was the development of duplex and colour Doppler scanning, these advances have led to many clinical applications. Only in recent years have microprocessors, capable of handling this task, become available at suitable prices and sizes. The information regarding the speed of blood flow through critical arteries within and near the heart is provided by the ability to combine the two sets of information simultaneously. The additional information gained from an analysis of the frequency shift of the reflected sound wave is used to measure the velocity of the blood flowing through the heart. Two critical aspects in the development of this technology is the combination of using an improved transducer (using piezoelectric technology) and the application of the Doppler effect when analysing the reflected signal.

Older forms of ultrasound technology provided much less detail and no information about the motion of blood within the heart. Other forms of diagnosis, possibly involving radioisotopes, were required to provide information about blood flow in the heart (Andriessen, 2008).

Doppler is now used in many medical cases for the study of blood flow, tissue motion, and disease processes. Until Doppler ultrasound, the only way to study circulation was the invasive process of angiography, now we can non-invasively and safely study the circulation of the human body (Peace, 2011). Knowledge of the behaviour of waves due to advances in physics, particularly with reference to reflected waves from moving objects, has been essential to the development of Doppler ultrasound techniques and progress and innovations are still continuing.

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