A level Physics assignment-'Waves'.

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Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines. In ultrasound, the following events happen: The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone). Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected. The reflected waves are picked up by the probe and relayed to the machine. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second). The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below. In a typical ultrasound, millions of pulses and echoes are sent and received each second. The probe can be moved along the surface of the body and angled to obtain various views. Though ultrasound resolution is affected by several factors1, imaging frequency has the most direct impact. Ultrasound resolution improves in direct proportion to imaging frequency. In a typical 5 - 1O MHz system, the resolution cell measures roughly 0.7 x 0.35 mm. The result is that anatomical structures smaller than 1 mm are likely to be missed. In digital ultrasound systems, the maximum imaging frequency is limited by the speed of the system's analog-to-digital converter. Conventional systems use A/D converters running at approximately 20 MHz. This limits the maximum imaging frequency to 10 MHz according to the Nyquist sampling theorem. The situation is even more difficult for analog systems since adequate focusing precision becomes more difficult as the frequency increases. Moreover, as the imaging frequencies increase, transducer design and fabrication become increasingly difficult. (cont)

Reply 41

sazzarooo

Piezo electric transducers: The transducer probe is the main part of the ultrasound machine; it makes the sound waves and receives the echoes and is, so to speak, the mouth and ears of the ultrasound machine. The transducer probe generates and receives sound waves using a principle called the piezoelectric (pressure electricity) effect. In the probe, there are one or more quartz crystals called piezoelectric crystals and when an electric current is applied to these crystals, they change shape rapidly, which in turn produces sound waves that travel outward. Conversely, when sound or pressure waves hit the crystals, they emit electrical currents. Therefore, the same crystals can be used to send and receive sound waves. The probe also has a sound absorbing substance to eliminate back reflections from the probe itself, and an acoustic lens to help focus the emitted sound waves. Transducer probes come in many shapes and sizes. The shape of the probe determines its field of view, and the frequency of emitted sound waves determines how deep the sound waves penetrate and the resolution of the image. They may contain one or more crystal elements; in multiple-element probes, each crystal has its own circuit. Multiple-element probes have the advantage that the ultrasound beam can be "steered" by changing the timing in which each element gets pulsed; steering the beam is especially important for cardiac ultrasound. In addition to probes that can be moved across the surface of the body, some probes are designed to be inserted through various openings of the body (vagina, rectum, oesophagus) so that they can get closer to the organ being examined (uterus, prostate gland, stomach); getting closer to the organ can allow for more detailed views.
Schematic of transducer assembly.Diagram of probe or search unit showing transducer with 70 degree wedge angle attached and refracted sound beam entering test piece 20 degrees down from plane of part surface.Piezoelectric crystals convert electronic impulse to sound energy that is emitted as waves. Discrete waves immediately in front of each sound initiation point form the near field. Individual wave trains converge to form unified wave train called far field.(cont)

Reply 42

sazzarooo

In 3D ultrasound, the technologist sweeps a probe over the maternal abdomen. A computer takes multiple images and renders a life-like 3D image. With 4D ultrasound, the computer takes the images as multiple pictures while the technician holds the probe still and simultaneously renders a 3D image in real time on a monitor; the difference between the 3D and 4D is that 4D is real-time imagery. In most cases, the standard 2D ultrasound is taken, and then the 3D/4D scan capability is added if an abnormality is detected or suspected. The 3D/4D is then focused on a specific area, not the whole body, to provide the details needed to assess and diagnose a suspected problem.

The electromagnetic radiation emitted by a moving object exhibits the Doppler Effect. The radiation emitted by an object moving toward an observer is squeezed; its frequency appears to increase and is therefore said to be blueshifted. In contrast, the radiation emitted by an object moving away is stretched or redshifted. Ultrasonic blood flow Doppler has high sensitivity and power output. It is useful for the study of cardiac movements, arterial flow, foetal sounds, stomach, intestine,bowel /renal activity and air - emboli. Low intensity ultrasound frequency is beamed into the body from the small transducer probe. The beam is reflected back with slight change in frequency due to movement of blood particles or other moving organs. The reflected signal is received by the instrument, amplified and processed electronically to produce LED flashes and audible beeps on the built-in speaker or external earphone. It is ideal for numerous vascular and arterial applications such as :- Cerebral vascular in- sufficiency; detection of arteriosclerosis, blood flow monitoring in suspected cases of internal carotid stenosis and arterial injuries; acute varicose veins, occlusive vascular and arterial diseases; early detection of limb loss in cases of gangrene or diabetes ; post-surgical monitoring of grafted or reconstructed segments. (cont)

Reply 43

sazzarooo

The MRI scan uses magnetic fields and radio waves, so there is no exposure to X-rays or any other damaging forms of radiation. The patient lies inside a large, cylinder-shaped magnet, while radio waves are sent through the body. This affects the body's atoms, forcing the nuclei into a different position. As they move back into place they send out radio waves of their own. The scanner picks up these signals and a computer turns them into a picture. These pictures are based on the location and strength of the incoming signals. Our body consists mainly of water, and water contains hydrogen atoms. For this reason, the nucleus of the hydrogen atom is often used to create an MRI scan. Using an MRI scanner, it is possible to make pictures of almost all the tissue in the body. The tissue that has the least hydrogen atoms (such as bones) turns out dark, while the tissue that has many hydrogen atoms (such as fatty tissue) looks much brighter. By changing the timing of the radio wave pulses it is possible to gain information about the different types of tissues that are present. An MRI scan is also able to provide clear pictures of parts of the body that are surrounded by bone tissue, so the technique is useful when examining the brain and spinal cord. Because the MRI scan gives very detailed pictures it is the best technique when it comes to finding tumours (benign or malignant abnormal growths) in the brain. If a tumour is present the scan can also be used to find out if it has spread into nearby brain tissue. (cont)

Reply 44

sazzarooo

The technique also allows us to focus on other details in the brain. For example, it makes it possible to see the strands of abnormal tissue that occur if someone has multiple sclerosis and it is possible to see changes occurring when there is bleeding in the brain, or find out if the brain tissue has suffered lack of oxygen after a stroke. It is also able to show both the heart and the large blood vessels in the surrounding tissue. This makes it possible to detect heart defects that have been building up since birth, as well as changes in the thickness of the muscles around the heart following a heart attack. The method can also be used to examine the joints, spine and sometimes the soft parts of your body such as the liver, kidneys and spleen.

A single atomic nucleus can be thought of as a spinning charged body, which acts as a tiny magnet. An external magnetic field into which the sample material is placed exerts a torque on the nucleus that acts to align the nuclear magnetic field with the external field; however, since the nucleus is spinning, it will precess (axis of it will ‘wobble’)about the magnetic field instead of aligning with it. The angle of the nucleus's magnetic field is quantized (due to the quantization of angular momentum. However, when the angles are randomly oriented, in net, they will align with the magnetic field slightly. The sample to be tested is placed in a static external magnetic field. The nuclei (on a quantum mechanical level) are all precessing at approximately the same rate, and more precessing with net magnetic field aligned with the magnet. Then an antenna (usually a coil-shaped inductor) with the sample inside) is used to irradiate the sample with radio waves. At certain frequencies, atomic nuclei within the sample will absorb the radiation and align. so that they all precess in phase with each other, yielding a new changing magnetic field with a characteristic frequency.

The light released from lasers is monochromatic which means that it contains on specific wavelength of light which is determined by the amount of energy released when the electron drops to a lower orbit. It is coherent or organised and therefore each photon moves in step with the others and finally, it is directional and so has a very tight and strong beam. These properties occur simultaneously through a process called stimulated emission where photon emission is organised. The photon that any atom releases has a certain wavelength that is dependent on the energy difference between the excited state and the ground state. If this photon (possessing a certain energy and phase) should encounter another atom that has an electron in the same excited state, stimulated emission can occur. The first photon can stimulate or induce atomic emission such that the subsequent emitted photon (from the second atom) vibrates with the same frequency and direction as the incoming photon. There is also a pair of mirrors, one at each end of the lasing medium. Photons, with a very specific wavelength and phase, reflect off the mirrors to travel back and forth through the lasing medium. In the process, they stimulate other electrons to make the downward energy jump and can cause the emission of more photons of the same wavelength and phase. A cascade effect occurs, and soon we have propagated many, many photons of the same wavelength and phase. The mirror at one end of the laser is "half-silvered," meaning it reflects some light and lets some light through. The light that makes it through is the laser light.(cont)

Reply 45

sazzarooo

There are many different types of lasers that are used in the world of medicine. These include lasers for treating port wine stains and thread veins, leg veins, pigmented lesions and tattoos, resurfacing skin and hair removal etc. Lasers produce a single wavelength or colour of light, which can be varied in intensity. In cosmetic treatments, the energy of a laser is used to vaporize the top layers of skin. The laser can penetrate the skin to precisely controlled depths. Light laser treatments only penetrate the epidermis and papillary dermis. Deeper ones remove the reticular dermis.Lasers can be used in other ways to improve skin quality. In some procedures, the laser penetrates beneath the top layers of skin to stimulate collagen growth in the lower layers. This tightens the underlying skin, improving skin tone and removing fine lines. This is a popular technique that has few side effects and rapid healing. Low level lasers have been used successfully for many years. When the laser beam (coherent photons) hits a body cell, it is absorbed by the cell's power generator (mitochondrions) and used to produce cellular energy or ATP (adenosine triphosphate). The level of concentration of the cell energy rises considerably, optimising the performance of all the cell functions.CAT scans take the idea of conventional X-ray imaging to a new level. Instead of finding the outline of bones and organs, a CAT scan machine forms a full three-dimensional computer model of a patient's insides. Doctors can even examine the body one narrow slice at a time to pinpoint specific areas. Computerized axial tomography (CAT) scan machines produce X-rays, a powerful form of electromagnetic energy. X-ray photons are basically the same thing as visible light photons, but they have much more energy. This higher energy level allows X-ray beams to pass straight through most of the soft material in the human body. A conventional X-ray image is basically a shadow: You shine a "light" on one side of the body, and a piece of film on the other side registers the silhouette of the bones. Shadows give you an incomplete picture of an object's shape as shown below:

With a CAT scan machine, the X-ray beam moves all around the patient, scanning from hundreds of different angles. The computer takes all this information and puts together a 3-D image of the body. The patient lies down on a platform, which slowly moves through the hole in the machine. The X-ray tube is mounted on a movable ring around the edges of the hole. The ring also supports an array of X-ray detectors directly opposite the X-ray tube. A motor turns the ring so that the X-ray tube and the X-ray detectors revolve around the body (in an alternative design, the tube remains stationary and the X-ray beam is bounced off a revolving reflector). Each full revolution scans a narrow, horizontal "slice" of the body. The control system moves the platform farther into the hole so the tube and detectors can scan the next slice. In this way, the machine records X-ray slices across the body in a spiral motion. The computer varies the intensity of the X-rays in order to scan each type of tissue with the optimum power. After the patient passes through the machine, the computer combines all the information from each scan to form a detailed image of the body. (cont)

Reply 46

sazzarooo

Solid state detectors are the most recent class of detector developed, using advanced materials such as semiconductors. These detectors convert the incident photons directly into electrical pulses and are generally used in the same manner as scintillator-based detectors. Advanced materials such as germanium or the recently popular cadmium zinc telluride (CdZnTe) offer better energy resolution, less noise, and better spatial resolution than the standard scintillators. This will allow scientists to more carefully measure gamma-ray line emission. Some materials, such as germanium, require more care than scintillators, such as cooling them to low operating temperatures. They also tend to be more expensive. As with scintillators, these detectors mainly rely on a photoelectric ionization of the material by the gamma-ray, but in this case electron/hole pairs are created in the semiconductor material rather than electron/ion pairs as in a scintillator.

Diagram showing relationship of x-ray tube, patient, detector, and image reconstruction computer and display monitor:
Multiple computers are used to control the entire CT system. The main computer that orchestrates the operation of the entire system is called the "host computer." There is also a dedicated computer that reconstructs the "raw CT data" into an image. A workstation with a mouse, keyboard and other dedicated controls allows the technologist to control and monitor the exam. The CT gantry and table have multiple microprocessors that control the rotation of the gantry, movement of the table (up/down and in/out), tilting of the gantry for angled images, and other functions such as turning the x-ray beam on an off.

Cancer is a group of diseases characterized by uncontrolled cell division and the ability of these cells to invade other tissues and spread to other areas of the body where the cells are not normally located (metastasis). Cancer is caused by damage to DNA (genetic material) through genetic and environmental factors, leading to aberrant growth regulation of cells. Cell multiplication (proliferation) is a normal physiologic process that occurs in almost all tissues and under many circumstances, such as response to injury, immune responses, or to replace cells that have died or have been shed as a part of their lifecycle (in tissues such as skin or the mucous membranes of the digestive tract). Normally the balance between proliferation and cell death is tightly regulated to ensure the integrity of organs and tissues. Mutations in DNA that lead to cancer appear to disrupt these orderly processes. The uncontrolled and often rapid proliferation of cells can lead to either a benign tumour or a malignant tumour (cancer). Benign tumours do not spread to other parts of the body or invade other tissues, and they are rarely a threat to life. Malignant tumours can invade other organs, spread to distant locations (metastasize) and become life-threatening.(cont)

Reply 47

sazzarooo

Radiation therapy (also called radiotherapy, X-ray therapy, or irradiation) is the use of a certain type of energy (called ionizing radiation) to kill cancer cells and shrink tumours. Radiation therapy injures or destroys cells in the area being treated (the "target tissue") by damaging their genetic material, making it impossible for these cells to continue to grow and divide. Although radiation damages both cancer cells and normal cells, most normal cells can recover from the effects of radiation and function properly. The goal of radiation therapy is to damage as many cancer cells as possible, while limiting harm to nearby healthy tissue. Radiation therapy may be used to treat almost every type of solid tumor, including cancers of the brain, breast, cervix, larynx, lung, pancreas, prostate, skin, spine, stomach, uterus, or soft tissue sarcomas. Radiation can also be used to treat leukemia and lymphoma (cancers of the blood-forming cells and lymphatic system, respectively). Radiation dose to each site depends on a number of factors, including the type of cancer and whether there are tissues and organs nearby that may be damaged by radiation.In nuclear imaging, short-lived radioactive drugs that emit gamma rays (radiopharmaceuticals) are injected into a patient's bloodstream and are attracted to the particular organ being analyzed. A nuclear camera then takes a time-exposure image of the pharmaceutical as it enters the bloodstream and concentrates in the tissues or organs. A nuclear physician then is able to trace the blood flow activity and analyze information about the biological activity of the organ and its related vascular system.Photomicrograph showing examples of radiation-induced chromosome damage in cancer cells following radiotherapy treatment (Bushong 1980). Abnormal formations are readily seen at high dose levels, but are also observed at the lower doses received by diagnostic patients and highly exposed workers. Abnormal formations are readily seen at high dose levels, but are also observed at the lower doses received by diagnostic patients and highly exposed workers.Abnormal formations are readily seen at high dose levels, but are also observed at the lower doses received by diagnostic patients and highly exposed workers.

And that's it. I hope that someone or maybe more may find something here helpful to them as I have been helped so much myself.
Don't know why the font is different-not in my essay.
Anyway-thanks again to all the physics nutters out there.
C ya. :smile: