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Quality Assurance

Quality assurance is a series of planned and systematic actions necessary to provide adequate confidence that a piece of hospital equipment will meet the requirements for quality. It involves providing a list of equipment capabilities, acceptance testing after purchase, commissioning by the site physicist and ongoing quality control tests. Quality control for hospital equipment plays a role in improving the diagnostic quality, reducing dose, reducing medical costs and improving departmental management. Thus, QA programs contribute to the delivery of high quality health care. Quality assurance helps to: Prevent accidents or errors Increase the chance that an accident or error will be detected prior to incidence Reduce uncertainties Provide reliable inter comparison between centres Provide full exploitation of improved technology and more complex treatments in radiology and radiotherapy In radiotherapy, quality assurance programs are of particular importance because dose de...
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Nuclear Medicine

There are three methods through which artificial radionuclides are form: Irradiation of a stable nuclide in a reactor with thermal neutrons, i.e. reactor produced (e.g. Tc-99m) Fission of heavier nuclides to produce a radioactive substance, i.e. fission produced (e.g. Ba-141 and Kr-91 from the fission of U-235) Irradiation of a nuclide in a cyclotron or accelerator, i.e. cyclotron produced (e.g. F-18) The two most common radionuclides are Tc-99m and F-18. Tc-99m is produced from Mo-99 and is used in nuclear medicine. Mo-99 is reactor produced from Mo-98. F-18 is cyclotron produced and is used widely in Positron Emission Tomography. Fluorine-18 Deoxyglucose This substance is commonly used in PET to demonstrate uptake of glucose by cells. It is manufactured by replacing a hydroxyl group in glucose with a cyclotron-produced F-18 molecule. It has a half-life of 110 minutes and can be used to demonstrate cellular metabolism. Decay Reactor-produced radionuclides decay...
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Doppler Ultrasound

What is Doppler Ultrasound? Doppler ultrasound is based on the shift in frequency in an ultrasound wave caused by a moving reflector, i.e. blood cells. The change in frequency is termed the Doppler shift . Doppler ultrasound is used to measure the velocity of a moving object. The doppler frequency is given by the product of 2, the incident frequency, the doppler angle and the velocity of blood (m/s) divided by the speed of ultrasound in soft tissue. By comparing the incident ultrasound frequency with the reflected ultrasound frequency from the blood cells, the velocity of the blood can be calculated. In general, movement towards the transducer causes an increase in frequency, and vice versa. Doppler frequencies are in the audible range of 15-20kHz. Often a loud speaker or headphones are used by the sonography to aid in positioning and diagnosis. As the angle of incidence increases with reference to the long axis of blood vessels, the Doppler shift decreases. The preferred Doppl...
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Ultrasound 2

Variable Focusing in Transmit Mode Linear array transducers have a set focal spot distance, meaning variable focusing is not possible. The focal spot distance for linear array transducer depends on transducer diameter, frequency and presence of acoustic lenses on the element surface. For phased array transducer, the focal spot is determined by time delays. Time delays applied to discrete elements results in phase shifts in the ultrasound pulses across the face of the transducer element. This results in the wave converging at a certain distance in the patient. Time delays can be changed according to the required focal distance. For shallow focal spot distances , the outer elements are fired before the inner elements. For greater focal spot distances , the outer elements are still fired before the inner elements but the time delay is reduced. For multi focal zones, we apply repeated transmissions but with difference time delays. Rephasing In Receive Mode For phased array ...
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Ultrasound 1

Ultrasound involves the transmission of sound waves which are reflected to different extents by tissue boundaries back to the transducer, which is converted into a digital signal and grey scale image. Audible sound waves range from 20 to 20,000Hz. However, ultrasound operates in the range of 2 to 10MHz, deeming it inaudible to the human ear. Sound must propagate through an elastic medium by compression, high pressure, or rarefaction, low pressure of the particles that comprise that medium. Rarefaction  is a reduction in the density of a medium, especially of air or gas. Differences Between Sound and Electromagnetic Waves      1.   Medium Requirement Sound waves, unlike electromagnetic waves, require a medium through which they propagate. Electromagnetic waves are capable of propagation through a vacuum.      2.   Frequency and Penetration As the frequency of the sound wave increases, penetration decreases. For electromagnetic wave...
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Radiobiology

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Ionising radiation causes damage to cells and must be dealt with carefully. The lowest possible dose should be delivered at all times, and special cases, e.g. pregnancy and infancy, should be evaluated for examination necessity. Stochastic Effects Stochastic effects are those where the probably of the effect increases with dose. These effects do not have a threshold dose. The primary biological effect is cell modification, e.g. radiation-induced cancer. The principle health risk is at low doses. Non-Stochastic Effects Non-stochastic effects are those whose severity increases with dose. The effects have a threshold value below which no effects are seen. The primary biological effect is cell death, e.g. skin erythema, cataracts and fibrosis. The principle health risk is at high  doses.  Damage to Cells When a photon interacts with biological tissues, it produces energetic electrons through Compton scattering. Through a process of thermal heating, ionisatio...
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Computed Tomography 2

Cone Beam CT Cone beam CT uses a large fan beam (>20 degrees) and a large array of detectors, meaning a large amount of the x-axis can be included in one scan and the table does not need to be moved. For example, a recent model uses 64 detectors, each of 0.5cm meaning 32cm of the z  axis can be imaged. CBCT is used in perfusion studies of the head, kidneys and heart, producing images of high temporal resolution. CBCT is also very common in radiotherapy. However, using cone beam CT introduces increased scatter and reduced image resolution. Cardiac CT Imaging the beating heart has proven difficult, because such a small window is required to image the heart without motion artefact. This window would ideally be around 100ms. Although electron beam CT comes close with a window of 50ms, fifth generation CT is expensive. Thus, third generation CT is used but by employing prospective cardiac gating. Prospective cardiac gating uses an ECG linked to the x-ray tube, which activates...
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