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*Quiz No. 6

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What does Nuclear Medicine involve? In nuclear medicine, we use gamma photons emitted from within the body to provide physiological and metabolic information. In radiography, we expose patients externally with x-rays to provide anatomical information. What are the types of nuclear medicine imaging modalities? Planar scintigraphy (2D projection images) SPECT (single photon emission computed tomography) PET (positron emission tomography) *Describe radiopharmaceuticals and their desirable properties. Radiopharmaceuticals consist of an agent, which concentrates in a particular organ, and a gamma-emitting radionuclide. They must have the following properties: Emit mono-energetic gamma photos (no α or β as these will be absorbed in tissue and will increase patient dose) Emit photons in the range of 70-300keV, which the PMTs are sensitive to and provide enough energy to escape the patient but still be detected but the gamma camera Have a half-life of minutes to several ho...
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*Quiz No. 5

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What is the effect of pixel size on image quality? An increased pixel size decreases the spatial resolution and thus detail of an image. Generally, the smallest object to be imaged must be two times the size of the smallest pixel. What is the effect of pixel number on image quality? An increased pixel number increases the contrast of an image, i.e. shades of grey. *Describe the process of computed radiography. Computed radiography uses a photostimulable phosphor plate instead of film, which is housed in an imaging cassette made of Gd₂O₂S. The phosphor plate is made of europium activated barium fluoride halide compounds, and this is where a latent image is formed when exposed to x-rays. The reason europium activated barium fluoride halide compounds are used is because the latent image does not fade for many hours and the output range is 300-500nm, which the used photomultiplier tubes are sensitive to. The also separate the stimulated and emitted spectrums well. When exposed ...
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*Quiz No. 4

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Define the following terms : Variable aperture collimator: these are leaves of lead that can be adjusted independently to make a rectangular or square field size, making sure that only the body part to be analysed is being imaged thereby reducing patient dose Contrast improvement factor: this refers to a grid's ability to increase film contrast and can be found by calculating the radiographic contrast with a grid vs the radiographic contrast without a grid - it depends on x-ray spectrum, tissue thickness and field size *Bucky factor: the bucky or grid factor refers to the incident radiation vs the transmitted radiation and the effect that the grid has on the transmitted radiation. It is therefore an indication of patient dose and can be found by calculating the patient dose with a grid vs without a grid. Bucky factor increases with grid ratio because more scatter radiation is being produced and then absorbed by the grid *Selectivity: this refers to the primary radiation trans...
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Quiz No. 3

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What are the three possible outcomes of x-rays interacting with matter? Transmission Absorption Scattering What are the 5 ways photons may interact with matter? Coherent scattering Compton scattering Photoelectric absorption Pair production Photodisintegration What is coherent scattering? Coherent scattering occurs when an x-ray photon interacts with the entire electron cloud of an atom, and the electron cloud then reemits a photon of equal energy but off in a different direction. What is compton scattering? Compton scattering occurs when an x-ray photon interacts with a loosely bound outer shell electron and ejects it, therefore ionising the electron. The electron is called a Compton or recoil electron. A new photon of longer wavelength and lower energy is created, which can move off in any direction, even in the direction of the incident photon, known as backscatter. The energy of the incident photon is equal to the output energy, which is shared between the ...
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Quiz No. 2

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What is the heel effect? The heel effect refers the greater attenuation of x-rays produced on the anode side when compared to those produced on the cathode side. Generally x-rays are produced below the surface of the tungsten target. Because of the way it is positioned, x-rays produced on the anode side must travel through a greater thickness of the tungsten target before escaping. This means that there can be up to a 45% difference in x-ray intensity of the beam. Thus, the thicker body part to be image can be positioned on the cathode side, with the thinner body part on the anode side. What is the heat unit? The heat unit is a unit for thermal energy used by radiographers. It is defined on the basis of full-wave rectification and single phase power, while joules are defined on the basis of full-wave rectification and three phase power. How is heat produced in the target of the X-ray tube? 99% of the kinetic energy of electrons is converted into heat energy. This means that a...
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Quiz No. 1

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A cathode  is an electrode connected to the negative terminal of the voltage supply. It consists of a wire filament which contains electrons. An anode  is an electrode connected to the positive terminal of the voltage supply. It is usually composed of Tungsten because of tungsten's high melting and boiling points, and also its high atomic number (increases x-ray production efficiency). Thermionic emission  is the process through which electrons boil off the wire filament in the cathode. A current which flows through the filament increases the filament temperature. At a certain temperature, electrons start jumping out of the wire and form a space charge around the filament. Exposure factors  are exposure time, tube current and tube voltage. These are the variables we can manipulate as radiographers to obtain best images for lowest patient dose. A line compensation circuit  ensures that the 240V from the mains supply is constant. It must be supplied c...
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