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exposure objectives
radt 412
| Question | Answer |
|---|---|
| Explain how chest radiography should be performed (even with difficult or uncooperative patients) | semi-erect |
| Approximately how many degrees would a radiographer need to elevate the thorax to demonstrate a fluid level | 10 degrees from supine |
| State the ideal way a radiographer should position the patient to demonstrate an air-fluid level | patient completely erect, using a horizontal beam |
| State the two AP projections that a radiographer should perform when an air fluid level is a priority | one to demonstrate air-fluid levels and the other for a normal projection of the chest |
| List the 8 rules for mobile radiography | duty to protect your patient & others people to leave area of exposure announce when making exposure have 2 lead aprons never place your body part in primary beam provide gonadal protection max distance from the patient handle IR carefully |
| state the most reliable method of eliminating exposure fluctuations due to distance | 40 and 72 (additionally 56 for mobile) |
| State when the radiographer should use a 56 inch distance | 40 inch is undesirable because of magnification, yet 72 inch is not possible due to room and or equipment limitations |
| State the rule of doubling or having halving mAs with distance change (ex. 40 to 56 or 56 to 72) | multiply the old mAs by the factor in the corresponding box to the distance change |
| Explain angling off-center to a focused grid during a mobile exam | Angling 5 degrees can result in sufficient grid cutoff to visibly reduce image receptor exposure |
| Explain why low-ratio grids are often preferred for mobile radiography | They permit wide exposure and centering latitude assist in these problems |
| Define fluoroscopy | Dynamic exam that is static in character; involves active diagnosis |
| Fluoroscopy is mainly the domain of: | radiologist |
| Name the inventor of the fluoroscope | Thomas A. Edison in 1896 |
| Explain how Roentgen discovered xrays fluorscopically | he noticed their ability to demonstrate skeletal anatomy as he brought a lead disc into the beam and observed the dynamic movement of his own fingers projected onto a florescent screen |
| what is the fluoroscopic imaging receptor is called | Fluoroscopic screen |
| the first fluoroscopes were | Held by hand in front of the patient and xray tube and included a viewing hood to eliminate extraneous light |
| State how the fluoroscopic equipment changed once the biological hazards of radiation became apparent | The design was changed to permit viewing by an arrangement of mirrors |
| Know when the image intensification tubes were developed | 1948 |
| Know what began to predominate in 2005 | Digital fluoroscopic systems |
| Know what caused fluoroscopy to become less popular | needed to document findings, immense improvements in the resolution capabilities of diagnostic, and reductions in the dose to the patient |
| Know what percentage of the time that radiographers should obtain a satisfactory image | 95 % of the time |
| Know that arm that supports the equipment suspended over the table is called | Carriage |
| Know what mA the typical diagnostic tube operates at | 50-1,200 mA |
| Know what the fluoroscopic mA range is | 0.5-5.0 mA |
| Know the minimum SOD of a fluoroscopic xray tube | 15 inches |
| Know when the brightness of the fluoro was raised to daylight levels | When image intensification technology was developed in 1948 |
| Image intensifiers were capable of increasing the image brightness by how many times | 500-8,000 |
| Know the input phosphor of the image-intensifier tube | Fluorescent screen and the first part of the image intensifier tube that the x-ray beam hits after it exits the patient |
| Explain what happens when the input phosphor interacts with xray photon | Emits light photons which then hits the photocathode |
| What is the photocathode composed of? | cesium and antimony |
| Know what the number of electrons emitted by the photocathode is directly proportional to | The absorption, or the number of light photons which have struck it |
| Define photoemission | photocathode absorbing light photons and emitting electrons (similar to thermionic emission, only with light instead of heat) |
| Briefly explain the design of the anode in the image-intensifier tube | Positively charged and supplied with 25 kV; positioned inside the glass envelope, immediately in front of the output screen, hole in its center that permits accelerated electrons to pass through to the output screen. |
| Explain the function and location of the electrostatic focusing lenses | series of charged electrodes located inside the glass envelope of the tube; the charge of the lenses accelerates and focuses the electron stream, carries the fluoroscopic image |
| List three systems used to automatically maintain satisfactory fluoroscopic image density and contrast | Automatic brightness control (ABC), automatic dose control (ADC), automatic brightness stabilization (ABS) |
| Describe contrast | Controlled by increasing the amplitude of the video signal; difference in densities |
| Describe resolution | resolve recorded detail depending on the geometrical factors; recorded detail |
| Describe distortion | misrepresentation of original size or shape |
| Describe quantum mottle | A blotchy or grainy appearance caused by insufficient radiation to create a uniform image (noise) |
| Know the most common range of sizes for dual-focus tubes | 6-9 inches |
| Calculate the magnification factor (multifield image intensifiers) | Magnification=input screen diameter/diameter of input screen used during magnification |
| State the primary function of the fluoroscope | To provide real-time dynamic viewing of anatomic structures |
| Know what the radiologist generally uses during fluoroscopy | Contrast media to highlight the anatomy |
| State the two main areas of angiography | Neuroradiology and vascular radiology |
| Know what the fluoroscope is used for examination of | Moving internal structures and fluids |
| Know the mA that the tube is operated at for fluoro exams | less than 5 mA |
| Know what determines the kVp used for fluoro exams | Depends on the section of the body that is being examined |
| Know the name of the feature of the fluoroscopic equipment that allows the radiologist to select an image brightness level | Automatic brightness control (ABC) radiologist selects an image brightness level that is maintained automatically by varying the kVp or mA |
| Know the part of the eye that are sensitive to low light levels (night vision) | Rods |
| Know the parts of the eye that are used primarily for day light vision | Cones |
| Be able to define visual acuity | The stability to perceive fine detail |
| Define contrast perception | detects difference in brightness levels |
| What part of the eye perceives color | Cones |
| List three things that the brightness of the fluoroscopic image depends primarily on | The anatomy that is being imaged, kVp, mA |
| Define the image-intensifier tube | receives the image-forming xray beam and converts it into a visible-light image of high intensity |
| State the compound that makes up the input phosphor | Cesium iodide |
| What is the energy of the xray photon transferred to when it interacts with the input phosphor | Converted to visible light |
| What makes up the photocathode (two compounds) | Cesium and antimony |
| State the function of the photocathode | Emits electrons when illuminated by the input phosphor |
| Define photoemission | The process of the emission of electrons when illuminated by the input phosphor |
| State the average length of the image-intensification tube | 50 cm long |
| Know the potential difference maintained across the tube between photocathode and anode | 25,000 V |
| Define electron optics | Engineering aspects of maintaining proper electron travel |
| Explain the function and location of the electrostatic focusing lenses | *device along the length of the image *intensifier tube to maintain the proper electron travel *the electrons emitted from the large cathode end of the image-intensifier tube must be reduced to the small output phosphor |
| Know what makes up the output phosphor | Zinc cadmium sulfide |
| Define the flux gain | ratio of the number of light photons at the output phosphor to the number of xrays at the input phosphor |
| Know the formula for flux gain | # of output light photons/# of input xray photons |
| Know the formula for brightness gain | minification gain x flux gain |
| Define minification gain | ratio of the square of the diameter of the input phosphor to the square of the output phosphor |
| Know the formula for minification gain | Square of the diameter of the input phosphor/square of the diameter of the output phosphor |
| List three modes of operation for an image-intensifier tube | *Spot film camera (105 mm) *Cine camera (35 mm) (motion/heart studies) *TV camera |
| Know the most common ranges for trifield tubes | 25/17/12 |
| Briefly explain how an increase in patient dose affects the image quality (contrast resolution) | better image quality, lower noise, and improved contrast resolution |
| Define vignetting | Reduction in brightness at the periphery of the image (inherently unfocused) |
| Match the kVp with the fluoroscopic exams | *Gallbladder: 65-75 *Nephrostogram: 70-80 *Myelogram: 70-80 *BE (air contrast): 80-90 *Upper GI: 100-110 *Small bowel: 110-120 *BE: 110-120 |
| Label the image intensifier tube: Figure 25-5, Bontrager, page 405 | Glass envelope Focal point Anode Output phosphor Electrons Photocathode Input phosphor Electrostatic lenses |
| Size distortion | caused by factors primarily OID. |
| Shape distortion | geometric problems in the shape of the image intensification |
Created by:
meechthebeech91
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