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exposure objectives

radt 412

QuestionAnswer
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