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65 Cards in this Set
- Front
- Back
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What resulted from the invention of image intensifiers
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replaced flourescent screens
increased image brightness |
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What is the primary function of the flouroscopy
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The primary function of fluoroscopy is real-time
imaging to provide visualization of dynamic pro cesses as they occur. |
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What has a higher radiation exposure rate; flouro or plain film
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flouro
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What is the exposure rate of typical flouro
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45mGy/min
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What is the exposure rate of a typical plain film
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900mGy/min
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What is higher the TOTAL exposure time for plain film or flouro
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flouro (x rays occur for a much shorter period of time
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What is the total exposure for a 10 minute flouro study of the abdomen
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450mGy
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what is the exposure total for an abdominal film
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3mGy
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What is done to compensate for the increased radiation dose
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the exposure rate (as mentioned before) is less.
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What is a flourescent screen
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theis is s a matererial that immediates visible light in response to a stimuli such as an x ray
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Does red light have a short or long wavelength
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long
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What was the purpose of red adaption googles
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to allow the flouroscopist to remain adjust to dark room and peform activity outside to retain dark room adaptation
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Why were image intensifiers developed
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To overcome the deficiencies of viewing the
dim fluorescent screen image, image intensifier devices were developed and introduced in 1953. |
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What are the components of a flouroscopy machine
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How does the X ray generator work
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it allows selection of kVp and mA that is delivered to the x ray tube
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What are 3 additional controls added to a flouroscopy machine that are different than what is seen in a typical x ray machine
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low continuous tube current
rapid pulsed exposure automatic brightness control |
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What are 3 types of X-ray generators used for flouro
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single phase
three phase constant potential high frequency |
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What 2 methods are used to energize the x ray tube for flouroscopy
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continous exposure
pulsed exposure |
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What is the current in continous flouroscopy
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For continuous fluoroscopy, the genera-
tor provides a steady tube current while the fluo- roscope is activated. |
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How fast are the images acquired in continous exposure
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. Images are acquired at a rate
of 30 frames per second, resulting in an acquisi- tion time of 33 msec per image |
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How is the exposure during a pulsed flouroscopy
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For pulsed fluo-
roscopy, the exposure is delivered in short pulses, 3–10 msec in length. |
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How fast are the images acquired in pulsed exposure
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ypically, a pulse rate of 30
pulses per second is used, with some units allow- ing the selection of lower pulse rates (15 or 7.5 pulses per second) |
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What is an advantage of pulsed exposure
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improved temporal resolution...motion artifact is reduced by shorter acquisition time
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What are pulsed exposures particularly useful for
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pulsed fluoroscopy useful for examining
rapidly moving structures such as those seen in cardiovascular applications. |
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Can pulsed exposure reduce radiation dose
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yes, especially when it is set lower
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Why is reproducibility so important
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Good exposure reproduc-
ibility is critical for fluoroscopic systems equip- ped with digital subtraction angiography (DSA), because differences in tube voltage between maskand contrast images can cause incomplete subtraction. |
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What type of generator produces the best reproducibility
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high frequency generators
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What type of generators are capable of producing the shortest exposure pulse
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constant potential
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Do high frequency generators and three phase generators produce as good a short pulse as constant potential
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no, slighly longer
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What is the function of the automatic brightness control (ABC)
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this acts to keep the overall image brightness seen on the monitor at a
constant level as the image intensifier is panned over body parts of differing thickness and attenuation |
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How does the ABC work
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by automatically adjustion the kVp and the mA settings
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What does the X-ray tube do
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The x-ray tube converts electrical energy pro-
vided by the generator into an x-ray beam |
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How does the X-ray tube work
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Within the x-ray tube, electrons are produced by
a heated filament and accelerated toward a posi- tively charged tungsten anode. The interaction of the electrons with the anode results in the emis- sion of x rays. |
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Is the anode postively charged
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yes
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What is the anode made out of
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tungsten
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What is the focal spot
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the area of the anode struck by electrons
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What is desired; large or small focal spot
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small (sharper image)
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How is the focal spot size adusted
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by changing the anode angle
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How is the anode angle changed
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What is the typical range of an anode angle
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7-20 degrees
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What is a problem of inherent fluoroscopy (especially with interventional procedures where there is a long exposure time)
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heating of the anode
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Does the anode need a large heat capacity
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yes
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What is done to improve the heat capacity of the anode
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To improve heat dissi-
pation, high-speed anode rotation may be used (over 10,000 rpm). In addition, a circulating water or oil heat exchanger with cooling fans is commonly installed |
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What is the type of exposure control that can be used for interventional or angiographic procedures
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grid-con-
trolled pulsing to produce very short (millisec- ond) exposures for cine image recording or pulsed fluoroscopy. In a grid-controlled tube, the cathode is at a variable negative potential, ca- pable of pinching the electron flow off and on for short exposure pulses. |
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How does the grid controlled tube stop the flow of electrons
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In a grid-controlled tube, the
cathode is at a variable negative potential, ca- pable of pinching the electron flow off and on for short exposure pulses. |
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What is a problem when using maximum FOV in interventional or angiogrphic procedures
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limits the heat capacity
When a large FOV is needed to image with a large image intensifier or film changer, the anode angle must be large enough to allow adequate coverage without cut- off of the beam intensity. |
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How does the filament size and anode angle effect the focal spot size
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Diagram on the left (a)
shows a large anode angle, which provides large radiation field cov- erage and a small effective focal spot size. However, the actual focal spot track on the anode is narrow, resulting in low heat capacity. The center diagram (b) illustrates a configuration with the same ef- fective focal spot size and a small anode angle. This configuration results in greater heat capacity but small field coverage. To satisfy the requirements of both large field coverage and large heat capac- ity, the filament size must be increased, resulting in a larger effec- tive focal spot size, as shown in c |
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What is the result of a large anode angle, small filament size on radiation field and effective focal spot
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LEFT IMAGE: shows a large anode angle, which provides large radiation field cov-
erage and a small effective focal spot size. However, the actual focal spot track on the anode is narrow, resulting in low heat capacity |
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What does a smaller anode angle do to the effective focal spot size
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decrease it
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What does a large anode angle do to the effective focal spot size
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increase is
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What does a LARGE anode angle and a large filament size do to the effective focal spot and radiation field size IMAGE ON RIGHT
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INCREASE
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What happens to heat capacity with a small focal spot
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decreases the heat capacity of the tube
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What is the function of a collimator
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define the shape of the X-ray beam
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What are the 2 sets of bades that are present within the collimator
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round and rectangular
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What is the function of a round collimator
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conforms the X-ray beam to a circular FOV
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What is the function of the rectangular collimator
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this can be used manually during the examination to reduce the size of the X-ray beam
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What is the benefit of manual collimation
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Collimation reduces
the exposed volume of tissue, resulting in re- duced scatter production and improved image contrast. |
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How does manual collimation reduce radiation to the patient
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coning the x-ray
beam to the area of clinical interest will reduce overall patient dose by minimizing direct expo- sure and scatter exposure to sensitive organs that may be adjacent to the beam |
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After the Xray is generator and moves through the collimator where does it go next
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What are the filters of a flouroscopy machine called
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countour or wedge filters
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What is the function of filters
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to provide further beam shaping and collimation
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What is another type of filter besides wedge or contour
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equilization filters
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What is the function of an equilzation filter
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Equalization filters re-
duce glare from unattenuated radiation near the edge of the patient and equalize light exposure to the video camera. |
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What do filters look like
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it operates in the radiographic mode. Tube current is measured in hundreds of mA instead of less than 5 mA, as in image-intensifying fluoroscopy.
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it operates in the radiographic mode. Tube current is measured in hundreds of mA instead of less than 5 mA, as in image-intensifying fluoroscopy.
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