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93 Cards in this Set
- Front
- Back
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What are 2 ways radiation exposure is measured in flouro
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receptor entrance exposure (II)
skin entrance exposure |
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What are 6 ways to reduce radiation exposure in flouro
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intermittent exposures
grid removal last image hold dose spreading beam filtration pulsed fluoroscopy |
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What has lead to reports of high skin dosage in radiology
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flouroscopic guided procedures
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Why are radiation injuries sometimes not noticed initially
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An insidious
aspect of the problem is that onset of injury is de-layed and the extent of damage may not be evi-dent until weeks after the procedure. |
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What are some results of skin burns from radiation
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some of the radiation-induced wounds have required skin grafts, resulting in permanent disfigurement.
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What are examples of procedures that require extended time and may result in radiation injury
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What are the 2 main categories of biologic effects of radiation
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stochastic
non-stochastic |
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What is a stochastic effect
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A stochastic effect is one in which the probability of
the effect, rather than its severity, increases with dose |
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What is a non-stochastic effect
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effects for which the probability of causing certain types of
harm will be zero at small radiation doses. Above some threshold level, damage will become appar-ent, with severity increasing as dose rises above the threshold. |
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What is an example of a stochastic effect
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The probability
of radiation-induced leukemia is substantially greater after exposure to 1 Gy (100 rad) than after exposure to 1 cGy (1 rad), but there will be no difference in the severity of the disease if it occurs. |
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1000mGy = 1Gy = 100rad
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1000mGy = 1Gy = 100rad
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What are some examples of non-stochastic effects
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1000mGy = 1Gy = 100rad
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Do stochastic effects have a threshold dosage
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no, stochastic effects are believed to lack a threshold
dose because injury to few cells or even a single cell could theoretically result in production of the effect. |
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What is another name for non-stochastic effects
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deterministic effects
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Are cataracts, erythema, epilation non-stochastic or stochastic
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non-stochastic (deterministic effect)
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What are the 2 most common effects of non-stochastic or deterministic effects of radiation
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hairloss
skin damage |
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Why is measuring dosage when using flouroscopy so difficult
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there are many different setting with different radiation exposure
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What are 4 examples of DYNAMIC settings that have different radiation exposure
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normal fluoroscopy, high-dose fluoroscopy, and conventional
and digital cine fluoroscopy |
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What are examples of settings that are record static images
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conventional photospot images
digital photospot images |
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What 2 ways is it best to characterize radiation exposure
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radiation dose is best characterized by the recep-tor entrance exposure rates and skin entrance ex-posure rates
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What pt characteristic plays a large role in radiation exposure
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pt thickness
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What does receptor entrance exposure rates measure
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Receptor entrance exposure measures the effec-tive “speed” of the imaging system, that is, the
amount of radiation used in image formation |
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What characteristic of the image is dependent on receptor entrance exposure rate
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the level of image noise, and thus the perceptibil-ity of low-contrast detail, is also dependent on it
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Is skin radiation dosage proportional to the receptor entrance exposure rate
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yes
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What exactly is receptor entrance exposure rate
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Receptor entrance exposure is normally speci-fied as the entrance exposure at the surface of the
image receptor (with the grid removed) required to produce a single image for a given x-ray spec-trum |
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What is the set up for measuring the receptor entrance exposure rate
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Note the distance from the II
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How far is the ionizing chamber placed from the II when measuring receptor entrance exposure rates
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In the measurement geometry, the ioniza-tion chamber is placed 20 –30 cm from the image
intensifier surface |
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How is the entrance exposure rate corrected to the actual entrance of the II
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The expo-sure rates are corrected to the entrance surface of
the image intensifier by using the inverse square law |
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Is the grid removed when measuring the receptor entrance exposure rate
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yes,Receptor entrance exposure rates are mea-sured with the grid removed (12); however, it is
often impractical to remove the grid from some systems, in which case the manufacturer-specified grid transmission factor can be used to correct for the presence of the grid |
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Chart comparing different dynamic settings and their exposure rate
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How are the exposure rates of static and dynamic imaging standardized so they can be compared
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dynamic recording modes acquire a series of static images, usu-ally at 25–30 images per second. Expression of
receptor entrance exposure on a per-image basis permits comparison of both dynamic and static imaging techniques. |
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1 nanocoulomb/kg (nC/kg)
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1 nanocoulomb/kg (nC/kg)
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What is the 3rd and 4th row looking at
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3rd- How many Film images (400-speed) with an REE of 77.4 nC/kg (300 R) per image.
4th row compares how many Digital photospot images with an REE of 25.8 nC/kg (100 R) per frame. |
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What is a digital spot film
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Digital videofluorography (DVF) refers to a new computer-aided televised fluoroscopy technique that uses short (10–20 ms) intense pulses of radiation to produce a motion-free latent image, which is then transferred into digital storage
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Is a digital spot film what we use all the time in GI
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yes
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How is deterministic effects determined
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from the skin entrance exposure rate
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What is used to measure the skin entrance exposure rate
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the skin
entrance exposure, quantifies the dose at the beam entrance surface to a patient-simulating medium (17 cm of acrylic with 5 mm of alumi-num) on a fluoroscopy system |
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What are the maximum skin entrance exposure rates for flouro
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The skin
entrance exposure limitations set by regulatory bodies are 2.58 mC/kg per minute (10 R/min) for normal fluoroscopy and 5.16 mC/kg per minute (20 R/min) for high-dose fluoroscopy |
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What is the laws for skin entrance exposure rate limited to
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regular flouroscopic mode. Currently,
there are no maximum limitations on other fluo-roscopic imaging modes, such as cine and digital subtraction angiography |
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What are 4 examples of variables that cause skin entrance exposure to vary
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x-ray tube voltage (kilovolt peak) and patient
thickness, presence or absence of a grid, source-to-image distance |
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When do deterministic effects become a factor
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at 2 Gy
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Chart comparing normal Vs high dose flouroscopy
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How much can skin entrance exposure vary in normal and high dose flouroscopy
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exposure rates during normal fluoroscopy and
high-dose fluoroscopy can yield a patient en-trance exposure of 0.6 –3 Gy and 6 –12 Gy, re-spectively |
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What is a technique to get a rough estimate of the skin entrance exposure
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one can multiply recorded fluoroscopy time with
typical skin entrance exposure values to obtain a rough estimate of skin dose |
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What is the normal skin entrance exposure for a patient with normal flouro
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10–50 mGy/min (multiply this times the total time to get a rough estimate of exposure)
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Is it feasible to accurately predict the skin entrance exposure to a particular pt
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no, even if we use rough estimate rages and scale it to the kVp and mA used there will be large variation based on pt sizes AND imaging modes which make estimates unreliable
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Is it possible to determine the real skin dose of a patient
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Real in-terventional procedures are often complex and
may involve dynamic changes in field size, geom-etry, position, kilovolt peak, imaging mode, and so on; moreover, few patients are really “average” in size. In reality, the clinician has no idea of skin dose and cannot tell when doses are reaching harmful levels |
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What are 2 broad categories of methods for measuring skin dose
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direct and indirect
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What is the direct method of measuring a patient skin dose
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The direct method of skin dose estimation in-volves use of small detectors placed on the pa-tient’s skin at the beam entrance location
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What type of devices have been used for direct measurement of skin dose
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types of detectors have been used, including ther-moluminescent dosimeters (TLDs), photographic films (16 –19), and, more recently, diodes or
metal-oxide semiconductor field-effect transistor (MOSFET) detectors |
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What are some issues with using direct detectors
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it has to always be region of peak radiation dose which is imposibble to know
pt can move and move detector out of assumed peak dose area pt has to lie on the detector because the x-ray tube is under the table |
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What are the issues with MOSFET detectors
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they are visible and interfere with study
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What are the advantages and disadvantages of photographic films
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hotographic films have several advantages
such as low cost, an easy-to-locate high-dose re-gion, and dose measurement by using densitom-eters. However, there are only a few films avail-able in large sizes that have the sensitivity to mea-sure several ranges of doses. |
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What is the most convienient and widely used way of measuring skin entrance exposure indirectly
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Dose area product (DAP) meter
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What is the DAP and where is it located
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he DAP meter uses a transmis-sion type air-ionization chamber mounted on the
face of the x-ray tube collimator |
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Does a DAP measure dosage of the entire field
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yes, exposure over the entire image field
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What 2 factors determine the dose area product
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The DAP
measurement is a function of the x-ray field size and the x-ray exposure at the collimator |
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Does the distance from the focal spot effect DAP
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The measured DAP is independent of distance
from the focal spot. |
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What does the focal spot look like
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What is the DAP not effected by the distance from the focal spot
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The distance factor cancels
because the exposure rate varies inversely and the x-ray field area varies inversely as the square of the distance from the focal spot to the point of measurement |
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A given DAP reading can result
from a high dose over a small field or a low dose over a large field. |
yes
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What is the dose area product
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Dose Area Product (DAP), is a multiplication of the dose and the area exposed, often expressed in Gy.cm2
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Where is DAP measured
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Can a DAP meter be used to calculate stochaistic effects
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yes
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What is a shortfall of a DAP meter
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for the patient a high dose over a small
field is not equivalent to a low dose over a large field |
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Example of how DAP has to be recalculated
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Skin entrance dose can be computed from
DAP readings only at a specific dose rate and field size. For example, if a 1-minute fluoroscopic pro-cedure produces a DAP reading of 2,000 Gy cm 2 , this result could be obtained with a 20 20-cm field at 5 Gy/min or a 10 10-cm field at 20 Gy/min, a factor of four difference in skin dose |
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What happens when magnification mode is used
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When magnification mode is selected, the
input field size is reduced, which results in de-creased brightness. The automatic brightness sta-bilizers on many systems then respond by increas-ing the x-ray dose to maintain constant image brightness |
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If you are using magnification when using flouro will the DAP be accurate
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no, because the field of exposure was changing
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Chart comparing skin entrance exsposure for various flouro studies
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Note the estimated flouro time for a Barium enema and a swallow study
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Chart comparing the skin entrance exposure for interventional procedures
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Where is the dosage the greatest for a patient
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The
dose rate to the patient is greatest at the skin where the x-ray beam enters the patient |
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What is the typical skin entrance exposure rate for an average size adult with normal flouro mode
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The
typical fluoroscopic entrance exposure rate for a medium-sized adult is approximately 30 mGy/ min (3 rad/min) (since 10 mGy 1 rad) but is typically higher in image-recording modes |
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How much can skin entrance exposure rate vary in flouroscopy
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with entrance skin dose
ranging from 44 to 340 mGy (4.4 –34 rad). (this is a different study so minimum is different) |
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What is the major difference in the mean skin entrance exposure
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the procedure length
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What are the typical radiation doses for cardiac procedures
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What are typical radiation doses for radiofrequency catheter ablation
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Is intermittent flouroscopy with last minute hold features useful for reducing radiation dosage
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yes
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What is the purpose of using grids during flouroscopy
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The presence of grids in x-ray systems primarily
increases the contrast and hence the image qual-ity |
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What is the disadvantage of grid use
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they increase the dose to the patient
and staff by a factor of two or more. |
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What particular demographic should grid removal always be considered
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children
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Is last image hold useful for reducing radiation
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yes
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What is the idea behind dose spreading
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Some reduction of
maximum skin dose can be achieved by periodi-cally rotating the fluoroscope about a center within the anatomy of interest |
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What does dose spreading look like
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What is a drawback of using a high kVP
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The drawback of using a high-energy
beam is some loss of image contrast |
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Does increased kVp decrease radiation
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yes, For a fixed receptor entrance expo-sure, the skin entrance dose varies inversely with
the kilovolt peak, more precisely as (kVp) |
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What is the general rule of thumb for adjusting kVp
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Maintaining the highest peak kilo-voltage that will provide acceptable image con-trast leads to lower skin dose.
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Is filtration another technique to reduce skin dosage
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yes
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Does magnification increase the skin dose
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The ability to create magnified images can be
clinically very useful but in almost all cases results in a higher patient dose. |
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What are 2 ways to magnify an image
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There are two basic ways
to magnify the image in fluoroscopy: geometric and electronic |
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How does geometric magnification work
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geometric magnification advantage of the diverging x-ray beam to project a
smaller region in the patient to a larger area on the image intensifier. |
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How does geometric magnification effect the skin dose
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When source-to–image re-ceptor distance is fixed, what happen to both image magnification
and skin dose as the patient is moved closer to the x-ray source |
increased
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