chapter 12 EXAM 6 FINAL Flashcards
radiographers must limit the patient’s exposure by doing what
employing appropriate radiation reduction techniques
using protective devices
patient exposure can be reduced by:
effective communication proper body part immobilization motion reduction techniques beam limitation devices filtration of xray beam shielding suitable exposure factors elimination of repeat exposures
2 types of patient motion
voluntarty
involuntary
voluntary motion
motion controlled by will
involuntary motion
motion is caused by muscle groups that cannot be willfully controlled
voluntary motion may be attributed to
pts. age breathing patterns/problems anxiety physical/mental discomfort fear of exam/ bad diagnosis mental instability
voluntary motion may be eliminated by
gaining cooperation of pt.
immobilization
involuntary motion may be caused by
chills tremors (aka parkinsons) muscle spasms pain withdrawal
involuntary motion is reduced by
using high mA with a short exposure time
areas of the body that should be shielded whenever possible
lens of eye
breasts
reproductive organs
gonadal shielding is used to protect reproductive organs when they are in or within approximately what distance of a properly collimated beam
5 cm
what is the first line of defense for protecting the gonads
collimation
female reproductive organs receive about how many more times exposure than males for radiographic exams of the pelvic region
three times more exposure than males do
for female pts. the use of a flat contact shield placed over reproductive organs reduces exposure by
about 50%
for male pts. the use of shielding over the gonads can reduce exposure by
90-95%
for females the shield should be placed where
2.5cm (1inch) medial to each ASIS to protect the ovaries
4 types of gonadal shielding devices
- flat contact shields
- shadow shields
- shaped contact shields
- clear lead shields
flat contact shields
made of lead strips or lead materials 1mm thick
normal ones
shadow shields
suspended over the region of interest and casts a shadow over the area to be shielded
just as effective as a contact shield
shaped contact shields
contain 1mm lead and contoured to enclose the male reproductive organs
(looks like a cup)
shaped contact shields are not recommended for what
for PA projections because they only cover the anterior surface
clear lead shields
replacing some older shields
made of lead acrylic material with about 30% lead
for a scoli series what projection is always preferred
PA projections
gonadal shielding minimizes
the number of potentially harmful xray induced mutations expressed in future generations
specific area shielding reduces exposure to those areas and should be used whenever possible to minimize
the possibility of stochastic effects
for both digital and analog exams a high quality image has
sufficient density
appropriate level of contrast
maximum amt. of recorded detail
minimal amount of distortion
with digital imaging, quantum mottle is cause when
too few xrays reach the IR
by establishing technique charts in imaging departments it ensures
consistency in the diagnostic quality of digital exams and minimizes the potential for exposure technique errors
T or F
the use of high kVp and low mAs reduces pt. dose
true
with screen film imaging as kVp increases and mAs decreases, the contrast is
reduced and the amt. of useful info in the recorded image is less
increasing kVp by what with the appropriate decrease in mAs reduces pt. dose
increasing kVp by 15%
a quality control program ensures
the production of optimal quality images
Air gap technique
an alternative procedure to the use of a grid for reducing scatter
in the air gap technique, scatter is reduced by
increased OID
in the air gap technique, selection of exposure factors are comparable to those used with a what ratio grid
an 8:1 ratio grid
T or F
with kVp settings of 90 or above air gap techniques are not as effective
true
repeat image
any image that must be performed more than once because of human or mechanical error during the production of the initial image
repeat analysis program
an attempt to record the various causes of inadequate quality on occasions when an image has to be retaken
categories established for discarded images
images too dark or light because of wrong exposure factors incorrect positioning incorrect centering pt. motion improper collimation presence of foreign bodies processing artifacts
benefits of a repeat analysis program
- increase awareness among staff/students for the need to produce optimal quality images
- radiographers become more careful in producing images cuz they know they’re being reviewed
- in service education programs may be designed for imaging personnel
the quantity of radiation received by a pt. during an imaging procedure can be specified in 3 ways
- entrance skin exposure ESE
- gonadal dose
- bone marrow dose
out of the 3 ways the quantity of radiation received by a pt. during an imaging procedure which is the easiest to obtain and the most widely used
entrance skin exposure ESE
conversion of entrance skin exposure to pt. skin dose
ESE may be converted to pt. skin dose by using established well documented multiplicative factors
what is most often used to measure skin dose
TLD thermoluminescent dosimeters
what is the sensing material in TLDs
Lithium fluoride LiF
in fluoro, the amt of radiation a pt. receives is estimated by
measuring the exposure rate at tabletop and multiplying it by the fluoro time
skin dose represents
the absorbed dose to the most superficial layers of the skin
the epidermis is composed of 5 layers
- horny, outer layer
- translucent, clear layer
- granular layer
- prickle cell layer
- germinal, basal cell layer
genetically significant dose (GSD)
the equivalent dose (EqD) to the reproductive organs, that if received by every member of the population, would produce the total genetic effect on the population as the sum of the individual doses actually received
according to the US public helath service the estimated GSD for population of the united states is aprox.
0.20 mSv (20mrem)
bone marrow dose (mean marrow dose)
the average radiation dose to the entire active bone marrow
radiation dose to bone marrow may be responsible for
radiation induced leukemia
in the US the mean marrow dose from diagnostic xray exams averaged over the entire population is
1mGt/year (100mrad/year)
fluoroscopically guided positioning
practice of using fluoro to determine the exact location of the CR before taking a radiographic exposure
ASRT says its unethical
the repeat rate depends on
the techs skills in operation of fluoro equipment
communication between radiographer and pt.
pts. cooperation
pts. condition
t or f
“blind positioning” provides the patient with the lowest dose
true
t or f
studies have shown that pt. ESE increases with the use of FGP when repeat exposure is needed
true
who’s responsibility is it to question the pt. of childbearing age about pregnancy
the radiographer
it’s estimated that less than how many women referred for an xray exam are potentially pregnant
less than 1%
if the pt. has an xray and is pregnant, the RSO or medical physicist must
determine the absorbed EqD to the embryo fetus
patient dose in mamography should not exceed
3mGyt (300rad)
in mamo doses are usually not more than
2mGyt
for women age 40-49 ACR recommends mamo screenings at least
every other year
for women 50 and older, ACR recommends mamo screenings to be done
annualy
hos is the dose reduced in mamo
by limiting the number of projections taken
helical CT scan
the xray tube rotates continuously and the couch moves the pt. through the plane of the rotating xray beam
helical pitch ratio (pitch)
the relationship between the couch movement and the xray beam width
expressed as a ratio
a lower pitch like 0.5:1 does what to pt. dose
increases pt. dose
a higher pitch like 2:1 does what to pt. dose
decreased pt. dose
what are the 2 concerns related to pt. dose in CT scans
skin dose and dose distribution
skin dose from a succession of adjacent slices is lesser or greater than the skin dose from a single scan
greater than the skin dose from a single scan
the entrance exposure from a CT exam may be compared with the entrance exposure received during
a routine fluoro exam.
approximate doses for head imaging in CT
30-50 mGy (3000-5000mrad)
approximate dose for body imagin in CT scan
20-40 mGy (2000 to 4000mrad)
In CT what is used for shielding
the collimators. because of the rotational nature of the exposure a shield is not more effective than the collimators that exist on the scanner
when the pitch ratio is 1:1 the spiral CT scan dose is
comparable to conventional CT
other factors that influence pt. dose
pixel size
slice thickness
tube mA
4 dose parameters in CT
- CTDI
- CTDIw
- CTDIvol
- dose length product (DLP)
- CTDI
an ionization chamber is inserted into an acrylic phantom similar in diameter to human head or abdomen. all other holes are filled with acrylic plugs
- CTDIw
A weighted average of two measured CTDI values, one that is obtained in the center of the phantom and the other from the average of the 4 peripheral cavity measurements
- CTDIvol
the average absorbed dose within a scanned volume
- dose length product DLP
the product of CTDIvoL and the irradiated scan length
what is DLP expressed in
mGy/cm
EfD is calculated by
EfD=DLPxEfDIP
the goal of CT imaging
to obtain the best possible image while delivering acceptable level of ionizing radiation to the pt.
alliance for radiation safety in pediatric imaging was founded in and is what
founded in 2007
a partnership of medical societies whose purpose is to reduce the dose for pedi pts.
image gently campaign started in
january 22 2008
what is the goal of image gently campaign
to increase awareness of the need to reduce pt. dose for pedi pts. especially in CT
lowers pts. dose by child sizing the kV and mA
what is the goal of image wisely campaign
to address concerns about the increase of public exposure to ionizing radiation from medical radiation
what state became the first state to endorse the image wisely and image gently campaigns and when
Minnesota in December 2012
t or f
for pedi pts. you use short exposure times with high mA stations
true
most medical procedures result in fetal exposures of less than
0.1 Gyt (1rad)
