Study Guidelines 5

what are the regulatory agencies that enforce radiation protection standards to protect the general public, patients and occupationally exposed personal

EPA, NRC, FDA and OSHA

ionizing radiation is most harmful to a

developing embryo especially during the first trimester of pregnancy

what is the only time it is acceptable to perform a CT scan on a know pregnant patient is

when the radiologist determines that the benefit outweighs the risk

conditions like cataracts and reduced fertility ( or sterility) may be causes by a single exposure of radiation of over

200 rad and 300 rad

what are some non threshold conditions

cancer and genetic alterations

with non threshold conditions the probability of the occurrence

(is proportional to the dose) which means there is a greater probability of getting cancer form a higher dose than a lower dose but it does not mean that the cancer would be any worse from a higher dose than a lower dose.

the unit for rad is for

measuring absorbed radiation dose form x-ray radiation

how much is 1Gy in rads

100 rads

the unit for rem is for

measuring the dose equivalent of any type of ionizing radiation and 1 Sv = 100 rem

1 Sv = how many rem

100 rem

1 rem = how many rad

1 rad

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what is CTDI

A indicator of radiation dose which accounts for the radiation located in the intended slices along with radiation penumbra

on single row detector scanners there is a radiation penumbra _________ __________ ___________

around every slice

the CTDI does not take into account if the slices _________

overlap

what is the MSAD

it is another indicator of radiation dose but it does consider whether adjacent slices overlap

when slices overlap which is greater the MSAD or the CTDI

MSAD is greater

in a CT scan, increasing __________ would reduce the dose to the patient, assuming all other parameters and variables are held constant

pitch cause it will allow fewer rotations to cover the same anatomical region of interest

what will happen to the patients dose if we increase the anatomical coverage without changing any other parameters

slice thickness will stay the same and more slices will be added So we would expose more of the patient and increase dose

how can we scan a given amount of anatomy faster and maintain the same slice thickness

increasing the pitch

what does increasing the pitch covering the same amount of anatomy do to the dose

decreases the dose

if the radiologist requests additional detail what are some ways to get the detail without additional scanning

1. if scan was done helical then we can change the reconstruction interval and reconstruct images with overlapping slices.
2. if scan was done helical on a MDCT scanner we could reconstruct thinner slices
3. we can perform multi-planar reconstructions thr

if scan was done helical on a MDCT scanner we could reconstruct thinner slices down to the thickness of the

acquired attenuation data

if the techniques for not scanning a patient additional times can not be done and the radiologist wants additional detail what can we do when we scan the patient again.

rescan at the region of interest using thinner slices

what is the federal government limit for occupational exposure

5 rem in a given year

where must the film badge be worn of a worker

chest or waist level

the cumulative dose equivalent is

years of exposure and is directly proportional to age

rem must not exceed the age of the worker in years is the

cumulative dose equivalent

how do typical contrast agents used in x-ray based imaging modalities work

by perfusing passageways and tissues, and acting to increase the attenuation of the x-ray beam

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how does IV contrast agents work

perfuse vascular structures and tissues.. help to differentiate structures and highlight abnormalities by increasing the attenuation of the x-ray beam

what is the most common active ingredient responsible for the increased attenuation of the x-ray beam

iodine

what do oral contrast agents do

opacify the stomach and bowel, displacing air and fluid

where is intrathecal contrast media injected

is injected through the theca of the spinal cord into the subarachnoid space

CT angiography is

a minimally invasive study to visualize the vessels.

during a CT angiogram it requires IV contrast (not intrathecal contrast) injected at what site.

cubital fossa

is there any greater risks associated with CTA exam than any other CT exam with IV contrast

no

what does a CTA allow us to visualize

1. stenoses
2. occlusions
3. dissections
4. emboli
5. calcified plaque

what are the types of structures that are perfused with contrast on a CT enhanced study

1. blood vessels
2. vascular lesions
3. abdominal organs

how long of a delay for MS plaques to enhance in the brain on a CT enhanced exam

45 to 60 minutes

what is an agent that breaks into ions in solution called

ionic

patients tend to be less tolerant of ________ contrast agents than _____________ agents

1. ionic
2. non-ionic

the compounds osmolality is related to

the number of particles in solution

contrast agents with a lower molecular concentration have a lower ____________ and generally cause less what?

1. osmolality
2. less pain and heat at the injection site

the viscosity of the agent determines

the force required for injection and is also related to how easily the agent is cleared from the kidneys

just for your information

all states do not have the same policy regarding the qualifications of the individual who is permitted to administer IV contrast. in some states only a nurse or doctor can administer and other states will allow the CT tech to administer as long as a docto

what technique must be used when injecting a patient with contrast

sterile technique

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when using a power injector you should always check what for catheter size with various injection rates

manufacturers recommendations

what does the viscosity of a liquid refer to

its thickness

how can a contrast agent be reduced by

warming the compound

how much do the contrast warmers warm the contrast

around body temperature

by warming the contrast what does it do

thins the contrast and makes it easier to inject

the rate at which the contrast is injected determines the

length of the bolus (window of opportunity for scanning) and the concentration of the bolus

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what is the typical choice as the site for an IV injection

basilic vein

what are some ways to distend the vein for starting an IV

1. applying a tourniquet
2. slapping the vein briskly
3. applying heat to the area

what is the first phase of enhancement immediately following the injection of contrast

bolus phase

where is the contrast during the bolus phase

the contrast travels away from the heart through the arteries

what phase comes after the bolus phase after an contrast injection

non-equilibrium phase

where is the contrast during the non-equilibrium phase

the contrast disburses into the capillaries and begins to enter the veins

what is the last phase after the non-equilibrium phase

equilibrium phase

where is the contrast during the equilibrium phase

the concentration of contrast is in the veins and arteries is very similar

when scanning the abdomen what phase of enhancement is essential for attaining the best contrast between the organs and lesions.

non-equilibrium phase

how does the inferior vena cava appear with the abdominal aorta during the equilibrium phase of enhancement

isodense

what phase or phases is not recommended when scanning the abdomen with contrast

scanning the abdomen during the bolus phase or during the equilibrium phase

the time period that is known as the non-equilibrium phase of enhancement is defined as a time when there is between _____HU and _______HU between the abdominal aorta and the inferior vena cava

1. 10 HU
2. 30 HU

how many seconds after the start of the IV injection is non-equilibrium present in an abdominal exam and why does it differ slightly with every patient

1. around 70 seconds
2. because the patients cardiac output

at what time after an contrast injection is both the liver and any lesions enhanced

3 minutes after the injection

the liver has a dual blood supply and receives about 80% of its blood from the ________ ________ and about 20% from from the _________ _________.

1. portal vein
2. hepatic artery

a biphasic liver study means

a scan at 20 to 40 seconds after the start of contrast and another scan at 60 to 90 seconds after the start of the injection

during a biphasic liver study during the 20 to 40 second scan what can be depicted and what phase is it during

hypervascular tumors during the hepatic arterial phase

during a biphasic liver study during the 60 to 90 seconds scan what can be depicted and what phase is it during

hypovascular tumors during the portal venous phase

extravasation is

the condition that occurs is the contrast being injected misses the blood vessel and instead goes directly into the soft tissue

what is the initial treatment of extravasation

elevation of the extremity and application of ice

what can happen is extravasation occurs but not likely

tissue necrosis and may require surgical drainage

what can be done to minimize the occurrence of reactions is a patient has an allergy

premedication of antihistamines or steroids given by doctor

in abdominal exams the contrast will make the abdominal organs appear

more dense relative to lesions (provided the contrast was appropriately timed)

oral contrast can be given

orally or rectally

how is the CT barium sulfate oral contrast different than the one given in conventional radiography and why

it is more dilute so it will not introduce artifacts on the CT image

barium sulfate is known to pass through the GI tract more _______ than iodinated contrasts

slowly

what can be done to the barium sulfate in order to get it to pass through the GI tract more rapidly.

add some iodinated contrast to it

what is a contraindication for barium sulfate

patients with a perforated colon

intrathecal contrast is injected into the _________ of the patient's spine for a _______________.

1. theca
2. myelogram

during a CT myelogram if the contrast is too ___________ it can cause ___________ ___________ on the CT image

1. dense
2. streak artifact

usually as long as more than ________ has passed after the myelogram injection streak artifact should not be a problem

an hour

during a myelogram if the patient is stationary for a long time the contrast may separate from and layer on the CSF. How can this be remedied

by rolling the patient to mix the contrast and CSF

what is an infants pulse rate and what kind of respirations

100 BPM to 180 BPM with shallow respirations

what can be done to monitor an infants vital signs during a scan because of their high pulse rate and shallow breathing

use a pulse oximeter

blood pressure is expressed as

the systolic pressure over the diastolic pressure

a normal adult pressure consists of a systolic pressure between ____________ and a diastolic pressure between ________________

1. 90 and 140
2. 60 and 80

CT tech should be comfortable measuring the patient's __________ __________ in the event that the patient codes

vital signs

when administering IV contrast to a child the dose is about _______________.

1 ml to 2 ml per kilogram of body weight

with a very small child the injection rate

should be lower than an adult

on a pediatric study to minimize dose what is typically done

the mAs is typically reduced along with the kVp because there is less tissue to penetrate

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