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CT Theory > Contrast > Flashcards

Contrast Flashcards

1
Q

3 phases of tissue enhancement

A

Bolus
Non-equilibrium
Equilibrium
phases are classified by rate of contrast enchantment

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2
Q

Bolus/Arterial Phase

A

Immediately follows a contrast injection
Arterial structures are filled with contrast - venous structures aren’t yet
IVC and aorta have 30 HU difference
Takes about 15-22 sec to reach this, plateau lasts about 10-15sec
CT angiography images are taken in this phase

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3
Q

Organs enhanced during bolus phase

A

Most organs that have an arterial blood supply
Pancreas - 5-15 sec after peak aortic enhancement
Kidney - peak enhancement is 8-120 sec after injection, will also excrete contrast
Liver - has dual blood supply, portal venous scans occur 60 sec after a bolus injection

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4
Q

Brain scanning during bolus phase

A

Done for Metastases or PNS system tumors
Enchantment is due to disruption in the BBB
Injection rate is of no importance
Scan delay is about 4 mins or longer
CT angiography/ brain perfusions scenes must follow routine protocol injections (done for strokes)

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5
Q

Non-equilibrium/Venous Phase

A

Follows arterial phase, about 1 min after bolus injection
Has 10-30 HU difference
Contrast is still brighter in the arteries than the parenchyma of organs but venous structures are opacified
Lasts about 1 min - depends on volume and flow rate of injection
Most routine images are taken in this phase

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6
Q

Equilibrium/Delayed Phase

A

Beings 2 mins after bolus injection
CM is emptied from the arteries and diluted from the veins and soaked the organ parenchyma
Arteriovenous iodine difference (AVID) of less than 10HU
Worst phase for liver scans

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7
Q

Timing factors for 3 phases

A

Pharmacokinetic - dose
Patient - age, cardiac output, body habitus
Equip - system speed

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8
Q

Cardiac Output

A

Increase heart rate = no effect on magnitude of peak enhancement
Increase heart rate = decrease time to peak enhancement

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9
Q

Body habitus

A

Increase weight = decrease magnitude of peak enhancement
Increase weight = no effect on time to peak enhancement
Increase flow rate/iodine concentration = increased enhancement

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10
Q

Effects of flow rate

A

Increase FR = increase magnitude of peak enhancement
Increase FR = decreased time to peak enhancement
Increase FR = decrease duration of contrast injection

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11
Q

Effects of volume and dose

A

Increase volume - increase magnitude of peak enhancement
Increase volume - increase time to peak enhancement
Increase volume - increase time a given level of enhancement is maintained

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12
Q

Contrast volume scan duration

A

Optimal imaging @ 200 HU

Equipment can complete imaging in 14-20sec

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13
Q

Pharmacokinetic factors

A 
Volume  - affect peak enhancement time 
Flow rate - " " 
Flow duration
Scan delay time 
Total scan time
Osmolality of contrast
Viscosity of contrast
Concentration of contrast
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14
Q

When using a high concentration CM

A

Compensate with a lower injection rate and decreased volume
To maintain adequate enhancement
Higher injection rate increases risk of extravasation
Higher volumes also challenge stability of the IV
Viscosity is higher
Good for CT angiography studies

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15
Q

Time-Density Curves

A

Depicts the effects of aortic and hepatic enhancement
Aortic effects are more pronounced
Contrast injection rates
Increase FR = decreased time to peak enhancement
FR are typically uniphasic - can be manipulated to change characteristics of the time - density curve

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16
Q

Equipment factors

A

Faster scanners - delay b/w injection of cm and scan acquisition must be increased
Decrease time = increased scan delay
May enable the use of a smaller volume of contrast media
If volume is decreased peak enhancement will also be decreased

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17
Q

Test bolus and bolus triggering are used for

A

Ensuring imaging during peak enhancement regardless of patient age, disease, cardiac output

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18
Q

Test Bolus

A

Injection of 10-20ml IV bolus of contrast media
Test injection is delivered at the same rate as the diagnostic scan
Trail scan are performed using the lowest mA possible, takes about 10-15 slices
Determines the length of time from injection to peak aortic enhancement (better if 3 seconds are added to calculate delay)

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19
Q

Bolus/automated triggering

A

Uses the contrast bolus itself to initiate scan acquisition
A single sectional slice is used to place an ROI - uses a low dose scans to monitor contrast bolus progression over ROI
Once the desired HU is achieved computer/tech will trigger the scan acquisition

20
Q

Limitations/considerations of Bolus triggering

A

Delay b/w last monitor scan and the start of scanning may decrease accuracy of imaging during peak aortic enhancement
Increased risk of extravasation
A test injection with saline should be performed prior to contrast admin
Bolus triggering should only be used for vascular studies

21
Q

Most common to least commonly used injection methods

A

Mechanical injection - drip infusion - hand bolus

22
Q

Mechanical injector control panel parameters

A

Flow rate
Volume
Psi
of injection can all be altered

23
Q

Mechanical injector risks

A

Infiltration - cm leaking into surrounding tissues
Extravasation - cm accidentally injected into surrounding tissues and IV becomes dislodged
- both are painful at injection site, have swelling at injection site and possible hematoma
- if this happens stop injection immediately and remove needle and apply pressure, then treat with cold pack to reduce pain

24
Q

Mechanical injector considerations

A
  • connection tubing must be able to withstand pressure of injection
  • air bubbles in syringes/tubing must be removed prior to injection (can be fatal if not)
  • patency of established IV site must be checked with blood aspiration, resistance and saline flush prior to use
25
Q

Methods of cm injection

A

Most common - mechanical injector
Drip fusion
Least common - hand bolus

26
Q

Documentation required for cm administration

A

Name of agent used
Dose
Flow rates
Injection site

27
Q

Contraindications for injection cm with a CVAD

A
  • inability to demonstrate blood aspirate can indicate catheter malposition or occlusion
  • resistance to flushing a CVAD may cause the catheter to rupture
  • dialysis catheters should never be used for cm injections
28
Q

Method of IV injection depends on

A

Vascular access
Type of exam
Exams clinical indications

29
Q

IV access for cm administration

A
  • can be established in CT department
  • or IV line could be pre-established (PICCS and CVAD)
  • AC or large vein is preferred when using pressure injector
  • bending at the IV site may cause injection to fail, flow rates need to be decreased if accessing a vein and smaller gage needle is required
30
Q

Contrast media definition

A

An agent that temporarily enhances difference b/w anatomical structures

  • viewing
  • localization
  • differentiation
31
Q

Main types of cm used in CT

A 
Air
Carbon dioxide 
Water
Barium sulfate 
Iodinated water soluble solutions
32
Q

Air and gases qualities

A
  • nontoxic and provide unobstructed visualization of anatomical structures
  • distends GI tract for improved pathology detection
  • improved contrast and readily absorbed by the body
33
Q

Administration of gas and air

A

Injection
Orally
Rectally

34
Q

Advantages of CO2

A

Insufflation - inflates Bowles
Absorption - absorbs more easily by the body than air
Patient comfort

35
Q

Air and gas in is used in these exams

A

Virtual colonoscopy
GI studies
Arthrograms
Myelograms

36
Q

Water is use and disadvantages

A
  • pt’s will not have allergic reaction, cheap, easily accessible
  • waters low density will not impede 3D Reformats
  • decrease superimposition and increase contrast
    Disadvantages
  • Poor bowl distension
  • rapid transit time (absorbed by the body)
37
Q

Water used for these exams and administration

A
  • evaluation of the pancreas, GI studies, gastric neoplasms

- orally typically

38
Q

Why is barium sulfate used in CT and cons

A
  • specially formulated radiopaque agents, usually 1-3%
  • 2 forms = liquid (low concentration/viscosity) and paste (high viscosity)
  • can cling to bowel walls
    Cons
  • can cause streaks (low concentrations) - poor mucosal evaluation
  • needs to be diluted - allergies can occur - contraindications
39
Q

What is VoLumen and pros/cons

A
  • unique CT barium solution (expensive not often used)
  • low HU 15-30 - 0.1% barium sulfate concentration (resembles water)
    Pros
  • better bowel distension than water - slower transit time
  • improved bowel wall and mucosal visualization
    Cons
  • allergies to additives - complications (stool impaction)
  • contraindications bowel perforation
  • artifacts is concentration is too high
40
Q

VoLumen use and administration

A
  • GI studies (stomach, large/small bowel)

- orally(more common) and rectally

41
Q

What is iodinated water soluble solutions

A
  • iso-Osmolar is best then LOCM then HOCM least favourable b/c it causes more adverse reactions
  • not metabolized by the body and filters out via the kidneys
  • provides differential enhancement, increasing visualization of a variety of structures
42
Q

Pros/cons of iodinated water soluble cm

A

Pros
- increase attenuation differences
- water soluble
- safe and easy to administer
Cons
- difference enhancement - contraindications - diarrhea
- allergic like reactions - poor mucosal lining

43
Q

Iodinated Contrast media is used for which exams and administration

A
  • GI studies, Arthrograms, postmyelograms, vascular and arterial studies, solid organ contrast enhancement
  • orally, rectally, via injection, IV
44
Q

Most commonly used cm for IV injections

A

Omnipaque
Optiray
Visipaque

45
Q

When is IV contrast used

A

For imagining the arterial or venous circulation system as well as the solid organs of the chest abdomen or pelvis

46
Q

Administration of cm can be done by

A

IV - veins and arteries
Oral - mouth or nasogastric tube
Rectal - via specialized catheters
Injection - intra articular or intrathecal

CT Theory (5 decks)

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