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1

why is contrast media used in CT?

because radiographic contrast of structures may be difficult to differentiate (similar appearance, HU values ex windowing)

2

role of tech with contrast administration

special knowledge and application of:

  • patient assessment
  • preparation
  • administration of contrast media
  • precautions

3

contrast media

An agent that temporarily enhances differences between anatomical structures

Affects:

  • Viewing
  • Localization
  • Differentiation

4

Types of contrast media

Main forms:

  • Liquid (most common in CT)
  • Gas/ air
  • Paste/Powder (barium, add liquid)

Classifications:

  • Dependant on attenuation value of enhanced structure

             -Negative

             -Positive

5

Classifications of contrast media

  • Negative contrast appears black or dark

Example: Air & Gases (CO2)

  • Positive contrast appears white or light

Example: Iodinated Solutions & Some Barium Sulfate Solutions (IV injections)

  • Double contrast studies can use a combination of contrast agents to help distinguish between structures on a CT scan

6

Selection Criteria for contrast media

The use of contrast material in any given study is determined by evaluating a variety of factors:

Radiographic appearance

  • Necessary for diagnosis

Protocol

  • Equipment limitations
  • Type of contrast agent

Patient

  • Contraindications
  • Condition

Administration Route

  • Example: Barium can only be used for GI tract imaging

********* NEVER inject barium into veins

7

types of contrast media used in CT

  • air
  • carbon dioxide (preferred over air)
  • water
  • barium sulfate solutions (formulated for CT usage)
  • iodinated water-soluble solutions (most commonly used in CT imaging)

8

why air and gases are used in CT

air and gases:

  • are non-toxic and provide unobstructed visualization of anatomical structures
  • distends GI tract (colon and stomach) for improved pathology detection
  • readily absorbed by the body

advantage of carbon dioxide:

  • insufflation
  • absorption
  • patient comfort

9

usage and administration of air and gas

air and gas can be used for the following exams:

  • virtual colonoscopies
  • GI studies
  • arthrograms
  • myelograms

air and gases can be administered:

  • via injection
  • orally
  • rectally

10

why water is used in CT

water:

  • patients will not present with allergies, and it is cheap and easily accessible
  • waters low density will not impede 3D reformatting

cons:

  • poor bowel distention
  • rapid transit time

11

usage and administration of water

water can be used for the following exams:

  • evaluation of the pancreas
  • GI studies
  • gastric neoplasms

water is typically administered:

  • orally

12

why barium sulfate is used in CT:

Barium sulfate solutions:

  • specially formulated radiopaque agents use 1 to 3% concentration for CT usage
  • 2 forms can be used to improve anatomic visualization:
  1. liquid: low concentration and viscosity
  2. paste: high viscosity for esophageal studies
  • can cling to bowel walls
  • ex: Readi-cat

cons:

  • can cause streaks
  • needs to be diluted
  • allergies can occur
  • poor mucosal evaluation
  • complications
  • contraindications

13

VoLumen

"unique" CT barium sulfate solution:

  • low HU (classifications can vary)
  • 0.1% barium sulfate concentration
  • resembles water

advantages over water:

  • better bowel distension
  • slower transit time
  • improved bowel wall and mucosa visualization

 

14

usage and administration of barium sulfate solutions

can be used for:

  • GI studies

Barium solutions are typically administered:

  • orally (more common)
  • rectally

15

why iodinated media is used in CT

iodinated water-soluble solutions:

  • provide differential enhancement, increasing visualization of a variety of structures
  • there are many non-ionic forms that can be used (osmolality and viscosity is variable)
  • not metabolized

Cons:

  • differential enhancement
  • allergic-like reactions
  • poor mucosal coating
  • contraindicatioons
  • diarrhea

16

usage and administration of iondinated contrast media

iodinated contrast media can be used for:

  • GI studies
  • arthrograms
  • postmyelograms
  • vascular and arterial studies
  • solid organ contrast enhancement

Iodinated agents can be administered:

  • orally
  • rectally
  • via injection
  • IV

17

iodinated oral contrast media

  • oral conrast media is used for CT scans investigating pathology in the GI tract
  • most commonly Telebrix, Lactulose, or Gastrografin are used
  • Normal responses to iodinated oral contrast can include the onset of diarrhea either immediately while ingesting the oral contrast or post-procedure

18

injected and IV iodinated contrast media

  • IV contrast is the most common administration method in CT
  • IV contrast is used when imaging the arterial or venous circulation system as well as the solid organs of the chest, abdomen or pelvis
  • Optiray, Visipaque or Omnipaque will most commonly be used for IV and injection administration methods

19

administration of contrast media

contrast media can be introduced into the body in the following ways:

  • IV (veins and arteries)
  • Oral (by mouth or nasogastric tube)
  • rectal (via specialized catheters)
  • injection (intra-articular or intrathecal)

there are pros and cons to each method

20

rectal administration

  • one some occasions, rectal contrast is required for CT scans
  • the contrast is administered using an enema tip that is attached to a catheter
  • only useful for large bowel visualization
  • typically all contrast media except water will be administered rectally

21

injection administration

  • useful for post-arthrogram and intrathecal imaging
  • the contrast is administered outside of the CT department using a needle

-injection of contrast into a joint or space surrounding the spinal cord is accomplished under fluoroscopic guidance

  • CT imaging provides visualization of the soft tissue and bony anatomy
  • special considerations must be followed for post myelogram CT imaging
  • barium and water cannot be administered

**there are additional precautions for intrathecal iodinated agents

22

administration of oral contrast

  • oral contrasts are diluted with water (concentration of oral contrast used can vary)
  • patients drink the oral contrast in intervals over a period of time(this allows the contrast to fill the entire GI tract, the length of time the pt is required to ingest the contrast is department dependent; usually a couple of hours)

-pts are required to be NPO for these exams (diabetic pts should be monitored closely)

  • all forms of contrast can be administered via this method

23

intravenous contrast media

iodinated agents are used for IV administration

  • non-ionic contrast has become the only contrast media to be used for intravascular injection

-adverse effects are uncommon

-most commonly used: Optiray, and Omnipaque

  • HOCM (4-5 times higher incidence of adverse effects vs LOCM)
  • LOCM (more expensive than HOCM)
  • IOCM (example: Visipaque; is the most expensive)

24

intravenous contrast media

Contrast is NOT metabolized

  • excreted by the kidneys (causes stress to the kidneys and urinary tract)
  • blood work must be done to determine safety (must have "normal" ranges)
  • GFR has become the gold standard

-measures renal function

-site dependent protocols determine kidney function

  1. pts with normal renal function will eliminate half the dosage of contrast from their body within 2 hours; with complete elimination within 24 hours
  2. impaired renal function can increase half life to 30 hours

25

blood work-safety indicators

(SeCr) Creatinine overestimates GFR

  • due to metabolism of creatinine in muscle

-this causes creatinine levels to be higher in:

-men vs women

-younger vs older patients (age)

-blacks vs whites (race)

-other considerations that affect SeCR readings:

-malnourished patients/muscle wasting decrease SeCR

-protein (consumption of cooked meat) increase SeCR

  • despite SeCR limitations; it remains a fast and inexpensive way to assess renal function (should be used in conjunction with GFR)

26

iodinated contrast safety considerations

impossible to predict which patients will have an adverse reaction to IV contrast

  • iodinated contrast agents are one of the most widely used of all medications
  • also considered one of the safest (fatal reactions are rare)
  • excessive doses of contrast can be toxic:
  • safe dose limits
  • over doses can be fatal (affects the pulmonary and cardiovascular systems)
  • hydration can affect safe dose limits
  • upper limit= 64gI (grams of iodine)
  • pediatric patient dosages calculated by wieght: 2mL/kg
  • common practice is to limit the pt to 1 contrast injection per 48 hours

27

iodinated contrast safety considerations: pregnancy 

  • iodinated contrast can cross the placenta and enter the fetus
  • studies unable to prove if risk exists

28

iodinated contrast safety considerations: lactation

  • contrast media can be excreted into breast milk
  • infant absorbed dose = 0.01%
  • safe to continue breastfeeding
  • option to abstain for 24 hrs 

29

adverse effects of iodinated contrast:

iodinated contrast reactions can be broadly categorized as:

  1. subjective/normal
  2. chemotoxic
  3. idiosyncratic

30

subjective (normal) responses to IV contrast

Normal responses to injection of IV contrast (aka side effects):

  • feeling of heat/ warmth (voiding sensation)
  • mild flushing
  • metallic taste
  • nausea and/or vomiting

symptoms are generally very brief

  • anxiety may increase probability of reactions
  • patients should be informed of normal responses prior to administration of contrast