MRI CONTRAST

Question 1

Why is contrast used in MRI

Answer 1

Alters the appearance of the tissues of interest to enhance clinically relevant
information
* Physiologic functions/performance
* Vasculature
* Assist in defining borders between normal and abnormal structures/processes

Question 2

What is the most common contrast agent used in MRI

Answer 2

Gadolinium -> considered safe with low risk of adverse effects

Question 3

How does Gadolinium affect the visualisation of flowing blood?

Answer 3

Normally flowing blood has a high free fluid content:
* Long T1 recovery time.
* Relatively dark on T1 imaging

Gadolinium, when mixed with our blood:
* Changes the intrinsic frequency of blood much closer to the Lamour frequency.
* Shortens the T1 recovery time of blood considerably
* Therefore blood and highly vascular tissue will appear bright on T1 imaging

Question 4

How is contrast administered?

Answer 4

Gadolinium is commonly injected intravenously from the upper limb.

Question 5

How is gadolinium most commonly applied?

Answer 5

Most common application used with Gd is as an extracellular contrast agent:
* Contrast circulates through blood vessels and all perfused organs
* This circulation excludes the blood brain barrier (bbb) routinely
* However brain pathology breaches this barrier to allow Gd enhancement

Question 6

Patient consent requirements prior to the use of constrast

Answer 6

Patients must sign a consent form stating the risks associated with Gadolinium administration

Whilst generally considered to have a high safety profile, Gd administration still
contains risks:
* Survey on allergies and previous use
* Pregnancy risk
* Medical conditions
* Patient must have the opportunity to ask questions

This signed document is stored in the patient’s database

Question 7

Must the reporting radiologist give consent for contrast use?

Answer 7

The reporting Radiologist must give consent for required contrast
* Can be protocol directed or based on scan findings
* This doesn’t have to be a supervising Radiologist however there needs to be one present in case of any acute adverse reactions

Question 8

Mild/Moderate allergic or immediate acute adverse reactions

Answer 8

Hives, rash, itchiness, coughing, temporary nausea

Question 9

Severe Acute allergic or immediate acute adverse reactions

Answer 9

Difficulty breathing, heart racing, anaphylaxis

Question 10

How does Gd affect laboratory tests?

Answer 10

• Laboratory blood test results can be influenced by the presence of Gadolinium
  contrast agents in the blood pool and urine samples

Question 11

When is it best to take a lab test after Gd use?

Answer 11

Minimum time is 4 hours before undertaking a urine or blood test

Best after 24 hours and per The European Society of Urogenital Radiology

Question 12

The relation between Hypotension and Ferumoxytol

Answer 12

MRI applications for Ferumoxytol is off label as not approved by the FDA or TGA

The FDA has released a warning related to hypotension and a few documented
deaths related to bolus injection of a full bottle of Ferumoxytol.

Question 13

FDA guidelines on safe injection of Ferumoxytol

Answer 13

• 5 fold dilution in saline solution
• Slow infusion to take at least 15 mins
• Monitor blood pressure before during and after infusion

Question 14

Gadolinium Ligand stability is the best in what types of Chelate

Answer 14

Macrocyclic/Ionic

Question 15

Acute reactions to Gadolinium is least documented in what type of Chelate

Answer 15

Linear/Non Ionic

Question 16

Can a lactating mother have gadolinium for her MRI scan?

Answer 16

Yes she can

Question 17

How are mild to moderate reactions most likely to be treated?

Answer 17

Antihistamine

Question 18

Contraindications for contrast use

Answer 18

Patients at highest risk of negative outcome

Contraindications
* Previous severe reactions
* Renal Failure
* Pregnancy

Question 19

Patients with highest risk of negative outcome from contrast use

Answer 19

• Previous reaction to a gadolinium chelate;
• Previous reaction to iodinated contrast,
• Previous reaction to other medical or non-medical substances;
• Have asthma;
• Are pregnant
• Are lactating and/or

Question 20

Contrast use in people with renal failure

Answer 20

For patients with acute or chronic renal failure (Stage 5), GBCA should not be used at all

Question 21

Contrast use in those pregnant

Answer 21

No adverse effect of gadolinium-based contrast agents on the mother or conceptus has been convincingly demonstrated

These agents should therefore be used only where warranted by the potential clinical benefit
to the mother and/or conceptus, over and above any benefit from non-contrast MRI
examination; the risks and benefits of gadolinium use must be discussed with the pregnant patient and referring clinician.

Question 22

Precautions for patients that are pregnant, have a previous reaction to gadolinium chelate, patients with end-stage severe, and renal failure

Answer 22

• Seek possibility of alternate non contrast solution or alternate imaging modality
• Rare that this risk would outweigh benefit

Question 23

Precautions for patients with asthma and allergies

Answer 23

Monitor closely for any adverse reaction as increased chance of immediate
hypersensitivity reactions such as itching/hives within 1hour

• Will not guarantee that they will have adverse reaction however some patients are reactive to almost any basic injections/medications

Question 24

Precautions for breast feeding patients

Answer 24

Informed consent that the trace amount that may be present has not presented evidence of harm to a baby

• Is ok to proceed with Gd if required for diagnosis in the MRI scan
• Has the option of expressing and discarding milk prior to breast feeding again after 24 hours is the advice for concerned mothers who want full
  precautions

Question 25

What are the two basic levels of supervision that must be followed in the use of intravenous contrast administration

Answer 25

Medical Doctor:
* Clinical decision to use Gd contrast

• On Site response to the worst case scenario of an acute reaction such as respiratory
  arrest and/or anaphylaxis

Technologist
* Must keep constant communication with the patient during and after any injection throughout the remainder of their time to ensure they catch any early signs of any level reaction

Question 26

How are patients with acute difficulty breathing, heart racing and anaphylaxis treated

Answer 26

If your patient starts to have an acute and severe response, immediately raise the alarm for medical assessment and response through your
emergency alarm system or available communication

With medical personnel arriving
* Close the door to the MRI scanning room and monitor that no responders enter this environment
* Commence emergency procedures as per your departmental emergency plan and CPR as required
* Assist in retrieving emergency trolley/equipment/drugs as required

Question 27

What is a ligand?

Answer 27

a. Ion or molecule that binds to a central metal atom

Question 28

What is a GBCA?

Answer 28

a. Gadolinium-based contrast agents
b. Contain the metal gadolinium, chelated to a carrier ligand.
c. Type of paramagnetic contrast agent
d. Intravenous route of administration is the most common

Question 29

What are the two main structurally different forms of GBCA available

Answer 29

a. Linear contrast agents
b. Macrocyclic contrast agents

Question 30

What is a paramagnetic contrast agent

Answer 30

a. Used to enhance MRI images
b. Displays areas of hypervascularity and associated pathology
c. Have their strongest effect in T1w imaging – predominantly alter the T1 relaxation time.

Question 31

What is the difference between ionic and non-ionic ligands?

Answer 31

a. Classification is dependent on their net charge within a solution.
b. Ionic agents are considered more stable than non-ionic agents.
c. Linear agents which are non-ionic are considered least stable ligand

Question 32

GBCA effect of T2 relaxation time

Answer 32

a. Shortens T2 relaxation time – results in hypointense signal
b. At very high concentrations - a signal void may appear to be present

Question 33

GBCA effect on T1w image

Answer 33

a. Shorten the spin-lattice relaxation time (T1) -> brighter signal in T1w images.
b. Can be used to detect focal lesions and image vessels

Question 34

Difference between linear and macrocyclic agents

Answer 34

Both Linear and Macrocyclic agents can either be ionic or non-ionic

Variation is due to differences in molecular structure

Question 35

Macrocyclic Agents

Answer 35

i. Closed/ring-like ligand structure with the ion trapped in a preformed central cavity.
ii. Longer time for ligand/chelate failure in comparison to linear agents.
iii. Considered to be more stable than Linear GBCA’s