MRI Contrast

Question 1

Why is Contrast used?

Answer 1

• Enhances clinically relevant areas/information
  - Vascular, Physiology, Anatomy
• Pathology, inflammation, infection
• Required tool in initial diganosis, staging and treatment monitoring

MRI - gadolinium (GD) (paramagnetic agent)

Question 2

Gadolinium and Flowing Blood

Answer 2

Normally flowing blood has a high free fluid content:
• Long T1 recovery time.
• Relatively dark on T1 imaging
• When introduced into the blood stream:
• Temporarily changes the magnetization properties of blood
• Alters the appearance of all perfused organs
• dependent on their standard perfusion rate.
- Shortens the T1 recovery time of blood considerably
-Changes intrinsic fedrequency of blood much closer to lamour frequency

Question 3

T1 and T2 effects of Gadolinium

Answer 3

• Shortens T1 relaxation - lesser effect on T2. Higher concentrations T2 is more pronounced
• At extremely high concentration - GD has negative effects on T1 and T2

Question 4

Contrast Administration

Answer 4

• Intravenously from upper limb
  -Circulates through blood vessels and perfused organs
  Contrast enhancement of tissue etc proportional to:
• Local Vascular concentration
• Molar Concentration and associateed T1 relaxivity of the contrast
• Relaxivity dependent on the strenght of the magnetic field.

Question 5

Gd applications

Answer 5

• Enhancement - define borders of tumours
• Timed injection can reflect relative arterial, venous and delays phases of circulation (show routes of circulation)
• Changes in vascular supply due to tumours, infections, radiation necrosis, active ms plaques

Some abnormalities have little to no enhancement

• Low vascular tumours - high grade or low grade
• Non active MS plaques
• Calcification present

Question 6

Patient Consent

Answer 6

Must sign, risk associated - generally safe
Check pt history/ allergies
Pregnancy
Done by RO/ Radiologist
Diagnostic benefit must outweigh any adverse event risk
Should be avoided if not necessary

Question 7

MRI contrast options

Answer 7

Gd based: Cytotoxic affects
-Extracellular fluid: perfuses through blood pool
-Hepatobillary: Liver specific study
Iron based
-Intravascular: high t1 shortening of blood pool. Off label use as not approved by FDA for MRI. ferumoxytol used for anemia detection. Has hypotension adverse reaction

Question 8

MRI adverse reactions

Answer 8

Allergic or immediate acute adverse reactions
• Mild/Moderate Allergy - Hives, rash, itchiness, coughing, temporary nausea
• Acute – Difficulty breathing, heart racing, anaphylaxis
• Acute adverse reactions are the most serious risk
Should not be administered when renal function comprimised as can cause acute renal failure.