MRI Flashcards
What are the stages of hemorrhage graded on MRI? What length of time does each stage represent?
Intracranial hemorrhage: principles of CT and MRI interpretation. Eur Radiol (2001)
Hyperacute: first few hours Acute: 1-3days Early subacute: 3-7 days Late subacute: 7-14 days up to 1m Chronic: 1 months - years
What are the four types of magnetic behavior/susceptibility?
Intracranial hemorrhage: principles of CT and MRI interpretation. Eur Radiol (2001)
Diamagnetic
Paramagnetic
Supraparamagnetic
Ferromagnetic
What is diamagnetic?
Give an example
A type of magnetic behavior.
Substances without unpaired electrons. Without magnetic field - dipole moment is zero. With magnetic field - small negative suscpetibility (takes away from field strength).
Ex: oxy-hemoglobin. Carbon (diamond, graphite), water, bismuth
What is paramagnetic?
Give an example
A type of magnetic behavior
Substances with unpaired electrons. Without magnetic field - dipoles cancel each other out. With magnetic field - align in direction of the magnet and moments add together - positively effects magnetic field.
Ex: deoxy and methemoglobin, gadolinium, tungsten, cesium, aluminum, sodium
What is superparamagnetic?
Give an example
Substances with large #’s of unpaired electrons. Intermediate positive magnetic susceptibility
Example: hemosiderin, iron oxide contrast agents
What is ferromagnetism?
Half filled electron shells.
Strong attraction and alignment (projectiles across room). Will retain magnetization after removal from the magnetic field. –> permanent magnet
Examples: iron, steel, gadolinium in native state
What is classified as hyperacute hemorrhage? What will it appear as on T1 and T2 weighted images? Why?
Hyperacute - Within 24 hours
T1: Iso to hypointense - oxyhemoglobin - acts as fluid
T2: hyperintense - acts as fluid
What is classified as acute hemorrhage?
How will acute hemorrhage appear on T1 and T2 sequences?
What stage of hemoglobin breakdown is occurring?
Acute - 1-3 days
T1: Iso to hypointense
T2: hypointense
Deoxyhemoglobin
What is classified as early subacute hemorrhage?
What will early subacute hemorrhage appear on T1 and T2 images?
What stage of hemoglobin breakdown is occurring?
Early subacute 3-7 days
T1: Hyperintense
T2: Hypointense
Hemoglobin: Methemoglobin (intracellular)
What is classified as late subacute hemorrhage?
What will late subacute hemorrhage appear on T1 and T2 images?
What stage of hemoglobin breakdown is occurring?
Late subacute: 7-14d (up to 1m)
T1: Hyperintense
T2: Hyperintense
Hemoglobin: Met-hemoglobin (extracellular from red cell lysis)
Which sequence is important in differentiation between acute and early subacute hemorrhage?
Why?
T1
Acute: iso to hypointense
Early subacute: hyperintense
late subacute: hyperintense
What sequence is important in differentiation between early and late subacute hemorrhage?
Why?
T2
Early subacute: Hypointense
Late subacute: Hyperintense - increased extracellular fluid
What is classified as chronic hemorrhage?
What will late chronic hemorrhage appear on T1 and T2 images?
What stage of hemoglobin breakdown is occurring?
Chronic: >1 month
T1: Hypointense
T2: Hypointense
Hemoglobin: hemosiderin and ferriting - crystalline storage forms of iron
What is the equation of the magic angle artifact?
When 3 cos^2(angle)-1 = 0
54.74 (55)
How can the magic angle artifact be avoided?
Using longer TE times (most common in
