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
Why does the magic angle artifact occur?
The angel at which the dipolar interaction between two nuclei is zero.
Dipole-dipole interactions will result in loss of T2 magnetization and loss of signal within a signal. Without interactions -signal will be increased.
