Chapter 22: MRI - Understanding The Principles And Recognizing The Basics Flashcards
What does a Musculoskeletal MRI scan for?
Menisci = tears Tendon injuries Bone marrow contusion; occult of stress fractures Muscles Osteomyelitis Spine = disk disease, scarring
What does a Neurologic MRI scan for?
Brain = post. fossa, tumor, infarction, MS
Peripheral Nerves = impingement
What does a GI MRI scan for?
Liver = lesions, cysts, cancer
Biliary System = Ductal dilation
Small and Large Bowel = appendicitis in pregnant females
What does an endocrine/reproductive MRI scan for?
Adrenal glands = adenomas and hemorrhage
female pelvis = uterus, ovaries, cancer, cysts, endometriosis
Male pelvis = rectal, bladder, and prostate cancer staging
What does a Genitourinary MRI scan for?
Kidneys = renal masses and cysts
What does the strong magnetic field of an MRI influence?
Hydrogen nuclei/protons
What direction do the protons align when placed into a powerful magnet such as an MRI?
They align with the external magnetic field instead of their own minimagnetic field
What displaces the protons from their original alignment with the external magnetic field of the scanner?
Radiofrequency pulses transmitted by the transmitter coil
What is produced when the RF pulse is turned off and the displaced protons relax back to their original alignment with the main magnetic field?
an RF signal (echo)
What receives the RF signal (echo)?
Receiver coil
What happens to the RF signal once the receiver coil receives its echo?
A computer reconstructs the information from the echo to generate an image
What is the main kind of magnet in a MRI?
a superconducting magnet cooled to extremely cold temps
What is a pulse sequence? What are the two main ones?
Spin Echo (ES) and Gradient recalled echo (GRE)
set of imaging parameters that determine how a tissue will appear
What is T1?
longitudinal relaxation time
What is T2?
transverse relaxation time
What is TR?
repetition time between two RF pulses
What is TE?
echo time between a pulse and its resultant echo
What does a short TR produce?
T1
What does a long TE produce?
T2
What appears bright white on images in a T1-weighted MRI?
Fat Hemorrhage Proteinaceous Fluid Melanin Gadolinium
What appears bright white on images in a T2-weighted MRI?
WATER Fat Edema Inflammation Infection Cysts hemorrhage
Fat is…
T1-bright and T2-bright
Water is…
T1 dark and T2 bright
What is suppression?
feature of MRI that cancels out signals from certain tissues; most often used for fat on T1-fat supressed images
What is fat suppression useful for?
tissue characterization after administering gadolinium
What is the most common IV contrast used in MRI?
Gadolinium
What is the effect of Gadolinium?
shortens T1 relaxation time causing a brighter signal
Vascular structures, tumors, and areas of inflammation are enhanced
What must you obtain before taking an MRI of a patient suspected of having metal objects in eyes?
you must get an orbital xray
What cannot go near an MRI machine?
ferromagnetic objects
What stage of pregnancy can an MRI be taken in?
Second and Third Trimester
Can you use Gadolinium in a pregnant patient?
NO
What is Nephrotic Systemic Fibrosis?
debilitating fibrotic disease which occurs if patient with renal insufficiency receives Gadolinium
AVOID GADOLINIUM IN RENAL DISEASE PATIENTS
