MRI part 1

quickster2008's version from 2016-10-22 18:52

Section 1

Question Answer
MRI definitionnon-invasive procedure that produces a 2D image of a body
imaging that does not use ionizing radiationMRI(xrays, C.T)
MRI indicationsST masses, bone lesions, infection, charcot, arthritidies, AVN, fx, trauma, coalition, tendon/ligament pathology, heel pain, occult pathology
MRI planesAxial, sagittal, coronal(can analyze any plane, cant do this with CT)
MRI is an imaging modality that allows for the visualization of ? in the human bodyhydrogen protons
Hydrogen protons are ideal for differentiating btw different tissue types because1. present in nearly all materials 2. electrically charged, 3. spins on its own axis, 4. possesses magnetic properites thus within a magnetic field
The anyalysis of hydrogen proton concentration gives clues tothe chemical makeup of the tissues analyzed
The most important component of an MRI scanner is the ? which initiates the process of hydrogen protons being visualizedmagnet
1st step of MRIMagnetic field
2nd step of MRIradiofrequency pulse
3rd step of MRIrelaxation
frequency of electromagnetic energy in accordance with precession of hydrogen atomslarmor frequency
Magnetic fieldmagnet is activated around patient's body in area to be visualized
radiofrequency pulsea pulsing of electromagnetic energy in accordance with the precession of the hydrogen atoms
what causes all the hydrogen protons to spin in the direction of the magnetic filedradiofrequency pulsing at the larmor frequency
relaxation stageMagnetic field turned off and hydrogen atoms return to normal spin axes. The time it takes is termed relaxation & each tissue has dif relaxation rate
measurement of ? is the basic principle behind how the MRI produces an imagespin relaxation
the intensity with which tissues show up on the image relate to time valuses(T1,T2) associated withrelaxation
the time it takes for a particular tissue to regain 63% of its longitudinal spinT1
Time it takes for a proton to lose 63% of its transverse spinT2
TR stands fortime to repeat-the duration of one imaging cycle
TE stands fortime to echo-time in which magnetization is converted to RF signal
images that emphasize a particular time value, to focus on a particular tissue typeweighted image
A type of image that is a balance of long TR and short TE interval proton density
image that does not emphasize any particular time valueproton density
Image that is a special form of inversion recovery in which the T1 time is very shortSTIR
image also called "fat suppression" bc fat tends to show up blackSTIR
Gadolinium is a contrast added to visualize ?vascular lesions
long imaging timeT2

Section 2

Question Answer
T1 and T2 for short relaxation timehigh intensity T1 and low intensity T2
T1 weighted imageTR short TE short
How would fat and fluid show up on T1fat-bright(white) fluid-dark
T2 weighted imageTR long, TE long
How would fat and fluid show up on T2fat-intermediate to bright, fluid-BRIGHT

Section 3

Question Answer
hypointenseblack in color, low intensity
Hyperintensewhite in color, high intensity
bone marrowHigh intensity for T1, low intensity on T2
cortical bonelow signal intensity on all images(lacks free hydrogen)
tendons and ligamentslow hydrogen content(though higher than bone) and has low intensity in all images.Contrasted best in T1 images however
subcutaneous fathigh T1 low T2 intensity
fathigh T1 low T2
vascular supplylow intesntity due to movement(flow void)-why u need contrast
flow voidlow intensity due to movement
when would you use contrast in MRIto visulize vascular supply.
muscleintermediate intensity in all images(intermediate hydrogen density)

Section 4

Question Answer
superficial homogenous lesions with the same intensity as surrounding fat, unless calcifications are presentlipomas
homogenous and located with a high T2 and STIR intensity due to cartilageenchondroma
ganglion cystslow T1 intensity, high T2 intensity
ST tumorslow T1, high T2
bone tumorsintermediate signal on T1, high intensity on T2
charcotdecrease signal intensity on T1 and T2
osteomyelitishigh intensity on T2 for cortical bone, low intensity on T1 for medullary bone
ST infectionincreased intensity on T2 and STIR due to inflammation in area
how to differentiate abscess from cellulitis on MRIthe degree of contrast on STIR or T2 image
osteochondritis dessicanslow intensity on T1 in acute stage but intensity increases as it becomes chronic
avascular necrosiswell defined line of demarcation btw viable bone adn devascularized bone on T1
osseous trauma such as stress fxlow intensity on T1, diffuse increase in intensity on T2(due to localized inflammation in area) STIR can be utilitzed to see marrow edema

Section 5

Question Answer
MRI contradicitionsmagnetic implants(pacemakers, defibrillators, cohlear implants), gravid females,