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Purpose of MRI
noninvasive test that provides sectional imaging of anatomy that is especially helpful for visualizing soft tissues.These images can be configured into detailed 3-D models. TERM 2
MRI uses what kind of energy?
DEFINITION 2 MRl uses radio waves and magnetic fields to provide detailed imaging of the body that is often not visible to other types of imaging TERM 3
Types of MRI
DEFINITION 3 T1T TERM 4
Principles of MRI
DEFINITION 4 uses strong magnetic fields to align atomic nuclei (usually hydrogen protons) within body tissues.It then uses a radio signal to disturb the axis of rotation of these nuclei and observes the radio frequency signal generated as the nuclei return to their baseline states.The radio signals are collected by small antennae, called coils, placed near the area of interest TERM 5
Amount of radiation in an MRI
DEFINITION 5 none
Advantages of MRI
MRI is its ability to produce images in transverse (axial, X), coronal (frontal, Y), sagittal (Z), and multiple oblique planes with equal ease.MRI scans give the best soft tissue contrast of all the imaging modalities. TERM 7
Functional MRIs
DEFINITION 7 are used to detect metabolic changes in the brain.measures brain activity by detecting associated changes in blood flow. TERM 8
When are fMRI's used?
DEFINITION 8 Physicians use fMRI to assess how risky brain surgery or similar invasive treatment is for a patient and to learn how a normal, diseased or injured brain is functioning.Clinical use of fMRI still lags research because patients with brain pathologies are more difficult to scan with fMRI than are young healthy volunteers. TERM 9
Which structures show up best on an MRI?
DEFINITION 9 Valuable for soft tissue such as muscles, menisci, ligaments, tumors, and internal organs(CT/CAT for spinal lesions, chest, and brain). TERM 10
How are MR images made?
DEFINITION 10 made by the energy emitted by protons during their re- alignment with the main magnetic field
Scanner
magnetgradient coils (one for each orthogonal plane)radiofrequency coils transmit RF pulses serve as antennas for signals emitted from protons TERM 17
Workstation/Computers
DEFINITION 17 Protocols selected Image is reconstructed Communication with patient TERM 18
How is an image made?
DEFINITION 18 Patient is slid into the scannerMagnetic field is turned onMagnetic field aligns the protons parallel or perpendicular to the field TERM 19
Describe how the magnetic field alters the
protons?
DEFINITION 19 Protons spin on their long axes in phase Radiofrequency waves are applied at right angles to the protons Protons reorient to the transverse plane Protons then move from the transverse plane to realign and in the process release energy that they absorbed The released energy produces data that is sent to the computer The computer uses the data in sequences TERM 20
What are sequences?
DEFINITION 20 different methods for capturing the MR signal
Types of
sequences
SE Sequences: Called T1 & T2. These are at 90 angles, the typical orthogonal planes (X, Y, Z). Standard images. GRE Sequences: these are from 0 90, not in orthogonal planes, and are used in complex imaging TERM 22
What are protocols?
DEFINITION 22 the choice of imaging planes and combinations of sequences used for certain clinical conditions TERM 23
TE =
DEFINITION 23 time to echo (when signal captured) TERM 24
TR =
DEFINITION 24 time to repetitions (time when the RF pulse is repeated to displace the protons) TERM 25
Why do we sequence?
DEFINITION 25 The point is to highlight different tissues This makes those tissues look bight white (aka high signal intensity) Because different tissues and different pathologies have different water amounts in them Remember we are trying to align the hydrogen protons in water. Most common sequences: T1 and T
magnetic agents for enhancement
Gadolinium injected in the veins or joints TERM 32
Proton density imaging
DEFINITION 32 Similar to T1 and gives best anatomy picture TERM 33
STIR (short tau inversion recovery)
DEFINITION 33 Similar to T2 and is best for a subtle fracture TERM 34
Gradient echo imaging
DEFINITION 34 3D capability TERM 35
Signal intensity varies
how?
DEFINITION 35 High density structures like cortical bone, ligaments, menisci, and tendons appear dark. This is call low signal INTENSITY. (less water)Most other structures will show varying signal intensities depending if the image is shown onT1 image: protons gain longitudinal magnetizationT image: protons lose transverse magnetization
MRI excels at what?
showing changes in bone marrow, soft tissue, and inflammation TERM 37
Use of contrasts
DEFINITION 37 Contrasts such as gadolinium can be used intravenouslyThis will highlight structures or pathology with rich blood supply (tumors with angiogenesis)Contrasts can be used intra- articularly (MR arthrography) TERM 38
New Trends in MRI
DEFINITION 38 Open and upright scanners reduce claustrophobiaWeight- bearing imaging can be performed with upright scannersOpen and upright scanners are associated with lower field strength and longer imaging times TERM 39
How to view MRI images?
DEFINITION 39 Coronal images are viewed from front to back as if facing the patientSagittal images are always viewed from the left side to the right side regardless of where the body part is locatedAxial images are viewed from below from the feet to the head (pts right is on your left) TERM 40
What does MRI show best?
DEFINITION 40 Staging neoplasms Changes in bone marrow (edema, tumors, AVN) Partial vs complete tendon/ligament tears Meniscal tears Disk herniations Nerve root impingements Labral tears of the hip and shoulder Note: these are primarily soft tissues
MRI is best suited
for?
The physics of MRI is different than CT and can show different densities better Suited for ligament and tendon injury Spinal cord injury Brain tumors show better on MRI SOFT TISSUES
