MRI Flashcards
name origianlly used for MR
disassociated from MRI because of public apprehension about nuclear energy
Nuclear Magnetic Resonance (NMR)
bloch and purcell discovered properties of MR which led to the use of MRE spectroscopy
1940s
bloch and purcell awared nobel prize in physics
1952
damadian showed that the relaxation of water in a tumor differed from that of water in a normal tissue
relaxation time represents the rates of signal decay and the return pf protons to equilibrium
1960s
paul lauterbur published the first crude cross-sectional images of objects obtained with MRI
1973
Peter mansfield further showed how the signals could be mathmatically analyzed which made it possible to develop a useful imaging technique
1973
nobel prize in physiology or medicine was awarded to bot lauterbur and mansfiel for their discovers in MRI
2003
protons in certain nuclie, if placed in a magnetic field
can be stimulated by radio waves of the correct frequency
basic principle of MRI
nucleus, electrons, protons,
structures of atom
after protons align with magnetic field rotation occurs
action called precession
role of magnetic field
RF introduced as very fast burst of radio waves
introdcution of RF pulses
based on nuclear density, relaxation rates and flow
strong signals appear white, weak signals, appear black
MRI signals
number of processing nuclie in a give volume of tissue
becuase the hydrogen nucleus is a single proton, its nuclear concenetration is referred to as
proton density
one component of relaxation is the release of energy by the excited protons
occurs at different rates in different tissues
relaxation time
process of nuclei releasing excess energy to the general environment or lattice, also called spin-lattice relaxation
T1 relaxation rate
release of energy by excited nuclei through interaction amoung themselves
T2 realaxation rate
moving substance usually have weak MRI signals
flow
specific radio-wave pulses that stimulate the nuclei
pulse sequence
controls the computer
displays the images
images may be printed
console
houses the electronics necuessary for transmitting radio-wave pilse sequences
can store raw and reconstructed date temporarily
computer room
contains major components of the MRI unit, the magnet
magnent room
simple but large electromagnet consisting of coils of wires
large amount of current is passed through a large number of coils to produce high magnetic fields
requires cooling system to offset heat produced
resistive magnent
wire loops are cooled to very low temperatures with liquid helium to reduce electrical resistance thereby producing higher magnetic field strenghts compared to resistive magnets
superconductive (cryogenic) magnent
constant field that does not require additional electriciyt or cooling
permanent magnent
antennas required for transmitting the RF pulse and receiving MRI signals
coils
sagittal, coronal, transverse, oblique
planes
important for visualizing pathology
slice thickness
long time, more signal available
imaging time
depending on pulse sequence, resulting images may be more weighted toward proton density, T1 or T2 information
imaging sequence
classic sequence for T1 weighted images
can also provide proton density- weighted images and T2 weighted images
useful when high signal from extensive fat overwhelms small signal intenstiy differences in the tissue of interest
spin echo
a sequence that accentulates T-1 information and provides timimg parameter to minimize signla intensity in tissue
inversion recovery
useful when high signal from extensive fat overwhelms small signal intensity difference in the tissue of interest
fat-suppressed
the only MRI contrast approved in the US, commonly used in CNS studies
metal with paramagentic effect shortens T1 relaxation time producing high contrast images
intravenoulsy administered
gadolinium
imaging technique used to improve image quality
gating
MRI superior over CT for imaging posterior fossa and white matter disease such as MS
Central Nervous System
lungs and blood in the great vessel have low MRI signals
FDA approved MRI in 1991 for supplemental mammogrpahy
chest
MRI more sensitive than CT in detecting primary and metastic tumors of the liver
abdomen
MRI advantageou in coronal and saggittal plane in examing the curvature of the pelvis
pelvis
limbs, bone marrow as well as joints are well visualized
musculoskeletal system
carotid arteries for stenoses, aneurysms plaques
vessles
