magnetism at the atomic level Flashcards
that dense, central core of an atom, containing nearly all of its mass. its made up of protons and neutrons, held together by the strong nuclear force, one of the four fundamental forces of nature
atomic nucleus
electrons, or bit the nucleus in regions called
electron shells or orbitals
comes from the motion of charged particles inside atoms
magnetism
electrons have a property called ___, and generates tiny magnetic fields
spin
refers to a fundamental property of protons (and other elementary particles) related to their intrinsic angular momentum
proton spin
the proton has a spin of
1/2
exploit the spin and magnetic properties of protons (mainly in hydrogen atoms in water molecules) in the human body to create detailed images
MRI scans
- provides a mathematical way to determine the frequency at which a charged particle (such as a proton or electron) precesses in a magnetic field
- describes the connection between the Larmor frequency and the magnetic field strength
Larmour relationship
- motion of the protons as they wobble around the magnetic field after being disturbed by the RF pulse
precession
frequency of precession is also called
larmor frequency
sometimes used to describe the wave character of electromagnetic radiation but it is basically equivalent to the wavelength since the wavelength is just the speed divided by the frequency and the speed of light is a constant
radiofrequency
mri images are made with RF in the range from approx
10 to 300 MHz
after the protons align with the magnetic field, short RF pulse (burst of electromagnetic energy) is applied at a specific frequency. this is the _____
Larmor frequency
refers to the uniformity and synchronization of the precessional motion of protons (or other nuclei) in response to an applied magnetic field
phase coherent
when all protons are precessing in a phase, the signal they emit is ____. because the magnetic fields produced by the spinning protons can add up constructively, amplifying the overall signal
stronger and easier to detect
motion of nuclear spins in a magnetic field when there is no external influence, such as radiofrequency (RF) pulse, acting on them
Free Precession
time constant that describes when a signal decreases with time as the proton spins begin to lose phase coherence or diphase is known as ____
Relaxation Time
refers to the time it takes for protons to return to their equilibrium state after being disturbed by a RF pulse
Relaxation Time
2 main types of relaxation times
T1 and T2 relaxation time
T1 relaxation time is also called
Spin-lattice Relaxation Time
time it takes for protons to return to their original alignment with the magnetic field after being disturbed by an RF pulse
T1 Relaxation Time
important for creating contrast between T1-weighted images
T1 relaxation time
shorter T1
like fat, show up brighters
longer T1
like water, show up darker
T2 Relaxation time is also known as
Spin-spin Relaxation Time
time it takes for protons to lose phase coherence in the transverse plane after the RF pulse is turned off
T2 Relaxation Time
crucial for creating contrast in T2 weighted images
T2
longer T2
like water, appear brighter
shorter T2
like fat, appear darker
term used to describe the concentration of magnetic nuclei (typically protons) that are available to contribute to the MR signal
Spin Density
refers to the number of protons in a given tissue column that can be detected during an MRI scan
Spin Density
closely related to proton density bcs in MRI the signal is primarily generated by hydrogen nuclei (protons)
Spin Density
plays a significant role in the overall image contrast of proton density weighted images
spin density
tissues like muscle (high proton density)
brighter
fat or bone (lower proton density)
darker
