MAGNETIC RESONANCE IMAGING (MRI) Flashcards
______ associated with atoms and nuclei were first described in the ___ (year).
Magnetic fields; 1930s
____ and ___ each received a Nobel Prize in physics for their work on atomic and nuclear magnetism. Rabi coined the term ____.
Otto Stern and Isador Rabi; nuclear magnetic resonance (NMR)
In (year), ____ and ____ at Harvard independently described NMR in a solid. They shared the 1952 Nobel Prize in physics for this work. Bloch continued extensive studies with the ___ , thereby laying the groundwork for later developments that led to MR
1946; Felix Bloch at Stanford and Edward Purcell ; NMR of water
is known as the father of MRI
Felix Bloch
He proposed some novel properties for the atomic nucleus, including that the nucleus behaves like a small magnet. He described this nuclear magnetism by what are now called
Bloch equations
He explain that a nucleus, because it spins on an imaginary axis, has an associated _____ This field is called a ____. Nucleons that have charge (e.g., protons) and that spin have even stronger magnetic fields.
magnetic field; magnetic moment
In the late (year)s engineer-physician ____, while working with NMR spectroscopy, showed that malignant tissue has a different _____ spectrum from normal tissue.
1960s; Raymond Damadian ; NMR (relaxation time of water)
This finding suggested that images of the body might be obtained by producing _____.
maps of relaxation rates.
He produced a crude NMR image of a __ tumor in ___ and the first body image in ___ . That image took almost (how long) to produce.
rat ;1974 ; 1976; 4 hours
_____, an NMR chemist at State University of New York in Stony Brook, developed the first imaging method using NMR that is similar to what is used today. He called this method ____, which was sort of Greek for saying that this imaging method requires a whole bunch of magnetic fields whizzing and buzzing around. I
Paul Lauterbur; zeugmatography
In (year) Lauterbur published the first cross-sectional images of objects obtained with MRI techniques. These first images were crude, and only ___ objects could be distinguished.
1973; large
Meanwhile in Nottingham, England, ____, a solid-state physicist, was engaged in similar research and eventually developed the ____method that is used for functional MR neuro imaging today.
Peter Mansfield; echoplanar MRI method
The basic principle of MRI is that protons in certain atomic nuclei, if placed in a ____, can be stimulated by (absorb energy from) ____ of the correct frequency. After this stimulation the protons ___ while energy is induced into a receiver antenna (the MRI signal), which is then digitized into a viewable image.
magnetic field; radio waves. relax;
____ represent the rates of signal decay and the return of protons to equilibrium.
Relaxation times
The earliest magnets were described ___ years ago as naturally occurring ___ stones that attracted iron. These “leading stones,” or lodestones, were thought to be magic by the natives in a region of present-day ___ , then known as ___ in the Greek language
2000; black ; western Turkey; Magnesia
A magnet is a material or object that produces a magnetic field. Magnets used for MRI are of three types:
permanent, resistive and superconductive.
In the space between the poles, the ____ is uniform enough for imaging.
magnetic field
A ____ is generated by a moving charge (electrical current). The direction of the magnetic field can either be ___ with respect to the direction of flow of the current.
magnetic field ; clockwise or counter-clockwise
___ or ___ determines the magnitude and direction of the magnetic field due to a current
Ampere’s law or Fleming’s right-hand rule
When a magnet is moved in and out of a closed circuit, an ___ current is produced, which ceases the moment the magnet stops moving. Such a current is called an ___ .
oscillating; induced electric current
___ explains the phenomenon of an induced current.
Faraday’s law of induction
____ is defined as the energy available from a unit of charge travelling once around a loop of wire. The ___ drives a current in the circuit and is the result of a changing magnetic field inducing an electric field.
electromotive force (emf)
formula for magnetic field
B=F/p, where B-field strength in tesla (T), F is force in newton (N), and p is pole strength in ampere meter (Am)
The tesla (T) is the standard international (SI) unit for the magnetic field. An older unit still very much in use is the gauss (G); 1 T equals ___ G.
10,000 G.
The atomic nucleus is the small, dense region consisting of___at the center of an atom, discovered in (year) by__based on the 1909 Geiger–Marsden ____
protonsandneutrons; 1911; Ernest Rutherford; gold foil experiment.
An atom is composed of a positively charged nucleus, with a cloud of negatively charged electrons surrounding it, bound together by___.
electrostatic force.
The direction of spin is random, so that some particles spin clockwise and others anticlockwise.
Proton spin
When a nucleus has an ___ mass number, the spins cancel each other out so the nucleus has no net spin. When a nucleus has an __ mass number, the spins do not cancel each other out and the nucleus spins.
even; odd
Due to the laws of ____, a moving unbalanced charge induces a magnetic field around itself.
electromagnetic induction,
The direction and size of the magnetic field are denoted by a ___
magnetic moment.
The total magnetic moment of the nucleus is the ___ of all the magnetic moments of protons in the nucleus.
vector sum
Nuclei with an odd number of protons are said to be called __ .
MR active
The common MR active nuclei, together with their mass numbers, are:
hydrogen 1 carbon 13 nitrogen 15
fluorine 19 sodium 23 oxygen 17
___ is used to calculate the frequency or speed of precession for the magnetic moments of a specific nucleus in a specific magnetic field strength. The Larmor equation is simply stated as ___
Larmour equation; ω0 = γB0
____ is denoted by ω0 and expressed in ___ (unit).
precessional frequency; megahertz (MHz)
The strength of the external field is expressed in (unit) and denoted by the symbol B0.
tesla (T)
___ is the precessional frequency of the magnetic moments of a specific nucleus at 1T and has units of MHz/T. It is denoted by γ.
gyromagnetic ratio
As it is a constant of proportionality,
the precessional frequency or Larmor frequency is proportional to the ___ and can be calculated for any type of MR active nucleus and field strength.
strength of the external field
An electromagnetic emission such as a ____ is composed of an oscillating electric field positioned 90° to an oscillating magnetic field.
radiofrequency (RF)
The applied RF must be at the Larmor frequency, and its orientation must be ___ to the external magnetic field.
perpendicular
When the RF is switched off, the magnetization will have rotated through an angle called ___. It depends on applied RF field strength and the total time that it is on
flip angle
The component of the net magnetization vector parallel to the main magnetic field is called ___. ●By convention, the longitudinal magnetization is taken to point in the ___.
longitudinal magnetization; z-axis
The component perpendicular to the main magnetic field is called ___. ●By convention, the transverse magnetization is taken to be in the ___.
transverse magnetization; x-y plane
A magnetic moment travels through ___ radians during one rotation.
360 radians
_____ means that the magnetic moments of hydrogen spins are at different places on the precessional path at a moment in time.
Out of phase or incoherent
____ refers to the position of the magnetic moments of spins on their precessional path at any moment in time. Its units are ____ .
Phase Coherent; radians.
____ means that the magnetic moments of hydrogen spins are at the same place on the precessional path at a moment in time
In phase or coherent
____ is the sequence that obtains images that have a sufficiently long TE to measure T2 decay when using the ____ while still using a short TR.
steady state free precession
In SSFP, there are usually two time periods to consider:
actual TE and effective TE
(the time between the stimulated echo and the next excitation pulse);
actual time
(the time from the stimulated echo to the excitation pulse that created it. This is the TE that determines the T2 weighting of the image)
effective time
___ in MRI this is energy delivered to the spins via excitation.
Relaxation Time
The amplitude of the voltage induced in the receiver coil therefore gradually decreases. This is called ___
free induction decay or FID.
The magnetization in each tissue relaxes at different rates. This is one of the factors that create___. The withdrawal of the RF produces several effects
magnetization; image contrast
Spins emit energy absorbed from the RF pulse through a process known __ and shift their magnetic moments from the high‐energy state to the low‐energy state. The NMV recovers and realigns to B0. This relaxation process is called ___
spin lattice energy transfer; T1- recovery
The magnetic moments of the spins lose precessional coherence or dephase and the NMV decays in the transverse plane. The dephasing relaxation process is called
T2 decay
T1 is also called the____. The term longitudinal refers to events occurring along the axis of the net magnetization vector, which is parallel to B0. T1 relaxation describes the growth and decay of MZ; therefore it is ___ in nature.
longitudinal or spin-lattice relaxation time; longitudinal
Generally, for T1W images, tissue with short T1 appears___ ; tissue with long T1 appears __
bright; dark
T1 relaxation is represented by an ___ value with time, whereas T2 relaxation is represented by a ___ value.
increasing ; decreasing
T2 is called the ____ . Because T2 relaxation represents a loss of net XY magnetization, it represents the loss of phase coherence in a plane perpendicular to or transverse to M0. M0 lies along the Z-axis.
transverse relaxation time or spin spin relaxation time
The concentration of nuclei in tissue processing at theLarmour frequency in a given region; one of the principal determinants of the strength of theNMR signal from the region.
Spin Density
