MRI (2) Flashcards
discovered the __ in __in Budapest, Hungary. This was a fundamental discovery in physics
Nikola Tesla; Rotating Magnetic Field ;1882
In 1956, the __ was proclaimed by the International Electro-technical Commission-Committee of Action. All MRI machines are calibrated in __
“Tesla Unit”
THE STRENGTH OF A MAGNETIC FIELD IS MEASURED IN __
TESLA OR GAUSS UNITS.
The stronger the magnetic field, the ___ which can be elicited from the body’s atoms and therefore the higher the quality of MRI images.
stronger the amount of radio signals
1 Tesla = __Gauss
10,000
Low-Field MRI
Under .2 Tesla (2,000 Gauss)
Mid-Field MRI - __
.2 to 0.6 Tesla (2,000 Gauss to 6,000 Gauss)
High-Field MRI - __
1.0 to 1.5 Tesla (10,000 Gauss to 15,000 Gauss)
In 1937,__ observed the quantum phenomenon dubbed nuclear magnetic resonance (NMR).
He recognized that the atomic nuclei show their presence by absorbing or emitting radio waves when exposed to a sufficiently strong magnetic field.
Professor Isidor I. Rabi,
discovered that hydrogen signal in cancerous tissue is different from that of healthy tissue because tumors contain more water.
RAYMOND DAMADIAN
a chemist and an NMR pioneer at the State University of New York, Stony Brook, produced the first NMR image.
PAUL LAUTERBUR
one of the graduate students cobbled a wearable antenna coil to monitor the hydrogen broadcast detected by the coil.
MIKE GOLDSMITH
first mri exam performed on a human being.
Dr. Raymond Damadian, Dr. Larry Minkott & Dr. Michael Goldsmith.
JULY 3, 1977
ORIGINAL NAMED OF THE FIRST MRI MACHINE.
“INDOMITABLE”
- the most visible and probably the most often discussed component of the MRI system
- it provides the powerful static (constant strength ) magnetic field about which the nuclei precess.
MAGNET
TYPES OF MAGNETS
Permanent magnets, Temporary Magnets, Electro-magnets
emit a magnetic field without the need for any external source of magnetism or electrical power.
Permanent magnets
behave as magnets while attached to or close to something that emits a magnetic field, but lose this characteristic when the source of the magnetic field is removed.
Temporary magnets
require electricity in order to behave as a magnet.
Electro-magnets
Materials for Ferromagnetism
Iron, Nikel, Cobalt
Materials for Paramagnetism
Aluminum, Tungsten, Platinum, Manganese
Materials for Diagmagnetism
Copper, Silver, Mercury, Carbon
- is responsible for the alignment of nuclei
1. Solenoid electromagnets the fields is usually horizontal
2. Permanent magnets the fields is generally vertical - it exerts an induction force on ferromagnetic and paramagnetic substances
MAGNETIC FIELD
__ is the sum of protons in the nucleus
__ is the sum of protons and neutrons in the nucleus
An__ is electrically stable, if the number of negatively charged electrons orbiting the nucleus equals the number of positively charged protons in the nucleus.
Atomic number
Atomic mass number
atom
Three types of motion are present within an atom:
- Electrons spinning on their own axis
- Electrons orbiting the nucleus
- The nucleus itself spinning about its own axis
In addition, hydrogen has a different precessional frequency at different field strengths.
At 1.5 TESLA the precessional frequency of hydrogen is__
At 0.5 TESLA the precessional frequency of hydrogen is __
63.86 MH; 21.28 MHZ
THE GYROMAGNETIC RATIO OF HYDROGEN IS ___
42.51 MHZ/T
Electromagnetic radiation just lower in energy than infrared. RF used in MRI is commonly in the __
Radiofrequency; 10 – 100 MHZ
is the position of each magnetic moment on the precessional path Bo.
Phase Coherent
comparatively slowly gyration of the axis of a spinning body so as to trace out a cone ; caused by the application of a torque tending to change the direction of the rotation axis.
- The second spin of magnetic moment around Bo
Precession
the speed of precession
Precessional (Larmor) Frequency
spin, lattice, or longitudinal relaxation time
- the characteristics time constant for spins to tend to align themselves with the external magnetic fields
T1 Relaxation Time
- spin – spin, transversal relaxation time
- spins begin to precess oit of phase with each other
T2 Relaxation Time
- If transverse magnetization of the spins is produced, a transient MR signal will result, which will decay with a characteristics time constant T2.
- As the magnitude of transverse magnetization decreases, so does the magnitude of the voltage induced in the coil.
- Loss of signal due to relaxation
Free Induction Decay (FID)
the precessional frequency of an element at 1.0 TESLA
Gyromagnetic ratio
- denotes the direction of the north/south axis of a magnet and the amplitude of the magnetic field
Magnetic moment
- ability of a substance to become magnetized.
Magnetic susceptibility
- a property of all matter that depends on the magnetic susceptibility of the atom
Magnetism
the magnetic vector produced as a result of the alignment of excess hydrogen nuclei with magnetic field.
Net Magnetization Vector (NMV)
- is a phenomenon whereby an object is exposed to an oscillating perturbation that has a frequency close to its own natural of oscillation
Resonance
ATOMS THAT ARE ELECTRICALLY UNSTABLE DUE TO DEFICIT, OR AN EXCESS NUMBER OF ELECTRONS, ARE CALLED __
IONS.
MRI is based on the spinning motion of a specific kind of nuclei present in biological tissues. These are called __
MR active nuclei
These are characterized by their tendency to align their axis of rotation to an applied magnetic field.
MR ACTIVE NUCLEI
- it is the vector sum of the individual magnetic moments of all the protons in the nucleus
TOTAL MAGNETIC MOMENT
Due to the laws of quantum mechanics only nuclei with an __ of protons have a total magnetic moment and can interact with an external magnetic field.
odd number
The hydrogen nucleus contains a single proton (atomic number 1).
- It is used because it is very abundant in the human body.
- Its solitary proton gives a large magnetic moment
HYDROGEN NUCLEUS
- Low thermal energy nuclei
- Low energy to oppose the external magnetic field.
PARALLEL NUCLEI
- High thermal energy nuclei
- High thermal energy, do posses enough energy to oppose the strength of external magnetic field
- ANTI-PARALLEL NUCLEI
- The static external magnetic field is called B0
- The interaction of the NMV with B0 the basis of MRI
- The unit of is tesla or gauss.
Magnetization Vector (NMV)
- are loops of wire or thin conductive sheets on a cylindrical shell lying just inside the bore of an MR scanner. When current is passed through these coils a secondary magnetic field is created.
Gradients
-is the generator of the radiofrequency current which is delivered to the transmitting coil. This creates a signal which is used to excite protons in the imaging field.
TRANSMITTER COIL
Radiofrequency coilscan be both __ and __of the radiofrequency signal or receivers alone.
- A radiofrequency coil that performs both of these actions is called a __
transmitters andreceivers; transmit receiver coil or a transceiver coil.
Acoil, or antenna, positioned within the imaging volume and connected to thereceivercircuitry that is used to detect or receive the MR signal from the patient as the disturbed spins relax back into their equilibrium distribution.
RECEIVER COIL
MRIcomputercan be divided into
central processing unit (CPU), consisting of instruction, interpretation and arithmetic unit plus fast access memory.
Computercontrols the __ and __ necessary to acquire data, and process the data to produce__or images.
RF pulses and gradient; spectra
