Module 1 Flashcards
Felix Bloch
Godfather of MRI
Images are created using 3 regions of the electromagnetic spectrum.
X-rays use transmitted x-rays
Photographs use reflected visible light.
MRI uses emitted radiofrequencies
Non-ionizing radiation.
Spatial resolution (the ability to distinguish two points or structures as separate)
Contrast resolution
Multiplanar Imaging
Sensativity-the ability to detect subtle differences in tissue
MRI advantages
is a test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body
What is MRI
in a patients tissues behave like tiny magnets themselves and are susceptible to an external magnetic field due to its magnetic moment
hydrogen nuclei
Consists of central nucleus with one proton no neutron and one orbiting electrons
Hydrogen Atom
- Electrons spinning on own axis
- Electrons orbiting the Nucleus
- The Nucleus itself spins on own axis
3 Types of Motion within the Hydrogen Atom
sum of Protons in Nucleus
Atomic Number
sum of Protons and Neutrons in the nucleus
Atomic Mass
refers to three inividual forces, motion, magnetism and electrical charge. If two of the three are present then the third will be induced
Faraday’s law of electromagnetic induction
hydrogen we have a positive charge and motion
the third force magnetism will be induced thus giving the hydrogen atom a magnetic moment allowing in to align with an external magnetic field.
Hydrogen Atom Nucleus is rotating around its axis and the Proton or charged particle is also rotating >
This causes the Hydrogen atom to contain its own Magnetic Field
due to its odd number of Protons (one) in its nucleus. (hydrogen atom)
Magnetic Moment that is relatively large
2 energy states with the Hydrogen nuclei
Low State
High State
align with the External Magnetic Field, termed Spin Up Nuclei.
Low energy state
align against the External Magnetic Field, termed Spin Down Nuclei.
high energy state
It takes less energy to
line up with the Magnetic Field
It takes more energy to
fight against the direction of the Main Magnetic
Field.
direction of the North and South axis of a Magnet and the amplitude of the magnetic field
magnetic moment
The larger the field strength, the ________hydrogen will align in the spin up (low energy) state
more
Size and Direction of the magnetic moment in the Z plane.
has both magnitude and direction
Vector
With no external magnet field magnetic moments are randomly situated
Once exposed to a Magnet Field M. M. start to_______with and against Magnetic field (North and South)
alignment
Battle between Spin Up and Spin Down Nuclei create a common ground. The result of this battle is the
N.M.V. w0
Net Magnetization Vector
These are the winners or the remaining Vectors that now align with the external field…
These are what will be manipulated by the external R.F. pulse to create M.R.I images.
Net Magnetization Vectors
Hydrogen Nuclei spin on there own axis.
Once subjected to an External Magnetic Field they also start to wobble
This wobble is called its Precession
More powerful the External Magnetic Field
the more N.M.V. there are to manipulate
3T images have _______ signal than 1.5T.
higher
Speed at which the Hydrogen Atoms spin we also call this wobble
Precessional Frequency:
Path by which the Hydrogen Atoms follow.
Precessional Path:
Determines the Precessional Frequency
Larmor equation:
equal to the gyromagnetic Ratio of Hydrogen (42.57MHZ/Tesla) Times the Magnetic Field Strength
The Precessional Frequency /
The field strength of the magnet is displayed
in tesla represented as T
or Bo
The gyromagetic ratio is represented by
Greek gamma symbol
Precessional Frequency is represented
as f or Wo
42.57 MHZ/T
larmar equation ratio
Expensive
Long scan times
Audible noise (65-115dB or higher)
Isolation of patient (claustrophobia, monitoring of ill patients)
Exclusion of patients with conventional pacemakers and certain implants.
Disadvantage of MRI
