Quiz 1- Lecture 2: Structural Imaging MRI Basics Flashcards
The human body contains around ___ different elements.
20
Elements in the human body:
Oxygen (65%)
Carbon (18%)
Hydrogen (9.5%)
Nitrogen (3.2%)
Calcium (1.5%)
Phosphorus (1.2%)
Potassium (0.4%)
Sulfur (0.2%)
Sodium (0.2%)
Chlorine (0.2%)
Magnesium (0.1%)
Others listed in the diagram of the human body:
Water (62%)
Protein (16%)
Minerals (6%)
Carbohydrate (1%)
Fat (16%)
What are atoms?
Extremely small particles that are the basic building blocks of ordinary matter
Atoms can join together to form ____, which make up most objects
Molecules
What do atoms consist of?
An extremely small, positively charged nucleus surrounded by a cloud of negatively charged electrons
Although the nucleus is less than one tenth-thousandth the size of the atom,
the nucleus contains more than 99.9% of the mass of the atom
What are nuclei made of?
Positively charged protons and electrically neutral neutrons held together by a nuclear force
The nuclear force is much stronger than the electrostatic force that binds electrons to the nucleus, but it’s
Range is limited to distances of the rose of 1x10^-15 meters
What are isotopes?
Atoms of the same element that have different number of NEUTRONS
What are hydrogen’s isotopes (3)?
Hydrogen-1 (hydrogen)
Hydrogen-2 (deuterium)
Hydrogen-3 (tritium)
How did Lauterbur contribute to MRI?
By introducing variations in the magnetic field during the 1970s
How did Mansfield contribute to MRI?
By developing calculation methods during the 1970s
What 2 things provide a basis for magnetic resonance imaging (MRI)?
The incidence of hydrogen atoms is measured, Differences in the water content of different tissues
What does MRI use to produce detailed images from any part of the body?
The body’s natural magnetic properties
What is used for MRI’s imaging purposes and why?
Hydrogen nucleus (a single proton); abundance in water and fat
The hydrogen proton is like planet Earth spinning on its axis with a north-south pole. In this respect, it
Behaves like a small bar magnet
What happens to hydrogen protons under normal circumstances? How can they be influenced?
These “bar magnets” spin in the body with their axes randomly aligned; They can be influenced by a strong magnetic field
What happens to protons when the body is placed in a strong magnetic field like an MRI scanner?
What does this uniform alignment create?
The protons’ axes all line up
A magnetic vector oriented along the axis of the MRI scanner
What are the different field strengths of MRI scanners?
Usually between 0.5 and 1.5 tesla
What is the main magnetic field termed in MRI?
How is it aligned?
B 0
Aligned in the direction of B0 (parallel), Aligned in the opposite direction of B0 (anti parallel)
A parallel and anti parallel hydrogen nuclei…
HOWEVER
What is this termed? What symbol is it given?
Have equal but opposite magnetic moments and cancel each other out
However, there are always slightly more hydrogen nuclei parallel to B0.
This is termed the NMV (Net Magnetization Vector). It’s given the symbol “M.”
What is precession?
Nuclear spin; the rotation of the spins
What creates signal in MRI?
The precession is part of the MRI phenomenon and creates signal
Larmor Equations:f0=yB0
What is f0?
What is y?
What is B0?
f0 means “Precession frequency”
y means “gyromagnetic ratio (specific to each specific nucleus or element)”
B0 means “strength of the applied magnetic field”
Radio frequency (RF): Pulses (90 degrees and 180 degrees)
What is the purpose of applying RF magnetic fields?
What does the RF energy aim to do?
To excite the spins
Flip the net magnetization
What is the RF energy referred to as? Why?
RF pulse; Since the RF energy is applied for a short period of time and then switched off
What occurs exponentially?
The recovery of the longitudinal magnetization of a proton
What is called the T1 time?
The point at which 63% of the longitudinal magnetization has been recovered
What is called the T2 time?
The time at which 63% of the transverse magnetization has been lost
What are the T1 and T2 times unique to?
Each tissue type
What is an MR examination made up of?
A series of pulse sequences
How are different tissues identifies separately in T1 and T2?
Different tissues (like fat and water) have different relaxation times
T1 Weighted:
CSF
White Matter
Cortex
Fat (within bone marrow)
Inflammation (infection, demyelination)
CSF - DARK
White Matter - LIGHT
Cortex - GRAY
Fat (within bone marrow) - BRIGHT
Inflammation (infection, demyelination) - DARK
T2 Weighted:
CSF
White Matter
Cortex
Fat (within bone marrow)
Inflammation (infection, demyelination)
CSF - BRIGHT
White Matter - DARK GREY
Cortex - LIGHT GREY
Fat (within bone marrow) - LIGHT
Inflammation (infection, demyelination) - BRIGHT
Are there any known biological hazards of MRI?
Which types do have biological hazards?
No; X-ray and Computed tomography (CT)
MRI uses what kind of radiation?
MRI uses radiation in the radiofrequency range which is found all around us and it does not damage tissue as it passes through
What can be dangerous in MRI scanners? Why?
Pacemakers, metal clips, and metal valves
Because of potential movement within a magnetic field
(Metal joint prostheses are less of a problem, but there may be some distortion of the image close to the metal)
MRI departments always check for implanted metal and can advise on their safety
