Fundamentals of Image Formation

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What type of magnetization is the RF receive coil able to measure directly?
Transverse
The wobbling motion of the nucleus as it spoins qbout the magnetic field
Precession
Refers to the type of motion that protons spinning on their own axis experience when in the presence of an external magnetic field
Precession
The precessional frequency of hydrogens exposed to a .5T magnetic field
21.29 mHz
What is the static magnetic field is directly proportional to?
Precessional frequency
Prior to entering the main magnetic field, why is the patient's net magnetization zero?
The spins of the hydrogen atoms are randomly aligned
What is the kG equivalent of a magnetic field strength of 1T?
10kG = 10,000G = 1T
What are the two characteristics must a vector have?
- Magnitude (amount)
- Direction
What formula describes the relationships between the precessional frequency and the applied magnetic field of atoms?
Larmor Equation
What is the Larmor equation?
magnetic field / precessional frequence = gyromagnetic ration
When hydrogen atoms are exposed to a strong homogeneous magnetic field, what do they have a tendency to do?
Slightly more than half align parallel and the remaining align antiparallel
What can an MRI signal be made from?
Hydrogen in water, fat, and mobile hydrogen protons
In a homogeneous magnetic field, what rate of precession does hydrogen in water have compared with hydrogen in fat?
Hydrogen in water precesses faster than hydrogen in fat
What is the atomic number for hydrogen atom used to create the NMR signal?
One
How do small molecules with a higher rate of molecular motion affect T1 relaxation?
They are inefficient at returning energy and have a long T1 relaxation time
What interaction does dipole-dipole magnetic interaction refer to?
- A proton & electron
- Proton & proton
The absorption and re-emission of RF energy by the tissues w/in the patient
Resonance
What would the result be if a volume of protons in a magnetic field were suddenly exposed to a graduated magnetic field?
- The protons would begin to precess at the new magnetic field strength

- Dephasing of the volume would occur & there would be a range of precessional frequencies