PET and MRI in RT Flashcards
What is the main advantage of MRI machines?
Superior soft tissue contrast, especially for CNS compared to CT
T of F
The nucleus spins around its own axis
True
List important MR nuclei and their mass numbers
- Hydrogen 1
- Carbon 13
- Nitrogen 15
- Oxygen 17
- Fluorine 19
- Sodium 23
- Phosphorus 31
The parallel alignment of hydrogen nuclei to B0 at a lower energy state is called _____
Spin-up nuclei
The anti-parallel alignment of hydrogen nuclei to B0 at a higher energy state is called ____
Spin-down nuclei
What is Net Magnetization Vector (NMV)?
The sum of all the vectors of the H nuclei
T or F
The interaction of the NMV with Bo is the basis of MRI
True
What is precession?
The additional spin or wobble of the magnetic moments of H nuclei caused by Bo
What is the precessional frequency of H in a 1.5 Tesla magnetic field?
63.86 MHz
What is Resonance?
This occurs when an object is exposed to an oscillating perturbation that has an oscillation close to its own frequency
What is another name for precessional frequency?
Larmor Frequency
What is the flip angle?
The angle the NMV moves out of alignment with Bo
If the H nuclei magnetic moments are not in the same processional path, then they are ________
out of phase (incoherent)
The magnitude of the MR signal depends on what?
It depends on the amount of magnetization in the transverse plane
MRI schematic:
What is the function of the main magnet?
Creates a strong uniform magnetic field that aligns H nuclei in the body
What is the function of the gradient coils?
They create small variations in magnetic field to create MRI signal
What is the function of the radiofrequency coils?
Transmit RF pulses to excite H nuclei and receive emitted signals
What happens after relaxation?
Recovery of magnetization in the longitudinal plane (Bo) and decay of magnetization in the transverse plane
T1 recovery is caused by _________
The nuclei giving up their energy to the surrounding environment
NB: Numerically, it is the time it takes for 63% longitudinal magnetization to recover
What is another name for T1 recovery?
Spin-lattice relaxation
What causes T2 decay?
The interaction of the magnetic fields of neighbouring nuclei with each other
NB: It is the time it takes for 63% of transverse magnetization to be lost
What is Repetition Time (TR)?
The time from the application of one RF pulse to the application of the next pulse for each slice. Measured in milliseconds
What is Echo Time (TE)?
The time from the application of the RF pulse to the peak of the signal in the coil. Measured in milliseconds
T or F
TR determines amount of T1 relaxation and
TE determines the amount of T2 relaxation
True
For anatomical purposes which type of MRI is preferred?
T1 weighted
For functional purposes (pathology) which type of MRI is preferred?
T2 weighted
Rule of thumb:
Black CSF =
T1 weighted
Rule of thumb:
White CSF =
T2 weighted
Rule of thumb:
Bright fat =
T1 weighted
Rule of thumb:
Dark fat =
T2 weighted
What is proton density contrast?
This refers to the differences in signal intensity between tissues that are a consequence of their relative number of mobile H protons per unit volume
The RF pulse is:
Equal to the Larmor frequency of H
In MRI the external magnetic field (Bo), causes nuclei to align:
Mostly parallel
Precessional frequency close to an objects own frequency calculated by using the:
Larmour equation
In MRI, the flip angle is:
The amount the NMV moves out of alignment with Bo
Where do MRI signals come from?
The hydrogen nucleus
What is used to map metastatic lymph node onto the pelvis vessel?
Lymphotropic iron nanoparticle contrast agent
Describe the process of MR image creation
MRI creates images using a strong magnetic field to align hydrogen protons in the body. A radiofrequency (RF) pulse disrupts this alignment, causing protons to absorb energy. When the RF pulse stops, protons relax back to their original state, emitting signals. These signals vary based on tissue properties and are detected by coils. A gradient magnetic field helps encode spatial information. The signals are processed by a computer using Fourier transformation to generate detailed cross-sectional images. Different pulse sequences highlight various tissues, making MRI highly effective for soft tissue imaging, such as the brain, muscles, and organs.
What is Diffusion Tensor Imaging (DTI)?
An MRI technique that can pick up tumour infiltration into white matter
What are Specific Absorption Rate (SAR) standards?
They exist to limit the maximum acceptable dose for patients under MR scanning. The safety standards are designed to ensure that no tissue is subjected to a temperature increase of over 1°C.
FDG =
Fluorine-18 Fluorodeoxyglucose
What radionuclide is used for PET prostate?
Gallium 68
NB: It is administered by IV
