MRI Flashcards
What is the function of magnetic field gradient
Magnetic field gradients are needed to encode the signal spatially. They produce a linear variation in magnetic field intensity in a direction in space.
How is an image produced in MRI very simply
Patient placed in a magnet
Radio wave is sent in
Radio wave is turned off
Patient emits a signal
Image is reconstructed
How is an MRI image produced?
Protons have a spin, which creates an electrical current, so has its own magnetic field
When external magnetic field is applied, protons align of either axis (which is longitudinal patient to machine)
External wave is sent (RF) which causes longitudinal marganilisatiom to decrease and creates new transverse marganilisation
Then pulse is switch off and longitudinal marganilisation increases and transverse marganilisation decreases
What is the role of the magnetic field
Causes protons to spin and align
What are some risks to patients with MRI?
Animals need to go under general anaesthesia
Sensitive to risks of metal,
What are the three planes that MRI uses?
Sagittal
Dorsal
Transverse
In T1 images what would the following structures look like?
Cortical bone
Fat
Water/ fluid (static)
Soft tissue
Pathology
Black
White
Black
Grey
Grey
In T2 images what would the following structures look like?
Cortical bone
Fat
Water/ fluid (static)
Soft tissue
Pathology
Black
White
White
Grey
White
How to tell the difference between T1 and T2 images?
CSF is darker in T1 and T2
What are STOR sequences and when are they most useful
Fat suppression images
T2 images where signal from fat has been removed
useful when examining structures which contain or are surrounded by fat such as the brachial plexus
What are FLAIR images and when are they useful
T2 images with signal from CSF removed
Useful for assessing structures adjacent to the ventricles to the brain
What sequence does T1 have
A short TR and short TE
What sequence do T2 weighted images have
Long TR and long TE
What sequence does a proton dense image have
Long TR and short TE
What is a magnetic gradient
An additional magnetic field that may be added manually to the MRI device’s magnetic field. This creates an additional subdivision in the ‘total’ magnetic field. Gradient coils are used among other things to determine the location of the protons in the X, Y and Z axis.
What is a proton dense image
Related to the number of nuclei in the image rather than the magnetic characteristics of the nuclei
What is the main contrast used for MRIs
Gadolium
What happens when radio frequency is turned off in terms of producing an image?
When the radiofrequency field is turned off, the MRI sensors are able to detect the energy released as the protons realign with the magnetic field. The time it takes for the protons to realign with the magnetic field, as well as the amount of energy released, changes depending on the environment and the chemical nature of the molecules.
What can gadolinium detect
Inflammation
Increased blood flow
What is TR
Repetition Time (TR) is the amount of time between successive pulse sequences applied to the same slice.
What is TE
Time to Echo (TE) is the time between the delivery of the RF pulse and the receipt of the echo signal.
