PRACTICE QUESTIONS FROM CLASS Flashcards
- What are the two theories used to describe the basic prinicples of MRI?
Classical Theory and Quantum Theory
- What is the Lamor equation and describe each parameter of this equation?
It is used to measure the precessional frequency using the strength of the magnetic field and the gyro-magnetic constant of hydrogen.
- What is free induction decay?
As T2 decay occurs, there is a decrease in the signal produced and this is the FID (induction of reduced signal)
- What are the MRI weightings used?
T1, T2 and Proton Density
- Why is imaging contrast needed?
To show pathologies and differentiate between different anatomy structures
- Name two categories that diagnostic imaging contrast usually depends on.
Intrinsic and Extrinsic (Can change ext)
- A spin echo T1 weighted sequence uses a ____ TR and ____ TE.
- A spin echo T1 weighted sequence uses a short TR and short TE.
A T2 weighted image has a____ TR and a ____ TE
A T2 weighted image has a long TR and a long TE
A proton density has a ___ TR and a ____ TE
A proton density has a long TR and a short TE
- Name a disadvantage of a GRE (Gradient Echo) MRI sequence?
It is very susceptible to any metal as there is no compensation for the field inhomogeneities.
- What are three types of magnets?
Permanent magnets, super conducting (what we use) and electromagnets
- Name the three types of magnetisim
iamagnetism, ferromagnetism, paramagnetism
- Three motions of an atom?
Nucleus spins on axis, electrons spin on own axis, electrons orbit nucleus
- What does the the yellow triangle with MR on it mean?
MRI conditional – can take into room and around magnet then can under certain conditions stated.
- Give any four tips for dealing with claustrophobic patients?
Feet first, support person, can perform some prone, do not strap down, worst case scenario = GA, give breaks, give a mirror / fan
- What is phase mismapping artefact also known as?
Ghosting or blurring artefact
- What is the artefact called seen on the outer edges of the this abdominal Fiesta MRI coronal image?
Moire artefact
- Which two cranial nerves are seen when imaging the IAMs?
Vestibulocochlear and facial nerve (VII and VIII)
- What is the Magic angle artefact?
An artefact seen in certain tendons – going to get a high signal artefact that is not real. Can see this in the knee with the patellar tendon and under the shoulder. May mimic pathology and is caused when certain structures with tightly bound fibers lie at an angle of 55 degrees to the main magnetic field, altering its signal intensity.
- Explain the difference between cross talk and cross excitation?
Cross excitation: energy given to nuclei in adjacent slices by RF
Cross talk: energy given to adjacent slices due to spin lattice relaxation. Cannot do anything about this.
- What do the arteries of the brain COW stand for?
Circle of Willis
- What would you do to reduce peristalses in an abdominal MRI?
Buscopan. Anterior sat band can be prescribed also (but probably not for an abdomen) and get them to hold their breath.
- Why is the use of pre-saturation bands important to use when imaging the C-spine?
To cut out swallowing and pulse of carotid arteries
- What sort of an RF pulse does a spin echo use to eliminate the effects of inhomogeneities?
180 pulse
- Name two advantages of a Spin Echo Sequence.
Good image quality, versatile, true T2 weighting, available on all systems, gold standard for image contrast and weighting
- What are a pixel and a voxel?
Pixel: picture element
Voxel: Volume element
- Name any two factors T1 and T2 relaxation depends on.
Inherent energy of tissue, how close molecules are packed, how much molecules tumbling rate matches Larmor frequency
- Family members and additional personnel accompanying the patient into the scan room:
Should be screened as if they are going through MRI procedure themselves
- In preparation of the MRI exam patients are encouraged to?
Either arrive at MRI centre wearing a tracksuit without any metal zips or studs or change into a hospital gown.
- Is it good practice for all MRI patients that undergo MRI to be monitored?
Visually and verbally
- When using MRI cables from RF coils and ECG leads should be?
Placed straight, without touching the patient or the magnet bore, through the imager.
- Magnetic field shielding can be achieved either actively or passively. In order to achieve passive shielding, the room can be lined with:
Steel
- RF shielding can be achieved by lining the MRI room with:
Copper
- A quench is used to:
Rapidly removed the superconductivity and the magnetic field.
- The purpose of shimming the magnet is to:
Make the B0 field as homogenous as possible
- The term used to describe RF absorbtion is:
Specific absorbtion rate
- Aliasing (wrap around) occurs because the tissue outside the FOV is:
Undersampled
- To eliminate chemical shift artefact use:
Chemical saturation
- It is the ability to distinguish between two points as separate and distinct and is controlled by voxel size:
Spatial resolution
- T2 relaxation time is defined as when
63% of the transverse magnetisation has decayed
- Hydrogen nuclei have a magnetic moment because they possess a property called:
Spin
- The liquid cryogen is commonly used to maintain the magnet at superconducting temperatures is:
Helium
- In a spin echo sequence the time between the 90 degree pulse and the peak of the signal is the
TE
- This sequence is often used in MS imaging to demonstrate plaques
FLAIR
- An inversion recovery spin echo sequence begins with a
180
