Topic 3 - Medical Imaging and contrast media Flashcards
Define these terms: Anterior, posterior, medial, lateral, proximal, distal, superior, inferior, transverse (axial), saggital and coronal.
anterior + posterior = front + back
Medial + lateral = towards mid line + away from it
Proximal + distal = close to body + far from it
Superior + inferior = top + bottom
Transverse = a magicians cut, gives you top and bottom
Saggital = left and right
Coronal = crown hands cut, gives you front and back
Rank these subjects in ascending density: soft tissue, fat, bone,blood metal, air, water.
- Air (least dense, shows up black)
- fat
- water
- blood
- soft tissue
- bone
- metal (most dense, shows up white)
Explain the process of x rays giving an image.
- focused beam of high energy electrons
- pass through body onto receiver
- Attenuation occurs where some are absorbed or scattered
- the more dense the substance the more attenuation so it appears lighter
Give advantages and disadvantages of x ray film imaging.
Advantages: - cheap - easy - quick - portable (onto the wards) Disadvantages: - ionising radiation is used - two dimensional - poor soft tissue imaging
What is fluoroscopy?
- A low frame per second movie of x rays put together (like a flip book drawing)
- often enhanced by contrast
What are the forms of cross sectional imaging?
- Computed Tomography (CT)
- Magnetic Resonance Imaging (MRI)
Explain the process of MRI (Magnetic Resonance Imaging).
- Each hydrogen atom spins according to its own magnetic field
- The MRI provides a new magnetic field which makes them all align, half pointing north and half pointing south
- however, there are some unmatched atoms who didn’t get the memo about 50/50 split
- a radio frequency pulse is applied and the unmatched atoms absorb energy and flip the opposite way
- the pulse is turned off and the atoms spin back again releasing the energy which is picked up by a computer.
Why does the polo mint MRI machine need to have such a small gantry?
- to keep the magnetic field strong for a quality image
MRI weighting’s are T1 and T2, what do these mean?
T1 - Fat is white, water is black
T2 - Water is white, fat is black
White = high signal
Black = low signal
Advantages and disadvantages of MRI?
Advantages: - no radiation! - Good contrast resolution (difference between densities is clear) Disadvantages: - Expensive - Claustrophobic - some patients wont fit - need to lay still
Briefly explain Scintigraphy.
- Uses injection of gamma ray emitting pharmaceuticals which can then be detected
What does a PET (Positron Emission Tomography) scan show up very well?
- Areas of high glucose metabolism (for example cancers)
What is ultrasound?
- the use of high frequency sound waves which is reflected back by tissues where density differs
- helps us compare densities
What is acoustic impedance/shadowing in ultrasound?
- if there is a large difference in densities then sound is completely reflected so cant see behind bone, air and stones.
When is Doppler ultrasound incredibly useful?
- for imaging a blood vessel as it takes into account movement of blood and the change of frequency associated.
