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.
What are the ideal properties of a contrast medium?
- low osmolality and viscosity
- Water soluble
- biologically inert
- safe
- heat and chemical stability
- cost effective
What must be considered before pursuing a procedure involving contrast media?
- whether the patient has functioning kidneys to filtrate it
- allergies
Why is it better to image the heart using an PA x ray scan than an AP one?
- because the heart is magnified in an AP scan to be bigger than usual as its further forward in the body (anterior)
What proportion of the chest width is the width of the heart?
50%
