Lecture 3 - Introduction to Medical Imaging Flashcards
What are the 3 anatomical sections an image can be taken in?
- Trasnverse (top and bottom)
- Coronal (front and back)
- Saggital (left and right)
How do X-rays work? What determines whether a structure appears as light or dark on the X-ray?
- Focus beam of high energy electrons passed through body and onto detector
- Some electrons absorbed, some scattered (known as attenuation)
- More dense/higher atomic number = more attenuation = Lighter appearance on X-ray
Order these from lightest to darkest on X-ray:
- Soft tissue
- Fat
- Bone
- Air
- Metal
Lightest
- Metal
- Bone
- Soft tissue
- Fat
- Air
Darkest
What is the difference between an AP and PA X-ray?
- AP = anterior to posterior (front facing)
- PA = posterior to anterior (back facing)
Name 2/3 advantages + disadvantages of X-rays
Adv:
- Cheap
- Portable
- Quick & Simple
Disadv:
- Can’t see all pathology
- Uses radiation (although small)
- Only 1 plane per image so always in 2D
- Poor soft tissue imaging
Name 3 uses of X-rays
- Chest X-rays for lung abnormalities
- Abdominal X-rays for bowels and organs
- Orthopaedic X-rays for fractures
Explain how fluoroscopy works and what it allows examination for.
- Constant stream of X-rays creates a moving image, enhanced by contrast (i.e.: barium) by strongly absorbing X-rays.
- Allows for examination of both anatomy and motion
What are the uses of fluoroscopy?
- Angiography
- Contrast GI studies
- Therapeutic joint infections
- Screening in theatre
Give an advantage + disadvantage of fluoroscopy
Adv = Dynamic studies, cheap, interventional Disadv = Uses radiation so clinical exposure must be minimised
How do CT scans work? How is density described in CT scans?
- Rotating gantry with X-ray tube one side and detector on the other.
- Images put together by computer using same principal of attenuation
- Transverse imagine produced where everything is flipped to other side.
- Density measured in HU (water = 0HU, less dense = negative, more dense = positive)
Describe advantages, disadvantages and uses of CT scans.
adv:
- Quick
- Can scan most areas
Disadv:
- Radiation
- Affected by artefacts
- Requires breath holding
- Incidental findings
Uses = diagnosis, e.g.: head scans, or monitoring conditions like cancer.
How does MRI work?
- Magnetic field aligns hydrogen atoms
- Some point towards head, some toward feet, some are unmatched
- They emit energy when radiofrequency pulse is applied
- this is turned into an image by a computer
What are uses of MRI scans?
- Scan brain + SC for tumours
- Scan bones + joints
- Scan gallbladder for stones
- Scan internal organs
Name a couple adv + disadv for MRI scans
Adv:
- Uses magnets so NO ionising radiation
- Good contrast resolution
Disadv:
- Expensive + Time consuming
- Claustrophobic for patients/some wont fit
- Need to lie very still
How do ultrasound scans work? What are the terms that are used?
- High frequency sound waves from a transducer probe
- Sound wave reflected back from tissues where density (impedance) differs
- Probe detects sound waves and creates electrical signal.
- Hyperechoic = more reflective (shows white)
- Hypoechoic = vice versa (shows dark grey)
- Anechoic = no reflection (shows black)
