S9 Medical Imaging Flashcards
What is an X-ray?
Focused beam of high energy electrons pass through body onto receiver (some are absorbed/scattered dependent on density)
Thinking about fat, air, metal, bone and soft tissue, label from high density to low density in X-ray.
Air, fat, soft tissue, bone, metal
On an X-ray is white high or low density?
High density
What are the advantages of using an X-ray?
- Quick
- Cheap
- Portable
- Simple
What are the disadvantages of using an X-ray?
- Radiation
- 2D imaging
- Can’t visualise all areas
What are the uses of X-ray?
Checking for bone fractures and trauma in e.g. the chest
What is fluoroscopy?
Uses a constant stream of xrays and is enhanced by contrast media e.g. barium (absorbs xrays)
What are the two examples of plain film imaging?
Xray
Fluoroscopy
What are the two examples of cross-sectional imaging?
CT
MRI
What are the uses of fluoroscopy?
- Contrast GI studies
- Study of joints
- Therapeutic joint injections
- Screening in theatre
What are the advantages of fluoroscopy?
- Cheap
2. Allows for dynamic studies
What are the disadvantages of fluoroscopy?
- Radiation
2. Clinical exposure must be minimised
What is computed tomography (CT)?
Rotating gantry (with X-ray tube on one side, detectors on the other side)
What are the uses of CT scans?
Diagnosis (cancer/stroke), guide for tests/treatments (cancer treatment)
What are the advantages of CT scans?
- Quick
2. Good spatial resolution
What are the disadvantages of CT scans?
- Radiation
- Can be overused
- Requires breath holding
What is an MRI scan and how does it work?
Has a narrow gantry and uses a magnetic field to align hydrogen atoms in the body, some point one way, the other in the other way (not 50/50), the unmatched atoms absorb energy when radiofrequency pulse applied, it spins and when pulse is turned off, spins back and emits energy which is detected
What is the difference between T1 and T2 in terms of MRI?
T1 - fat is white, water is black
T2 - fat is black, water is white
White is the high signal
What are the advantages of MRI?
- No radiation
2. Good contrast resolution
What are the disadvantages of MRI?
- Expensive
- Some patients don’t fit
- Time-consuming
- Loud
- Claustrophobic
- Not safe if have metal work
What is a positron emission tomography (PET) scan?
Decay of radionuclides by positron emission. Binds to glucose (see ‘hot spots’ (darker areas) where there is a high glucose metabolism)
What are the uses of PET scans?
Oncology - determining if a tumour is benign or malignant, what stage a tumour is in, etc.
What is ultrasound and how does it work?
Using high frequency sound waves which are reflected back where density differs and are detected by a probe.
More reflective areas (bone/air/stones) are white, non-reflective areas (pure fluid) are black
Why can’t you see behind bone, air or stones on a ultrasound?
There is such a great difference in tissue density that means the sound waves are completely reflected (acoustic shadowing)
How does blood affect an ultrasound?
Doppler effect - moving objects influence sound waves.
Blood moving towards sound waves increases the frequency and moving away the opposite.
What are the uses of ultrasound?
- Obs/gynae - pregnancy and uterus
- Looking in body cavities
- Looking at the urinary tract - stones?
- Looking at solid organs - liver, kidneys, spleen, etc
What are the advantages of ultrasound?
- Cheap
- Portable
- Can be inserted into body cavities
- Dynamic (blood flow)
- No radiation
- Can be used on babies
What are the disadvantages of ultrasound?
- Operator dependent
2. No bone/gas penetration
How many days/months/years of background radiation do chest and abdominal X-ray scans cause?
Chest - 3 days
Abdominal - 4 months
How many days/months/years of background radiation do chest and abdominal and head CT scans cause?
Chest - 3.6 years
Abdominal - 4.5 years
Head - 1 year
How many days/months/years of background radiation do ultrasound scans cause?
0
How many days/months/years of background radiation do MRI scans cause?
0
What is nuclear medicine?
Administration of radio-pharmaceuticals labelled with radioactive tracers into the body - drugs have affinity for specific body tissues.
What is nuclear medicine useful for?
Displaying physiological function e.g excretory function of the kidneys, blood flow to heart muscle, etc.
What is angiography?
Medical imaging technique to visualise blood vessels
Why is contrast media useful?
Helps better differentiate tissues
What is an example of contrast media?
Barium sulphate (Barium meal)
Contrast media can be negative or positive, give examples of each and which colour they show up as.
Positive - barium, iodine and gadolinium - white
Negative - water, air, CO2 - black
What are the ideal factors for contrast media to be effective?
- Low osmolality and viscosity
- High water solubility
- Biologically inert
- Safe
- Heat and chemical stable
- Cost effective
How can contrast media be administered?
- Orally
- Rectally
- By IV
How is contrast media excreted?
What is its half life?
By the kidneys (consider consequences of using if person has kidney damage)
30-60mins
What are the side effects of contrast media?
What two types of side effects are there?
- Endothelial damage
- Thrombosis
- Vasodilation
- Vascular pain
- Idiosyncratic (can’t predict)
- Non-idiosyncratic (aware patient has an issue)
What is interventional radiologist?
Give an example of when it can be used.
Minimally invasive, image-guided treatments.
Used to remove a blood clot causing a stoke
