Module 1 - Fundamentals Flashcards
Describe method of acquisition of XR
Contrast is based on different x-ray scatter produced by tissues proportional to the electron density and thickness of the body part
Describe scientific principles underpinning nuclear medicine and PET/CT Studies
The radiation source is inside the patient and photons are captured as they are emitted from the patient.
Tracer taken up in proportion to activity eg. accumulates in areas of high activity
What are stochastic effects of radiation?
Stochastic: DNA modification causing possibility of cancer causing mutation, risk increasing with increasing dose, can be solid organ or haematological up to 30 years after exposure
What are deterministic effects of radiation?
Deterministic effects: harmful tissue reactions, occurs when threshold dose after which body unable to repair itself
Skin erythema, necrosis, bone marrow suppression, death
How is radiation risk different for different patient groups? eg pregnant women, paediatric patients
paeds: greater cell proliferation, greater risk of stochastic effects
pregnant: significant risk in 8-15th week, malformation if dose exceeds 100 mSV or 150 mGy
breastfeeding: proliferating breast tissue sensitive in 1st month postpartum
Describe method of acquisition of CT
Xray tube -> photons -> pass through patient to detector (tube and detector rotate around patient)
Photons absorbed by patient and CT images created via computation
What are the hounsfield units of Air Fat Water Muscle
AIR -1000
FAT -100
WATER 0
MUSCLE 50
What is SUV in relation to PET imaging?
” standardised uptake value” quantifies how much tracer ends up in tissues of interest
SUV high = extra uptake
- Liver 2.5 to 3
- Malignancy 5 to 6
What substances appear bright, intermediate and dark on T1 weighted images?
T1 bright: lipid, gadolinium, iron
T1 intermediate: myocardium, brain
T1 dark : water and blood
What substances appear bright, intermediate and dark on T2 weighted images?
T2 bright : CSF, oedema, simple fluids
T2 intermediate: myocardium, brain
T2 dark : old haemorrhage, high protein fluids
What contrast medium is best used if suspecting intraperitoneal leak?
Iodine: less irritating to peritoneum than barium
What is mA in reference to CTs?
mA = photon dose
more mA, less grain, less noise but more radiation
What is kV in reference to CT?
energy of photons
if kV is close to that of the tissue being looked at, greater enhancement
what is the difference between gray and sievert
absorbed dose = gray (Gy)
equivalent dose measuring biological effect of radiation taking into account tissue and type of radiation = sievert (Sv)
