Medical physics

Question 1

X-rays

Answer 1

Thermionic release of electrons
Accelerate towards anode
Collide and lose KE
X Ray photons released 
Ionising radiation 
X-rays detected by film

Question 2

X-ray interaction

Answer 2

Photoelectric effect
Direct collision with electron and ejection

Compton effect
Scattering of x Ray photon, so low energy

Pair production
Hit nucleus, produce electron and positron, positron annihilate and make 2 photons

Question 3

Attenuation

Answer 3

Intensity of X-ray bean decreases exponentially further into material they travel
High Z value = high attenuation coefficient = more absorbed = shows up more
Iodine and barium : contrast material have a high AC and show outline of soft tissue

Question 4

CAT scanners

Answer 4

Computerised axial tomography
Thin x ray beam rotated around patient
Enters at different angles
Show outline of soft tissue without contrast media

Question 5

Gamma cameras

Answer 5

Collimator, scintillator, light guide, photo multiplier

Question 6

PET scanners

Answer 6

Fluorine-18 used
Positron interacts with electron in body
Delay time between each of 2 gamma rays being picked up determines position

Question 7

Ultrasound

Answer 7

> 20kHz pulses
Amount of reflection depends of acoustic impedance
Time delay determines thickness
Reflected signals intensity determines tissue
A scan:
Short pulse, displays amplitude, I direction only
B scan:
No of sensors in different positions to build up 2D/3D image

Question 8

Piezoelectric effect

Answer 8

Crystals cause movement by alternating PD passing through it and vice versa

Question 9

Coupling media

Answer 9

Gel
Impedance matching
Prevent large reflection between air and skin as they do not have very similar acoustic impedance