Medical physics

Question 1

Explain the principles of the detection of ultrasound waves for medical diagnosis

Answer 1

-Pulses of ultrasound are sent into the human body
-Ultrasound is reflecting along the boundaries and is incident on the transducer quatz crystal which also acts as a detector
-this incident ultrasound vibrates the qaurtz crystal
-oscillating crystal generates an alternating p.d across the crystal, this p.d is detected

Question 2

Explain the principles behind the generation of ultrasound waves for diagnosis in medicine

Answer 2

-a transducer with peizo electric crystal is used
-when an alternting p.d is applied across the crystal, the crystal is distorted + vibrates
-if the alternating p.d has the same frequency as the natural frequency, the crystal resonates
-natural frequency of the crystal should be in alternating range

Question 3

Explain the main principles behind the use of ultrasound to obtain diagnostic info about internal body structure

Answer 3

-pulses of ultrasound is sent into the human body
-ultrasound is reflected at the boundaries between media
-reflected ultrasound is detected by the transducer
-reflected ultrasound’s intensity gives information about the nature of the boundary
-time delay between transmission and detection of ultrasound gives information about the depth of the boundary
-degree of reflection depends on the acoustic impedenace of the two media at the boundary

Question 4

Explain why there is a continuous distribution of wavelength

Answer 4

-photons emitted when incoming electron is suddenly accelrated
-there are a range of accelerations of electrons in metal target
-there is a continuous distribution of λ

Question 5

Explain why there is a sharp cut-off at short wavelength

Answer 5

-incoming electron is stopped in a single collison so all enery is given to one phototn

Question 6

To control intensity of x-ray

Answer 6

To increase intensity, you increase the anode filament current to make the anode hotter, creating more electrons

Question 7

Control hardness of X-ray(higher frequency means harder X-rays)

Answer 7

to increase hardness, you increase the accelerating potential used to bombard the target metal at a higher speed