# Medical physics

?
• Created by: emy105
• Created on: 11-06-18 15:36
What is the frequency of an x-ray?
3X10^16 Hz - 3X10^19 Hz
1 of 22
What is the wavelength of an x-ray?
1X10^-8 - 1X10^-11
2 of 22
How does an X-ray tube work?
A heater excites the electrons to move out from the atom. A Tungsten anode will accelerate these. (The electrons accelerate towards it).The electrons are then emitted as x-ray photons.
3 of 22
Why does the Tungsten anode have a special shape?
It enables the photons to be emitted in the required direction.
4 of 22
Why is the tube incased in lead?
For safety as the x-rays cannot pass through.
5 of 22
What is pair production?
A procces where an X-ray photon produces a an electron-positron pair
6 of 22
Describe the photoelectric effect
In the photoelectric effect, a single photon interacts with a single electron at the surface of a metal. In this, energy is conserved. In Einstein equation, hf is the energy of the photon and 1/2mv^2 is the max Ke of the electron.
7 of 22
What is the Compton effect?
scattering An interaction between an x-ray photon and an electron in which the photon is scattered with a longer wavelength.
8 of 22
Using logarithms solve: 8^(4-x)=33
x=2.319
9 of 22
Using logarithms solve: e^(7-x) +7=1009
x=0.09....
10 of 22
What is meant by the attenuation of x-rays?
Attenuation is the reduction of the intensity of an x-ray beam as it traverses matter. The reduction may be caused by absorption or by deflection (scatter) of photons from the beam
11 of 22
For medical x-rays would it be more beneficial to use x-rays with a high or low energy?
Lower- biggest difference between attenuation of materials
12 of 22
How do CAT Scans work?
X-ray tube and detectors are rotated around the body. It is a thin fan shaped beam of x-ray photons. The detectors send the intensities detected to a computer which forms an image of a slice. It is then moved down the body for another slice.
13 of 22
What are the advantages of CAT Scans over normal x-rays?
3D images are produced in CAT scans. Also, CAT scans can see soft tissues.
14 of 22
What is human hearing range?
20Hz - 20KHz
15 of 22
What is ultrasound?
Ultrasound is sound too high for a human to hear so is greater than 20KHz.
16 of 22
How does the wavelength effect the image produced?
A smaller wavelength will produce a clearer image with more detail. Ultrasounds hove a small wavelength.
17 of 22
What is a B-scan?
Is a brightness scan. Produces brightness levels based on echo strengths.
18 of 22
What is an A-scan?
Boundary echos are detected.
19 of 22
What will be the result of a greater difference in acoustic impedance be to the rays?
More rays will be reflected
20 of 22
What is the Piezoelectric effect?
Piezoelectric crystals produce ultrasound. This is done using an alternating current to create fast vibrations are made. This is called a Piezoelectric transducer- creates patterns of echos.
21 of 22
What is Doppler imaging?
The Doppler effect states that when a wave is reflected off a moving medium the frequency of the wave changes.By measuring the change in frequency of reflected waves Doppler scans can be used to scan blood vessels & flow of blood.
22 of 22

## Other cards in this set

### Card 2

#### Front

What is the wavelength of an x-ray?

#### Back

1X10^-8 - 1X10^-11

### Card 3

#### Front

How does an X-ray tube work?

### Card 4

#### Front

Why does the Tungsten anode have a special shape?

### Card 5

#### Front

Why is the tube incased in lead?