# Physics - Recall for Chapter 27: Medical Imaging

> Source: https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-27-medical-imaging/ · Updated: 2022-04-20 · Tags: physics, a-level, school, recall-questions

## Flashcards
##### When are X-rays produced??
When high-energy X-rays are slowed down.

##### What are the typical wavelengths of X-rays in meters??
$$
10^{-8} - 10^{-13}
$$

##### What process causes the creation of X-rays in an X-ray machine??
Thermionic emission.

##### Roughly what percentage of electron energy is converted to X-rays in an X-ray machine??
$$
1\\%
$$

##### How can the intensity of X-rays be increased in an X-ray machine??
Increase the current in the cathode.

##### How can the maximum energy of X-rays be increased in an X-ray machine??
Increase the accelerating potential difference.

##### What are the four ways X-rays can interact with matter??
* Simple scattering
* Photoelectric effect
* Compton scattering
* Pair production

##### For what energies does simple scattering of X-ray photons occur??
$$
1 - 20 \text{KeV}
$$

##### For what energies does the photoelectric effect occur for X-ray photons??
$$
<0.1 \text{MeV}
$$

##### For what energies does Compton scattering of X-rays occur??
$$
0.5 - 5 \text{MeV}
$$

##### For what energies does pair production occur for X-ray photons??
$$
1.02 \text{MeV}
$$

##### How does the intensity of a parallel beam of X-rays change as it passes through a material??
It decreases exponentially.

##### What are the units of the attenuation coefficient of a material??
$$
m^{-1}
$$

##### How can bone and soft tissue be differentiated in simple X-ray images??
Bone has a higher attenuation coefficient and so absorbs more X-rays.

##### Why is it difficult to identify soft tissue and muscle in simple X-ray images??
They have similar attenuation coefficients.

##### How can the contrast between tissues with similar attenuation coefficients be increased??
Use a contrast medium.

##### What is true about the proton numbers of contrast mediums??
They have high proton numbers.

##### What does CAT stand for??
Computerised axial tomography.

##### What are two advantages of CAT scans??
* Can better differentiate between soft tissues
* Can produce a 3D image

##### What is a disadvantage of CAT scans??
* Patients are exposed to more radiation
* More expensive

##### What does the X-ray beam used in CAT scans look like??
Thin and fan-shaped.

##### How is a 3D scan built in a CAT scanner??
Many thin 2D X-ray images are compiled together by a computer.

##### What energy photons does Technetium-99m emit??
$$
140 \text{KeV}
$$

##### How can Technetium-99m be used in medical imaging??
It can be combined with a medical tracer to target a specific organ and investigate its function.

##### What piece of equipment is used to detect gamma rays from a radiopharmaceutical??
A gamma camera.

##### What are the three main parts of a gamma camera??
* Collimator
* Scintillator
* Photomultiplier tube

##### What is the function of the collimator component of a gamma camera??
Only allows photons travelling along the axis of the detector to reach the scintillator.

##### What is the function of the scintillator component of a gamma camera??
To absorb gamma photons and convert them into thousands of visible light photons.

##### What is the function of the photomultiplier tube in a gamma camera??
Convert visible light photons into an electrical pulse.

##### What does PET stand for??
Positron emission tomography.

##### What is the half life of fluorodeoxyglucose??
Roughly 2 hours.

##### Where does fluorodeoxyglucose (FDG) gather inside a patient??
In organs or tissues with high rates of respiration.

##### Why are PET scans expensive??
As medical tracers need to produced on-site.

##### What is the limit of human hearing??
$$
20\text{kHz}
$$

##### What is ultrasound??
Sound waves with a frequency above $20\text{kHz}$.

##### How can ultrasound be produced and detected??
Using an ultrasound transducer.

##### What is the piezoelectric effect??
The production of an EMF when certain materials are compressed or extended, and vice versa.

##### How does an ultrasound transducer work??
A high-frequency AC PD is applied across a piezoelectric crystal, causing it to produce an ultrasound wave of that frequency.

##### What is true about the frequency of the alternating current produced by a piezoelectric crystal detecting a sound wave??
It is equal to the frequency of the sound wave.

##### What are three advantages of ultrasound images??
* Non-ionising
* Can provide contrast between soft tissues
* Real-time images

##### What is the acoustic impedance of a material in words??
The product of the density of the material and the speed of ultrasound in the material.

##### What is true when there are large reflected intensities of ultrasound waves between tissues??
There is a large difference in acoustic impedance.

##### How can ultrasound reflections between air and a patient's skin be reduced??
Using a coupling gel.

##### How can the speed and direction of a patient's blood flow be determined using ultrasound??
Measuring the frequency change of the reflected wave due to the Doppler effect.

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