Applied Science AQA/Imaging Methods

P01 Researching and Comparing Imaging Methods

Context

... to be familiar with all of the diagnostic techniques available in the NHS.   

Performance outcomes	Pass	Merit	Distinction
	To achieve a pass the learner must evidence that they can:	In addition to the pass criteria, to achieve a merit the learner must evidence that they can:	In addition to fulfilling the pass and merit criteria, to achieve a distinction the learner must evidence that they can:
PO1 Understand imaging methods	P1 Describe the underlying theory behind two of the imaging methods listed.	M1 Link the underlying theory behind both of the imaging methods to explain how the images are produced.	D1 For both methods, use calculations to support descriptions of the underlying theory.
	Outline dangers e.g. of ionising radiation. Diagrams of equipment and images formed will be useful to support your description.	Refer to the nature of the waves involved. Explain how their properties relate to their energy, frequency or wavelength.	At least two calculations for each method. (See examples below.) Link your calculations to e.g. image quality or dangers.)
	P2 Select one medical condition and identify a suitable and an unsuitable technique for investigating the condition.	M2 Explain why the selected technique is suitable and why the unsuitable technique selected is not appropriate.
	Focus here on the description of the condition - including its location in the body and what the specific problem in. Stating the suitable / unsuitable methods is brief here - with more detail for M2.	Refer to e.g. the quality of the images produced by each method (resolution, contrast...), as well as possible dangers. Example images are useful to help you to explain why one technique is better than another.

Brief

In general, point students towards the approach to take, as opposed to just giving them information.

Advice

- pick two methods

- explain how they work to produce images (include diagrams)

- describe and explain suitable and unsuitable conditions for imaging with each technique

ultrasound image (4d)

- include example calculations to support your explanation of how the techniques work

Calculations

Setting out your Calculations for D1

1. Introduction - what you can work out and why it is useful.

(e.g. I will show the calculation of acoustic impedance because it is useful when...)

2. The equation (words or symbols) - and what the terms represent.

(e.g. write the equation here - when explaining the terms, it is useful to include units.)

3. Context - introducing the relevant numbers that you are going to use in your calculation.

(e.g. the density of bone is...; the speed ultrasound travels through bone is...)

4. Workings - showing how the numbers go into the equation.

(set this out clearly)

5. Answer - with units and a comment about what it means.  e.g. what it tells you about the image quality or a comparison.

(e.g. this value is much higher than soft tissue, which tells us...; this number can then be used in the calculation of the reflection coefficient, which can tell us...)

Ideas for Calculations to Include

Research into these ideas - aim to include at least two different calculations for each imaging method to be sure of meeting the distinction criterion.

Technique	Possible Calculations
Ultrasound	1. Acoustic impedance of different materials - and what this means for sound transmission. 2. Reflection coefficient - why this is crucial in understanding why different materials do or don't show up on scans. 3. The wave equation. Calculating the wavelength from frequency gives you information linked to the resolution of the image.
X-rays	1. You should already have explained how an X-ray tube works. Can you link the voltage of the tube with the energy and frequency of the X-rays produced? 2. Use the wave equation to calculate the wavelength of the X-rays produced. 3. Dose received - what is the typical dose of an X-ray scan, in Sv? - how does this compare to daily living / other imaging technologies? - explore the stochastic risk of this dose - how does this link to the % chance of it causing a new cancer? - what is a Sievert?  What calculation shows how much energy is deposited in the body? 4. Half-Value-Thickness (HVT) - what is the HVT for different energies of X-rays in different materials. How would you do an experiment that allowed you to calculate the HVT? 5. Look at the rates of attenuation of X-rays in different tissues and use these to explain why some tissues show up, while others don't. (Clue: HU)
CAT Scan	Because CAT scans make use of X-ray technology, most of the above calculations can be used here. 1. You should definitely look into the dose calculations to make comparisons. 2. Try thinking about the resolution and number of scans - what implications do these have for dose, time taken and data storage required? 3. Look into contrast media - and how their attenuation rates improve contrast.
MRI	1. Magnetic field strength is measured in Tesla, T. How does the strength of an MRI's magnetic field compare to the magnetic field strength of the Earth? 2. The coils produce radio signals to resonate certain types of atoms. Use the wave equation to show the link between the frequency and wavelength of the radio waves. 3. Can you look into what the resonant frequencies of different biological molecules are - and use this to explain why some show up on an MRI while others don't? 4. Can you refer to A' Level Physics courses and look for an equation that tells you how much voltage is needed to produce a magnetic field of a certain strength?
PET	1. Half-lives of isotopes used. - what does this mean for how long they remain active in the body? - what are the implications for their storage / manufacture? 2. Dose received - what is the typical dose of a PET scan, in Sv? - how does this compare to daily living / other imaging technologies? - explore the stochastic risk of this dose - how does this link to the % chance of it causing a new cancer? - what is a Sievert?  What calculation shows how much energy is deposited in the body?
Thermography	1. Use the wave equation to relate the wavelengths and frequencies of the IR emitted. 2. Can you find an equation that links the temperature of the body with the frequency or wavelength of heat given off? 3. Different surfaces emit different amounts of thermal radiation. You could investigate the idea of emissivity, in the context of human tissue / skin. 4. Many thermographic cameras have an error of +/- 2%. Can you use this idea to calculate the error range in temperatures of different parts of the human body?

thermal image

Checklist

	Have you...
Pass	1. written about two imaging methods? 2. described the underlying theory behind method 1? 3. described the underlying theory behind method 2? 4. identified a specific medical condition and identified one of the imaging techniques as suitable for investigating it? 5. named one of the imaging techniques which is unsuitable for investigating the medical condition?
Merit	6. used scientific theory to explain how method 1 works? 7. used scientific theory to explain how method 2 works? 8. explained why the imaging technique (in 4) is suitable for investigating the condition? 9. explained why the imaging technique (in 5) is unsuitable for investigating it?
Distinction	10. used calculations to support your explanations (6) of how method 1 works? 11. used calculations to support your explanations (7) of how method 2 works?

Links

to other sections within this book

chest x-ray

to good external websites (including AQA website, Wikipedia, relevant applications / companies) - also considering links in spec

References / Bibliography

of recommended text books

including mapped refs to existing books

Back to Contents