Outline the formation of a B scan in medical ultrasound imaging.

State what is meant by half-value thickness in X-ray imaging.

A monochromatic X-ray beam of energy 20 keV and intensity I₀ penetrates 5.00 cm of fat and then 4.00 cm of muscle.

Calculate, in terms of I₀, the final beam intensity that emerges from the muscle.

Compare the use of high and low energy X-rays for medical imaging.

many/array of transducers send ultrasound through body/object

B scan made from many A scans in different directions

the reflection from organ boundaries gives rise to position

the amplitude/size gives brightness to the B scan

2D/3D image formed «by computer»

[3 marks]

the thickness of tissue that reduces the intensity «of the X-rays» by a half

OR

\({x_{\frac{1}{2}}} = \frac{{\ln 2}}{\mu }\) where \({x_{\frac{1}{2}}}\) is the half value thickness and μ is attenuation coefficient

Symbols must be defined for mark to be awarded

[1 mark]

after fat layer, I_fat = I₀e^{–0.4499 × 5.00}

after muscle layer, I = I_fate^{–0.8490 × 4.00}

I = 0.003533 I₀ or 0.35%

[3 marks]

«high energies factors:»

less attenuation/more penetration

more damage to the body

«so» stronger signal leaves the body

OR

«so» used in «most» medical imaging techniques

«low energy factors:»

must be used with enhancement techniques

greater attenuation/less penetration

«so» more damage to the body «on surface layers»

OR

«so» unwanted in «most» medical imaging techniques

[3 marks]