2016 Exam

Question 1

Qualitive B-mode US Image characteristics (4)

Answer 1

• Backscatter signals appear as white lines, shaded areas represent general speckle throughout the image
• Tumour appears elongated in direction of US propagation since the speed of sound in the tumour is much slower than surrounding muscle
• As a result, the liver directly behind the tumour appears to lie at a greater depth than the two sections either side
• Attenuation in the tumour is much lower than tissue, there is an acoustic enhancement for the live/muscle boundary directly behind the tumour

Question 2

Two intrinsic quantum properties of MRI

Answer 2

• Spin
• Magnetism

Question 3

Calulcation of Gyromagnetic Ratio

Answer 3

= angular vel / Magnetic Field Strength

Question 4

Dfference between x,y plane and x’.y’ plane (2)

Answer 4

• The x,y plane has it’s normal along the z and does not rotate
• The x’.y’ plane has the same normal but is rotating at Larmor Frequency of the ucleus under consideration. This rotating freq matches that of the radiofrequency pulse

Question 5

Paramter T1 (2)

Answer 5

• T1 is the spin-lattice relation constant and paramterises the restoration of MO magnetisation back the BO axis
• The restoration of the thermal equilibrium

Question 6

Paramter T2 (3)

Answer 6

• Known as the spin-spin relation constant
• Paramterises the decay of the transverse magnetisation of the MO due to dephasing of the mulitple isochromatic magnetic vectors
• Decorrelation of magnetisation vectors due to local magnetic field disturbances at th molecular level

Question 7

How many distinct grey levels will a histogram equalised image have in comparison with the original?

Answer 7

A histogram equalised image will have the same number of grey levels as the original image since each grey level is mapped to a new distinct grey level.

Question 8

Procedure for computing the median of an nxn neighbourhood?

Answer 8

Numerically sort the n² values.

The median is [(n²+1)/2] -nth largest values

Question 9

Method for updating the median as the centre of the neighbourhhod is moved from pixel to pixel?

Answer 9

Once the values have been sorted once, simply delete the values in the trailing edge of the enighbourhood and insert values into the leading edge in appropriate locations in the sorted array.