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MPY205 TURN OVER
Data Provided: A formula sheet and table of physical constants is attached to this paper.
DEPARTMENT OF PHYSICS AND ASTRONOMY
Autumn semester exam (Academic year 2011-12)
MEDICAL PHYSICS: Aspects of Medical Imaging and Technology 2 HOURS
The paper is divided into two sections: A and B
The student should answer all questions in Section A. One sentence answers are sufficient for all questions in this section.
The student should answer two questions from section B.
MPY205 CONTINUED
SECTION A
(Answer all questions in this section: 2 marks each)
What is the principal difference between the binary and denary number systems?
High spatial frequencies relate to which characteristics of an image?
Write down the integral that defines the convolution operation between two functions ( f * g ).
The unit of the Gray is applicable to which quantity in radiation physics?
- A 6-bit digital-to-analogue converter is configured to provide an output signal in 15 mV steps. What is the largest output that can be generated?
To which area of diagnostic imaging do the Bloch equations apply?
- The Gaussian function is often used as a representation of the Point Spread Function in an imaging system. In the limit, which mathematical function does it approximate when its Full Width Half Maximum (FWHM) tends to zero?
If a hydrogen atom proton is precessing at 85 MHz in a magnetic resonance scanner, what is the magnitude of the B-field responsible for its precession?
What is the name given to the expression that describes the elemental B-field from a
current element of magnitude I , at a distance r and angle ?
Which magnetic resonance relaxation parameter is attributable to field inhomogeneity and tends to dominate signal decay in sequences such as saturation recovery?
What do the letters SAR stand for in the context of MRI safety?
What is the name given to the coefficient that correlates closely with the quality factor and RBE of an ionising radiation?
Consider an entity comprised of 6 protons, 6 neutrons and 5 electrons. It is an ion of which element?
An annihilation interaction produces two gamma rays of energy 510 keV. Which two particles were involved?
What is the absolute minimum power required of an X-ray generator to drive an X- ray tube at 70 kV and 15 mA?
In ionizing radiation physics, which SI units are associated with exposure?
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MPY205 CONTINUED
SECTION B
(Answer two questions from this section: 30 marks each)
B a)
b)
c)
d)
e)
Write down the mathematical definition of a derivative. Use the definition of the derivative to derive (from first principles) the derivative of the function y = 1 /x. Take care to show your working.
Write down the mathematical definition of the integral. Using the definition of the integral, rewrite the Fourier Transform of the generalised function y ( t ) as a discrete summation.
A delta function ( x ) is defined as zero everywhere except at the origin, where it is
non-zero with an area equal to unity. Evaluate the Fourier Transform of the delta function and show that it is a constant. In imaging theory, how might a delta function in object space be interpreted?
Consider an imaging system in which the point spread function (PSF) of a delta
function is a Gaussian of the form exp ( – x^2 ). Derive the image function h ( x ) of an
object that is described by an intensity distribution given by....
f ( x ) = ( x + 1) + 2. ( x ) + 0.5 ( x – 2)
Illustrate this scenario with a 1-D intensity plot, showing object and image functions superimposed.
What do the letters MTF stand for in imaging theory, and how does it relate to the PSF?
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MPY205 TURN OVER
B
a)
b)
c)
d)
e)
Express Coulombs Law in (i) words and (ii) mathematics. Illustrate with a diagram.
Consider 3 charges, each of magnitude q , placed on the x - axis at positions x = – 1, x = 2, and x = 3. Calculate the magnitude of the force acting on a charge Q placed on the y - axis at (0,2).
What arrangement of charges constitutes a hydrogen atom? With which imaging modality does the hydrogen atom have specific relevance, and why is it suited to this particular modality?
Outline three principal relaxation mechanisms encountered in MRI and indicate the MRI relaxation constants with which each is related.
With the aid of a diagram, outline the principles of the spin echo technique used to capture T2 characteristics in the presence of significant T2* effects.
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