Medical Biophysics 4475A/B Study Guide - Final Guide: Spin Echo, Gamma Camera, Dead Time
Course CodeMEDBIO 4475A/B
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MBP 4475a / MBP 9515a / BME 9513a
Friday, December 14, 2010, 9 a.m.
Duration: 2 hours
ANSWER ALL (3) QUESTIONS.
• use a separate answer booklet for each section
• write the name of the instructor as well as your name on each booklet.
• at the end of the exam place the question sheet and all booklets in the envelope
• do not seal the envelope; do not write your name on the envelope.
An aid sheet (single side 8.5” x 11”, hand written) and a calculator are allowed.
1. MAGNETIC RESONANCE IMAGING (DRANGOVA) [24 MARKS]
 1.1 True or false? Record the answers in your booklet.
a) Superconducting magnets are the only type of magnet used to provide the main
magnetic field of MRI scanners.
b) A T1-weighted image can be obtained with a spin-echo sequence with long TR.
c) Aliasing occurs only in the phase-encode direction.
d) For a gradient echo image a flip angle much less than 90° is required.
e) For the same pixel size, slice thickness, number of slices and total scan time, the
images acquired using a 3DFT acquisition will have a lower SNR than images
obtained with a series of 2DFT acquisitions.
f) P31 is one of the MR-visible nuclei of biological importance.
 1.2 A vial of water is placed in a 1 T magnet. The sample’s NMR spectrum is recorded
while a 5 G/cm frequency-encoding gradient is applied along the x-axis. The
spectrum contains frequencies between 298 200 Hz and 340 800 Hz relative to the
a) How far is the centre of the water vial, with respect to isocenter?
b) What would the location be if the magnetic field strength were 7 T?
c) What is the width of the vial?
 1.3 Multiple choice – please transfer your answers to the booklet.
a) T2 is also referred to as:
i) transverse relaxation time ii) spin-lattice relaxation time
iii) spin relaxation time iv) i) and ii)
b) When using an inversion-recovery pulse sequence, setting the inversion time equal
to ln(2) T1 (fat) will result in:
i) double the signal from fat ii) no signal from fat
iii) equal signal from fat and muscle iv) none of the above
c) Which of the following lists the pulse sequence from slowest to fastest:
i) spin echo, gradient echo, EPI ii) EPI, spin echo, gradient echo
iii) EPI, gradient echo, spin echo iv) spin echo, EPI, gradient echo
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