Questions	pts
Problem 1 Sketch the timing diagram for a a two echo spin echo pulse sequence providing second order (velocity and acceleration) moment nulling on the readout axis for the second echo, and first order (velocity) nulling on the slice selection axis. Assume that a selective 180° pulse has no dephasing effects on moving spins. NOTE: a sketch is fine. You do not need to calculate the gradient amplitudes or figure in gradient rise times. See Motion artifacts in MRI for help.	15
Let's suppose that you are fortunate enough to have a scanner available with the following specs: * the signal ratio in dB fo rtwo signals A and B is calculated as follows: Ratio in dB = 10 log(A/B). Field Strength 4 Tesla Room Temp Shims X, Y, Z, Z2, ZX,ZY, XY, X2-Y2, Z3 ADC 16 bit to 250 kHz, 14 bit to 1 MHz Maximum Gradient Current 250 Amps Gradient Coil Inductance 1 milli Henry Maximum Gradient Voltage 500 Volts Gradient Efficiency 100 A/gauss/cm Field Homogeneity 0.2 ppm Peak to Peak RF Frequency Stability +/- 0.1 ppm peak to peak over any ten minute period OOPS-> RF Amplitude Stability +/- 0.2 dB over any ten minute period*
Problem 2 What is the maximum gradient amplitude? Tesla/m	5
Problem 3 What is the gradient rise time to its maximum? milliseconds	5
Problem 4 Assuming that you will tolerate at most a two pixel chemical shift artifact, what is the minimum field of view with a 256 x 256 matrix? mm	20
Problem 5 In the acquisition described below, on your new scanner described above: Estimate the variation in MR signal strength over a ten minute period in a region of interest located in a region of the phantom having essentially homogeneous signal. Phantom 20 cm uniform sphere filled with doped water to have a nominal T1 of 500 msec tr 4 sec te 20 msec Matrix 128 x 128 Sequence Single-shot gradient echo EPI Flip Angle 45 ° Field of View 30 cm Matrix 128 x 128 Thickness/Gap 5 mm/5 mm % Peak to Peak	15
Problem 6 Using the instrument specs listed above, and assuming that we are collecting data during the trapezoidal gradient rise and fall times, what is the readout time required to collect an EPI image with 64 phase encoding steps and a 3 mm (in-plane) pixel size. Do not assume that we are using half k-space methods. msec	20
Problem 7 What is the bandwidth per pixel in the sequence from problem 6 (along the phase direction!)? Hz What is the approximate separation between fat and water on the above image? mm What is the magnitude of the shape distortion caused by the field non-uniformity? mm	20
Problems 8 and 9 refer to this figure. Assume that alpha, beta and gamma are each less than 180° NOTE: REVISED
Problem 8 At what times do echoes appear, and what type are they (please list them in order by time)? Echo Number Time Type 1 msec Spin Echo Stimulated Echo None 2 msec Spin Echo Stimulated Echo None 3 msec Spin Echo Stimulated Echo None 4 msec Spin Echo Stimulated Echo None 5 msec Spin Echo Stimulated Echo None 6 msec Spin Echo Stimulated Echo None 7 msec Spin Echo Stimulated Echo None 8 msec Spin Echo Stimulated Echo None	10
Problem 9 Which echoes are being used for imaging (consider the gradients, and check all that apply)? Echo 1 Echo 2 Echo 3 Echo 4 Echo 5 Echo 6 Echo 7 Echo 8	15
Problem 10 Describe two methods for suppression of fat signals in MRI	15
Problem 11 Does the chemical shift (in ppm) vary as a function of MR field strength? YES NO	10
Problem 12 Which drawing best describes the effects of temperature on T1? This One This One This One	10
Problem 13 With a three axis body gradient (such as that described in Problem 2 above) that can produce rapidly varying magnetic fields, which axis (X-horizontal/sagittal, Y-vertical/coronal, Z longitudinal/axial) is mostly likely to induce magneto stimulation in humans? Gradient Name Anatomical Axis X Right-Left Y Anterior-Posterior Z Superior-Inferior X axis Y axis Z axis Why?	15
Problem 14 Keeping matrix size, field of view, tr, te, pulse sequence, slice thickness constant, when the readout bandwidth (Hz/pixel) is lowered, is aliasing more likely to occur? Yes No	10
Problem 15 On the General Electric Signa system, spin echo scanning is available in two flavors: Classic(tm) and the default. The timing diagram above shows the pulse sequences when you press the buttons corresponding to these taste sensations. As field strength is increased, the signal intensity on the Classic scans DECREASES as compared to the Default scans (i.e. SIclassic/SIdefault decreases with field strength). Why? (HINT: the 90 and 180 degree pulses are both frequency modulated to excite the same slice location (giving a spin echo from that slice)	15