Clinical Practice Mock Exam
In a fast spin echo using an ETL of 24, how many refocusing pulses are performed in one TR period? > 22 > 43 > 23 > 53
> 23 The echo train length is 24, thus there are 23 refocusing pulses and 1 initial 90 deg pulse.
If the precessional frequency is 127.8 MHz, what would the magnetic strength of the magnet be? > 7T > 1T > 1.5T > 3T
> 3T Frequency of Hydrogen Chart 42.6 x 0.5T = 21.3 MHz 42.6 x 1T = 42.6 MHz 42.6 x 1.5T = 63.9 MHz 42.6 x 3T = 127.8 MHz
What is the precessional frequency constant of Hydrogen. > None of the above > 57.3 > 42.6 > 63.9
> 42.6
What is the voxel size of a 3D volumetric gradient scan with a matrix of 256x160, a FOV of 20cm and a slice thickness of 3 milimeters? (Remember conversion) > 12.89mm/cubed > 8.78mm /cubed > 6.09mm/cubed > 9.98mm/cubed
> 8.78mm /cubed Voxel size = Matrix/FOV x Slice thickness Since slice thickness is mm and FOV is cm we must convert both to mm since the answer is usually in mm. Always look at the answers first to see if they are all mm or cm. To go from cm to mm you simply multiply by 10 so 20 x 10 = 200 so our FOV is 200mm. So since we have two components of the matrix you would do the equation for each component of the matrix: 200/256 x 3 = 2.34 200/156 x 3 = 3.75 Then multiply those together so 2.34 x 3.75 = 8.77mm which is answer C 8.78.
A fast spin echo sequence acquired with a Long TR and Long TE, scan time can be reduced by selection of: > Lower frequency encoding value > Shorter ETL > Longer ETL > Echo train length has no effect on time
> ? Increasing echo train
In comparison, an MR matrix of 256x384 would be called a ______ matrix, while an MR matrix of 192x256 would be a ______ matrix. > fine; coarse > coarse; fine > better, not so good > course; good
> fine; coarse Matrix resolution term "coarse" would be lower resolution (low matrix value) but high SNR compared to "fine" which is higher resolution (high matrix value) and lower SNR.
The gradient that is on during phase filling is called the: > receiver > slice select gradient > frequency encoding gradient > phase encoding gradient
> phase encoding gradient
Which gradient must be used for slice selection in order to produce an axial slice? > z > a > y > x
> z
