You want to image a slice that is 5cm off-center along z-axis. When the strength of the slice selection gradient is 0.2 G/cm, what is the difference between the transmission frequencies for excitation of the 5cm off-center and the isocenter (0cm off-center)? (Hint : γ^=γ/2π = 42.58MHz/T = 4258 Hz/G)
To find the difference between the transmission frequencies for excitation of the 5cm off-center slice and the isocenter (0cm off-center), we need to calculate the frequency offset caused by the off-center slice.
First, we need to convert the strength of the slice selection gradient from Gauss per centimeter (G/cm) to Tesla per meter (T/m).
1 T/m = 1 G/cm * 0.0001
So, the strength of the slice selection gradient in T/m is:
0.2 G/cm * 0.0001 = 0.00002 T/m
Next, we can calculate the frequency offset using the formula:
Frequency Offset = γ * G * d
Where:
- γ is the gyromagnetic ratio (42.58 MHz/T or 4258 Hz/G)
- G is the slice selection gradient (0.00002 T/m)
- d is the distance from the isocenter (5 cm)
Using the given values, we can calculate the frequency offset as follows:
Frequency Offset = (42.58 MHz/T)(0.00002 T/m)(5 cm)
= 0.004516 MHz
= 4516 Hz
The difference between the transmission frequencies for the 5cm off-center and the isocenter is 4516 Hz.