In a fast (turbo) spin echo pulse sequence, what follows the initial slice excitation pulse?

• A. A series of 180 degree radio frequency induced echoes
• B. A series of gradient pulses
• C. A series of fat saturation pulses
• D. Static magnetic field pulses

Answer: (A)

In a fast (turbo) spin echo pulse sequence, after the initial slice excitation pulse, a series of 180-degree radio frequency (RF) pulses are applied. These 180-degree RF pulses are crucial for refocusing the spins within the excited slice. The application of these pulses creates multiple echoes as the spins dephase and then rephase, resulting in the collection of data points over a shorter time period compared to traditional spin echo sequences.

The purpose of the 180-degree pulses is to correct for any inhomogeneities in the magnetic field and to maximize the signal from the excited region. This is what allows for fast imaging, making turbo spin echo desirable in clinical settings where speed is a factor.

The other options do not accurately describe the sequence following the slice excitation pulse. Gradient pulses, for example, are utilized to encode spatial information and are present throughout the sequence but do not follow directly after the excitation pulse. Fat saturation pulses are used selectively to suppress fat signals and would not directly follow the initial excitation. Static magnetic field pulses are not a component of the pulse sequence as they pertain to the B0 field that creates the overall magnetic environment for the MR system rather than the dynamic processes involved in a sequence. Therefore, the sequence of