What is the correct formula for calculating scan time of FSE images?

The correct formula for calculating the scan time of Fast Spin Echo (FSE) images incorporates several factors that impact the imaging time. For FSE imaging, the scan time is determined by the repetition time (TR), the number of phase encoding steps (NPE), and the number of signal averages or number of shots (NSA), but it is crucial to also consider the echo train length (ETL).

In FSE sequences, multiple echoes are acquired per TR period, which is reflected by the echo train length. This means that the total number of phase encoding steps must be adjusted by the ETL, as multiple lines of data are read for each TR. As a result, the formula incorporates the division by the echo train length to accurately reflect the reduction in overall scan time due to the simultaneous acquisition of multiple echoes in one TR period.

Therefore, the correct calculation that accounts for the influence of the echo train length on scan time is as follows: Scan Time = TR × NPE × NSA ÷ ETL. This formula ensures that the effective imaging time reflects how FSE utilizes its multi-echo capabilities to optimize data collection.