Magnetic Resonance Imaging (MRI) Practice Test

In fast spin echo (FSE), the number of shots is calculated using which formula?

1. #PE’s/SE

2. #PE’s/ETL

3. #ETL/SE

4. #TRs/FSE

The correct answer is: #PE’s/ETL

The correct response involves understanding the relationship between the number of phase encoding (PE) steps, the echo train length (ETL), and how they relate to the shots in fast spin echo (FSE) imaging. In FSE, multiple echoes are captured in a single repetition time (TR) due to the use of a longer echo train length. When calculating the number of shots needed, the formula takes into account the total number of phase encodings required for the image, denoted as #PE's, and the number of echoes that can be acquired per TR, represented by the echo train length (ETL). Thus, dividing the total number of phase encodings by the echo train length allows you to determine how many shots are necessary to acquire the complete data set while maintaining optimal imaging time. This principle ensures that the imaging process is efficient and that the desired resolution is achieved without unnecessary prolongation of the overall scan time. The correct choice succinctly captures this relationship, indicating how FSE manages the acquisition of multiple data points through calculated relationships between the primary imaging parameters.