How does increasing the number of excitations (NEX) affect scan time?

• A. It reduces scan time
• B. It has no effect
• C. It increases scan time
• D. It improves image resolution without affecting time

Answer: (C)

Increasing the number of excitations, also referred to as NEX or Number of Excitations, directly influences the scan time in magnetic resonance imaging (MRI). When the NEX is increased, the sequence acquires more signal averages per voxel. Each additional excitation requires additional time to complete the sequence, leading to a proportional increase in the overall scan duration.

This increase in scan time occurs because each subsequent excitation adds to the time it takes to gather the necessary data for image reconstruction. In practice, while increasing NEX enhances the signal-to-noise ratio and can improve image quality, this comes at the cost of longer scan times.

Therefore, as the NEX grows, it directly correlates with an increase in the time required to perform the MRI scan. Understanding this relationship is crucial for balancing scan time and image quality effectively when planning MRI procedures.