Increasing NEX/NSA yields which of the following effects?

• A. Increased scan time and SNR
• B. Decreased scan time and SNR
• C. Increased spatial resolution and lower SNR
• D. Higher output and scan time

Answer: (A)

Increasing the number of excitations (NEX) or number of signal averages (NSA) directly influences the quality of MRI images by enhancing the signal-to-noise ratio (SNR). When you increase NEX/NSA, the MRI system acquires more data with each image, which allows for greater averaging of the signals. This better averaging helps in diminishing the noise relative to the actual signal, thereby improving the SNR.

However, this increase in data collection inherently results in longer scan times, as the system has to go through additional excitation cycles to gather the increased number of signal averages. Thus, the combination of increased scan time and improved SNR is a key characteristic of increasing NEX/NSA in MRI practices. The balance of these two factors is essential for optimizing image quality while managing patient comfort and workflow efficiency.