What is the relationship between noise and NEX in MRI imaging?

In MRI imaging, the relationship between noise and the number of excitations (NEX) is foundational to understanding image quality. As the NEX increases, the amount of signal data collected is amplified, which correlates with noise behavior. Specifically, noise is known to increase by the square root of NEX. This means that if you double the NEX, the noise level will increase only by a factor of about 1.41 (the square root of 2) rather than doubling the noise in a linear manner.

This property is crucial because it illustrates that while increasing NEX improves the signal-to-noise ratio (SNR) by enhancing the overall signal collected, the increase in noise does not escalate proportionately. Therefore, employing a higher NEX can result in clearer images without a corresponding excessive increase in noise, leading to better diagnostic efficacy without requiring vastly longer scan times.

Understanding this concept helps practitioners optimize imaging protocols to balance scan efficiency and image quality, which is essential in a clinical setting.