What is the maximum SNR achieved at the "Ernst Angle" for sequences where TR is greater than T1?

The maximum signal-to-noise ratio (SNR) in magnetic resonance imaging (MRI) is achieved at the Ernst Angle, which is the optimal flip angle for a given repetition time (TR) and relaxation time (T1) of the tissues being imaged. When the TR is greater than T1, the Ernst Angle approaches 90 degrees. At this angle, the longitudinal magnetization is maximally transferred to transverse magnetization, resulting in the highest possible SNR for T1-weighted imaging.

The concept behind the Ernst Angle is to optimize the flip angle to enhance the signal while keeping the noise levels relatively stable. At a flip angle of 90 degrees, the system takes full advantage of the magnetization components, maximizing the signal detected during the readout phase of the imaging sequence.

For sequences where the TR is greater than T1, the effective manipulation of the flip angle enables the MRI system to attain a balance between signal enhancement and noise suppression, and 90 degrees has been established as the point where this balance is most favorable, thereby yielding the highest SNR.

The other angles do not provide the same level of signal optimization in this specific context, leading to lower SNR. Thus, 90 degrees is recognized as the best