Final answer:
Increasing ETL or TSE in MRI leads to a decrease in spatial resolution because more echoes with less distinction between them fill the k-space, reducing the system's ability to differentiate detailed spatial variations.
Step-by-step explanation:
Increasing ETL (Echo Train Length) or TSE (Turbo Spin Echo) in the context of MRI (Magnetic Resonance Imaging) typically results in a decrease in detail or spatial resolution. This is because a longer ETL implies that more echoes are being used to fill the k-space (a space that represents spatial frequencies), each of which is slightly less resolved than the last due to T2 decay. As ETL increases, the time between each echo is shorter, which leads to less time for the system to differentiate between signals of differing spatial locations, thus reducing spatial resolution.
On the other hand, shorter ETL values mean that fewer echoes are used to produce the image, which often leads to higher detail in the image representation. In practical terms, this means that increasing ETL for speedier acquisition comes at the cost of reduced resolution. Care must therefore be taken to balance these factors when setting MRI parameters to ensure the necessary detail is captured for accurate diagnosis.