Magnetic Resonance Imaging (MRI) Practice Test

When performing a FSE sequence, an increase in ETL will typically lead to what outcome?

1. Increased scan time

2. Decreased image resolution

3. Reduced blurring

4. Higher contrast for T1 images

The correct answer is: Decreased image resolution

In a Fast Spin Echo (FSE) sequence, increasing the Echo Train Length (ETL) essentially means that more echoes are collected within a single repetition time (TR). This can significantly affect the imaging outcome in several ways. While image resolution can be influenced by various factors, increasing the ETL does not inherently improve or maintain resolution. Instead, as the ETL increases, the time taken to complete the sequence can lead to potential compromises in the clarity and definition of fine details in the image. The relative speeds at which the echoes are collected can introduce motion artifacts or blurring, particularly if patient movement occurs during the longer collection time. This can make details appear less distinct than they would with a lower ETL, where echoes are acquired more rapidly. The other aspects of FSE imaging are important too. For example, increased scan time can be a consequence of longer ETL, but it is not the primary outcome that is typically highlighted when discussing image resolution. Additionally, blurring typically increases with higher ETL due to the effects of longer relative acquisition times. Lastly, the contrast characteristics of images, especially for T1 or T2 weighted images, do not improve solely based on ETL and depend largely on other imaging parameters and the specific tissue