Study of susceptibility-induced artefacts in GRASE with different echo train length

Area of Science:

• Radiology
• Medical Imaging
• Neuroimaging

Background:

• Susceptibility effects in MRI can obscure details in brain imaging, particularly in cases of hemorrhage.
• Gradient-and-spin-echo (GRASE) sequences are an alternative to conventional fast spin-echo (FSE) sequences.
• Understanding the sensitivity of different MRI sequences to susceptibility is crucial for accurate diagnosis.

Purpose of the Study:

• To evaluate the sensitivity of gradient-and-spin-echo (GRASE) MRI sequences to magnetic susceptibility effects.
• To compare GRASE sequences with varying echo train lengths (ETLs) against T2-weighted FSE sequences.
• To determine the optimal sequence for imaging old hemorrhagic brain lesions.

Main Methods:

• Comparison of GRASE (21 and 33 echoes) and FSE (5 echoes) sequences on a 1.0-T MRI system.
• Experiments conducted using phantoms with iron oxides, volunteers, and patients with old brain hemorrhages.
• Calculation of contrast-to-noise ratios (CNRs) for iron-containing tissues and qualitative analysis of susceptibility effects.

Main Results:

• GRASE sequences showed decreased CNR with increasing echo train lengths.
• GRASE sequences exhibited lower CNR compared to FSE sequences (GRASE 21-echo vs. FSE 5-echo: 23.8 vs. 26.7).
• FSE with a shorter ETL (5) demonstrated stronger susceptibility effects than GRASE with a longer ETL (21).

Conclusions:

• GRASE sequences do not inherently compensate for susceptibility effects seen in FSE sequences.
• Conventional SE, gradient echo, or FSE sequences with shorter echo trains are preferable for evaluating intracranial hemorrhage.
• The complex signal behavior of GRASE may limit its utility in susceptibility-weighted imaging of hemorrhage.