Comparison of accelerated T1-weighted whole-brain structural-imaging protocols

Area of Science:

• Neuroimaging
• Radiology
• Medical Physics

Background:

• 3D Magnetisation-Prepared Rapid Gradient-Echo (MPRAGE) is crucial for high-resolution brain imaging in neuroscience and clinical trials.
• Current MPRAGE protocols (~1mm resolution) require 5-10 minutes acquisition time, often using only 2x acceleration.
• Advances in MRI technology enable higher acceleration factors, potentially reducing scan times and improving efficiency.

Purpose of the Study:

• To evaluate four variants of a 4x-accelerated MPRAGE protocol against a standard 2x-accelerated ADNI MPRAGE protocol.
• To compare clinical utility, image quality metrics (SNR, CNR), and automated brain tissue segmentation.
• To assess the impact of increased acceleration on morphological assessments of brain structures.

Main Methods:

• Four 4x-accelerated MPRAGE variants (2D-GRAPPA, CAIPIRINHA, CAIPIRINHA elliptical, segmented) were tested.
• 22 healthy subjects underwent imaging with all variants and a reference 2x-accelerated ADNI MPRAGE protocol.
• Clinical readings, SNR, CNR, and automated segmentation were analyzed and benchmarked.

Main Results:

• All accelerated MPRAGE protocols were rated as clinically useful, with CAIPIRINHA comparable to the reference ADNI-2 protocol for clinical readings.
• SNR and CNR measurements aligned with theoretical expectations for 4x acceleration.
• Systematic biases were observed in the segmentation of certain brain structures in accelerated protocols compared to the reference.

Conclusions:

• 4x-accelerated MPRAGE protocols offer clinically useful image quality and comparable diagnostic value to standard protocols.
• Increased noise levels in accelerated scans appear to contribute to segmentation biases.
• Further optimization is needed to mitigate noise-induced biases for accurate morphological assessments with accelerated MPRAGE.