The Paradox of Radial MRI: When Repeated Sampling of K-Space Center Becomes a Double-Edged Sword

Radial MRI has been extensively investigated for decades and has become one of the most widely studied non-Cartesian sampling schemes in MRI research. Major advances in image reconstruction, free-breathing imaging, and highly-accelerated MRI have further expanded interest in radial acquisition. However, despite remarkable methodological advances and rapidly growing literature, Cartesian acquisition continues to dominate routine clinical MRI today. This observation suggests that it may be time to step back and revisit a question that is often under-discussed: why has radial MRI, despite decades of innovation and strong research enthusiasm, not evolved into a dominant clinical acquisition strategy? This Mini Review addresses this question from an image formation perspective, with the central argument that the repeated sampling of k-space center, which defines radial MRI, is inherently a double-edged sword. While this sampling scheme provides intrinsic robustness to motion and enables continuous data acquisition, flexible retrospective reconstruction, and incoherent undersampling, it also introduces a series of fundamental tradeoffs, including residual motion blurring, strong streaking artifacts from bright signal sources, reconstruction-related image smoothing, and increased sensitivity to system imperfections. Importantly, these limitations arise from the same mechanism that gives radial MRI its unique strengths and may not be fully overcome even with modern reconstruction approaches. This Mini Review further discusses why radial MRI may ultimately serve a complementary rather than universal role in clinical imaging and argues that the more important question today is not whether radial MRI works, but when and where it provides the greatest clinical value in modern clinical MRI.