Comparing spectral pre-saturation with inversion recovery (SPIR) and spectral adiabatic inversion recovery (SPAIR) fat suppression techniques in magnetic resonance imaging of the knee joint

Abstract

Magnetic Resonance Imaging (MRI) is the gold standard for musculoskeletal imaging owing to its excellent soft-tissue contrast and multiplanar capability. However, the high signal intensity of fat can obscure subtle anatomical and pathological detail, underscoring the need for effective fat suppression techniques. Spectral Pre-saturation with Inversion Recovery (SPIR) and Spectral Adiabatic Inversion Recovery (SPAIR) are frequency-selective inversion recovery methods widely used to enhance tissue contrast in musculoskeletal MRI. To compare SPIR and SPAIR fat suppression techniques in knee MRI and determine which method provides superior overall image quality for clinical evaluation. This intra-individual comparative imaging study was conducted at the Department of Radiodiagnosis, Aarupadai Veedu Medical College and Hospital, Puducherry, from March to August 2025. Seventy-two patients referred for knee MRI were enrolled by purposive sampling. Imaging was performed on a Philips Achieva 1.5-Tesla scanner using a dedicated knee coil. Proton Density-Weighted SPIR (PDW-SPIR) and PDW-SPAIR sequences were acquired for each patient under identical imaging parameters. Images were independently scored by two blinded musculoskeletal radiologists using a three-point Likert scale across seven anatomical structures. The Wilcoxon signed-rank test served as the primary analysis, with paired t tests as a secondary robustness check. Effect sizes and inter-observer agreement (Cohen's κ) were computed using IBM SPSS Statistics. PDW-SPAIR demonstrated more homogeneous fat suppression, fewer artifacts, and improved visualization of the cruciate ligaments, menisci, articular cartilage, and periarticular soft tissues compared with PDW-SPIR. Differences in image quality were statistically significant across all seven structures (p < 0.001), with medium-to-large effect sizes (Cohen’s dz = 0.55–0.77; Wilcoxon r > 0.87), indicating clinically meaningful superiority. Inter-observer reliability was excellent (κ = 0.88–1.00). SPAIR provides more homogeneous fat suppression and superior image quality than SPIR in knee MRI, supporting its use as a technically preferable fat suppression method at 1.5 T. Its impact on diagnostic accuracy was not directly assessed and warrants further study.