Influence of Image Contrasts and Reconstruction Methods on the Classification of Multiple Sclerosis-like Lesions in Simulated Sodium Magnetic Resonance Imaging

Purpose: To evaluate the classifiability of small multiple sclerosis (MS)-like lesions in simulated sodium ( Na) MRI for different Na MRI contrasts and reconstruction methods.

Methods: Na MRI and Na inversion recovery (IR) MRI of a phantom and simulated brain with and without lesions of different volumes (V = 1.3-38.2 nominal voxels) were simulated 100 times by adding Gaussian noise matching the SNR of real 3T measurements. Each simulation was reconstructed with four different reconstruction methods (Gridding without and with Hamming filter, Compressed sensing (CS) reconstruction without and with anatomical H prior information). Based on the mean signals within the lesion volumes of simulations with and without lesions, receiver operating characteristics (ROC) were determined and the area under the curve (AUC) was calculated to assess the classifiability for each lesion volume.

Results: Lesions show higher classifiability in Na MRI than in Na IR MRI. For typical parameters and SNR of a 3T scan, the voxel normed minimal classifiable lesion volume (AUC > 0.9) is 2.8 voxels for Na MRI and 19 voxels for Na IR MRI, respectively. In terms of classifiability, Gridding with Hamming filter and CS without anatomical H prior outperform CS reconstruction with anatomical H prior.

Conclusion: Reliability of lesion classifiability strongly depends on the lesion volume and the Na MRI contrast. Additional incorporation of H prior information in the CS reconstruction was not beneficial for the classification of small MS-like lesions in Na MRI.