Coupling of state space modules and attention mechanisms: An input-aware multi-contrast MRI synthesis method.

Background: Medical imaging plays a pivotal role in the real-time monitoring of patients during the diagnostic and therapeutic processes. However, in clinical scenarios, the acquisition of multi-modal imaging protocols is often impeded by a number of factors, including time and economic costs, the cooperation willingness of patients, imaging quality, and even safety concerns.

Purpose: We proposed a learning-based medical image synthesis method to simplify the acquisition of multi-contrast MRI.

Methods: We redesigned the basic structure of the Mamba block and explored different integration patterns between Mamba layers and Transformer layers to make it more suitable for medical image synthesis tasks. Experiments were conducted on the IXI (a total of 575 samples, training set: 450 samples; validation set: 25 samples; test set: 100 samples) and BRATS (a total of 494 samples, training set: 350 samples; validation set: 44 samples; test set: 100 samples) datasets to assess the synthesis performance of our proposed method in comparison to some state-of-the-art models on the task of multi-contrast MRI synthesis.

Results: Our proposed model outperformed other state-of-the-art models in some multi-contrast MRI synthesis tasks. In the synthesis task from T1 to PD, our proposed method achieved the peak signal-to-noise ratio (PSNR) of 33.70 dB (95% CI, 33.61, 33.79) and the structural similarity index (SSIM) of 0.966 (95% CI, 0.964, 0.968). In the synthesis task from T2 to PD, the model achieved a PSNR of 33.90 dB (95% CI, 33.82, 33.98) and SSMI of 0.971 (95% CI, 0.969, 0.973). In the synthesis task from FLAIR to T2, the model achieved PSNR of 30.43 dB (95% CI, 30.29, 30.57) and SSIM of 0.938 (95% CI, 0.935, 0.941).

Conclusions: Our proposed method could effectively model not only the high-dimensional, nonlinear mapping relationships between the magnetic signals of the hydrogen nucleus in tissues and the proton density signals in tissues, but also of the recovery process of suppressed liquid signals in FLAIR. The model proposed in our work employed distinct mechanisms in the synthesis of images belonging to normal and lesion samples, which demonstrated that our model had a profound comprehension of the input data. We also proved that in a hierarchical network, only the deeper self-attention layers were responsible for directing more attention on lesion areas.