Advanced MRI for targeting the pallidothalamic region in magnetic resonance-guided focused ultrasound: the mammillothalamic tract as an adjacent imaging landmark.

Magnetic resonance-guided focused ultrasound (MRgFUS) has expanded the therapeutic landscape for movement disorders, with growing interest in circuit-based targets such as pallidothalamic tractotomy (PTT) for Parkinson's disease. Structural MRI provides indirect orientation through surrounding landmarks, including the subthalamic nucleus, red nucleus, and internal capsule, while advanced sequences such as FGATIR and susceptibility-based imaging improve delineation of deep gray matter structures but remain limited for direct fiber visualization. Diffusion-based imaging offers complementary information by enabling in vivo reconstruction of white matter pathways, although tractography of pallidothalamic fibers remains constrained by crossing fiber architecture and spatial resolution. Within this context, the mammillothalamic tract represents a consistent and reproducible adjacent structure with reliable visibility on both structural and diffusion imaging. Its stable anatomical relationship to the pallidothalamic region supports its use as a practical landmark to refine stereotactic orientation when direct target visualization is not feasible. Together, these observations support a multimodal imaging framework that integrates structural and diffusion techniques to improve targeting accuracy in MRgFUS PTT. In this mini review, we aimed to synthesize the relevant anatomy of the pallidothalamic pathways and critically evaluate current MRI techniques for their localization. Additionally we sought to describe the role of identifying the mamillothalamic tract in MRgFUS-PTT planning.