Dual-modal fiber needle probe for optical coherence tomography imaging and in situ temperature sensing

Integrating intraoperative imaging guidance with in situ acquisition of tissue functional information is of great importance for precision interventional diagnosis and therapy of deep-seated lesions, yet achieving both within a single compact fiber probe without compromising either modality remains challenging. Here we report a dual-modal all-fiber needle probe integrating forward-viewing optical coherence tomography (OCT) with in situ fiber Bragg grating (FBG) temperature sensing in a single-mode fiber-FBG-multimode fiber (MMF) architecture. Multimode interference in the MMF section generates a quasi-Bessel beam with a lateral resolution of 5 μm and a depth of focus of 1.25 mm, representing a 7.9-fold improvement over conventional Gaussian-beam probes. The FBG centered at 1550 nm provides photobleaching-free temperature sensing at 10.68 pm/°C without perturbing the OCT channel. The probe is validated across multiple biological tissue specimens and applied to a murine breast tumor model undergoing in vivo photothermal therapy (PTT). In situ FBG-recorded intratumoral temperatures exceed surface thermal camera readings by approximately 1 °C at peak heating, underscoring the indispensable role of co-localized thermometry for accurate thermal dose control. In addition, periodic artifacts observed in M-mode OCT images may offer a potential route for respiration monitoring, requiring no additional sensor hardware. This dual-modal probe establishes a versatile platform for image-guided, thermometry-monitored interstitial cancer therapy.