Ex vivo validation of photo-magnetic imaging

Abstract

We recently introduced a new high-resolution diffuse optical imaging technique termed photo-magnetic imaging (PMI), which utilizes magnetic resonance thermometry (MRT) to monitor the 3D temperature distribution induced in a medium illuminated with a near-infrared light. The spatiotemporal temperature distribution due to light absorption can be accurately estimated using a combined photon propagation and heat diffusion model. High-resolution optical absorption images are then obtained by iteratively minimizing the error between the measured and modeled temperature distributions. We have previously demonstrated the feasibility of PMI with experimental studies using tissue simulating agarose phantoms. In this Letter, we present the preliminary ex vivo PMI results obtained with a chicken breast sample. Similarly to the results obtained on phantoms, the reconstructed images reveal that PMI can quantitatively resolve an inclusion with a 3 mm diameter embedded deep in a biological tissue sample with only 10% error. These encouraging results demonstrate the high performance of PMI in ex vivo biological tissue and its potential for in vivo imaging.

Fig. 1.

(a) Schematic of the PMI breast imaging interface: the sample is placed at the center of the coil and illuminated from both sides. The light is transferred to the interface using optical fibers and collimated using aspherical lenses. (b) The PMI data acquisition timeline: the temporal resolution of the dynamic MRT sequence is 8 s. The laser is turned on after the acquisition of the first MRT baseline image, and phase images are acquired during this heating-phase as the temperature of the medium rises.

Fig. 2.

(a) T1-weighted MR cross section of the phantom. The position of the inclusions is indicated with black circles due to the absence of contrast in the MR image. The illumination spots are indicated by red arrows. (b) The measured temperature increase obtained by MRT at the first frame after 8 s of heating. (c) The reconstructed absorption map using PMI. The profiles performed on both the temperature and absorption maps along (d) line AB and (e) line CD in (a).

Fig. 3.

(a) T1-weighted MR cross section of the chicken breast sample. The illumination spots are indicated by red arrows. (b) The reconstructed absorption map using PMI. The profiles performed on the absorption map along (c) line AB (x-axis) and (d) line CD (y-axis) in (a).