Department of Biomedical Engineering
Diffuse Optical Imaging of Tissue Lab
Diffuse Optical Imaging of Tissue Lab

Dual-slope imaging

The basic dual-slope arrangement of two sources and two detectors can be configured in a variety of spatial arrangements to feature multiple dual-slope sets with overlapping regions of sensitivity. This is an ideal scenario for an imaging approach that leverages the intrinsic advantages of dual-slope measurements (namely, an insensitivity to instrumental factors and a preferential depth sensitivity). Such imaging capability is illustrated in Fig. 1, where a circular source detector array with 8 sources (red squares) and 9 detectors (blue circles) features 16 dual-slope sets. One linear set and one trapezoidal set are indicated by the dashed lines in Fig. 1 that join the associated pairs of sources and detectors. The dual-slope imaging array is placed on top of a highly scattering phantom that contains two absorbing inclusions, one more superficial and the other deeper in the medium. The dual-slope images shown in Fig. 1 demonstrate the intrinsically stronger sensitivity of dual-slope phase to the deeper inclusion (the one at negative x) while dual-slope intensity is mostly sensitive to the shallower inclusion.
 

. Image reconstruction with dual slope FD-NIRS of two absorption inclusions embedded in a strongly scattering medium at different depths.


Fig. 1. Image reconstruction with dual slope FD-NIRS of two absorption inclusions embedded in a strongly scattering medium at different depths. The left inclusion (at negative x) is deeper and mostly appears in the dual-slope phase image, whereas the right inclusion (at positive x) is shallower and mostly appears in the dual-slope intensity image. 

Arrays with larger number of sources and detectors can be designed to realize dual-slope imaging over larger tissue areas or with a greater density of spatial sampling. For example, Fig. 2 shows an array with 16 sources and 10 detectors that features 27 dual-slope sets for imaging an area of approximately 8 cm by 10 cm.
 

Source-detector array for dual-slope imaging with 16 sources and 10 detectors.

Fig. 2. Source-detector array for dual-slope imaging with 16 sources and 10 detectors. Left: geometrical arrangement. Right: 3D rendition of the mold design to accommodate illumination optical fibers (red) and detector optical fibers (black).

Dual-slope imaging (PDF)

See also:

  • G. Blaney, A. Sassaroli, and S. Fantini, “Dual-slope imaging in highly scattering media with frequency-domain near-infrared spectroscopy,” Opt. Lett. 45, 4464-4467 (2020).
  • G. Blaney, A. Sassaroli, and S. Fantini, “Design of a source-detector array for dual-slope diffuse optical imaging,” Rev. Sci. Instrum. 91, 093702 (2020).