Angle correction for small animal tumor imaging with spatial frequency domain imaging (SFDI).

Yanyu Zhao,Mohan Sobhana Nandhu,Shaheer Piracha,Darren Roblyer,Syeda Tabassum,Mariano Viapiano

doi:10.1364/boe.7.002373

Abstract

Spatial frequency domain imaging (SFDI) is a widefield imaging technique that allows for the quantitative extraction of tissue optical properties. SFDI is currently being explored for small animal tumor imaging, but severe imaging artifacts occur for highly curved surfaces (e.g. the tumor edge). We propose a modified Lambertian angle correction, adapted from the Minnaert correction method for satellite imagery, to account for tissue surface angles up to 75°. The method was tested in a hemisphere phantom study as well as a small animal tumor model. The proposed method reduced µa and µs` extraction errors by an average of 64% and 16% respectively compared to performing no angle correction, and provided more physiologically agreeable optical property and chromophore values on tumors.

Highlights

Spatial Frequency Domain Imaging (SFDI) is a widefield imaging technique that can be used to quantify optical properties of diffusive media including biological tissue [1,2]
Experimental results show that Modified Lambertian Correction (MLC) yields similar improvements compared to standard Lambertian correction for low angles, and outperforms no-angle correction and standard Lambertian correction at higher angles, and MLC provides more physiologically reasonable optical property and chromophore values on live mouse tumor data, especially at the tumor edge, as will be reported here
The calibration phantom is first measured with the Spatial frequency domain imaging (SFDI) system, and a forward model is used to determine the expected Rd values based on prior optical property knowledge

Summary

Introduction

Spatial Frequency Domain Imaging (SFDI) is a widefield imaging technique that can be used to quantify optical properties (absorption and reduced scattering) of diffusive media including biological tissue [1,2]. Tumor edges, and other surfaces with a high surface normal angle in reference to the camera line of sight, suffer from extreme edge artifacts in SFDI, leading to physiologically implausible optical properties and chromophore concentrations in these regions These artifacts manifest as underestimates of diffuse reflectance at low spatial frequencies. Gioux et al reported a Lambertian correction method for SFDI which could mitigate edge imaging artifacts for surface angles up to 40° [17] For this method, a cosine divisor term was applied to SFDI data after image demodulation to increase diffuse reflectance values for surfaces at tilt angles. A cosine divisor term was applied to SFDI data after image demodulation to increase diffuse reflectance values for surfaces at tilt angles This method was shown to improve optical property extraction on tissue-simulating phantoms and human hand data, corrections were limited to angles less than 40°. Experimental results show that MLC yields similar improvements compared to standard Lambertian correction for low angles, and outperforms no-angle correction and standard Lambertian correction at higher angles, and MLC provides more physiologically reasonable optical property and chromophore values on live mouse tumor data, especially at the tumor edge, as will be reported here

Methods

Height correction

Experimental validation

Optical properties of fabricated hemisphere phantoms

Mac line profiles for varied k coefficients

Discussion and conclusion