Integration of image exposure time into a modified laser speckle imaging method

Abstract

Speckle-based methods have been developed to characterize tissue blood flow and perfusion. One such method, called modified laser speckle imaging (mLSI), enables computation of blood flow maps with relatively high spatial resolution. Although it is known that the sensitivity and noise in LSI measurements depend on image exposure time, a fundamental disadvantage of mLSI is that it does not take into account this parameter. In this work, we integrate the exposure time into the mLSI method and provide experimental support of our approach with measurements from an in vitro flow phantom.

Figure 1

Sensitivity as a function of the number of coherence intervals captured over unit of time (i.e. 1/N_t).

Figure 2

(a) Both SFI and 1/N_t values maintain a linear relationship to the actual flow rate for an actual flow rate greater than 5 mm s⁻¹ and an image exposure time of 1 ms. For an actual flow rate less than 5 mm s⁻¹, it is necessary to employ a longer exposure time to achieve a linear response as demonstrated in (b) for T = 10 ms.

Figure 3

(a) 1/N_t and (b) SFI values as a function of the actual velocity for four exposure times (T). Note that, for a given actual flow rate, the 1/N_t value depends on exposure time, while the SFI value is unaffected.

Figure 4

Maps of in vitro flow rates predicted with the mLSI model for actual flow rates of (a) 10 mm s⁻¹ and (b) 3 mm s⁻¹.

Figure 5

Maps of in vitro flow rate predicted with our mLSI model (equation (5)) for actual flow rates of (a) 10 mm s⁻¹ and (b) 3 mm s⁻¹. Exposure times of 1 and 10 ms were used to work within the linear response range of our instrument for the two actual flow rates.