Optoacoustic sensing of hematocrit to improve the accuracy of hybrid fluorescence‐ultrasound intravascular imaging

Abstract

Hybrid intravascular fluorescence-ultrasound imaging is emerging for reading anatomical and biological information in vivo. By operating through blood, intravascular near-infrared fluorescence (NIRF) detection is affected by hemoglobin attenuation. Improved quantification has been demonstrated with methods that correct for the attenuation of the optical signal as it propagates through blood. These methods assume an attenuation coefficient for blood and measure the distance between detector and the vessel wall by observing the intravascular ultrasound images. Assumptions behind the attenuation employed in correction models may reduce the accuracy of these methods. Herein, we explore a novel approach to dynamically estimate optical absorption by using optoacoustic (photoacoustic) measurements. Adaptive correction is based on a trimodal intravascular catheter that integrates fluorescence, ultrasound and optoacoustic measurements. Using the novel catheter, we show how optoacoustic measurements can determine variations of blood absorption, leading to accurate quantification of the detected NIRF signals at different hematocrit values.

Accounting for blood attenuation in intravascular near-infrared fluorescence-ultrasound imaging using a fluorophore-coated guidewire

“… 23 , 24 Light attenuation by blood in intravascular fluorescence imaging was modeled as an exponential function of the distance between the outer wall of catheter sheath and the vessel wall or fluorophore-coated guidewire. 4 , 8 – 11 The NIRF signals of the guidewire were segmented from tissue signals using the coregistered IVUS data.…”

“…The parallel operation of NIRF and IVUS allows for accurate coregistration of the two modalities, a feature that has been previously explored to measure the distance between the NIRF detector and the vessel wall on the ultrasound images. 2 , 4 , 8 – 11 This distance is then utilized in a correction model for each point measured on the vessel wall. Previous works assumed blood attenuation using ex vivo reference measurements or approximate average values estimated in vivo .…”

“…Previous works assumed blood attenuation using ex vivo reference measurements or approximate average values estimated in vivo . 4 , 9 – 11 However, such approximations can introduce errors since they do not account for deviations of each patient from the average value employed in the correction model; for example, due to variations of hematocrit, 8 oxygenation state, 12 or fluctuations in blood flow 13 , 14 as a function of vessel type, intravascular location, and pathological state. 15 …”

“…Then, combination of this position-(frame-)dependent blood attenuation with NIRF detector-to-vessel wall distance computed on the IVUS images can be employed to offer an accurate correction scheme for intravascular NIRF imaging. Intravascular imaging methods such as IVUS/IVOCT and optoacoustic have been employed to sense parameters, such as blood flow 16 – 19 and hematocrit, 8 and hence could be used to estimate aspects of blood attenuation dynamically. However, to achieve accurate correlation to light attenuation, the required number of such readouts, which have to be laboriously compiled into an extensive look-up-table, is unknown at present.…”

Design Principles Governing the Development of Theranostic Anticancer Agents and Their Nanoformulations with Photoacoustic Properties

“…Notably, Bozhko et al [27] utilized the photoacoustic modality along with intravascular NIRF (near-infrared fluorescence) and IVUS (intravascular ultrasound) to develop a trimodal NIRF-IVUS-optoacoustic catheter, which was validated in phantoms and excised rabbit aortas. This novel catheter promoted the exact determination of the variations of blood absorption at various hematocrit values and resulted in the accurate quantification of the observed NIRF signal.…”