In vivo functional human imaging using photoacoustic microscopy: response to ischemic and thermal stimuli

Abstract

We report results of two in vivo functional human imaging experiments using photoacoustic microscopy. In Experiment 1, the hemodynamic response to an ischemic event was measured. The palm of a volunteer was imaged and a single cross-section was monitored while periodic arterial occlusions were administered using a blood pressure cuff wrapped around the upper arm and inflated to ~280 mmHg. Significant relative decreases in oxygen saturation (sO 2 ) and total hemoglobin (HbT) were observed during periods of ischemia. Upon release of the occlusion, significant relative increases in sO 2 and HbT due to post-occlusive reactive hyperemia were recorded. Experiment 2 explored the vascular response to a local, external thermal stimulus. Thermal hyperemia is a common physiological phenomenon and thermoregulation function in which blood flow to the skin is increased to more efficiently exchange heat with the ambient environment. The forearm of a volunteer was imaged and a single cross-section was monitored while the imaged surface was exposed to an elevated temperature of ~46°C. Due to thermal hyperemia, relative increases in sO 2 and HbT were measured as the temperature of the surface was raised. These results may contribute as clinically relevant measures of vascular functioning for detection and assessment of vascular related diseases.

PHOTOACOUSTIC TOMOGRAPHY: PRINCIPLES AND ADVANCES (Invited Review)

“…For instance, the light attenuation limits the ultimate imaging depth. Currently, the maximum demonstrated PAT imaging depth is 8.4 cm in chicken breast tissue [39]. To address this limitation, novel light illumination schemes have been explored.…”

“…Over the past ten years, PAT has been evolving rapidly, and applications of PAT have been established in vascular biology [13–16], oncology [17–24], neurology [25–29], ophthalmology [30–34], dermatology [35–39], gastroenterology [40–44], and cardiology [37, 45–47]. The purpose of this review is to provide a general overview of the PAT technique.…”

Sensitivity of photoacoustic microscopy

“…By offering high-resolution images with unique optical contrast, PAM has so far been applied to numerous preclinical and clinical studies, including vascular biology [88–90] , oncology [42,70,91–95] , neurology [96–99] , ophthalmology [100–104] , dermatology [105–109] , gastroenterology [110–114] , and cardiology [41,115–117] . In the interest of brevity, only a few representative applications that have demonstrated high detection sensitivity are highlighted in this Review.…”

Seeing through the Skin: Photoacoustic Tomography of Skin Vasculature and Beyond

“…4c). In fact, sO 2 has been successfully imaged by PAT at different length scales in a number of cases, including during cuffed occlusion of the arm (Favazza et al, 2010), controlled temperature changes (Favazza et al, 2010), and relatively homeostatic situations (Dean-Ben and Razansky, 2014, Favazza et al, 2011, Zhang et al, 2006a, Zhang et al, 2007a. sO 2 has even been resolved down to the single-cell level in a human cuticle (Hsu et al, 2016).…”