Grueneisen relaxation photoacoustic microscopyin vivo

Abstract

Abstract. Grueneisen relaxation photoacoustic microscopy (GR-PAM) can achieve optically defined axial resolution, but it has been limited to ex vivo demonstrations so far. Here, we present the first in vivo image of a mouse brain acquired with GR-PAM. To induce the GR effect, an intensity-modulated continuous-wave laser was employed to heat absorbing objects. In phantom experiments, an axial resolution of 12.5 μm was achieved, which is sixfold better than the value achieved by conventional optical-resolution PAM. This axial-resolution improvement was further demonstrated by imaging a mouse brain in vivo, where significantly narrower axial profiles of blood vessels were observed. The in vivo demonstration of GR-PAM shows the potential of this modality for label-free and high-resolution anatomical and functional imaging of biological tissues.

Nonlinear mechanisms in photoacoustics—Powerful tools in photoacoustic imaging

“…However, if two identical laser pulses are applied sequentially within the absorbing target’s thermal relaxation time ( ), the heat induced by the first laser pulse at the voxel of interest influences the amplitude of the second PA signal, owing to the increased Grueneisen parameter produced by the heat from the first laser excitation. This effect is referred to as the Grueneisen-relaxation (GR) effect and has been widely applied in PA techniques [ [36] , [37] , [38] , [39] , [40] , [41] ]. To further elucidate the GR effect, the PA signal generated by the first pulse is expressed as follows, …”

“…There are a number of conditions where the linear correlation no longer holds true and nonlinear dependence occurs. So far, several types of nonlinear mechanisms have been investigated and developed, including absorption saturation-based nonlinearity [ [21] , [22] , [23] , [24] , [25] ], thermal-based nonlinearity [ [25] , [26] , [27] , [28] , [29] , [30] , [31] , [32] ], resolution-dependent nonlinearity [ [33] , [34] , [35] ], Grueneisen-relaxation-based nonlinearity [ [36] , [37] , [38] , [39] , [40] , [41] ], reversible-switching-based [ 42 ] and photobleaching-based nonlinearities [ 43 ]. Currently, these nonlinear effects have been applied to a wide range of applications, such as measuring tissue temperature [ 39 ], achieving super-resolution [ [36] , [37] , [38] , 42 , 43 ], discriminating between different absorbers [ 30 ], enhancing imaging contrast [ 37 ], enabling quantitative and functional imaging [ 24 , 34 , 44 ], and extracting important parameters such as absorption relaxation time [ 23 ].…”

Linear-array-based photoacoustic tomography for label-free high-throughput detection and quantification of circulating melanoma tumor cell clusters

“…By integrating optical excitation with acoustic detection, photoacoustic tomography (PAT) combines rich optical absorption contrasts with high ultrasonic spatial resolution at depths 12 . With 100% relative sensitivity to optical absorption, i.e., a given percentage change in the optical absorption yields the same percentage change in the photoacoustic signal, PAT achieves structural, functional, metabolic, and mechanical imaging of biological tissue [13][14][15][16][17] . Taking advantage of the strong optical absorption of melanin, photoacoustic techniques have been successfully used for imaging and sensing melanoma CTCs.…”

Label-free high-throughput detection and quantification of circulating melanoma tumor cell clusters by linear-array-based photoacoustic tomography

“…12 With 100% relative sensitivity to optical absorption, i.e., a given percentage change in the optical absorption yields the same percentage change in the photoacoustic signal, PAT achieves structural, functional, metabolic, and mechanical imaging of biological tissue. [13][14][15][16][17] Taking advantage of the strong optical absorption of melanin, photoacoustic techniques have been successfully used for imaging and sensing melanoma CTCs. Photoacoustic flowmetry successfully detected circulating melanoma cells in human blood.…”