It is of interest also to refer to photothermal imaging (PTI), an imaging modality which is based on the same contrast mechanism as optical absorption, and which has been widely researched for the imaging of GNPs.13,28,29 While in PAM the optical absorption generates a pressure wave which is detected ultrasonically, in PTI the absorption generates local heating which changes the local refractive index, a change that can be detected optically using digital holography or OCT. The different detection mechanisms make it difficult to compare the methods’ performances quantitatively. However, there are a few important differences to note. First, PTI has the advantage of optical detection, which does not require a coupling medium, and for a dual-modality imaging system, the detection can be done using the same camera as for QPI. However, the ultrasonic detection of PAM, which is completely separated from the QPI detection, can be an advantage. It can allow for fully simultaneous imaging in both modalities, while in PTI, the photothermal image cannot be acquired at the same time as the QPI image if the same camera is used for both modalities. It is also important to note that the spatial resolution in PTI is defined by the heat diffusion and a lower excitation modulation frequency results in poorer spatial resolution but a higher SNR.13,29 On the other hand, in PAM, the resolution is defined only by the size of the excitation beam, which does not affect the SNR as long as the beam illuminates a spatially homogenous absorbing target.