Non-invasive Parenchymal, Vascular and Metabolic High-frequency Ultrasound and Photoacoustic Rat Deep Brain Imaging

Abstract

Photoacoustics and high frequency ultrasound stands out as powerful tools for neurobiological applications enabling high-resolution imaging on the central nervous system of small animals. However, transdermal and transcranial neuroimaging is frequently affected by low sensitivity, image aberrations and loss of space resolution, requiring scalp or even skull removal before imaging. To overcome this challenge, a new protocol is presented to gain significant insights in brain hemodynamics by photoacoustic and high-frequency ultrasounds imaging with the animal skin and skull intact. The procedure relies on the passage of ultrasound (US) waves and laser directly through the fissures that are naturally present on the animal cranium. By juxtaposing the imaging transducer device exactly in correspondence to these selected areas where the skull has a reduced thickness or is totally absent, one can acquire high quality deep images and explore internal brain regions that are usually difficult to anatomically or functionally describe without an invasive approach. By applying this experimental procedure, significant data can be collected in both sonic and optoacoustic modalities, enabling to image the parenchymal and the vascular anatomy far below the head surface. Deep brain features such as parenchymal convolutions and fissures separating the lobes were clearly visible. Moreover, the configuration of large and small blood vessels was imaged at several millimeters of depth, and precise information were collected about blood fluxes, vascular stream velocities and the hemoglobin chemical state. This repertoire of data could be crucial in several research contests, ranging from brain vascular disease studies to experimental techniques involving the systemic administration of exogenous chemicals or other objects endowed with imaging contrast enhancement properties. In conclusion, thanks to the presented protocol, the US and PA techniques become an attractive noninvasive performance-competitive means for cortical and internal brain imaging, retaining a significant potential in many neurologic fields.

Non‐invasive three‐dimensional power Doppler imaging for the assessment of acute cerebral blood flow alteration in a mouse model of subarachnoid haemorrhage

“…There are some limitations to our study. Measurements of volumetric/flow signal parameters based on 3D power Doppler analysis are dependent on gain settings and attenuation at acquisition, [19][20][21][22] and there are contradictory reports regarding their reproducibility because of differences in machine settings, calculation of region/ volume of interest, data acquisition time, and analysis. 19 To minimize these obstacles, we attempted to keep the acquisition and F I G U R E 1 Serial changes in %vascularity in the whole brain after murine SAH.…”

“…17 Figure S1a). 10,11,21 A 3D reconstructed vascularity of the flow signals was then acquired with the power Doppler mode ( Figure S1b) to calculate %vascularity 22 within the scanned brain volume (step size of 0.2 mm for ±15 coronal slices from the level of basal ganglia; scan time: 7 minutes 21 seconds) using an offline analysis software. Reference CBF was measured using a laser Doppler probe, and the values were normalized relative to baseline for each animal.…”

The Role of Ultrasound as a Diagnostic and Therapeutic Tool in Experimental Animal Models of Stroke: A Review

“…Moreover, imaging ultrasound was also applied in an animal model of ICH using 13–14 MHz transcranial Doppler ultrasonography and did not report secondary hemorrhages [ 37 ]. Other studies examined the brain’s blood flow and anatomical structures in healthy animals using a 13 MHz linear transcranial transducer [ 61 ] and 16 MHz transducer [ 62 ]. Considering these studies, the range of 12–16 MHz frequencies to be safe for imaging in the animal brain.…”

Real-Time Noninvasive Bioluminescence, Ultrasound and Photoacoustic Imaging in NFκB-RE-Luc Transgenic Mice Reveal Glia Maturation Factor-Mediated Immediate and Sustained Spatio-Temporal Activation of NFκB Signaling Post-Traumatic Brain Injury in a Gender-Specific Manner

“…High-resolution real-time noninvasive PAI was performed 24 hours and 72 hours post TBI using the Vevo LAZR photoacoustic imaging system (Fujifilm, Visualsonics Inc, Canada). The detailed protocols are described in the Vevo LAZR photoacoustic imaging system manual as well as were adapted and modified from another study describing ultrasound and photoacoustic rat deep brain imaging (Giustetto et al 2015). The mice were anesthetized using 2.5% isoflurane with oxygen level set to 0.5-1L/minute for anesthesia induction and secured to a heating pad to maintain thermoregulation.…”