In this paper, we demonstrate the first PACT of human brain function 13. Nevertheless, human brain PACT has not yet been achieved. PACT has been successfully demonstrated in angiology, oncology, gastroenterology, cardiology, and neurology 12.
Their distinct spectral signatures allow quantification of their concentrations, convertible to total hemoglobin (HbT) concentration and oxygen saturation (sO 2). In contrast to BOLD fMRI, PACT is directly sensitive to deoxyhemoglobin (HbR) and oxyhemoglobin (HbO 2) 11. Photoacoustic (PA) computed tomography (PACT) is a hybrid imaging tool that reconstructs molecular-specific light absorption distribution through irradiating tissues with a non-ionizing diffused laser pulse and recording the photoacoustically induced ultrasonic waves.
Although functional ultrasound can image human neonatal brains through the fontanelles, it is insensitive to blood flows parallel to the probe surface 10. Electroencephalography, magnetoencephalogram, and functional near-infrared spectroscopy provide high temporal resolution but suffer poor spatial resolution 8, 9. Alternatively, positron emission tomography images brain function by measuring metabolic process changes but requires radioactive tracers and lacks high spatiotemporal resolution 7. In general, MRI is contraindicated in patients with ferromagnetic implants or claustrophobia and can be painful to tolerate due to the loud noise 5, 6. A state-of-the-art 7 Tesla MRI system can provide sub-millimeter/sub-second spatiotemporal resolution but is hugely bulky and costly 3, 4. Blood-oxygen-level-dependent (BOLD) imaging, the primary form of functional magnetic resonance imaging (fMRI), is currently the mainstay and gold standard for functional human brain imaging 1, 2. With over 100 billion neurons and 100 trillion connections, the brain remains one of the greatest mysteries in the human body.
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