Acoustocerebrography (ACG) is a

medical test A medical test is a medical procedure performed to detect, diagnose, or monitor diseases, disease processes, susceptibility, or to determine a course of treatment. Medical tests such as, physical and visual exams, diagnostic imaging, genetic ...

used to

diagnose Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different disciplines, with variations in the use of logic, analytics, and experience, to determine "cause and effect". In systems enginee ...

changes and

problems A problem is a difficulty which may be resolved by problem solving. Problem(s) or The Problem may also refer to: People * Problem (rapper), (born 1985) American rapper Books * ''Problems'' (Aristotle), an Aristotelian (or pseudo-Aristotelian) co ...

in the

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

and the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

. It allows for the noninvasive examination of the brain's cellular and

molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

structure. It can also be applied as a means to diagnose and monitor

intracranial pressure Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury ( mmHg) and at rest, is normally 7–15 mmHg for a supine adul ...

, for example as incorporated into continuous brain

monitoring Monitoring may refer to: Science and technology Biology and healthcare * Monitoring (medicine), the observation of a disease, condition or one or several medical parameters over time * Baby monitoring * Biomonitoring, of toxic chemical compounds, ...

devices. ACG uses molecular

acoustics Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acousticia ...

, in audible and

ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies ...

frequency ranges, to monitor changes. It may use

microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publ ...

accelerometer An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acce ...

s, and multifrequency

ultrasonic transducer Ultrasonic transducers and ultrasonic sensors are devices that generate or sense ultrasound energy. They can be divided into three broad categories: transmitters, receivers and transceivers. Transmitters convert electrical signals into ultrasoun ...

s. It does not use any

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

and is completely free of any side effects. ACG also facilitates

blood flow Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously m ...

analysis as well as the detection of obstructions in cerebral blood flow (from cerebral

embolism An embolism is the lodging of an embolus, a blockage-causing piece of material, inside a blood vessel. The embolus may be a blood clot (thrombus), a fat globule (fat embolism), a bubble of air or other gas ( gas embolism), amniotic fluid (am ...

) or bleeding (from

cerebral hemorrhage Intracerebral hemorrhage (ICH), also known as cerebral bleed, intraparenchymal bleed, and hemorrhagic stroke, or haemorrhagic stroke, is a sudden bleeding into the tissues of the brain, into its ventricles, or into both. It is one kind of bleed ...

Passive and active acoustocerebrography

Passive acoustocerebrography

All brain tissue is influenced by blood circulating in the brain's vascular system. With each heartbeat, blood circulates in the skull, following a recurring pattern according to the oscillation produced. This oscillation's effect, in turn, depends on the brain's size, form, structure and its vascular system. Thus, every heartbeat stimulates minuscule motion in the brain tissue as well as

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the ...

and therefore produces minimal changes in intracranial pressure. These changes can be monitored and measured in the skull. Today, mostly passive sensors like accelerometers are used to identify these signals correctly. Sometimes highly sensitive microphones are utilized. With a digital signal, it becomes possible to study the patterns of the blood flow moving inside the skull. These patterns form unique signatures that can be analyzed with specially designed algorithms, identifying them either as an inconspicuous, “normal” pattern or as a pattern showing an “abnormal” behavior.

Active acoustocerebrography

In active ACG applications, a multi-frequency ultrasonic signal is used to detect and classify adverse changes at the cellular or molecular level.On ultrasound classification of stroke risk factors from randomly chosen respondents using non-invasive multispectral ultrasonic brain measurements and adaptive profiles
Wrobel et al. (2015) In addition to all of the advantages that passive ACG provides, with active ACG it is possible to conduct a spectral analysis of the acoustic signals received. These spectrum analyses not only display changes in the brain's vascular system, but also those in its cellular and molecular structures. One common application of active ACG is the

Transcranial Doppler Transcranial Doppler (TCD) and transcranial color Doppler (TCCD) are types of Doppler ultrasonography that measure the velocity of blood flow through the brain's blood vessels by measuring the echoes of ultrasound waves moving transcranially ...

test. More recently, its color version (TCCD) has been deployed. These ultrasonic procedures measure blood flow velocity within the brain's blood vessels. They are used to diagnose

embolisms An embolism is the lodging of an embolus, a blockage-causing piece of material, inside a blood vessel. The embolus may be a blood clot (thrombus), a fat globule (fat embolism), a bubble of air or other gas (gas embolism), amniotic fluid (amniot ...

, stenoses and vascular constrictions, for example, in the aftermath of a

subarachnoid hemorrhage Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. Symptoms may include a severe headache of rapid onset, vomiting, decreased level of cons ...

Fields of application

In contrast with applications that provide only momentary images, such as

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...

and CT, the results of ACG procedures can be obtained continuously, thus facilitating effortless and non-invasive real-time monitoring. This can be especially helpful during the acute phase directly after a stroke or a traumatic brain injury. The measured data is mathematically processed continuously and displayed on a monitoring device. The computer-aided analysis of the signals enables the physician/nursing staff to precisely interpret the results immediately after device setup. Furthermore, ACG allows for preventive detection of pathological changes in brain tissue.

References

{{reflist Neuroscience