These modes of medical imaging conduct a spectral analysis of the acoustic signals they receive and can therefore be classified as methods of active acoustocerebrography.

[1] The equipment used for these tests is becoming increasingly portable, making it possible for a clinician to travel to a hospital, to a doctor's office, or to a nursing home for both inpatient and outpatient studies.

The second method of recording uses only the second probe function, relying instead on the training and experience of the clinician in finding the correct vessels.

[citation needed] The ultrasound probe emits a high-frequency sound wave (usually a multiple of 2 MHz) that bounces off various substances in the body.

Because the bones of the skull block most of the transmission of ultrasound, regions with thinner walls (called insonation windows), which offer the least distortion to the sound waves, must be used for analyzing.

Patient age, sex, race, and other factors affect bone thickness and porosity, making some examinations more difficult or even impossible.

Various drugs (e.g. aspirin, streptokinase, and tissue plasminogen activator (TPA) in ascending order of effectiveness and cost)[4][5][6] can reverse the stroke process.

[7] Battery-powered, it would use an RF link to a portable computer running a spectral analysis routine together with input from an oximeter (monitoring the degree of blood oxygenation, which a stroke might impair) to make the automatic decision to administer the drug.

[citation needed] Functional transcranial Doppler sonography (fTCD) is a neuroimaging tool for measuring cerebral blood flow velocity changes due to neural activation during cognitive tasks.

[8] Functional TCD uses pulse-wave Doppler technology to record blood flow velocities in the anterior, middle, and posterior cerebral arteries.

Similar to other neuroimaging techniques such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), fTCD is based on a close coupling between regional cerebral blood flow changes and neural activation.

Due to a continuous monitoring of blood flow velocity, TCD offers better temporal resolution than fMRI and PET.

Since its introduction the technique has contributed substantially to the elucidation of the hemispheric organization of cognitive, motor, and sensory functions in adults and children.

[16] Moreover, most established neuroanatomical substrates for brain function are perfused by the major cerebral arteries that could be directly insonated.

To accomplish this objective, one method is to apply Fourier analysis to the periodic time series of MFV acquired during cognitive stimulations.

Fourier analysis would yield peaks representing pulsatile energy from reflection sites at various harmonics, which are multiples of the fundamental frequency.

The probe holder headgear (e.g. LAM-RAK, DWL, Sipplingen, Germany) are used with a base support on two earplugs and on the nasal ridge.

The distance approximates the visible arterial length from the main stem of the MCA, through vascular tortuosity and around the cerebral convexity, to the end vessels at distal cortical sites such as the occipito-temporal junction on carotid angiograms of adults.

Fast Fourier transform calculations are used to obtain the spectral density and cross amplitude plots in the left and right middle cerebral arteries.