(TIC) The cranial bone thermal index is an exposure model for the case that the ultrasound beam passes through bone near the beam entrance into the body.

(TI) The definition of the thermal index is the ratio of the total acoustic power to that required raising a maximum temperature increase of 1 °C under defined assumptions. A thermal index of 1 indicates the acoustic power achieving a temperature increase of 1 °C. A thermal index of 2 has the doubled power but would not necessarily indicate a peak temperature rise of 2 °C. The temperature rise is dependent on tissue type and is particularly dependent on the presence of bone.
Classifications of thermal indices:
For fetal ultrasound, the highest temperature increase would be expected occurring at bone. Therefore, TIB gives the worst-case conditions. If the ultrasound system can exceed an index of 1, the mechanical index and thermal index must be displayed. The displayed indices are based on the manufacturer's data.

See also Cranial Bone Thermal Index, Bone Thermal Index, Soft Tissue Thermal Index.

(TCCS) Transcranial color coded sonography is a combination of B-mode and pulsed wave Doppler. TCCS is used to study morphological and functional assessment of the circle of Willis, intracranial hemodynamics caused by extracranial artery stenosis, collateral flow and the vascular supply of intracranial lesion. Color imaging of the intracranial vessels allows placing the spectral Doppler volume correctly. This modality has encouraged the widespread use.
Contrast enhanced TCCS analysis of cerebral arteriovenous transit time (cTT) is used as a measure of cerebral microcirculation.
The windows that are used for transcranial Doppler examinations include regions where the skull bones are relatively thin or where naturally occurring gaps allow proper penetration of the sound beam.

See also A-Mode, Cranial Bone Thermal Index, Transcranial Doppler and Transcranial Window.

(TCD) Transcranial color Doppler sonography allows to evaluate the presence and flow direction of vessels as well as their relationships to surrounding structures.
A disadvantage of cerebrovascular ultrasonography is the attenuation of the ultrasound signal by the skull. The loss of power through the skull is considerable, the signal to noise ratio is poor and so contrast enhanced Doppler imaging is advantageous. The use of ultrasound contrast agents provides a diagnostic window of sufficient duration and imaging quality to improve an evaluation of the cerebral vessels. Contrast TCD also results in visualization of small arteries and veins and greater length of these vessels.

See also A-Mode, Cranial Bone Thermal Index, Transcranial Color Coded Sonography and Transcranial Window.