Quantitative echography — The basis of tissue differentiation

Abstract

Abstract Quantitative echography performed with a simple but optimally designed and standardized commercial A‐scan instrument has become the basis of acoustic tissue differentiation in the examination of the eye, orbit and periorbital region. The reflectivity of a lesion is determined by comparing the signal intensities obtained from the lesion with „standard”︁ signals. Two types of quantitative echography are applied: In Type I identical system sensitivities are used to display and compare the signal intensities from an unknown lesion and from known standards. If a high defined, comparable system sensitivity and a standardized A‐scan unit are used, the display of the standard pattern is not necessary; it is then sufficient to measure the height of the lesion spikes and to determine its percentage of the display height. With Type I quantitative echography mass lesions such as tumors can be classified into five groups. Type I quantitative echography requires a special design of the A‐scan instrument used (e.g., S‐shaped amplifier characteristics, dynamic range of 36 dB, calibration of system sensitivity in dB). In Type II quantitative echography identical intensities of both abnormal and “standard” signals are displayed by adjusting the system sensitivity at the proper levels. The difference between the two sensitivity settings indicates the reflectivity of the lesion. Type II quantitative echography is used for the evaluation of single surfaces (e.g., the surface of a tumor). This type of quantitative echography requires an A‐scan instrument with a sensitivity control which is calibrated in dB and can be adjusted continuously. This technique can be applied in any other region of the human body as well if high‐frequency ultrasound (frequencies above 6m Hz) can be used.