Some observations on the practical uses of A-mode ultrasound.

D URING the past decade there has been an increasing recognition and acceptance of the value and capabilities of diagnostic ultrasonography as an important addition to the armamentarium of medical diagnostic procedures. Echoen-cephalography for the determination of the position of the diencephalic midline brain structures has an established position as a favorable standard procedure in many hospitals and medical centers.2 Echocardi-ography for the evaluation of cardiac val-vular disease and for pericardial effusion also occupies a respected position.4 " In the United States initial interest in diagnostic ultrasound has been concentrated on the uses of A-mode ultrasonic techniques;'4 however, many of the more recent investigations have been devoted to the application of the more complicated and complex two-dimension B-scan ultra-sonic displays and 9,10,12 Recently, there has been a renewed interest in the simpler and less complex procedure of A-mode studies and their use as applied to a variety of diagnostic applications. It is the purpose of this presentation to discuss further some of our experiences in the use of A-mode ultrasonography as applied to echo fetal cephalometry, echo-aortography and echodifferentiation of masses as to their cystic or solid nature. Additional observations have been made since our previous publications on these subjects3'' '6'7 " 3 and will be presented. In the A-mode presentation the reflected ultrasound or echoes are displayed on the face of the oscilloscopic screen as vertical deflections on a time base horizontal trace. The stronger the echo, the greater will be the deflection. The strength of the echo will vary depending upon the nature of the acoustic interface (reflecting surface) encountered by the ultrasonic beam. Thus, an interface composed of substances of marked acoustic mismatch (acoustic impedance), such as a tissue-air interface, will produce almost complete reflection and the st-ron-gest echo, while a solid-to-solid interface of tissues having only slight-differential acoustic mismatch will produce a comparatively weak echo. The distance of the vertical deflections (echoes) on the time base trace is a measure of the time between transmission of the ultrasonic pulse and the reception of the echoes. With a knowledge of the ye-locity of ultrasound in tissues, the distance between echoes may be calibrated in cent-i-meters on the oscilloscopic trace. Hence, a measurement-of a mass or structure having boundary reflecting interfaces is accom-pushed. Using these principles, A-mode techniques are capable of measuring the dimension and diameters of a number of organs, structures and masses. Since, as previously mentioned, …