Early Equipment

The ultrasonic reflectance technique A-mode was used for the evaluation of fat thickness of swine[1] in the late 1950s. The ultrasonic equipment used in the early studies was metal flaw detection systems. Ultrasonic waves at frequencies of 1 to 3 MHz were used to detect tissue interfaces as well as flaws in metal. This equipment was also used to evaluate beef and lambs. Clipping of hair at the examination site and the application of motor oil as a couplant was required because of the limited performance of the equipment available at that time.

Although the fat thickness was associated with a lot of the variation in composition, it soon became clear that the ability to measure lean depth and muscle area was required for increased accuracy. Subsequent studies[2] utilizing an improved technique were carried out on live market hogs and beef cattle. Depth readings of fat and muscle were made, starting at the backline and moving lateral at one-half-inch intervals and at recorded angles up to the lateral border of the rib eye muscle at specific desired rib locations on live hogs and cattle. These depth readings were then plotted on graph paper and the depths and muscle areas were plotted and measured.

The A-mode scanning, plotting, and measuring on several groups of market hogs and beef cattle[3] demonstrated that this technique offered good potential, but it required much time and effort and was not practical. This encouraged the next generation of technology. A continuous mechanical scanning procedure was developed, whereby a simulated B scan resulted from the movement of film across the signals originating from an A-mode unit in coordination with the movement of a single-element transducer on the animal. This technology was further developed and commercially marketed as the Scanogram in 1969. It was the primary ultrasonic system developed for evaluating animals that was marketed for the next decade. In order to produce a satisfactory image with the Scanogram, the animal had to remain still for approximately 10 seconds for a complete scan, and the film developed before the evaluation could be completed.

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