How To Detect Chronic Heel Pain With Musculoskeletal Ultrasound

By John Tassone Jr., DPM

How Does The Ultrasound Machine Work?

    The transducer or probe has a dual function. As the transmitter produces electrical energy, this energy is sent to the transducer. This signal changes the shape of the piezoelectric crystals housed in the transducer. These crystals produce a mechanical energy (sound waves) that subsequently emits into the body. This same probe also takes the returning echoes and converts them back to electrical energy, which will then form the image on screen. It should come as no surprise that this probe is usually at least one-fifth the price of the whole unit.     As mentioned above, the probe size will affect the quality of the sound wave. A smaller probe can lessen the detail of the image. This is obviously important when dealing with small anatomic structures in the foot. The acoustic window is simply the amount of tissue that one can scan at one time. It directly correlates to the size of the probe.     Some clinicians utilize a standoff pad with the probe. A standoff pad is a flexible attachment that one can fasten to the end of the probe. This converts an inflexible stiff probe into a flexible one. This will allow the probe to conform around curved surfaces (i.e. malleoli). Also, probing near field tissue can produce reverberations (static) that hinder imaging. Utilization of the pad can help reduce this. One sees this static more in lower frequency probes and thus the higher quality ultrasound does not need these pads as much. Cutaneous imaging may improve with utilization of a standoff pad.     The sound waves that travel deeper will be more attenuated than those that encounter superficial tissue. Tissue gain compensation (TGC) is a control that can increase the intensity of those attenuated waves. This feature can be automated in the newer units. The gain is a control that either increases or decreases the intensity of the returning echoes. It is a control that is frequently employed while imaging. Higher quality units will also have a separate contrast control.

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