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INTRODUCTION

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Lazzaro Spallanzani is credited with the initial discovery of ultrasound (US) navigation by bats in 1790. But it was Pierre Curie’s invention of the US-generating piezoelectric crystal that heralded further development of US technology. Following its utilization in medical imaging and guidance, US imaging has seen tremendous progress in its applications and technology in the last 5 decades. Recent years have seen a surge in the use of US for diagnosis and therapeutic interventions in regional anesthesia. US is now making progress in the field of pain medicine because of its utility both in the diagnosis of several nerve, muscle, and joint pathologies and for the ability to see the target and the needle for injection of therapeutic substances (Table 3-1).

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TABLE 3-1.Advantages of Ultrasound Guidance
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Following its initial use in regional anesthesia, US was quickly adopted for a variety of pain medicine interventions (Table 3-2). Many feasibility studies have been published that attest to its safety and convenience. Studies have also documented elimination of radiation exposure secondary to the use of US imaging for pain medicine interventions.

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TABLE 3-2.List of Common Procedures Performed in Pain Medicine Where US Guidance is Utilized
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BASIC PHYSICS OF ULTRASOUND

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  • Sound waves at frequencies greater than 20 kHz are called US.

  • Medical US uses frequencies in the range of 2 to 20 MHz.

  • When an electrical current is passed through piezoelectric crystals, they vibrate and produce ultrasound waves.

  • The US waves travel through tissues at a velocity that depends on the tissue with an average velocity of 1540 m/s assumed for all biologic tissues.

  • This velocity is utilized to calculate the depth (the time from pulse generation to detection times half the velocity).

  • The distance from one crest of the waveform to the next is the wavelength.

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Attenuation

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  • As the waves travel through tissues, there is a loss in intensity or attenuation. This is due to the wave-induced motion of the tissues, absorption, reflection, and scattering. Attenuation is directly proportional to the frequency and the length of the path. This is described ...

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