Diagnostic Ultrasound Principles

• Sound requires a medium to propagate through, such as water or soft tissue
• Sound consists of longitudinal vibrations
• Diagnostic Ultrasound ( Ultrasonography) use ultrasound-based diagnostic imaging to visualize subcutaneous tissue and examine body structures.
• Body structures examined: tendons, muscles, joints, vessels, internal organs
• Diagnostic ultrasound can detect acoustic energy reflected off tissues, producing 2D gray-scale images
• Variables in ultrasound production, detection, and treatment are controlled by the operator
• Ultrasound is greatly affected by the operator's skill and experience, for image acquisition and interpretation
• Ultrasound's advantages: no ionizing radiation, safer during pregnancy, real-time imaging

Ultrasound Features

• No ionizing radiation

• Safe in pregnancy

• No known side effects

• Inexpensive

• Portable

• Minimal patient preparation

• Painless

• Allows direct vision for biopsies

• Diagnostic images may be unobtainable due to patient size

• Ultrasound beams can't always navigate air-filled or bony areas; CT or MRI can be used instead.

• Roentgen introduced ionizing radiation (x-ray) in 1895 to visualize the body's interior

• The use of ultrasound became common in medical practice during the last decade of the twentieth century

• Ultrasound carries energy, like radiation, but needs matter to transfer energy

• Sound waves vibrate through material

Sound Frequency

• Defined as the rate of vibration of a sound source and the material it passes through

• Measured in hertz (Hz), where one hertz equals one vibration or cycle per second

• Pitch is a synonym for sound frequency

• Medical field uses high-frequency sound waves to examine the inside of the body

• Human adults can hear frequencies from 20 Hz to 20,000 Hz

• Frequencies higher than this limit, are called ultrasonic frequencies (Ultrasound)

• Diagnostic ultrasound uses frequencies between 2 MHz to 20 MHz, which is too high for human ears

• Ultrasound is focused into small, well-defined beams to probe the body, interacting with tissue structures to form images

• A small scanner called a transducer touches the patient's skin to produce an image

• The transducer has a crystal that vibrates, unlike a scanner using sound or echo

• The transducer (probe) is a small hand-held device that resembles a microphone, performing main functions

  • Producing/sending ultrasound pulses when electrical pulses are applied
  • Receiving echo waves when pressed against the skin
  • Converts those waves back into electrical pulses to be processed and to form the image

• Echo producing surfaces or tissue boundaries create bright white spots in the image

• Areas lacking reflecting surfaces within fluid, such as cysts appear as dark spots in the image

• An ultrasound image is sometimes is a Brightness modulation "B mode" image, which displays echo-producing sites within the anatomical area.

• Ultrasound devices can image the echoes produced by flowing blood and blood vessels

• The Doppler principle measures the direction and speed of blood cells moving through vessels

• A computer uses sounds to graph or constitute images, using colors to represent the flow.

Definition Ultrasound

• Physical Definition; Ultrasound (ultrasonic) is sound frequencies above 20 000 Hertz (Hz), which is beyond the range of human hearing and uses the term "ultrasonic."
• Medical Definition; Diagnostic Medical Ultrasound uses high-frequency sound to aid in the diagnosis and treatment of patients with the medical frequency ranges in medical ultrasound imaging are 2 - 15 MHz.

Properties of Ultrasound

• Sound acts as a pressure disturbance (vibration) that transmits through gases, liquids, solids, and plasma as mechanical pressure waves.
• Kinetic energy is carried through a medium and sound will not travel through a vacuum
• Ultrasound and sound waves propagate through fluid as longitudinal waves
• Ultrasound waves propagate through hard tissues like bone, as both longitudinal (compression) and transverse (shear) waves.
  • Particles move perpendicularly to the direction of propagation in the latter case.

Explore the fundamental principles of diagnostic ultrasound. This includes wave types, propagation requirements, and advantages over other imaging techniques. Also covered are safety aspects and limitations.