ultrasound and visible light

• source and detector of ultrasound: transducer
• high-frequency sound waves produced by a transducer made of a piezoelectric crysta
• piezoelectric crystal : produces echoes and receives echoes coming back from the patient
• The source transducer also functions as a receiver of reflected sound (echoes) and converts the signal into an electric current, which is subsequently processed into a grayscale image
• sound waves travel through the body, are affected by the different types of tissues encountered and reflected back
• a moving image is obtained as the transducer is passed across the body
• ultrasound has relatively low cost
• ultrasound has non-ionizing energy source and safe; can scan in any plane
• equipment in ultrasound is portable and can be used for bedside imaging
• ultrasound is particularly useful for monitoring pregnancy, imaging the neonatal brain, visualizing the uterus, ovaries, liver, gallbladder, pancreas, and kidneys
• ultrasound is also useful for confirming pleural effusions and masses
• ultrasound is useful for assessing the thyroid, testes, and soft-tissue lesions
• ultrasound is operator-dependent
• ultrasound has poor visualization of structures underlying bone or air
• Scattering of sound through fat yields poor images in obese patients
• visible light is non-invasive but has limited ability to penetrate tissues deeply like the energies used in radiological imaging.
• Visible light imaging is used in light microscopy for pathological diagnosis, hematology, dermatology to photograph the skin, gastroenterology (colonoscopy/endoscopy), ophthalmology to image the retina, and during surgical procedures.