ultrasound

• The development of sonar (Sound Navigation and Ranging) 

  • precursor to medical ultrasound.

   Sonar equipment was initially constructed for the defense effort during World War II to detect the presence of submarines. Various investigators later proved that ultrasound had a valid contribution to make in medicine.
• B-Mode Ultrasound - Also known as two-dimensional or gray scale ultrasound, this technique creates cross-sectional images using reflected sound waves. B-mode scans are commonly used to visualize internal organs such as the heart, liver, kidneys, and uterus.
• A-Mode Ultrasound - The earliest form of ultrasound imaging, it uses sound waves to create images by measuring the time delay between when a pulse is sent and when it returns from tissue boundaries. It produces a single line image on a screen called an "echo trace".
• (1947) Karl Theodore Dussick 

  • positioned two transducers on opposite sides of the head to measure ultrasound transmission profile. 
  • He also discovered that tumors and other intracranial lesions could be detected by this technique. 

  Initial clinical applications monitored changes in the propagation of pulses through the brain to detect intracerebral hematoma and brain tumors based on the displacement of the midline.
• • In the early 

  (1950s) Dussick, with Heuter, Bolt, and Ballantyne,

  •  continued to  use through transmission techniques and computer analysis to diagnose brain lesions in the intact skull. 
  • However, they discontinued their studies after concluding that the technique was too complicated for routine clinical use.
• late 1940s Douglas Howry

   (a radiologist), John Wild (a diagnostician interested in tissue characterization), and  George Ludwig (interested in reflections from gallstones)

  independently demonstrated that when ultrasound waves generated by a piezoelectric crystal transducer were transmitted into the human body, these waves would be returned to the transducer from tissue interface of different acoustic impedances. 

   At this time, research efforts were directed toward transforming naval sonar equipment into clinically useful diagnostic tool.
• In 1948 Howry developed the 

  • first ultrasound scanner, consisting of a cattle watering tank with a wooden rail anchored along the side. 
  • The transducer carriage moved along the rail in a horizontal plane, while the object to be scanned and the transducer werepositioned inside the water tank. 
• (1954) Hertz and Edler 

  • Echocardiographic techniques were developed  
  • Sweden. 

  These investigators were able to distinguish normal heart valve motion from the thickened, calcified valve motion seen in patients with rheumatic heart disease.
• (1957) Tom Brown and Ian Donald in Scotland

  • an early obstetric contact-compound scanner was built by Tom Brown and Ian Donald in Scotland. 
  • This scanner was used primarily to evaluate the location of the placenta and to determine the gestational age of the fetus. 

  Further developments have resulted in the real-time ultrasound instrumentation used in hospitals and clinics today. High frequency transducers with improved resolution now allow the sonographer to accumulate several images per second at a rate of up to 30 frames per second. 
• • Diagnostic ultrasound as used in clinical medicine has not been associated with any harmful biologic effects and is generally accepted as a safe modality. 

  Ultrasound rapidly progressed through the 1960s from simple 

  • "A-mode" scans to
  • "B-mode" applications and compound 

  "B-scan" images using analog electronics. Advances in equipment design, data acquisition techniques, and data processing capabilities have led to electronic transducer arrays, digital electronics, and real time image display.