Chapter 3: History, current and future of Sono applications

Sound

A form of energy produced when a vibrating source causes molecules within a medium to move back and forth; the back-and-forth motion allows waves of sound energy to travel; the human body is made of different mediums that allow sound to propagate

Boethius

Identified the pebble theory, which visualizes sound waves traveling like the waves created by a pebble dropped in water

Robert Boyle

Recognized there must be a medium through which sound can travel in order for it to propagate; his research laid the groundwork for the use of coupling gel

Abbe Lazzaro Spallanzani

“Father of ultrasound”; Studied how bats use sound waves to detect their victims and to guide their flight and by recalling this, we can recognize how the ultrasound transmitter utilizes the pulse-echo technique

Christian Johann Doppler

Discovered that the pitch of a sound wave varies if the source of the sound was moving (Doppler effect) (when a firetruck is driving closer the siren gets louder)

The Currie brothers

Recognized the piezoelectric effect which is the process whereby a material, such as a crystal or element within an ultrasound transducer, generates electricity and changes shape with application of pressure; the crystals in the transducer produce ultrasound waves

History of Sonography

During World War I, ultrasound was used to detect submarines which led to the development of sonar technology; sound was sent through the water, bounced off an object, and then returned to the source; Floyd Firestone used this to develop and use the reflectoscope, which used ultrasound to detect flaws in metal which was the technique first used in medicine.

The first application of ultrasound in medical diagnosis was in 1941. Karl Dussik used it to image the lateral ventricles in the brain and as research progressed, scientists realized the ultrasound waves returned to the transducer and may be able to form an image.

Efforts to use the pulse-echo technique were first made in the late 1940s and early 1950s; one early attempt demonstrated reflections from a gallstone and another by a Swedish cardiologist borrowed a sonar device from a shipyard and recorded echoes from his own heart

Pulse-Echo Effect/Technique

sought to exploit reflected sound back from within the body to create an image; sound must be pulsed or allowed to be alternated rapidly on and off so the transducer can listen for the echo; upon hearing the echo, the machine calculates distance and presents the reflector’s location on the monitor.

B-Mode Imaging (brightness mode)

Displays the returning ultrasound signal as a dot on the monitor; the dots has varying degrees of brightness, based on the strength of the retuning echo; the stronger the retuning echo, the brighter the dot, also referred to as grayscale sonography

M-Mode Scanning (motion mode)

Documents the movement of structures in the body along a single scan line; y-axis shows depth and x-axis shows time; used in echocardiography as a critical part of standard protocols

We will use for 1st, 2nd, and 3rd, trimester and fetal heartrate scanning

Doppler Technology

Robert Rushmer and his colleagues established the varying uses of continuous-wave (CW) Doppler and spectral analysis in 1963; CW transducers combine an element continuously sending waves with one that continuously listens for the return signal; in the 1970s, there were several advancements, including: pulsed-wave Doppler, duplex imaging which is a handheld duplex pulsed system, and advancements in color Doppler imaging and instrumentation (the combination of B-mode, spectral, and color Doppler is called triplex imaging)

Color vs Power Doppler

Color: will show velocity or speed and direction of blood flow

Power: only shows the presence of flow but not direction or velocity

Harmonic Imaging

Additional frequencies, other than the transmitted frequency sent into the body, that are generated by differing human body tissues; collected by the transducer and used to create a crisper, higher-resolution image

3D and 4D Technology

3D allows one to see the width, height, and depth of images.

• It is useful in obstetrics for clear visualization of the form of the fetal

face.

• Also used in breast, vascular, gynecologic, and abdominal

sonographic imaging.

• The images are made of two 2D images placed next to each other

and reconstructed by a computer into a 3D format.