In sharp contrast to the potentially mutagenic radiation emitted by x-ray based scanning devices, ultrasound has a long-standing reputation of being extremely safe – to the extent that it has even been trusted with imaging the delicate structures of the developing foetus. The surprising truth about this medical scanning modality so commonly associated with growth and new life, is that it was developed in response to a tragic mass death.
In the aftermath of the sinking of the Titanic, physicist Paul Langevin invented the world’s first transducer, the hydrophone – a scanning device which could detect hidden threats in the depths of the sea. Inspired by Langevin’s innovation, in 1942, neurologist Karl Dussik designed an ultrasound transducer capable of detecting hidden threats of tumours lurking in the depths of the brain. From that moment onwards, the field of medical ultrasound scanning blossomed.
The 1970s saw major advances in ultrasound technology which made it possible to view the organic structures of the human body as they truly are – dynamic, changing forms that can only be fully understood through their movement.
Doppler Ultrasound
The Doppler ultrasound was one of the first medical scanning devices designed to monitor the flow and velocity of blood. The transducer emits a series of pulses at the blood vessel; whilst the echoes received from stationary tissue are identical from pulse to pulse, the time taken for the echoes to return from the blood vary slightly with each ultrasound pulse. The resulting Doppler frequency is observed and can be used to calculate the blood velocity with the following equation
Blood velocity abnormalities can indicate the presence of blockages, including blood clots and vascular tumours, radically improving diagnosis of a range of conditions from deep vein thrombosis to atherosclerosis.
Ultrasound Needle
Most recent developments in ultrasound technology have been focused on designing portable devices perfectly suited to niche, yet critical, situations. An all-optical ultrasound transducer, which can be fitted into the tip of a needle, has recently proven successful in a preclinical swine study by researchers at University College London and Queen Mary University of London.
Currently, during keyhole procedures, surgeons are forced to rely on external ultrasound probes and pre-operative scans to visualise soft tissues and structures. This minimally invasive ultrasound device images tissue in real time to assist in surgery.
The compactness of the ultrasound transducer is crucial for its use in keyhole surgery. Instead of a bulky electronic transducer, the ultrasound needle uses an all-optical transducer which exploits the photoacoustic effect (in which ultrasound waves are formed when light is absorbed). The tip of the needle consists of two 300μm optical fibres. The transducer optical fibre is coated in a multiwalled carbon nanotube polydimethylsiloxane composite capable of absorbing laser light and generating ultrasound pulses. These pulses are reflected off the tissue and detected by the receiver optical fibre which converts the ultrasound echoes back into light.
The figures quoted in this essay have been meticulously researched and documented. Below is the bibliography for this section of my essay:
Constantin, Chilowsky, and Paul Langevin. Production of submarine signals and the location of submarine objects. US 1471547 A, United States Patent and Trademark Office, 19 May 1917. [Last Accessed: 05 Feb 2019]
Deane, Collin. “Doppler Ultrasound: principles and practice.” Doppler in Obstetrics, ISUOG Educational Committee, [Last Accessed: 16 Feb 2019] https://sonoworld.com/client/fetus/html/doppler/capitulos-html/chapter_01.htm
Freeman, Tami. “Medical innovations: All-in-one imaging.” physicsworld: Focus On
Biomedical Physics. June 2018: 6. Print. [Last Accessed: 18 Feb 2019]
Finlay, Malcom et al. “Through-needle all-optical ultrasound imaging in vivo: a preclinical swine study.” Light: Science & Applications (2017) Nature. Web. [Last Accessed: 19 Feb 2019]
Image Credits:
Deane, Colin. Diagram of Doppler ultrasound. Doppler in Obstetrics, ISUOG
Educational Committee, 2002. Web.
https://sonoworld.com/client/fetus/html/doppler/capitulos-html/chapter_01.htm#fig02
Finlay, Malcom et al. Schematic and inset photo of sharp inner needle. Light: Science
& Applications, Nature, 01 December 2017. Web. nature.com/articles/lsa2017103.pdf
Curiosity Killed The Cation 