Editing Medical ultrasound (section)

==Types<span class="anchor" id="Modes"></span>==
The imaging mode refers to probe and machine settings that result in specific dimensions of the ultrasound image.<ref>{{cite book | vauthors=Postema M | title=Fundamentals of Medical Ultrasonics | doi=10.1201/9781482266641 | publisher=CRC Press | location=London | year=2011 | isbn=9780429176487| url=https://hal.science/hal-03192439 }}</ref>
Several modes of ultrasound are used in medical imaging:<ref>The Gale Encyclopedia of Medicine, 2nd Edition, Vol. 1 A-B. p. 4</ref><ref name="Cobbold 422">{{cite book|author=Cobbold, Richard S. C. |title=Foundations of Biomedical Ultrasound|url=https://books.google.com/books?id=Hwb5D60vb5IC&pg=PA422|year=2007|publisher=Oxford University Press|isbn=978-0-19-516831-0|pages=422–423}}</ref>
* '''A-mode''': Amplitude mode refers to the mode in which the amplitude of the [[transducer]] voltage is recorded as a function of two-way travel time of an ultrasound pulse. A single pulse is transmitted through the body and scatters back to the same transducer element. The voltage amplitudes recorded correlate linearly to acoustic pressure amplitudes. A-mode is one-dimensional.
* '''B-mode''': In brightness mode, an array of transducer elements scans a plane through the body resulting in a two-dimensional image. Each pixel value of the image correlates to voltage amplitude registered from the backscattered signal. The dimensions of B-mode images are voltage as a function of angle and two-way time.
* '''M-mode''': In motion mode, A-mode pulses are emitted in succession. The backscattered signal is converted to lines of bright pixels, whose brightness linearly correlates to backscattered voltage amplitudes. Each next line is plotted adjacent to the previous, resulting in an image that looks like a B-mode image. The M-mode image dimensions are however voltage as a function of two-way time and recording time. This mode is an ultrasound analogy to streak [[video]] recording in high-speed photography. As moving tissue transitions produce backscattering, this can be used to determine the displacement of specific organ structures, most commonly the heart.

Most machines convert two-way time to imaging depth using as assumed speed of sound of 1540&nbsp;m/s. As the actual speed of sound varies greatly in different tissue types, an [[ultrasound]] image is therefore not a true tomographic representation of the body.<ref>{{cite book|vauthors=Postema M, Kotopoulis S, Jenderka KV|chapter=Physical principles of medical ultrasound|edition=2nd|publisher=EFSUMB|location=London|year=2019|pages=1–23|editor=Dietrich CF|title=EFSUMB Course Book|doi=10.37713/ECB01|s2cid=216415694 |url=https://hal.archives-ouvertes.fr/hal-03191256/file/2019EFSUMB2.pdf }}</ref>

Three-dimensional imaging is done by combining B-mode images, using dedicated rotating or stationary probes. This has also been referred to as '''C-mode'''.<ref name="Cobbold 422"/>

An imaging technique refers to a method of signal generation and processing that results in a specific application.
Most imaging techniques are operating in B-mode.
* '''[[Doppler ultrasonography|Doppler sonography]]''': This imaging technique makes use of the [[Doppler effect]] in detection and measuring moving targets, typically blood.
* '''Harmonic imaging''': backscattered signal from tissue is filtered to comprise only frequency content of at least twice the centre frequency of the transmitted ultrasound. Harmonic imaging used for perfusion detection when using ultrasound [[contrast agents]] and for the detection of tissue harmonics. Common pulse schemes for the creation of harmonic response without the need of real-time [[Fourier analysis]] are pulse inversion and power modulation.<ref name="Starkoff 2014"/>

[[File:B-flow ultrasonography of venous reflux.jpg|thumb|B-flow image of [[chronic venous insufficiency|venous reflux]]. {{noprint|[[:File:B-flow ultrasonography of venous reflux.gif|Video is available]].}}]]
*'''B-flow''' is an imaging technique that digitally highlights moving reflectors (mainly [[red blood cell]]s) while suppressing the signals from the surrounding stationary tissue. It aims to visualize flowing blood and surrounding stationary tissues simultaneously.<ref name="WangChou2005">{{cite journal |last1=Wang |first1=Hsin-Kai |last2=Chou |first2=Yi-Hong |last3=Chiou |first3=Hong-Jen |last4=Chiou |first4=See-Ying |last5=Chang |first5=Cheng-Yen |title=B-flow Ultrasonography of Peripheral Vascular Diseases |journal=Journal of Medical Ultrasound |date=2005 |volume=13 |issue=4 |pages=186–195 |doi=10.1016/S0929-6441(09)60108-9 |doi-access=free }}</ref> It is thus an alternative or complement to [[Doppler ultrasonography]] in visualizing blood flow.<ref name="Wachsberg2007">{{cite journal |last1=Wachsberg |first1=Ronald H. |title=B-Flow Imaging of the Hepatic Vasculature: Correlation with Color Doppler Sonography |journal=American Journal of Roentgenology |date=June 2007 |volume=188 |issue=6 |pages=W522–W533 |doi=10.2214/AJR.06.1161 |pmid=17515342 }}</ref>

[[Therapeutic ultrasound]] aimed at a specific tumor or calculus is not an imaging mode. However, for positioning a treatment probe to focus on a specific region of interest, A-mode and B-mode are typically used, often during treatment.<ref>{{cite journal |last1=Tzou |first1=David T. |last2=Usawachintachit |first2=Manint |last3=Taguchi |first3=Kazumi |last4=Chi |first4=Thomas |title=Ultrasound Use in Urinary Stones: Adapting Old Technology for a Modern-Day Disease |journal=Journal of Endourology |date=April 2017 |volume=31 |issue=S1 |pages=S–89–S-94 |doi=10.1089/end.2016.0584|pmid=27733052 |pmc=5397246 }}</ref>