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    Ultrasound in Rheumatology: A Practical Guide for Diagnosis
    Ultrasound in Rheumatology: A Practical Guide for Diagnosis
    Ultrasound in Rheumatology: A Practical Guide for Diagnosis
    Ebook424 pages1 hour

    Ultrasound in Rheumatology: A Practical Guide for Diagnosis

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    About this ebook

    This book provides a practically applicable manual to the utilisation of ultrasound in rheumatology. Each chapter includes high-quality diagrams of each anatomical region covered, accompanied by an ideal scan with written and pictorial demonstrations, as well as an ideal ultrasound image, that has been obtained via a high-end machine for optimal image quality. This systematic approach to describing the application of ultrasound in rheumatology enables the reader to develop a deep understanding of how to correctly make use of ultrasound technologies in their daily practice.
     Ultrasound in Rheumatology: A Practical Guide for Diagnosis is an easy to follow guide to the application of ultrasound in rheumatology and is a valuable resource for the trainee and practising rheumatologist seeking a guide on the correct use of ultrasound.   
    LanguageEnglish
    PublisherSpringer
    Release dateMay 15, 2021
    ISBN9783030686598
    Ultrasound in Rheumatology: A Practical Guide for Diagnosis

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      Book preview

      Ultrasound in Rheumatology - Qasim Akram

      © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021

      Q. Akram, S. Basu (eds.)Ultrasound in Rheumatologyhttps://doi.org/10.1007/978-3-030-68659-8_1

      Essentials of Ultrasound for Practical Scanning

      M. Takhreem¹ and Q. Akram²  

      (1)

      Wrightington Hospital, Wigan, Greater Manchester, UK

      (2)

      Stockport NHS Foundation Trust, Stockport, Greater Manchester, UK

      Q. Akram

      Email: qasim.akram.qa@gmail.com

      Keywords

      UltrasoundGrey scaleDoppler signalColour dopplerAnisotropyFrequencyWavelengthDepthAcoustic impedancePenetration

      What is Ultrasound and How Does It Work?

      Ultrasound refers to sound waves that are above the acoustic spectrum, which in the human ear is usually at a frequency of 20–20,000 Hz (or 20 kHz). Every 1,000 Hz equates to 1 kHz. Some animal can hear up to 100,000 Hz (or 100 kHz). Medical ultrasound equipment ranges from a frequency of 1 MHz (1,000,000) to 50 MHz (50,000,000) [1].

      Frequency refers to the number of cycles per unit of time i.e. one cycle per second is 1 Hz. On the other hand, wavelength is the distance between each cycle of sound [1].

      Frequency and Wavelength are inversely related. For example, as the frequency increases the wavelength is reduced and as the frequency is lowered the wavelength is increased (Fig. 1) [1, 2].

      ../images/481155_1_En_1_Chapter/481155_1_En_1_Fig1_HTML.png

      Fig. 1

      Diagram showing relationship between frequency and wavelength

      Ultrasonic waves with a higher frequency tend to penetrate less than a lower frequency waves. The resolution will, however, increase with increased frequency . Conversely, a lower frequency means a higher wavelength of sound waves and a better penetration . However, this will result in a lower resolution. Relating to this in practical scanning in rheumatology, most joints i.e. hands and feet are located superficially so will require a higher frequency meaning less penetration and shorter wavelengths but a higher resolution [1, 2].

      Attenuation is a reduction in power and intensity of sound as it travels through tissue. Higher frequencies attenuate or absorbed faster than lower frequencies (i.e. less tissue penetration ) (Fig. 2) [3].

      ../images/481155_1_En_1_Chapter/481155_1_En_1_Fig2_HTML.png

      Fig. 2

      Acoustic impedance of different tissues

      Acoustic impedance, resistance encountered by US waves as pass through a tissue, is related to the density of the material and the speed of sound in the material. The greater the difference in impedance between tissues, the more sound will be reflected rather than transmitted. Acoustic impedance is slow in air, higher in muscle and even higher in bone so sound beams do not penetrate bone at all hence the high reflectivity. Liquids such as blood and synovial fluid do not reflect sound waves (Fig. 2) [2].

      The acoustic interface refers to the boundary between two different tissues. Ultrasound waves that are emitted are reflected at the interface of two different tissues. The greater the difference in tissue density the more reflective the boundary will be while similar densities pass easily through the tissues. The amount of reflection and transmission is dependent on speed of the sound waves and the specific acoustic impedance [2].

      Due to there being an interface between skin and air, large amounts of gel have to be applied as a medium (Figs. 3 and 4). If the surface of an object is flat and no air is present between source and object, almost all the US waves transmitted from the transducer will be reflected at right angles from the object (Fig. 5). The returning ultrasound waves are detected by transducer which contains crystals of lead creating an electric current. The electronic potential is then converted into an ultrasound image by the computer and interpreted by the operator (Fig. 6) [2].

      ../images/481155_1_En_1_Chapter/481155_1_En_1_Fig3_HTML.jpg

      Fig. 3

      Gel standoff required on ultrasound probe for accurate image acquisition

      ../images/481155_1_En_1_Chapter/481155_1_En_1_Fig4_HTML.png

      Fig. 4

      Diagram showing gel standoff and good image acquistion

      ../images/481155_1_En_1_Chapter/481155_1_En_1_Fig5_HTML.png

      Fig. 5

      Diagram showing inadequate gel stand off resulting in sound wave being reflected at a right angle from the object

      ../images/481155_1_En_1_Chapter/481155_1_En_1_Fig6_HTML.png

      Fig. 6

      Diagram showing image acquistion- US transducer sends sound waves towards the object [1] and they are reflected back to the tranducer from the tissue [2] and then converted into an electrical signal [3] which displays as an US image on the monitor [4]

      Modes Used in Ultrasound?

      B mode or grey scale is the precursor of grey scale ultrasound and is limited by defining boundaries of structures and differentiating fluid from solid. It cannot differentiate between fibrous tissue and active synovitis.

      Doppler is the detection of movement by measuring a frequency shift in the returned echo (Figs. 7 and 8).

      ../images/481155_1_En_1_Chapter/481155_1_En_1_Fig7_HTML.png

      Fig. 7

      Doppler principles- red cells moving towards the probe

      ../images/481155_1_En_1_Chapter/481155_1_En_1_Fig8_HTML.png

      Fig. 8

      Doppler principles with red cells moving away from the probe

      Power doppler (PD) ultrasound displays the doppler power in colour. Power doppler uses the strength of a returned sound wave from anything that is moving to give the position and brightness. It increases the sensitivity of the machine to small vessels and slow blood flow which is present in hyperaemia in inflamed tissues. Hence, its usefulness to detect active inflammation in synovial joints [3, 4].

      The doppler principle states that sound waves increase in frequency when they reflect from objects moving towards the transducer and then decrease when they reflect from objects moving away from the transducer (Figs. 7 and 8). As with grey scale, if the frequency is higher it gives a more detailed image of vessels but less penetration. A lower frequency gives a deeper penetration but a poor resolution. The gain determines the sensitivity to flow and increasing the gain will the increase the sensitivity of the signal returning from the machine. A lower gain reduces any noise and motion artefacts (see below) but also the sensitivity. Thus, to obtain the most accurate power doppler image, the gain should be increased till background noise is detectable and then reduce it gradually until it has gone [4,

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