AQA · A-Level · Physics

    Course version: 7408 · Version from Sept 2016

    Ultrasound imaging (A-level only): Examples of applications.

    Ultrasound imaging is used widely in medicine because it is non-ionising and can clearly differentiate soft tissue boundaries.

    Checked against the AQA 7408 specification (opens in a new tab) on .

    • Point 5 of 5
    • 3 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Ultrasound imaging is used widely in medicine because it is non-ionising and can clearly differentiate soft tissue boundaries. Medical applications include prenatal scanning to monitor foetal growth and position, echocardiography to view heart valves and chambers in real time, and A-scans of the eye to measure axial length before lens implantation. In each case, a transducer emits high-frequency sound pulses into the body. Echoes return from boundaries where the acoustic impedance changes between tissues. The time delay of the echoes provides depth information, while the amplitude indicates the nature of the boundary. A coupling gel is used to match acoustic impedance and prevent reflection at the skin.

    What earns the marks

    • States at least two valid medical applications of ultrasound imaging, such as prenatal scanning, echocardiography, or eye measurement.
    • Explains that ultrasound is used because it is non-ionising and therefore safer than X-rays for repeated or prenatal imaging.
    • Links applications to the pulse–echo principle: a pulse is reflected at a boundary where acoustic impedance changes, and the echo time gives depth.
    • Describes how a coupling medium such as gel is used to reduce reflection at the transducer–skin boundary and transmit ultrasound into the body.
    • Explains how the amplitude of the returning echo depends on the difference in acoustic impedance between two media.
    • Applies the depth equation distance = speed × time ÷ 2 to a stated medical application, for example measuring the distance to a foetal skull.

    Common mistakes and how to put them right

    • Including industrial applications like testing welds.

      Put it right by focusing exclusively on medical applications such as echocardiography for this option.

    • Claiming ultrasound is ionising radiation.

      Put it right by stating ultrasound consists of longitudinal pressure waves and is non-ionising.

    • Using the one-way distance equation.

      Put it right by calculating depth as speed × time ÷ 2, since the pulse travels to the boundary and back.

    Exam tips

    • When asked for applications, give named medical examples and state the physical principle each relies on, rather than listing names alone.
    • Use the phrase non-ionising when explaining the safety advantage of ultrasound over X-rays.

    Try the lesson

    The start of the Ultrasound imaging (A-level only): Examples of applications. lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which application commonly uses ultrasound imaging rather than X-ray imaging?

    Listen

    Ultrasound imaging is used widely in medicine because it is non-ionising and can clearly differentiate soft tissue boundaries. Medical applications include prenatal scanning to monitor foetal growth and position, echocardiography to view heart valves and chambers in real time, and A-scans of the eye to measure axial length before lens implantation. In each case, a transducer emits high-frequency sound pulses into the body. Echoes return from boundaries where the acoustic impedance changes between tissues. The time delay of the echoes provides depth information, while the amplitude indicates the nature of the boundary. A coupling gel is used to match acoustic impedance and prevent reflection at the skin. A strong answer earns marks for these points. States at least two valid medical applications of ultrasound imaging, such as prenatal scanning, echocardiography, or eye measurement. Explains that ultrasound is used because it is non-ionising and therefore safer than X-rays for repeated or prenatal imaging. Links applications to the pulse–echo principle: a pulse is reflected at a boundary where acoustic impedance changes, and the echo time gives depth. Describes how a coupling medium such as gel is used to reduce reflection at the transducer–skin boundary and transmit ultrasound into the body. A common slip: Including industrial applications like testing welds. Instead, focusing exclusively on medical applications such as echocardiography for this option. Exam tip: When asked for applications, give named medical examples and state the physical principle each relies on, rather than listing names alone.

    See it

    A top-down flowchart. The transducer emits high-frequency sound pulses, which leads to coupling gel matching acoustic impedance at the skin. This leads to the pulse travelling into the body. From there, an echo is reflected at a boundary where acoustic impedance changes. That reflection splits into two outcomes: the time delay gives depth, and the amplitude indicates the nature of the boundary. The time delay outcome leads to the depth equation, depth equals speed times time divided by two. The step of the pulse travelling into the body also leads to a node listing the medical applications: prenatal scanning, echocardiography and eye A-scans.
    It shows the pulse–echo sequence of ultrasound imaging, from emission through the coupling gel and reflection at an impedance boundary to depth and amplitude information, with the medical applications.

    Key words

    Say what each word means before you turn the card.

    Acoustic impedance

    Try answering aloud or in your head before turning the card.

    Pulse–echo depth measurement

    Try answering aloud or in your head before turning the card.

    Non-ionising radiation safety

    Try answering aloud or in your head before turning the card.

    See every definition
    Acoustic impedance
    Echoes return from boundaries where this changes between tissues, and its difference between two media determines the amplitude of the returning echo.
    Pulse–echo depth measurement
    A transducer emits high-frequency sound pulses into the body, and the time delay of the echoes provides depth information.
    Non-ionising radiation safety
    Ultrasound is used because it is non-ionising and therefore safer than X-rays for repeated or prenatal imaging.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. The transducer emits high-frequency sound pulses, which leads to coupling gel matching acoustic impedance at the skin. This leads to the pulse travelling into the body. From there, an echo is reflected at a boundary where acoustic impedance changes. That reflection splits into two outcomes: the time delay gives depth, and the amplitude indicates the nature of the boundary. The time delay outcome leads to the depth equation, depth equals speed times time divided by two. The step of the pulse travelling into the body also leads to a node listing the medical applications: prenatal scanning, echocardiography and eye A-scans.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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