Ultrasound physics, transducers and artefacts

56 Gulf Prometric Radiographer (DHA, DOH, MOH, SCFHS, QCHP) practice questions on Ultrasound physics, transducers and artefacts, part of Ultrasound. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Easy

   The time gain compensation (TGC) control is used to:

   1. AChange the transmitted frequency of the pulse
   2. BAlter the frame rate of the real-time image
   3. CFreeze the image on the screen
   4. DAmplify deeper echoes to offset attenuation

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   Answer: D · Amplify deeper echoes to offset attenuation

   Echoes from deeper structures are weaker because of attenuation, so the scanner amplifies them progressively with depth. The aim is uniform brightness of similar tissue.

   • A: Frequency is chosen by the probe selection.
   • B: Frame rate depends on depth and line density.
   • C: Freeze is a separate button.

   Remember this

   TGC equalises brightness with depth.

2. Question 2 · Hard

   Two tissues have acoustic impedances of 1.5 and 4.5 MRayl. What fraction of the incident intensity is reflected at their interface?

   1. A6 per cent
   2. B75 per cent
   3. C25 per cent
   4. D50 per cent

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   Answer: C · 25 per cent

   R = ((Z2 - Z1) / (Z2 + Z1))^2 = (3 / 6)^2 = 0.25, so 25 per cent is reflected and 75 per cent is transmitted.

   • A: 6 per cent would arise from squaring twice.
   • B: 75 per cent is the transmitted fraction.
   • D: 50 per cent forgets to square the ratio.

   Remember this

   Intensity reflection = ((Z2 - Z1) / (Z2 + Z1)) squared.

3. Question 3 · Medium

   Posterior acoustic enhancement is typically seen behind:

   1. AA simple cyst
   2. BA calcified plaque
   3. CA bone surface
   4. DA gallstone

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   Answer: A · A simple cyst

   Fluid attenuates less than the surrounding tissue, so the beam behind it is stronger, and the tissue behind appears brighter.

   • B: A calcified plaque also casts a shadow.
   • C: Bone shadows strongly.
   • D: A stone produces shadowing.

   Remember this

   Enhancement means a fluid-filled, low-attenuation structure.

4. Question 4 · Medium

   A radiographer notices a fine noise pattern throughout the image and a loss of contrast. The most likely cause is:

   1. AGain set too low
   2. BOverall gain set too high
   3. CFrequency too low
   4. DFocal zone placed too deep

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   Answer: B · Overall gain set too high

   Excess gain amplifies noise and low-level echoes, so fluid-filled structures look grey and the image contrast falls.

   • A: Low gain darkens the image.
   • C: Low frequency gives deeper but coarser images.
   • D: Focal zone changes lateral resolution.

   Remember this

   Use the minimum gain that gives a good image, and use TGC for depth.

5. Question 5 · Easy

   Acoustic impedance (Z) of a medium is the product of:

   1. ADensity and frequency
   2. BFrequency and wavelength
   3. CAttenuation and thickness
   4. DDensity and the speed of sound

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   Answer: D · Density and the speed of sound

   Z = density x speed of sound, measured in rayls. Reflection occurs at boundaries between media with different acoustic impedance.

   • A: Density x frequency has no physical meaning here.
   • B: Frequency x wavelength gives speed.
   • C: Attenuation x thickness gives the loss in decibels.

   Remember this

   Z = rho x c, and the echo strength depends on the impedance difference.

6. Question 6 · Hard

   A pulse takes 130 microseconds to return from a reflector. Using 13 microseconds per cm of depth, how deep is the reflector?

   1. A10 cm
   2. B1 cm
   3. C5 cm
   4. D20 cm

   Answer and explanation in LearnFree account

7. Question 7 · Medium

   A short, bright, tapering streak extending from a small metallic clip or gas bubble is called a:

   1. AComet-tail artefact
   2. BEdge shadow
   3. CAliasing
   4. DSide-lobe artefact

   Answer and explanation in LearnFree account

8. Question 8 · Medium

   The attenuation coefficient of soft tissue is approximately:

   1. A50 dB per cm per MHz
   2. B0.5 dB per cm per MHz
   3. C5 dB per cm per MHz
   4. D0.05 dB per cm per MHz

   Answer and explanation in LearnFree account

9. Question 9 · Hard

   A transverse scan of the lower abdomen through the rectus muscles shows two copies of a small early gestational sac side by side. On a sagittal scan only one sac is seen. What is the most likely explanation?

   1. AAliasing from a pulse repetition frequency set too low
   2. BReverberation between the probe and the sac
   3. CMirror-image reflection from the bladder wall
   4. DRefraction at the rectus muscle and fat boundary

   Answer and explanation in LearnFree account

10. Question 10 · Hard

    A 5 MHz beam in soft tissue (0.5 dB/cm/MHz) travels to a reflector 4 cm deep and back. What is the total attenuation?

    1. A10 dB
    2. B40 dB
    3. C20 dB
    4. D5 dB

    Answer and explanation in LearnFree account

11. Question 11 · Medium

    A narrow dark shadow runs from the edge of a rounded structure such as the neck of a gallbladder. This edge shadowing results from:

    1. AGas in the adjacent bowel loop in front of the structure
    2. BRefraction and reflection at curved surfaces
    3. CAliasing of the pulsed Doppler signal at the edge
    4. DExcess overall gain setting on the scanner console

    Answer and explanation in LearnFree account

12. Question 12 · Easy

    The main purpose of ultrasound coupling gel is to:

    1. AIncrease the frequency of the transmitted pulse
    2. BRemove the air between the probe and the skin
    3. CCool the transducer during a long examination
    4. DReduce the speed of sound in the superficial tissue

    Answer and explanation in LearnFree account

13. Question 13 · Easy

    Which probe is the usual choice for general abdominal imaging in an adult?

    1. AA high-frequency linear array
    2. BA pencil CW Doppler probe only
    3. CA low-frequency curvilinear array
    4. DAn intravascular probe on a catheter

    Answer and explanation in LearnFree account

14. Question 14 · Medium

    Damping (backing) material behind the piezoelectric crystal is used to:

    1. ARaise the operating frequency only
    2. BShorten the pulse and improve axial resolution
    3. CIncrease the intensity of the pulse
    4. DReduce the frame rate of the image

    Answer and explanation in LearnFree account

15. Question 15 · Medium

    A vessel runs exactly perpendicular to the ultrasound beam, and no Doppler signal is seen. The reason is:

    1. AThe frequency is set too high
    2. BThe vessel is occluded by thrombus
    3. CThe gain is set too low
    4. DThe cosine of 90 degrees is zero

    Answer and explanation in LearnFree account

16. Question 16 · Medium

    Lateral resolution is best at the:

    1. AFar field where the beam diverges
    2. BFocal zone, where the beam is narrowest
    3. CNear the transducer surface only
    4. DGreatest depth

    Answer and explanation in LearnFree account

17. Question 17 · Medium

    The resistive index of a vessel is calculated from:

    1. AEnd-diastolic velocity minus the minimum velocity
    2. BPeak systolic velocity divided by end-diastolic velocity from the same trace
    3. C(Peak systolic velocity minus end-diastolic velocity) divided by peak systolic velocity
    4. DMean velocity divided by peak systolic velocity measured in the same trace

    Answer and explanation in LearnFree account

18. Question 18 · Medium

    Echoes appear inside an anechoic gallbladder next to a strong reflector, as if sludge were present. A likely cause is:

    1. ATrue gallbladder sludge in all cases and views
    2. BPosterior enhancement behind the fluid
    3. CA side-lobe or slice-thickness artefact
    4. DA Doppler artefact from the colour box

    Answer and explanation in LearnFree account

19. Question 19 · Medium

    Echoes from fat on an image show a structure displaced slightly in depth. This speed-error artefact occurs because:

    1. AThe scanner assumes 1540 m/s but the speed in fat is lower
    2. BFat absorbs all of the echoes from the beam
    3. CFat has a higher attenuation than bone does
    4. DThe gain is set too high by the operator

    Answer and explanation in LearnFree account

20. Question 20 · Medium

    In spectral Doppler, aliasing occurs when the Doppler shift exceeds:

    1. AHalf the pulse repetition frequency
    2. BThe Doppler angle
    3. CThe transmitted frequency
    4. DTwice the pulse repetition frequency

    Answer and explanation in LearnFree account

21. Question 21 · Hard

    A transducer produces pulses of 2 cycles at 5 MHz in tissue (c = 1540 m/s). What is the axial resolution?

    1. AAbout 0.6 mm
    2. BAbout 3 mm
    3. CAbout 0.3 mm
    4. DAbout 1.2 mm

    Answer and explanation in LearnFree account

22. Question 22 · Medium

    Which factor most directly determines axial resolution?

    1. ASlice thickness
    2. BSpatial pulse length
    3. CNumber of focal zones
    4. DBeam width at the focus

    Answer and explanation in LearnFree account

23. Question 23 · Medium

    On the output display of an ultrasound scanner, the mechanical index (MI) is mainly an indicator of the risk of:

    1. AAliasing of the Doppler signal
    2. BHeating of the tissue
    3. CCavitation, the formation and collapse of gas bubbles
    4. DDepolarisation of the piezoelectric crystal

    Answer and explanation in LearnFree account

24. Question 24 · Easy

    Ultrasound is sound with a frequency above:

    1. A20 kHz
    2. B20 Hz
    3. C2 kHz
    4. D200 Hz

    Answer and explanation in LearnFree account

25. Question 25 · Medium

    Spatial compounding reduces which feature of the image?

    1. AFrame rate and temporal resolution of the image
    2. BDepth of penetration of the beam in tissue
    3. CSpeckle and some angle-dependent artefacts
    4. DFrequency of the beam that is sent into the patient

    Answer and explanation in LearnFree account