In ultrasound B-scan imaging, the image is formed from ultrasound that is
reflected at boundaries between different tissues
absorbed completely by bone
refracted through the whole body
emitted by the tissues themselves
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WhyIt is reflected at boundaries between different tissues.
2Multiple choice · Hard
The intensity reflection coefficient between fat (Z = 1.38×10⁶ kg m⁻² s⁻¹) and muscle is 1%. The acoustic impedance of muscle is closest to
1.7×10⁶ kg m⁻² s⁻¹
1.4×10⁶ kg m⁻² s⁻¹
2.8×10⁶ kg m⁻² s⁻¹
0.7×10⁶ kg m⁻² s⁻¹
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WhyZ2 = Z1×(1+√0.01)/(1-√0.01) = 1.38×10⁶×1.1/0.9 ≈ 1.7×10⁶ kg m⁻² s⁻¹.
3Multiple choice · Easy
One advantage of ultrasound over X-rays for medical imaging is that ultrasound
is non-ionising and safer for soft tissue and a fetus
gives sharper images of bone
penetrates the whole body more easily
is a form of nuclear radiation
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WhyUltrasound is non-ionising, so it is safer for soft tissue and fetuses.
4Fill in the blank · Medium
In a B-scan, ultrasound is at the boundaries between different tissues to build up the image.
Answer:
reflected
WhyEchoes are reflected at boundaries.
5Fill in the blank · Medium
The product of a medium's density and the speed of sound in it is its acoustic .
Answer:
impedance
WhyZ = ρc is the acoustic impedance.
6Fill in the blank · Hard
A gel is used between the transducer and skin to reduce the strong reflection that would otherwise occur at a layer of air, because of air's very low acoustic .
Answer:
impedance
WhyGel provides impedance matching (coupling).
7Multiple choice · Medium
Technetium-99m is widely used as a medical imaging tracer because it
emits gamma radiation and has a short half-life
emits only alpha particles
has a very long half-life
is chemically inert and cannot bind to molecules
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WhyIt emits gamma radiation and has a short half-life.
8Multiple choice · Hard
In a thyroid scan using iodine-131, a gamma camera shows a region of higher gamma intensity. This region has
taken up more of the radioactive iodine tracer
absorbed more gamma radiation
failed to absorb iodine
abnormally high attenuation
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WhyIt has taken up more of the radioactive iodine tracer.
9Multiple choice · Easy
For a diagnostic tracer, gamma radiation is preferred over alpha because gamma
can penetrate the body to reach the detector
is more strongly ionising
cannot leave the body
has a shorter range in tissue
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WhyGamma can penetrate the body to reach an external detector.
10Fill in the blank · Easy
A radioactive substance introduced into the body to follow a process and be detected from outside is called a .
Answer:
tracer
WhyThis is a tracer.
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