1. (a) (to
a maximum of 7 marks) e.g.
• X-ray source + detectors round patient …
• … rotated around patient …/ the signal /
X-ray passes through the
same section of the body from different directions.
same section of the body from different directions.
• … producing a (thin) slice / cross-section.
• Idea of absorption / less gets through /
more is absorbed …
• by dense material / bone / material of high
Z / High Z related to
materials such as bone / Low Z to materials such as soft tissue
materials such as bone / Low Z to materials such as soft tissue
• attenuation is by the photo-electric effect
• the possibility of using a contrast medium.
• better than a simple X-ray at
differentiating other organs.
• patient is moved a small distance and the
process is repeated /
process continues in a spiral.
process continues in a spiral.
• a computer (analyses the data) / identifies
the position of organ/bone …
• … and forms a 3-D image. 7
(b) • Patients are exposed to ionising
radiation. (1)
• (Ionising radiation) could cause cancer /
damage cells (1)
Plus a maximum of ONE from:-e.g.
(1)
• It’s expensive.
• Time consuming / uses valuable resources,
etc.. 3
[10]
2. (a) Low energy X-rays are absorbed by the skin
/ undesirable as can cause
damage / greater ionising (1) 1
damage / greater ionising (1) 1
(b) I
= I0e–µx (1) ln I = ln Io – µ x
Io =
(1) ln
Io = ln 347 + 250 × 0.025
Io = 1.79 × 105 Wm–2 (1) 3
Io =
(1) ln
Io = ln 347 + 250 × 0.025Io = 1.79 × 105 Wm–2 (1) 3
(c) P
= I × A (0)
P = 347 × π × (0.10 × 10–2)2 (1)
P = 1.09 × 10–3 W (1) 2
P = 347 × π × (0.10 × 10–2)2 (1)
P = 1.09 × 10–3 W (1) 2
(d) (i) P = 18 × 100 / 0.15 (1)
P = 12000 W (1) 2
P = 12000 W (1) 2
(ii) 12000
/ 7.5 × 1017 (= 1.6 × 10–14 J = energy of each electron) (1)
0.5 m v2 = 1.6 × 10–14 (0)
v = 1.9 × 108 ms–1 (1) 2
0.5 m v2 = 1.6 × 10–14 (0)
v = 1.9 × 108 ms–1 (1) 2
(iii) tube current = 7.5 × 1017 × 1.6 × 10–19 = 0.12 A (1)
V × I = 12000 (1)
V =12000 / 0.12 = 100,000 V or 100 kV (1) 3
V × I = 12000 (1)
V =12000 / 0.12 = 100,000 V or 100 kV (1) 3
[13]
3. Formation
of image to a max 3 e.g.
X-rays are detected by a film /
scintillation counter etc., (1)
High ‘Z’ means high attenuation / low transmission
[Allow atomic mass / nucleon number] (1)
shadow on the film / reference to exposure after attenuation (1)
Reference to photoelectric effect / energy range around 1–100keV /
absorption ∞ Z3 (1)
High ‘Z’ means high attenuation / low transmission
[Allow atomic mass / nucleon number] (1)
shadow on the film / reference to exposure after attenuation (1)
Reference to photoelectric effect / energy range around 1–100keV /
absorption ∞ Z3 (1)
Explanation of the use of a
contrast medium to a max.4 e.g.
X-rays do not differentiate / show up
soft tissues well …(1)
… as similar absorption / ‘Z’ is similar / ‘Z’ is low for these tissues. (1)
Contrast medium has high ‘Z’ / absorbs X-rays strongly.(1)
It is usually taken orally / as an enema / can be injected.(1)
… as similar absorption / ‘Z’ is similar / ‘Z’ is low for these tissues. (1)
Contrast medium has high ‘Z’ / absorbs X-rays strongly.(1)
It is usually taken orally / as an enema / can be injected.(1)
Example of type of structure that
can be imaged to a max.1 e.g.
digestive tract / throat / stomach.(1) to
a max. 8
[8]
