Question 19M.3.HL.TZ1.16
| Date | May 2019 | Marks available | [Maximum mark: 4] | Reference code | 19M.3.HL.TZ1.16 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Calculate, Explain | Question number | 16 | Adapted from | N/A |
A parallel beam of X-rays travels through 7.8 cm of tissue to reach the bowel surface. Calculate the fraction of the original intensity of the X-rays that reach the bowel surface. The linear attenuation coefficient for tissue is 0.24 cm–1.
[2]
I0e−0.24 × 7.8 ✔
0.15I0 ✔
Award [2] for bald correct answer.
Air as a contrast medium. Part (a) was well calculated by most of the prepared candidates.
The fluid in the bowel has a similar linear attenuation coefficient as the bowel surface. Gases have much lower linear attenuation coefficients than fluids. Explain why doctors will fill the bowel with air before taking an X-ray image.
[2]
to produce an X-ray image there must be constrast/a difference in the intensity of the beam transmitted through tissue and the bowel ✔
introduction of air will produce contrast ✔
In (b) only the best candidates well identified the importance of the change in contrast of the image (resulting from different attenuation values) needed to locate the organ.