Question 32.7: The data in Table 32.2 shows how the attenuation coefficient...
The data in Table 32.2 shows how the attenuation coefficient μ depends on the energy of the X-rays in bone and muscle. When making a diagnostic X-ray image, it is desirable that bone should be clearly distinguished from muscle. Use the data in Table 32.2 to explain why it would be best to use lower energy (50 keV) X-rays for this purpose.
| Maximum X-ray energy | Bone: µ / cm^{-1} | Muscle: µ / cm^{-1} |
| 4.0 MeV | 0.087 | 0.049 |
| 250 keV | 0.32 | 0.16 |
| 100 keV | 0.60 | 0.21 |
| 50 keV | 3.32 | 0.54 |
Table 32.2 Data for Questions 7 and 8.
Consider the ratio of attenuation coefficients bone :muscle. This is approximately 6 for 50 keV X-rays, so bone is a much better absorber at this energy than is muscle. At 4.0 MeV, the ratio is less than 2, so bone and muscle will not appear very different on the image. (You could also calculate the fraction of X-rays absorbed by, say, 1 cm of tissue. At 4.0 MeV, only a small fraction is absorbed, so the X-ray image will be flooded with unabsorbed X-rays.)