| 摘要 |
A computed tomography arrangement using a polychromatic source can give rise to errors in image reconstruction due to the effect of beam hardening. In the improved method, the normalised spectral intensity Ti and the energy Ei relating to the spectral distribution of the source, are determined and stored 4. The length L of each measurement path lying within the body, and the corresponding detector measurement value I are also stored 2, 1. To compute a sectional image in 12, the usual measurement value I is replaced by a computed value A1 representing the absorbed part of the radiation, or by a value <IMAGE> which also accounts for radiation lost by Compton scattering. For each value I, successive test values A1 are applied from a data store 3 to a computing stage 5 which evaluates <IMAGE> where A2 =a2L (a2 is a constant value for example in the range 0.15cm<-1></=a2</=0.18cm<-1>), n APPROX 3, and f(E1) is a factor dependent on Compton scattering. A comparator 7 senses either I=Î and feeds the value A1 directly to a store (9), or determines the adjacent values Îa> I(for A1a) and Îb <I (for A1b) which are stored 6 and provide the final value for A1 by interpolation in computing stage 8. The corresponding value P is computed by 10 and stored 11 with values relating to other measurement paths prior to image computation in 12. <IMAGE> |
