Beam hardening correction

In actual practice, one uses modifications to Eq. (2), which include the so-caUed beam-hardening corrections to account for deviations from Eq. (1) caused by the broad-spectrum nature of the incident X-ray beam.)... 

Sophisticated correction techniques are needed to obtain C-arm CT results with good low-contrast visibility. They are explained below. We start with overexposure correction, then turn to scatter correction, and next look into beam-hardening correction. After that, we briefly visit truncation correction and finish up with ring correction. 

Correction for beam hardening artefacts in computerised tomography... 

After dealing with overexposure and scatter removal, 2D projections can be corrected for beam hardening. X-ray tubes emit photons with different energies. Low-energy photons are absorbed and attenuated more strongly by matter than higher energy photons. As a consequence. 

Second Method Mount the sample and detector in line with the glory hole. Measure the transmission of a l/v absorber (of close to 50% transmission to "eliminate" the hardening correction) by taking count rates with sample in and out of beam, and take the corresponding background counts. Calculate g p ising Eq. (10) and thus = 0. in this case. Then cal-... 

Subtracting a known scattering cross section from a-p gives the absorption cross section desired. If a sample of 50% transmission is used, no correction for the hardening of the beam is necessary, and the Op obtained is equal to The basis for this second method is the same as for the first,... 

Eq. (12) was derived under the assumption that tAe l/v absorber did not harden the neutron spectrum. A thin sample of high transmission (transmission T = i/Iq) would approximate the above condition, but then the accuracy of the cross section would be poor due to any small error in the count rates Iq and I, which differ by a small amount. Therefore, a thicker sample has to be used to increase the accuracy. But the thick sample hardens the neutron beam spectrum that passes through it, and so Eq. (12) no longer holds. A correction for hardening now has to be applied to relate correctly the experimentally obtained cross section with the cross section... 

For the interpretation of the cross section thus obtained (which is actually an average) and the correction for hardening of the beam, see Appendix II. 

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