Louise Rainford, Abstract Co-Author: Nothing to Disclose

Naomi N. Galvin, Presenter: Nothing to Disclose

Patrick C. Brennan PhD, Abstract Co-Author: Nothing to Disclose

The relevance of AHE on radiographic examinations, although well established has focused on screen-film examinations. There is a paucity of data on AHE-induced intensity gradients on direct digital technology, particularly with regard to photon fluence effects on quantum mottle and subsequent impact on diagnostic efficacy. The current psychophysical and anthropomorphic study establishes optimum combinations of exposure factors with the AHE to promote image quality.

Images were produced using an X-ray tube with 3.6mmAl total filtration, an anode angle of 12 degrees and a focal spot size of 1mm and were captured with an amorphous silican detector with caesium iodide scintillation (41cm x 41cm). An anti scatter grid with a ratio of 13:1 was employed. AHE intensity distribution was calculated using a water phantom containing five 2mm rings placed along the anode-to-cathode axis at 70kVp and a varying source-receptor distances (SRDs) from 100 - 140cm at 10cm intervals. The clinical image quality assessment involved the acquisition of lumbar spine images, using an anthropomorphic phantom, at 5 beam energies from 70-110kVp and with 5 SRDs from 100cm -140cm with specific positioning of the cathode anode axis. All images were assessed by a panel of expert observers using a reference image and a visual grading analysis methodology. Photometric details of the impact of the AHE were recorded.

The results demonstrated that the AHE was responsible for up to a 51% reduction in beam intensity towards the anode. Significant improvements (p<0.05) in all imaging criteria was evident for specific exposure conditions when the caudal aspect of the phantom was towards the anode with the overall image scores being highest at 90kvp and 130cm for all observers. A statistically significant correlation was shown between image density and clinical image scores (p<0.05).

The anode heel effect is currently under-utilised within imaging departments. The current results demonstrate that with correct alignment of the anode-cathode axis with the patient body and appropriate exposure techniques, significant improvements in image quality can be achieved, the extent of benefit being dependent on specific kVp and SRD values.

This cost-free technique with no dose implications should be adopted in a projection-specific way as a matter of priority.

Rainford, L, Galvin, N, Brennan, P, Appropriate Employment of Exposure Factors with the Anode Heel Effect (AHE) Using Digital Receptors Optimizes X-ray Examinations.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6015758.html