Effects of convolution filter with beam hardening correction on computed tomography image quality

Abstract

Purpose: To quantify the effects of convolution filters (FC) with beam hardening correction (BHC) compared to FC without BHC on the computed tomography (CT) image quality.

Methods: This study was conducted on a Canon® Aquilion Lightning scanner. The exposure protocol includes acquisitions at 120 and 100 kVp. Sixteen FCs (8 with and 8 without BHC) were investigated using a Catphan®504 phantom. Uniformity, slice thickness, spatial resolution, Hounsfield unit and noise were analysed using the SPICE-CT ImageJ plugin and the noise power spectrum was analysed using the Imquest software.

Results: It was observed that the BHC did not significantly influence the uniformity, slice thickness, noise and noise power spectrum. Comparisons of 10% MTF between FC01 and FC11 showed relative differences of -29% and -5% at 120 and 100 kVp, respectively, while those between FC09 and FC19 were -55% and -25%. The Hounsfield unit of the Catphan's region of highest electron density was reduced by -7.29% at 120 kVp for FC with BHC. In both cases (FC with and without BHC), the noise values agreed with CT operating manual. At 120 kVp, FC11 and FC09 presented the maximum and minimum noise values, respectively.

Conclusion: In CT procedures that quantitatively evaluate the bone or calcium Hounsfield unit, FC with BHC should be avoided due to its effects on Hounsfield units, in special at higher voltage, such as 120 kVp.

Keywords: Computed tomography; Convolution filter; Image quality; Phantom.