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Fourier-Domain Bandpass Filtering to Enable Spatial Resolution Sensitivity of a Channelized Hotelling Observer Applied to X-Ray Angiography

K Fetterly1*, D Gomez Cardona2, (1) Mayo Clinic, Rochester, MN, (2) Gundersen Health System, La Crosse, WI

Presentations

SU-J-201-3 (Sunday, 7/10/2022) 4:00 PM - 5:00 PM [Eastern Time (GMT-4)]

Room 201

Purpose: Traditional channelized Hotelling observers (CHOs) are insensitive to blur because their detectability index (d’) estimates are dominated by the large area, low frequency features of test objects. The purpose of this work is to describe the spatial resolution sensitivity of a Fourier-domain CHO (fCHO) applied to X-ray angiography images.

Methods: Test images (n=2x1200) were acquired using nominal 0.3, 0.6, and 1.0 mm focal spots and geometric magnification factor 1.4. Test objects included iodine contrast disks (diameter: 0.5-4.0 mm) and 0.19 mm nitinol wires of an implantable cardiac device. Raw images with pixel pitch 0.154 mm were acquired using manual X-ray control; ROIs (51x51) extracted; a Tukey apodization window applied; the 2D Fourier transform of the ROIs calculated (fROIs); low-frequency components of the fROIs excluded by bandpass filters applied in 0.05*fNyquist increments; and the real part of the fROIs submitted to the fCHO framework. Within the fCHO, methods to include only fROI elements containing unique information; manage bias; and estimate d’ uncertainty were applied.

Results: For the disk objects, the mean ratio of d’ estimated by the unfiltered fCHO to that by a spatial-domain Gabor CHO was 0.94 (range 0.87-1.0). Bandpass filters applied to fROIs containing nitinol wires resulted in exponential decrease of d’ with increasing bandpass frequency. For the wires and bandpass frequency 0.30*fNyquist, d’ for the 0.3, 0.6, and 1.0 mm foci decreased by 74, 78, and 87% compared to the unfiltered reference. Importantly, the relative difference between d’ estimates for each focal spot increased with bandpass frequency up to f=0.30*fNyquist. For that bandpass, the ratio of d’ for the 0.3 versus 1.0 mm foci was 2.1 (d’=4.0 and 1.9, z-score=22.8).

Conclusion: Application of bandpass filters to Fourier-space representations of X-ray angiography ROIs submitted to a fCHO provides high sensitivity to resolution loss by focal spot penumbral blur.

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