Low-count SPECT images are
well known to be smoothed strongly by a Butterworth filter for statistical
noise reduction. Reconstructed images have a low signal-to-noise ratio (SNR)
and spatial resolution because of the removal of high-frequency signal
components. Using the developed robust adaptive bilateral filter (RABF), which
was designed as a pre-stage filter of the Butterworth filter, this study was
conducted to improve SNR without degrading the spatial resolution for low-count
SPECT imaging. The filter can remove noise while preserving spatial resolution.
To evaluate the proposed method, we extracted SNR and spatial resolution in a
phantom study. We also conducted paired comparison for
visual image quality evaluation in a clinical study. Results show that SNR
was increased 1.4 times without degrading the spatial resolution. Visual image
quality was improved significantly (p < 0.01) for clinical low-count data.
Moreover, the accumulation structure became sharper. A structure embedded in
noise emerged. Our method, which denoises without degrading the spatial
resolution for low-count SPECT images, is expected to increase the
effectiveness of diagnosis for low-dose scanning and short acquisition time
scanning.
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