Beyond Contrast Transfer: Spectral SNR as a Dose-Aware Metric for STEM Phase Retrieval
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arXiv
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2025
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| author | Varnavides, Georgios Bekkevold, Julie Marie Ribet, Stephanie M Scott, Mary C Jones, Lewys Ophus, Colin |
| author_facet | Varnavides, Georgios Bekkevold, Julie Marie Ribet, Stephanie M Scott, Mary C Jones, Lewys Ophus, Colin |
| contents | The contrast transfer function (CTF) is widely used to evaluate phase retrieval methods in scanning transmission electron microscopy (STEM), including center-of-mass imaging, parallax imaging, direct ptychography, and iterative ptychography. However, the CTF reflects only the maximum usable signal, neglecting the effects of finite electron fluence and the Poisson-limited nature of detection. As a result, it can significantly overestimate practical performance, especially in low-dose regimes. Here, we employ the spectral signal-to-noise ratio (SSNR), as a dose-aware statistical framework to evaluate the recoverable signal as a function of spatial frequency. Using numerical reconstructions of white-noise objects, we show that center-of-mass, parallax, and direct ptychography exhibit dose-independent SSNRs, with close-form analytic expressions. In contrast, iterative ptychography exhibits a surprising dose dependence: at low fluence, its SSNR converges to that of direct ptychography; at high fluence, it saturates at a value consistent with the maximum detective quantum efficiency predicted by recent quantum Fisher information bounds. The results highlight the limitations of CTF-based evaluation and motivate SSNR as a more accurate, dose-aware metric for assessing STEM phase retrieval methods. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2507_19476 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Beyond Contrast Transfer: Spectral SNR as a Dose-Aware Metric for STEM Phase Retrieval Varnavides, Georgios Bekkevold, Julie Marie Ribet, Stephanie M Scott, Mary C Jones, Lewys Ophus, Colin Optics Materials Science The contrast transfer function (CTF) is widely used to evaluate phase retrieval methods in scanning transmission electron microscopy (STEM), including center-of-mass imaging, parallax imaging, direct ptychography, and iterative ptychography. However, the CTF reflects only the maximum usable signal, neglecting the effects of finite electron fluence and the Poisson-limited nature of detection. As a result, it can significantly overestimate practical performance, especially in low-dose regimes. Here, we employ the spectral signal-to-noise ratio (SSNR), as a dose-aware statistical framework to evaluate the recoverable signal as a function of spatial frequency. Using numerical reconstructions of white-noise objects, we show that center-of-mass, parallax, and direct ptychography exhibit dose-independent SSNRs, with close-form analytic expressions. In contrast, iterative ptychography exhibits a surprising dose dependence: at low fluence, its SSNR converges to that of direct ptychography; at high fluence, it saturates at a value consistent with the maximum detective quantum efficiency predicted by recent quantum Fisher information bounds. The results highlight the limitations of CTF-based evaluation and motivate SSNR as a more accurate, dose-aware metric for assessing STEM phase retrieval methods. |
| title | Beyond Contrast Transfer: Spectral SNR as a Dose-Aware Metric for STEM Phase Retrieval |
| topic | Optics Materials Science |
| url | https://arxiv.org/abs/2507.19476 |