ultrasound_metrics.metrics.snr

Signal-to-Noise Ratio (SNR) metric for ultrasound, commonly used for speckle.

This module provides functions to calculate the Signal-to-Noise Ratio (SNR) for ultrasound speckle patterns. The SNR is calculated as mean/standard-deviation.

References

[1]

C. B. Burckhardt, “Speckle in Ultrasound B-mode Scans,” in IEEE Transactions on Sonics and Ultrasonics, vol. 25, no. 1, pp. 1-6, Jan. 1978, doi: 10.1109/T-SU.1978.30978.

[2]

D. Perdios, M. Vonlanthen, F. Martinez, M. Arditi and J. -P. Thiran, “CNN-Based Image Reconstruction Method for Ultrafast Ultrasound Imaging,” in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 69, no. 4, pp. 1154-1168, April 2022, doi: 10.1109/TUFFC.2021.3131383.

Functions

snr(→ float)

Calculate Signal-to-Noise Ratio (SNR) of an image.

Module Contents

ultrasound_metrics.metrics.snr.snr(values: jaxtyping.Num[ultrasound_metrics._utils.array_api.ArrayAPIObj,  *pixels], *, db: bool = False) → float

Calculate Signal-to-Noise Ratio (SNR) of an image.

This function computes the Signal-to-Noise Ratio (SNR) for ultrasound speckle patterns by calculating mean/standard-deviation. This metric provides a single value per ROI/image.

\[\text{SNR} = \frac{\mathbb{E}[X]}{\sqrt{\text{Var}(X)}}\]

where:

• \(\mathbb{E}[X]\) is the mean (average pixel value) across the (post-envelope) image

• \(\text{Var}(X)\) is the variance of pixel values across the (post-envelope) image

In ultrasound, the statistics of fully developed speckle signals (post envelope detection) follow a Rayleigh distribution, and the SNR of a Rayleigh distribution is equal to:

\[\text{SNR}_{\text{Rayleigh}} = \sqrt{\frac{\pi}{4 - \pi}} \approx 1.91\]

Parameters:

• values (array) – Input values. - spatial dimensions are flattened - Can be real or complex floating-point data

• db (bool, optional) – If True, return the SNR in decibels (dB). Default is False.

Returns:

Signal-to-Noise Ratio (SNR) of the values. If db=True, the SNR is returned in decibels (dB).

Return type:

float

Warns:

UserWarning – If variance is zero (would cause division by zero).

Notes

• This implementation is an amplitude ratio, not a power ratio.

• Complex data is handled by computing the magnitude (absolute value) before processing

• For Rayleigh-distributed speckle, the theoretical SNR is approximately 1.91

• If ROI is used, it should be applied to the input values before calling this function