Table 3. A comparison between the new method, the pixel counting, and simple thresholding detection methods based on a sample of bubbles with and without artefacts.

	Sensitivity (%)	Specificity (%)	Accuracy (%)	Youden’s J (%)
No Artefact
New Method	99.72	100.00	99.95	99.72
Pixel Counting	96.26	96.01	96.06	92.28
Thresholding	99.86	99.79	99.80	99.65
Artefact
New Method	100.00	99.12	99.31	99.12
Pixel Counting	98.36	95.59	96.18	93.96
Thresholding	100	38.33	51.39	38.33
Combined
New Method	99.73	99.98	99.94	99.71
Pixel Counting	96.31	96.01	96.06	92.31
Thresholding	99.86	98.73	98.94	98.60

Note: The combined sample consisted of 15837 bubbles (2950 marked), 288 with artefacts (61 marked), and 15837 without artefacts (2889 marked). Cut-offs for the pixel counting and simple thresholding methods were set to maximize the Youden’s J statistic for the combined sample.