Method for reducing noise in a sequence of fluoroscopic images by temporal and spatial filtering

A method for reducing noise in a sequence of fluoroscopic images acquired by an X-ray detector, each image (xn) being formed in the spatial domain by a matrix of pixels, each pixel having a value representative of a signal level, the method comprising the following successive steps for each image (xn):

• applying temporal filtering to the image (xn) acquired at an instant n, the application of said temporal filtering comprising the following substeps for each pixel of the image:
• determining a difference between the value of the pixel considered in the image (xn) acquired at the instant n and the value of the corresponding pixel in the image (yn-1) acquired at an instant n−1 to which the temporal filtering (22) has been applied,
• if the difference is below a first predetermined threshold S1, correcting the value of the corresponding pixel with a first set of parameters,
• if the difference is above a second predetermined threshold S2, correcting the value of the corresponding pixel with a second set of parameters,
• applying spatial filtering to the image (yn) acquired at the instant n, the application of said spatial filtering comprising the following substeps:
• transforming the image (yn) acquired at the instant n from the spatial domain into the curvelet domain using a curvelet transform, each image in the curvelet domain being represented by a set of coefficients,
• thresholding the coefficients of the image (yn) using a thresholding function, the thresholding function cancelling the coefficients below a third predetermined threshold, and preserving or adjusting the coefficients above the third predetermined threshold,
• transforming the image (yn) whose coefficients have been thresholded from the curvelet domain into the spatial domain using an inverse curvelet transform.