Scatter estimation and/or correction in x-ray imaging

A method for x-ray tomographic imaging of an object while correcting for scatter, wherein said method comprises:

• providing a source of x-ray radiation and detector comprising two layers of direct conversion semiconductor diodes pointing back to the source, wherein a spacing between individual diodes is provided in both a top and bottom layer that corresponds to the diode width, and a displacement of the bottom layer in the rotational direction such that primary x-rays missing the top layer diodes pass unattenuated to the lower level diodes;
• providing beam stops, covering less than 50% of all detector channels and distributed across the entire detector, in the bottom layer or both the top and bottom layers, making them essentially blind to primary unscattered x-rays;
• moving the source and detector around the object obtaining projection x-ray images at different rotation angles;
• detecting radiation from the source by the detector;
• estimating, for each rotation angle, the distribution of the sum of object and internal scatter of each layer by fitting a parametric surface to the counts of the detector elements with beam stops mounted on top of them;
• and
• subtracting the estimated sum of object and internal scatter from each detector element not covered with beam stops, thus obtaining an estimate of the scatter free signal of each detector element not covered with beam stops.

A device for x-ray tomographic imaging of an object while correcting for scatter, wherein said device comprises:

• a source of x-ray radiation and detector comprising two layers of direct conversion semiconductor diodes pointing back to the source,
• wherein there is a spacing between individual diodes in both a top and bottom layer that corresponds to the diode width, and a displacement of the bottom layer in the rotational direction such that primary x-rays missing the top layer diodes pass unattenuated to the lower level diodes,
• wherein beam stops are provided, covering less than 50% of all detector channels and distributed across the entire detector, in the bottom layer or both the top and bottom layers, making them essentially blind to primary unscattered x-rays;
• wherein the source and detector are arranged to be moved around the object obtaining projection x-ray images at different rotation angles, controlled by a movement controller;
• and
• an estimator, connected to the detector and arranged for obtaining measurement data from the detector, or being an integrated part of the detector, wherein the estimator is configured for estimating, for each rotation angle, the distribution of the sum of object and internal scatter of each layer by fitting a parametric surface to the counts of the detector elements with beam stops mounted on top of them, and the estimated sum of object and internal scatter is subtracted from each detector element not covered with beam stops, thus obtaining an estimate of the scatter free signal of each detector element not covered with beam stops.