# US 10,945,682 B2 · Geometric misalignment correction method for chest tomosynthesis reconstruction

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- Number: US 10,945,682 B2
- Document ID: US10945682B2
- Status: Granted
- Kind: B2
- Application number: 16/308,303
- Filed: 2017-06-08
- Published: 2019-07-18
- Granted: 2021-03-16
- Earliest claimed: 2016-06-09
- Assignees: Agfa Healthcare NV
- Applicants: Agfa Healthcare NV
- Inventors: Jeroen Cant; Jan Sijbers
- Web page: https://patentgrep.com/patent/US10945682B2

## CPC

- A61B 6/025: {Tomosynthesis}
- A61B 6/5205: {involving processing of raw data to produce diagnostic data}
- A61B 6/587: {Alignment of source unit to detector unit}
- G06T 12/10: Image preprocessing, e.g. calibration, positioning of sources or scatter correction
- G06T 2211/416: Exact reconstruction
- G16H 30/40: for processing medical images, e.g. editing
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G16H: HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA

## Abstract

A method and system to correct for alignment errors between assumed and actual geometric parameters of an acquisition geometry during image reconstruction in a chest tomosynthesis application includes receiving at least 2 raw projection images acquired on at least 2 different positions in a known acquisition geometry, determining an actual geometric parameter value by determining the minimum of a redundant planes cost function which is calculated for a varying range of the geometric parameter values, and which is determined by: a) at least one plane which intersects an X-ray source trajectory with at least two points, b) an intersection between the planes and a detector surface for which points the source positions are determined, and c) for which the parameters determining the intersection (λ, μ, l) are used for the construction of the cost function, applying the calculated actual geometric parameter value of the acquisition geometry for the image reconstruction of the plurality of images, characterized in that, a weighting function is applied to the plurality of acquired images prior to calculating the cost function.

## Claims

### Claim 1

A method to correct for alignment errors between assumed and actual geometric parameters of an acquisition geometry during image reconstruction in a tomosynthesis application, the method comprising the steps of:
receiving at least two projection images acquired at least two different positions in a known acquisition geometry;
applying a weighting function to the at least two projection images;
after applying the weighting function, determining a minimum of a redundant planes cost function for the at least two projection images, which is calculated for a varying range of geometric parameter values, and which is determined by:
a) planes each of which intersects an X-ray source trajectory at at least two points;
b) intersection points between the planes and a detector surface for which source positions are determined; and
c) for which parameters determining the intersection points are used for construction of the redundant planes cost function;
calculating an actual geometric parameter value based on the determined minimum of the redundant planes cost function; and
applying the calculated actual geometric parameter value of the acquisition geometry for the image reconstruction of the at least two projection images.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the calculated actual geometric parameter of the acquisition geometry is an angle between an actual orientation of an image detector relative to one of the planes that intersects with the at least two points defining the X-ray source trajectory in an imaging modality.

### Claim 3 (depends on 1)

The method according to claim 1, wherein the weighting function is a Gaussian function, and weights of pixel values, or redundant cost function values, are increased from 0 to 1 according to a Gaussian distribution in which 3σ=L1 and 3σ=R1, and L1 and R1 are relative widths of an applied truncation filter.

### Claim 4 (depends on 1)

The method according to claim 1, wherein the weighting function is a sigmoid function, and weights of pixel values, or respectively redundant cost function values, are increased from 0 to 1 according to a sigmoid distribution between 0 and L1 and between R1 and 0, in which L1 and R1 are relative widths of an applied truncation filter.

### Claim 5 (depends on 1)

The method according to claim 1, wherein the weighting function is a linear function, and weights of pixel values, or respectively redundant cost function values, are increased from 0 to 1 according to a linear distribution between 0 and L1, and between R1 and 0, in which L1 and R1 are relative widths of an applied truncation filter.

### Claim 6

A medical imaging apparatus for a tomosynthesis application, the medical imaging apparatus comprising:
an image detector that acquires at least two projection images from an imaged object at two different positions in an acquisition geometry;
a first data processor that calculates alignment errors between assumed and actual geometric parameters of the acquisition geometry, the first data processor configured for:
applying a weighting function to the at least two projection images;
after applying the weighting function to the at least two projection images, calculating a minimum of a redundant planes cost function, which is determined by:
a) planes each of which intersects an X-ray source trajectory at at least two points;
b) intersection points between the planes and a detector surface for which source positions are determined; and
c) for which parameters determining the intersection points are used for construction of the redundant planes cost function; and
calculating the actual geometric parameters based on the calculated minimum of the redundant planes cost function; and
a second data processor that calculates parameters of the acquisition geometry for an image reconstruction of a plurality of images.

### Claim 7 (depends on 6)

The medical imaging apparatus according to claim 6, further comprising:
an X-ray source that exposes the imaged object with X-rays and moves along a predetermined trajectory including a first position and a second position; and
an X-ray detector that faces the X-ray source and detects X-rays emitted from the X-ray source and transmitted through the object.

### Claim 8 (depends on 7)

The medical imaging apparatus according to claim 7, wherein the calculated parameters of the acquisition geometry includes an angle between an actual orientation of an image detector relative to one of the planes that intersects with the at least two points defining the X-ray source trajectory.

### Claim 9 (depends on 7)

The medical imaging apparatus according to claim 7, wherein the weighting function is a Gaussian function, and weights of pixel values, or respectively redundant cost function values, are increased from 0 to 1 according to a Gaussian distribution in which 3σ=L1 and 3σ=R1, and L1 and R1 are relative widths of an applied truncation filter.

### Claim 10 (depends on 7)

The medical imaging apparatus according to claim 7, wherein the weighting function is a sigmoid function, and weights of pixel values, or respectively redundant cost function values, are increased from 0 to 1 according to a sigmoid distribution between 0 and L1 and between R1 and 0, and L1 and R1 are relative widths of an applied truncation filter.

### Claim 11 (depends on 7)

The medical imaging apparatus according to claim 7, wherein the weighting function is a linear function, and weights of pixel values, or respectively redundant cost function values, are increased from 0 to 1 according to a linear distribution between 0 and L1 and between R1 and 0, and L1 and R1 are relative widths of an applied truncation filter.

### Claim 12 (depends on 6)

The medical imaging apparatus according to claim 6, wherein the calculated parameters of the acquisition geometry includes an angle between an actual orientation of an image detector relative to one of the planes that intersects with the points defining the X-ray source trajectory.

### Claim 13 (depends on 6)

The medical imaging apparatus according to claim 6, wherein the weighting function is a Gaussian function, and weights of pixel values, or respectively redundant cost function values, are increased from 0 to 1 according to a Gaussian distribution in which 3σ=L1 and 3σ=R1, and L1 and R1 are relative widths of an applied truncation filter.

### Claim 14 (depends on 6)

The medical imaging apparatus according to claim 6, wherein the weighting function is a sigmoid function, and weights of pixel values, or respectively redundant cost function values, are increased from 0 to 1 according to a sigmoid distribution between 0 and L1 and between R1 and 0, and L1 and R1 are relative widths of an applied truncation filter.

### Claim 15 (depends on 6)

The medical imaging apparatus according to claim 6, wherein the weighting function is a linear function, and weights of pixel values, or respectively redundant cost function values, are increased from 0 to 1 according to a linear distribution between 0 and L1 and between R1 and 0, and L1 and R1 are relative widths of an applied truncation filter.