Pre-reconstruction calibration, data correction, and material decomposition method and apparatus for photon-counting spectrally-resolving x-ray detectors and x-ray imaging

Patent metadata

Field	Value
Publication number	US-2016287205-A1
Application number	US-201514676594-A
Country	US
Kind code	A1
Filing date	Apr 1, 2015
Priority date	Apr 1, 2015
Publication date	Oct 6, 2016
Grant date	—

Abstract

An apparatus and method of processing X-ray projection data obtained using photon-counting detectors and having multiple spectral components. The processing of the projection data includes correcting for nonlinear detector response, where the detector response model includes: pileup, ballistic deficit effects, polar effects, and characteristic X-ray escape. The processing of the projection data also includes a material decomposition mapping the projection data from spectral components into material components corresponding to high-Z and low-Z materials. The material decomposition includes a noise balancing process where the allocation of spectral components between a high-energy and a low-energy combination of spectral components is adjusted such that both high- and low-energy components have signal-to-noise ratios of similar magnitude. For computed tomography (CT) applications, material decomposition can be followed by image reconstruction and then image post-processing and presentation. For non-CT applications, material decomposition can be followed by image post-processing and presentation.

First claim

1 . An apparatus to process projection measurements, the apparatus comprising:
processing circuitry configured to
obtain a plurality of datasets, wherein each dataset represents radiation detected by a plurality of detectors, the radiation having been transmitted through an object, wherein each dataset corresponds to a respective energy bin having an energy-detection spectrum that is narrower than a bandwidth of an energy spectrum of the transmitted radiation;
calculate a nonlinear detector response of each dataset and subtract the nonlinear detector response from the dataset to obtain a corresponding linear-response dataset; and
perform a material decomposition of the plurality of linear-response datasets into a plurality of projection lengths of a first material and a second material.

2 . The apparatus according claim 1 , wherein the processing circuitry is further configured to obtain the plurality of datasets, which represent the detection of X-ray radiation.

3 . The apparatus according claim 2 , wherein the processing circuitry is further configured to:
calculate the nonlinear detector response using a detector response model, which includes at least one of pileup effects and ballistic deficit effects, polar effects, and characteristics X-ray escape effects.

4 . The apparatus according claim 3 , wherein the processing circuitry is further configured to:
calculate the nonlinear detector response of each respective detector using a corresponding nonlinear response function including a dead time of the corresponding detector τ, a quadratic response function of the corresponding detector R 1 , an X-ray flux at the corresponding detector, and an incident spectrum that is a spectrum of the energies of the X-rays incident on the corresponding detector.

5 . The apparatus according claim 4 , wherein the processing circuitry is further configured to calculate the nonlinear detector response using the X-ray flux at the detector that is determined using a reference intensity representing an X-ray intensity at an X-ray source that is related to the X-ray flux at the detector using a corresponding intensity calibration value A, and the X-ray flux at the detector and the incident spectrum are each calculated using the plurality of projection lengths, which includes a projection length of the first material and a projection length of the second material.

6 . The apparatus according claim 5 , wherein the processing circuitry is further configured to:
calibrate the plurality of detectors by determining calibration values, including the detector response model, using calibration data that includes the dead time τ of each respective detector, the quadratic response function R 1 of each respective detector, and the corresponding intensity calibration value A of each respective detector; wherein adjusting the calibration values changes a spectrum of the detector-response model, and the calibration of the plurality of detectors is performed in an iterative calibration loop by iteratively adjusting the calibration values until either a value returned by a cost function measuring the difference between a spectrum of the plurality of data sets and the spectrum of the detector-response model falls below a predefined threshold or a maximum number of calibration loop iterations is reached.

7 . The apparatus according claim 2 , wherein the processing circuitry is further configured to:
perform a material decomposition of the plurality of linear-response datasets using noise balancing to
combine the plurality of linear-response datasets into a low-energy projection-data component having a first X-ray energy spectrum, and
combine the plurality of linear-response datasets into a high-energy projection-data component having a second X-ray energy spectrum,
wherein an energy expectation value of the first X-ray energy spectrum is less than an energy expectation value of the second X-ray energy spectrum.

8 . The apparatus according claim 7 , wherein the processing circuitry is further configured to:
perform the material decomposition of the plurality of linear-response datasets into the plurality of projection lengths by calculating for each of the detectors a projection length of the first material and a projection length of the second material, wherein the calculation of the plurality of projection lengths includes calculating perturbations of beam hardening corrections for variations of attenuation values of the first and second materials around mean attenuation values.

9 . The apparatus according claim 2 , further comprising:
a polychromatic X-ray source radiating X-rays; a photon counting spectrally discriminating X-ray detector configured to detect the X-rays that are radiated from the X-ray source, where the X-ray detections are arranged into energy bins according to the detected energy of each X-ray detection, and each energy bin is assigned to a corresponding dataset of the plurality of datasets.

10 . The apparatus according claim 2 , wherein the processing circuitry is further configured to:
reconstruct a plurality of images using the plurality projection lengths of the first material and using the plurality projection lengths of the second material, where the reconstruction method is one of a filtered back-projection method, an iterative image-reconstruction method, and a statistical image-reconstruction method.

11 . The apparatus according claim 2 , wherein the processing circuitry is further configured to:
solve for the plurality of projection lengths of the first material and plurality of projection lengths of the first material by performing in an iterative loop the steps of
calculating the nonlinear detector response and subtracting the nonlinear detector response from each respective dataset to obtain the corresponding linear-response dataset, and
then performing the material decomposition on each linear-response dataset;
wherein the plurality of projection lengths of the first material and of the second material resulting from a previous iteration of material decomposition are used as the plurality of first and second material projection lengths for calculating the nonlinear detector response of a next iteration, and the iterative loop stops when a predefined stopping criteria is satisfied.

12 . A computed tomography apparatus, comprising:
a radiation source configured to emit radiation toward an image object; a plurality of detectors configured to detect the radiation having been transmitted through the image object and to generate projection data representing an intensity of the radiation at the plurality of detectors; a rotation mount configured to rotate the radiation source around the image object, wherein the radiation source is fixedly connected to the rotation mount; processing circuitry configured to
obtain a plurality of datasets of the projection data, wherein each dataset represents radiation detected by the plurality of detectors, the radiation having been transmitted through the image object, wherein each dataset corresponds to a respective energy bin having an energy detection spectrum that is narrower than a bandwidth of an energy spectrum of the transmitted radiation;
calculate a nonlinear detector response of each dataset and subtract the nonlinear detector response from the dataset to obtain a corresponding linear-response dataset; and
perform a material decomposition of the plurality of linear-response datasets into a plurality of projection lengths of a first and a second material.

13 . A method of processing X-ray projection data, comprising:
obtaining a plurality of datasets, wherein each dataset r

Assignees

• Toshiba Kk
• Toshiba Medical Sys Corp

Inventors

• Zou Yu
• Wang Xiaolan
• Petschke Adam
• Cao Chunguang
• Zhang Yuexing

Classifications

• G06T12/10

  Image preprocessing, e.g. calibration, positioning of sources or scatter correction · CPC title

• A61B6/4266

  characterised by using a plurality of detector units (A61B6/4014 takes precedence) · CPC title

• G06T2211/408

  Dual energy · CPC title

• A61B6/4241

  using energy resolving detectors, e.g. photon counting · CPC title

• A61B6/032

  Transmission computed tomography [CT] · CPC title