Count-weighted least squares parameter estimation for a photon-counting detector

Patent metadata

Field	Value
Publication number	US-9801595-B2
Application number	US-201414479955-A
Country	US
Kind code	B2
Filing date	Sep 8, 2014
Priority date	Sep 8, 2014
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

A method and apparatus for estimating a parameter vector including a plurality of parameters of a detector response model of a photon-counting detector. The method includes calculating a modeled spectrum based on an input spectrum and an initial value of the plurality of parameters. For each detector, a difference between the normalized photon count of the measured spectrum and the normalized modeled spectrum is calculated. A root mean square error (RMSE) between the measured and modeled spectra is obtained by squaring the normalized difference and weighting the normalized difference by a weighting factor. The parameter vector is updated until an optimum RMSE value is achieved. Upon determining optimal values of the parameter vector, measured data that is obtained via a patient scan is corrected based on the optimal parameter vector.

First claim

The invention claimed is:

1. A method for determining an optimal parameter vector, the parameter vector including a plurality of parameters of a detector response model of a photon-counting detector, the method comprising:
determining a normalized measured photon count for each energy bin of the photon-counting detector;
setting an initial incident photon spectrum and an initial value for each parameter of the plurality of parameters;
calculating, using the detector response model, a normalized modeled photon count for each energy bin of the photon-counting detector, based on the incident photon spectrum and the plurality of parameters;
computing, for each energy bin, a square of a difference between the normalized measured photon count and the normalized modeled photon count;
weighting the computed square of each energy bin by a weighting factor to generate weighted squares;
summing the weighted squares of each energy bin and computing a root-mean-square error for the photon-counting detector;
updating at least one of the parameters of the parameter vector;
repeating the calculating, computing, weighting, summing, and updating steps until a stopping criteria is met, so as to determine the optimal parameter vector;
correcting measured count data obtained from a scan of a subject based on the deter mined optimal parameter vector to generate corrected count data; and
reconstructing an image of a subject using the corrected count data.

2. The method of claim 1 , wherein the determining step comprises:
dividing a measured photon count of each energy bin by a total measured photon count of the photon-counting detector to determine the normalized photon count for each energy bin.

3. The method of claim 1 , wherein the calculating step comprises:
dividing a modeled photon count of each energy bin by a total modeled photon count of the photon-counting detector to calculate the normalized modeled photon count for each energy bin.

4. The method of claim 1 , wherein the weighting step comprises weighting the computed square of each energy bin by the weighting factor for each energy bin of the photon counting detector, which is the normalized measured photon count of the energy bin.

5. The method of claim 1 , wherein the step of computing the root-mean-square error (RMSE) of the photon counting detector comprises computing the RMSE as:

RMS
⁢

⁢
E

=

∑

k
=
1

k
=
N

⁢

φ
k

⁡

(

C
k

_

-

S
out

⁡

(

a
_

)

k

_

)

2

,

wherein C k is the normalized measured photon count of detector bin k, S out (a) k is the normalized modeled photon count of the detector bin k, φ k is the weighting factor for detector bin k, and N is a number of detector bins in the photon counting detector.

6. The method of claim 1 , wherein the optimal parameter vector is the parameter vector that yields a smallest value of the root-mean-square error.

7. The method of claim 1 , wherein the updating step comprises updating the parameter vector according to an exhaustive search method.

8. The method of claim 1 , wherein the updating step comprises updating the parameter vector according to one of Newton's method, a steepest descent method, a nonlinear conjugate gradient method, and a nonlinear least-squares method.

9. The method of claim 1 , wherein the repeating step comprises repeating the calculating, computing, weighting, summing, and updating steps for a predetermined number of iterations.

10. A device for determining an optimal parameter vector, the parameter vector including a plurality of parameters of a detector response model of a photon-counting detector, the device comprising:
a processing circuit configured to
determine a normalized measured photon count for each energy bin of the photon-counting detector;
set an initial incident photon spectrum and an initial value for each parameter of the plurality of parameters;
calculate using the detector response model, a normalized modeled photon count for each energy bin of the photon-counting detector, based on the incident photon spectrum and the plurality of parameters;
compute, for each energy bin, a square of a difference between the normalized measured photon count and the normalized modeled photon count;
weight the computed square of each energy bin by a weighting factor to generate weighted squares;
sum the weighted squares of each energy bin and compute a root-mean-square error for the photon-counting detector;
update at least one of the parameters of the parameter vector;
repeat the calculating, computing, weighting, summing, and updating steps until a stopping criteria is met, so as to determine the optimal parameter vector;
correct measured count data obtained from a scan of a subject based on the determined optimal parameter vector to generate corrected count data; and
reconstruct an image of a subject using the corrected count data.

11. The device of claim 10 , wherein the processing circuit is configured to determine the normalized measured photon count for each energy bin of the photon-counting by dividing a measured photon count of each energy bin by a total measured photon count of the photon-counting detector.

12. The device of claim 10 , wherein the processing circuit is configured to weight the computed square of each energy bin by the weighting factor for each energy bin of the photon counting detector, which is the normalized measured photon count of the energy bin.

13. The device of claim 1 , wherein processing circuit is configured to compute the root-mean-square error (RMSE) of

Assignees

• Toshiba Medical Sys Corp

Inventors

• Cao Chunguang
• Wang Xiaolan
• Zou Yu

Classifications

• A61B6/4241 Primary

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

• A61B6/585

  Calibration of detector units · CPC title

• G01T1/36

  Measuring spectral distribution of X-rays or of nuclear radiation {spectrometry (pulse selection circuits per se H03K; investigation of materials by radiation diffraction G01N23/20; spectrometer tubes H01J49/00)} · CPC title

• G01T1/17

  Circuit arrangements not adapted to a particular type of detector {(pulse-selection circuits H03K, G01R)} · CPC title

• G01T1/247

  Detector read-out circuitry (for processing gain or off-set correction H04N) · CPC title