Method of fast image reconstruction
View Patent ↗The present invention provides a method of fast image construction. The wavelength information is extracted in advance based on characteristics of a Fourier domain Optical Coherent Tomography (OCT) system, to obtain a vector of wavelengths which are in a uniform distribution in a wave number space, and thus to obtain a virtual position coefficient of this wavelength vector at a CCD, from which a weight matrix is calculated based on a transfer function for a discrete Fourier transform with zero-padding interpolation. In operation of the system, the interpolation is carried out based on the weight matrix and collected data, or is carried out based on the weight matrix which has been truncated by being subject to windowing and the collected data, to obtain interpolated data satisfying requirements. The method according to the present invention is simple and easy to implement, by which, it is possible to improve the precision and speed of the Fourier domain OCT data process, and thus to improve the capacity of real-time image reconstruction of the Fourier domain OCT system.
1. A method of fast image reconstruction, comprising steps of:
determining wavelengths, which, after being diffracted by a diffracting grating ( 9 ) and then passing through a lens ( 10 ), are incident on a linear scanning CCD ( 11 ) with N points of pixels, to obtain a vector {right arrow over (λ)} 1 ={λ 1 , λ 2 , . . . λ N } of wavelengths which are in an uniform distribution in a wavelength space, with a wavelength difference Δλ, an actual position coefficient of the wavelength vector at the CCD ( 11 ) being In{right arrow over (d)}ex1={=1, 2, . . . , N};
converting a vector of wave numbers, which are uniformly distributed in a wave number space between a wave number corresponding to the shortest wavelength λ 1 and a wave number corresponding to the longest wavelength λ N , into a vector {right arrow over (λ)} 2 ={λ 1 ′, λ 2 ′, . . . , λ N ′} of wavelengths which are not in an uniform distribution in the wavelength space, and calculating a virtual position coefficient In{right arrow over (d)}ex2={s n ; n=1, 2, . . . , N} of the wavelength vector {right arrow over (λ)} 2 at the CCD ( 11 ) based on the wavelength difference Δλ;
based on a transfer function TF(n,s n ) for zero-padding interpolation, deriving a N*N weight matrix H N*N (n,s n ) from In{right arrow over (d)}edx1={n; n=1, 2, . . . N} and In{right arrow over (d)}ex2={s n ; n=1, 2, . . . , N};
upon collecting a data vector x={x 1 , x 2 , . . . , x N } by the CCD ( 11 ), carrying out interpolation on the data vector x={x 1 , x 2 , . . . , x N } by means of the weight matrix H N*N (n,s n ) to obtain interpolated data x′(s n )={x s1 ′, x s2 ′, . . . , x sN ′}; and
carrying out a discrete Fourier transform on the interpolated data x′(s n ) {x s1 ′, x s2 ′, . . . , x sN ′}, for image reconstruction.
2. The method of fast image reconstruction according to claim 1 , wherein the transfer function for zero-padding interpolation is based on the following equation
TF
(
n
,
s
n
)
=
1
+
∑
i
=
1
N
/
2
cos
(
2
π
N
i
(
n
-
s
n
)
)
.
3. The method of fast image reconstruction according to claim 1 , wherein the transfer function for zero-padding interpolation is based on the following equation
TF
(
n
,
s
n
)
=
1
+
∑
i
=
1
N
/
2
cos
(
2
π
N
i
(
n
-
s
n
)
)
+
(
2
-
2
)
cos
(
π
(
s
n
-
n
)
)
.
4. The method of fast image reconstruction according to claim 1 , wherein the transfer function for zero-padding interpolation is based on the following equation
TF
(
n
,
s
n
)
=
1
+
∑
i
=
1
N
/
2
cos
(
2
π
N
i
(
n
-
s
n
)
)
-
cos
(
π
(
s
n
-
n
)
)
.
5. The method of fast image reconstruction according to claim 1 , wherein the virtual position coefficient Index2={s n ; n=1, 2, . . . , N} is based on the following equation
s
n
=
λ
n
′
-
λ
1
′
Δλ
+
1.
6. The method of fast image reconstruction according to claim 1 , wherein the virtual position coefficient Index2={s n ; n=1, 2, . . . , N} is based on the following equation
s
n
=
λ
n
′
-
λ
1
′
Δ
λ
.
7. The method of fast image reconstruction according to claim 1 , wherein the weight matrix H N*N (n,s n ) is truncated by being subject to windowing based on a window function, and the interpolation is carried out on the data vector x={x 1 , x 2 , . . . , X N } by means of the truncated weight matrix.
8. The method of fast image reconstruction according to claim 1 , wherein the interpolation on the data vector x={x 1 , x 2 , . . . , X N } is based on the following equation
x
′
(
s
n
)
=
∑
n
=
Min
Max
x
n
H
N
*
N
(
n
,
s
n
)
W
(
n
-
Min
)
,
wherein W(*) is the window function, and values of Max and Min are determined by a window length of the window function and respective virtual positions together.
9. The method of fast image reconstruction according to claim 1 , wherein the discrete Fourier transform is carried out on the interpolated data x′(s n )={x s1 ′, x s2 ′, . . . , x sN ′} to obtain intensity relative data X′(s), and the image reconstruction is carried out based on the following equation
Intensity=Contrast*(10*log 10( X ′( s )+Brightness_Bias))+255,
wherein Intensity indicates a gradation vale, Contrast indicates a contrast, and Brightness_Bias indicates a brightness bias, and
if the calculated gradation value Intensity is smaller than 0, then a value of 0 is assigned to Intensity; and if the calculated gradation value Intensity is greater than 255, then a value of 255 is assigned to Intensity.