CN103530858B - Frequency domain filtering-based CBCT (Cone Beam Computed Tomography) panoramic image enhancement method - Google Patents

Frequency domain filtering-based CBCT (Cone Beam Computed Tomography) panoramic image enhancement method Download PDF

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CN103530858B
CN103530858B CN201310491508.1A CN201310491508A CN103530858B CN 103530858 B CN103530858 B CN 103530858B CN 201310491508 A CN201310491508 A CN 201310491508A CN 103530858 B CN103530858 B CN 103530858B
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cbct
enhancement method
high frequency
image
panorama sketch
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CN103530858A (en
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徐建军
王远军
聂生东
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Nantong City Mu Jingwei Electricity Development In Science And Technology Co Ltd
University of Shanghai for Science and Technology
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Nantong City Mu Jingwei Electricity Development In Science And Technology Co Ltd
University of Shanghai for Science and Technology
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Abstract

The invention discloses a frequency domain filtering-based CBCT panoramic image enhancement method, which includes the following steps: Fourier transform is carried out on an original image, a high-pass filter is produced, high-pass filtering is carried out on the original image, an offset is added according to the high-frequency emphasis filter, and finally, Fourier inverse transform is carried out, so that a spatial-domain image is obtained. The method overcomes the defect of low contrast in conventional CBCT images, enriches the edge information of images, and offers effective help to clinical applications for doctors.

Description

Based on the CBCT panorama sketch Enhancement Method of frequency filtering
Technical field
The present invention relates to a kind of CBCT panorama sketch Enhancement Method, be specifically related to a kind of CBCT panorama sketch Enhancement Method based on frequency filtering.
Background technology
Cone beam (pencil-beam) CT is that development in recent years is rapid, the three-dimensional imaging device that clinical oral has superiority most.CBCT uses flat panel detector and pencil-beam X ray to do rotation sweep (180 times-360 times, different according to product difference) around detection bodies.Two-dimensional projection image will be obtained and utilize cone beam ct reconstruction algorithm in a computer, obtain three-dimensional volume data.The maximum difference of it and spiral CT is, during CBCT scanning, the data for projection in each direction is two-dimentional, it directly obtains three-dimensional volume data after rebuilding, and the data for projection in each direction is one dimension during Spiral CT scan, can only obtain the monolayer slices data of two dimension after reconstruction, three-dimensional volume data needs the multiple two dimension slicing of continuous sweep.Although the projection theory of CBCT and spiral CT are diverse, their reconstruction algorithm is very similar.Due to CT imaging, relative to traditional CT, its x-ray utilization factor is high, and roentgen dose X is low, and very high isotropic spatial resolution, its cost is lower, and floor area is little, and surface sweeping is more flexible.
CBCT imaging technique developed a kind of emerging 3 Dimension Image Technique rapidly in recent years.Especially well developed on clinical oral.CBCT is convenient and swift, and radiation dose is low, and the spatial resolution of image is high, has isotropic, and have accurate and stable CT value, but its density resolution is low, soft tissue rendering is unintelligible, and border is affected by noise larger.Improve the detailed information of image, need to carry out sharpening enhancement, to provide image boundary clearly, facilitate doctor's delineating target area.
It is all character based on local pixel that filter in spatial domain carries out calculating at every turn, integral image characteristic can not be embodied better, as improved the contrast of integral image, the CBCT image enhaucament of high resolving power, low contrast cannot be met, and frequency domain sharpening technique to calculate be all utilize all data in image at every turn, have the feature of the overall situation, therefore we improve the frequency filtering algorithm of classics.
Summary of the invention
Goal of the invention: the object of the invention is the contrast in order to solve integral image in prior art, the deficiency of CBCT image enhaucament of high resolving power, low contrast cannot be met, a kind of global property utilizing image is provided, strengthen the overall contrast of image, thus reach the Enhancement Method based on frequency filtering of the marginal information strengthening CBCT image.
Technical scheme: a kind of CBCT panorama sketch Enhancement Method based on frequency filtering of the present invention, comprises the steps:
(1) read piece image f (x, y), size is M × N, calculates pad parameter P and Q, and fills with 0 pair of f (x, y), forms the image f that size is P × Q p(x, y);
(2) Fourier transform of computed image f (x, y), obtains F (u, v);
(3) that generate a real number, symmetrical High frequency filter function H hP(u, v), its size is P × Q, and the center of wave filter is on four angles of matrix boundaries;
(4) high frequency emphasis wave filter is produced according to expression formula;
(5) high frequency emphasis wave filter and F (u, v) is calculated according to computing formula;
(6) image obtained in step (5) is carried out Fourier inversion, transfer spatial domain picture to;
(7) from step (6), the left upper quadrant of gained image extracts M × n-quadrant, obtains final result.
As preferably, P=2M, Q=2N described in step (1).
As preferably, described in step (3), High frequency filter function is Butterworth High frequency filter H HP ( u , v ) = 1 1 + [ D 0 / D ( u , v ) ] 2 n Or be Gaussian High frequency filter H HP ( u , v ) = 1 - e - D 2 ( u , v ) / 2 D 0 2 , Wherein D 0for filter radius, n gets 1 or 2.
As optimization, described D 0for 0.05 of wave filter size.
As preferably, described in step (4), expression formula is H (u, v)=k 1+ k 2* H hP(u, v), wherein k 1>=0 controls the side-play amount apart from initial point, k 2the contribution of>=0 control high frequency, produces high frequency emphasis wave filter.
As optimization, described k 1=1, k 2=1.
As preferably, computing formula described in step (5) is G (u, v)=H (u, v) * F (u, v).
As preferably, described in step (6), Fourier inversion formula is
Beneficial effect: the present invention compensate for the deficiency of existing CBCT image low contrast, has enriched the marginal information of image, for doctor's clinical practice provides effective help.
Accompanying drawing explanation
Fig. 1 is process flow diagram of the present invention.
Fig. 2 is the original image of oral cavity CBCT panorama sketch.
Fig. 3 is the high frequency emphasis algorithm that the present invention adopts Butterworth high frequency filter, to the design sketch after Fig. 2 sharpening enhancement.
Fig. 4 is the high frequency emphasis algorithm adopting Gaussian high frequency filter, to the design sketch after Fig. 2 sharpening enhancement.
Embodiment
A kind of CBCT panorama sketch Enhancement Method based on frequency filtering as shown in Figure 1, comprises the steps:
(1) read piece image f (x, y), size is M × N, calculates pad parameter P and Q, and fills with 0 pair of f (x, y), forms the image f that size is P × Q p(x, y);
(2) Fourier transform of computed image f (x, y), obtains F (u, v);
(3) that generate a real number, symmetrical High frequency filter function H hP(u, v), its size is P × Q, and the center of wave filter is on four angles of matrix boundaries;
(4) high frequency emphasis wave filter is produced according to expression formula;
(5) high frequency emphasis wave filter and F (u, v) is calculated according to computing formula;
(6) image obtained in step (5) is carried out Fourier inversion, transfer spatial domain picture to;
(7) from step (6), the left upper quadrant of gained image extracts M × n-quadrant, obtains final result.
P=2M, Q=2N described in above-mentioned steps (1), described in step (3), High frequency filter function is Butterworth High frequency filter or be Gaussian High frequency filter wherein D 0for filter radius, n gets 1 or 2, wherein D 0for 0.05 of wave filter size; Described in step (4), expression formula is H (u, v)=k 1+ k 2* H hP(u, v), wherein k 1>=0 controls the side-play amount apart from initial point, k 2the contribution of>=0 control high frequency, produces high frequency emphasis wave filter, wherein k 1=1, k 2=1; Computing formula described in step (5) is G (u, v)=H (u, v) * F (u, v), and described in step (6), Fourier inversion formula is
As Fig. 2 and Fig. 3, Fig. 4 contrast can be found out, after method process of the present invention, the marginal information of image is obviously enhanced, for doctor's clinical practice provides effective help.
Comparatively speaking, the treatment effect of Gaussian high frequency filter is more excellent than Butterworth high frequency filter treatment effect, Butterworth high frequency filter treatment effect has ringing, the spatial domain that the inverse fourier transform of Gaussian wave filter generates also is Gauss, therefore completes and does not have ringing.

Claims (8)

1., based on a CBCT panorama sketch Enhancement Method for frequency filtering, it is characterized in that: comprise the steps:
(1) read piece image f (x, y), size is M × N, calculates pad parameter P and Q, and fills with 0 pair of f (x, y), forms the image f that size is P × Q p(x, y);
(2) Fourier transform of computed image f (x, y), obtains F (u, v);
(3) that generate a real number, symmetrical High frequency filter function H hp(u, v), its size is P × Q, and the center of wave filter is on four angles of matrix boundaries;
(4) high frequency emphasis wave filter is produced according to expression formula;
(5) high frequency emphasis wave filter and F (u, v) is calculated according to computing formula;
(6) image obtained in step (5) is carried out Fourier inversion, transfer spatial domain picture to;
(7) from step (6), the left upper quadrant of gained image extracts M × n-quadrant, obtains final result.
2. a kind of CBCT panorama sketch Enhancement Method based on frequency filtering according to claim 1, is characterized in that: P=2M, Q=2N described in step (1).
3. a kind of CBCT panorama sketch Enhancement Method based on frequency filtering according to claim 1, is characterized in that: described in step (3), High frequency filter function is Butterworth High frequency filter or be Gaussian High frequency filter wherein D 0for filter radius, n gets 1 or 2.
4. a kind of CBCT panorama sketch Enhancement Method based on frequency filtering according to claim 3, is characterized in that: described D 0for 0.05 of wave filter size.
5. a kind of CBCT panorama sketch Enhancement Method based on frequency filtering according to claim 1, is characterized in that: described in step (4), expression formula is H (u, v)=k 1+ k 2* H hp(u, v), wherein k 1>=O controls the side-play amount apart from initial point, k 2the contribution of>=0 control high frequency, produces high frequency emphasis wave filter.
6. a kind of CBCT panorama sketch Enhancement Method based on frequency filtering according to claim 5, is characterized in that: described k 1=1, k 2=1.
7. a kind of CBCT panorama sketch Enhancement Method based on frequency filtering according to claim 1, is characterized in that: computing formula described in step (5) is G (u, v)=H (u, v) * F (u, v).
8. a kind of CBCT panorama sketch Enhancement Method based on frequency filtering according to claim 1, is characterized in that: described in step (6), Fourier inversion formula is
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1947154A (en) * 2004-04-21 2007-04-11 皇家飞利浦电子股份有限公司 Cone beam CT apparatus using truncated projections and a previously acquired 3D CT image
CN103034989A (en) * 2013-01-09 2013-04-10 清华大学 Low-dosage CBCT (Cone Beam Computed Tomography) image denoising method based on high-quality priori image

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US20120019512A1 (en) * 2010-07-22 2012-01-26 Dong Yang Noise suppression for cone-beam image reconstruction

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1947154A (en) * 2004-04-21 2007-04-11 皇家飞利浦电子股份有限公司 Cone beam CT apparatus using truncated projections and a previously acquired 3D CT image
CN103034989A (en) * 2013-01-09 2013-04-10 清华大学 Low-dosage CBCT (Cone Beam Computed Tomography) image denoising method based on high-quality priori image

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