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Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 1
Digital image self-adaptive acquisition in medical x-ray imaging
Bao Jie, Gao Jun et.al.Lab on Image Information Processing
Hefei University of Technology , China
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 2
Content
What is X-ray fluoroscopy system and digital acquisition systemThe principle and implementation of self-adaptive digital acquisition
Experiment and Conclusions
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 3
1. What is X-ray fluoroscopy system and digital acquisition
system?
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 4
What’s X-ray fluoroscopy system?
X-ray fluoroscopy system is a system formedical diagnosing that can render image ofthe body of patient by convert X-ray whichpass through and attenuated by the body intovisible light and record it on film or othermedia. It’s a very common method forexamination in hospitals.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 5
Construction of X-ray fluoroscopy system
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 6
Why study the digital acquisition of X-ray fluoroscopy system?(1)
The digitalization of x-ray imaging is very important for PACS (Picture Archiving and Communication system); high-quality digital X-ray medical images are indispensable for PACS data source.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 7
Why study the digital acquisition of X-ray fluoroscopy system?(2)
There are three ways to digitalize x-ray imaging
Computed Radiography (CR)
Digital Radiography (DR)
Video digital acquisition.
Advantages of video digital acquisition : ability to see dynamic change of organs, device simplicity, operating convenience, and low-cost
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 8
The main difficulties in video digital acquisition
x-ray fluoroscopy image detection noise and digital quantum noiseAdjusting imaging contrast and resolution
Device background signal
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 9
How to deal with them?
Improve hardware quality of x-ray imaging system
Choose grabber board with high quantization precision
Voltage stabilization and electromagnetic shielding
choose a appropriate working point automatically and suppressed background signal by software
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 10
x-ray video NSPgrabber board Host
Control
PACS
Enhancement
Annotation
Display
Diagnosemanual
Informationnavigation
Report
Aided diagnose
Aided treatment
Archiving and backup
Query and management
Digital video processing system(1)
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 11
Digital video processing system(2)
Host should analyze the input signal while sampling and quantization to adjust grabber board setting for valid signal to utilize the dynamic range sufficiently, and to make device working in linear range.
The grabber board we used is NSP (Native Signal Process) frame-grabber board DT3153-LS, it can adjust reference, offset, gain, black level and white level by software, which make it possible for self-adaptive acquisition by software.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 12
2. The principle and implementation of self-adaptive
digital acquisition
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 13
Self-adaptive digital acquisition
To resolve problems brought forward in section 1, we use digital subtraction technique to realize background removing for self-adaptive acquisition, and monitor the dynamic range of image valid region to search for the best acquisition working point automatically.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 14
Self-adaptive digital acquisition system
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 15
3.1Valid region recognition
The acquired image is not entirely valid. Generally speaking, the valid region is a circle.
We should only count on valid region while removing background and analyzing the image feature to adjust acquisition parameters, so we must recognize the valid region at first.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 16
(a) Whole valid observeregion. White line isdetected region edge byimproved seed algorithm.
(b) Valid observe region with occlusion
Valid observe region
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 17
Valid region detection algorithm (1)
1. Compute the histogram of left and right narrow edges of the image, the gray-level corresponding to histogram peak value is the gray-level of invalid region.
2. Perform median filtering to remove noise.
3. Grow region using classical seed growing algorithm starting from any invalid point.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 18
Valid region detection algorithm (2)
4. Generate initial mask(bilevel ) image of valid region. Perform Sobel operator to this image to extract its edge.
5. Detect circle by general Hough transform; get the radius and the center of the circle.
6. Generate valid region mask using result of step 5.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 19
3.2 Background removing
Nonuniform background will affect image quality and the computing of image characteristic to adjust acquisition parameters.
So a digital subtraction will remove background signal while keep the validity of information.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 20
Background removing algorithm
1. Acquire and save device background signal (I1) when device is idle.
2. Acquire images to be observed (I2).
3. Perform image operation in valid region : I3=I1-I2 ; I4=NOT I3;
4. I4 is the image signal removed of background.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 21
After above-mentioned pre-processing, we will adjust black level, white level, gain, reference and offset automatically based on histogram analysis of image valid region to obtain best acquisition quality. Black level = - offset
White level = reference / gain -offset
3.3 Setting acquisition working point
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 22
Meaning of offset, gain and reference
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 23
Meaning of black level and white level
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 24
Decreasing offset will shift image to light zone, increasing offset will shift image to dark zone, namely offset behaves as brightness adjusting; decreasing reference will compress image to light zone, increasing reference will compress image to dark zone, namely reference behaves as contrast adjusting.
Working point setting rule
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 25
Analyze the proportion of dark zone and light zone in the histogram of image valid region, the aim of adjusting is to keep proper proportion of dark zone and light zone for best image acquisition performance.
Setting brightness at first to ensure dark zone isn't too much then setting contrast( that is, properly setting white level by adjusting reference).
Dynamic range analysis of valid region
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 26
Self-adaptive acquisition parameters setting
B e g i n R e a d i n e s s j u d g m e n t
I m a g e a c q u i s i t i o n V a l i d r e g i o n r e c o g n i t i o n , b a c k g r o u n d r e m o v i n g
V a l i d r e g i o n a n a l y s i s D y n a m i c
T o o d a r k r a n g e
T o o b r i g h t W h i l e ( d a r k z o n e i s t o o m u c h & & o f f s e t
i s n o t o u t o f l o w e r b o u n d ) W h i l e ( d a r k z o n e i s t o o f e w & & o f f s e t i s
n o t o u t o f u p p e r b o u n d ) D e c r e a s e o f f s e t I n c r e a s e o f f s e t
I m a g e a c q u i s i t i o n , b a c k g r o u n d r e m o v i n g
I m a g e a c q u i s i t i o n , b a c k g r o u n d r e m o v i n g
V a l i d r e g i o n a n a l y s i s
V a l i d r e g i o n a n a l y s i s L i g h t
L e s s z o n e a n a l y s i s
M o r e W h i l e ( l i g h t z o n e i s t o o m u c h & &
r e f e r e n c e i s n o t o u t o f u p p e r b o u n d ) W h i l e ( l i g h t z o n e i s t o o f e w & &
r e f e r e n c e i s n o t o u t o f l o w e r b o u n d ) D e c r e a s e r e f e r e n c e I n c r e a s e r e f e r e n c e
I m a g e a c q u i s i t i o n , b a c k g r o u n d r e m o v i n g
I m a g e a c q u i s i t i o n , b a c k g r o u n d r e m o v i n g
V a l i d r e g i o n a n a l y s i s
V a l i d r e g i o n a n a l y s i s
E n d
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 27
It's very inefficient and unnecessary to setting best working point every time we take fluoroscopy.
In practice, expert judgment and adjusting is used to choose universal acquisition parameters.
Universal acquisition parameters choosing
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 28
3. Experiment and Conclusions
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 29
Run interface of self-adaptive acquisition module
Run interface of self-adaptive acquisition module in ImagePro™ implemented by Visual C++6.0
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 30
Valid region detection
Original Image Valid region mask image Sobel edge-detect image
integrated valid region Rim of Valid Region by improved algorithm
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 31
Background removing
acquired image with nonuniform background
device background signal
image after removing device background
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 32
self-adaptive adjusting(1):
Acquired image before self-adaptive adjusting. Black level=0V, white level =0.7V, offset=0V, gain=1, reference =0.7V
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 33
self-adaptive adjusting(2):
Histogram of valid region in (1). mean = 70.48, median value=54. Image is too dark.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 34
self-adaptive adjusting(3):
Acquired image after self-adaptive adjusting. Black level =-0.042V, white level =0.258V, offset=0.042V, gain=2, reference= 0.6V
scapula
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 35
self-adaptive adjusting(4):
Histogram of valid region in (3). mean = 121.19. median value = 113.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 36
Conclusions
It's possible to implement self-adaptive acquisition of medical video image automatically by integrating various images processing method. The proposed method has recognized the valid region of image and removed the background, then adjusted acquisition parameters by analyzing image dynamic range to obtain best acquisition quality. But there still some problem remained to be resolved.
Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology 37
Thank you!