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

What is X-ray fluoroscopy system and digital acquisition system Content What is X-ray fluoroscopy system and digital acquisition system The principle and implementation of self-adaptive digital acquisition Experiment and Conclusions Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

1. What is X-ray fluoroscopy system and digital acquisition system? Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

What’s X-ray fluoroscopy system? X-ray fluoroscopy system is a system for medical diagnosing that can render image of the body of patient by convert X-ray which pass through and attenuated by the body into visible light and record it on film or other media. It’s a very common method for examination in hospitals. Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

Construction of X-ray fluoroscopy system Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

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

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

The main difficulties in video digital acquisition x-ray fluoroscopy image detection noise and digital quantum noise Adjusting imaging contrast and resolution Device background signal Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

Improve hardware quality of x-ray imaging system How to deal with them? choose a appropriate working point automatically and suppressed background signal by software Improve hardware quality of x-ray imaging system Choose grabber board with high quantization precision Voltage stabilization and electromagnetic shielding Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

Digital video processing system(1) Enhancement Annotation Display Diagnose manual x-ray video Information navigation NSP grabber board Host Report Aided diagnose Aided treat ment Control Archiving and backup Query and management PACS Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

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

Jie BAO , ImageInfoLab , Hefei University of Technology 2. The principle and implementation of self-adaptive digital acquisition Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

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

Self-adaptive digital acquisition system Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

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

Jie BAO , ImageInfoLab , Hefei University of Technology Valid observe region (a) Whole valid observe region. White line is detected region edge by improved seed algorithm. (b) Valid observe region with occlusion Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

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

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

Jie BAO , ImageInfoLab , Hefei University of Technology 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

Background removing algorithm Acquire and save device background signal (I1) when device is idle. Acquire images to be observed (I2). Perform image operation in valid region : I3=I1-I2 ; I4=NOT I3; I4 is the image signal removed of background. Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

3.3 Setting acquisition working point 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 Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

Meaning of offset, gain and reference Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

Meaning of black level and white level Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

Working point setting rule 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. Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

Dynamic range analysis of valid region 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). Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

Self-adaptive acquisition parameters setting Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

Universal acquisition parameters choosing 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. Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

3. Experiment and Conclusions Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology

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

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

Jie BAO , ImageInfoLab , Hefei University of Technology 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

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

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

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

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

Jie BAO , ImageInfoLab , Hefei University of Technology 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

Jie BAO , ImageInfoLab , Hefei University of Technology Thank you! Aug.22,2000,WCC2000 Jie BAO , ImageInfoLab , Hefei University of Technology