Advantage : Good method in theory Disadvantage: Demand special X-ray devices (switch tube voltage in high speed) ； Bone and Soft tissue image differently in two tube voltage
(对比剂到达前后都做双能减影, 消除软组织, 再利 用结果做时间减影,消除骨组织)
DSA缺陷的弥补: 图像配准
Advantage of Digital X-ray Imaging Technology
• Contrast resolving power • Small Radiation Dose • Procession of image • Convenience storage • High sensitvity to detect X-ray and Low Dose • High dynamic range • PACS • Powerful function to do procession and analysis
Mixed subtraction
• Do 2 kinds of subtraction imaging in same time. • Do Three times of Subtraction • Do the first energy subtraction before contrast
agent injection, the second after injection, do the last with the two result.
Method of DSA
Location and anchor point
图像配准与运动伪影
• Time subtraction • Energy subtraction • Mixed subtraction
Time subtraction
• Concentration • Take
successive shots • Successive subtract • 得到的是图像 序列
Digital X-ray Imaging Technology
Digitize the X-ray imaging and adopt digital technology to do procession of image.
• DSA——Digital subtraction angiography 数字化摄影 • CR——computed radiograph • DR—— Digital radiography (DDR and IDR) • DSI——Digital Sport Imaging • DF —— Digital fluorography
物理含义
I I e(BdB T dT ) 0
I I e(BdB T (dT dI )I dI )
1
0
S ln I ln I1 (I T )dI
The image after DS is determined by the absorption coefficient of contrast agent and length, is independent with bone and soft tissues.
Energy subtraction/能量减影/双能 减影/K缘减影
• Iodine
• X-ray 33KeV (tube voltage :70KV and 120KV)
• Image(70KV, be equivalent to background) —— Image(120KV, be equivalent to contrast agent image)
Digital Subtraction Angiography DSA
Digital subtraction angiography is a kind of digital X-ray imaging technology used to research vascular system. By it we can subtract unnecessary portion from an X-ray image of vascular.
• Interventional therapy in cardiology • Interventional radiology therapy • Interventional medicine in neurology vascular
disease
Observe the position of catheter in vascular, control the motion of catheter to release drug or do a little operation (such as settle bracket in narrow vessels.
What is image subtraction Pixel to Pixel
45678
25678
7 8 9 3 7 —— 7 6 9 3 5
13735
13515
05985
05765
20000 == 0 2 0 0 2
00220 00220
Principle of DSA
• A: Image without contrast agent (Mask) • B: Image with contrast agent • C: Image of subtraction
Reason
在无血管情况下:
ln I L ln I0L (BLdB TL dT )
ln IH ln I0H (BH dB IL
(KLBL KH BH )dB (KLTL KH TL )dT KHCH KLCL
通过调整系数,可以减少其中一种组织的影响.