X线摄影基础理论

Wilhelm Roentgen
While passing the discharge, he suddenly noticed a shimmering light on the table top. He could not believe his eyes, so he again repeated the experiment. He released the discharge many times producing the same results each time. Greatly excited, he realized that the green fluorescence was emanating from the screen. He repeated the experiment again, this time moving the screen further and further away and he still received the same results.
Wilhelm Roentgen
He became so fascinated that he decided to forego his other studies and concentrate solely on the production of cathode rays. One Friday evening, on November 8, 1895, he worked alone in his laboratory. It was the beginning of the weekend and all of his assistants had gone home.
X线的发现及简史
1895年11月8日,德国物理学家威廉·康拉德·伦琴 （W·C·Rontgen）发现了X射线;当年12月22日伦 琴利用X线拍摄了夫人手的照片,这是人类历史上第 一张揭示人体内部结构的影像。
1896年X线就开始应用于医学,至今它经历了X线的 医学应用、X线诊断学的建立以及医学影像学的逐 步形成三个阶段.
Wilhelm Roentgen
He had set up his experiment using a Crookes tube fitted with an anode and cathode, separated from each other by a few centimeters in the tube. He used a Rhumkoff induction coil to produce a difference of potential of a few thousand volts, knowing that a stream of charged particles would originate in the cathode and would be attracted to the anode.
Wilhelm Roentgen
Later, in 1896, he accepted the Rumford gold medal of the Royal Society and in 1901 he would be the first to receive the Nobel Prize for physics, but he bequeathed the Nobel prize money to scientific research at Wurzburg.
Wilhelm Roentgen
When he placed a lead disk, which he was holding, in the cathode ray path he was astonished to find the shadow of the round circle appeared on the screen along with the outline of his thumb and forefinger and within them the bones of his hand! He replaced the screen with a photographic plate and employed his wife Bertha (Frau Roentgen) to place her hand on the photographic plate while he directed the rays at it for fifteen minutes.
诊断使用的X线有两种不同的放射方式： 连续放射 特性放射。
连续放射
连续放射又称为韧致放射,是高速电子与靶 物质原子核作用的结果.
当带有能量的高速电子接近靶物质的原子核 时，带有负电荷的电子在核电场（正电荷） 的吸引下．偏离原有方向。在改变方向时因 丢失能量而减速。此时电子所丢失的能量直 接以X线光子的形式放射出来。这种放射叫 连续放射（也称普通放射）。
X线物理基础
江汉大学卫生技术学院 医学影像系
X线物理基础
X线的产生 X线产生的原理 X线的本质与特性 X线与物质相互作用 X线质、X线量与X线强度 X线的吸收与衰减
X线的产生
X线的发现及简史 X线的产生 X线产生的条件
Wilhelm Roentgen
In October of 1895, Wilhelm Conrad Roentgen (18451923) who was professor of physics and the director of the Physical Institute of the University of Warburg, became interested in the work of Hillorf, Crookes, Hertz, and Leonard. The previous June, he had obtained a Leonard tube from Muller and had already repeated some of the original experiments that Leonard had created. He had observed the effects Leonard had as he produced cathode rays in free air.
连续放射
连续放射产生的X线是一束波长不等的混合线,其X线光子的 能量取决于:电子接近核的情况;电子的能量和核电荷.
如果一个电子与原子核相撞,其全部动能丢失转换为X线光子, 其最短波长为 λmin=hc/kVp=1.24/kVp(nm)
λ＝波长，nm＝波长单位，E0＝最大电子能量。而电子能量 又与管电压有关，所以，当施与X线管两端管电压为l00kVp 时，电子所获得的最大能量就是l00keV，它所产生的X线光 子的最短波长就是0.0124nm。
伦琴及第一张X线照片
X线的产生
X线的产生是能量转换的结果。X线在X线管 中产生，当X线管两极间加有高电压时，阴 极灯丝发散出的电子就获得了能量，以高速 运动冲向阳极。由于阳极的阻止，使电子骤 然减速,约98%的动能产生热量,2%动能转 换为X线。
X线产生的条件
灯丝加 热获得
X线产生必须具备以下3个条件:
Wilhelm Roentgen
Roentgen hurriedly prepared his notes so that his first report "On a New Kind of Rays" could be published in the Proceedings of the Physical Medical Society of Wurburg on December 28, 1895. Not knowing what these emanations were he uses the term x-ray to describe the rays he was producing.
电子源
定向直流高压； 维持管内真空
高速电子的产生 电子的骤然减速
阳极靶
X线源自文库产生示意图
X线机原理图
X线产生的原理
X线产生的原理，就是高速电子和阳极靶物质的原子相互作 用中能量转换的结果，这是一个复杂的过程。
X线的产生是利用了靶物质的3种特性：即核电场、轨道电子 结合能和原子存在于最低能级的需要。
Wilhelm Roentgen
Roentgen knew the fluorescence could not be produced by the cathode rays since it was well known that they could not penetrate through the wall of the tube. Visible light could not be the stimulus since the tube was covered with a shield which was opaque to light. He boldly hypothesized that he must have been producing some unknown type of radiation。
Wilhelm Roentgen
The laboratory Roentgen worked in that evening was very similar to all other laboratories of those who worked before him, but the conditions that existed that evening varied in three very important ways. His laboratory was dark, his tube was covered with a light-proof cardboard jacket and a screen of fluorescent material lay on a table a few feet away from the apparatus.
特性放射是在靶物质原子壳层电子的跃迁中产生的。特性放 射的X线光子能量与冲击靶物质的高速电子能量无关。它只 服从于靶物质的原子特性。
Wilhelm Roentgen
Roentgen spent the next eight weeks in his laboratory repeating his experiments. He ate and even slept in his laboratory as he attempted to determine if the rays could penetrate substances besides the air. He placed various objects between the tube and screen and he found that the screen still fluoresced but with different intensities depending on the material being used.
连续放射
特性放射
这是高速电子击脱靶物质原子的内层轨道电子，而产生的一 种放射方式。一个常态的原子经常处于最低能级状态，它永 远保持其内层轨道电子是满员的。当靶物质原子的K层电子 被高速电子击脱时，K层电子的空缺将要由L层电子补充，此 时L层电子将把多余的能量作为X线光子释放出来，此即K系 特性放射；而L层电子的空缺，则由M层电子补充，即产生L 系特性放射。