图像增强器由一个大圆柱体组成, 有几个内部结构的锥形管，其中入射的x射线分布被转换成相应的无限制亮度的光像. 图像增强电视(II-TV)系统的图片如下所示. x射线到光的放大是通过几个连续的步骤实现的. 第一个, x射线入射到碘化铯(CsI)结构荧光粉上并被其吸收，产生大量光子，这是由于x射线(平均30-50 keV)与光子(平均1 -3 eV)的能量差造成的。. Absorption and conversion efficiency is on the order of 60% and 10%, respectively. A fraction of the light photons interact with an adjacent photocathode layered on the backside of the input phosphor, releasing a proportional number of electrons (typically on the order of 5 light photons / electron). 带负电荷, the electrons are accelerated through a potential difference of approximately 25,000 volts towards the positive anode positioned on the tapered side of the evacuated tube. 电磁聚焦网格在保持焦点的同时减小了在输出荧光粉结构上相互作用的电子分布, 与在输入荧光粉处最初产生的光量相比，在光强度方面产生大量增加的. II的整体亮度增益是通过影响输出荧光粉的电子的加速度和动能增加(称为电子或通量增益)以及从大面积输入荧光粉到小面积输出荧光粉的电子密度的几何面积减小(称为缩小增益)来实现的, 等于输入与输出荧光粉面积之比, 或直径的平方之比). The combination of electronic and minification gain results on the order of 5000X increase in brightness. Variable brightness gain occurs with a change in the input phosphor active area; as the field of view (FOV) is reduced, 缩小增益减小, 降低整体亮度增益(反之亦然). 输出荧光粉到电视摄像机或光斑的光学耦合, 电影, or other light detector allows the detection of the image and subsequent display.

Control of the II "speed" is achieved with the inclusion of a light-limiting aperture in the conjugate lens system. 对于需要高剂量的情况(i.e., digital subtraction angiography), the aperture diameter is reduced (large f 数字)，而对于低剂量透视应用(i.e. 上GI荧光)，孔径增大(小) f 号).

图E说明了一个典型的桌上II/TV系统, 住房, 轿厢(允许垂直和水平定位, and table (the x-ray tube is mounted under the table with a fixed geometry relative to the II detector). 图F显示了II的内部截面, 和重要的结构，包括图像增强包络, the input phosphor comprised of structured cesium iodide (CsI) scintillator material, 光电阴极由光敏元件组成, 电子发射材料(Sb2Cs3), 电子聚焦电极, 阳极结构, 由锌镉硫化(ZnCdS:Ag)组成的输出荧光粉, the tandem conjugate lenses with light limiting apertures and partially silvered mirror (to partially reflect light), 以及光光子探测器(薄膜), 电视摄像机, CCD camera) to capture the output image and convert into a useful image for viewing.

图E. Image intensifier-TV system components are shown for a conventional fluoroscopic room.

图F. II-TV系统的横截面说明了用于创建高度放大的输出光图像的各种组件. A four stage process (x-rays to light; light to electrons; electrons to light; light to electronic signal) is shown.

图像增强器尺寸

Image intensifiers come in a range of input field of view (FOV) diameters for diagnostic imaging applications, 从6英寸(15厘米FOV)到16英寸(40厘米FOV), 中间还有很多维度, 取决于成像程序的类型. II型具有球形输入荧光粉结构, 与曲率设计，以承受大的力量上II外壳, 由运行所需的内部真空产生. 输出荧光粉尺寸通常约为1英寸(2英寸).54厘米)直径. The difference in size between the input and the output results in minification of the output image, 由此，在通过真空管的加速过程中，从输入的光电阴极出现的电子被聚焦和缩小. 通过缩小获得的亮度增益等于输入荧光粉的面积与输出荧光粉的面积之比, resulting from the increased electron density and corresponding increased light intensity at the output phosphor. 在图G中, 两个视场的例子说明了电子“放大系数”，是可用的大多数图像增强系统.

图G. An image intensifier can interactively change the input FOV from a large to a smaller area. 对输出图像的影响在图插入信息中描述. 除了, x射线管准直器组件内的孔径准直器必须将x射线束限制在II的有效区域.

图像增强器可以电子地改变输入辐射视场的大小，同时保持输出视场的固定, 等于2.54厘米(1英寸)，相当于大多数电视摄像机的尺寸. 如果输入视场减半, then the size of the patient being viewed is also halved which results in a two fold magnification of the image. This type of magnification, known as electronic zoom, doubles the spatial resolution performance. 例如, the limiting spatial resolution for a 25 cm field of view and a conventional television camera (525 lines) is ~ 0.7 line pairs per mm; reducing the input field of view to half this value (i.e., 12.5 cm) by the use an "electronic zoom" would improve the limiting spatial resolution performance to ~1.每毫米4线对.

图H. 图像增强电视系统4视场直径:37厘米, 30 cm, 22 cm, 17 cm, 以及相应的固有分辨率能力(在图像增强器的输入荧光粉旁边粘贴条形图案). 前 row shows full FOV image, and bottom row shows bar pattern magnified view.

如果输入视场减半, 然后只有四分之一的输入荧光粉被照射，因为该面积与视野的平方成正比. 将输入视野减半, 同时保持所有其他参数不变, would reduce the image brightness to a quarter of the original brightness at the full field of view. 为了弥补这种影响， the amount of radiation that is incident at the input of the image intensifier needs to be quadrupled 以补偿暴露面积的减少. 图像增强器/ x射线发生器系统中的自动亮度控制反馈电路通过反馈信号调节kVp (kV调制，mA固定)来实现这一点。, mA(固定kV调制的mA), or both (kV and mA are both modulated) to maintain the brightness at the output phosphor. The consequence to the patient is an increase in the dose when the "magnification mode" is utilized, 还有空间分辨率的增强.

骨盆幻像(透视)

图我	图J	图K

图我 shows a single frame from a fluoroscopy run using an image intensifier diameter of 38 cm; 图J shows an magnified image (electronic zoom) with an image intensifier diameter of 25 cm and 图K shows further magnification achieved by reducing the image intensifier input diameter to 15 cm. 相对于图1中的图像，图J中的放大倍数为x 1.5 (i.e. 38/25)，图K中的放大倍数为x2.5 (i.e., 38/15).

图1的技术选择为75kv和2.4毫安，这导致入口皮肤空气热为35毫安/分钟. 当图像被放大1倍时.5 (图J), the system increased the x-ray tube voltage to 85 kV and used a tube current of 2.7毫安，使入口空气的克玛率提高到50毫安/分钟. 当图像被放大2倍时.5(图K), the system further increased the x-ray tube voltage to 94 kV and used a tube current of 2.8毫安，使输入风量增加到61毫安/分钟.

在透视中使用放大模式通常与x射线管电压选择的增加有关，原因有两个:

(a)较高的电压将降低入口皮肤风量，该风量需要保持在90毫安/分钟(10 R/分钟)以下. Adjusting the x-ray tube voltage with increasing magnification resulted in only relatively modest increases in the entrance air kerma rate (35 mGy/minute -> 50 mGy/minute -> 61 mGy/minute).

(b) x射线管电流需要保持在~5毫安以下，以尽量减少x射线管的输入功率;阳极允许连续透视操作而不会使x射线管过热. The increased in power input to the anode (power is kV x mA watt) was also relatively modest (190 watt -> 230 W -> 260 W).

By contrast, maintaining a constant x-ray tube voltage with an increase in magnification of x 2.5 would have required an increase in entrance skin air kerma (and power loading to the x-ray tube anode) of 625% (i.e., 2.5^2) because of the six fold reduction in exposed area of the input phosphor.

骨盆幻像(数码光斑)

图1	图米	图N

图1 shows the digital photospot image that corresponds to the fluoroscopy frame depicted in 图我 (i.e.(视场直径38厘米). 用于获取该图像的技术选择为65 kV/9 ma, 对应的入口空气流速为1.4 mGy. 将放大倍率提高一倍.5通过将视场缩小到25厘米(图M)，产生了65千伏/18毫安的数字光斑技术和2的入口空气度.8 mGy. 将图像放大倍率进一步提高到2倍.5 by use of the 15 cm field of view (图N) resulted in a digital photospot technique of 65 kV/33 mAs, 入口空气系数为4.8 mGy.

在数字光斑成像中, 缩小视场通常不需要增加x射线管电压，原因如下:

(a)增加x射线管电压会降低图像对比度和相应的对比度噪比. Maintaining the contrast to noise ratio is desirable as this improves lesion detectability.

(b) Patient dose consideration is of much less concern than in fluoroscopy for several reasons. 诊断图像质量通常是最重要的问题, and one does not wish to compromise diagnostic performance by using too little radiation. 此外, 放射照相没有剂量限制, 哪一种用于诊断, whereas there are dose limits in fluoroscopy (entrance air kerma must normally be < 90 mGy/minute). 尽管病人每帧的剂量比透视高, 获得的光斑图像总数非常少.

(c)数字光斑成像不存在x射线管发热问题. The total energy deposited into the anode is a product of the power (kV x mA) and the total exposure time (s) (i.e.，能量(J) = kV x mAs). 上述三个例子中沉积的总能量范围为0.6kj (65kv和9ma)至2.2kj (65kv, 33ma). 在典型的透视/射线成像系统中，x射线管的阳极管容量通常为数百kJ, x射线管加热通常不是一个重要问题.

In contrast to the variation of x-ray tube voltage in magnification fluoroscopy, the x-ray tube voltage is normally kept approximately constant in magnification modes for digital photo spot imaging. 结果是, 进入x射线管阳极的皮肤空气密度和能量沉积与图像增强器输入荧光粉的暴露面积近似成反比. 视野减半, 它使放大倍率和相应的空间分辨率加倍, would be expected to (approximately) quadruple the entrance air kerma in digital photospot imaging.

颅骨幻象(透视)

图阿	图P

图阿 shows one frame of a fluoroscopy run of a head phantom obtained using a field of view of 25 cm. x线摄影技术为74 kV/2.2 mA，入口风量为26 mGy/min. 将视野(图P)从25厘米减少到16厘米(图1).e.，将放大倍率提高25/16或1倍.6)导致使用92千伏/2.8毫安，入口风量为49毫安/分钟.

在这个例子中, 请注意，图O(25厘米视场)包括头骨周围的一小块区域，该区域由x射线束直接照射的图像增强器组成. 这通常是不可取的(请参阅下面的准直部分), 并将导致考虑到这些直接照射区域的相对较大的检测信号的技术因素的选择. 预测所选放射照相技术的变化(千伏/毫安), patient dose and x-ray tube loading under such conditions is particularly tricky.