医疗城 · 设备实验室 · 第 68 台，共 69 台
X 射线机
X-ray
BMEssentia 医疗城设备实验室中的X 射线机。以可交互 3D 打开设备，逐个部件拆解，了解其工作原理，然后在 BMEssentia 平台上系统学习，并向 Essentia 提问。
本页的设备实验室内容为英文，与医疗城中的内容一致。
- 10 个部件
- 设备实验室中有 2 种配置
- 又称: X-Ray Machine, Radiography, X Ray
设备实验室
X-ray
A floor-mounted tube column on a rail, a high-frequency generator in a cabinet, a table with a floating top and a Bucky tray under it, an erect stand against the wall, and a control console behind lead glass. In the tray, in front of the digital detector, sit a twelve-to-one focused grid and three ionisation chambers.
配置
设备实验室中的各个版本。
Fixed radiographic room, table Bucky with grid and automatic exposure control
A floor-mounted tube column on a rail, a high-frequency generator in a cabinet, a table with a floating top and a Bucky tray under it, an erect stand against the wall, and a control console behind lead glass. In the tray, in front of the digital detector, sit a twelve-to-one focused grid and three ionisation chambers.
Mobile ward unit, no grid and no automatic exposure control
A trolley with a battery store, a column with a boom arm, the tube and collimator at the end of it, a console on the body and a flat detector that is carried to the patient and slid behind them. There is no grid and no chamber. The exposure is set from a chart on the machine and a judgement of how thick the patient is, and then it happens.
工作原理
在设备实验室中探索。
The exchange rate between the two knobs
Hold the receptor exposure where it is and raise the kilovoltage by fifteen per cent, taking out the milliampere-seconds that the extra penetration allows. Watch three numbers: what the receptor gets, what the patient absorbs, and the contrast.
Where the contrast actually comes from
Sweep the kilovoltage and watch one quantity that is not on any real console: the fraction of cortical bone’s attenuation that is NOT Compton scattering.
Two ways to deal with scatter, and only one is free
Set a thick patient and a wide field, then reduce the field and watch the scatter-to-primary ratio fall. Then restore the field and put a grid in instead, and watch the contrast recover at the price of a large increase in exposure.
Why the fixed system is the blurrier one
Compare the penumbra on the two configurations. 15 m and the mobile unit at one metre, so the fixed room should be the sharper of the two. It is not.
Measuring it, or predicting it
Make the patient six centimetres thicker on each configuration in turn and watch what happens.
部件
逐个部件讲解。
Cathode filaments and focusing cup
Two coils of tungsten wire, each a few millimetres long, lying in slots cut into a block of nickel at the far end of the tube from the target. One coil is short and one is longer.
Rotating anode, target track and rotor
A disc of molybdenum about ninety millimetres across with a band of tungsten and rhenium brazed onto a bevel at its rim, spinning at several thousand revolutions a minute inside the vacuum. The bevel is the most important angle in the device.
Tube housing, insulating oil and lead shielding
A heavy cylinder, lead-lined, filled with oil, with the tube insert suspended inside it and one square window in the wall where the beam is allowed out. It weighs far more than the tube it contains, and almost all of that weight is doing two jobs: holding off a hundred kilovolts and absorbing the photons that were not asked for.
Tube port and inherent filtration
A thin window in the envelope where the beam leaves, the oil in front of it, and the window in the housing wall beyond that. Together they are the filtration nobody chose.
Added aluminium filtration
Two thin sheets of aluminium in a drawer under the port, held by a clip, with a handle to pull them out. They are the cheapest and least interesting-looking part of the machine, and removing them raises the exposure a patient absorbs without improving the radiograph at all.
Collimator, light field and lead shutters
A box bolted under the port with two pairs of lead shutters inside it, a lamp, a mirror at forty-five degrees and a pair of cross-hair wires. The lamp and the mirror exist so that somebody can see where an invisible beam is going.
High-frequency generator and high-tension transformer
A cabinet the size of a wardrobe holding an inverter, a transformer in oil with two bushings on top, a rectifier stack and a control board. It decides how fast the electrons are going when they hit the target, and that single decision is what makes bone look different from soft tissue.
High-tension cables and receptacles
Two cables as thick as a wrist, running from the generator to the two ends of the tube housing, each ending in a plug that screws into a well full of insulating grease. They are the least glamorous expensive part of the room and the one most often damaged by the room being rearranged.
Operator console and exposure factors
A desk with a screen, two rotary controls, a row of anatomical programme keys and, on one of the two configurations, a chamber selector and a density control. Two of the controls on it do completely different things to the radiograph, and almost every misunderstanding in radiography is a confusion between them.
Two-stage exposure switch
A hand switch on a coiled lead with two positions under one button. The first spins the anode up and heats the filament.