The systems: mobile C-arms and fixed angiography
Recognise the type of C-arm or angiography system in front of you, name its main assemblies and say what each one does and how it usually fails, before you open a single cover.
Two families, one job
Every system in this course does the same basic job: it produces a live X-ray image, fluoroscopy, while a doctor works inside the patient. The doctor may be setting a fracture, placing a pacemaker lead, opening a coronary artery or blocking a bleeding vessel. In every case the image is used in real time to guide hands and instruments, so the system must start, stay up and give a usable picture for the whole procedure. That is the first thing to understand about this equipment: a failure is felt immediately, by a team that is scrubbed and a patient who is already on the table.
There are two families. The mobile C-arm is a self-contained unit on wheels: the C-shaped arm with the tube at one end and the image receptor at the other, mounted on a mobile stand, usually with a separate monitor cart or workstation joined to it by a long cable. It is wheeled between operating theatres, trauma rooms and sometimes wards. The fixed angiography system, often called a cath lab or interventional suite, is installed permanently in a shielded room: a floor-mounted or ceiling-mounted C-arm, a dedicated patient table, a generator cabinet, a cooling unit, monitor suspension, a control room and a network of image computers.
Fixed systems come as single-plane, with one C-arm, or biplane, with two: a frontal plane, usually on the floor or ceiling, and a lateral plane, usually ceiling-suspended. A biplane system takes two views of the same anatomy at the same time with one contrast injection, which matters in neuro and paediatric work. For you, biplane means twice the tubes, detectors, collimators and motion axes, plus coordination between them, including collision avoidance between the two arms.
The mobile C-arm in more detail
A mobile C-arm puts a whole X-ray room on wheels. Inside the stand you will find the mains input and power distribution, the generator electronics, the motion drives and the control boards. On many units the high-voltage generator and the tube share one oil-filled housing, the monoblock or tank, mounted at the bottom of the C. Smaller units use a stationary anode tube; larger ones a rotating anode. As an example, the service documentation for one GE mobile C-arm describes a monoblock with a stationary anode tube driven from a high-frequency inverter, while the Ziehm Solo documentation lists separate fuses for a rotating anode drive. The difference matters for heat: a stationary anode tolerates much less continuous load, which is one reason why mobile units limit fluoroscopy power and time.
At the top of the C sits the image receptor. Older and many current mobile units use an image intensifier (II) with a video camera behind it; newer ones use a flat detector (FD). Next to the tube is the collimator, normally with an iris for the round field and a pair of slot or leaf shutters that can be rotated, plus filters. The C-arm itself can move in several ways: orbital rotation along the C, rotation of the C around its horizontal axis, vertical travel of the column (often motorised), horizontal travel and a swivel, known on some units as wig-wag. Each movement has a brake or lock.
The second half of the system is the monitor cart or workstation: monitors, the image-processing computer, storage, a printer or DICOM interface, and often a UPS or battery pack to keep the computer alive during short power interruptions or during transport. Some mobile units also have an energy storage unit that helps the generator take high power from an ordinary socket; the Philips BV family documentation, for instance, keeps a record of the date the battery pack was installed. The interconnect cable between the stand and the cart carries power, control and video, and it is one of the most abused parts of the whole system.
The fixed angiography system in more detail
A fixed system splits the same functions across a room. The generator sits in a cabinet in the technical room or in the procedure room, feeding the tube through high-voltage cables. The tube is a powerful rotating anode type designed for long fluoroscopy runs and fast acquisition series, and it is cooled by oil that is in turn cooled by a heat exchanger, often with a water or water-glycol loop and a chiller. Engineers report cooling problems as a frequent cause of tube overload messages on angiography systems, which is why you meet cooling again in lesson 5.
The C-arm is mounted on a floor stand or a ceiling carriage on rails, with motorised rotation and angulation, often at high speed. Sensors for position, speed and collision cover the arm, the detector housing and the tube cover. The patient table is long, floating and motorised, with a radiolucent tabletop, and is often the most touched part of the system. Above or beside the table hangs a monitor suspension with several displays or one large screen, and a ceiling-mounted lead shield and a table-mounted lead skirt protect staff.
Behind the scenes there are several computers: one for acquisition and real-time image processing, one for system control and geometry, a reference or review station, and links to the hospital network and the PACS. Many systems also have an interface to the contrast injector, so that injection and acquisition can start together. Each of these computers boots, talks to the others and can lose that conversation, and a large share of field calls start there.
Image intensifier or flat detector
You need to tell an II system from an FD system at a glance, because their faults and their maintenance differ. An image intensifier is a large vacuum tube: X-rays hit an input screen, are converted to light and then to electrons, which are accelerated and focused onto a small output screen where a bright, reduced image is formed and picked up by a camera. It is round, heavy and needs high voltage of its own. Typical II problems are loss of brightness with age, distortion towards the edges, sensitivity to magnetic fields, focus and camera iris drift, and failure of the II power supply.
A flat detector converts X-rays to an electrical signal pixel by pixel on a flat panel and sends the image digitally. It has no geometric distortion, gives a square or rectangular field and needs calibration of offset, gain and defective pixels, as you know from the DR detector material in the X-ray course. Typical FD problems are lost communication, cooling or power-supply faults in the detector electronics, and calibration-related artefacts. We return to both in lesson 3.
How to read an unfamiliar system
You will meet brands you have never trained on. Start the same way every time: find the nameplates and the system type, note the software version shown at boot or in the system information, and ask the users what the system is used for and what they complained about. Then trace the four chains you already know from the X-ray course: power from the wall to the generator and the computers; the image chain from tube to monitor; the control chain from the hand switch, foot switch and control panels to the generator and the motion drives; and the data chain to storage and the network.
Ask where the documentation is. A system without its service manual, its configuration backup and the previous service reports is a system you will struggle to restore. Make a note of what is missing and tell the owner in writing; it is part of the risk they carry.
| Part | What it does | How it fails | |
|---|---|---|---|
| 01 | High-voltage generator | Converts mains into regulated kV and mA for the tube | Inverter or IGBT failure, kV/mA errors, supply problems |
| 02 | X-ray tube or monoblock | Produces the beam; on mobile units often shares an oil tank with the HV generator | Filament (focus) open, arcing, overheating, oil leak |
| 03 | Tube cooling | Removes heat from the tube oil: fan, heat exchanger or water/chiller loop | Clogged filters or radiator, pump or fan failure, overload messages |
| 04 | Collimator | Shapes the beam: iris, shutters, filters, often rotatable | Motor, potentiometer or encoder errors, sticking mechanics |
| 05 | Image receptor (II + camera or flat detector) | Turns the X-ray image into a video or digital signal | II brightness loss, camera drift, FD communication or power faults |
| 06 | C-arm mechanics and drives | Positions tube and receptor; brakes, motors, sensors | Brake wear, drive faults, position sensor drift, collision sensor faults |
| 07 | Patient table (fixed systems) | Floats, lifts and tilts the patient; carries controls | Brake and lift faults, feedback potentiometers, worn bearings |
| 08 | Workstation, monitors and image computers | Image processing, display, storage, network | Boot errors, disks, BIOS battery, power supplies, lost communication |
| 09 | Interconnect cables and cable chains | Carry power, control and video between assemblies | Crushed, kinked or worn cables, broken pins, damaged sheaths |
| 10 | Injector interface (fixed systems) | Synchronises contrast injection with acquisition | No injection trigger, cable or configuration problems |
The computer that only worked when the C-arm was attached
An engineer took the system computer out of a Siemens Arcadis Varic mobile C-arm to restore it from the original recovery discs on the bench. The computer started, printed its start-up messages and then switched itself off every time. He suspected the video card and was about to order one. A colleague asked what the computer was connected to on the bench. The answer was nothing: no C-arm. Once the computer was reconnected to the C-arm stand, it booted completely and the system worked. The start-up sequence expected to find the rest of the system, and without it the computer shut down by design rather than because of a fault.
A C-arm is one system, not a PC with accessories. Before you condemn a part tested on its own, ask whether it can run at all without the rest of the system.
The expensive monitor with a cheap power supply
A 19-inch medical LCD monitor on a Siemens angiography system died, and the replacement offered through the manufacturer was very expensive. The engineer opened the monitor and found that the internal switch-mode power supply, a 12 V module, had failed while the panel and the controller board were intact. He fitted an equivalent supply and the monitor came back with a normal picture. Colleagues reported similar repairs on other medical monitors, where faults such as ripple after a long idle period were traced to the power supply or a poorly soldered chip.
Monitors and computers in an angiography system are ordinary electronics inside. Before replacing a whole assembly, check its power supply, but make sure any repair keeps the monitor's medical and electrical safety approval and is recorded.
Sizing a UPS for a C-arm that had not arrived yet
An engineer had to choose a UPS for a Philips BV Pulsera mobile C-arm that was still being delivered. Colleagues suggested taking the nameplate power with a margin, and a figure found on the internet suggested a moderate demand from the socket. According to the engineer, the manufacturer's representative then gave a peak demand roughly twice as high and recommended a UPS rated well above that peak; the discussion did not report the final installation. The difference came from short high-power exposures, which the average figure did not show.
For power and UPS sizing, use the manufacturer's installation documentation and peak demand, not an average or a figure from a forum.
On-site checklist
- Identify the system family: mobile C-arm, fixed single-plane or biplane.
- Note nameplates, serial numbers and software version before any work.
- Identify the image receptor: image intensifier with camera or flat detector.
- Identify the tube type and where the HV generator is: monoblock or separate cabinet.
- Locate the cooling arrangement of the tube.
- List the computers and how they connect to each other and the network.
- Check that the service manual, configuration backup and previous reports exist; report gaps in writing.