Slip rings for cT scanners & medical imaging: requirements and specification

What the slip ring has to handle

Very large bore (patient aperture) with the slip ring wrapped around it
Several kilowatts of power transferred through contacting rings to the X-ray generator and rotating electronics
Non-contacting high-speed data link (optical or RF/capacitive) for detector data, typically 1-20+ Gbps aggregate
Bidirectional control channel between stationary and rotating gantry electronics
High surface speed at the ring circumference: gantry speeds of 120-280 rpm on a large diameter
Low wear debris, low audible noise and long maintenance-free life
Tight control of EMI from the data link and power rings, plus patient-safety insulation and leakage requirements

Typical figures

Speed	Gantry rotation 120-280 rpm; slip rings run at 200+ rpm on a 1 m ring
Bore	Inside diameter up to 1270 mm (50 in)
Data	Non-contacting data channels 1-20+ Gbps; single optical or RF channels typically 1.25-5 Gbps, spatially multiplexed optical links above 10 Gbps
Power	Several kilowatts through contacting power rings

Example figures from the published sources listed below. Your requirement may differ; an engineer will confirm against your duty cycle.

Recommended slip ring types

Large-diameter slip rings Pancake slip rings High-speed slip rings Fibre optic rotary joints

Standards to consider

IEC 60601-1 - general safety and essential performance of medical electrical equipment (insulation, leakage current, protection)
IEC 60601-1-2 - EMC requirements for medical electrical equipment, relevant to the gantry data link and power rings
IEC 60601-2-44 - particular requirements for X-ray equipment for computed tomography

The complete system

A slip ring rarely works alone. For cT scanners & medical imaging it is usually specified together with:

large-diameter gantry bearing
direct-drive or belt-drive gantry motor
servo drive
high-resolution encoder
contactless data link
brake

Specifying these together avoids mismatched connectors, cable routes and feedback interfaces, and gives you one point of contact for the whole axis.

Common problems to design out

Data link errors or EMI affecting image reconstruction
Brush wear debris contaminating rings and causing arcing or noise
Audible noise and vibration at high gantry speed
Contact resistance rise on power rings leading to heating

Series used in this application

Motion Control Products PR/PSR Series Pancake Slip Ring Moog Large Diameter Slip Rings (CT6455, CT6536, CT6764, CT6970, CT7013, CT7093, CT7138, CT7311)

Frequently asked questions

Why do CT scanners use contactless data transmission?

Detector data from a modern scanner typically exceeds 1 Gbps in aggregate, which sliding contacts cannot carry reliably. Optical or RF near-field links move the image data across the rotating gap while brushes are kept for power.

How fast does a CT gantry slip ring rotate?

Gantries commonly turn the tube and detector at roughly 120 to 280 rpm. Because the ring is around a metre across, the contact surface speed is very high, which drives brush material choice.

Optical or RF data ring - which is better for CT?

Optical links avoid high-frequency electrical signals on the large ring and can be fully isolated from the structure, which helps EMC. RF near-field links are usually slightly cheaper in electronics. Both typically run 1.25-5 Gbps per channel and can be multiplexed for more.

Slip rings for cT scanners & medical imaging