C-arm orientation and positioning: a working guide

Know the movements of the C-arm

Every mobile C-arm offers a similar set of movements: vertical lift of the column, horizontal travel of the arc, orbital rotation along the arc, angular (wig-wag) rotation about the horizontal axis, swivel of the whole unit and rotation of the arc about the beam axis (flip). Learning which movement changes which view prevents the trial-and-error exposures that add dose.

Orbital rotation tilts the beam along the arc and is used to obtain lateral and oblique views of the limbs or spine. Angular rotation tips the beam cranially or caudally and is the movement used to square end plates or to open a joint space. Mechanical brakes or electric assistance should hold every position without drift.

Standard AP, lateral and oblique set-ups

For an AP view, position the tube below the table and the detector above the patient, as close to the patient as practical. This keeps scatter away from the operator's head and neck and improves geometry. For a lateral, rotate the arc to horizontal; the detector side should face the surgeon or the empty side of the table, and the tube side should be farther from the staff, because scatter is highest near the entrance side.

Oblique views are obtained by orbital rotation, usually in 15 to 30 degree steps, then fine-tuned under pulsed fluoroscopy. Always collimate to the area of interest before exposing, and use the laser localisers, where fitted, to centre on the target before the beam is switched on.

• Tube below, detector above for AP to reduce operator scatter
• Detector as close to the patient as possible
• Collimate first, then expose
• Save position memory for views you will repeat

C-arm orientation: avoiding left-right confusion

A C-arm image can be rotated or flipped on the screen, so a consistent orientation convention matters. Agree with the surgeon before the case that, for example, the top of the image is cranial and that markers are placed to show the patient's right side. Check that image-flip and image-rotate functions are reset between cases.

A short C-arm orientation cheat sheet fixed to the monitor trolley, showing the arc position, the expected image and the correct movement for each standard view, helps new staff and locums. It is particularly useful where several surgeons share one unit with different preferences.

Equipment features that speed up positioning

Laser positioning on both the tube housing and the detector lets staff align the beam with the skin mark before radiation is used. The Perlove PLX C1520/1521 provides laser positioning on both and remote exposure, which moves the radiographer out of the room for non-sterile work. It also uses a wireless link between the C-arm and the workstation, so there are no floor cables to catch on the arc.

Other useful features are electric vertical lift, saved positions, a smooth counterbalanced arc and a clear display of the arc angle. See the mobile C-arm buying guide for the full checklist, and the article on how to operate a C-arm for the control-panel basics.

Positioning and dose

Good positioning is the cheapest form of dose reduction. Fewer repeat exposures, correct tube-patient distance and tight collimation all lower patient and staff dose. Combine them with pulsed fluoroscopy and last image hold, described in our guide to C-arm dose reduction techniques.

If your team needs on-site application training with a C-arm such as the PLX C1520/1521, Beckfinity's specialists can arrange it together with installation. Contact us to request a quote or a demonstration.