Module 1

C-arm basics

Before you can read an angiogram you need a mental model of the machine: what moves, what the names mean, and how the 3D world maps onto the 2D monitor.

1 · The machine

The C-arm is a C-shaped gantry with an X-ray tube on one end and a flat-panel detector on the other. In the standard frontal (AP) position the tube sits under the table and the detector hangs over the patient's chest.

The C moves in two ways, and both pivot around a fixed point called the isocentre. Put the heart at the isocentre and it stays centred whatever angle you choose.

Rotation (LAO ↔ RAO): the whole C spins around the patient's long axis, swinging the detector toward the patient's left or right.
Angulation (cranial ↔ caudal): the C slides through its collar, tilting the detector toward the head or the feet.

Try it: move one slider at a time and watch which part of the C-arm moves in the 3D room.

2 · Naming views: follow the detector

A projection is named by where the detector is. Picture the patient lying on the table, seen from their feet (like a CT slice). Move the detector around:

Detector position	Name
Straight above the chest	AP (antero-posterior) — the name is convention; with the tube under the table the beam really travels back to front
Over the patient's left chest	LAO — left anterior oblique
Over the patient's right chest	RAO — right anterior oblique
Beside the patient's left side (90°)	Left lateral

"Oblique" is named the same way as in a plain chest film: in an LAO view, the patient's left anterior chest is closest to the detector.

3 · Cranial & caudal

Now look at the patient from their side. Tilting the detector toward the head is cranial (CRA); toward the feet is caudal (CAU). The X-ray tube, under the table, moves the opposite way.

Any view is a combination: RAO 30 / CAU 25 means rotate the detector 30° to the patient's right, then tilt it 25° toward the feet.

Cranial views look down on the heart from above the diaphragm; caudal views look up at the base of the heart from below.

4 · Reading the monitor

The image is displayed as if you were standing at the detector looking at the patient. In AP, that means the patient's left is on the right of the screen (like a chest X-ray), and the head is at the top. Two landmarks tell you the view on almost any frame:

Where is the spine?

LAO → spine on the right of the screen.
RAO → spine on the left of the screen.
AP → spine in the middle.

Is the diaphragm in view?

Cranial → the dome of the diaphragm/liver rises into the lower field.
Caudal → the diaphragm drops out; you see lung and the base of the heart.

Follow the catheter

The catheter comes up the descending aorta beside the spine, then over the arch: another way to find the spine when it's faint.

Prove it to yourself: in the simulator, sweep from RAO 90 to LAO 90 and watch the spine travel across the screen.

5 · Why so many views?

The heart sits obliquely in the chest: its long axis points left, anterior and inferior. The coronaries wrap around it in three dimensions, but an angiogram is a 2D shadow. Any single projection will:

Foreshorten vessel segments that run toward or away from the detector, hiding stenoses.
Overlap branches so a lesion hides behind another vessel.

So every segment must be seen in at least two, ideally orthogonal, views, each chosen to lay that segment flat across the detector with nothing on top of it.

Heart-based shorthand

RAO views lay the AV groove (RCA, LCx) and interventricular groove (LAD, PDA) side by side, seen from the right.

LAO views look down the septum: the LAD runs straight down the middle, the LCx and RCA wrap around the sides.

Cranial opens the LAD and its branches; caudal opens the left main, LCx and bifurcation.

6 · A typical sequence

Labs differ, but most operators run something like this, adding views to clear any doubtful segment:

Left coronary

RAO caudal — LM, LCx, OMs.
AP cranial or RAO cranial — mid/distal LAD, diagonals.
LAO cranial — LAD and diagonal bifurcations.
LAO caudal ("spider") — LM bifurcation, proximal LCx.

Right coronary

LAO — the "C": ostium, proximal and mid RCA.
RAO or AP cranial — mid RCA, PDA and PLV.

Explore each view in 3D →

7 · Radiation: geometry matters

Scatter is greatest on the tube side of the patient. The operator stands on the patient's right, so LAO angles (tube swings to the right) increase operator dose.
Steep angles mean a longer path through the patient: more dose and a noisier picture. Steep LAO cranial/caudal views are the highest-dose shots.
Keep the detector close to the patient and the tube far away; collimate; use shields; step back during cine runs.

Every degree should earn its dose. Choose angles that answer a question, not a checklist.

8 · Beyond the native coronaries

The LV gram

A pigtail catheter across the aortic valve fills the LV with contrast. You judge a wall only where it forms the edge of the silhouette, so you need two views: RAO 30 (anterior, apex, inferior) and LAO 45 (septum, lateral).

Bypass grafts

Sternal wires and surgical clips tell you it's a post-CABG patient. The LIMA comes off the left subclavian; vein grafts start on the front of the ascending aorta. Always show the anastomosis and the native run-off beyond it.

Find the lesion

A stenosis can look severe in one projection and vanish in another through foreshortening or overlap. Switch on Lesions in the simulator and see for yourself.