How to learn C-arm angles for body IR
This page explains the angle names AngioSim uses and a way to practice them. The only vascular tree in the simulator is the prostatic artery model, so every worked example links into PAE angiography practice. Citations link to Sources.
AngioSim is an educational simulator, not a medical device. The arteries are a schematic model. It must not be used for diagnosis, planning or treatment. Read the disclaimer.
LAO and RAO
LAO/RAO and cranial/caudal named by detector (image intensifier) position: cranial (+) = detector toward the head, beam travelling caudal→cranial; ipsilateral = RAO for right PA, LAO for left PA (Bilhim 2023).
In the simulator, LAO is a positive obliquity: the detector moves toward the patient’s left. RAO is negative: the detector moves toward the patient’s right. Zero obliquity is a straight AP view. For a prostatic artery, ipsilateral oblique is RAO on the right and LAO on the left, so the same “ipsilateral 35°” is RAO 35° on the right and LAO 35° on the left.
On the angle pad, RAO is to the left, LAO to the right, cranial toward the top and caudal toward the bottom. The readout writes those names, for example RAO 35° / CRAN 10°.
Cranial and caudal
Cranial is positive. The detector (image intensifier) moves toward the head, and the beam travels from caudal to cranial. Caudal is the opposite tilt: the detector moves toward the feet.
The module’s standard identification view is stored as: Ipsilateral anterior oblique 35–45° + ~10° CRANIAL (source wording: 'caudal-cranial projection of −10°'; direction confirmed as cranial by Varun Danda). Bilhim 2023.
The reported practice range on Sources is: 25–45° + 8–12° 'caudal-cranial' angulation (Moschouris 2021, unsigned; read as cranial); 20–50° ipsilateral with no tilt stated (Pilan 2022). Moschouris 2021, Pilan 2022.
Cited practice spans 20–50° ipsilateral oblique with about 8–12° cranial tilt (standard 35–45° + ~10° cranial). Sources write the tilt as 'caudal-cranial' without a clear sign; AngioSim uses cranial (image intensifier toward the head) per Varun Danda's clinical review. Treat as a starting range, not a rule.
A cone-beam CT preprint is stored separately and is not peer reviewed: Contralateral in 51%; mean 3° contralateral; only ~16% within 25–55° ipsilateral; n=21. Fassia 2025. The module’s contralateral 15° view uses that preprint and labels it preliminary.
How obliquity separates overlapping vessels
On a straight AP view, internal iliac branches overlap heavily. An oblique moves the detector around the patient so vessels that stack along the AP beam can project side by side. Cranial or caudal tilt changes how end-on a vessel running head to foot appears.
That is the projection this simulator draws. It is not a claim that one angle fits every patient. In the prostatic model, the straight AP note says internal iliac branches overlap heavily, and the classic starting view is ipsilateral oblique with cranial tilt. The type II preset says that, in this model, the origin opens best near AP or slightly contralateral. Details of each origin are on the PAE practice page.
The simulator’s origin meter calls a prostatic origin open when the first part of the artery is not too foreshortened and no other opacified vessel overlaps that window. The numeric thresholds are estimates on Sources.
A practice method
- Open the simulator.
- Start on straight AP of the right type IV tree and notice the overlap described for the internal iliac branches.
- Open the classic right-sided view (RAO 35° / CRAN 10°). That is 35° ipsilateral for a right prostatic artery, with 10° cranial.
- Open the matching left-sided view (LAO 35° / CRAN 10°) so ipsilateral flips from RAO to LAO.
- Use the saved views (classic 35°, ipsilateral 45°, ipsilateral 25°, AP, steep ipsilateral 55°, contralateral 15°) and compare them with the cited starting range above. Then change the origin preset. The PAE practice page lists what each preset is for.
Questions
What do LAO and RAO mean in AngioSim?
They name the detector position. LAO is positive, detector toward the patient's left. RAO is negative, detector toward the patient's right. For a prostatic artery, ipsilateral oblique is RAO on the right and LAO on the left.
What do cranial and caudal mean in AngioSim?
Cranial is positive: the detector moves toward the head, and the beam travels from caudal to cranial. Caudal is the opposite tilt. The module's classic prostatic view uses about 10 degrees cranial.
How does obliquity separate overlapping vessels in this model?
On a straight AP view, internal iliac branches overlap heavily. An oblique moves the detector around the patient so vessels that stack along the AP beam can project side by side. Cranial or caudal tilt changes how end-on a vessel running head to foot appears.
How should I practice the angles?
Open the simulator on a straight AP view, then on the classic right-sided view (RAO 35 degrees, cranial 10 degrees), then on the matching left-sided view (LAO 35 degrees, cranial 10 degrees). Compare those with the saved views and the cited starting range.
Does this page give working angles for every body IR procedure?
No. AngioSim practices these angles on its prostatic artery model. It does not include other vascular territories.