Rhese View X-Ray (Optic Foramen): Parieto-Orbital Positioning Notes

The Rhese view Method (Parieto-Orbital Oblique Projection) is the primary radiographic view specifically engineered to project the optic canal (optic foramen) end-on, demonstrating its cross-sectional circular profile, bony margins, and surrounding sphenoid structures in the lower outer quadrant of the orbit.

Both the Right and Left orbits are routinely imaged for bilateral comparative analysis.

1. Clinical Indications & Contraindications

Detailed Indications:

Optic Foramen Pathology & Neoplasms:
- Evaluation of asymmetric enlargement, erosion, or cortical thinning of the optic canal due to Optic Nerve Glioma or Meningioma of the optic nerve sheath.
- Bony narrowing/stenosis of the optic canal causing visual impairment or optic nerve compression.
Orbital Apex Trauma & Fractures:
- Identification of fractures involving the lesser wing of the sphenoid bone, anterior clinoid process, and optic canal margins following blunt cranial trauma.
Foreign Body Localization:
- High-detail localization of radiopaque metallic foreign bodies within the orbital apex or posterior orbital cavity prior to MRI clearance.
Fibrous Dysplasia & Paget’s Disease:
- Assessment of hyperostosis, bony encroachment, or osteosclerosis encroaching upon the optic nerve pathways.

Contraindications & Limitations:

Unstable Cervical Spine Injury: Prone or forward-rotated head positioning is strictly contraindicated. A Reverse Rhese (Orbito-Parietal Oblique / AP Axial Oblique) can be performed in the supine position without rotating the cervical spine, utilizing compensatory tube angulation.
Severe Facial Bone Fractures: Direct pressure on the zygoma, nose, and chin against the Bucky can aggravate unstable facial fractures.

2. Technical Factors & Exposure Physics

Parameter	Recommended Specification	Radiographic Rationale
Patient Posture	Erect (Seated) or Semi-Prone	Erect seated provides superior control over subtle angle adjustments
Image Receptor (IR)	18 × 24 cm (Portrait)	Tight format centered on the affected orbit and optic apex
SID	100 to 115 cm ( 40 to 44 inches)	Standard focal distance balances spatial resolution and beam divergence
Grid Ratio	8 : 1 to 12: 1 focused grid	Essential to absorb scatter from dense cranial structures
Tube Potential (kVp)	70 – 75 kVp	High-contrast resolution to define thin cortical margins of the foramen
mAs Range	20 – 30 mAs	Calibrated for bony orbit and sphenoid strut (AEC center cell active)
Focal Spot	Small (0.6 mm)	High spatial sharpness required to visualize the tiny (4 to 5 mm) optic ring
Breathing	Suspended respiration	Eliminates respiratory motion and ocular movement blur

3. Step-by-Step Patient & Part Positioning

Rhese Method Positioning Diagram

Rhese Method (Parieto-Orbital Oblique)

Optic Foramen

║ Vertical Bucky Surface ║

◄── 3-Point Touch: Chin, Cheek & Nose

AML ⟂ Image Receptor (90°)

MSP 53° to IR (Rotated 37°)

▲ [ Central Ray: 0° Perpendicular ]

Enters Parieto-Occiput ➔ Exits at Affected Downside Orbit

3-Point Contact Rule

Chin, cheek (zygomatic prominence), and tip of the nose of the affected side touch the Bucky simultaneously.

AML Perpendicular (90°)

Acanthiomeatal Line (AML) is aligned strictly perpendicular to the plane of the image receptor.

37° Rotation / 53° Angle

Head rotated 37° toward affected side, forming a 53° angle between the Mid-Sagittal Plane (MSP) and the IR.

Perpendicular Beam Exit

Central Ray is directed at 0° to exit through the center of the downside orbit (lower-outer quadrant projection).

The “3-Point Touch” (Malar, Nose, Chin) Rule

Starting Posture: Patient sits or stands erect facing the vertical Bucky (or lies semi-prone on the radiographic table). Place the orbit of interest closest to the image receptor.
Reference Point Contact: Adjust the head so that the chin, cheek (malar prominence/zygoma), and tip of the nose rest firmly against the center of the vertical Bucky surface.
Reference Line Alignment (AML):
- Adjust neck flexion/extension until the Acanthiomeatal Line (AML) is strictly perpendicular (90⁰) to the plane of the image receptor.
Plane Rotation (MSP):
- Rotate the patient’s head away from the lateral position so that the Mid-Sagittal Plane (MSP) forms an angle of 53⁰ with the plane of the IR (which corresponds to rotating the head 37⁰ toward the affected side away from a standard PA projection).

4. Central Ray (CR), Centering & Collimation

Central Ray (CR) Tube Angle: Strictly 0⁰ (Perpendicular) to the image receptor.
CR Centering / Alignment:
- Enters the superior-posterior aspect of the skull (parietal region opposite the side of interest).
- Exits precisely through the center of the downside orbit (the orbit resting against the Bucky).
Collimation: Four-sided collimation tightly restricted to a a 7.5 × 7.5 cm (3 × 3 inches) field over the orbit of interest to minimize secondary radiation scatter and optimize contrast resolution.

5. Positioning Errors & Diagnostic Corrective Actions

Positioning Error	Morphological Appearance of Optic Foramen	Cause & Corrective Action
Over-Rotation of Head (37° /MSP < 53°)	Optic foramen projects into the lateral orbital margin or outside the orbit.	Head turned too far toward lateral; rotate head back toward the PA stance.
Under-Rotation of Head ( 37° /MSP > 53°)	Optic foramen projects into the medial orbital wall or ethmoidal sinus.	Head kept too close to PA; rotate head further toward the affected side.
Over-Extension of Neck (AML not 90°)	Optic foramen projects into the upper half/superior quadrant of the orbit.	Chin tilted too far up; flex neck slightly to restore AML perpendicularity.
Over-Flexion of Neck (Chin tucked too much)	Optic foramen projects inferior to the orbital floor into the maxillary antrum.	Chin tucked too low; extend head upward until AML is perpendicular.

6. Radiographic Anatomy & Quality Evaluation Criteria

Rhese View Optic Foramen Quadrant Anatomy

Rhese Method: Optic Canal Quadrant Alignment

Parieto-Orbital Oblique

Lower-Outer Quadrant Target Benchmark

Diagnostic Quality Criteria

Optic Ring

Lower-Outer Quadrant Location

Optic foramen must project strictly end-on in the inferolateral (lower-outer) quadrant at the 5 o’clock (right) or 7 o’clock (left) position.

Strut

Sphenoid Strut Delineation

Clear cortical margin of the inferior root of the lesser wing of the sphenoid forming the inferolateral border of the canal.

Margin

Orbital Boundary Clearance

Optic canal must remain inside the orbital circumference without superimposing on the dense lateral orbital rim.

Errors

Rotational Error Detection

Over-rotation (>37°) throws the foramen laterally; under-rotation (<37°) throws it medially into the ethmoid shadow.

Target Quadrant Rule (Golden Benchmark):
- The optic foramen must be clearly projected in the lower-outer (inferolateral) quadrant of the orbit, adjacent to the junction of the lateral wall and orbital floor.
Optic Ring Morphology:
- Optic foramen seen end-on as a clean, rounded radiolucent ring with distinct cortical margins.
- Clear visualization of the sphenoid strut (inferior root of the lesser wing of the sphenoid) forming the inferolateral border of the canal.
Orbital Apex Clarity:
- Unobstructed view of the superior orbital fissure and lateral orbital wall free of movement blur or excessive collimator cut-off.

7. Comparison: PA Oblique (Rhese) vs. AP Oblique (Reverse Rhese)

Feature	PA Oblique (Standard Rhese)	AP Oblique (Reverse Rhese)
Patient Stance	PA (Cheek, nose, chin touch IR)	AP (Back of head on IR, orbit away)
Lens Radiation Dose	Low (Ocular lens on exit side)	High (Ocular lens directly in entrance beam)
Geometric Magnification	Minimal (Low OID)	Increased (Higher OID of the orbit)
Primary Utility	Routine elective & diagnostic imaging	Trauma patients with immobilized C-spine