The FOV (Field of View) is probably the most important decision when acquiring a CBCT scan: it determines the patient dose, achievable spatial resolution, and the amount of information available for diagnosis. This guide summarizes which FOV to use depending on the clinical indication.
FOV basic principles
- Small FOV = lower patient dose, higher spatial resolution (finer voxel), but covers only a limited area.
- Large FOV = higher dose, lower resolution (coarser voxel to keep acquisition times reasonable), but covers more anatomy and enables full studies.
- The golden rule is ALARA: use the smallest FOV that is diagnostically sufficient to answer the clinical question.
- Repeating a CBCT scan because of an insufficient FOV doubles the patient dose. When in doubt between two sizes, prefer the next larger one rather than risking a repeat scan.
Common FOV categories
CBCT manufacturers classify FOVs in standard categories (names vary across brands, but ranges are consistent):
- Small / focal (≤ 6 × 6 cm): covers a localized area, typically 1–3 teeth with adjacent structures. Smallest voxel (0.075–0.15 mm).
- Medium / sectorial (8 × 8 to 10 × 10 cm): covers a wide sector or a full quadrant. Typical voxel 0.15–0.3 mm.
- Large / extended (≥ 10 × 10 cm in height, up to 17 × 23 cm): covers full upper and lower jaws, bilateral TMJ or cephalometry with soft tissues. Voxel 0.2–0.4 mm.
Reference table by indication
| Indication | Recommended FOV | Suggested voxel | Estimated dose (mSv) |
|---|---|---|---|
| Endodontics / root fracture / periapical lesion | ≤ 5 × 5 cm | 0.075–0.15 mm | 0.02–0.1 |
| Single implant | 5 × 5 to 6 × 6 cm | 0.15–0.2 mm | 0.02–0.15 |
| Impacted third molar / wisdom tooth | 5 × 5 to 8 × 5 cm | 0.15–0.2 mm | 0.03–0.2 |
| Sectorial implants (same quadrant) | 8 × 5 to 8 × 8 cm | 0.2–0.3 mm | 0.05–0.3 |
| Full quadrant / sectorial cystic pathology | 8 × 8 to 10 × 8 cm | 0.2–0.3 mm | 0.1–0.4 |
| Full upper jaw (maxilla) | 10 × 8 to 12 × 8 cm | 0.2–0.3 mm | 0.1–0.5 |
| Full lower jaw (mandible) | 10 × 8 to 12 × 8 cm | 0.2–0.3 mm | 0.1–0.5 |
| Both jaws (full-arch implants) | 12 × 8 to 16 × 10 cm | 0.25–0.4 mm | 0.2–0.8 |
| Bilateral TMJ | 12 × 8 to 15 × 10 cm | 0.2–0.3 mm | 0.2–0.6 |
| Orthodontics / 3D cephalometry / airway | ≥ 16 × 13 cm (up to 17 × 23) | 0.3–0.4 mm | 0.3–1.0 |
| Extensive tumor pathology / facial trauma | ≥ 17 × 13 cm | 0.3–0.4 mm | 0.3–1.2 |
| Sinus lift / maxillary sinus assessment | 6 × 6 to 10 × 8 cm | 0.2–0.3 mm | 0.05–0.3 |
* Dose values are indicative, drawn from published literature (SEDENTEXCT, ICRP, AAOMR). They vary between machines by up to a factor of 5×: a nominal 8 × 8 cm FOV may deliver 0.05 mSv on a modern unit and 0.3 mSv on a less optimized one. Refer to the measured DAP values of your own equipment.
Practical rules by specialty
Endodontics
Spatial resolution is paramount: you are looking for accessory canals, vertical root fractures, or small apical lesions. Use voxel ≤ 0.15 mm and small FOV centered on the specific tooth. A 5 × 5 cm FOV with 0.1 mm voxel is typically optimal.
Implant dentistry
For a single implant, a small FOV (5 × 5 cm to 6 × 6 cm) centered on the site is sufficient and delivers less dose. For multiple implants in the same quadrant, use a medium FOV (8 × 8 cm). Only use a both-jaws FOV when placing implants in both arches and the full intermaxillary relationship is needed. A 0.15–0.2 mm voxel allows accurate measurements to the inferior alveolar nerve.
Oral surgery / third molars
Small-to-medium FOV (5 × 5 to 8 × 5 cm) centered on the third molar area. The critical point is to clearly see the relationship of the root with the mandibular canal in the lower case, or with the maxillary sinus in the upper case. Voxel 0.15–0.2 mm.
Orthodontics and 3D cephalometry
A large FOV is mandatory to include the full skull, TMJ, airway, and facial soft tissues (Frankfurt, vertex, chin). Typical orthodontic units offer 16 × 13, 17 × 17, or 17 × 23 cm. Voxel 0.3–0.4 mm is sufficient; little is gained with finer voxel for cephalometric analysis, but dose is saved.
TMJ (Temporomandibular joint)
Medium-to-large FOV to include both condyles when the study is bilateral. If unilateral with a clear suspicion of pathology on one side only, a small-to-medium FOV centered on that condyle may be sufficient. CBCT in TMJ is restricted to cases where panoramic or CT are not diagnostic; first-line imaging is usually MRI for disc dysfunction.
Cystic / tumor pathology
FOV adapted to the extent of the lesion visible on a prior panoramic view. Large lesions crossing the midline or involving both quadrants require a large FOV. Voxel 0.2–0.3 mm is generally enough to assess margins, content, and anatomical relationships.
Pediatrics
Regardless of indication, in pediatric patients always prefer the smallest FOV compatible with the diagnosis. Developing tissues (especially thyroid, salivary glands, bone marrow) are more radiosensitive. Some units offer a "pediatric mode" that reduces kVp/mA in addition to the FOV. If the indication can be resolved with a panoramic or periapical, prefer those modalities.
Pregnancy
If the CBCT scan is justified and cannot be deferred, use the smallest FOV, the unit's lowest-dose mode, and a leaded abdominal apron and thyroid collar. Direct fetal dose in dental CBCT is very low (typically ≪ 0.01 mSv), but reinforced ALARA always applies.
How FOV affects diagnostic quality
- Spatial resolution: directly related to voxel size, not FOV. However, smaller FOVs allow finer voxels without prohibitive acquisition times.
- Metallic artifacts: in a large FOV with pre-existing implants, artifacts can propagate and affect the region of interest. If there is metal far away but relevant, consider this when choosing the FOV.
- Truncation: if the FOV is too small and crops relevant tissues, truncation artifacts appear and degrade quality. Better a slightly larger FOV than one right at the limit.
- Dose does not scale linearly: doubling FOV in height does not necessarily double the dose (depends on equipment and algorithm). But the general rule holds: larger FOV = more dose.
Dose equivalents for context
- Natural background radiation: ~2.4 mSv/year
- Transatlantic flight (8 h): ~0.03–0.05 mSv
- Periapical radiograph: ~0.001–0.005 mSv
- Panoramic radiograph: ~0.01–0.02 mSv
- Small-FOV dental CBCT: ~0.02–0.1 mSv
- Large-FOV dental CBCT (cephalometric): ~0.3–1.0 mSv
- Medical head CT: ~2 mSv
- Mammography: ~0.4 mSv