Comparison of SOMATOM On.site vs O-arm vs AIRO CT in Intraoperative Imaging

Intraoperative imaging systems are essential in modern image-guided surgery, especially in neurosurgery and spinal procedures. They allow surgeons to verify implant placement, tumor resection, and anatomical alignment in real time.

This article provides a technical and objective comparison between three widely used intraoperative CT systems:

  • SOMATOM On.site
  • O-arm
  • AIRO CT

We will compare them across engineering design, imaging performance, clinical applications, workflow integration, and operational constraints.

1. System Overview (Engineering Perspective)

SOMATOM On.site

SOMATOM On.site

  • Manufacturer: Siemens Healthineers
  • Country: Germany
  • System Type: Mobile multi-slice CT (MSCT-based intraoperative imaging system)
Engineering Position

SOMATOM On.site is based on a multi-slice CT architecture, similar in principle to diagnostic CT scanners but redesigned for mobility and intraoperative deployment.

Core Design Philosophy
  • Bring diagnostic-level CT imaging directly into the operating room
  • Maintain high image quality for soft tissue visualization
  • Reduce patient transport between OR and radiology departments
Key Engineering Feature

Unlike cone-beam systems, this device relies on:

  • Advanced reconstruction algorithms similar to hospital CT systems
  • High-resolution axial imaging
  • Multi-detector row geometry
O-arm

O-arm

  • Manufacturer: Medtronic
  • Country: United States
  • System Type: Cone-Beam CT (CBCT) intraoperative imaging system
Engineering Position

The O-arm is designed specifically for surgical navigation and orthopedic precision, particularly in spine surgery.

Core Design Philosophy
  • Optimize imaging for bone structure visualization
  • Integrate tightly with surgical navigation systems
  • Provide rapid intraoperative 3D imaging
Key Engineering Feature

The system uses:

  • C-arm rotational geometry
  • Cone-beam X-ray projection
  • Flat-panel detector reconstruction

This results in:

  • Lower soft-tissue contrast compared to MSCT systems
  • Excellent spatial resolution for bone
AIRO CT

AIRO CT

  • Manufacturer: Brainlab
  • Country: Germany
  • System Type: Mobile multi-slice CT (MSCT-based intraoperative CT system)
Engineering Position

AIRO CT is a mobile multi-slice CT system designed for flexible intraoperative imaging across multiple surgical specialties.

Core Design Philosophy
  • Provide CT-quality imaging in a mobile intraoperative platform
  • Enable multi-specialty use (neurosurgery, spine, trauma)
  • Integrate seamlessly with digital surgical navigation ecosystems
Key Engineering Feature
  • Strong interoperability with navigation software platforms
  • Multi-detector CT architecture
  • Iterative reconstruction for dose and noise optimization

2. Engineering Architecture Comparison

2.1 Imaging Technology
SystemImaging PrincipleDetector TypeReconstruction
SOMATOM On.siteMulti-slice CT (conventional geometry)Multi-row detector arrayIterative + filtered back projection
O-armCone-beam CT (CBCT)Flat-panel detectorCBCT reconstruction algorithms
AIRO CTMulti-slice CTMulti-detector CT arrayAdvanced iterative reconstruction
Key Insight
  • SOMATOM On.site and AIRO CT behave closer to diagnostic CT systems.
  • O-arm uses CBCT, which is better for geometry visualization but has lower soft-tissue contrast.
2.2 Mechanical Design & Mobility
  • SOMATOM On.site: Fully mobile CT gantry on a transport system designed to move into OR suites.
  • AIRO CT: Mobile CT scanner optimized for flexible positioning around surgical tables.
  • O-arm: C-shaped gantry rotating around the patient, often docked around the operating table.
Engineering implication:
  • Mobile CT systems (On.site, AIRO) require vibration isolation and transport stability.
  • O-arm requires precise rotational geometry but less physical relocation.

3. Imaging Performance Comparison

3.1 Spatial Resolution & Soft Tissue Contrast
  • SOMATOM On.site: High soft-tissue contrast (closest to diagnostic CT)
  • AIRO CT: High-quality CT imaging suitable for multiple anatomical regions
  • O-arm: Excellent bone visualization, lower soft-tissue contrast compared to multi-slice CT systems
3.2 Field of View
  • SOMATOM On.site → Larger field of view (closer to standard CT)
  • AIRO CT → Moderate to large field depending on configuration
  • O-arm → Limited field of view, optimized for spine and cranial procedures
3.3 Radiation Dose Considerations

All systems must balance:

  • Image quality
  • Radiation exposure
  • Intraoperative time constraints

CBCT systems (O-arm) may require different dose optimization strategies compared to multi-slice CT systems.

4. Clinical Applications

SOMATOM On.site
  • Neurosurgery (tumor resection, hematoma evacuation)
  • Intraoperative brain imaging
  • Complex cranial procedures
  • Some spinal applications
O-arm
  • Spine surgery (primary use case)
  • Pedicle screw placement
  • Orthopedic navigation
  • Cranial navigation procedures
AIRO CT
  • Neurosurgery
  • Spine surgery
  • Trauma surgery
  • General intraoperative CT imaging

5. Workflow Integration

SOMATOM On.site
  • Integration with surgical navigation systems
  • DICOM-based hospital systems
  • Designed for OR mobility and imaging-on-demand workflows
O-arm
  • Deep integration with navigation platforms (e.g., Medtronic StealthStation ecosystem)
  • Highly optimized for spine surgical workflows
AIRO CT
  • Flexible integration with multiple navigation systems
  • Designed for multi-specialty OR environments

6. Engineering Strengths and Limitations

6.1 SOMATOM On.site

Strengths

  • High image quality (multi-slice CT)
  • Strong soft tissue visualization
  • Broad clinical use beyond spine surgery

Limitations

  • Large system footprint in OR environment
  • Complex setup and workflow planning
  • Higher infrastructure requirements
6.2 O-arm

Strengths

  • Excellent for spinal instrumentation
  • Fast intraoperative imaging
  • Tight integration with navigation systems
  • Compact OR integration

Limitations

  • Limited soft-tissue imaging
  • Smaller field of view
  • Less versatile outside spine surgery
6.3 AIRO CT

Strengths

  • Multi-purpose intraoperative CT
  • Good balance of mobility and imaging quality
  • Flexible surgical applications

Limitations

  • Still less widely adopted than competitors
  • Operational complexity in mixed surgical environments

7. Key Engineering Differences

7.1 Imaging Modality Trade-offs
  • SOMATOM On.site → Diagnostic CT-level imaging
  • O-arm → CBCT optimized for bone structure
  • AIRO CT → Hybrid performance between both systems
7.2 System Design Philosophy
  • SOMATOM On.site → Mobile diagnostic CT in OR environment
  • O-arm → Surgery-integrated imaging system (spine-focused)
  • AIRO CT → Flexible multi-surgical imaging platform
7.3 Clinical Workflow Strategy
  • SOMATOM On.site → Imaging support for complex neurosurgery
  • O-arm → Navigation-driven orthopedic precision tool
  • AIRO CT → General-purpose intraoperative CT solution

8. Future Trends in Intraoperative CT Systems

Across all systems, biomedical engineering research is moving toward:

8.1 AI-Based Reconstruction
  • Faster image reconstruction
  • Lower radiation dose
  • Improved noise suppression
8.2 Hybrid Imaging Systems
  • CT + optical tracking
  • MRI-CT hybrid operating rooms
8.3 Automation in Surgery
  • Real-time feedback loops
  • AI-guided surgical corrections
8.4 Smaller and More Mobile CT Units
  • Compact gantry designs
  • Improved OR integration efficiency

These trends suggest that future intraoperative imaging systems will become more autonomous, faster, and more integrated with surgical robotics.

9. Conclusion

The comparison between SOMATOM On.site, O-arm, and AIRO CT highlights three distinct engineering approaches to intraoperative imaging.

  • SOMATOM On.site prioritizes high-quality diagnostic imaging within the OR environment
  • O-arm prioritizes surgical navigation precision for spine procedures
  • AIRO CT aims to balance mobility, image quality, and multi-specialty usability

From a biomedical engineering perspective, these systems represent different solutions to the same problem: delivering accurate, real-time imaging during surgery without disrupting workflow.

The future direction of intraoperative CT systems will likely converge toward:

  • AI-assisted imaging
  • Lower radiation dose systems
  • Better integration with surgical robotics
  • Faster and more automated reconstruction pipelines

References (APA Style)

Medtronic. (n.d.). O-arm imaging system. https://www.medtronic.com

IMRIS / Brainlab / AIRO CT resources. (n.d.). Intraoperative CT imaging systems. https://www.airoct.com

Siemens Healthineers. (n.d.). SOMATOM CT systems overview. https://www.siemens-healthineers.com/computed-tomography

National Institute of Biomedical Imaging and Bioengineering (NIBIB). (n.d.). Computed tomography (CT). https://www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct

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