Siemens PET Flow Technology: Continuous Motion PET for Better Image Quality and Workflow Efficiency
Topic Explanation: Siemens PET Flow Technology
In this edition of the PhysicsPulseTM Series, we explore Siemens PET Flow technology, an advanced acquisition method that replaces traditional step-and-shoot PET imaging with continuous bed motion. This innovation improves image uniformity, enhances workflow efficiency, and allows flexible protocol optimization while maintaining excellent quantitative accuracy.
Understanding how PET Flow works helps technologists optimize scan protocols, improve patient throughput, and ensure consistent image quality across the entire scan range.
What Is Siemens PET Flow Technology?
Traditional PET imaging uses a step-and-shoot approach, where the patient table moves to a fixed bed position, stops, acquires data, and then moves to the next position. Each bed position typically covers approximately 15–26 cm depending on scanner design.
In contrast, Siemens PET Flow (also known as FlowMotion™ technology) uses continuous bed motion, where the patient table moves smoothly through the scanner while data is acquired continuously along the entire axial field of view.
Instead of discrete bed positions, acquisition is defined by table speed, typically expressed in millimeters per second. The slower the table speed, the longer the acquisition time per region, improving image quality.
This continuous acquisition is supported by advanced reconstruction algorithms that accurately map detected events to their spatial location despite table motion.
Physics Advantage: Uniform Sensitivity and Image Quality
One limitation of step-and-shoot PET is sensitivity variation at bed position edges. Because detector sensitivity is highest at the center of the field of view and decreases near the edges, overlapping bed positions are required to maintain uniform image quality.
PET Flow eliminates these transitions.
Key benefits include:
- Uniform axial sensitivity across the entire scan range
- Elimination of bed transition artifacts
- Improved consistency in SUV measurements
- Better image quality in long scan regions such as skull-to-thigh oncology studies
Continuous acquisition allows smoother and more uniform count distribution, improving quantitative accuracy.
Improved Workflow Efficiency and Scan Flexibility
PET Flow simplifies acquisition workflow and improves scanner utilization.
Major workflow advantages include:
- No start-stop table motion between bed positions
- Reduced scan time variability
- Faster patient setup and scan initiation
- Improved patient throughput
Technologists define acquisition by selecting a table speed instead of defining multiple bed positions.
Typical equivalent acquisition speeds include:
- Slow speed (high image quality): Oncology or low-dose studies
- Moderate speed: Standard oncology protocols
- Faster speed: Whole-body screening or follow-up studies
This allows protocol optimization based on clinical indication and patient size.
Better Image Quality in Larger Patients
Continuous motion acquisition improves image quality in larger patients by maintaining consistent sensitivity across the scan length.
Advantages include:
- Improved signal-to-noise ratio (SNR)
- Reduced image noise variability
- More reliable lesion detectability
- Improved quantitative consistency (SUV accuracy)
This is especially beneficial when imaging obese patients, where uniform count density is critical.
Integration with Modern PET Detector Technologies
PET Flow is used in Siemens PET/CT systems including:
- Biograph mCT
- Biograph Horizon
- Biograph Vision
- Biograph Vision Quadra
These scanners use advanced detector technologies such as:
- Lutetium oxyorthosilicate (LSO) crystals
- Silicon photomultiplier (SiPM) detectors (Vision systems)
- Time-of-Flight (TOF) capability
Combining continuous bed motion with TOF and SiPM improves:
- Timing resolution
- Spatial resolution
- Quantitative accuracy
- Scan efficiency
Practical Considerations for Technologists
To optimize PET Flow imaging:
- Ensure the patient is properly centered in the scanner bore
- Select appropriate table speed based on clinical indication and patient size
- Use slower table speeds when higher image quality is required
- Verify scan coverage matches physician protocol requirements
- Monitor reconstructed images for uniform image quality across the scan range
Understanding the relationship between table speed and acquisition time is essential for protocol optimization.
Radiation Dose and Quantitative Accuracy
PET Flow maintains accurate quantitative measurements while enabling dose and scan optimization.
Key advantages include:
- Improved SUV consistency across scan regions
- Ability to reduce injected activity while maintaining image quality
- Ability to shorten scan time without compromising diagnostic performance
This supports ALARA principles while maintaining diagnostic reliability.
Patient Comfort and Motion Reduction
Continuous motion improves patient experience compared to step-and-shoot acquisition.
Benefits include:
- Smooth table motion without abrupt stops
- Reduced patient movement due to improved comfort
- Less anxiety during scanning
- Improved scan completion rates
Reducing patient motion also improves image quality and reduces motion artifacts.
Conclusion
Siemens PET Flow technology represents a major advancement in PET acquisition by replacing step-and-shoot imaging with continuous bed motion. This approach improves image uniformity, enhances quantitative accuracy, and increases workflow efficiency while improving patient comfort.
By understanding and properly using PET Flow technology, technologists can optimize PET imaging protocols, improve diagnostic image quality, and enhance overall clinical workflow efficiency.
References
Siemens Healthineers. Biograph Vision PET/CT System Technical Documentation.
Siemens Healthineers. FlowMotion™ Technology Overview.
Cherry SR, Sorenson JA, Phelps ME. Physics in Nuclear Medicine, 4th Edition.
Bushberg JT et al. The Essential Physics of Medical Imaging, 3rd Edition.
IAEA Human Health Series No. 1: PET/CT Atlas on Quality Control and Image Artifacts.