Why does the image quality of the orthopedic C-arm machine deteriorate over time?

A hospital purchased an orthopedic C-arm and found that the image quality deteriorated after one to two years. The manufacturer explained this as normal degradation, and the after-sales engineer was able to adjust it and restore quality. So why do some orthopedic C-arms experience declining image quality with use? Let’s take a look at the analysis from professionals.

The reasons for image quality degradation in orthopedic C-arms mainly come from two aspects: the detector and the X-ray tube.

Whether it’s a flat panel detector or an image intensifier, these are provided by major manufacturers. When used in small C-arms, the cumulative dose over the entire 10-year lifecycle is far below the maximum dose allowed for the detector’s lifecycle, so detectors typically do not experience sensitivity degradation that leads to image quality decline.

The other potential source of degradation is the X-ray tube. Factors that may contribute to X-ray tube degradation include insufficient kV, reduced tube current (mA), or unchanged kV and mA but reduced dose. Let’s analyze these one by one.

1. Lower kV

National standards stipulate that the accuracy range for kV is 10%. This means that for an orthopedic C-arm with a nominal output voltage of 110kV, a measurement of 99kV or higher is considered acceptable. However, some manufacturers, due to design issues with integrated X-ray tubes and oil injection processes, may adjust the kV to the lower limit to prevent tube arcing. In other words, while the displayed kV is 110, the actual kV could be only 99. If there’s even a slight change, the kV might drop below 99, resulting in insufficient penetration for slightly thicker patients and leading to poor image quality.

2. Lower mA

The tube current, or mA, even slight variations or inaccuracies can lead to changes in image quality. If a manufacturer lacks closed-loop control for mA, the nonlinear relationship between mA and filament current means that even minor adjustments may lead to inaccuracies over time due to temperature fluctuations, resulting in what is referred to as image quality degradation in orthopedic C-arms.

Additionally, if the manufacturer’s control over the filament is not precise, the filament may operate at a consistently high temperature, or each exposure might create a large current surge. This can lead to gradual evaporation of the tungsten filament, resulting in decreased electron emission capacity and a drop in mA.

3. Constant kV and mA but Reduced Dose

If the manufacturer’s integrated X-ray tube design utilizes kV/mA that exceeds the anode target’s power capacity, this can cause the target surface to become rough over time, leading to small pits that prevent rays from fully emitting. Consequently, kV and mA might remain unchanged, but the dose can significantly drop.

Conclusion

A well-designed orthopedic C-arm should not exhibit image quality degradation over its lifecycle. If image quality does degrade, engineers can often resolve the issue by increasing the kV or mA. This usually indicates a lack of closed-loop control leading to drift, or it could be due to design flaws causing changes in resistance or filament evaporation. Additionally, rotating anode tubes might suffer from poor thermal management leading to target surface damage.

The X-ray tube is a core component of medical imaging devices like orthopedic C-arms. Unfortunately, most medical imaging manufacturers in China lack the capability to independently develop and produce core components. However, Puyi Medical, a leading domestic manufacturer of orthopedic C-arms, is one of the few core component manufacturers that now possesses independent R&D and production capabilities for X-ray tubes and high-voltage generators. Since 2020, Perlove Medical’s C-arms and mobile DR devices have gained recognition from many customers, securing a leading market share.