Enhanced Anti-Noise Performance of Gamma Camera Power Supply Systems

Gamma cameras, as critical devices in nuclear medicine imaging, require highly stable power systems. Power supply noise can interfere with gamma-ray detection signals, leading to image distortion or reduced signal-to-noise ratios. Enhancing noise immunity necessitates a comprehensive approach covering noise source suppression, circuit design optimization, and system-level shielding. 
1. Noise Source Analysis and Suppression 
Power noise in gamma cameras primarily falls into two categories: 
Conducted Noise: High-frequency harmonics (MHz range) generated by switching actions (e.g., MOSFET switching), coupled via power lines to detection circuits. 
Radiated Noise: Electromagnetic fields (0.15–30 MHz) from transformer leakage inductance and parasitic capacitance, disrupting weak current signals in photomultiplier tubes. 
Suppression Strategies: 
Transient Voltage Suppressors (TVS): Deployed at power inputs to clamp voltage spikes (e.g., 10 kV/μs) from lightning or load switching, with nanosecond response times. 
Soft-Switching Technology: Achieves zero-voltage switching (ZVS) via resonant circuits, reducing switching losses by >40% and minimizing high-frequency noise. 
2. Multi-Stage Filtering Circuit Design 
Conducted noise paths require multi-stage filtering: 
Input-Stage Filtering: π-filters (common-mode chokes + ceramic capacitors) suppress common-mode interference (150 kHz–30 MHz) with >60 dB insertion loss. Choke cores should exhibit high permeability (μ > 10,000) and low saturation. 
Output-Stage Regulation: Low-dropout regulators (LDOs) combined with LC filters reduce ripple voltage to millivolt levels. Tantalum capacitors (ESR < 10 mΩ) and magnetically shielded inductors minimize radiated noise. 
RC Snubbers: Parallel RC networks across switches and diodes absorb voltage oscillations from reverse recovery currents (diode recovery time < 50 ns). 
3. Electromagnetic Compatibility (EMC) Optimization 
Layered Shielding: 
  Electric Field Shielding: Copper foil between power modules and signal circuits, with ground impedance < 0.1 Ω. 
  Magnetic Field Shielding: Mu-metal enclosures reduce transformer flux leakage by >90%. 
PCB Layout Principles: 
  Minimize high-frequency loop area (e.g., ≤1 cm² for switching loops), and route differential signals in parallel to reduce inductive coupling. 
  Dedicated layers for photomultiplier power supply to avoid ground bounce. 
Low-Temperature-Drift Components: Metal-film resistors (TCR < 5 ppm/℃) mitigate DC offset from thermal drift. 
4. Noise Monitoring and Dynamic Adjustment 
Real-time noise spectrum analysis modules (sampling rate ≥1 GS/s) monitor power output, enabling dynamic filter tuning via FPGA: 
Adaptive algorithms (e.g., LMS) suppress specific frequencies (e.g., 100 kHz switching harmonics). 
Temperature sensors trigger cooling systems to limit component temperature rise to <20°C, preventing thermal noise. 
> Key Table: Noise Suppression Techniques Comparison 
> | Noise Type       | Suppression Method       | Performance Metric       | 
> |----------------------|------------------------------|------------------------------| 
> | Conducted High-Freq  | π-Filter + TVS               | Insertion Loss >60 dB        | 
> | Radiated EMI         | Mu-Metal Shielding           | Flux Leakage Reduction >90%  | 
> | Switching Ripple     | LDO + LC Filter              | Ripple Voltage <5 mV         | 
> | Transient Spikes     | Soft-Switching + RC Snubbers | Response Time <100 ns        |