The flat-panel detector (FPD) is the core component of a digital X-ray system. In an X-ray imaging setup, the high-voltage generator and X-ray tube control the emission of X-rays. These X-rays pass through the object and are attenuated. The attenuated X-rays then reach the flat-panel detector, where they are converted into visible light and subsequently transformed into electrical signals through photoelectric conversion. These signals are then digitized by an Analog/Digital Converter (ADC) and transmitted to a computer for image processing.
According to the energy conversion method, flat-panel detectors are divided into indirect conversion and direct conversion types. The amorphous silicon (a-Si) flat-panel detector, which we are most familiar with, belongs to the indirect conversion category.
The performance and function of an amorphous silicon flat-panel detector largely depend on its structural composition. Below, Perlove Medical introduces the basic structure and the role of each layer in an amorphous silicon flat-panel detector.
Structure of an Amorphous Silicon Flat-Panel Detector
From top to bottom, the detector typically consists of six layers:
- Protective Layer:
Made of aluminum or carbon fiber, this top layer provides mechanical support and protection for the internal components. - Reflective Layer:
This is a white reflective film that ensures total reflection of visible light within the scintillator, reducing light loss and improving X-ray utilization efficiency. - Scintillator Layer:
The CsI (cesium iodide) scintillator layer, typically 400–500 μm thick, is tightly bonded to the microelectrode array surface. Its function is to absorb X-rays and convert their energy into visible light (fluorescence). - Photodiode Array Layer:
Composed of an amorphous silicon photodiode matrix with thin-film transistors (TFTs), where each photodiode and TFT together form a single pixel unit. This layer captures the emitted visible light and converts it into electrical signals. - Signal Processing Circuit Layer:
This layer includes amplifiers, multi-channel A/D converters, and control circuits. It reads out the electrical signals from each pixel, digitizes them, and transmits them to the computer for image reconstruction. - Supporting Substrate Layer:
Made of a glass substrate, this layer provides structural stability and protection for the entire detector assembly.
Additionally, amorphous silicon flat-panel detectors can also be described as comprising four key parts:
- CsI scintillator layer
- Amorphous silicon photodiode array
- Row driver circuit
- Image signal readout circuit
Currently, amorphous silicon flat-panel detectors remain mainstream in medical X-ray imaging systems.
For example, Perlove Medical’s PLX7500 Series mobile 3D C-arm adopts a 30 cm × 30 cm CsI amorphous silicon flat-panel detector, capable of producing high-resolution, large-format 2D and 3D images.
With up to 16-bit grayscale depth and a high dynamic range, it delivers clear visualization of implants and anatomical details. Combined with Perlove’s integrated X-ray tube and high-frequency pulse generator, the system provides high-quality imaging at low radiation doses—ensuring sharp, transparent images even for patients with thicker or denser tissues.
