171 Flashcards
(16 cards)
What are the two types of digital image receptors?
Computed Radiography (CR) and Direct Radiography (DR)
These types differ in their image acquisition processes.
What is the process of Computed Radiography (CR)?
2-step process involving a cassette-based system and a separate reader for image acquisition.
The imaging plate is coated with phosphor, specifically barium fluorohalide with europium.
What does the imaging plate in CR do when struck by radiation?
Gives off light and stores energy in its layers.
The energy is released when the plate is placed in the reader.
What is the sequence of operations in CR imaging?
IP is exposed to radiation, latent image stored, IP placed in reader, stored energy released, computer processes into image.
The latent image is held until the reader processes it.
What are the key components of a CR reader?
- Helium-neon laser
- Photomultiplier tube (PMT)
- Analog-to-digital converter (ADC)
The PMT collects light and converts it to an electrical signal, while the ADC digitizes this signal.
What is a characteristic of Direct Radiography (DR) systems?
Self-scanning readout system that provides images within seconds.
Most systems display images in 3-5 seconds.
What is the function of a Flat Panel Detector (FPD) in DR?
Receives x-ray energy and converts it to an electrical signal for storage and readout.
The FPD is constructed in layers and can operate in both indirect and direct conversion modes.
What are the two types of conversion in DR systems?
- Indirect conversion DR
- Direct conversion DR
Each type differs in how x-ray energy is converted to electrical signals.
What happens in indirect conversion DR?
X-ray energy is converted to light, which is then converted to an electrical charge.
The electrical charge is digitized by an ADC.
What materials are commonly used in scintillators for indirect DR?
- Thallium-doped cesium iodide (CsI[TI])
- Gadolinium oxysulfide (Gd2O2S)
CsI is structured while Gd2O2S is turbid, affecting image quality.
What is a key advantage of using CsI scintillator?
Prevents light from spreading, resulting in better image detail.
The structured needle-like structure enhances spatial resolution.
What does direct conversion DR use to convert x-rays?
Uses a photoconductor, typically amorphous selenium (a:Se).
This allows for direct conversion of x-rays to electrical signals.
What is the role of the TFT array in a Flat Panel Detector?
Stores electrical charge in individual matrix boxes called detector elements (DELs).
The TFT array is crucial for readout in DR systems.
What is dynamic range in the context of digital receptors?
Ability of a detector to accurately capture a range of photons exiting the patient.
Digital receptors have a wide dynamic range, allowing for varied techniques.
True or False: Overexposed images in digital radiography may still appear diagnostic.
True
The wide dynamic range of digital receptors helps in maintaining diagnostic quality.
What is the responsibility of the radiographer regarding exposure?
Responsible for ALARA (As Low As Reasonably Achievable).
This principle emphasizes minimizing radiation exposure to patients.
