Radiography Chapter 6 Flashcards

Questions and Answers

What is a CCD?

A charge coupled device is the oldest indirect conversion digital radiography system used to acquire a digital image.

How does a CCD work?

X-ray photons interact with a scintillation material, and the signal is transmitted to the CCD. Charges are stored in capacitors in a pattern and released line by line to the ADC.

What is a CCD made of?

A photosensitive receptor and electronics embedded in a substrate material in a silicon chip.

What is the chip in the CCD made of?

Polysilicon layer, a silicon dioxide layer and a silicon substrate. Signup and view all the answers

What is a Del?

A detector element that contains three electrodes that hold the electrons in an electrical potential well. Signup and view all the answers

What causes a blooming effect?

Overfill of Del's. Signup and view all the answers

What will the scintillator and the way it is constructed determine?

How many photons are absorbed, how much light is produced, the wavelength or color of the light. Signup and view all the answers

Why are CSI detectors structured?

Needles focus light onto a very narrow area, reducing light spread. Signup and view all the answers

When reducing the image size, it involves what important components?

The scintillator, light collection component, noise. Signup and view all the answers

Why is gadolinium considered unstructured?

Turbid phosphors produce more light spread, resulting in decreased efficiency of the detector. Signup and view all the answers

How efficient are CCDs?

The more light that is sent to the chip without the creation of noise, the more efficient the system is. Signup and view all the answers

What can change the performance of the optics in a CCD?

Issues arise with geometric distortion such as light scattering or lens or optic flaws. Signup and view all the answers

What is the quantum efficiency of the CCD?

The amount of electrons produced relative to the incident light from the scintillator. Signup and view all the answers

What does quantum efficiency represent?

The absolute efficiency of the light collection and signal created in the chip. Signup and view all the answers

Does quantum efficiency affect detective quantum efficiency?

True Signup and view all the answers

What increases the efficiency of the CCD?

The polysilicon layer must be transparent enough so that light can pass into the deeper substrate storage area. Signup and view all the answers

The less sensitive the CCD to the light spectrum of the scintillator, the less efficient the DQE?

True Signup and view all the answers

What are the most common types of noise associated with a CCD?

Statistical noise, dark or current noise, amplification noise. Signup and view all the answers

What is statistical noise?

Created by lack of light photons from the scintillator, this is known as quantum mottle. Signup and view all the answers

What applications are CCDs used in?

Digital fluoro, breast biopsy, digital mammography, general radiography. Signup and view all the answers

How is the CCD used in digital fluoro?

Replaces the television pickup tube and provides linear readout with greater dynamic range. Signup and view all the answers

How is the CCD used in stereo static breast biopsy?

Single CCD detector (50mm x 50mm) where demag is the process of reducing the phosphor output image. Signup and view all the answers

How is the CCD used in general radiography?

Tiled in a 16 x 12 array. Signup and view all the answers

What are the advantages and disadvantages of CCD technology?

Simple and easy, easy to repair and replace, cheaper than TFTs, but demag issues reduce DQE. Signup and view all the answers

What is a CMOS?

Developed by NASA, uses a scintillator, each pixel has its own amplifier. Signup and view all the answers

Study Notes

CCD Overview

A CCD (Charge Coupled Device) is the oldest indirect conversion system for digital radiography, used to obtain digital images.
X-ray photons interact with a scintillation material, generating signals captured by the CCD, which stores charges in a patterned array.

CCD Construction

Comprised of photosensitive receptors and electronics embedded in a silicon chip substrate.
Contains components like a polysilicon layer, silicon dioxide insulator, and silicon substrate for charge storage.

Detector Elements and Functionality

A Del (Detector Element) features three electrodes, forming an electrical potential well that holds electrons, functioning like a bucket brigade to collect charges.
The blooming effect occurs when Del's overflow; this is controlled using built-in overflow drains.

Scintillator Properties

The design of the scintillator influences the absorption of photons, light production, and the resultant color or wavelength of emitted light.
CSI (Cesium Iodide) detectors possess structured needles that focus light, minimizing spread and allowing for thicker scintillators without loss of spatial resolution.

Image Size Reduction Considerations

Important components for reducing image size include scintillator properties, light collection efficiency, and noise levels.
Gadolinium is dubbed unstructured due to turbid phosphors causing light spread, thereby reducing detector efficiency.

Efficiency Metrics

CCD efficiency relies on maximizing light directed to the chip while minimizing noise generation.
Quantum efficiency of a CCD measures electron production related to incident light from the scintillator, representing the effectiveness of signal generation.

Performance Influencers

Geometric distortions, including light scattering and lens imperfections, can negatively affect optical performance.
The quantum efficiency is directly linked to Detective Quantum Efficiency (DQE), which is a ratio of output signal to noise, making it critical for performance evaluation.

Noise Types in CCDs

Common noise types include statistical noise (quantum mottle), dark or current noise, and amplification noise which affect image quality.
Statistical noise arises from insufficient light photons emitted by the scintillator.

Applications of CCD Technology

CCDs are employed in various medical imaging modalities such as digital fluoroscopy, breast biopsy, digital mammography, and general radiography.
In digital fluoro, CCDs replace older television pickup tubes and offer improved dynamics and compactness without susceptibility to scanning errors.

Advantages and Disadvantages of CCD

Benefits of CCD technology include simplicity, ease of repair, and cost-effectiveness compared to TFTs (Thin Film Transistors).
Limitations include demagnification issues that can impair DQE.

CMOS Technology

CMOS (Complementary Metal Oxide Semiconductor) was developed by NASA, utilizing scintillators with individual pixel amplifiers and built-in ACDs for enhanced efficiency and reduced space requirements.

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Test your knowledge on Chapter 6 of Imaging with these flashcards. Covering key concepts such as CCD, its functionalities, and components, this quiz is perfect for reinforcing your understanding of digital radiography systems. Ideal for students and professionals alike!