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What is the purpose of the multiplexer in the Flat Panel Detectors?
What happens to the switches after the charge is transferred down the signal lines?
What is the sequence of operations in the Flat Panel Detectors?
What is the role of the ADC in the Flat Panel Detectors?
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What happens when the switch is closed in the Flat Panel Detectors?
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What is the purpose of the switching control in the Flat Panel Detectors?
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What is the sequence of operations in each row of the Flat Panel Detectors?
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What is the relationship between the multiplexer and the ADC in the Flat Panel Detectors?
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What is the purpose of digitization in the Flat Panel Detectors?
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What is the role of the Flat Panel Detectors in the overall system?
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Study Notes
Chest Exams
- Conventional chest exams using film have a longer exam time (6:05 minutes) and more repeats compared to exams using computed radiography (CR) or digital detectors.
Computed Radiography (CR)
- CR uses a cassette and reader to process the image.
- Exam time is shorter (7:02 minutes) with minimal repeats.
Digital Detector
- Digital detectors use a direct or indirect conversion of x-rays to charge.
- They have a shorter exam time (2:18 minutes) with minimal repeats.
Digital Detectors
- There are two types of digital detectors: direct and indirect.
- Direct detectors convert x-rays to charge directly, while indirect detectors convert x-rays to light and then light to charge.
Direct Radiography (DR)
- DR uses a fixed detector panel, which is less portable but more expensive than CR.
- DR has faster results, lower dose, and typically fixed within the table or vertical bucky.
- Amorphous silicon/selenium arrays are used in DR.
Indirect Digital Detectors
- Indirect detectors involve conversion of x-rays to light (CsI) and then light to electrical charge.
- The charge accumulates in a storage capacitor and is read out sequentially using an FET switching element (TFT array).
Flat Panel Detectors
- Flat panel detectors are solid-state analogs of gas ionization chambers.
- They use photoconductors (a-Si or a-Se) to detect x-rays.
- The electrons generated via ionization are collected via the application of an electric field.
- The band gap is typically 1 or 2 eV.
Indirect Flat Panel Detectors
- Indirect flat panel detectors use a scintillator (Gd2O2S:Tb or CsI:Tl) to convert x-rays to light.
- The light is collected by a photodetector (film emulsion or silicon photodiode).
- The charge is stored in each pixel element, and the magnitude of the charge in each pixel is the latent image.
Direct Flat Panel Detectors
- Direct flat panel detectors use a layer of photoconductive material (amorphous silicon or selenium).
- The x-rays produce charge, which is attracted to the electrode and capacitive storage element.
- The charge is read out using an FET switching element (TFT array).
Flat Panel Radiography
- Flat panel radiography uses a flat plate and sends the signal directly to storage and the monitor.
- It removes the need for a cassette and readout system.
Process of Flat Panel Radiography
- X-rays hit CsI, which produces light.
- The light hits a-Si, producing electrons and holes.
- The electrons and holes are drawn towards the positive bias, and holes are stored in the charge storage wells beneath the electrodes.
- When enough charge is stored, a voltage runs across the a-Si, and the electronics read this voltage.
Readout Process
- The signals from individual sensors are read out in sequence.
- All sensors in the first row are activated, and the signals are led on parallel in the column direction to pre-amplifiers, amplifiers, and an ADC.
- When the first row has been digitized, the second row is activated, and so on.
Flat Panel Detector Array
- The detector array is a two-dimensional array of imaging pixels.
- Each pixel is configured from a switching element and a storage element.
- Other lines control the readout of the stored charge from the array of pixels.
- Peripheral circuitry amplifies, digitizes, and synchronizes the readout.
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Description
This quiz assesses understanding of chest radiography exams, including patient positioning, film exposure, and quality control. It is suitable for medical students and professionals in radiology.
