Patient Dose and Contrast Resolution
Contrast resolution depends directly on these two key system characteristics.
What are dynamic range and SNR (Signal-to-Noise Ratio)?
This clinical term describes an imaging system's ability to distinguish and display a wide variety of subtle differences in tissue densities as distinct shades of gray.
What is contrast resolution?
Instead of film or a flat-panel digital detector, CR utilizes this type of reusable plate to capture the latent image.
What is a photostimulable phosphor (PSP) plate?
While CR requires a physical plate reader, DR (Digital Radiography) systems bypass this step entirely to produce an image almost instantly using these types of fixed detectors.
What are flat-panel detectors (FPDs)?
Spatial resolution refers to the imaging system's ability to render these two distinct objects as separate and distinct structures when they are placed close together.
What are small objects?
Even if a digital detector can record many shades of gray (possessing a good dynamic range), this imaging factor can severely limit a clinician's ability to actually see them.
What is noise?
While film-screen radiography has a highly limited dynamic range, digital imaging detectors are praised for possessing this type of dynamic range response.
What is a wide (or linear) dynamic range?
This is the specific chemical element (often used as a dopant with barium fluorohalide) that acts as an activator to trap electrons and store the latent image in a CR plate.
What is Europium?
This is the fundamental difference between Direct and Indirect DR: Indirect DR requires this extra step to convert X-rays into light before turning them into an electrical charge.
What is a scintillator (or scintillation layer)?
This unit of measurement, which counts pairs of black and white strips per millimeter, is used to quantitatively express the spatial resolution of an imaging system.
What are line pairs per millimeter?
Although this step helps maximize clinical visualization of the anatomy, it is fundamentally incapable of recovering fine details that have already been lost to noise.
What is postprocessing?
This postprocessing technique allows technologists to manipulate the brightness and contrast (grayscale) of the digital image on a monitor after exposure.
What is windowing (or window level and window width)?
To release the stored energy and read the latent image, the CR reader scans the PSP plate with this type of light source.
What is a helium-neon laser (or red laser light)?
Direct DR flat-panel detectors skip the light conversion step entirely and use this specific semiconductor material to convert X-rays directly into an electrical charge.
What is amorphous selenium?
This mathematical concept describes how faithfully an imaging system reproduces the true structure of an object on a scale from 0 to 1, with 1 representing perfect fidelity.
What is the Modulation Transfer Function (MTF)?
This term refers to the range of exposures (or shades of gray) over which a medical imaging detector can record useful diagnostic information.
What is dynamic range?
In the Signal-to-Noise Ratio (SNR), this component represents the random, useless background interference that obscures diagnostic detail (Grainy Appearance)
What is noise (or quantum mottle)?
After the laser scans the plate, this blue-purple light emitted by the phosphor is collected and converted into an electronic signal by this device.
What is a photomultiplier tube (PMT) or photodiode?
In Indirect DR systems, this material is commonly used as the photodetector to convert the light emitted by the scintillator (such as Cesium Iodide) into an electrical signal.
What is amorphous silicon
In flat-panel detectors, this electronic component is structured as an active matrix array and behaves like a switch to release the stored electrical charge from each individual pixel element (DEL) to the computer.
What is a Thin-Film Transistor (TFT)?
This is the primary reason why increasing patient radiation dose is sometimes inappropriately used to improve image quality—specifically to overcome this degradation factor.
What is noise (or to increase the Signal-to-Noise Ratio/SNR)?
Between a high-SNR image and a low-SNR image, this is the one that will display a much clearer, sharper, and less "grainy" representation of the patient's anatomy.
What is a high-SNR image?
This step must occur inside the CR reader using intense white light before the PSP plate can be safely reused for another patient exposure.
What is erasing the plate (or erasure)?
Because it avoids the lateral spreading of light (light diffusion) inherent in scintillators, this DR method inherently provides the highest spatial resolution.
What is Direct DR?
This indirect digital radiography technology uses a photosensitive silicon chip coupled to a scintillator via fiber-optic bundles or lenses to focus light and convert it into an electronic signal.
What is a Charge-Coupled Device (CCD)?