Image recording

• Radiography aims to produce an image with the highest amount of detail, which requires careful control of a number of different variables such as kVp, mA, S that can affect image quality.
• The purpose of a radiographic procedure is to provide visibility of the internal structures and conditions within the human body.
• Image should be produced with the optimum quality image and with the lowest possible radiation exposure to the patient and staff.
• SID (Source - to - image receptor distance) and SOD (Source - to - object Distance) are technical terms in radiography.
• CR (Central Ray) is a technical term in X-ray Beam Quality.
• The quality of the x-ray beam or its penetrating ability affects its interaction with anatomic tissue.
• The anode in a fluoroscopic unit has a circular plate with a hole in the middle, through which electrons will pass and hit the output phosphor.
• A typical radiographic and imaging-intensified fluoroscopic unit is shown in Figure 10-2.
• Electrons emitted from the photocathode gain kinetic energy from the electric field inside the intensifier tube.
• The light image produced may be up to 9000 times brighter than the input phosphor image.
• This energy is converted into light at the output phosphor.
• The area of the output phosphor image is about one hundredth that of the input phosphor, increasing the image brightness one-hundred times.
• Fluoroscopy is used in many types of tests and procedures including:
• The image light intensities from the output phosphor are converted to an electronic video signal and sent to a television monitor for viewing.
• Fluoroscopy components include Photoelectric (PE).
• Additional filming devices, such as spot film or cine (movie film), can be attached to the fluoroscopic system to create permanent radiographic images of specific areas of interest.
• Higher-penetrating x-rays are more likely to be transmitted through anatomic tissue without interacting with the tissues’ atomic structures.
• Blurring, also known as low-pass filtering, averages out big changes in intensity and is the most basic of filtering operations.
• Smoothing (also known as low-pass filtering) is a postprocessing technique that suppresses image noise but degrades spatial resolution.
• Distortion results from the radiographic misrepresentation of either the size (magnification) or the shape of the anatomic part.
• Three possibilities in digital image processing include methods to reduce image noise, increase visibility of detail, and adjust and optimize the image contrast characteristics.
• Shape distortion can occur due to misalignment of the object and image receptor.
• Misrepresentation of object size or shape is a controlling factor in distortion.
• Subtraction is a technique that can remove superimposed structures so that the anatomic area of interest becomes more visible.
• Motion unsharpness (Um) gets worse with increased OID Distortion.
• Noise is any content in the image that limits the ability to visualize objects in the image.
• Equalization is a postprocessing function whereby underexposed areas are made darker and overexposed areas are made lighter, resulting in an image that appears to have lower contrast so that dense and lucent structures can be better seen within the same image.
• A low-pass filter, also called a "blurring" or "smoothing" filter, just calculates the average of a pixel and all of its eight immediate neighbors.
• Smoothing/Blurring, Sharpening, and Convolution are three common postprocessing techniques in digital image processing.
• High-pass filtering, also known as sharpening, emphasizes fine details in the image but amplifies noise.
• Controlling factors in distortion include SID, OID, Object-IR alignment, and Central Ray (CR) alignment.
• Edge enhancement, also known as high-pass filtering, is a postprocessing technique that improves the visibility of small, high-contrast structures but may increase image noise slightly.
• When an image is distorted, spatial resolution is also reduced.
• Noise is a random variation in intensity and has a grainy or mottle appearance.
• Lower-penetrating x-rays are more likely to interact with the atomic structures and be absorbed.
• Geometric unsharpness (UG) depends on focal spot size.
• Geometric unsharpness is called penumbra.
• The closer the object to the film/detector, the sharper the detail.
• An area of increased brightness viewed on a computer monitor shows decreased density on a film image, whereas an area of decreased brightness visualized on a computer monitor has increased density on a film image.
• Compensating filters in radiography are used to alter the intensity of the primary beam and are added to image anatomic areas that are non-uniform in makeup.