Chapter 28 Spatial Resolution

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Define Spatial Resolution and synonymous terms
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Define Spatial Resolution and synonymous terms
One of the geometric properties of image quality; the degree of geometric sharpness or accuracy of structural lines actually recorded in the image; also referred to as detail, definition, sharpness, and recorded detail. In digital images, it can be expressed in terms of three dimensions of the image.
Definition, sharpness, recorded detail, or detail
Explain the effect of various distances on spatial resolution
Increase SID Increases Resolution.
Decrease OID Increases Resolution.
Resolution is improved when SID increases and degraded when it decreases. Resolution is improved when OID decreases and degraded whenever it increases.
Describe the factors that affect penumbra/point spread function size
SID, OID, Attenuation/Absorption Sharpness.
Penumbra decreases when the focal spot or OID decreases, and when the SID increases.
Penumbra increases with objects that aren't perfectly trapezoidal, since the attenuation of the beam creates a gradual edge instead of a sharp one.
Describe the effect of digital imaging systems and film-screen combinations on spatial resolution
Digital systems have limitation factors of phosphor size, layer thickness, and concentration, and also scanning and processing. High fill factors of detectors produce higher resolution. The size of the detector element is the major factor limiting digital systems.

Film-Screen Combinations have an inverse relationship between combination speed and resolution.
A slow film-screen combination yields better resolution than a fast one.
Resolving power of an intensifying screen is based on phosphor size, phosphor layer thickness, and phosphor concentration.
Explain Digital Image Receptor Factors that control Spatial Resolution
Geometry: The geometry of the beam is the most important factor in establishing the level of resolution desired. If is affected by the focal spot size (the smaller the focal spot, the higher the resolution) and distance (OID and SID).

Image Receptor: The IR is based on Film-Screen systems and Digital Systems.

Motion: There are three types of motion; involuntary (seizures, heartbeat), voluntary (breathing, movement of the patient on purpose), and equipment motion (x-ray tube movement, drifting, vibrating).
Describe appropriate techniques to prevent patient motion
Communication is the best method to reduce motion.
Exposure time reduction will help with an uncooperative patient.
Immobilization with foam pads, angle sponges, and sandbags help as well and reduces repeat exposures.
Synthesize various geometrical factors into a clinical protocol for improving resolution.
In order to get the best resolution possible for an image, shoot the x-ray with the greatest SID allowed, the lowest OID achievable, and the smallest focal spot applicable for the part being imaged. Use the best digital system combination possible to have the film-screen speed be as low as possible to have increased resolution, but not so low as to inflict high patient dose. Reduce motion by effective communication, fast time and high mA as needed based on patient cooperation.
Recommend techniques for reducing motion, including immobilization devices
Positioning aids, tape across the forehead or to fan out toes, Pig-O-Stat machines for pediatric cases, parental or tech restraint of peds, sandbags, and sheet wrapping or compression bands.
Aliasing
When spatial frequency exceeds the Nyquist frequency and the incoming data are sampled less than twice per cycle.
Contrast-to-Noise Ratio
the ratio of the difference of signal intensities of two regions of interest to the imaging noise
DefinitionOne of the geometric properties of image quality; the degree of geometric sharpness or accuracy of structural lines actually recorded in the image; also referred to as detail, recorded detail, sharpness, and spatial resolution.Edge Spread Function (ESF)expression of the boundaries of an imageImaging NoiseTotal noise the the Image Receptor receives; system noise, ambient noise, and quantum noise.Line Spread Function (LSF)Measurement of recorded detail, sharpness, and resolution; the ability of a film/screen system to accurately measure the boundaries of an image.Low contrast resolutionthe ability of the system to differentiate between objects with similar densitiesModulation Transfer Function (MTF)The accuracy of an image compared to the original object on a scale of 0-1. 1=perfect. 0-worst.Nyquist CriterionThe sampling of the spatial resolution frequency signal twice from each cycle in digital systemspoint spread function (PSF)Expression of the boundaries of an image; determined by a mathematical measurement of an image produced at a single point.SharpnessOne of the geometric properties of image quality; the degree of geometric sharpness or accuracy of structural lines actually recorded in the image; also referred to as detail, definition, recorded detail, and spatial resolution.spatial resolutionOne of the two geometric properties of image quality; the degree of geometric sharpness or accuracy of structural lines actually recorded in the image; also referred to as detail, definition, sharpness, and recorded detail. In digital images, it can be expressed in terms of three dimensions of the image.temporal resolutionthe relationship between the duration of data acquisition and motion of the structures under study. Shorter acquisition times will demonstrate better TR since it means minimizing voluntary and involuntary motion.UnsharpnessPenumbra. lack of sharp definition of fine detailWhat is spatial resolution?The ability to distinguish two separate objects close togetherHow is resolution measured?Line pairs/mm that can be clearly seen on filmHow do the SID and the OID affect spatial resolution?the higher the SID and the lower the OID, the higher the spatial resolution.What is the relationship between focal spot size and spatial resolution?The smaller the focal spot, the greater the resolutionWhat is the difference between umbra and penumbra?"Penumbra" and "umbra" are terms pertaining to the parts of shadows. Umbra is the darkest area while the penumbra is the lighter region which is found at the perimeter. Penumbra-unsharpnessWhat factors affect the resolving power of CR and DR digital receptors?Phosphor size, layer thickness, and concentration. CR systems; scanning and processing. DR factor is the size of the detector element.What is the difference between voluntary and involuntary motion?Voluntary can be controlled by proper communication and breathing and involuntary cannot be controlled.What are the methods that can be used to reduce the possibility of motion?Communication is the best method to reduce motion. Exposure time reduction will help with an uncooperative patient. Immobilization with foam pads, angle sponges, and sandbags help as well and reduces repeat exposures.