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Physics
Ch 10
| Question | Answer |
|---|---|
| What defines a high‑quality radiograph? | It should faithfully reproduce the structures and tissues of interest with proper contrast, minimal distortion, and acceptable density. |
| What is spatial resolution? | The ability to image two separate objects that are close together and distinguish them as separate. |
| What types of blur degrade spatial resolution? | Screen blur, motion blur, and geometric blur. |
| What is radiographic noise? | Random fluctuation in optical density that reduces image clarity. |
| How does image receptor speed affect noise and resolution? | Faster receptors increase noise but decrease spatial resolution; slower receptors reduce noise and improve detail. |
| What is contrast resolution? | The ability of the image receptor to distinguish between small differences in tissue density. |
| What is recorded detail? | The sharpness of structural lines on a radiograph; essentially spatial resolution. |
| What is visibility of detail? | The capacity to see recorded detail when optical density and contrast are optimal. |
| What is quantum mottle? | Noise resulting from too few x‑ray photons reaching the image receptor. |
| How can quantum mottle be reduced? | By increasing mAs or using a slower (lower‑speed) receptor. |
| What is image latitude? | The range of exposure over which the receptor will produce acceptable image density. |
| What does the slope of the straight‑line portion of the characteristic curve represent? | Film contrast (slope ≈ contrast sensitivity). |
| What is “base + fog” on a characteristic curve? | The inherent film base density plus density from background radiation or processing; the minimum density. |
| What does a “wide latitude” receptor allow? | Greater flexibility in exposure settings while still producing usable images. |
| What are the three primary geometric factors affecting image quality? | Magnification, distortion, and focal‑spot blur. |
| What is magnification factor formula? | MF = SID / SOD. |
| How can magnification be reduced? | Increase SID or decrease OID (object-to-image receptor distance). |
| What is geometric distortion? | Misrepresentation of object shape or size on the image due to improper alignment or divergence. |
| How can distortion be minimized? | Keep object and receptor parallel and align central ray perpendicular to object and receptor; minimize OID; use proper SID. |
| What is focal‑spot blur? | Loss of spatial resolution caused by the finite size of the x‑ray focal spot. |
| How does reducing focal‑spot size affect image quality? | Improves spatial resolution/detail but limits tube loading capacity (heat). |
| What is subject contrast? | Differences in tissue absorption due to atomic number, density, and thickness. |
| How do tissue atomic number and density affect subject contrast? | Higher atomic number or greater density → more absorption → higher contrast. |
| How does patient (subject) thickness affect radiographic contrast? | Thicker part → more absorption and scatter → lower contrast and more noise. |
| What are five major factors affecting image quality? | Film (or receptor) factors, geometric factors, subject factors, processing factors, and scatter/noise factors. |
| What is scatter radiation’s effect on image quality? | Adds unwanted exposure (noise/fog), reduces contrast, and reduces visibility of detail. |
| How can scatter be reduced? | Use collimation, grids, compression, and lower field size when possible. |
| What is a grid? | A device between patient and image receptor that absorbs scatter before it reaches the receptor. |
| How does grid ratio affect scatter removal and exposure technique? | Higher grid ratio removes more scatter but requires higher mAs (more exposure). |
| What is grid cutoff? | Loss of primary beam (useful photons) due to misalignment between grid and x‑ray beam, leading to underexposure or uneven density. |
| What causes grid cutoff? | Improper alignment, wrong SID, incorrect angle, or off‑center receptor/grid. |
| What is the relationship between image receptor speed and contrast resolution? | Slower receptors → better contrast resolution (less noise, better detail); faster receptors → poorer contrast resolution. |
| What is the difference between recorded detail and visibility of detail? | Recorded detail refers to which structures are captured; visibility of detail refers to how well those structures can be seen (contrast + density). |
| Why is proper processor quality control important? | To ensure film density, contrast, and consistency — otherwise poor processing degrades image quality. |
| What are artifacts? | Unwanted marks, densities, or distortions on the image that do not represent actual anatomy. |
| What geometric factor affects magnification the most? | OID (object‑to‑image receptor distance). |
| What happens to optical density if mAs is increased while kVp is constant? | Optical density increases (darker image). |
| What is optical density? | The degree of blackness on a radiograph — related to the amount of light transmitted through film or number of photons in digital imaging. |
| What receptor characteristic influences contrast latitude? | Receptor latitude (wide latitude allows a broader range of exposure producing acceptable density). |
| What is film contrast? | The degree of difference between densities on the film — steep slope characteristic curves produce high contrast. |
| What is subject contrast? | The variation in absorption by different tissues — determined by tissue composition, thickness, and x‑ray energy. |
| What is image contrast? | The combined effect of subject contrast, receptor contrast, and scatter — how well different structures are seen. |
| How does increasing SID affect magnification and resolution? | Increasing SID reduces magnification and improves resolution (less blur), but reduces receptor exposure (requires more mAs). |
| What is detail unsharpness? | Loss of clarity due to motion, geometric blur, distance blur, or poor receptor resolution. |
| What is the effect of motion on image quality? | Motion blur reduces spatial resolution and detail — must have motion control (short exposure times, patient instructions). |
| What is radiographic fog? | Uniform exposure of receptor by scatter radiation or background exposure, reducing contrast. |
| What is the “speed‑detail tradeoff”? | Faster receptors = more speed (less exposure) but decreased detail and increased noise; slower receptors = better detail but require more exposure. |
| What is contrast‑detail analysis? | Assessment of how small differences in density (contrast) and detail size can still be visualized — used in QC and receptor testing. |
| What is undercutting in imaging context? | Loss of image density or cut‑off due to poor grid alignment or SID/angle errors. |
| What is magnification radiography? | Technique where OID is increased intentionally to enlarge a small area for better visualization — increases detail of small structures but increases magnification and blur. |
| Why do magnification radiographs often lose sharpness? | Because increased OID increases blur and reduces resolution. |
| What is resolution vs contrast tradeoff in radiographic settings? | Increasing resolution (small focal spot, slow receptor) often decreases contrast resolution (longer exposure, more noise) and vice versa. |
| What is “visibility of recorded detail”? | When the receptor has captured detail (recorded), and exposure and contrast are adequate to reveal that detail to the viewer. |
| How does screen‑film versus digital receptors differ in terms of latitude and contrast resolution? | Digital systems have wider latitude but lower inherent contrast resolution than film‑screen systems. 3 |
| What is “contrast resolution” in digital imaging? | The ability to differentiate small differences in signal intensity (pixel values) — influenced by bit depth, noise, and receptor sensitivity. |
| What are the four principal characteristics of any medical image in digital radiography? | Spatial resolution, contrast resolution, noise, and artifacts. 4 |
| What does “speed” refer to in image receptors? | The sensitivity of the receptor — how many photons are needed to create a usable image (higher speed = fewer photons needed). |
| What happens to image quality if speed is increased too much? | Noise and graininess increase; detail and contrast decrease. |
| What is the effect of patient motion on recorded detail? | It causes motion blur, reducing spatial resolution. |
| What is subject blur? | Unsharpness caused by difference in tissue thickness, motion, or insufficient contrast between tissues. |
| What is distortion? | Misrepresentation of object shape or size on the image — can be size distortion (magnification) or shape distortion (elongation/foreshortening). |
| What can cause shape distortion? | Misalignment of tube, object, and receptor; angling the tube improperly; or object not perpendicular to receptor. |
| What is foreshortening? | When the object appears shorter in the image than it actually is due to misalignment. |
| What is elongation? | When the object appears longer than actual due to improper angulation. |
| Why is collimation important for image quality? | Reduces scatter, improves contrast, lowers patient dose, restricts beam to area of interest. |
| What is subject motion? | Movement of patient anatomy during exposure — leads to blur and poor image detail. |
| What is image receptor blur? | Loss of detail due to receptor characteristics (speed, screen blur, phosphor size, etc.). |
| What does “optimum image quality” represent? | Balance of spatial resolution, contrast resolution, minimal noise, minimal artifacts, and acceptable dose to patient. |
| What is the technologist’s primary role in achieving image quality? | Proper positioning, selecting appropriate exposure factors (kVp, mAs), collimation, receptor selection, and minimizing motion and scatter. |
| What are “tools for improved radiographic quality”? | Collimators, grids, proper receptor choice, motion control, technique charts, quality control of processing/digital receptor. |
| What is “subject density”? | The combined effect of thickness and composition of tissue in the beam path — influences absorption and contrast. |
| What does successful radiographic technique depend on? | Understanding of physics (beam properties), anatomy (subject factors), and technical control (equipment & exposure settings). |
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