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Ch 10 Image Quality
Rad Physics
| Question | Answer |
|---|---|
| ______ resolution refers to the ability to image small objects that have high subject contrast. (breast microcalcification, calcified lung nodule). | Spatial |
| ______ resolution is the ability to distinguish anatomical structures of similar subject contrast. (liver-spleen, grey/white matter) | Contrast |
| An increase in _____ will decrease resolution. | magnification |
| Spatial resolution _____ as screen blur, motion blur and geometric blur decrease. | improves |
| _____ refers to the degree of sharpness of structural lines on a radiograph. | Detail (recorded detail) |
| Radiographic _____ is the random fluctuation in the OD of the image. | noise |
| Lower noise results in a better radiographic image because it improves ______ resolution. | contrast |
| The use of high-mAs, low-kVp and of slower IR's reduces _____ _____. | quantum mottle |
| Fast image receptors have ___ noise and ____ spatial resolution and ___ contrast resolution. | high; low; low |
| High spatial resolution and high contrast resolution require ___ noise and slow image receptors. | low |
| Low noise accompanies slow IR's with high spatial resolution and ____ contrast resolution. | high |
| What are the three interrelated characteristics of radiographic quality? | resolution, noise and speed |
| The study of the relationship between the intensity of exposure of the film and the blackness after processing is called _____. | sensitometry |
| What are the three portions of the characteristic (H & D) curve? | toe, straight-line portion and shoulder |
| At low and high radiation exposure levels, large variations in exposure result in a _____ change in OD. | small |
| At intermediate radiation exposure levels, small changes in exposure result in ____ changes in OD. | large |
| The _______ portion of an H&D curve is the region in which a properly exposed radiograph appears. | intermediate (straight-line portion) |
| An optical step wedge (sensitometer) and a densitometer (measures OD) are needed to construct a _____ _____. | characteristic curve |
| The characteristic curve is a digital representation between ___ and ______. | OD; exposure |
| An increase in LRE (log relative exposure) of 0.3 results from _____ the radiation exposure. | doubling (similar to doubling mAs) |
| What is the OD formula? | OD=log10 Io/It |
| ____ density is the OD that is inherent in the base of the film. | Base (value of 0.1) |
| Higher fog density ______ the contrast of the radiographic image. | reduces |
| The useful range of OD is approximately ___ to ___. | 0.25; 2.5 |
| Base plus fog OD has a range of approximately ___ to ___. | 0.1; 0.3 |
| The reciprocity law states that the OD on a radiograph is ________ only to the total energy imparted to the radiographic film and independent of the time of exposure. | proportional |
| The reciprocity law fails for screen-film exposures at exposure times less than approximately ___ ms or longer than ___ seconds. | 10; 2 |
| Variations in adjacent densities defines ____ _____. | radiographic contrast |
| _____ contrast is determined bu the size, shape and x-ray attenuating characteristics of the anatomy that is being examined and the energy (kVp) of the beam. | Subject |
| ___ density results from inadvertent exposure of film during storage, undesirable chemical contamination, improper processing and should not exceed an OD of ___ on a radiograph. | Fog; 0.1 |
| Film contrast is related to the ___ of the straigh line portion of the chacteristic curve. | slope (a curve with a greater slope will have greater contrast) |
| Most radiographic IR's have an average gradient in the range of ___ to ___. | 2.5; 3.5 |
| Average gradient is the measure of radiographic _____. | contrast |
| What is the formula for average gradient (IR contrast)? | average gradient=OD2-OD1/LRE2-LRE1 |
| ___ gradient is more important for general radiography. | Toe |
| Midgradient or shoulder gradient is more important for _____. | mammography |
| The ability of an IR to respond to a low x-ray exposure is a measure of its _____. | speed (or sensitivity) |
| An IR with a "high" speed will require less ___ but the image quality is ____ because of increased radiographic noise. | mAs;decreased |
| IR's with speeds less than 100 require an increase in ____ which will result in increased pt ____. | mAs; dose (more mAs=less noise= +pt dose) |
| If IR speeed is doubled, the mAs must be ____. | halved |
| What is the Speed vs. mAs formula? (pg171) | New mAs=old mAs*old IR speed/New IR speed |
| ____ refers to the range of exposures over which the IR responds with OD's in the diagnostically useful range. | Latitude (margin of error - remember the fudge factor?) |
| With ____ latitude, mAs can vary more and still produce a diagnostic image. | wider |
| Latitude and contrast are _____ proportional. | inversely |
| Four factors that may affect the finished radiograph? | concentration of processing chemicals, degree of chemistry agitatoin during development, development time/temperature |
| IRs with wide latitude are said to have ___ gray scale; those with narrow latitude have ___ gray scale. | long; short |
| Speed and fog increase with ____ development time. | increased |
| When development time is extended beyond recommendation, IR contrast ___, relative speed ___ and fog level ___. | decreases; increases; increases |
| Fog level and IR speed _____, with increasing temperatures. | increase |
| All images on the radiograph are larger than the objects they represent, a condition called ____. | magnification |
| What is the magnification factor formula? | MF=Image size/object size MF=SID/SOD |
| Minimize magnification by _____SID or _____ OID. | increasing; decreasing |
| Unequal magnification of different portions of the same object is called ____ _____. | shape distortion |
| Object ____, ____ and ____ are three conditions that contribute to image distortion. | thickness, position, shape. |
| Thick objects are more ____ than thin objects. | distorted |
| If the object palne and the image plane are not parallel, ____ occurs. | distortion |
| _____ is a reduction is image size; related to the angle of inclincation of the object. | Forshortening |
| The amount of forshortening, that is, the extent of reduction in image size, _____ as the angle of inclination increases. | increases |
| An ____ image is made to appear longer than it really is beacuse the inclined object is not located on the central x-ray beam. | elongated |
| With multiple objects positioned at varioius OIDs, ____ distortion can occur. | spatial |
| ____-____ blur is the blurred region on the radiograph which the technologist has littl control. | Focal-spot (occurs because the focal spot is not a point) |
| Focal spot blur is the most important factor for determining _____ _____. | spatial resolution |
| Focal spot blur is decreased when ___ is decreased. | OID |
| Focal spot blur formula? | Focal spot blur= (Effective focal spot)OID/SOD |
| The focal-spot blur is ____ on the anode side and ____ on the cathode side of the image. | small;large |
| The contrast of a radiograph viewed on an illuminator is called ____ contrast. | radiographic |
| Radiographic contrast formula? | Radiographic contrast = IR contrast x subject contrast |
| The degree of subject contrast is ______ proportional to the relative number of x-rays leaving those sections of the body. | directly |
| The high atomic numbers of iodine(53) and barium(56) result in ____ subject contrast. | increased |
| Contrast media are effective because they accentuate subject contrast through _____ absorption. | photoelectric |
| The characteristic of the subject that affects subject contrast is called ____ ____. | absorption blur. (reduces spatial and contrast resolution) |
| ____ is the most important influence of subject contrast. | kVp |
| A low kVp results in high subject contrast, sometimes called ___ gray scale. | short (few shades of gray) |
| High kVp results in low subject contrast or ___ gray scale. | long (many shades of gray) |
| Two disadvantages of low-kVp radiography: | less penetrating beam= + mAs = + pt dose |
| Four ways to reduce motion blur: | 1) shortest possible exposure time 2) communication or restraining device 3) use large SID 4) use small OID |
| Two types of patient motion? | Voluntary (movement of muscles/limbs) and involuntary (motion of heart/lungs) |
| Use of intensifying screens decreases patient dose by a factor of ___. | 20 |
| The primary controller of radiographic contrast is ___. | kVp |
| As kVp is increased, both the ____ and ____ of radiation are increased. | quantity; quality |
| _____ interaction increases, with increasing kVp. | Compton (reduced subject contrast - long scale) |
| Increased kVp will increase radiographic _____ and ____ will decrease. | noise; contrast |
| The principal advantages of the use of high kVp include a reduction in _____ ____ and ____ latitude of exposures. | patient dose; wide |
| _____ can compensate for the loss of contrast accompanying a high kVp technique. | Grids |
| The primary controller of OD is ___. | mAs |
| Increased mAs results in ____ quantity, ____ OD, ____ noise and ____ patient dose. | increased; increased; decreased; increased |
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