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Ch 10 Image Quality

Rad Physics

QuestionAnswer
______ 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