Mosby Chapter 4 - Image Production (Digital Image Acquisition)
mathematical codes used to generate the digital image are called
algorithms
given an original technique of 30 mAs and 80 kVp, which of the following would produce an image with double the receptor exposure? a. 60 mAs, 90 kVp b. 30 mAs, 92 kVp c. 15 mAs, 80 kVp d. 30 mAs, 70 kVp
b. 30 mAs, 92 kVp
the available gray scale of an imaging system is determined by:
bit depth
when a nongrid technique using 10 mAs and 75 kVp is changed to a 12:1 grid using 75 kVp what new mAs must be use to create the same image
50 mAs
the smallest exposure change able to be captured by a detector is called
contrast resolution
visible differences in adjacent structures on a radiographic image describe:
contrast resolution
distortion that occurs when the xray beam is angled along the long axis of a part:
elongation
the adjustment in technical factors required when using beam restriction is:
increase mAs to compensate for the number of rays removed from the primary beam
which of the following governs the relationship between SID and receptor exposure? a. reciprocity law b. 15% rule c. inverse square law
inverse square law
improper use of grids may result in an image artifact known as:
Moire pattern
a high SNR provides an image with
higher spatial resolution
the CR reader unit scans the IP with what device?
laser
magnification is caused by: 1. short SID 2. long SID 3. short OID 4. long OID
1 & 4
a radiographic image with few gray tones, would be described as having what type of contrast? 1. long scale 2. short scale 3. low 4. high
2 & 4
bit depth is equal to:
2^n (n = the number of bits)
the actual patient dose as measured by a meter embedded in the collimator is:
DAP (dose area product)
an indicator of the dose level needed to acquire an optimal image is
DAP - dose area product
the expression of image quality provided by a detector is called
MTF - modular transfer function
what describes the highest spatial frequency that can be recorded by a digital detector?
Nyquist frequency
choose all of the following statements that are accurate pertaining to the role of kVp in image production: a. as kVp is increased, penetrating ability of the xrays increases b. as kVp is increased, more xrays exit the patient to strike the image receptor c. as kVp is decreased, wavelength decreases d. as kVp increases, receptor exposure increases e. as kVp decreases, receptor exposure remains constant because mAs controls receptor exposure
a, b, & d
choose all that describe the outcome of using low kVp (3): a. high contrast b. few gray tones c. long scale contrast d. short scale contrast e. low contrast f. many gray tones
a, b, d
choose all that are true concerning grids (3): a. contrast improvement factor is the measure of the ability of a grid to enhance contrast b. grid selectivity is the ratio of primary radiation transmitted through the grid to secondary radiation transmitted though the grid c. grids are used when part thickness is less than 10 cm d. GCF is the amount of increase in kVp necessary when concerting from nongrid to grid technique e. the primary purpose of girds is radiation protection f. the main function of grids is to prevent compton scatter from reaching the IR g. grids prevent the production of scatter
a, b, f
choose all that will result in higher spatial resolution (3): a. long SID b. long OID c. short SID d. short OID e. large focal spot f. small focal spot
a, d, f
the variation of xray intensity along the longitudinal axis of the xray beam describes:
anode heel effect
what maintains image brightness over a wide range of exposures?
automatic rescaling
choose all factors below that result in poor spatial resolution (choose 4): a. long SID b. long OID c. large focal spot e. small focal spot f. magnification
b, c, e, f
which of the following describes the relationship between receptor exposure and the use of grids? a. grids always reduce receptor exposure b. grids reduce receptor exposure unless mAs are increased to compensate c. grids reduce receptor exposure by only absorbing scatter radiation
b.
which of the following affects receptor exposure? a. atomic mass of the xray tube anode b. xray tube angle c. atomic number of the cathode filament
b. xray tube angle
an artificial increase in display contrast at an edge of the image is:
edge enhancement
choose all that describe the outcome of using high kVp (3): a. high contrast b. few gray tones c. long scale contrast d. short scale contrast e. low contrast f. many gray tones
c, e, f
the thicker part of anatomy should be placed unde which aspect of the wray tube?
cathode
as the amount of beam filtration is increased
contrast decreases
the best scatter cleanup is achieved with the use of
crosshatch grids
spatial resolution is: a. photographic representation of the part being radiographed c. controlled by kVp c. controlled by mAs d. geometric representation of the part being radiographed
d.
the use of filtration: a. greatly reduces receptor exposure because of the absorption of short wavelength xrays b. greatly reduces exposure because of the absorption of high energy xrays c. increases exposure by removing long wavelength xrays d. has little effect on receptor exposure because xrays removed from beam are not image producing rays
d.
grid cutoff may ne described as
decreased density on a radiograph as a result of absorption of image forming rays
excessive processing of the digital image may
degrade visibility of anatomy
receptor exposure was formerly called
density
quantum moise limits ability to see
detail
the smallest resolvable area in a digital imaging device is
detector element
the useful image acquisition area of an image receptor is
detector size
the relationship between kVp and receptor exposure is described as:
direct, although not proportional (15% rule)
receptor ecposure may be defined as
dose area product
what allows more anatomic structures to be captured during an exposure?
dynamic range
quality assurance and maintenance of CR cassettes include cleaning and inspection the plates at least:
every 3 months
quality assurance and maintenance of CR cassettes include erasing plates at least:
every 48 hours
the radiographic image is formed by
exit rays striking the image receptor
digital imaging is driven by:
exposure
the range of receptor exposures that provides a quality image is called
exposure latitude
a grid with lead strips and aluminum interspacers that angled to coincide with the divergence of the xray beam is called a
focused grid
distortion that occurs when the xray beam is angled against the long axis of a part:
foreshortening
the range of SIDs that may be used with a focused grid is called
grid radius
when AEC is used increasing the kVp
has no effect on the image quality
more uniform penetration of anatomic structures occurs when what level of kVp is used?
high
in digital fluoroscopy, what equipment should be used to view the image?
high resolution monitor capable of displaying millions of pixels
what is a graphical representation of pixel values?
histogram
in digital radiography inappropriate collimation causes
histogram analysis error
quality and assurance of digital imaging requires the uniformity of processing codes to ensure:
image appearance consistency
undesirable fluctuations in brightness are called
image noise
to reduce patient dose exposure technique in digital imaging should be adjusted by
increaseing kVp
what effect does beam restriction have on contrast?
increases contrast because of reduction in the number of compton interactions that occur
what effect does the use of radiographic grids have on contrast?
increases contrast by absorbing scatter radiation
use of technique charts:
is helpful when manual techniques are used
what are the primary controlling factors of contrast?
kVp & bit depth
the appearance of digital images on technologists' monitors is what compared to the radiologists' monitor?
not as good as on the radiologists' monitors
smoothing software may result in
loss of fine detail
the number of electrons boiled off the cathode and consequently the number of xrays produced are controlled by:
mAs
the primary controlling factors of receptor exposure are
mAs & SID
the function of contrast is to
make detail visible
the number of pixels making up the digital image is the
matrix size
distortion may be described as
misrepresentation of an anatomic structure on the image
optimal spatial resolution may be created using what factor?
narrow pixel pitch
if the exposure filed is not accurately recognized the histogram will contain data
outside the exposure field, widening the histogram
as speed class decreases:
patient exposure increases
what converts light into a charge?
photodiode
differential absorption of xray beam is a function of:
photoelectric interaction
the smallest area represented in a digital image is the
pixel
the number of pixels/mm in an image is called what?
pixel density
the space from the center of a pixel to the center of the adjacent pixel is called
pixel pitch
a primary advantage to diital fluyoroscopy is:
postprocessing manipulation of the image
the process of assigning a value to each pixel to represent a ray tone is called
quantization
as beam restriction increases (tighter), what happens to receptor exposure?
receptor exposure decreases
what is the relationship between mAs and receptor exposure?
receptor exposure is directly proportional to mAs
if SID is doubled what may be said about receptor exposure?
receptor exposure is reduced to one fourth
the 15% rule states that
receptor may be halved by decreasing kVp by 15%
if SID is reduced by one half what must be done to mAs to maintain a constant receptor exposure?
reduce mAs to one fourth its original value
digital image receptors are more sensitive to
scatter and background radiation
a material that absorbs xray energy and emits part of that energy as visible light is called
scintillator
elongation and foreshortening are examples of:
shape distortion
a software function that evens the brightness displayed in the image is called
smoothing
the portion of contrast that is caused by variations in the anatomy or that is secondary to pathologic changes is called
subject contrast
the active portion of a CR IP is what?
the PSP (photostimulable phosphor)
grid frequency is define as
the amount of lead in the grid (expressed as the number of lead strips per inch)
beam-part-receptor alignment latitude describes
the latitude of collimation that still allows the software to detect collimated edges
a speed class increases:
the likelihood of noise increases
mAs directly control:
the quantity of xrays produced at the anode
grid ratio is defined as:
the ratio of the height of the lead strips over the distance between the lead strips
digital systems operate as what speed class?
the speed class chosen by the radiographer
lower spatial resolution may be caused by which of the following facotrs?
wide pixel pitch
use of the air gap technique:
works because scatter radiation travels in divergent paths and misses the IR as a result of increased OID