chapter 23 technical considerations in digital imaging

-small FSS

-short OID

-large SID

-shorter exposure times with high mAs

Image resolution still improved by?

Grids and collimation

In digital imaging, _____ and tighter ____________ is important as ever

Kvp and contrast

____ and ________ no longer directly related like analog radiography digital detectors not necessarily impacted this way

Primary concern

Total exposure to the detector is the ________________

Higher kvp

Slightly ___________ values are now recommended with digital detectors

-reduction in ESE

-lower mAs values

Benefits of higher kvp include

-mAs

-kvp

-SID

-OID

-collimation

-patient

-grids

-filters

Total exposure to the detector is significantly impacted by?

-fixed kvp

-variable kvp

What are the 2 major exposure systems?

By Fuchs in 1943

When was fixed kvp systems developed?

Image density

The kvp in fixed kvp systems are held constant for a given range of subject densities and contrasts while the mAs is varied to achieve the appropriate?

-decrease patient dose

-consistent contrast level

-increases tube life

What are fixed kvp systems advantage?

-provide lower contrast than variable kvp system

-exposure changes in small increments difficult to achieve due to less mA and time stations to choose from

What are fixed kvp systems disadvantages?

Optimal kvp

Fixed kvp systems begin by establishing the?

Maximum

The ____________ kvp level that will produce images with appropriate contrast that are consistently within acceptance limits

Acceptable contrast level

Must have sufficient penetration of subject to produce?

Patient dose

The optimal kvp produces lower contrast and minimum _______________ not the best image

50-60 kvp

Infant extremities =

65-75 kvp

Adult extremities =

75-90

Bucky extremities =

85-95

AP spine =

85-100

Lateral spine =

110-130 kvp

Chest =

80-90 kvp

Skull =

120 kvp

Barium based contrast media =

5 cm of subject thickness

Once the optimal kvp is determined adjust mAs in increments by doubling or halving mAs for every ____________________

By jerman in 1925

When was the variable kvp systems proposed?

2 kVp per cm

The rule that adjusts _________ of subject thickness and does opposite if fixed kVp

subject densities

the mAs is held constant for a given range of?

15% rule

the variable kVp system is fairly consistent to the?

CR and DR

exposure selection is important in both?

digital receptors

fixed kvp systems are better suited for use with?

fixed kvp

most medical facilities used ___________ over variable kvp charts

variable kvp

veterinarian offices are still using the ______________ charts

-phantom test exposures

-produce range of acceptable images

step 1 =

theoretical chart by extrapolation

step 2 =

clinical trail

step 3 =

clinical fine tuning

step 4 =

continuous quality assurance

step 5 =

exposure quality

image noise is affected by?

quality

image noise compromises?

wider latitude

digital image processing contains?

4-5

DR accommodates ________ times OVERexposure and still produce acceptable image quality

decrease

historical wide latitude, radiographers slightly add to their technique selection to ___________ the chance of image noise and avoid repeats

deviation index

aside from proper EI value, we also must have correct DI number or?

EI values

calculation of exposure deviation index if formulated based upon?

DICOM

DI values have ______ header info on images

variance

indication of ___________ from established target EI values

ALARA violations

DI of 3+ considered possible?

graininess

underexposure yields a noisy image with?

photon starvation

inadequate exposure to detector elements

data drop

extreme overexposure yields?

electronic masking

-cropping/shuttering display image masking can impact the accuracy if exposure indicator values

-NOT a substitute for collimation

electronic image annotation

-crucial to accuracy of medical image

-added R/L markers unacceptable and can be questioned legally

anatomy and medical condition

medical images are record of patients?

phantom/ghost images

due to incomplete erasure of plate?

dust

light spots caused by _____ or foreign objects on IP. CR may be cleaned but carefully and according to manufacturer recommendation

quantum mottle

caused by inadequate exposure, insufficient mAs

laser film transport artifacts

caused by uneven transport of film material through a laser imaging system

algorithm artifacts

has to do with manufacturers present values

white line

caused by bad DELs in TFT

white line along the length of travel

on image caused by dust in the light guide blocking light from CR plate

scratches or tears or peeling

caused by damage to CR plates. CR plate replacement is expensive

fogging

from background radiation or scatter due to IP being much more sensitive than film

histogram analysis error

due to improper collimation, improper technique, beam alignment, scatter, and extreme density differences

poor grid alignment

grid lines or poor image quality as the computer may not necessarily display the grid lines

Data drop image

White line image

White line along the length of travel image

Scratches, tears and peeling image

Fogging image

Histogram analysis error image

Poor grid alignment image