Technical Considerations in Digital Imaging (Ch. 23)

Image resolution is improved by?

• Small FSS

• Short OID

• Large SID

• Shorter exposure times with high mA

What two things are very important with digital?

• Grids

• Tighter collimation

What two things are no longer directly related with digital that are with film?

kVp and contrast

What are the benefits of higher kVp with digital?

Reduction in ESE, and lower mAs values

What is the total exposure to the detector still significantly impacted by?

• mAs

• kVp

• SID

• OID

• Collimation

• Patient

• Grids

• Filters

What are the two major technique exposure systems?

1. Fixed kVp

2. Variable kVp

Fixed kVp systems: the kVp is held ______ for a given range of subject densities and contrasts with the mAs is ______ to achieve the appropriate image density

Constant, varied

When were fixed kVp systems developed and by who?

Fuchs in 1943

What are the advantages of fixed kVp systems?

• Decrease patient dose

• Consistent contrast levels

• Increases tube life

What are the disadvantages of fixed kVp systems?

• 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

Fixed kVp systems begin by establishing what?

Optimal kVp

What is optimal kVp selection?

The maximum kVp level that will produce images with appropriate contrast that are consistently within acceptable limits

The optimal kVp produces ______ contrast and ________ patient dose (not the best image)

Lower, minimum

For infant extremities, what is the optimal kVp range?

50-60 kVp

For adult extremities, what is the optimal kVp range?

65-75 kVp

For Bucky extremities, what is the optimal kVp range?

75-90 kVp

For the AP spine, what is the optimal kVp range?

85-95 kVp

For the cervical, thoracic, and lumbar spine, what is the optimal kVp range?

85-100 kVp

For the chest, what is the optimal kVp range?

110-130 kVp

For the skull, what is the optimal kVp range?

80-90 kVp

For barium-based contrast media, what is the optimal kVp range?

120 kVp

Once the optimal kVp is determined, adjust the mAs in increments by doubling or halving mAs for every _____ of subject thickness

5 cm

When were variable kVp systems introduced and by who?

Jerman in 1925

Variable kVp systems: use the rule that adjusts ____ kVp per cm of subject thickness and dose opposite of fixed kVp

2

Variable kVp systems: the ______ is held constant for a given range of subject densities

mAs

What are variable kVp systems consistent with?

15% rule

For variable kVp systems, what does the base of the chart begin with?

(2 kVp x part cm) + 30 kVp = new kVp

What kVp system is better suited for use with digital receptors?

Fixed

What are the steps when establishing an exposure technique system (fixed or variable)?

1. Phantom test exposures, produce range of acceptable images

2. Theoretical chart by extrapolation

3. Clinical trial

4. Clinical fine tuning

5. Continous quality assurance

When assessing digital exposure techniques, _______ affected by exposure quantity

Image noise

Digital image processing contains _____ latitude

Wider

DR accommodates _____ times overexposure and still produces acceptable image quality

4-5

Historically because of wide latitude, radiographers slightly _____ to their technique selection to decrease the chance of image noise and avoid repeats

Add

What is dose creep?

When the whole system will need more radiation to do the same task because it is used to being overexposed

Aside from proper EI value, we must have correct _____ numbers, or __________

DI, deviation index

Calculation of exposure deviation index is formulated based upon target _____ values

EI

Indication of ________ from established target EI values

Variance

DI of 3+ considered possible ______ violations

ALARA

DI value: less than -3.0 =

Repeat

DI value: less than -1.0 =

Underexposure; consult radiologist for repeat (quantum mottle)

DI value: -0.5 to + 0.5 =

Target range

DI value: +1 to + 3.0 =

Overexposure; repeat only if relevant anatomy is clipped or “burned out”

DI value: > +3 =

Excessive radiation exposure, repeat only if anatomy is clipped, require immediate management follow-up

Photon starvation

Inadequate exposure to detector elements

Extreme overexposure yields ________

Data drop

Data drop

Detector elements are overwhelmed with photon energy; incapable of recognizing high-energy values

What is this image showing?

Data drop

What are the digital post-processing considerations?

• Electronic masking

• Electronic image annotation

Electronic masking

Cropping/shuttering display image; masking can impact the accuracy of 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

Medical radiographs are considered a _____ document, just like patients medical records

Legal

Radiologists assume the images are produced in _______ compliant manner

ALARA

Radiographers must be diligent in recognizing low-contrast image _______ and seek to remove them, or at minimum, alert the radiologist

Artifacts

Image artifacts: phantom/ghost images

Due to incomplete erasure of plate

Image artifacts: light spots

Caused by dust or foreign objects on IP

What is quantum mottle caused by?

Inadequate exposure, insufficient mAs

Image artifacts: laser film transport artifacts

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

Image artifacts: algorithm artifacts

Has to do with manufacturers preset values

Image artifacts: white line

Caused by bad DELs in TFT (requires correction program)

Image artifacts: white line along the length of travel

Caused by dust on the light guide blocking light from CR plate

Image artifacts: scratches or tears or peeling

Caused by damage to CR plates

Image artifacts: fogging

From background radiation or scatter due to IP being must more sensitive

Image artifacts: histogram analysis error

Due to improper collimation (edges must be parallel to sides of IP), improper technique, beam alignment, scatter, extreme density differences

Image artifacts: poor grid alignment

Results in grid lines or only as poor image quality because the computer may not necessarily display the grid lines

What is the artifact and what is it caused by?

White line, caused by dust on the light guide blocking light from CR plate

What is the artifact and what is it caused by?

Scratches or tears caused by damage to CR plates, and peeling of IP

What is the artifact and what is it caused by?

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

What is the artifact and what is it caused by?

Histogram analysis error due to improper collimation, improper technique, beam alignment, scatter, extreme density differences

What is the artifact and what is it caused by?

Poor grid alignment leading to grid lines or poor image quality