Ch 31-34 Flashcards by Courtney W

Measure of the sensitivity and accuracy by which the image receptor converts the incoming data to the output viewing device
Measures ability to view small or low-contrast structures
Very important for digital mammography
SNR^2output/SNR^2input
Higher value increases the ability to view small/low-contrast structures that are greatly valued

Detective quantum efficiency (DQE)

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All activities that provide adequate confidence that a radiology service will render consistently high-quality images and services
Evolutionary process that provides quality images and services
Medical, technical, or managerial in nature
Identifies, monitors, and resolves problems

Quality assurance

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The aspect of quality assurance that monitors technical equipment to maintain superior standards
Rooted in the need to stabilize the various equipment components of the rad imaging chain

Quality control

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Figure that is calculated as a percentrage of the total number of images produced during the period of the study

Total repeat rate

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SNR

Signal-to-noise ratio (want it to be high)

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4 things HIPAA set standards for

Electronic record security
Electronic formats for record keeping
Electronic identifiers and codes
Requirements for confidentiality and privacy rules

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Largest hospital accreditation agency
Establishes quality standards, assesses them and provides certification that individual institutions have met the agency’s standards

Joint Commission on the Accreditation of Healthcare Organizations (JCAHO)

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How often are x-ray machines checked?

Twice a year

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Important for proper recorded detail

Biggest range that they can be & still be accurate: + or - 50%

Focal spot size estimation

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3 types of focal spot test tools

Line pair resolution tools
Star test patterns (most common)
Pinhole cameras (least common)

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Measured by using dosimetry equipment to determine amount of filtration (total filtration = inherent + added) that will reduce beam intensity to one-half of its original value
Physicists come in & test this
Computerized quality control dosimeters provide a digital readout of the HVL

Half-value layer

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Why do you want the collimator to be accurate?

You could overexpose or clip anatomy

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What percentage of accuracy must a collimator test tool be?

+ or – 2% SID

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What percentage of accuracy must light field and x-ray beam congruence be?

SID allowance of +/-2%

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What percentage of accuracy must the centering mark within the light field CR?

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What percentage of accuracy must the central ray be?

SID allowance of 1%

What accuracy should the distance indicator be?

±10%

What accuracy should the centering indicator be?

±2%

Computerized dosimeter provide digital readouts/printouts of avg & single-pulse kVp
Make sure machine is using kVp that’s set

Kilovoltage accuracy

What accuracy should the kilovoltage be?

±5 kVp

3 types of timer accuracy tools

Computerized dosimeters (more accurate and easier to use than tops)
Spinning top (single phase)
Motorized spinning top (can still be use today, three phase)

What accuracy should the timer be?

±5%

mA station accuracy confirmed by mR/mAs measurement

Computerized dosimeter

mR/mAs and Milliamperage Linearity

What accuracy should mR/mAs and milliamperage linearity be?

+/-10% between mA stations

+/-10% between high and low mA stations

Multiple exposures made with the same tech factors and seeing if it’s producing the same amount of radiation each time Computerized dosimeter

Exposure reproducibility

What accuracy should exposure reproducibility be?

±5%

What are the source to skin distance limits in fluoroscopy?

Shouldn’t be capable of placing the tube target closer than 15” (38 cm) or for mobile/c-arm 12” (30 cm) to the patient’s skin surface

What accuracy should ion sensitivity be in AECs?

±10%

What accuracy should exposure reproducibility be in AECs?

±1%

Commonly utilized computerized exposure control units that combine an AEC system with exposure factors to correspond to specific anatomical procedures

Automatically programmed radiography

Device used to measure part thickness

Caliper

Maximum kVp that result in images with appropriate contrast Produces lower contrast and minimum patient dose Has sufficient penetration

Optimal kVp

4 advantages of fixed kVp exposure systems

Reduces x-ray tube wear because when lower mAs is used it doesn’t get as hot & wear down as easily Allows for shorter exposure times Thus reduces patient motion Easier to memorize

What is a disadvantage of fixed kVp exposure systems?

Higher amount of scatter results in reduced image contrast (more shades of gray)

2 advantages of variable kVp exposure systems

Allows for small changes in exposure for small changes in part thickness Higher contrast

3 disadvantages of variable kVp exposure systems

More patient dose Higher repeat rate Tube wear, etc.

kV used for a particular projection is varied depending on measured body part thickness The thicker the body part the higher the value of kV assigned A mAs value is specified for each body part to be examined; its value depends on IR exposure and other parameters In use the radiographer sets the mAs specified for the part and measured part thickness; the value of kVp corresponding to that thickness is found on the chart

Variable kVp exposure system

kVp is held constant for a given range of subject densities and contrasts while the mAs is varied to achieve an appropriate IR exposure

Fixed kVp exposure system