Quality Control (2/4/2025)

List the regulatory agencies

• department of health and human services

• national center for devices and radiological health

• FDA

• OSHA

• EPA

• NRC

List the 2 most important government actions

• 1990 - safe medical devices act (SMDA)

• 1992 - mammography quality standards act (MQSA)

Who provides the standards in radiology?

American College of Radiologists (ACR) and American Association of Physicists in Medicine (AAPM)

DICOM standardized transmission behavior of all devices with a ___

PACS system

___ sets standards for images

DICOM

___ sets standards for transmission of written data

HL-7

What is the goal of quality control?

calibrate and monitor technical equipment to maintain image quality and ensure radiation exposure as low as reasonable achievable

Quality control is based on the need to ___

stabilize various equipment components

What are the 2 ACR recommendations for digital QC?

• must have documented policies and procedures for monitoring and evaluating equipment

• QC program should be designed to maximize quality and accessibility of dx information

List the 3 components of QC

• acceptance testing

  • performed at equipment installation

• diagnosis of deviations from acceptable equipment tolerances

  • routine maintenance tolerances

  • diagnosis deviations from baseline and tracks errors

• documentation of corrections made

  • if it isn’t documented, it didn’t happen

Explain acceptance testing as a component of quality control

• at time of installation equipment is checked by service engineer and bio med, IS and PACS administrator, and a medical physicist

• purpose is to confirm equipment is functioning according to specifications set by vendor

• establishes baseline for equipment performance

• manager signs off that equipment meets performance expectations

List some aspects of performance monitoring

• evaluates performance of generator and tube

• simple to complex equipment can be used

• ACR requires medical physicist to perform tests

• most testing is performed annually

What are some tools used to monitor equipment performance?

• ion chamber dosimeter (gas filled chamber)

• solid state dosimeter (newer, smaller, and accurate)

Explain the control booth and exposure switch specifications as mandated by the FDA

• control booth

  • minimum of 7.5 sq ft

  • walls 7 ft high

• window

  • 1.5 mm lead equivalent

• exposure switch

  • fixed

  • minimum of 30” from booth wall

X-rays must scatter ___ times before entrance to control booth

2

Explain the high voltage generator

• converts low voltage to kilovolts

• step-up transformer for kV

• step down transformer for tube filament (current)

• rectifiers convert incoming alternating voltage to pulsating direct current

Explain high frequency generators

• single source of alternating current

• require less space and power

• produce more efficient energy

• very little ripple (<1%)

What is used to assess timer accuracy on single phase equipment?

spinning top

What is used to assess timer accuracy on 3 phase equipment?

motorized synchronous top

Time accuracy with equipment operating at MORE THAN 10 ms = ___

Time accuracy with equipment operating at LESS THAN 10 ms = ___

more: ±5%

less: ±20%

Back-up timer should terminate the exposure at ___

6 seconds or 600 mAs

Explain the spinning top test

• circular steel/lead disc with small hole is mounted on a base that allows it to move freely

• test can indicate a problem with rectifier or timer

In the spinning top test, if half of the dots are there, this is a ___ issue

rectifier

In the spinning top test, if a number other than half of the dots are there, this is a ___ issue

timer

Single phase rectifier equipment has ___ on the spinning top test

3 phase rectifier equipment has ___ on the spinning top test

single: dots

3: arc

In a 1 second exposure, the spinning top test should produce an image with ___ dots

120

In a 1 second exposure, the spinning top test should produce an image with ___ arc

a 360^o

Line focus principle

when the target angle is less than 45 degrees, the projected focal spot is smaller than the actual focal spot

What is blooming?

• FS size increases as tube ages (and with high mA)

• causes electron cloud to swell

• unwanted change in actual focal spot size during change in exposure

Explain the pinhole camera focal spot test tool

• CR is aligned through metal sheet with 0.03 & 0.075 mm holes (difficult to align)

• exposure is made

• image of focal spot displayed

• actual size of effective focal spot is measured using micrometer

• long exposure is hard on tube

• causes blooming (more blooming with higher tube current)

Explain the slit camera focal spot test tool

• preferred method

• metal template with series of finely cut slits in groups of 3

• make exposure to determine smallest set of lines resolved

Explain the star focal spot test tool

• measure resolution

• estimated FSS

List the NEMA specifications for FS variations

• FS smaller than 0.8 may be 50% larger

• FS between 0.8mm and 1.5mm may be 40% larger

• FS larger than 1.5 may be 30% larger

a 0.5mm FS may actually be 0.75mm and still be within the allowable tolerance

As FSS goes up, the tolerance ___

goes down

kV and mA accuracy refers to ___

stability of relationship between kV or mA and the resulting exposure intensity

kV setting must be within ___ of kV output

±5%

Measure tube potential using:

• Wisconsin test cassette

• Arden & Cook’s cassette

• digital kVp meter

  • more accurate and easier to use

Explain mA linearity

sequential increases in mA should produce the same increase in the exposure rate

exposures must not vary more than ±10%

Explain mA reproducibility

output intensity must be consistent form one exposure to the next

same technique should have same exposure rate (must be within ±5%)

Explain the law of reciprocity

any combination of mA and time that equals the same mAs should produce the same exposure intensity

Fluctuations in mA readings = ___

“gassy” tube

Explain HVL

• expresses beam quality

  • test used to determine if equipment has adequate filtration

• filtration of primary beam

  • filter absorbs low energy waves

  • improves image quality/reduces patient dose

  • increases average energy of beam

• expressed in terms of Al/Eq

  • beam quality/penetrability

• measured with computerized dosimeter

  • provides readout of HVL

NCRP requires equipment operating

Explain the effect of collimation on the beam

• limit size of x-ray field

• improve image quality

  • less scatter

  • improved contrast

• reduce patient dose

Explain collimation congruency

• measures how well collimator regulates field size

• NCRP requires it must be accurate to within ± 2% of SID

• 8 penny test

• tested annually

Explain central ray accuracy

• beam alignment tool (cylinder with metal washer)

• must be within ± 1% of SID

  • 0.4'“ at 40” SID

  • 0.72” at 72” SID

• tested annually

Explain distance accuracy

• measuring devices and detents must be accurate

• accuracy is checked with tape measure

• tube angles should be accurate to within 2^o

Explain distortion checking

• checked with wire mesh test

• mesh is placed on cassette

• dark area indicate poor contrast

• pincushion: warped image appearance from curved surface of input screen to flat surface of output screen

What is the max exposure rate for fluoroscopic systems?

exposure rate must not exceed 10 R/min at tabletop

entrance dose not to exceed 5 R/min

What are some safety specifications on fluoro machines?

• primary barrier of 2 mm Pb/eq for housing

• bucky slot cover .25 mm Pb/eq

• fluoro curtain .25 mm Pb/eq

• cumulative fluoro timer (5 min alerts)

• minimum source to table distance:

  • 15” for stationary

  • 12” for mobile

What is field uniformity?

image is visually checked for defects

What is ghosting?

• inadequate CR erasure

  • loss of lamp intensity or short erasure time

• residual charge is trapped in DEL of digital IR

• off-focus/STEM radiation

What are some examples of CR quality control tests?

• dark noise

• uniformity

• spatial accuracy

• erasure thoroughness

What is the weakest link in the digital imaging chain?

the monitor

Explain primary vs secondary display monitors

Primary:

Secondary: