RTE 2457 Radiographic Quality Control Bushong Chapter 19

Define Quality Assurance (QA)

Deals with people

Define Quality Control (QC)

Deals with instrumentation and equipment

What does Quality Assurance Monitors

-Proper patient scheduling

-Reception

-Preparation

-Appropriateness of the exams

-Whether proper instruction is given

-Whether patients condition agree with radiologist's diagnosis(

outcome analysis)

-Was the radiology report available for the ordering physician in a timely manner

What does Quality Control Monitors

-Equipment conditions

-Image processing facilities

-Image analysis for artifacts and deficiencies

-Repeat rate

-Radiation dose to the patient

How often should Monitoring of Equipment performace

Annually unless a major component is replaced 1) Replacing X-Ray Tube 2) Replacing the entire machine

Who is responsible for Quality Control (QC)?

-Principally the responsibility of the medical physicist

-Requires a team effort

-QC program focuses on various characteristics and strength of the image

QC program focuses on various characteristics and strengths of the image which is

-Spatial resolution

-Contrast resolution

-Temporal resolution

-Signal to noise ratio

-Artifacts

Define Spatial Resolution

Is the ability to image small objects that have high subject contrast

Contrast Resolution

Is the ability to image two separate objects and visually distinguish one from the other

Temporal Resolution

The time needed to acquire the data to generate an image

Signal to Nosie Ratio

Is calculated from the ratio of the mean signal and the standard deviation of the noise within a region of interest

Artifacts

Is any feature which appears in an image which is not present in the original imaged object

Who developed the guidelines for QC of Screen Film Radiography

American College of Radiology (ACR)

American Association of Physicists in Medicine

Filtration

Ensures patient protection

2.5mm Al required by the state

Measured in terms of HVL

Evaluated annually or after a change in x-ray tube or tube housing

Collimation

Misalignment should not exceed 2% of the SID

Distance indicator must be accurate to 2% of SID

Centering indicator must be accurate to 1% of the SID

Semi annually

Focal Spot Size

-Determines the spatial resolution

-Pinhole camera

-Star pattern

-Slit camera

-Checked annually or when new equipment or replacement x-ray tube is installed

Alternate to focal spot size measurement

- Line pair test tool

- Provide spatial frequency

-Higher spatial frequency indicate better spatial resolution

kVP Calibration

Annually or whenever generator components are changed

4% change in kVp is required for a visible change in OD

Measured kVp should be within 10% of the indicated kVp

Exposure Timer Accuracy

Accuracy of 5% of the indicated exposure time for the exposures greater than 10 ms

Accuracy of 20% for exposure time less than 10 ms

Annually or when components are changed

Automatic Exposure Control (AEC)

Backup timer should terminate the exposure at 6s or 600 mAs whichever occurs first

Or 1.5 times the actual exposure time

Exposure Linearity

Exposure linearity must be within 10% of the adjacent mA stations

mR/mAs value must within 10% between adjacent mA stations

Exposure Reproducibility

Radiation exposure should be reproducible to within 5%

Output radiation intensity should not vary more than 5%

Annually