PRESENTED BY ANJU THAKUR

FINAL YEAR

DEPARTMENT OF RADIODIAGNOSIS AND IMAGING

PGIMER, CHANDIGARH

QA-it is the planned $ systematic action that a diagnostic x-ray facility will produe consistently high images with min exposure of patient $ healing arts personnel.

QC-it deals with the technique used in the monitoring (or testing) and maintenance of thetechnical elements or components of an X-ray system.

(CR) Computed Radiography

Digital way of doing general radiography with Conventional X-ray machines

is a process of capturing radiographic data from a conventional X-ray machine and processing the data digitally to produce crisp and high quality radiographic images

Basic Components of CR

M A TRIX LR 3300

DigitizerProcessing Server

ID Tablet

Laser Camera

Cassette withImaging Plate

Preview & ID Station

CR WORKFLOW

M A TRIX LR 3300

Rx

Network

Digitizer

Printing

Identification

Processing server

Exposure

Digital Radiography

Performed by digital X-ray machines with flat panel detectors

INTRODUCTION to QA QC of CR and DR

Direct digital radiography (DR) and computerized radiography (CR) systems are now being used routine for radiography Screening Programme

Routine quality control (QC) is essential to ensure that the equipment is performing as expected meets standards

Recommended routine QC tests for DR systems

Frequency Test Section

Daily Checks on acquisition and reporting monitors

Daily System check Daily Printer checks using test pattern Weekly Check of contrast-to-noise ratio Weekly Image quality tests Weekly Uniformity check Monthly AEC thickness check Monthly Test of reporting monitors

Monthly Mechanical safety and function checks As required Detector flat-field calibration

As required Repeat analysis

As required Printer checks following software upgrade

Recommended routine QC tests for CR systems

Frequency Test Section Daily Checks on acquisition and reporting

monitors Daily System check Daily Printer checks using test pattern Weekly Check of contrast-to-noise ratio Weekly Image quality tests

Weekly Uniformity check Monthly AEC thickness check Monthly Test of reporting monitors Monthly Mechanical safety and function checks

Six monthly Image plate matching and artefact check

As required Image plate erasure

As required Image plate cleaning As required Repeat analysis As required Printer checks following software upgrade

Artifacts

CR- Dust on the ip, scraches/cracks on ip,dirt on reader,roller marks

DR- faulty individual pixel,cluster of pixel, loss of resolution in one or both direction

MONITOR- CRT(distortion,possibly due to interference from other electrical devices)

PRINTER- if artifacts not seen on hard copy then it is caused by printer, bandling, streaking, fine line in direction of film appear

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Artifacts in computed Artifacts in computed radiography radiography

Hardware artifactsHardware artifacts

Soft ware artifactsSoft ware artifacts

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Hard ware artifacts Hard ware artifacts

Reasons Reasons dust particle dust particle

&scratches &scratches Damage to the Damage to the

laser beam head of laser beam head of CR systemCR system

Dust on the laser beam head appearas an irregular white lines

Remedy Head has to be cleaned by Camel hair brush by vendor

engineer

Appearance

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Damaged laser beam head in CR Damaged laser beam head in CR readerreader

Laser beam headHas to be replaced

Remedy

AppearanceAppears as multiple linear white lineAppears as multiple linear white line

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Software artifactsSoftware artifacts

Excessive edge enhancementA B

Artifact simulate acute phase of Paget's disease as a result Of excessive edge enhancement .(B) normal E.E

Computed Radiography and Quality Control Computed radiography still uses

conventional radiographic equipment so basic radiography quality control testing is still needed. This would include: Calibration of the generator Collimation Beam Alignment Linearity of exposure Spatial resolution (focal spot)

MONITOR CHECKS

Monitor checks should be performed on both the acquisition and reporting* monitors under recommended working conditions. It should be noted that cathode ray tube (CRT) and flat panel displays (FPD) may have different types of problems.

Daily checks on acquisition and reporting monitors

Method

• Check for obvious faults such as flicker, gross distortion, artefacts

• Check general condition.• Clean if necessary (follow the supplier’s

instructions).• Look at the text and lines on the screen – are

they sharp and straight?• Keep a record of all checks, note any problems

and take action to get them corrected

Monthly test of reporting monitors Using the SMPTE Test Pattern

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SMPTESMPTE

This organization developed a test pattern that can This organization developed a test pattern that can be used to determine grey scale image quality on be used to determine grey scale image quality on videos and computer videos and computer

display monitor.display monitor.

Other parameter which can be evaluated are-Other parameter which can be evaluated are- Spatial resolution Spatial resolution Brightness Brightness ContrastContrast AliasingAliasing

Contt………….. There should be no blurring or bleeding of bright display areas into

dark areas or aliasing of the spatial imaging patterns. All monitors used for interpretation should be tested at least

monthly. For the dynamic range test, both the 5% and 95% contrast areas

should be visible and distinctly different than the adjacent 0% and 100% areas.

Therefore: The brightness and contrast of the monitor is adequate if the 5% squares at both ends of the gray scale are visible.

The gray scale is shown as a series of squares in the center of the image that range from black (0%) to white (100%).

It may be difficult to get the monitor to show both of these inner squares perfectly.

Most monitors do better showing the 95% square than the 5% square.

However, you might try adjusting the ambient light to improve the visibility of the 5% square.

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Diagnostic video monitorluminance & uniformity

For Digital Systems: • Display SMPTE test pattern to evaluate initial

quality of monitor Determine manufacturers recommended settings – ensure monitor is set accordingly

• If no guidance material available follow: – Video Monitor Manual Brightness & Contrast

Setting Procedure Diagnostic quality monitors typically include this measurement in calibration check - perform test following vendor recommendations

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Luminance and uniformity contd

•Use the TG-18 UNL -80 or SMPTE test Use the TG-18 UNL -80 or SMPTE test pattern ,or set an entirely white displaypattern ,or set an entirely white display

•Use a photo timer to measure luminance Use a photo timer to measure luminance -Measure maximum luminance in the -Measure maximum luminance in the

centre and four corners of displaycentre and four corners of display -Measure minimum luminance in centre -Measure minimum luminance in centre

of displayof display

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Diagnostic video monitorluminance & uniformity

•Determine monitor type

•Calculate % difference of each of corners to centre

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Monitor type Monitor type Maximum luminance Maximum luminance

Color CRT Color CRT > 80 Cd/m2> 80 Cd/m2

Color LCD Color LCD > 100Cd/m2> 100Cd/m2

Grey scale CRT Grey scale CRT secondarysecondary

> 150 Cd/m2> 150 Cd/m2

Grey scale diagnosticGrey scale diagnostic >200 Cd/m2>200 Cd/m2

Grey scale LCD Grey scale LCD 350 Cd/m2350 Cd/m2

Minimum luminanceMinimum luminance

CRT CRT <1.0 Cd/m2<1.0 Cd/m2

LCD LCD <1.5 Cd/m2<1.5 Cd/m2

% diff% diff

All All With in 15%With in 15%

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Image quality Image quality uniformity & artifactsuniformity & artifacts

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Image qualityImage quality high contrast (spatial) resolution high contrast (spatial) resolution

For photo stimulable phosphor systemsFor photo stimulable phosphor systems Determine standard set up& technical factors- do once Determine standard set up& technical factors- do once

- low KV- low KVp, p, Extended SIDExtended SID

use a lead –bar resolution test pattern phantomuse a lead –bar resolution test pattern phantom

- slightly angle phantom - slightly angle phantom Minimize moiré &line pairing pattern Minimize moiré &line pairing pattern Process with high-contrast algorithmProcess with high-contrast algorithm

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Image qualityImage qualitylow contrast resolution low contrast resolution (delectability)(delectability) photo stimulable phosphor systems:photo stimulable phosphor systems: erase cassetteserase cassettes Obtain several contact images of a low contrast Obtain several contact images of a low contrast

phantom phantom

process using a high –contrast algorithm & edge process using a high –contrast algorithm & edge

enhancementenhancement

algorithm. algorithm.

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Image quality low contrast Image quality low contrast resolution (delectability)resolution (delectability)

Weekly check of contrast-to-noise ratio (CNR)

If region of interest (ROI) facility is availableMethod• Use the image of the test object from the daily test• Draw two ROIs • Record the mean (M1) and standard deviation (SD) of the

pixel value in ROI 1.• Record the mean (M2) of the pixel value in ROI 2.• Subtract M2 from M1 and divide by SD to calculate the

signal-to-noise ratio (CNR):

CNR =M1- M2 SDCNR baseline ± 20%If this level is exceeded then take action to correct the

problem.

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Reader reboot Reader reboot

Reboot Reboot weekly Or as required weekly Or as required

Follow the schedule as prescribed by Follow the schedule as prescribed by the manufacturethe manufacture

Daily wiping of the insertion slot reduces the chance of dust getting into the readout chamber

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Daily wiping of the insertion slot reduces the chance of

dust getting into the readout chamber

Weekly uniformity check

Uniformity should be visually checked on a weekly basis using the image of the test object or plain Perspex

from the daily test. By setting a narrow grey scale window areas of non-uniformity will be seen. Magnify or zoom the image electronically and inspect it in a systematic fashion to look for artefacts such as faulty clusters of pixels or areas of unusually low noise (where the background mottle appears blurred or smoother than otherareas of the image). This is particularly important for some DR systems

Monthly AEC thickness check

If region of interest (ROI) facility is available • Measure SNR and compare with baseline values • Measure CNR and compare with baseline values Remedial levels Detector dose indicator baseline for that thickness ± 10% SNR baseline for that thickness ± 20% CNR baseline for that thickness ± 20% No disturbing artefacts should be visible. If any of the levels are exceeded then take action to correct

the problem.

Set up test just as done for filmSet up test just as done for filmMake Ist exposure on the thinner phantom Make Ist exposure on the thinner phantom - expose thicker phantom at the same setting - expose thicker phantom at the same setting - record the mAs - record the mAs If a printer is available , print both images and measure optical If a printer is available , print both images and measure optical densities.densities.If using the on screen tool , select same size region- of – interestIf using the on screen tool , select same size region- of – interest (ROI) at same location on both images and record average (ROI) at same location on both images and record average measurement.measurement.

DETECTOR FLAT-FIELD CALIBRATION (DR SYSTEMS ONLY) Some DR detectors may have a non-uniform response (due to

variations in sensitivity, faulty pixels etc). Also,there are non-uniformities in the x-ray beam due to the anode heel effect and x-ray beam divergence.

Some DR systems correct for these inherent non-uniformities by a process of flat-fielding. Flat-field correction maps are obtained using a standard beam attenuator (usually a Perspex block) for one or more exposure conditions

(eg different target/filter combinations and focal spot sizes).

Some system require the user to carry out this flat-fielding process periodically, and it is therefore included here although it is not strictly a QC test. On other systems this is carried out by the service engineer at routine service visits.

Method

• Carry out the flat field calibration according to manufacturer’s protocols.• Record and initial that the procedure has been performed.

IMAGE PLATE (IP) CHECKS (CR SYSTEMS ONLY)

Image plate erasure It is recommends that any cassettes left in the

x-ray room, or left un-used for a few days (eg over a weekend)

should be erased using the image reader ‘secondary erasure’ cycle before use, to remove any ‘fog’ from the IP.

Six-monthly image plate matching and artefact check This procedure should also be carried out on new image

plates. Image plates and cassettes should be matched in both their sensitivity (S value per unit exposure) and

in the mAs derived under automatic exposure control. Full size Perspex blocks are preferable for these tests

so that the whole IP can be checked for artefacts.

MethodUsing each IP in turn:• Conduct primary erasure before starting.• Place 4 cm thickness of Perspex on the table (if more convenient, other thicknesses such as 4.5 or 5 cm would also be suitable).• Place IP cassette in the bucky.• Operate the unit in a fixed kV, automatic mAs mode – select kV in normal use, • Make an exposure and record the mAs value.• Read the IP after a standard delay time (eg 1 minute) –

• Record the S value.

• View image with a narrow display window and check for artefacts.

• Repeat for each IP.Then:

• Calculate the mean (average) mAs value for all IPs.• Calculate the mean S value for all IPs.Remedial levelsmAs value mean ± 5%S value mean ± 10% (this allows for variation due to mAs and variation in IP sensitivity).

Plates showing scratches or marks should be cleaned and the test repeated. Plates with permanent scratches or marks should be removed from service

MONTHLY MECHANICAL SAFETY AND FUNCTION CHECKS

Check the safety and function of the system. It is recommended that a local checklist is drawn up for each

system to identify relevant features to be checked (eg items that are safety-critical or areas known to be prone to faults).

the local system, for example: • environmental checks (some digital systems

are particularly sensitive to environmental conditions such as temperature and humidity)

• checks relating to the reporting workstation . Keep a record of all checks, note any problems

and take action to get them corrected

PRINTER CHECKS

The printer is set up on installation when the engineer should ensure that the hard copy matches the soft copy image.

Daily printer checks using test pattern Printer checks should be carried out using

standard viewing conditions each day that the printer is used. Print

SMPTE test pattern or the manufacturer supplied test pattern and perform the following checks:

• Geometrical distortion – check image is printed without geometrical distortion; borders should be completely visible and straight lines should be straight.

• Contrast visibility – SMPTE test pattern, the 5% and 95% squares should be clearlyvisible.

• Printer artefacts – check test pattern for printer artefacts no disturbing artefacts shouldbe visible.• If a densitometer is available, measure densities and compare with baseline values. Printer checks following software upgradeAfter software changes or an upgrade, it may be advisable to print both a test pattern and a clinical image to confirm that the hard copy remains similar to the soft copy display

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