PRESENTED BY ANJU THAKUR FINAL YEARDEPARTMENT OF RADIODIAGNOSIS AND IMAGING PGIMER, CHANDIGARH
QA-it is the planned $ systematic action that adiagnostic x-ray facility will produe consistently highimages with min exposure of patient $ healing artspersonnel. QC-it deals with the technique used in themonitoring (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 aconventional X-ray machine and processing thedata digitally to produce crisp and high qualityradiographic images
Basic Components of CR Preview & ID Station ID Tablet Cassette with Imaging Plate Digitizer Laser Camera Processing Server M A IX 3300 TR LR
CR WORKFLOW M A IX 3300 TR LRRx Exposure Printing Network Processing server Identification Digitizer
Digital Radiography Performed by digital X-ray machines with flat panel detectors
INTRODUCTION to QA QC of CR andDRDirect 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 testsfor DR systemsFrequency 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
ArtifactsCR- Dust on the ip, scraches/cracks on ip,dirt on reader,rollermarksDR- faulty individual pixel,cluster of pixel, loss of resolution inone or both directionMONITOR- CRT(distortion,possibly due to interference fromother electrical devices)PRINTER- if artifacts not seen on hard copy then it is causedby printer, bandling, streaking, fine line in direction of film appear
Artifacts in computedradiography Hardware artifacts Soft ware artifacts 11
Hard ware artifacts Appearance Reasons dust particle &scratches Damage to the laser beam head of CR system RemedyHead has to be cleaned byCamel hair brush by vendor Dust on the laser beam head appear engineer as an irregular white lines 12
Damaged laser beam head in CRreader Appearance Appears as multiple linear white line Remedy Laser beam head Has to be replaced 13
Software artifacts A Excessive edge enhancement B Artifact simulate acute phase of Pagets disease as a result Of excessive edge enhancement .(B) normal E.E 14
Computed Radiography andQuality 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 reportingmonitors Using the SMPTE Test Pattern
SMPTE This organization developed a test pattern that can be used to determine grey scale image quality on videos and computer display monitor. Other parameter which can be evaluated are- Spatial resolution Brightness Contrast Aliasing 19
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.
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 21
Luminance and uniformity contd •Use the TG-18 UNL -80 or SMPTE test pattern ,or set an entirely white display•Use a photo timer to measure luminance -Measure maximum luminance in the centre and four corners of display -Measure minimum luminance in centre of display 22
Diagnostic video monitorluminance & uniformity•Determine monitor type •Calculate % difference of each of corners to centre 23
Monitor type Maximum luminanceColor CRT > 80 Cd/m2Color LCD > 100Cd/m2Grey scale CRT secondary > 150 Cd/m2Grey scale diagnostic >200 Cd/m2Grey scale LCD 350 Cd/m2 Minimum luminanceCRT <1.0 Cd/m2LCD <1.5 Cd/m2 % diffAll With in 15% 24
Image quality high contrast (spatial) resolutionFor photo stimulable phosphor systems Determine standard set up& technical factors- do once - low KVp, Extended SID use a lead –bar resolution test pattern phantom - slightly angle phantom Minimize moiré &line pairing pattern Process with high-contrast algorithm 26
Image qualitylow contrast resolution(delectability) photo stimulable phosphor systems: erase cassettes Obtain several contact images of a low contrast phantom process using a high –contrast algorithm & edge enhancement algorithm. 27
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.
Reader reboot Reboot weekly Or as required Follow the schedule as prescribed by the manufactureDaily wiping of the insertion slotreduces the chance of dust gettinginto the readout chamber 30
Daily wiping of the insertion slot reduces the chance ofdust getting into the readout chamber 31
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 Set up test just as done for film Make Ist exposure on the thinner phantom - expose thicker phantom at the same setting - record the mAs If a printer is available , print both images and measure optical densities. If using the on screen tool , select same size region- of – interest (ROI) at same location on both images and record average measurement. 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.
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 (CRSYSTEMS 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 platematching 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. Method Using 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 forartefacts.• 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 andvariation in IP sensitivity).Plates showing scratches or marks should be cleaned and thetest repeated. Plates with permanent scratches or marks shouldbe 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 printerartefacts no disturbing artefacts shouldbe visible.• If a densitometer is available, measure densitiesand compare with baseline values. Printer checks following software upgradeAfter software changes or an upgrade, it may beadvisable to print both a test pattern and a clinicalimage to confirm that the hard copy remainssimilar to the soft copy display