Artifact ,QA and QC of CR and.ppt
Transcript of Artifact ,QA and QC of CR and.ppt
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Artifact ,Artifact ,Artifact ,Artifact ,QA and QC of CRQA and QC of CR
Titipong Kaewlek M.Sc.Department of Radiological Technology
Naresuan University
Artifact of CR
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ArtifactArtifact ใน การถายภาพทางรงส เปนสงทไมพงArtifact ใน การถายภาพทางรงส เปนสงทไมพง
ประสงค และทาใหมผลตอความแมนยาในการวนจฉยโรค
ในเครองเอกซเรยแบบComputed radiography (CR) กพบปญหาเหลานเชนเดยวกนกบ C i l di h แตปญหาปญหาเหลานเชนเดยวกนกบ Conventional radiography แตปญหาทเกดขนมลกษณะการเกดทแตตางกน
Artifact
Artifact ทเกดขนใน CR จะเกดไดทงจาก Imaging plate ,Plate reader, image processing software หรอ อาจจะเกดจะ Laser printer หรอ Operator error
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Imaging plate artifactsImaging plate artifacts
Imaging plate artifact
Artifact แบบนเกดจากลกษณะของ Imaging plates (IPs) ทมความออนทาให ตว plate เกดการโคงงอหรอเกดการแตก ในขณะทใสเขาไปในตว plate reader
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l
Imaging plate artifact
ลกษณะการแตกของ Plate มกเกดบรเวณขอบๆของตว plate ซงจะไมมผลตอภาพถายทางรงส
แตเมอใชไปในระยะเวลานาน ตว plate กจะเสอมคณภาพ และเกดการแตกบรเวณของกลาง plate ได
Imaging plate artifact
ใ ป บรเวณทแตกจะทาใหการBlock การปลอยแสงทเกดจากการ scan ของ Laser
และใหภาพบรเวณนน เกดเปนรอยสขาว(White Artifact)
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Thumb radiograph showing cracks (white arrow) that usually first become visible on the IP edges.
This crack appears as a lucency near the radius, which could be confused with a foreign body
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Imaging plate artifact
Artifact ท imaging plate ยงสามารถเกดไดจาก Backscatter Artifact ท imaging plate ยงสามารถเกดไดจาก Backscatter เพราะ Storage phosphor มคณสมบต high sensitivity ตอ scattered radiation
สามารถกาจด ไดโดยใชLead foil ตดบรเวณดานหลงของ Cassette
Imaging plate artifact
Residue from adhesive tape used to attach lead markers to the outside of the cassette has caused artefacts (arrow) when the tape came in contact with the IP.
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Static caused a hair to cling to the IP on this skull image.
Th d k li l th l t l ti f thi The dark line along the lateral portion of this upper abdomen is caused by backscatter transmitted through the back of the cassette. The line corresponds to the cassette hinge where the lead coating was weakened or cracked.
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Plate reader artifactsPlate reader artifacts
Plate reader artifactsPlate reader artifactsเกดจากความผดปกตของการลบขอมลภาพทอยใน plate
ลบไมสมบรณ, หรอเกดจากการตงคา Exposure ทไมเหมาะสม ทาใหตองใชเวลาในการลบขอมลนาน จงม light มากเกนกวาปกต
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Plate reader artifact. The pattern of lines seen on this oblique hip view occurred intermittently.
The artifact was traced to the plate reader’s electronics.
The horizontal white line (arrow) shown on this upright chest radiograph was caused by dirt on the light guide in the platereader.
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This artifact occurred because the plate reader loaded two imaging plates (IPs) in a single cassette
This bilateral knee image was spoiled when the i iincorrect erasure setting was used to eliminate a previous femur image.
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Image processing artifactsImage processing artifacts
Image processing artifactsImage processing artifacts
Artifact จาก Image processing อาจเกดไดจาก การเลอกใช processing บางอยาง เชน Unsharp mask processing เพอให enhance image sharpness ซงจะทาใหเกด Artifact ขนหาก เลอกใช kernal size ไมเหมาะสม
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(a) (b)(a) When too large a kernel size is selected for image enhancement, artefacts
like the black halo surrounding the prosthesis can create the appearance that the prosthesis is loose.
(b) The same image as (a) processed with a smaller kernel size.
(a) (b)
(a) (b)a) Edge enhancement was increased from the default level for this
paediatric chest image. Notice the marked increase in lung markings, which could indicate interstitial infiltrates.
(b) Thesame image processed with normal edge enhancement.
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Owing to lack of primary beam collimation on this lateral lumbar spine, the amount of unattenuated radiation striking the imaging plate (IP) (anterior and posterior to the patient) altered the histogram so that it was outside the normal range for that body part selection.
The prosthesis in this knee adds too many extreme pixel values to the image histogram. This results in an image where the difference between prosthesis and glue, or glue and bone is not well demonstrated
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Laser printer artifactsLaser printer artifacts
Laser printer artifactsLaser printer artifactsเกดจากความผดปกต ของ Laser ทใชในการสแกน plate หรอ
ม dirt อยบรเวณ polygon mirror ทาใหการเกดสงแปลกปลอมบนภาพ เปนลกษณะเสนสขาวตามแนวยาวของภาพ(ตามแนวการสแกน)
เกดจากการทม dirt บรเวณ plate reader’s light guide จะทาใหเกด เปนเสนสขาว
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The fine white line (black arrow) running parallel with the long dimension of the film is an artefact from the laser printer.
The line running perpendicular to the long dimension of the film (white arrow) is caused by dirt on the light guide of the photomultiplier tube in the plate reader.
The horizontal white line (arrow) shown on this upright chest radiograph was caused by dirt on the light guide in the platereader.
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Operator ErrorOperator Error
Operator ErrorOperator Errorในเครองการสรางภาพทางรงส ทกอยางสามารถเกด ในเครองการสรางภาพทางรงส ทกอยางสามารถเกด
Artifacts ทเกดจาก Operator error ไดทงนน
การเกบ CR cassettes ควรเกบในทอณหภมไมสง ,ความชนตาๆ และหางจากแหลงกาเนดรงส และ Scatterความชนตาๆ และหางจากแหลงกาเนดรงส และ Scatter
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A wire mesh cart loaded with unexposed imaging plates (IPs) was placed too near a source of scatter radiation.
Operator ErrorOperator Error
การเลอกใชกรดกมผลตอภาพถายเหมอนกน หากเลอกกรดทมความถตาๆ จะทาใหเกด Moiré pattern จะเหนเปนเสนลายกรดบนภาพถาย ขนานกบแนว reader’s scan lines
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MMoireoire´ ´ patternpattern
The moire´ pattern seen in this k i d b i id
pp
knee image was caused by using a grid with a frequency of 33 lines cm -1, which was oriented with the grid lines parallel to the plate reader’s scan lines.
This axillary shoulder was exposed through the back of a cassette.
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Other Artifact of CR
Light bulb effectg
เกดจาก photostimulable phosphor ไดรบ back scattered radiation จาก เตยงของคนไข ซงจะพบบอยครงเมอมการเพมคา exposureในคนไขตวใหญ หรอการเปดcollimated มากเกนไป
เนองจาก phosphor ม dynamic range กวาง และ sensitivity ตอรงสสงมาก
ลดไดโดยใชคา kVp ตาๆ หรอเปด collimator เฉพาะบรเวณทจะถายเทานน
Light bulb effectLight bulb effect
Lower, outer portions of this computed radiograph(arrows) are darkened because of back-scattered radiation from patient’s bed.
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Fogging
เนองจาก imaging plate มคณสมบต dynamic range กวาง และ sensitivity ตอรงสสงมาก จงอาจทาใหเกด Artifact ทเรยกวา Fogging ได จากการใชคา exposure สงเกนไป
Fogging
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Fogging
Double Exposure
ในการถายภาพแบบ Conventional film screen system การ Double exposure ทาใหภาพถายดา ไมสามารถอานผลได ใน CR กเชนกน มกเกดจากการลบขอมลภาพออกไมหมด
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Horizontally oriented abdominal examination is seen overlying dominant chest study.
Portions of right ribs (arrow) and right iliac crest(arrowhead) are apparent.
Double exposure
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Quantum mottle
ในภาพทถายดวยเทคนคท Underexposure ภาพจะเกดลกษณะทเรยกวา Quantum mottle ทาใหไมสามารถแปลผลได เพราะทาให signal to noise ratio ลดลง
Quantum mottle
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Simulated Diaphragmatic Calcification
เกดจากการใช edge enhancement processing ทาใหเกด เกดจากการใช edge enhancement processing ทาใหเกด เสนสขาวและดา บรเวณรอยตอของอวยวะ
Foreign Bodiesเกดจากฝนละออง ตดบรเวณ plate หรอมของเหลวหกใส plate
ขณะทาการอานขอมลภาพ หรอระหวางการเคลอนผาน roller ของขณะทาการอานขอมลภาพ หรอระหวางการเคลอนผาน roller ของreader
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Zipper artifact
เกดจากการอานขอมลภาพผดพลาด ไมมความตอเนองของการ อาน หรอ plate เคลอนทไมตอเนอง จงทาใหเกดเปนเสนในแนวตง
(vertical band)
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QQualityuality CControlontrol ofof CRCR
Quality ControlQuality ControlThree levels of system performance for quality l d icontrol and system maintenance
1. Routine: Technologist level- no radiation measurements
2. Full inspection: Physicist level- radiation measurements;non-invasive adjustments
3. System adjustment: Vendor service level- hardware and software maintenance
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Periodic Quality Control( Periodic Quality Control( AAPM)AAPM)
• Daily (technologist)• Daily (technologist)– General inspection– Film processor / Laser printer– Erase imaging plates– Verify digital interfaces and network transmission
Periodic Quality Control ( Periodic Quality Control ( AAPM)AAPM)
• Weekly (technologist)• Weekly (technologist)– Verify CRT calibration– Test phantom images– System cleanliness– System cleanliness
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Periodic Quality Control ( Periodic Quality Control ( AAPM)AAPM)
• Monthly (Technologist)• Monthly (Technologist)– Film processor maintenance (if any)– Inspect and clean image receptors– Review film retake rate– QC review for “out-of-tolerance” issues
• Semi• Semi--Annually / Annually (Physicist)Annually / Annually (Physicist)
Periodic Quality Control( Periodic Quality Control( AAPM)AAPM)
– Evaluate image quality– Acceptance tests to re-establish baseline values– Review
• patient exposure trends• retake activity• QC records• Service history
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QQualityuality AAssurancessurance ofof CRCR
Protocal for the QA of CRProtocal for the QA of CR
Routine QA TestsRoutine QA TestsA series of tests to assess CR plate and reader
performance. The tests are intended to monitor image quality and sensitivity
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List of equipmentList of equipment-Tape measure -Adhesive tape-1 mm Copper filtration (>10 x 10 cm)-TOR RAD or TOR CDR test object
1 1 Detector dose indicator MonitoringDetector dose indicator Monitoring
Purpose:Purpose: To monitor system sensitivity, and consistency of relationship between cassette exposure and detector dose indicator.
Frequency: Frequency: 1 1 -- 3 3 monthlymonthly
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1 meter
colimator
)Pl ( 24 30 h h ld
couch
a)Place a cassette (e.g. 24cm x 30cm - the same cassette should be used each time this test is performed) on the couch at 1m from the focus and centred in the x-ray beam. Set the collimation to cover the entire cassette.
b)Place filtration in the beam and set a kVp as indicated in below.
CR system Filtration Tube Voltage (kVp)
Agfa 1mm Cu 75Kodak 1mm Cu 80Fuji 1mm Cu 80j
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c) Set a manual mAs (this value should be determined in consultation with medical physics) and expose.
d)Read the plate immediately using the following parameters
Agfa: S=200system diagnosis/flat field processing and linear sensitometry.
Kodak: Pattern mode.
Fuji: semi-auto, L=1 or 2
e) Record the detector dose indicator indicator,
i.e. lg M - AgfaEI - KodakS - Fuji.
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Tolerance:Tolerance: This detector dose indicator should be compared to a baseline value obtained under the same conditions (i.e. same x-ray tube, distance, kV, filtration, mAs, plate).
Remedial level:
Agfa: lg M value should lie between(Baseline +0.08) and (Baseline-0.10)
Kodak: EI should lie between (Baseline +80) and (Baseline-100)
Fuji: S value should lie between (Baseline+25%) and (Baseline –17%)
S i l lSuspension level:
Agfa: lg M value should lie between(Baseline +0.18) and (Baseline-0.30)
Kodak: EI should lie between (Baseline+175) and (Baseline-300)
Fuji: S value should lie between (Baseline+100%) and (Baseline-33%)
2 2 UniformityUniformityPurpose:Purpose: To monitor image quality by assessing the
uniformity of the system.Frequency: 1-3 monthly
a)Select any cassette (a different cassette should be tested each time this test is performed).
b)Use as large a focus to detector distance as possible and open the collimators so that the X-ray field covers the entire detector.
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c) Expose the detector at as described for test 1.
d)Visually inspect the images for non-uniformitiesd)Visually inspect the images for non uniformities.
Note: Images acquired for the detector dose indicator monitoring test should also be inspected for non uniformities.
Remedial level:Remedial level: Images should not have obvious artefacts.N.B. This is a test of the reader. To test the whole system it would be necessary to test several plates at each 1-3 monthly interval
3 Threshold Contrast Detail Detectability
Purpose:Purpose: To monitor image quality by assessing the visibility of low contrast details
Frequency: 3 - 6 monthly
a)Place TOR RAD or TOR CDR test object on the table with a focus –receptor distance of 1-1.5m.
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b) Collimate to the cassette.
c) Place 1mmCu filter in the beam.d) Expose at 70kVp with a manual mAs (this value should
be determined in conjunction with medical physics).e)Read the cassette using the following parametersAgfa: S=200, examination type - ‘System Diagnosis’processing – ‘Flat Field’Fuji: Readout mode – ‘semi-auto’ with test/sensitivity GA=1Kodak: Mode – ‘Pattern’ with raw data and no edge enhancement
f) Record the detector dose indicator.g) Make three more exposures under the same conditions.h) Window and level the images so that background
noise is perceptible.
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i) Print the images onto the largest film size available.
j) View the image on a masked light box, and score each detail size using fixed distance viewing (<1m). If no hardcopy printer is available, score the images on a reporting workstation, optimising window and level settings for each detail size.
k) Calculate the mean number of visible details (average over all detail diameters))
Remedial levelRemedial level:: Average number of visible details reduced by two from baseline
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4 Limiting spatial resolutionPurpose:Purpose: To monitor image quality by assessing the
resol tion of the s stemresolution of the systemFrequency: 3 - 6 monthly
a) Place resolution test grid (e.g. TOR RAD or TOR CDR) on a 24 cm x 30 cm cassette at ~1 m. The bars should be angled at 45o to th l t the plate.
N.B. Remember to remove the copper filtration from the beam.
b) Set 50kVp.c) Expose at ~ 2mAs. d) Read the image plate using the following parametersd) Read the image plate using the following parameters.
Agfa: S=200, examination type - ‘System Diagnosis’processing – ‘Flat Field’F ji R d t d ‘fi ’ ith L 2 d S 200Fuji: Readout mode – ‘fix’ with L=2 and S=200Kodak: Mode – ‘Pattern’ with raw data and no edge enhancement
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e)Determine the number of resolvable groups of lines.
Remedial level: Number of resolvable groups reduced by 2 from baseline.
N.B. Other plate sizes may give different resolutions N.B. Other plate sizes may give different resolutions and should ideally be tested.