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Qa & Qc for CR/DR
imaging 2a qa & Qc
| Question | Answer |
|---|---|
| importance of quality for digital equipment | 1. digital radiology is increasingly coming into use 2. detectors in digital systems have a large dynamic range 3. high doses are hardly noticeable in images 4. QC is essential to avoid unnecessary high doses and achieve good image quality |
| what does quality assurance consist of | activities that provide adequate confidence that a radiology service will render consistently high quality images and services |
| medical aspect of quality assurance | interpretation of images |
| technical aspect of quality assurance | maintenance of equipment, performance of examinations |
| operational aspect of quality assurance | filing systems, staff development, scheduling of examinations, supply lines |
| what is quality control | aspect of quality assurance that monitors technical equipment to maintain quality standards |
| checklist for quality control for printers | 1. geometric distortion 2. contrast visibility 3. printer artifacts 4. density response 5. uniformity |
| test patterns for monitors | 1. SMPTE 2. TG18 |
| what does SMPTE stands for | Society of Motion Picture & Television Engineers |
| what does TG18 stands for | Task Group 18 |
| TG18 is created by | AAPM |
| what does AAPM stands for | American Association of Physicists in Medicine |
| features of TG18-QC | 1. consists of small squared areas with different range of grey colours 2. each square of the 0% & 100% contains smaller squares of 5% & 95% 3. centre & edges 4. 6 squares |
| the centre and edges have | high contrast bar patterns of black & white pairs |
| the 6 squares are filled with | varying widths of alternating black/white horizontal and vertical lines |
| _______ lighting should be _______ but not off completely | ambient, reduced |
| what is the range avoids reflections and still provide sufficient lighting | about 25-40 lux |
| at about 25-40 lux _________________ most reflections and still provide _______________ ligthing | avoids, sufficient |
| luminescence of monitors should be at least _____________ for conventional radiographs | 200 cd/m2 |
| _______________ range leads to ____________ levels of contrast in displayed images | lower, inadequate |
| _________ range leads to _____ _________ of details due to the limited range of contrast ________ of human eye | higher, poor visualisation, sensitivity |
| frequency checks for QC for monitors is done | weekly |
| additional test patterns prescribed by manufacturers' QC programme is done | monthly |
| what is the QC done for Direct detectors | KCARE protocol |
| checklist for KCARE protocol | 1. dosimetry 2. dark noise 3. detector dose indicator consistency 4. uniformity 5. blurring and stitching artifacts 6. limiting spatial resolution 7. TCDD |
| what does TCDD stands for | Threshold Contrast Detail Detectability |
| characteristics of dosimetry | 1. range of output exposures produced by tube current exposure time (mAs) are measured and recorded 2. Exposures are a function of tube & generator performance |
| characteristics of dark noise | 1. assess level of noise inherent in the system 2. due to dark current : flowing leakage current when voltage is applied to the film to collect signal information 3. should be 0 in ideal state 4. generates noise on the pixel & reduces the signal intens |
| what is the factor for Fuji CR in dose detector index consistency | sensitivity S) |
| what is the relationship of sensitivity and exposure for Fuji CR | inversely proportional |
| what is the optimum range of dose detector index consistency of Fuji CR | 150 - 250 |
| what is the factor for Kodak CR in dose detector index consistency | exposure index (EI) |
| what is the relationship of EI and exposure for Kodak CR | proportional |
| what is the optimum range of dose detector index consistency of Kodak CR | 1800 - 2200 |
| what is the factor for Agfa CR in dose detector index consistency | log median exposure (LgM) |
| what is the relationship of LgM and exposure for Agfa CR | log system (increase of 0.3 means the dose was doubled) |
| what is the optimum range of dose detector index consistency of Agfa CR | 1.9 - 2.5 |
| what is the factor for Phillips DR in dose detector index consistency | exposure index (EI) |
| what is the relationship of EI and exposure for Phillips DR | inversely proportional |
| what is the optimum range of dose detector index consistency of Phillips DR | 200 - 800 |
| what is the factor for Siemens DR in dose detector index consistency | exposure index (EI) |
| what is the relationship of EI and exposure for Siemens DR | proportional |
| what is the optimum range of dose detector index consistency of Siemens DR | depends on organ programme |
| what is dose detector index consistency | a numerical value displayed with each exposure which correlates to dose |
| characteristics of dose detector index consistency | 1. indicative of the dose which the image receptor receives, not that of patient |
| variation of dose detector index should be | less than 5% |
| characteristics of uniformity | 1. assesses uniformity of recorded signal from a uniformly exposed detector (1mm Cu at tube head) 2. full analysis requires calculation of standard deviation measured at ROI 3. subjective analysis by looking for non-uniforms & imperfections |
| why are DR detectors inherently non-uniform | due to variations in electronic gain and offset & conversion layer thickness |
| how is limiting resolution and TCDD evaluated | 1. use of TOR LEEDS test objects 2. spatial resolution : Line pairs/mm 3. contrast detectability : lowest contrast perceivable 4. image quality factor calculated |
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