1 Image acquisition, display, & interpretation Image - PDF document

Design and Performance Characteristics Design and Performance Characteristics Design and Performance Characteristics of Digital Radiographic Receptors of Digital Radiographic Receptors of Digital Radiographic Receptors J. Anthony Seibert, Ph.D. J. Anthony Seibert, Ph.D. J. Anthony Seibert, Ph.D. University of California, Davis Medical Center University of California, Davis Medical Center University of California, Davis Medical Center Sacramento, California Sacramento, California Sacramento, California Learning Objectives Learning Objectives Learning Objectives • • Describe digital detector technologies for • Describe digital detector technologies for Describe digital detector technologies for radiography and mammography radiography and mammography radiography and mammography • Review functional attributes • Review functional attributes • Review functional attributes • Compare detectors in terms of IQ and dose • • Compare detectors in terms of IQ and dose Compare detectors in terms of IQ and dose • Summarize advantages/disadvantages • • Summarize advantages/disadvantages Summarize advantages/disadvantages Presentation Outline Presentation Outline Presentation Outline • • Acquisition System Overview Acquisition System Overview • Acquisition System Overview • Digital Detector Attributes • • Digital Detector Attributes Digital Detector Attributes • Digital Detector Technologies Digital Detector Technologies • • Digital Detector Technologies • • Factors affecting Image Quality & Dose Factors affecting Image Quality & Dose • Factors affecting Image Quality & Dose • Clinical Implementation and QC • Clinical Implementation and QC • Clinical Implementation and QC 1

Image acquisition, display, & interpretation Image acquisition, display, & interpretation Image acquisition, display, & interpretation X X- X-rays -rays rays Patient Patient Patient Detector Detector Detector Computer Computer Computer PACS PACS Human Human Human PACS kVp Size Efficiency Digitization Radiologist kVp kVp Size Size Efficiency Efficiency Digitization Digitization Data delivery Data delivery Data delivery Radiologist Radiologist mAs mAs Restraints Restraints Resolution Resolution Preprocessing Preprocessing Data display Data display Physician Physician mAs Restraints Resolution Preprocessing Data display Physician Tube filtration Tube filtration Tube filtration Exam type Exam type Exam type Scatter grid Scatter grid Scatter grid Postprocessing Postprocessing Postprocessing Data storage Data storage Data storage Experience Experience Experience Collimation Collimation ESE, dose ESE, dose DQE DQE Configuration Configuration Condition Condition Collimation ESE, dose DQE Configuration Workflow Workflow Workflow Condition Acquisition to Interpretation: Image Quality Acquisition to Interpretation: Image Quality Acquisition to Interpretation: Image Quality • • Image quality is an indicator of the relevance Image quality is an indicator of the relevance • Image quality is an indicator of the relevance of information presented in the image to the of information presented in the image to the of information presented in the image to the task we seek to accomplish using the image task we seek to accomplish using the image task we seek to accomplish using the image • Considered in terms of portrayal of Considered in terms of portrayal of • • Considered in terms of portrayal of – Normal anatomy Normal anatomy – Normal anatomy – – – Depiction of potential pathology Depiction of potential pathology – Depiction of potential pathology • • Not necessarily the Not necessarily the “ “same same” ” in all images in all images • Not necessarily the “same” in all images • A constraining factor is radiation dose • A constraining factor is radiation dose • A constraining factor is radiation dose Image Quality Image Quality Image Quality • • Screen Screen- -film radiography film radiography • Screen-film radiography – IQ “built in” to the characteristics of the film – IQ – IQ “ “built in built in” ” to the characteristics of the film to the characteristics of the film – Film is acquisition, display and archive medium Film is acquisition, display and archive medium – – Film is acquisition, display and archive medium – Dose is determined by screen – Dose is determined by screen- -film speed film speed – Dose is determined by screen-film speed • • Digital radiography Digital radiography • Digital radiography – IQ dependent on Signal to Noise Ratio (SNR) – IQ dependent on Signal to Noise Ratio (SNR) – IQ dependent on Signal to Noise Ratio (SNR) – Separation of acquisition, display, and archive Separation of acquisition, display, and archive – Separation of acquisition, display, and archive – – – Dose is variable and dependent on required SNR Dose is variable and dependent on required SNR – Dose is variable and dependent on required SNR 2

Presentation Outline Presentation Outline Presentation Outline • Acquisition System Overview • • Acquisition System Overview Acquisition System Overview • Digital Detector Attributes Digital Detector Attributes • Digital Detector Attributes • • Digital Detector Technologies • Digital Detector Technologies • Digital Detector Technologies • Factors affecting Image Quality & Dose Factors affecting Image Quality & Dose • Factors affecting Image Quality & Dose • • • Clinical Implementation and QC Clinical Implementation and QC • Clinical Implementation and QC Conventional screen/film detector Conventional screen/film detector 1. Acquisition, Display, Archiving 1. Acquisition, Display, Archiving Optical Density Optical Density Transmitted x- -rays rays Transmitted x through patient through patient Log Relative Exposure Log Relative Exposure Film processing: Film processing: light to optical density light to optical density Gray Scale Gray Scale encoded on encoded on film film Intensifying Screens Intensifying Screens Film Film rays → → light x- x -rays light Digital X- Digital X -ray Detector ray Detector 2. Display 2. Display Digital to Analog Digital to Analog Digital Pixel Digital Pixel Conversion Conversion 1. Acquisition 1. Acquisition Matrix Matrix Transmitted x Transmitted x- -rays rays through patient through patient Digital Digital processing processing Analog to Digital Analog to Digital Conversion Conversion X- X -ray converter ray converter Charge Charge rays → → electrons collection collection x- x -rays electrons device device 3. Archiving 3. Archiving 3

Analog versus Digital Analog versus Digital Spatial Resolution Spatial Resolution Exposure Latitude Exposure Latitude Detector Detector Element, Element, Film Film Sampling Sampling Signal output Signal output “DEL “ DEL” ” Digital Digital Pitch Pitch MTF of pixel aperture (DEL) 1 0.9 100 µ m 0.8 0.7 200 µ m M odulation 0.6 100:1 100:1 0.5 1000 µ m 0.4 10000:1 10000:1 0.3 0.2 0.1 0 Log relative exposure Log relative exposure 0 1 2 3 4 5 6 7 8 9 10 11 Frequency (lp/mm) Digital Detectors Digital Detectors Digital Detectors • Separation of acquisition, display and archive • • Separation of acquisition, display and archive Separation of acquisition, display and archive • Digital acquisition is • Digital acquisition is not contrast limited • Digital acquisition is not contrast limited not contrast limited – Image processing – – Image processing Image processing • Signal to Noise Ratio (SNR) and Contrast to • Signal to Noise Ratio (SNR) and Contrast to • Signal to Noise Ratio (SNR) and Contrast to Noise Ratio (CNR) impacts “ “image quality image quality” ” Noise Ratio (CNR) impacts “image quality” Noise Ratio (CNR) impacts • Detector DQE determines the exposure required Detector DQE determines the exposure required • Detector DQE determines the exposure required • to achieve a required SNR to achieve a required SNR to achieve a required SNR Digital Detectors Digital Detectors Digital Detectors • Sampling and quantization (new noise sources) • Sampling and quantization (new noise sources) • Sampling and quantization (new noise sources) • Detector pre • • Detector pre-processing (correct imperfections) Detector pre- -processing (correct imperfections) processing (correct imperfections) • Image post • Image post-processing (enhance image contrast) • Image post- -processing (enhance image contrast) processing (enhance image contrast) 4