Learning Objectives. Outline. Getting Started with CR. Converting the Radiology Department from Film-Screen to Digital: Making the Transition

Transcription

1 Converting the Radiology Department from Film-Screen to Digital: Making the Transition S. Jeff Shepard, MS, DABR University of Texas M. D. Anderson Cancer Center Houston, Texas di.mdacc.tmc.edu Learning Objectives Understand the issues that a Medical Physicist is likely to face when supporting a clinical operation that is undergoing (or is about to undergo) a conversion from film-screen based radiography to digitally acquired images. Continuing Education Course Radiographic and Fluoroscopy Physics and Technology Outline Image Acquisition Getting started with CR Introducing direct digital radiography Digital Mammography Quality control Acquisition device QC Display device QC Operational QC Patient Identification Replace F/S receptors with CR Straight-forward forward Cost effective Start in Portable X-RayX Traditional challenge in image quality F/S is unforgiving Over and under exposures are common Wider dynamic range of CR yields quick improvements Speed adjusts to technique automatically 1

2 Different detector sensitivity and energy dependence New technique charts Wide dynamic range Consistent image quality over a wide range of exposures Very beneficial (image consistency) Potential downsides Under- and Over- exposure Image consistency (contrast and brightness) is maintained Fewer photons = More noise Obscures low-contrast details More photons = More signal strength Signal-to to-noise ratio improves Beautiful images High patient dose! Flexibility in technique selection can lead to higher patient doses ( Exposure Creep ) Image Quality: Exposure Data Recognition Image Quality: Exposure Data Recognition Signal Strength Unused Dynamic Range Range of Exit Exposure Data (VOI) Unused Dynamic Range Signal Strength Incorrect VOI System Dynamic Range Exposure (mr) System Dynamic Range Exposure (mr) VOI recognition failure Body habitus (Pediatrics and post-surgery) surgery) Patient mis-position air peak Over-collimation, gonadal shields and prosthetics Special processing algorithms Fixed speed techniques 2

3 Technologist Feedback Detector Exposure Indicators (E.I.) Agfa CR - Lgm value (Logs available) Fuji CR - S Number (Logs available) Konica CR S Number Kodak CR EI (Exposure Index) Canon DR - REX Number Philips & Siemens DR - Speed value GE DR -????? Proprietary algorithms confusion AAPM (TG116), IEC and DIN are evaluating Technologist Feedback Detector Exposure Indicators (E.I.) Exposure to the detector Accurate and consistent (reproducible) Patient exposure index (DAP or ESE) not the same! Not editable!!! Tuning the image quality Verify QC console calibration conforms to DICOM PS3.14 first Compare JND intervals in a test pattern to those on a PACS monitor Set post processing to drive display to L min and L max Measure steps on the QC monitor with a photometer (OR-3) 3) Calculate JND at each step (DICOM 3.14, Table B1) Tuning the image quality Convert each step to a %JND of the entire range of JND s from L min to L max % JND (step) = 100% x JND(step)-JND(L JND(L min min ) JND(L max ) JND(L min min ) Repeat on PACS monitor and compare at each step For DICOM-compliant PACS, calculate JND index at each step and test for linearity from L min to L max DICOM is the registered trademark of the National Electrical Manufacturers Association for its standards publications relating to digital communications of medical information. 3

4 Display Matching %JND 100% 90% Modality QC 80% PACS 70% 60% 50% 40% 30% 20% 10% 0% Digital Driving Level %JND Display Matching Modality QC PACS 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Digital Driving Level QC console calibration is supported by few vendors Use contrast and brightness settings to get as close as possible Pressure vendors to add calibration capability to QC displays Calibrate it yourself Add 3 rd party software Replace display with self-calibrating 4

5 Tuning the Image Processing Start with vendor default settings on sample raw images Vendor-supplied unprocessed image data of real patients for tweaking Work with key technologists and radiologist(s) to find optimal default settings Change individual settings one at a time Phantoms first for contrast and dose, then 5 patients Adjust & repeat as necessary Portable X-RayX Start with chest Add abdomen/pelvis Add long bones Direct Digital Radiography General Radiography Recalibrate AEC Constant S/N ratio or detector exposure not O.D. Calibrate QC console Use same strategy as with portable X-Ray to get techniques and post- processing established in one room Migrate to other rooms when stable Introduction into the clinical operation: Same strategy as with CR Verify AEC calibration Verify QC console calibration Start with vendor default settings on sample raw images Phantoms first, then patients Adjust techniques and processing & repeat as necessary Get processing established in one room Migrate to other rooms when stable 5

6 Image Quality Moire patterns between the fixed grid lines and the and detector sampling matrix. Usually seen in CR, but can happen in DR Use high grid line frequency (> 4 lines/mm) Some systems employ low pass filters Decreases resolution Inappropriate for smaller plates Most DR s s use high line rate (~8 lines/mm) stationary or standard reciprocating grids Digital Mammography Acquisition Devices Full-Field Field Digital Mammography (FFDM) Scanning slot CCD with Cs-I Amorphous Silicon TFT with Cs-I scintillator Amorphous Selenium CR (Pending FDA) Digital Mammography Digital Mammography Introduction into the clinical operation: Same as DR and CR in general radiography Verify AEC & QC console calibration Tune the techniques in one room, then propagate to others kv selection may be limited Image post-processing processing flexibility is restricted by FDA Connectivity Huge data sets (up to 300 MB/study) require large local storage and fast hardware Dedicated workstations using point-to to- point connections can impose crippling additional transmission times Intermediate routing modules Bottleneck if not very robust Single point of failure 6

7 Digital Mammography Workflow What to store? Unprocessed images ( For( For Processing ) Interpretation workstation must apply FDA- approved processing Unprocessed images are ugly Processed images ( For( For Presentation ) Image is processed prior to archival Further processing is not possible (W/L only) Images in clinics look good Digital Mammography Workflow What to store? Both? Processed for clinics, unprocessed for Radiologist s s workstations Doubles storage space on PACS Doubles bandwidth requirements Slows everything down QC - Acquisition Device and Operation AAPM Report #74 Chapter 1 The QC process Chapter 2 QC Instrumentation Chapter 3 The Physics Report Chapter 4 Repeat Rate Analysis Chapter 5 Radiographic units Chapter 7 Conventional Tomography Chapter 8 Portable X-RayX Chapter 14 Photostimulable Phosphor Systems Quality Control Equipment selection Match performance and configuration to clinical needs Equipment QC Acquisition Devices Display Devices Technical Operation Patient Data Integrity 7

8 Quality Control of the Equipment Acquisition Device X-Ray generator (AAPM Report 74) kv ma linearity Exposure time Collimation Focal Spots Grids Beam alignment AEC (Constant raw SNR, or detector exposure) Quality Control of the Equipment Acquisition Device Exposure index calibration Exposure index dependence on beam quality VOI recognition algorithms Noise Uniformity Artifacts Contrast sensitivity Quality Control Quality Control of the Equipment Acquisition Device DR systems Detector sensitivity (SNR 2 vs Exposure) Verify quarterly DR QC Workshop - J. Seibert, L. Goldman (1:15 PM WE-D-W ) CR devices Erasure thoroughness AAPM Report #74, PSP System QC Siebert AJ, AAPM Monograph 20, 1994 Samei E, et al, Med Phys of the Equipment Acquisition Device DICOM calibration at the QC console Monthly Annual if self-calibrating Mammography MQSA - Vendors QC Program 8

9 QC - Primary Displays AAPM OR-3 3 Tests (Jerry Thomas and Mike Flynn, 8:30 tomorrow) Luminance Uniformity Veiling Glare (CRT only) Chromaticity Resolution (CRT only) Noise Geometric Distortion Luminance Response (CRT only) Diffuse and Specular Angular dependence Reflection of LR (@ +45 Pixel Defects degrees from normal, LCD only) Quality Control of the Equipment Film printers (AAPM Report #74) Density calibration (daily or as needed) Density uniformity (monthly) Geometric distortion (monthly) Artifacts (monthly) View boxes (annually) SMPTE or TG18-QC QC QC - Operation QC - Data Integrity Repeat/Reject Rate Analysis and Exposure Index Logs Expect same results as with Film/Screen Films no longer available for counting Software at console to track reasons for rejects and repeats By tech By anatomical view Easily accessible Formatted to facilitate interrogation Modality Work List Management (MWLM) Modality queries the RIS for a list of scheduled patients through a Broker RIS returns the requested list (through the broker) with patient demographics Automatically refreshes every 15 minutes Tech selects patient from the list at the acquisition console Exams are uniquely identified with Accession Number for later pairing with reports 9

10 QC - Data Integrity MWLM implementation Opportunity for patient mis-id ID greatly diminished Reiner B, et al, JDI, 2000 Overall patient ID failure rates decreased from 7.6% to 2% with introduction of MWLM in Baltimore VA s s CT operation Mandatory requirement for ALL modalities QC -Data Integrity Verification Errors are still possible Technologist or supervisor views EVERY exam on web viewer or QC workstation immediately after archival to verify status Missing images Patient mis-id Summary Other Considerations Conversion to DR requires: An in-depth depth understanding of the technology behind CR, DR, PACS, RIS, workstations, and printers. Understanding the impact of DR on workflow in exam rooms Understanding the impact of DR on the QC program Reading room illumination Prior, film-based comparisons with soft-copy Primary interpretation display devices Calibration QC Matrix size >3 MP? (Langer S, et al) Dead pixel definition M. Flynn - tomorrow, 8:55 10

11 Other Considerations Other Considerations Detector latent image decay Dual-Energy subtraction, tomosynthesis,, & image stitching Workflow? Optimization? Techniques? Latent image affects? Detector calibration uniformity Uncorrected flat-fields fields Film Digitizers Calibration Linear? Barten? QC DICOM Conformance statements Workflow enhancements Storage Commitment Performed Procedure Step Other Considerations The Role of the Physicist in Planning and Design of Digital Image Management Systems (PACS) D. Peck, M. Flynn (7:30 AM MO-A-I ) Overview of Digital Detector Technology - J. Seibert (8:55 AM MO-B-I ) Characteristics and Performance Evaluation of Digital Image Displays - H. Roehrig (7:30 AM TU- A-I-609-1) Evaluating Digital Mammography Systems - E. Berns (7:30 AM TU-A-I ) 1) Digital Image Processing in Radiography - D. Foos, X. Wang (7:30 AM WE-A-I ) Other Considerations Recent Advances in Digital Mammography - M. Yaffe,, R. Jong (7:30 AM WE-A-I ) 1) Testing Flat Panel Imaging Systems What the Medical Physicist Needs to Know - J. Tomlinson (8:30 AM WE-B-I ) 1) Digital Image Displays Resolution, Brightness and Grayscale Calibration - M. Flynn (8:55 AM WE-B-I ) Design and Performance Characteristics of Digital Radiographic Receptors - J. Seibert (7:30 AM TH-A-I ) 11

12 Other Considerations Display Evaluation Demonstration Workshop - E. Samei (1:30 PM MO-D-W ) 1) DR QC Workshop - J. Seibert, L. Goldman (1:15 PM WE-D-W ) Bibliography Digital Imaging and Communications in Medicine (DICOM), National Electrical Manufacturer s s Association (NEMA), Rosslyn,, VA, 2000, ( Freedman M, Pe E, Mun SK, Lo SCB, Nelson M. The potential for unnecessary patient exposure from the use of storage phosphor imaging systems. Proceedings of the International Society for Optical Engineering. 1993;1897: Gur D, Fuhman CR, Feist JH, Slifko R, Peace B. Natural migration to a higher dose in CR imaging. Eighth European Congress of Radiology; September 12-17, 17, 1993; Vienna. Abstract 154. Bibliography Bibliography Honea R, Blado ME, Ma Y. Is reject analysis necessary after converting to computed radiography? J Digit Imaging, v15 #2, Suppl 1 (May), 2002, Langer S, et al, Comparing the Efficacy of 5 MP CRT vs 3 MP LCD in the Evaluation of Interstitial Lung Disease, J Digit Imaging, v17 #3 (September), 2004, Reiner B, Seigel E, Kuzmak P, and Severance S, Transmission Failure Rate for Computed Tomography Exams in a Filmless Radiology Department, J Digit Imaging, v13 #2, Supp 1 (May), 2000, Samei E, Seibert JA, Willis CE, Flynn MJ, Mah E, Junck KL. Performance evaluation of computed radiography systems. Med Phys. 2001;28: Samei E, et al, Assessment of Display Performance for Medical Imaging Systems, AAPM On-Line Report #3 (OR-3), AAPM, Seibert JA. Photostimulable phosphor system acceptance testing. In: Seibert JA, Barnes GT, Gould RG, eds. Specification, Acceptance Testing and Quality Control of Diagnostic X-ray X Imaging Equipment. Woodbury, NY: American Association of Physicists in Medicine; 1994: Monograph No. 20. Shepard S J, et al, Quality Control in Diagnostic Radiology, AAPM Report #74 AAPM,

13 Bibliography Willis CE, Mercier J, Patel M. Modification of conventional quality assurance procedures to accommodate computed radiography. SCAR '96 Computer Applications To Assist Radiology. Great Falls, Va: : Society for Computer Applications in Radiology; 1996: Willis CE. Quality assurance: an overview of quality assurance and quality control in the digital imaging department. In: Quality Assurance: Meeting the Challenge in the Digital Medical Enterprise. Great Falls, Va: : Society for Computer Applications in Radiology; 2002: