Veterinary Imaging Past, Present and Future- Digital Radiography

Transcription

1 Veterinary Imaging Past, Present and Future- Digital Radiography ROBERT H. WRIGLEY Professor Veterinary Diagnostic Imaging University of Sydney Veterinary Teaching Hospital Professor Emeritus Colorado State University Colostate Uni Typical X-ray machine 1950s Colostate Uni Restriction of X-ray field Collimation X-Ray machine with slide in lead diaphragms 1

2 Light (projection) beam diaphragm with adjustable Lead Shutters X-RAY MACHINES Portable max output 20mA, 80KV 50 ma 100KV High Frequency X-RAY MACHINES Ceiling mounted, 2000mA 150KV Automatic Film Processors 1960s Dry, Processed Film in 90 seconds Underdevelopment From under replenishment per film From developer oxidization in too large a storage tank Courtesy Konica 2

3 Photographic film in cassette RARE EARTH SCREEN-FILM SINGLE EMULSION FILM SINGLE FINE SCREEN INCREASED DETAIL INCREASED EXPOSURE INCREASED RADIOGRAPHIC CONTRAST Computerised X-ray machine operating controls at the X-ray tube Courtesy of SEDECAL USA Inc. Radiology in the 20 th Century Diagnostic Imaging in the 21 st Century 3

4 Digital Radiography Film Radiography Digital Radiography Film Radiography X-Ray Capture Device Conversion to DICOM computer file Display on Workstation Monitor Film Darkroom Film Processing Light Box Image optimization software Computer file/folder PACS Computer database/archive Electronic delivery Paper envelope File shelves Hand/mail delivery Digital Imaging & Communications in Medicine Picture Archive & Communication Systems ADVANTAGES Image Auto correction of Image Whiteness This feature is available on some Systems -Simplifies X-ray Technique setting -If not a feature vendor must provide an accurate technique chart and patients measured and exposed as you would for film. Latitude allows for some manual correction of mild over or under exposure Film/Screen 80 KVp 44mAs DR Image processed with automatic correction selected 80 KVp 44mAs Film/Screen 60 KVp 16mAs Advantages of Filmless Digital Imaging Versus Film Radiography Gray Scale Latitude DR Image processed with automatic correction selected 60 KVp 16mAs Film Digital 4

5 Gray Scale Processing Non-linear Gray scale transformation using stored settings (Algorithms) optimized for anatomical region imaged Detail Enhancement Especially useful to improve visualization of bone + lung detail Unsharp mask filtering Customized for object size + level of enhancement Unsharp Mask Filtering Can create black lines along radiolucent structures such as metallic implants Artifact halation, over-shoot, uberschwinger ADVANTAGES Eliminate darkroom and film processing Potential for patient side image viewing ADVANTAGES Can use computer graphic software to optimize image brightness & contrast. Whiten mildly overexposed images Darken mildly underexposed images Cost saving as eliminates - Film - Processing supplies - Darkroom - Film jackets & Files Electronic distribution of images via Networks For diagnosis For consultation/second opinions Input into an electronic medical record 5

6 DISADVANTAGES Need to be a skilled computer user Need computer support personnel All systems more expensive than film/screen cassettes and an automatic processor Image detail less than good quality radiographs X-Ray exposure level effects Image detail Exposure settings - those appropriate for > 400 speed FS and faster result in suboptimal CR image detail - Exposure settings as used for 300 speed FS and higher exposures are optimal for CR imaging - Newer systems using double sided plates and other plate halides now allow exposure to be significantly reduced. Courtesy Fuji Medical Syst. Automatic Image correction Some systems provide feed back information on the radiation level to the patient. Fuji Sensitivity S# = equivalent FS exposure level S# 110 AGFA LGM Exposure Index # Optimal X-Ray Exposure = X Recommended Exp = 2.4 ½ Recommended Exp =1.9 Digital Image Rectangular matrix of differing colored squares (Pixels=Picture Elements) What has been the effect on resolution of bony detail? S# P Detail Resolution dependent on: Pixel size proportional to total number and size of pixels -- physical size/quality of computer monitor -- quality of computer video card 2000 Pixels 64 Pixels 8 0 P I Acquiston Device Film/screen (all sizes) Digital Radiology Detectors 5 x 7.5cm 22 x 27cm 35 x 43cm Resolution Matrix # of Pixels Crystals Diodes Transistors Dental 2,256x2878 2,208x2688 Pixel size Microscoptic 30 um um um 2 Spacial Resolution Line Pairs/mm 5-15 Lp/mm ~ 15 Lp/mm ~ 5 Lp/mm ~ 3 Lp/mm I X X E E L L S S 6

7 Film/screen (all sizes) Crystals Microscoptic 5-15 Lp/mm Film/screen (all sizes) Crystals Microscoptic 5-15 Lp/mm Digital Radiology Detectors 5 x 7.5cm 22 x 27cm 35 x 43cm Diodes Transistors Dental 2,256x2878 2,208x um um um 2 ~ 15 Lp/mm ~ 5 Lp/mm ~ 3 Lp/mm Digital Radiology Detectors 5 x 7.5cm 22 x 27cm 35 x 43cm Diodes Transistors Dental 2,256x2878 2,208x um um um 2 ~ 15 Lp/mm ~ 5 Lp/mm ~ 3 Lp/mm Courtesy Eklin Film/screen (all sizes) Digital Radiology Detectors 5 x 7.5cm 22 x 27cm 35 x 43cm Crystals Diodes Transistors Dental 2,256x2878 2,208x2688 Microscoptic 30 um um um Lp/mm ~ 15 Lp/mm ~ 5 Lp/mm ~ 3 Lp/mm American College of Radiology Teleradiology Display Monitor Standard (1999) Real size display of human chest = 35 x 43cm film ~monitor 53cm diagonal size Resolution not < 2.5 lead lines per mm > 2000K x 2500 pixels (5 Mega Pixels) Courtesy Eklin Monochrome BW Medical DICOM factory calibrated LCD Monitors 2 Mega Pixels 5 M Pix 3 M Pix 1600 x 1200 ACR display standard DR detector Computer Monitors Consumer Level High End Medical-US,CT Radiographic ( not ACR std) Resolution Size 35 x 43cm 35 x 43cm 22 x 27cm Variable 53cm diagonal 35 x 43cm Zoom x 2 Then Pan Pixel Matrix 2000x mega pixel 2,208x2688 2,256x x x Mega Pixel 2000x x x

8 Pan to view remainder of the magnified image Contrast Resolution dependent on: Brightness of monitor Number of colors per pixel (bits) Grey scale images (Radiographic images, grey scale is 1/3 rd of total number of colors) Dependent on -- quality of video card (number of colors) -- quality of computer monitor 10 bits (1,024) 8 bits (256) Brightness of Light Boxes Monochrome BW Medical DICOM factory calibrated LCD Monitors 2 Mega Pixels 1600 x M Pix 5 M Pix 8

9 Liquid Crystal Display LCD Grayscale Monitors Now preferred as brighter and more stable than TV type monitors Monitor Display Test Pattern 1022 Gray tones $4-15,000 32cm x 43cm Black/White DICOM Calibrated Gray Scale High Brightness (>600 cd/mm 2 ) 10 bit video card Self calibrating Courtesy of Computed Radiography (CR=DR) generates digital radiographic images (computer files) from scanning a reusable radiation sensitive imaging plate Film CR SPATIAL RESOLUTION 6 pixels/mm (for 35 x 43cm ) 8 pixels/mm (for 24 x 30cm) 10 pixels/mm (for 18 x 24cm) Courtesy of IDEXX Labs. Inc 9

10 Reading the Imaging Plate Rotating Prism Imaging Plate Light Guide PM Tube Laser Translation Acquisition Device Film/Screen CR Plate 35x43cm 24x30cm Matrix (Pixels) Microscopic Crystals Microscopic Crystals 3520x x x x2370 Resolution Pixels Adjustable by laser beam 10/mm 5/mm 15/mm 10/mm Spatial Resolution Line Pairs/mm 5-15 Lp/mm ~5 Lp/mm ~2.5Lp/mm ~7 Lp/mm ~5 Lp/mm CR SCANNERS Melbourne and Camden Uni Vet Hospital Fuji CAPSULA Courtesy of IDEXX Labs. Inc Courtesy Agfa HealthCare Courtesy of IDEXX Labs. Inc 10

11 Anatomic specific Image Processing Loading Cassette Courtesy of IDEXX Labs. Inc Courtesy of IDEXX Labs. Inc CR Specific Image Artifacts Scattered Radiation Unloading Cassette Courtesy of IDEXX Labs. Inc CR Plate Moiré Patterns The term originates from moiré in its French form, a type of textile, traditionally of silk but now also of other fibers, creating a rippled appearance. Effect of turning grid line sets 2 sets of parallel lines inclined at an angle 5 degrees to one another Superposition of 2 similar patterns rotated by an angle α Courtesy of: 11

12 CR image made with a stationary grid 110 lines per inch. What is the image quality artifact? Moire problem How to stop this? -Use a Bucky -Turn the grid lines right angle to scan axis -Replace with a grid recommended by CR vendor, lines per inch EXPENSIVE * FOGGING BY SCATTERED X-RAYS & BACKGROUND RADIATION Erasing Plates Dirt on plate or in scanner will create white artifacts CR Plates and the Scanner need to be cleaned regularly Plus Image mottle from too low an X-ray exposure Courtesy of IDEXX Labs. Inc Non Automated system Clipping of the thinnest densities of the lungs from over exposure Original Beyond the range of manual correction ORGINAL Clipping of the thickest densities of the spine Beyond the range of manual correction 12

13 ELECTRONIC PLATE X-RAY DETECTORS SMALL AREA DENTAL RADIOGRAPHY DR FILM LESS Dental Digital Radiography Using Charge Coupled Device CCD (light detector in digital cameras) small size ~ 2-3 SMALL AREA RADIOGRAPHY - DENTAL RADIOGRAPHY X-Ray Intensifying Screen directly attached to CCD under computer control Images displayed on computer in a few seconds Pixel size 30 um 2 Resolution 15 Lp/mm Dental Radiography, DR Courtesy Alameda Animal Hosp. Digital Dental Radiographs Large Area CCD DR Radiography Aim to Record Image of a 14 x17 Region (14 x 17 X-Ray Intensifying Screen) Image Recorded on Small CCD Chip (camera technology) Courtesy of SEDECAL USA Inc. 13

14 Vet Ray Technology Courtesy of SEDECAL USA Inc. Courtesy of Large Area Single CCD Chip DR Radiography Problems: Bulky device Inefficient collection of light, limits resolution Built in grid will increase exposure need for extremity imaging Precludes using horizontal beam radiography May require higher X-ray exposures than film/screen and other digital acquisition devices Large Area Multiple (Tiled) CCD Chips Smaller in size Improved collection of light 4 Stitching of input from adjacent CCD chips may create artifacts Courtesy of RF System Lab Digital Radiology Plate Types Indirect Types Direct Types Laser scanned Anatomic specific image processing No scanning image processing Anatomic specific processing No scanning 14

15 ADVANTAGES Eliminate cassettes Patient side image viewing Portable System Customized for Veterinary Imaging Indirect DR detector 9 x 11 Plate - Higher resolution megapixels - Pixel size 100 microns 2 14 x 17 Plate - Lower resolution megapixels - Pixel size 160 microns 2 Table Mounted for Small Animal Radiography Courtesy of Eklin Medical Systems, Inc. Courtesy of Eklin Medical Systems, Inc. Small Animal Imaging Table top or in Grid tray 2232 x 3200 pixels Pixel size 127 um 2, 3. 9 Lp/mm DR Electronic Plate Radiography Advantages No processing, almost immediate (5-10 sec) image acquisition No cassettes Potential for excellent image quality when image processing is optimized for animal anatomy Courtesy of Sound Technologies Inc. 15

16 DR Electronic Plate Disadvantages May require greater X-ray exposures than for faster speed film screen radiographs Considerably more expensive than other forms of DR & Computed Radiography Retrofitting to an existing X-Ray table may be challenging Cannot perform cross table radiography The imaging sensor is very expensive to replace 16