3/31/2011. Objectives. Emory University. Historical Development. Historical Development. Historical Development

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1 Teaching Radiographic Technique in a Digital Imaging Paradigm Objectives 1. Discuss the historical development of digital imaging. Dawn Couch Moore, M.M.Sc., RT(R) Assistant Professor and Director Emory University Medical Imaging Program 2. Review digital image receptor characteristics. 3. Identify methodologies suitable for teaching radiographic technique with digital imaging systems. Medical Imaging Program BMSc degree (2005) design 8 semesters Emory University Major Diagnostic Radiography Minor Tracks CT, MRI, IR, Ed., Adm. Historical Development Film Glass Base (1895) Cellulose nitrate base (1917) Cellulose triacetate (1923) Polyester (1960) Screens Zinc cadmium sulfide Calcium tungstate Rare earth phosphors (1974) Historical Development Historical Development Image Intensifier (1948) CT (1973) Computed Radiography (CR) 1984 MRI (1973) Photostimulable Phosphor (PSP) 1

2 Historical Development Instructional Methodologies Direct Radiography (DR) 1996 Traditional Lecture-based Direct Detectors Indirect Detectors Active Learning Group Activities Case-based Problem-based Instructional Methodologies Lecture Teacher centered Active learning Learner centered Image Acquisition (Conventional FS Radiography) X-ray source Film/ screen combination Processor Fileroom Reading room Bushong, 2004 Film-Screen Image Quality Film-Screen Image Evaluation Density Too light repeat Too dark hot light? Pertinent anatomy demonstrated mas controls image density Cummings,

3 Film-Screen Image Evaluation Film-Screen Image Evaluation Contrast Adequate penetration Acceptable grayscale 60 kvp Recorded detail Sharp edges Boney trabeculae visible Motion kvp controls image contrast 100 kvp Film-Screen Image Evaluation Teaching Methodologies Distortion Size Shape What teaching methodologies did you use with film-screen systems? Understand normal Digital Radiography Image Acquisition (Cassette/Phosphor-based Systems) CR- Photostimulable Phosphor (Cassette-based/ Phosphor-based) Digital Radiography Direct DRa-Se/ TFT (Cassette-less) Indirect DR- CsI, a-si/ TFT (Cassette-less) X-ray source Detector Plate Reader Monitor Reading room(pacs) 3

4 Cassette/Phosphor-based Image Acquisition Imaging Plate Three components Cassette Holds plate Photostimulable phosphor PSP Photostimulable phosphor imaging plate Latent image formation Imaging plate IP Plate reader Manifestation of the latent image Imaging Plate Imaging Plate Photostimulable Phosphors Materials that store information when exposed to one stimulus (x-rays) and release the information when exposed to another (laser light) Phosphor K-edge attenuation Best between kev 35 kev: average energy of 80 kvp beam More exposure needed if applied kvp is outside of this range * More sensitive to scatter than FS systems X-ray source Detector Monitor Image Acquisition (Cassette-less System) Reading room (PACS) Bushong, 2006 Image Acquisition (Cassette-less System) Types of Sensors (Image Receptors) Indirect Image Receptors Flat Panel CCD Direct Image Receptors 4

5 DR Image Receptor Comparison Indirect IR X-rays Light (phosphor) Electrical Charge Direct IR X-rays Electrical Charge (photoconductor) Lecture Written Assignment Compare the structure of a FS receptor to a CR receptor. Describe the steps in latent image production using FS, a PSP and a DR receptor. Labs 1. Expose a conventional screen and a PSP in a dark radiographic room. Describe the results. 2. Expose a medium-sized anatomical phantom (knee) at a low kvp, low mas level (50 kvp; 5 mas) using a PSP. Take additional exposures, increasing the mas each time and monitoring the exposure indicator. Evaluate the required mas to achieve an acceptable EI. Repeat at 60 and 70 kvp levels. Case-based Learning Provide students with a FS cassette and a CR cassette As a group, the students should explore the IR systems. This would require: Acquisition of critical knowledge Problem-solving proficiency Self-directed learning strategies Team participation skills Digital Image Quality Goals remain the same as FS Provide optimal diagnostic information Demonstrate pertinent anatomy Optimal brightness (density) Optimal contrast Optimal recorded detail Acceptable distortion Cummings,

6 Digital Image Quality Digital Image Quality Dynamic Range The exposure range over which the system can respond Digital receptors have a much wider dynamic range than FS Frank & Ballinger,2003 ARRT, Digital Image Quality Digital Image Quality Dynamic Range and Latitude Latitude: The range of exposures that allows a quality image to be captured. Because of digital image processing there is a false impression of wide latitude Film screen: +50% to -30%* Cassette-based (CR): + 200% to -50%* Will give similar brightness, but 33 Digital Image Quality > 50% underexposed Noisy, mottled image 3X overexposure Contrast degradation ( scatter) ALARA violation Potential loss of adjustment at PACS Cassette-based Exposure Indicators Fuji, Philips, Konica S number (Sensitivity number) 1.0 mr S= mr S= mr S=2000 Inverse, Linear relationship Carestream (Kodak) EI (Exposure Index) 1.0 mr 2.0 mr 0.5 mr EI=2000 EI=2300 EI-1700 Direct, Logrithmic relationship

7 Lecture Written Assignments Lab Problem-based Learning 1. Latent Image Creation receptor) 2. Image Readout (to computer) 3. Image Processing 4. Advanced Post-processing 38 Exam selection determines: Automatic Rescaling Brightness (Density) Look-up Tables Contrast Automatic Rescaling Automatic Rescaling Mapping grayscale to values of interest Provides images that have uniform display brightness over wide exposure range Controls Image Brightness (density) 41 4 mas 8 mas 16 mas 42 7

8 Image Processing Not Possible with Conventional Imaging Contrast Enhancement Look-up Tables (LUT) Windowing 4 mas 8 mas 16 mas Look-up Table Look-up Table Converts the original pixel value to another value to enhance image contrast Look-up Tables are specific to exam type Chest, Abdomen, etc Look-up Table Look-up Table

9 Image Brightness (Density) Controlled by Automatic Rescaling Not by mas Image Contrast Controlled by Look-up Table Not by kvp 2 mas 10 mas 20 mas 75 kvp 95 kvp 130 kvp 49 Lecture Written Assignments Lab Problem-based Learning Digital receptor systems are exposure driven Provide optimal exposure to the image receptor High SNR Optimal exposure (kvp and mas) Maximize the signal Minimize the noise Control scatter 52 kvp and mas selection Anatomical part determines selection Use higher kvp than used for film-screen (+15-20) Decreased mas results in lower patient dose Captures more anatomical data To maximize resolution and minimize distortion: Use smallest focal spot size practical Follow accepted standards for positioning, centering, etc. High subject contrast, high kvp Moderate subject contrast, moderate kvp Low subject contrast, low kvp Chest x-rays Adult extremities Pediatric extremities Contrast studies Prosthetic devices Abdominal studies Pelvis and hip 53 Use largest practical SID Use smallest practical OID 9

10 Optimal kvp range for adults: >120 kvp ~ decreased absorption efficiency kvp and mas can result in: Low signal (mottle) Increased scatter production (noise) A B Optimal kvp range for peds (<100 lbs.): Fuji CR do not use < 55 kvp Use standard rules (15%, 30%, etc.) to adjust technique 55 Image A = Correct exposure Image B ~ 60% Underexposed - objectionable mottle Lauren Noble, Ed.D., R.T.(R) UNC Chapel Hill School of Medicine 56 Grid selection Parallel FS imaging Critical for scatter (noise) control Increased grid ratio increased mas Avoid moiré effect generally 150 LPI or higher Collimation Collimation recognition critical in CR Symmetrical Sharp, well-defined borders Cassette-based systems use automatic exposure field edge detection (eliminates signals from outside collimated field) Scatter and off-focus radiation contribute to rescaling errors Collimation Cassette/ phosphor based systems Collimation (cassette/phosphor based systems) Proper collimation, proper rescaling Rescaling error due to improper collimation Results in faulty application of Pattern Recognizer for Irradiated Exposure Field (PRIEF) 59 Collimation OK Collimation NOT OK 60 10

11 Centering Non-centered, single sided collimation Histogram included the low intensity off-focus radiation IR size (Cassette/ phosphor based systems) Use smallest practical IR size Use consistent orientation of IR Ensures consistent and comparable display Non-centered single field Single collimation margin 61 Navicular on 18 by 24 Navicular on 24 by Similar to film-screen evaluation Check for: Proper positioning Proper centering Image Evaluation To evaluate for proper technical factors: Image Evaluation Check for penetration of the part Brightness Contrast Exposure index Noise Proper collimation 63 Integrate concepts throughout the curriculum Introduction Course Radiation Safety Course Physics and Equipment Courses Radiographic Technique Courses Procedures Courses Image Processing Course Clinical Education Courses Teaching Methodologies Concepts Lecture Independent Research Discussion Technique and Equipment Lab Assignments 11

12 Teaching Methodologies Clinical Education Courses Practical Experience Checklists Competency Evaluations Image Evaluation S #; EI; LGM Mottle evaluation Brightness/ contrast evaluation Cropping vs collimation Contact Information Dawn Couch Moore, M.M.Sc, RT(R) Emory University PO Box Atlanta, GA lmoore@emory.edu 12