Comparing Exposure Systems Unit V Comparing Exposure Systems

Developing Exposure Charts Chapter 34 Developing Exposure Charts

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Objectives Compare various exposure systems Describe advantages and disadvantages of fixed and variable kVp systems Discuss other exposure systems that have influenced radiographic technique Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Objectives Explain why measurement of part thickness is critical to the accurate use of technique charts Describe function of the radiographer when using automatic exposure control systems Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Objectives Describe how programmed exposure control systems function State the steps necessary to establish a technique chart Explain a basic phantom testing procedure Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Objectives Describe process of selecting an optimal image range Extrapolate a technique chart from a limited number of phantom test images Describe the clinical trial and fine tuning processes Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. System Selection Forefathers of technique 1920s – Ed C. Jerman 1940s – Arthur Fuchs Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. System Selection Radiographic exposure is a very complex process Best technique systems manipulate one variable while holding others constant Goal of any exposure system is consistency Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. System Selection Facilities that post and maintain exposure technique charts have lower repeat rates Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Comparing Exposure Systems Technologists may develop personal preference Should use system employed by imaging facility Students should learn all possible systems before making personal selection Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Fixed Kilovoltage Systems 1943 - Developed by Fuchs during WWII Theoretical support from literature and professionals Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Fixed kVp System Advantages: Reduction in patient dose Provides more information within the image Increased consistency in density and contrast Lengthens exposure latitude Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Fixed kVp System Advantages: Reduces x-ray tube wear Allows for shorter exposure times, thus reduces patient motion Easier to memorize Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Fixed kVp System Disadvantages: Higher amount of scatter results in reduced image contrast Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Variable Kilovoltage Systems 1925 - Developed by Jerman First exposure “method” Used when kVp range was limited by equipment generators Can adjust kVp more than mA or time Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Variable kVp System Advantages: Allows for small changes in exposure for small changes in part thickness Higher contrast Can affect the perceived image resolution Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Variable kVp System Disadvantages: More patient dose Higher repeat rate Tube wear, etc. Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Other Exposure Systems Log10 Systems DuPont Bit system XVS System Photographic roots Siemens point system Supertech Calculator Proportional anatomy system Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Part Measurement No exposure system can work effectively without accurate measurement of part thickness Failure to measure part correctly will result in increased exposures and patient dose Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Part Measurement Calipers Central ray entrance Thickest part Other Approach must be followed by all department radiographers Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. Phototiming Systems Automatic Exposure Control (AEC) Radiographer selects kVp and possibly back-up mA and time Equipment automatically terminates exposure Art of phototiming requires learning when to use it and when not to use it Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Anatomically Programmed Radiography Computerized technique charts Radiographer selects body part/projection Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Anatomically Programmed Radiography Radiographer can override technique to customize for individual patients If well maintained, only a mAs correction factor is necessary Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Establishing a Technique Chart Align image in middle with regard to: Part size kVp mAs Ideally 10-25 cm 60-80 kVp Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.