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Analysis of Exposure I ndices in Digital D iagnostic R adiography

Analysis of Exposure I ndices in Digital D iagnostic R adiography. Krystal Francique Samantha Brownwell Mentor: Dr . Beth Vealé. Introduction to Radiography. What we knew going in: We first used film radiography, where films were developed with chemicals to produce the image

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Analysis of Exposure I ndices in Digital D iagnostic R adiography

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  1. Analysis of Exposure Indices in Digital Diagnostic Radiography Krystal Francique Samantha Brownwell Mentor: Dr. Beth Vealé

  2. Introduction to Radiography • What we knew going in: • We first used film radiography, where films were developed with chemicals to produce the image • Due to modernization, we transitioned to digital radiography • Instead of film, we used a reusable cassette to transfer the image to the computer to be digitized. • Established values of mAs (milliamperage seconds) were used so that factor variation could be measured. • Lack of knowledge about these factors have caused a phenomenon known as “dose creep”; we have to lower dose.

  3. Introduction to Radiography • Due to the fact that digital is more sensitive than film screen, these influential factors will not have the exact effect as they would on film screen • Research Question: How do known imaging parameters affect digital images and in turn, patient dose? • In digital radiography there is a number given after the image has been read, which is known as the exposure index number. It is a direct measure of radiation exposure to the image receptor and indicates exposure to the patient.

  4. Exposure Number • Exposure index number is displayed on each image • Must fall between an established range. • Measures receptor exposure • The range differs between manufacturers • In the lab we have the iCR2600 made by iCRco. • It’s range is -1.00 to +1.00 with 0 being perfect exposure

  5. What are we looking for and Why? • Analyze the influential factors in digital radiography that affect the exposure index numbers that measure radiation dose to the patient • These factors include: • Kilovoltage peak • Collimation • Distance • Time after exposure processing

  6. Kilovoltage Peak (kVp) For both body parts, kVp was increased by 1 from the original value.

  7. Collimation One set of collimation shutters was held constant at 5” while the other set was varied by .25” increments.

  8. Distance Distance was varied by 1 inch from 35” – 45”

  9. Time after Exposure The image receptor was left in a place protected from radiation for 15 minute increments before processing the image.

  10. Conclusion • Every 1 kVp change results in ~10% increase or decrease in exposure number • Collimation (smaller FOV) results in 10% less exposure per 1 inch of change and 1% less per 1/8 inch change • Every 5 inch change in distance results in ~30% change in exposure number • Cassette left unprocessed showed a signal loss of 30% after 30 minutes and slowed considerably after that. • Much more to do!

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