Equipment Design for Radiation Protection Chapter 11, (7th ed) Equipment Design for Radiation Protection

Radiographic equipment which is designed to protect the Rt and the patient Leakage radiation must be held to 100n MR/ hr. at 1 meter for tube housing. Collimator right next to widow to stop off focus radiation.(off focus radiation is radiation created at a place away from target of the anode.)

Collimation is always important for the Pt. as well as the RT Collimation is one of the most important things the Rt can do to reduce pt dose. Proper filtration can reduce dose by 90%. That is why filtration cannot be removed by machines today.

This is known as a diaphragm This is what stops off focus radiation.

Seldom used currently due to computerized imaging systems Old collimators We should still use extension cones to increase collimation as much as possible. Rts don’t do that much anymore.

Filter (The best thing ever invented to reduce Pt. dose) Filtration stops those x-rays that don’t have a possibility of exiting the patients’ body. This is called hardening the x-ray beam. Remember that for x-rays to be of any value, the x-rays must: Come fro as close to a point source as possible. Travel in a straight line and spread Have some possibility of entering and exiting the patient's body. (low energy x-ray have no possibility of exiting the patients body and hence need to be stopped before they enter the pt.)

Moly anodes used in Mammo to create a more monochromatic beam New anode targets and filters have dramatically reduced mammo doses. Molybdenum & Rhodium targets give a more monochromatic radiation and hence lower dose.

Are grids radiation dose reduction devices? Grids actually increase patient dose, but ate necessary for increased need for adequate contrast , especially with heavier patients of today.

CR VS Film CR/DR can be good and bad. We need to have our techniques with the acceptable range. The acceptable technique range is MUCH wider than the old film systems. (technique doesn't need to be right on as it did with film. ) If technique is in the acceptable range, images have much better contrast and detail than the old film systems.

Pt. and Rt. protection Items for protection of patient & technologist: fluoro tube 15 inches from table top, filtration on x-ray tube, lead on skirt of table, bucky slot cover, curtain hanging from fluoro unit, iso-exposure lines designed to protect radiologist the most, (stand behind the radiologist. ), Image intensifier, 5 minute timer, last exposure hold, pulsed fluoro.

Image intensification Input phosphor– 1 x-ray photon from patient releases 1000 light photons Photocatode-- 1 light photon kicks off 50 electrons High voltage applied from photocathode to anode on the other end of the Image intensifier. (accelerate electrons toward anode) Electrostatic lenses-focus electrons to the output phosphor, NOT THE ANODE. Output phosphor– electron kinetic energy creates high intensity light at the output phosphor. IMAGE INTENSIFIER INTENSIFIES THE X-RAY IMAGE BY 2 METHODS. 1. MINIFICATION OF IMAGE. 2. FLUX GAIN WHICH IS THE ACCELERATION OF TH EELECTRONS AND INTENSIFYIING THE LIGHT OUT OF THE OUTPUT PHOSPHOR. Oldtime non- amplilfied fluoro was at 5 MA. New fluoro is .5 to 1.5 MA. Major reduction in dose fluoro today.

Dose reduction—What do you do? Where do you stand during a C arm fluoro study? Most books indicate you should stand 90 degrees to x-ray travel.

Fluoro dose reduction Time Collimate Where do you stand? Last image hold Pulsed fluoro High-level control VERY high dose to Pt & RT See p. 236-8 box & table Stand behind radiologist if possible in regular fluoro. High level control fluoro is a very high MA fluoro used iin the cath lab. It is ued when thye need t see VERY high detail of small arteries.

List of dose reduction measures X-ray housing/tube assembly: 3 phase & high frequency generators Stable high voltage generators Collimator on tube housing window to stop off focus radiation Filtration & heavy metal filters Adequate collimation Image Receptor: CR / DR systems allow for higher KVP & total dose reduction Reduction of repeats Windowing and leveling allow for less images being produced. Fluoro Image ingtensifier, 5 minute timer, dead man switch, filter on fluoro tube, lead in table to protect Rad. Last image hold Pulsed fluoro CT Protocols that reduce dose THERE IS GREAT INTEREST IN DOSE REDUCTION IN ALL AREAS OF DIAGNOSTIC IMAGING TODAY. (THERE ARE MORE. WHAT CAN YOU THINK OF?) Many advances intended to reduce dose to the patient and the Radiology practitioners.

End Ch. 11 (7th ed.) For an x-ray photon to be of any diagnostic value, what three things must happen to it? Originate for close to a point source Travel in a straight line Stop in the pt. or continue on to the IR