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RT 123 WK 3 Lecture #3

RT 123 WK 3 Lecture #3. PRINCIPLES OF TECHNIQUE AND EXPOSURE. Factors Affecting DETAIL. MAGNIFICATION DISTORTION TECHNIQUE SELECTION (TIME) FOCAL SPOT SIZE IR Speed (f/s) OID / SOD / SID Factors Affecting DENSITY PATIENT THICKNESS,PATHOLOGY MAS & KVP SID. OID.

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RT 123 WK 3 Lecture #3

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  1. RT 123WK 3Lecture #3 PRINCIPLES OF TECHNIQUE AND EXPOSURE

  2. Factors Affecting DETAIL • MAGNIFICATION • DISTORTION • TECHNIQUE SELECTION (TIME) • FOCAL SPOT SIZE • IR Speed (f/s) • OID / SOD / SID Factors Affecting DENSITY • PATIENT THICKNESS,PATHOLOGY • MAS & KVP • SID

  3. OID

  4. Part to IR position

  5. Detail

  6. OID

  7. Part to IR position

  8. TECH NICAL FACTORSAFFECTING QUALITY PRIME FACTORS • SID BEFORE YOU LEAVE THE ROOM • KVP CONTAST RANGE FOR PART • MAS CHANGES WITH PT SIZE , Pathology

  9. Producing optimal radiographs

  10. SID & SOD • SID –Source to Image Receptor Distance • TUBE TO CASSETTE • 40” (44) AND 72 “ STANDARD • SOD - Source to Object Distance • NOT LESS THAN 12 “ • SHOULD BE 15”

  11. SID • CHEST • 72 “ = 6’ (WING SPAN) • NOT 10’ (120”) • TUBE LOAD – Heat load on tube – the longer the SID the more Technique required to produce the image

  12. IMAGES • DENISITY = THE AMOUNT OF BLACKENING “DARKNESS” ON THE RADIOGRAPH • CONTRAST – THE DIFFERENCES BETWEEN THE BLACKS TO THE WHITES

  13. TECHNICAL FACTORS • KVP / MAS / SID • DEPENDING ON PART & SIZE of PART • Use FASTEST TIME POSSIBLE – TO REDUCE MOTION • ↑ kVp & ↓ Mas = lower Patient dose

  14. CONTRAST & DENSITYPRIME FACTORS How does the technique Influence the image Film screen / CR / DR ?????

  15. Radiographic Prime factors • The factors principally responsible for x-ray quality and quantity. • These are mAs, • kVp, • distance (SID).

  16. X-ray quantity (mAs) • is a measure of the number of x-ray photons in the beam. • Also called x-ray output, intensity or exposure. X-ray quality (kVp) • is a measure of the penetrating ability of the x-ray beam

  17. IMAGES • DENISITY = THE AMOUNT OF BLACKENING “DARKNESS” ON THE RADIOGRAPH • CONTRAST – THE DIFFERENCES BETWEEN THE BLACKS TO THE WHITES

  18. Digital Imaging Film Screen Overexposed Referring to a radiograph that is too dark because too Underexposed Referring to a radiograph that is too light because too x-radiation reached the image receptor AMOUNT OF ‘BRIGHTNESS” Can be controlled and changed with computer**** *** proper technique and exposure index still important

  19. Good techniques – importantfor GOOD images + lower PT doses

  20. EXPOSURE FACTORS STILL IMPORTANT!

  21. 80 Ma x.04s vs 160 ma X .02 ?mas 3.2

  22. MAS DOUBLED – DENSITY

  23. Kvp & contrast (F/S)

  24. “SHORT” VS “LONG” SCALE low kVp Higher kVp More on this in Ch 11, 25 & 26 Next week !

  25. X-rays are produced when electrons strike a metal target. The electrons are liberated from the heated filament and accelerated by a high voltage towards the metal target. The X-rays are produced when the electrons collide with the atoms and nuclei of the metal target. How Are X-rays Made? mAs – amount kVp - energy

  26. Milliamperage mAs • One kilovolt is = to 1000 volts • The amount of voltage selected for the x-ray tube • Range 45 to 120 kVp (diagnostic range) • kVp controls contrast • mA X s = mAs Kilovoltage Peak - kVp • One milliampere is equal to one thousandth of an ampere. • The amount of current supplied to the x-ray tube • Range 10 to 1200 mA

  27. Time • In seconds • How long x-rays will be produced • 0.001 to 6 seconds

  28. MAS Changes -at least 20 - 30 % mas change needed to see a visible change in density

  29. + 25% + 50 % mas

  30. + 15% kvp = 15% kvp

  31. Influencing factors: kVp 15% rule: • 15% kVp = doubling of exposure to the film  15% kVp = halving of exposure to the film 15% rule will always change the contrast of the image because kV is the primary method of changing image contrast. Remember : 15% change ( ) KVP has the same effect as doubling or ½ the MAS on density

  32. CHEST RADIOGRAPHY • UPRIGHT - WITH GRID • KVP RANGE (90 – 120 ) • MAS ( 1 – 3 PA) ( 5 – 20 LAT)

  33. “AVE” CHEST EXPOSURE - 2 IMAGES • (Ave – Pt meas 23cm pa 40cm lat) • PA 110 KVP 5 MAS 16:1 GRID 400RS 72” • LAT 110 KVP 20 MAS 16:1 GRID 400 RS 72”

  34. FOR CHEST – TO GO FROM PA TO LAT: • ↑ Technique by 4 x = Double the MAS and go up 10 kvp • INCREASE DENSITY BY 4 X you could: • Example: PA CHEST: 2 mas - 110 kvp FOR LATERAL: • Go up 4 X in mas 8 mas - 110 kvp Go up 2 X MAS & ↑ 15% Kvp 4 mas - 125 kvp

  35. MAINTAIN SAME ODFOR CHEST FILM • 80 KVP , 5 MAS, • 94 ?

  36. CHEST RADIOGRAPH: too light& want longer scale contrast • 4 mAs 85 KVP • ____ mAs ____ KVP

  37. Shorten TIME • 400 MA, 1/20s, 70 KVP • 100 MA, _____ , 80 KVP

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