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

6. OID

7. Part to IR position

8. Detail

9. OID

10. Part to IR position

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

12. Producing optimal radiographs

13. 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”

14. 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

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

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

17. How does the technique Influence the image Film screen / CR / DR ?????
CONTRAST & DENSITY PRIME FACTORS
How does the technique
Influence the image
Film screen / CR / DR ?????

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

19. 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

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

21. Digital Imaging Film Screen Overexposed
AMOUNT OF ‘BRIGHTNESS”
Can be controlled and changed with computer****
*** proper technique and exposure index still important
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

22. Good techniques – important for GOOD images + lower PT doses

23. EXPOSURE FACTORS STILL IMPORTANT!

27. 80 Ma x.04s vs ma X ?mas
3.2

28. MAS DOUBLED – DENSITY

29. Kvp & contrast (F/S)

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

33. How Are X-rays Made? mAs – amount kVp - energy
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

34. Milliamperage mAs Kilovoltage Peak - kVp
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
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

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

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

38. + 25% % mas

39. + 15% kvp = 15% kvp

40. 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

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

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

43. 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 kvp
FOR LATERAL:
Go up 4 X in mas mas kvp
Go up 2 X MAS & ↑ 15% Kvp mas kvp

44. MAINTAIN SAME OD FOR CHEST FILM
80 KVP , 5 MAS, ?

45. CHEST RADIOGRAPH: too light& want longer scale contrast
4 mAs KVP
____ mAs ____ KVP

46. Shorten TIME
400 MA, 1/20s, KVP
100 MA, _____ , KVP