PRINCIPLES OF TECHNIQUE AND EXPOSURE 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

Part to IR position

Detail

OID

Part to IR position

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

Producing optimal radiographs

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”

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

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

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

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 ?????

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

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

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

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

Good techniques – important for GOOD images + lower PT doses

EXPOSURE FACTORS STILL IMPORTANT!

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

MAS DOUBLED – DENSITY

Kvp & contrast (F/S)

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

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

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

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

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

+ 25% + 50 % mas

+ 15% kvp = 15% kvp

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

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

“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”

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

MAINTAIN SAME OD FOR CHEST FILM 80 KVP , 5 MAS, 94 ?

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

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