Spot Filming

• Spot Film Cassettes• Uses conventional radiographic cassettes.• Bypasses image intensifier for direct exposure.• Uses mA > 100 X that of photofluoro camera.

Spot Filming• Spot Film Cameras

• Image the output phosphor of II.• Same mA as fluoroscopy (1-3 mA

typically).• Exposes one frame/exposure.• Uses 70, 90, or 100/105 mm film size.• As you increase film size, increase

image quality and patient dose.• Method of choice for spot filming

compared to spot film cassettes.

Spot Filming• Framing (matching II output size to film

area)

Underframing Exact Framing

P. 31

• Fluoro image < frame

• Should be avoided

• Int. image = small dimension of frame

• No part of image lost

• Only 58% of frame used

Overframing Total Overframing

• Image circle > short film dimension

• Part of image lost

• Circular image = diameter of frame

• All of film used

• 39 % of image wasted

Cinefluorography

• The process of recording fluoro images on movie (cine) film.

• Film sizes– 16 and 35 mm– The larger the film size, the greater the

resolution and greater the patient dose.

12.6 mm

30 mm

Cinefluorography

• Synchronization• Camera shutter timed to the same

frequencyas the x-ray pulses.

• Shutter open only during x-ray pulses.

• Framing Frequency• Number of exposed frames/second.• Divisions or multiples of 60 Hz line rate.

• Examples: 7.5, 15, 30, 90, 120 frames/second.

Cinefluorography, cont’d

• Framing Frequency• Patient Exposure

• Directly proportional to framing frequency.

P. 30

Cinefluorography, cont’d

• Framing Frequency• Patient Exposure Conversions

• 2000 mR/frame X 1 mR/1000 mR = 2 mR/frame

• 2 mR/frame X 30 frames/second X 60 seconds/minute = 3,600 mR/minute

• 3,600 mR/minute X 1 R/1000 mR = 3.6 R/minute

P. 30

Cinefluorography, cont’d

• F-number• Number indicating the ratio of the focal

length of the camera lens to the diameter of the lens.

• F-number = Focal Length of Lens/Diameter of Lens

• The smaller the f-number = more light into the camera and less patient exposure.

P. 30

F-num =50 mm / 20 mm = F 2.5

Focal length of lensLe

ns D

iam

eter

The smaller the f-number - the larger the aperture opening.

The larger the f-number - the smaller the aperture opening.

Iris diaphragm

Spot Film and Cine Cameras

• Beam and image size match within 3 % of SID

• A small aperture (large f-number) will require greater patient exposure but result in low noise image.

• Patient entrance exposures of 50 - 150 rads or more.

P. 110

Structural Fluoro Room Shielding Provisions

• Barriers• Primary

• A barrier to attenuate the useful beam to the required degree.

• Secondary• Used to attenuate stray (scattered and leakage) radiation

to the required degree.

• Useful Beam • Radiation that passes through window, aperture, or cone.

• Stray Radiation • Leakage and secondary radiation. No useful purpose.

p. 121

Primary/Secondary Barriers

(Source: Principles of Imaging Science and Protection. Thompson, Hattaway, Hall, Dowd, 1994)

Exception would be in R/F room where all walls would be a primary barrier.

Structural Fluoro Room Shielding Provisions

• Tube Leakage• Maximum exposure @ 1 meter is 0.1 R/hour.

• Half-Value Layer (HVL)• Thickness of material that reduces beam

exposure rate by half of original value.

• Tenth-Value Layer (TVL)• Thickness of material that reduces beam

exposure rate to 1/10 of original value.

0

0.05

0.1

0.15

0.2

0.25

0.3

1 2 3 4 5 6

HVL Lead (mm)

40 kVp

60 kVp

80 kVp

100 kVp

125 kVp 150 kVp

1 meter

0.1 R/hr. @ 5 mA

Maximum permissible =

Radiation Areas• Radiation Area

• Any area where whole body dose could be = or > 0.005 rem/1 hr. at 30 cm from source.

• High Radiation Area• Any area where whole body dose could be = or > 0.1 rem/1 hr.

at 30 cm from source.

• Controlled Area• Any area where radiation safety rules enforced.

• Unrestricted Area• An area in which access is neither limited nor controlled.

Radiation Areas, cont’d.

• Restricted Area

• Any area where access is limited by thelicensee to protect individuals against undue risks from radiation exposure.

Unrestricted/Controlled Areas

QC-Semi-annual checks

Flare

Image Lag

mAs Linearity

Exposure ReproducibilityPhototimersCamera Exposures Spot FilmFilm

Cine Film

Exposure

Spot

Film

-

Cin

e Im

age

Beam LimitationResolution –

Distortion

Cine Film

Proce

ssorGrid

Alignment

Linea

rity

Image Quality

Film-Screen Contac t

Exposure Timer

Cameras

Spot film

Film

Cine Processo

r

• Video Tape

•Video Disc

•Electronic Radiography

• AdvantagesInstant ReplayNo increase in patient exposure

• DisadvantagesPoor image qualityFixed framing rate- 30 frames/sec.

• AdvantagesLast image freeze “sticky fluoroscopy”Instantaneous imagingShort exposure times95% dose reduction during fluoroVariable framing rates – 1-30 frames/sec.Multiple image storageRandom access of images

• DisadvantagesNone significant

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