Imaging Principles Unit 2

Eddy Clifford Jerman

“father of radiology”, American inventor and early expert in the techniques of radiology. one of the first people to focus on the details that created a quality xray like exposure and positioning

anatomically programed, fixed KVP, variable KVP, proportional anatomy approach, AEC

what are the 5 different types of technique charts?

anatomically programmed technique chart

technologist uses a control screen to select the anatomic part, projection, and relative size (S, M, L) of the part to be imaged. Unit uses microprocessor data to select KVP and mAs.

critical

it is ___ that all radiographers use a particular technique chart by the same method and in exactly the same manner

phantom images, optimal image, build chart, phantom testing using chart, clinical trials, clinical fine tuning, ongoing fine tuning

what are the steps to building a technique chart?

phantom images

series of test exposures made using a variety of technical factors above and below the average levels to determine the optimal quality image

fixed KVP system

optimum KVP is selected and remains constant for the given body part and thickness

optimum KVP

maximum KVP that achieve full penetration of all anatomy of interest resulting in the most desired level of contrast

uniform contrast, wide exposure latitude, lower mAs prolongs tube life

advantages to a fixed KVP system

lower contrast images and more scatter

disadvantages to a fixed KVP system

low KVP because low scatter

high contrast is caused by

high KVP b/c increased scatter

low contrast is caused by

optimal KVP

maximum KVP level that will produce images with appropriate contrast and ensure proper penetration

Produces lower contrast (wide latitude) and the minimum patient dose

5 cm rule (fixed KVP)

for every 5 cm of thickness in a body part, mAs needs to be halved or doubled

30%

On old school film what was the minimum change in mAs between steps?

Variable KVP charts

KVP is changed based on measurement of body part thickness and mAs is specified for each body part

allows for small changes; changes contrast

Advantages then disadvantages of variable KVP systems

15% rule (variable KVP)

changing KVP by 15% gives the appearance of doubling/halving mAs so if KVP increases mAs should be halved and if KVP decreases mAs should by doubledh

historical development example

2 KVP per CM (2kvp x CM) + minimum KVP

stepped variable KVP system

combination of adjusting kvp and using the 4-5 CM rule of doubling mAs

proportional anatomy approach

A proper radiographic technique can be derived from the known technique of another body part (ex. 1 foot is about 2 hands so double technique used for hands to get the technique used for foot)

AEC system

selection of exposure time factors are used thereby mAs selections are eliminated

professional judgment must still be used for proper mA kVp and distance chosen

AEC

help the radiographer in producing CONSISTENT images from patient to patient regardless of the size resulting in

decreased repeat rate

decreased patient exposure

increased department efficiency

Automatic exposure cntrol

tech sets kVp and mA initiating the exposure. Time is determined by the machine and stops when IR has sufficient density terminating the exposure

less then 5 mAs or on a free plate

when can AEC not be used

photo timers and flat ionization chambers

what are the two types of AEC devices?