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PRE Exposure systems

AEC only gives what KVP
Pre Programmed Exposure control Gives set KVP and mAs
What is the only 2 factors that change during exposures size of the patient and time the exposure needs to take so therefore mAS
Suggested Starting point pre programmed control console
Exposure is determined by thickness of body part
What is used to measure patients caliper
Where are you supposed to measure the patient at the central ray
What was the first methodical approach to radiographic tech ( 1925) variable KVP radiographic tech
formula for kvp vs body thickness 2kv/cm
System developed in 1943 by Fuchs Fixed KVP radiographic tech chart
Fixed KVP system gave ability to create more consistent images. The machine was preset with KVP for each body part which decreased patient dose. ( measurement no longer as critical ) mAs changes due to thickness of patient
Fixed KVP separated patients into 3 groups small, medium, large
when using proper kvp for proper size of the body the mAs will change by and if its swollen we increase by 30% , 50%
High KVP is only applied to studies that dont require a lot of penetration but instead require long scale contrast.
what does High KVP decreases mAs and patient dose
what study is high kvp used only in chest X-rays and Ba contrast examinations
Anatomically programmed radiography system/ automatic exposure tech We use this often today. Not completely automatic because u have to be perfect with positioning or tech factors will not work
What are the 7 steps of establishing an exposure system 1) produce phantom images 2) select optimal phantom image 3) Extrapolate technique chart according to selected exposure system guidelines ( fixed KV, Variable KV, Other system) 4)perform phantom testing using extrapolated tech chart
continued steps of exposure system 5)perform clinical trials ( experimenting on the patient ( short period) ) 6)perform clinical fine tuning 7)continue ongoing fine tuning
how many phantom sizes should be available 3 ) small medium large
Under no circumstances clinical trial can be done before the phantom imaging
Fixed KV exposure system makes contrast constant
Based on KV system comes what concept optimal KVP concept
what is Optimal KVP maximum kvp that produce images with appropriate contrast
what does Variable KVP show high contrast short scale
fixed kvp lower contrast then variable kvp but still short scale
optimal kvp lowest contrast longer scale
what factor is completely out of our control wen were using AEC time
Abdomen optimal kvp 70-80
skull images 70-80 kvp
femur 70-80 kvp
c spine 70-80 KVP
L- spine 70-80 kvp 90 kvp L5-S1
when using breathing tech time has to be at least 3 seconds
what do we do to mAs when placing patient lateral we need to double mAs
spot film tripple mAs
humerus shoulder scapula 70-80
elbow 60-70
forearm 50-60
wrist 50-60
hand 50-60
fingers 50
knee 60-70
tib fib 60-70
ankle 60-70
foot 50-60
chest 110-120
barium studies single contrast 100 - 110
double contrast 90 - 100
iodinated contrast media 80-90
AEC when was it introduced and by who Russell Morgan 1942
what was the intent of AEC wanted to lower patient dose by reducing exposure time
what is the most critical aspect of using AEC system positioning
what are AECs often called photo timers
what happens during AEC convert radiant energy to an electrical signal/ current
ionization chamber location between patient and image receptor
the photo multiplier is placed behind image recepetor
Ionization chamber when xray goes through it ionizes the air creating + and - ions that are attracted to the appropriately charged diode creating a current which closes the circuit and terminated exposure
photo multiplier tube converts X-rays into light the photo cathode emits light photons which produces current and stops exposure
thyristor a device that precepts the amount of density we see on the image
AEC only controls exposure time, thus controlling mAs ( density)
what can we do to shorten time on an AEC increase ma and the time will automatically decrease
MRT minimum response time
MRT is a concern wen using high speed receptor high power generatior high ma stations small anatomical part
optimum MA high enough ma at a given focal spot size to minimize motion
back up time used to prevent overexposure to the patient in case AEC units fails
back up time should be set to 1.5 times longer then anticipated exposure time or 150 % Longer
if your image is under exposed double mas
if ur image is over exposed half mas
what size body part should the AEC should not be used on body parts that are to small
do not use AEC on clavicle mandible lateral scapula sternum sinuses
if the CR hits an ionization chamber instead of body part premature termination of exposure will occur
What are four principle types of charts 1. fixed kvp 2. hight kvp 3. variable kvp 4.automatic exposure
true or false using technique charts from books and manufactures are a good idea false
Created by: knt5411