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PRE 1
PRE Exposure systems
| Question | Answer |
|---|---|
| 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 |
| T SPINE | 70-80 KVP LATERAL IS BEST IMAGED WITH BREATHING TECH |
| 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
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