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How many centimeters are equal to 1 inch?
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How many cm are in 40"?
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| Question | Answer |
|---|---|
| How many centimeters are equal to 1 inch? | 2.5 cm |
| How many cm are in 40"? | 100 cm |
| How many cm are in 72"? | 180 cm |
| What does distance affect? | density, size distortion and sharpness |
| What does FFD mean? | focal film distance |
| What does TFD mean? | target film distance |
| If you increase SID what happens to magnification? | decreases |
| If you increase SID what happens to density? | decreases |
| If you increase SID what happens to sharpness of detail? | increases |
| What affect does SID contrast? | SID does NOT affect contrast |
| In order for image contrast to change, what has to happen? | The ratio between compton and photoelectric interactions has to change |
| If you have a large body part, do you have more or less penumbra? | more penumbra |
| Does penumbra increase or decrease when SID is decreasd? | increases |
| For magnification to change, what has to happen? | Umbra and penumbra have to grow at the same rate. |
| How does SID affect shape distortion? | SID NEVER affects Shape distortion |
| How do you prevent shape distortion? | beam/ part/ film alignment |
| How much change in SID do you need in order to get a visible change in density? | 20% or 10" |
| How much change in distance do you need to require an adjustment in technique? | 20% or 10" |
| The intensity of the radiation is inversely proportional to the square of the distance is what law? | Inverse Square Law |
| What does the inverse square law predict? | density |
| The change in technique should be equal to the square of the change in distance is what law? | Square Law |
| What is another name for the Square Law? | Density Maintainance Formula |
| mAs is directly related to the square of the distance is what law? | Square Law also called the density maintainance formula |
| What is the Air Gap Technique used for? | Combat image fog |
| How many inches of OID are used for the Air Gap Technique? | 6"-8" |
| If you increase OID, what happens to contrast? | Contrast increases |
| If you increase OID, what happens to density? | Density decreases |
| When OID is increased, what should you do to SID? | increase SID to decrease magnification |
| Does OID affect distortion? | yes, size distortion |
| What factor should be adjusted when you have large OID or long SID | mAs |
| what is the formula to determine magnification? | magnification= SID/ SOD |
| Which has a greater affect on magnification SID or OID? | OID |
| What does AEC mean? | Automatic Exposure Control |
| What are the two types of AEC? | Photo-multiplier and Ionization Chamber |
| What is the more connon type of AEC? | Ionization chamber |
| What year was AEC developed? | 1942 |
| What are the advantages of AEC? | reduce inconsistancy, provides uniform density, radiologists are able to read uniform and consistant radiographs |
| What is the variable in AEC machines? | time mA and KVp are set |
| What does photomultiplier use to terminate the exposure? | Light |
| What does Ionization chamber use to terminate the exposure? | radiation |
| Is photomultiplier entrance type or exit type? | Exit |
| What tells where to center with AEC? | photo cells |
| Is Ionization chamber measured before or after the intesifying screens? | Before |
| Is ionization chamber entrance or wxit type? | entrance |
| Sufficient density is obtained when these fill and terminate the exposure. | Thyristor capacitator |
| What are modern ionization chambers formed from? | aluminum sheets |
| Why is higher KVP used in AEC? | the give a wider lattitude (which decreased the amount of repeats) |
| What is responsible for averaging out density? | photo cells |
| Where do you need to center for AEC? | must be centered over photo cells (choosing the proper cell is crucial) |
| The time it takes for the exposure to teminate is called? | reaction time |
| What is the typical minimum exposure time? | .002 seconds for new units .02 seconds for older units |
| What is it called when the AEC unit first detects radiation and then responds? | Minimun Response Time ( the shortest exposure time) |
| What is the longest amount of time an exposure can last before it is terminated? | Backup Time (patient protection) |
| How is the backup time determined? | Double the time used for an ideal radiograph (takes the reaction time and doubles it) |
| What is the most common error when using AEC? | Choosing the wrong IR (wall bucky vs. table) |
| What are the limitations of AEC? | selection of cell, can not use on extremities, can not use on table top exposures |
| What is AEC best for? | Trunk of body, femur, neck and cranium with the exception of the sinuses |
| Who is the biggest jerk in the class? | Joe |
| What are the 2 main factors of resolution? | Contrast and sharpness |
| What is resolution? | The ability to see 2 adjacent structures as separate structures within the image. |
| What are other terms that mean sharpness? | geometrical detail, recorded detail, sharpness of detail, definition |
| How are resolution and sharpness related? | directly proportional |
| How are distance and definition related? | They are inversely proportional |
| If you increase divergence, what happens to sharpness? | decreases |
| What are the visibilty factors? | density, contrast and noise |
| What are the recognizability factors? | Shape distortion (elongation and foreshortening) Size distortion (magnification) and Sharpness (detail) |
| How is FFD related to sharpness? | directly.. Increase FFD (also called SID) you increase sharpness |
| How is OFD related to sharpness? | indirectly.. Increase OFD (also called OID) you decrease sharpness |
| Do intensifying screens increase or decrease detail? | decrease |
| Do intensifying screens increase or decrease patient dose? | decrease |
| Is film sentitive to light or x-rays? | light |
| How does blur affect density? | NEVER affects density |
| What is the only thing focal spot size affects? | DETAIL (sharpness) |
| How do you know if you have motion of poor screen contact? | Motion would show all over the radiograph, poor screen contact shows as a localized blur that usually starts at the corners. |
| What are 4 types of motion? | Peristalsis, heart motion, breathing, and voluntary.. breathing can be voluntary or involuntary |
| What is the average respirations per minute for the average adult? | 16-18/ min |
| How do you minimize motion? | short exposure time, communication, and use of restraints |
| What affect does motion have on sharpness? | decreases it |
| How does slight motion show on the radiograph? | blur along the peripheral edges of the anatomy |
| How does severe motion show on the radiograph? | blur accross the whole image |
| What affect does motion have on contrast? | decreases contrast |
| Is motion considered a primary controller of image contrast? | No.. it is the only variable that reduces contrast without the affect of scatter |
| How does motion affect shape distortion? | gives a false image categorized as noise not shape distortion. |
| Does motion increase or decrease penumbra? | increase |
| What is the highest time you should use for a child? | 1/30th of a second |
| What type of patient is the most likely to cause motion? | pediatrics |
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