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Image prod U4
| Question | Answer |
|---|---|
| What are the three purposes of a phototimer? | Achieving more consistent film densities, reducing repeat rates, and reducing patient exposure |
| The phototimer operates based upon the ability of radiation detection devices to convert radiant energy into what? | An electrical current |
| Where is the phototimer located? | behind or under the bucky tray |
| What are the two most common types of phtocells? | Ion chamber and photo multiplier tube |
| What induces an electrical current when gas atoms are ionized by impinging x-rays? | ion chamber/ this frees electrons which are attracted to a positively charged anode |
| What photocell uses a fluorescent screen to convert x-rays to light. The light strikes a photocathode & induces a current to charge an electromagnet. The magnet then pulls the switch & terminates the exposure. | photo multiplier tube |
| What device holds or stores electrical charges? | Capacitor |
| What device sets a maximum charge which the capacitor may hold? | Thyristor |
| When the charge in the capacitor reaches the max setting, what allows the charge to be discharged thrrough the circuit to terminate the exposure? | Thyristor |
| Where is the density control knob located? | On the console |
| When should the density control knob be used? | As long as the system is working |
| With the density control knob there will be how much of a reduction in density for each -1 step? | 25% |
| With the density control knob there will be how much of a increase in density for each +1 step? | 25% |
| Where is the paddle ion chamber used? | portables |
| Phototimers should never be used on anatomy that is what? | Too small or narrow to completely cover the photocell(film will be to light if you do) |
| If the phototimer is not centered to the part what happens to the film? | it will be to light |
| Phototimers should not be used on what? | complex contrasty anatomy such as sinuses |
| With phototimers the x-ray field must be collimated to what? | Anatomy of interest |
| What will excessive scatter do with the phototimer? | shut it off too soon and the film will be to light |
| Why should the correct photocell or combination of photocells be used? | So that the density levels are not averaged out |
| Phototimers should not be used on what type of anatomy? | That which is peripheral in relation to the x-ray beam |
| What should never be compromised for AEC? | Proper positioning |
| Why should AEC not be used on repeat exams and what is the exception? | Because the same error will be made unless you know what caused improper density the first time. |
| What cell should used for a pelvis or PA chest? | off center cell |
| What cell should be used for a spine and most body parts? | Center cell |
| What cell should be used for the heart? | ALL |
| The percentage of accuracy in repeated exposures should not be no more than what? | +/-10% |
| The percentage of linearity between phototimers in different room should not be more than what? | +/-20 |
| When sufficient intensity of light or x-rays is detected what is automatically increased or decreased as needed to maintain brightness? | kVp |
| Where is the brightness control knob located? | fluoro tower |
| What are the techniques that are pre-programmed into the control panel? | programmed exposures |
| What is the advantage of programmed exposures? | simplicity |
| What is the disadvantage of programmed exposures | lack of flexibility |
| What is the response time needed for the shortest possible exposure with an AEC? | 1/60 sec |
| Increasing kVp will do what to exposure time? | decrease it |
| Decreasing SID will do what to exposure time? | decrease it |
| Increasing mAs will do what to exposure time? | decrease it |
| What is the back up timer? | Maximum exposure time allowed/limit exposure time should there be an error |
| What is the maximum exposure time that is built into every machine? | 2 sec |
| According to government regulations a maximum phototimed exposure shall not exceed? | 800mAs/ tube limit |
| For repeatability test what should you get? | a phantom, two exposures and measure density with a densitometer |
| What is used to measure the patient? | Calipers |
| How does a phototimer work? | It converts radiant (x-ray) energy into an electric current. When it receives enough it terminates the exposure |
| What are the 3 needs for Standardization of technique | Consistent Quality, Reduced Patient Exposure and, Reduced Operating Costs |
| What are the 3 needs for Standardized EXPOSURE Charts | new technologists, students, and to help with trouble shooting |
| What are the three phases to standardization? | exposure factor, projections and processing procedures |
| List the 7 criteria of a Satisfactory Radiograph | 1Translucent Densities 2)Silver deposits on the image 3)Part fully penetrated 4)mAs factor for best overall density 5)Differentiating contrast between all densities 6)Details not obscured by scatter 7)Max sharpness/true shape |
| Explain how to adapt a chart from one institution to another: | Need 3 phantoms (Skull, Chest, Extremity); Use optimum kV & old technique in new hospital; Go Up or Down w/ mAs Apply same mAs % difference to all similar exams; Repeat process for each part (skull, Extremity, Chest) |
| What are the two most common types of charts? | fixed kVp and variable kVp |
| Why is the fixed kVp called optimum? | you will use just enough kVp to penetrate the part(most oftened used mAs varies kVp is constant) |
| On a variable kVp chart, kVp is varied according to what? | thickness of the part |
| What are the steps to creating a Fixed kVp chart? | 1st Step: Separate anatomical parts into Small, Medium, Large(85% of patients) 2nd Step: Get phantom & make 3 exposures to determine optimum density 3rd Step: Small patient reduce mAs 30%/ large increase mAs 30% 4th step: Repeat for chest & extremities |
| Exposure time or mA may have to be increased meaning more exposure to the patient and a chance of motion is a disadvantage of what? | fixed kVp |
| How do you use a Variable kVp Chart? | 2 kVp change for every cm change from average; Measure part+double it+add 40= new kVp for that part & select mAs from a guide |
| For every cm change how much is kVp changed? | increased by 2 |
| What are 4 advantages of Fixed kVp charts? | 1)kVp tends to be higherthan in variable 2)patient receives lower exposure 3)greater latitude for error 4)contrast more consistent |
| How much change in mAs does there have to be to have a visible change in density? | 30% |
| With the conversion chart from an adult, mAs is multiplied by what for infants(birth to 2)? | .25 |
| With the conversion chart from an adult, mAs is multiplied by what for preschool(2 to 6 years)? | .50 |
| With the conversion chart from an adult, mAs is multiplied by what for school age(6 to 12 years)? | .75 |
| With the conversion chart from an adult, mAs is multiplied by what for teenagers(>12)? | nothing |
| Conversion for plaster cast for dry, small extremity? | 2x's mAs or +15% kVp |
| Conversion for plaster cast for wet, small extremity? | 3x's mAs or +22% kVp |
| Conversion for plaster cast for dry, large extremity? | 3x's mAs or +22% kVp |
| Conversion for plaster cast for wer, large extremity? | 4x's mAs or +30% kVp |
| Conversion for plaster cast for half cast? | +50% mAs or +8% kVp |
| Conversion for plaster cast for pure fiber glass or air splint? | No change |
| For soft tissue what is the kVp and mAs set? | reduce kVp 15% and maintain same mAs |
Created by:
atesta0824
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