Chpt. 9 Practice Test Questions-RI | Quizlet

What is the function of a phototimer?

Uses fluorescent light paddles to convert light into energy and terminate exposure when a large charge has been received

What is a mAs readout?

The actual amount of mAs used for that image is displayed immediately after the exposure.

What is backup time?

Refers to the max. amount of time the x-ray exposure will continue when using a AEC system. It is 150-200% of the expected time.

When does the x-ray exposure terminate with AEC?

When the predetermined amount of radiation has transmitted through the patient and reached the cells.

Where are the light paddles in relationship to the IR on phototimer AEC units?

Under the IR

Where is the ionization chamber in relation to the IR on a AEC unit?

Above the IR and under the patient

What are the advantages of a fixed kVp/ variable mAs technique chart?

Part measurement is less critical, increased accuracy w/ a range of procedures, more consistent image quality, and part penetration assured.

What is a good way to minimize the effects of movement during a radiographic study?

Using a short exposure time

What exposure factors are variable on an AEC system?

kVp, mAs, IR type, grid, and SID

What is the minimum response time?

Shortest exposure time that the system can produce a specific dose. (1 ms for modern systems)

What is density adjustment?

Allows the radiographer to adjust the preset radiation detection values in increments of 25% appear as -2, -1, +1, +2

What response does the AEC system have for an increase in patient thickness?

The exposure time will lengthen in order to reach the preset exposure

What percentage is used for backup time?

150-200% of expected time

What technical factor is used to control contrast?

kVp

What is the pre-set backup time on an AEC unit?

Max. 600 mAs

How would an image be underexposed or overexposed with an AEC unit?

If the patient was incorrectly positioned or the wrong cells were selected.

What information can be found on a technique chart?

Exposure factors (kVp, mAs, IR type, grid, and SID), collimation, AEC detector selection, and patient shielding

If an AEC cell is directly exposed how will the image appear?

Underexposed

What is the importance of mAs readout?

Allows the radiographer to make appropriate adjustments when images are suboptimal

What factor does the radiographer lose control of when using an AEC unit?

Time

What is the reason behind development of the AEC?

Protect patient from overexposure in case of an error while also maintaining image quality

What are the different parts of a phototimer AEC system?

Photomultiplier tube or photodiodes, light producing screen and light paddles

What are the different parts of an ionization chamber AEC system?

Ion chamber, electrical wire, and timer

What is an anatomically programmed technique?

A programmed set of exposure factors that can be used for specific anatomy

What is the reason for a technique chart?

They standardize manual or AEC exposure factors for each exam to allow consistent image quality

What are calipers used for?

To measure part thickness

What equipment needs a technique chart?

Each x-ray tube needs its own (table and upright bucky and portable)

What chart technique is part measurement most important?

Variable kVp/ fixed mAs chart

What is the goal of kVp in the fixed kVp system?

To ensure penetration of the part without diminishing contrast

For a variable kVp exposure chart, how much do you adjust kVp for measurement changes?

kVp is increased by 2 for every 1 cm of increase in part thickness

What departmental standards need to be established prior to making a technique chart?

Standardization of exposure factors and when accessory devices should be used (I.E. grid vs non-grid on a knee)

How can you ensure an effective technique chart development?

Accurate measurement of part thickness, a good quality control system for all equipment, and establishment of department standards

What technique chart is best for pedi patients or small extremities?

Variable kVp and fixed mAs

How is mAs adjusted on a fixed kVp and variable mAs chart?

Adjust mAs by a factor of 2 for every 4-5cm of thickness

How do techniques need to be altered for pedi patients (6 years and younger)?

Lower kVp and mAs, shorter exposure time, no grid if possible, conservative use of AEC

Why is accurate selection of wall vs table bucky important for AEC systems?

If the wrong bucky is chosen it will not receive the radiation required to terminate the exposure and the back up time will initiate.

How does exposure time vary with part thickness?

Exposure time is increased when kVp is decreased, if mA and time can be selected separate then increasing mA will decrease exposure time, which factor is adjusted for part thickness will affect exposure time

How does the underexposure or overexposure effect patient dose?

Both will likely result in increased patient dose, when an image is underexposed it may need to be repeated resulting in excessive dose

How is IR exposure affected by a change in kVp on an AEC system?

Higher kVp results in higher IR exposure

What is an additive and destructive condition?

Additive increases absorption and destructive decrease absorption. See table 8-5 on page 231

What are specific examples of a destructive disease?

SBO, free air, emphysema, pneumothorax, gout, osteolytic mets, multiple myeloma, pagets dz (early), atrophy, emaciation, and malnutrition

Tabletop vs bucky exams

Tabletop does not use AEC (make sure not to be selected on AEC)

Buckys have the AEC detectors

Child vs Adult measurements and variations in techniques

Children require lower kVp/mAs ,no grid, conservative use of AEC