Physics Test part 5

Question 1

Synchronous timer

Answer 1

Found on older single-phase units, they use a small electric motor that rotates at 60 rps.
They are accurate down to 1/20 s and minimum possible exposure is 1/60 s

Question 2

) Impulse timer

Answer 2

Measures impulses (or pulses) instead of time and are usually paired with synchronous timers in the same unit to measure the short exposure times.
Impulses/120 = time as a fraction.

Question 3

Electronic timer

Answer 3

Most commonly used in modern equipment, and accurate down to 1/1000 s (1 ms).
Come in 2 basic types:

Question 4

Resistor/capacitor combination

Answer 4

a capacitor continues to collect a voltage and holds it during the time that it is connected to a voltage source.

Question 5

Digital (not readout)

Answer 5

Microprocessor linked with a SCR that calculates the length of time the current will need to flow through the x-ray tube.

Question 6

Mechanical timer

Answer 6

Spring driven timer used in dental and portable x-ray machines.
Not accurate with times less than ½ s.

Question 7

mAs timer

Answer 7

Monitor the product of mA and time on the secondary side of the step-up transformer.
This simplifies the operation of the machine but takes away the flexibility from the operator.

Question 8

Anatomically programmed units

Answer 8

A digital microprocessor in the control console is pre-programmed to deliver proper technique for a particular exam.
Operator only has to select kVp, exam, and patient size.

Question 9

Automatic Exposure Control or AEC

Answer 9

Measures the proper amount of radiation for a particular radiograph and terminates the exposure one this has been reached.
There are 2 main parts to an AEC system:

Question 10

Sensors or Cells

Answer 10

Detects the x-rays that have passed through the patient and produces a corresponding electric current that is proportional to the quantity of x-rays that are detected.

Question 11

Photodetector or photocell

Answer 11

this was the first type or sensor developed for AEC systems.

Question 12

Ion chamber

Answer 12

made of a radiolucent material and placed between the grid and the front of the IR

Question 13

Solid state detector

Answer 13

most sensitive and expensive, and can placed between the grid and IR.

Question 14

) Comparator

Answer 14

Receives the current that is sent by the sensor.
A capacitor stores up a voltage as long as the current flows.

Question 15

Timer Accuracy

Answer 15

Regardless of the type of timer system, accuracy in terminating the exposure is critical.

Question 16

Digital Timer

Answer 16

records the exact amount of time it is being exposed by x-rays.

Question 17

Spinning top test

Answer 17

When the top is placed on top of an IR and an exposure taken, a series of dots or a solid arc will appear on the processed image that can be used to determine timer accuracy.

Question 18

1Φ equipment

Answer 18

dots will appear on image.

Question 19

½ wave correct number of dots

Answer 19

exposure time x 60

Question 20

Full-wave correct number of dots

Answer 20

exposure time x 120

Question 21

3Φ equipment

Answer 21

since x-ray production is constant, dots will not appear in the image but rather a solid arc. Correct arc size = exposure time x 360

Question 22

Too large an arc

Answer 22

indicate that the timer is too slow in stopping the exposure.

Question 23

Too small an arc

Answer 23

the timer is stopping the exposure too quickly.

Question 24

For high frequency units

Answer 24

a digital mAs meter is used to determine the accuracy of the microprocessor circuit in terminating the exposure.

Question 25

Power Circuit, High Voltage Section or High Voltage Generator

Answer 25

Converts the relatively low voltages supplied by the power company into the kilovoltages necessary to produce diagnostic x-rays. This section contains the step-up and step-down transformers as well as the rectifiers.

Question 26

High voltage or high-tension transformer

Answer 26

A large step-up transformer (usually shell-type) that increases the voltage selected by the autotransformer to the desired level.

Question 27

mA/mAs meter

Answer 27

Indicates the amount of current that is passing through the x-ray tube during exposure.

Question 28

analog

Answer 28

Uses a ballistic analog meter to register short exposure times on the meter

Question 29

digital

Answer 29

flashes digital readout of mAs

Question 30

Never leaves the 0 point during exposure

Answer 30

no current has passed through the tube, so no x-rays were produced.