Lecture 3

Question 1

CONTROL PANEL:

Answer 1

1. On/off switch
2. Exposure timer
3. mA Selector
4. kV Selector
5. kV meter
6. Rotor Switch
7. Exposure Switch
8. Accessory Controls
9. AEC

Question 2

• Many manufacturers produce radiographic
  equipment with different characteristics.
• Despite variations, most x-ray generators
  have common controls for radiographer
  selections.

Answer 2

Control panel:
Equipment Variability:

Question 3

Control Panel Features:

Answer 3

• Modern x-ray generators often have
  sophisticated computerized panel displays.
• Radiographers need advanced knowledge
  and understanding to operate the
  equipment.

Question 4

• Connects electrical power to the radiographic
  generator control device.
• Prepares the generator unit for x-ray production.
  Location and Familiarity:
• Usually part of the control console.
• Radiographers must be familiar with its location

Answer 4

ON/OFF SWITCH

Question 5

• Located on the control panel console.
• Determines the length of time x-rays will be
  produced.

Answer 5

EXPOSURE TIMER

Question 6

Types of Exposure Timers:

Answer 6

• Mechanical
• Synchronous
• Electronic

Question 7

• Simple type, like a spring-set dial.
• Timer knob is turned to a specific
  mark, winding a spring.
• During exposure, the spring
  unwinds according to the set
  time.
• Limited to a shortest setting of
  1/10 second.

Answer 7

MECHANICAL TIMER

Question 8

• More advantageous for
  radiographic imaging.
• Reduces issues with motion of the
  body part being examined.

Answer 8

MECHANICAL TIMER
Advantages of Shorter Times:

Question 9

• Motor-driven devices.
• Utilize the 60-Hertz alternating current in the United States.
• Exposure settings are intervals related to 1/60 second (e.g.,
  1/30 sec, 1/20 sec, 1/10 sec).
• Shortest available time is 1/120 second.

Answer 9

SYNCHRONOUS TIMERS

Question 10

ELECTRONIC TIMERS
Advantages:

Answer 10

• Exposure times of less than 1/120 second.
• High reliability.
• Less prone to malfunctions.

Question 10

• Most common type in radiographic equipment today.
• Designed with sophisticated, complex circuitry.
• Considered the most accurate of exposure timers.

Answer 10

ELECTRONIC TIMERS

Question 11

EVALUATION OF TIMERS
Importance of Exposure Time:

Answer 11

• Controls the amount of radiation the patient is exposed to.
• Timers must be periodically evaluated for accuracy.

Question 12

Evaluation of Timers:

Answer 12

1. Spinning Top Device
2. Oscilloscope
3. Pulse Counter Device

Question 13

• Single-phase, full-wave rectified units using a device
  called the spinning top.
• Consists of a round disk (approx. 3 inches in diameter)
  with a small hole near the edge, resting on a smaller
  circular pedestal.
• Placed on an x-ray cassette containing unexposed film.
• Set spinning with a flip of the fingers; exposure is made
  while it spins.

Answer 13

SPINNING TOP DEVICE

Question 14

EXPOSURE TEST PROCEDURE:
* Select exposure factors: 1/__, 1/__, or 1/__ second.
* Image produces dashes (or dots).
* Number of dashes relates to the exposure time:
* 1/&_ second: _ dashes
* 1/30 second: _ dashes
* 1/__ second: __ dashes
* For single-phase, full-wave rectified units, one dot
per 1/___ second of exposure.
* Calculate expected dots: multiply exposure time
(seconds) by 120.

Answer 14

EXPOSURE TEST PROCEDURE:
* Select exposure factors: 1/60, 1/30, or 1/10 second.
* Image produces dashes (or dots).
* Number of dashes relates to the exposure time:
* 1/60 second: 2 dashes
* 1/30 second: 4 dashes
* 1/10 second: 12 dashes
* For single-phase, full-wave rectified units, one dot
per 1/120 second of exposure.
* Calculate expected dots: multiply exposure time
(seconds) by 120.

Question 15

• Three-phase and capacitor discharge units do not produce the same pulsed radiation; spinning top is not suitable for these.
  To test a three-phase generator:
• Use a calibrated oscilloscope.
• Connect oscilloscope to the primary voltage of the step-up
  transformer.
• Compare actual exposure time with selected time.

Answer 15

Oscilloscope

Question 16

Used for both single-phase
and three-phase
generators.
* Placed in the primary x-ray
beam.
* Counts and records pulses
for evaluation.

Answer 16

Pulse counter device

Question 17

• Controls the amount of electrical current flowing through the cathode
  filament.
• Current flow through the cathode filament produces heat, causing
  thermionic emission.
  Thermionic Emission:
• Produces a “space charge” as electrons break away from the hot cathode
  filament.
• During exposure, electrons in the space charge move from the cathode to
  the anode

Answer 17

Milliampere Selector

Question 18

mA SELECTIONS:
* Radiographic units offer mA selections ranging from __ to
____ mA.
Focal Spot Size Determination:
* In many general radiographic units, the selection of mA
determines the focal spot size.
* “L” (Large) indicates selections using the ______ focal spot.
* “S” (Small) indicates selections using the _____ focal spot

Answer 18

mA SELECTIONS:
* Radiographic units offer mA selections ranging from 25 to
2000 mA.
Focal Spot Size Determination:
* In many general radiographic units, the selection of mA
determines the focal spot size.
* “L” (Large) indicates selections using the large focal spot.
* “S” (Small) indicates selections using the small focal spot

Question 19

• Located on the control console, provides information to the
  radiographer.
• Indicates the total amount of electrical current passing through the
  x-ray tube (from cathode to anode) during exposure.
  Total Tube Current (mAs):
• Calculated as the product of milliamperes (mA) and exposure
  time (seconds).
• mAs = mA x Time (seconds)

Answer 19

mA meter/mAs meter