Lesson 1, Topic 1
In Progress

X-Ray Control Panel

April 11, 2024

X-Ray Control Panel

Learning Objective: Explain the components of the x-ray control panel.

X-ray control panels and the labels of their components vary depending on the manufacturer (FIGURE 37.16). Newer, computerized models have digital controls and readouts. Some control panels are operated by touch control on a computer monitor. These computerized consoles automatically perform some functions that were previously done manually. All control panels provide some means for selecting kVp, mA, exposure time, and focal spot size. There will also be switches to control power to the console and the Bucky, plus rotor and exposure switches.

Power Control

Learning Objective: Describe how the power is controlled.

The on/off switch on the console corresponds to the main power switch in the schematic diagram (see FIGURE 37.13). This switch controls the power to the control panel and the entire x-ray generator.

Milliamperage Control and Exposure Time Control

Learning Objective: Differentiate between the milliamperage control and the exposure time control.

Conventional panels have an mA selector, which provides options for choices of mA, known as mA stations. Each cathode filament in the x-ray tube is connected to specific mA stations. The filament and its associated focal spot are chosen automatically when the mA is selected. Usually, mA stations of 200 to 250 or less employ the small filament; the large filament supplies mA requirements of 250 or more. Digital readouts on the console will state the mAs setting and the exposure time.
All control consoles contain an exposure timer, whether it is set directly by the operator or not. The time set is the length of time the x-rays are turned on. Computerized controls may select the exposure time using an electronic timer. Electronic timers are more capable of ultrashort exposure times (1 ms or less).

Kilovoltage Control

Learning Objective: Describe the kilovoltage control.

Computerized controls have a digital read-out for the kVp setting and arrow buttons that can be pressed to increase or decrease the kVp.

Bucky Control

Learning Objective: Describe the Bucky control.

The Bucky is a moving grid used for radiography of larger body parts (FIGURE 37.17). The Bucky device incorporates a motor to oscillate the grid. The operator will select the wall Bucky, the table Bucky, or turn off the Bucky on the control panel. The grid will be turned off for tabletop exposures or removed for nongrid exposures.

Manual Exposure Time

Learning Objective: Describe the manual exposure time.

Every x-ray exposure that is made will have three exposure factors set on the control panel: kVp, mA, and exposure time. These factors are typically selected manually by the operator.

FIGURE 37.16  The control panel or control console. Exposure controls are convenient pushbuttons with a visual display of selected exposure factors. In this version, exposures may be made using prep and expose buttons. From Adler AM, Carlton RR: Introduction to radiologic and imaging sciences and patient care, ed 7, St. Louis, 2020, Saunders.

Automatic Exposure Control

Learning Objective: Describe the automatic exposure control.

Many x-ray machines provide AEC, which terminates the exposure when a certain quantity of radiation has been detected at the IR. The AEC system is a complex microprocessor circuit built into the generator and x-ray table and linked directly to the mA, kVp, and exposure time controls. When activating the AEC on the generator, the mA and kVp values are set, as usual; however, the exposure time is automatically determined.
A sensing device is located under the table and detects when a given amount of x-ray photons has been reached. When this happens, the sensor will terminate the exposure. The sensors under the table are referred to as detectors or sensors. The AEC system may contain three or five detectors, so the operator must choose which detectors to activate (FIGURE 37.18). Determining which sensors to activate depends on the anatomy being imaged. The kVp and mA are set manually. When using the AEC, patient positioning must be accurate. Otherwise, the sensor could cause overexposure or underexposure.

Anatomically Programmed Radiography Control

Learning Objective: Describe the anatomically programmed radiography control.

One of the most widely used electronic functions for exposure control is anatomically programmed radiography (APR). With this function, a microprocessor controls the exposure factors. The kVp, mA, time AEC detectors, body habitus, Bucky, and SID will be selected automatically by selecting the body part and the projection. For example, if there is an order for a pelvis, the operator selects “pelvis” and then selects “AP Projection,” and the exposure is ready to be made. The operator does have the ability to override the automatic factor selection for specific patient situations. The AEC system can be used with the APR system. With proper and accurate positioning, APR systems can produce excellent images and fewer repeat examinations.

Exposure Controls

Learning Objective: Describe exposure controls.

The control to make an exposure is located on the control console. Two separate switches are needed to make an exposure. The first is the rotor switch, which may be labeled “Rotor,” “Prep,” or “Ready.” This switch has two functions. When activated, the rotating anode begins to spin, and heat is applied to the filament to create electrons via thermionic emission. When this switch is held in the “on” position for a few seconds, a signal will indicate that the tube is ready for exposure. When the x-ray tube is ready, the operator initiates the exposure by holding the rotor switch and pressing a second switch, the exposure switch. An exposure indicator (EI) on the control panel will indicate when the timer has terminated the exposure. Only then are the two buttons released. Most control panels have an exposure light, usually red, that is on during the exposure. When the light goes off, the exposure is complete, and an audible beep will be heard.

FIGURE 37.17  Bucky tray holding the IR. The Bucky tray is centered to the x-ray table under the grid. From Adler AM, Carlton RR: Introduction to radiologic and imaging sciences and patient care, ed 7, St. Louis, 2020, Saunders.

FIGURE 37.18  Automatic exposure control (AEC) system with upright Bucky unit. The locations of three AEC detector chambers are outlined on the face of the device. From Fauber TL: Radiographic imaging and exposure, ed 3, St. Louis, 2009, Mosby.

Setting the Control Panel on a Traditional Console

These are the steps for setting the controls and making exposure on a conventional console:

• Select mA.
• Select kVp.
• Set the Bucky.
• Activate and hold the rotor switch.
• Observe the exposure indicator to validate exposure and determine when it is complete.
• Release the rotor and exposure switches.