Chapter 8 Medical Imaging equipment

Diagnostic yield

The amount of clinically useful information on a diagnostic image

Diagnostic Efficacy

The accuracy of diagnostic information on a medical image is its diagnostic efficacy

X-Ray Machine Design Features

-X-ray tube and x-ray tube support

-Collimator assembly

-Radiographic table

-X-ray generator and control

-Upright image receptor

X-ray Tube Design

-Tube is inside a lead-lined metal housing

-Made of heat tolerant, Pyrex glass with high vacuum

-Produces X-radiation when high-energy electricity passes through the tube

-X-radiation exits the tube through a window in the housing and is directed toward a patient

Collimator assembly

-Controls the size and shape of the x-ray field directed toward the patient

-Projects a high-intensity light field on the patient, which represents the area of the x-ray field exposure

-May be manual or automatic (PBL) positive beam limitation

Radiographic Table

-May be fixed height or variable height

-Typically has a four-way "floating" tabletop

-Tabletop is highly radiolucent.

-Some table designs permit a variable-speed, tilting capability.

tilting radiographic table

These designs will tilt the table from horizontal position to vertical upright position to Trendelenburg.

-Most tables have four-way tabletop travel.

-These tables typically do not have variable height capabilities.

Tilting Radiographic table

A tilting radiographic/fluoroscopic table in the full upright position

Bucky Assembly

-Consists of a receptor tray and radiographic grid

-Tray holds receptor tightly in position and is centered to longitudinal axis of table.

-Radiographic grid oscillates during exposure to blur out the lead grid lines.

-Used with all image receptor systems

-Film-screen

-Computed Radiography

-Flat panel DR

Generator Control

Control console is the interface between the radiographer and the sophisticated electronics of the x-ray machine.

Console consists of:

-Main power switch

-Selection of exposure factors

-Exposure button

-Audio and visual display of actual x-ray exposure

-Visible display of all exposure factors

Generator Control

Most are microprocessor controlled and use a simple computer interface.

Permits selection of all exposure factors

-mAs

-kVp

-Focal spot size

-Automatic exposure control (AEC)

oAnatomical programming (APR)

Newer systems may be integrated into a digital radiographic (DR) detector.

Exposure Technique

-Consists of three key factors: mA, time, kVp

-Automatic exposure control (AEC) may be optional.

-Focal spot size selection

-Exposure technique selection may be anatomically programmed.

Exposure Technique Selection

-Generator consoles permit selection of kVp, mA, exposure time (S), and mAs.

-May be operated in mAs or timer mode

-Newer systems feature APR.

-Technique selection is critical to good radiography.

x-ray tube supports

Two basic designs

Facilitate easy and efficient positioning of the X-ray tube assembly around the patient in any orientation

Capable of various motions depending on need

Ergonomically friendly

Aesthetically pleasing and not intimidating to patients

Two types of x-ray tube support

Floor mounted tube stands and ceiling-suspended tuber cane system

Overhead Tubercane (OTC) Motions

Vertical travel

Longitudinal travel

Transverse travel

Vertical axis rotation

Tubehead rotation

Image Receptors

Cassette-based systems

oFilm-screen

oComputed radiography (CR)

Digital radiography (DR) systems

Referred to as flat-panel technology

oDR systems use thin-film transistors (TFTs)

Image receptor technology

receives remnant radiation from patient and captures the x-ray energy for processing

Classified as cassette-based and cassetteless

Historically, receptor was a cassette with intensifying screens and polyester film.

Newer systems are replacing the film-screen based technology with digital technology and image displayed on a video monitor

Important to remember

The only radiation that is of any clinical value is:

oRemnant radiation absorbed in the detector

oRemnant radiation is converted to an electrical signal, digitized, and sent to a computer for processing.

oFinally presented as a radiographic image for interpretation

Flat panel DR Technology

-replacing cassette based systems

-also known as flat panel detector (FPD)

-improved spatial resolution

-lower patient dose

DR technology

More dose efficient

Detectors are expensive and must be treated with care.

Sensitive to mechanical shock

Fluid invasion

Fluoroscopy

Provides live, real-time images of patients using X-rays

Standard of care for studying patient physiology and dynamics using x-radiation

Requires special equipment designs that feature an X-ray tube with attached image receptor in a perpendicular relationship

Used for a wide array of diagnostic procedures

Radiographic/Fluoroscopic (R/F) System

-Capable of static radiographic imaging (spot films) as well as live imaging (fluoroscopy)

-Capable of vertical tilting

-Spot film device with image intensifier is at right angle to x-ray tube during fluoroscopy.

-Table-side controls of tabletop motions

Interventional C-Arm Fluoroscopy System

-Used for interventional procedures

-Features a C-arm design with x-ray tube and image receptor

-Newer systems use a flat panel DR detector.

Mobile X-Ray Imaging

-Mobile radiographic units are used extensively in hospitals in many settings.

-Travel movement is motorized.

-Need to be plugged into wall outlet for charging when not in use

-X-ray capabilities similar to those of a fixed radiographic unit

-Designs are compact and user-friendly.

-Limited power for x-ray studies

Mobile X-Ray Features

-Motorized motion

-High-frequency output

-Exposure switch on a coiled cord to maximize distance from patient during exposure

-Newer systems use a wireless portable DR detector to replace cassette.

Cathode

-Creates free electrons through thermionic emission

-is the source of this negatively electrons

Anode

- where the x-rays are actually created

-Absorbs electrons and creates electrons from cathodes

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