Chapter 8. Medical Imaging Equipment

Automatic exposure control (AEC)

A system that terminates x-ray exposure based on the sensed x-ray energy; The termination of an x-ray exposure based upon optimum x-ray energy being sensed by a solid-state detector. This is user-selectable and its accuracy is position-dependent

Auto-tracking

Simultaneous vertical movement of the upright image receptor (IR) and the overhead x-ray tube; A feature of modern x-ray systems that enables simultaneous vertical movement of an upright image receptor and overhead x-ray tube

Anode

The positive electrode of the x-ray tube

Bucky mechanism

A grid located below the tabletop that reduces scatter radiation reaching the image receptor (IR); Grid that is an integral part of the x-ray table, located below the tabletop and above a cassette receptor tray. It decreases the amount of scatter radiation reaching the image receptor, and can improve image quality. It also moves during exposure so that no grid lines appear on the image

Cassette

A lightproof holder used for the image receptor (IR); Lightproof holder for the image receptor. It may be a computerized radiography (CR) plate or a wireless, digital radiography (DR) panel

Cathode

The negative electrode of the x-ray tube

Collimator

A device that controls the size and shape of the x-ray beam; An essential device designed to define the dimensions and direction of the x-ray beam. This device consists of four rectilinear, radiopaque blades that are adjustable to control the x-ray's field size and shape. The collimator may be operated manually or automatically

Cryogen

A cooling refrigerant used in high field magnetic resonance (MR) systems; A cooling refrigerant that is used to reduce external temperatures to a very low level. This is required in high field MR systems and typically is accomplished using liquid helium (-452°F) to create a state of magnetic superconductivity

Diagnostic yield

The amount of clinically useful diagnostic information produced by an imaging modality

DEXA

Dual emission x-ray absorptiometry, a technique used to assess bone density; Acronym for Dual Emission X-ray Absorptiometry; x-ray based technology that is used to assess bone density and bone health. Statistical calculations yield a T-score and fracture risk assessment (FRAX)

CT number

A numerical value that represents the differential absorption in a CT scan; Also called a Hounsfield Unit (HU), _____________ represent the numerical valuation of differential absorption that occurs as x-ray energy penetrates tissue in a CT scan acquisition. _______________________represent the degree of linear attenuation of a data point as compared to the linear attenuation coefficient of water, which is zero (0). _______________ can range from +1000 (average bone) to -1000 (air) and are an essential diagnostic tool for the radiologist in determining tissue composition on a CT image

Digital imaging

The acquisition of static images in electronic format; Acquisition of static images in an electronic fashion to create an electronic data set; conversion of images to a digital format for image manipulation, enhancement, archival, and networking; often referenced as DR (digital radiography)

Diode

An electrical component with polarity; Electrical component that possesses polarity with a negative and positive terminal

DR panel

A flat panel digital image receptor; Common term for a flat-panel digital image receptor using either indirect or direct digital capture technology

Flat panel detector (FPD)

A digital detector that uses amorphous silicon or selenium material; Type of digital detector employing amorphous silicon or selenium material bonded with thin-film transistor technology for digital image creation and amplification

Fluoroscope

Device used for dynamic radiographic examinations of patient physiologic functionality; consists of an x-ray tube and image receptor, aligned with each other in an orthogonal relationship; the x-ray tube and receptor may be above or below the patient depending upon system design

Fluoroscopy

An examination that utilizes a fluoroscope; Examination by means of the fluoroscope, employing image intensification or a flat panel detector

Gamma camera

A device used in radionuclide imaging to collect gamma photon emissions from patients creating nuclear medicine images. ________________________ may have one or two detector heads and may rotate around the patient as a series of images are taken to create a single photon emission computed tomographic (SPECT) image

Gantry

Term used to express the equipment component that contains major technological components comprising a CT or MR scanner

Goniometer

An angulation scale in the x-ray tube head assembly; Angulation scale incorporated into the x-ray tube-head assembly to indicate the degree of x-ray tube angle, relative to the image receptor

Hounsfield unit

A numerical value that represents tissue composition on a CT image; Numerical value used in CT as an expression of the attenuation coefficient of a particular tissue or material x-ray energies penetrate. Considered a vital feature of CT image interpretation and also referred to as CT number

Latent image

Invisible image created electronically after x-ray exposure and before image processing

Linear accelerator

An equipment used for radiation therapy; A major piece of equipment used for radiation therapy to administer x-ray or electron energies in the treatment of malignant tumors

Longitudinal

Refers to the lengthwise direction, along the long axis

MIMPS

A computer network used for transmission, viewing, and storage of medical images; Acronym for Medical Image Management and Processing System; computer network for the transmission, viewing, and archival storage of medical images; often integrated into a larger hospital information system (HIS) and radiology information system (RIS); replacing the older term PACS

Orthogonal

A perpendicular relationship between the x-ray beam central ray (CR) and image receptor (IR)

Overhead tube crane

Mechanical support for suspending the x-ray tube and collimator assembly from the ceiling of the radiography room

Perfusion

The flow of blood or lymphatic fluids into and out of cells as a function of cell metabolism. _____________ is critically important for normal cell and tissue physiology as it reflects the general health of tissues and their capability to transport oxygen, nutrients, and waste products

PACS

Computer network for the transmission, viewing, and archival storage of medical images; often integrated into a larger hospital information system (HIS) and radiology information system (RIS)

Piezoelectric crystal

A component of an ultrasound transducer that converts electrical energy into mechanical vibrations; An integral component of the ultrasound transducer that converts electrical energy into sound energies of various frequencies above the human audible range. These crystals also convert sound energy (echoes) into electrical signals that become the sonographic image

Positive beam limitation

An automatic x-ray beam collimation system that ensures the field size matches the size of the image receptor (IR); Form of automatic x-ray beam collimation of field size ensuring that the x-ray exposure field is no larger than the receptor size

Postprocessing

The manipulation of medical images after x-ray exposure; Manipulation of medical images after they have been acquired through x-ray exposure in order to improve image quality and diagnostic yield

Pulsed progressive fluoroscopy

A fluoroscopic mode in which the fluoroscopic milli-amperage (mA) characteristics can be modified to maintain optimum image quality at a lower radiation dose; mA traits such as pulse height, pulse width, pulse rate and pulse interval can be altered to optimize image quality

Pyrex glass

Special type of glass that can withstand very high temperatures from the x-ray tube anode

Primary barrier

A receptor of x-radiation that intercepts the primary beam and prevents exposure if not interlocked with the central ray of the x-ray beam. In fluoroscopy, the fluoroscopic digital panel or image intensifier tube are primary barriers

Quantum mottle

The image graininess and loss of visual acuity; An undesirable image quality characteristic that shows image graininess and a loss in visual acuity; most often the result of underexposure to the receptor

RF coil

Radio-frequency (RF) antennae that are used to transmit and receive RF frequencies, as an integral part of magnetic resonance (MR) image production

Radiolucent

Describes a material that easily transmits x-ray energy with very little absorption

Radiopaque

Describes a material that absorbs x-ray energy, predominantly through the photoelectric effect

Radionuclide

A radioactive substance used in nuclear medicine imaging; Radioactive substance that spontaneously emits nuclear particles and/or gamma radiation; chemically attached to a carrier material to assess tissue perfusion through the detection of gamma emissions

Real-time images

Images in which dynamic patient motion is visualized instantly as fluoroscopic imaging is occurring

Remnant radiation

All radiation exiting the patient during exposure and ultimately striking the receptor

Sequence

The choice of MR scanning protocols used in scanning patients. _____________ generally alter RF signal pulse amplitude and duration. An MR _________ can be likened to radiographic exposure technique selection

Soft copy

Visualization of x-ray images using a video monitor for display and interpretation

Spot image

Equipment used for acquiring static images during a dynamic fluoroscopic examination; Equipment that permits the acquisition of static images during a dynamic fluoroscopic examination; images acquired digitally and stored electronically

Teletherapy

Administration of therapeutic dosages of x-radiation or electrons to patient anatomy from a distance, in order to treat malignant tumors

Tether

Electrical wire connection between a digital detector and the x-ray generator and computer

Transducer

Hand-held device used by sonographers to emit and receive ultrasound energies in the production of sonographic images

Transverse

Placed crosswise; situated at right angles to the long axis of a part

Trendelenburg tilt

A patient position with the head and thorax lower than the legs; Table tilt angle in which the patient's head and thorax are lower than their legs

Tube angulation

Pivoting the tube at the point where it is attached to its support; measured and displayed in degrees

Vertical

Perpendicular to the plane of the horizon

X-ray tube

A device that produces x-rays

X-ray tube head

Equipment consisting of the x-ray tube, collimator, and operator controls; permits manipulation of the x-ray tube in many directions for proper positioning