Managed Medical Imaging (MMI) has been building this medical imaging industry glossary as a resource for those interested in learning more about the medical imaging industry.  Because of the dynamic nature of the industry, this glossary will always be growing so come back anytime you hear a new term and want to know what it means. 


2D: Two-dimensional


2D-TOF: Two-dimensional time of flight


2DFT: Two-dimensional Fourier Transform


3D: Three-dimensional


3D Multi Slab: An image mode used in time-of-flight vascular imaging for acquiring multiple overlapping 3D slabs.


3DFSE: Three-dimensional fast spin echo


3DFT: Three-dimensional Fourier Transform


3D GD MRA: Three-dimensional gadolinium magnetic resonance angiography


90 Pulse: A pulse that rotates the magnetization vector 90 from longitudinal static magnetic field direction. This converts the longitudinal magnetization into transverse magnetization.

ASHE - American Society for Healthcare Engineering


Accuracy: (1) In common usage, accuracy is the quality of being true or correct. (2) As a measure of diagnostic performance, accuracy is a measure of how faithfully the information obtained using a medical imaging agent reflects reality or truth as measured by a truth standard or gold standard. Accuracy is the proportion of cases, considering both positive and negative test results, for which the test results are correct (i.e., concordant with the truth standard or gold standard.)

ActiveX ActiveX is a loosely defined set of technologies developed by Microsoft for sharing information among different applications. ActiveX is an outgrowth of two other Microsoft technologies called OLE (Object Linking and Embedding) and COM (Component Object Model). One of the major features of ActiveX is its ability to be used by a number of development environments.

Alias All: Alias All turns scale to gray and scale to color on at display time. 


Analog-to-Digital Converter (ADC):  Most base devices produce images as an analog picture that must be converted to a digital image. An image acquisition component of the digital processor is responsible for converting analog information produced by a base unit into digital binary coded numbers. The device that performs this function is called an Analog-to-Digital Converter (ADC). In addition to converting image data to digital data the converter may manipulate the data and correct any deviations in it using an Input Look-Up Table.


Angiography: x-ray examination of blood vessels following the injection of a contrast agent



Angiographic Room: A radiographic/fluoroscopic system with rapid filming techniques and

with special capabilities for performing angiographic procedures. The system may be singleplane

or bi-plane.

Annotation Annotations are used to mark up text and attach notes and comments to images and documents.  The annotation objects are registered as an underlying image permitting zooming and scrolling of the overall display without losing registration of the annotation information. You can set the foreground, background, and font color as well as line width and style for annotations.

Anti-Aliasing: Anti-aliasing is a method of making graphics and text easy to read and pleasing to the eye on-screen. Black and white or color images, if displayed at a lower resolution than 1:1 (image pixels to screen pixels), cause the image to look unreadable. This is because linear interpolation methods used for display skip pixels in the horizontal and vertical directions. Thus, some information is lost on display. Anti-aliasing corrects for this by producing an average of neighboring pixels. The effect is to give the document a soft, grayscale look. The underlying image is unaffected if used for display purposes. However, functions also exist to permanently modify black and white images to grayscale.


AP – Anteroposterior:  An x-ray picture in which the beams pass from front to back.

API:  Application Program Interface (API) is the command-set for a set of routines that invoke a library or toolkit. It is a set of instructions that contain the rules that must be followed for two computer programs to talk to each other. For instance, a computer program can (and often must) use its operating system's API to allocate memory and access files.

Applet: An applet is a small Java application that can be sent along with a Web page to a user, much the same way an image is included. It is a software component that runs in the context of another program, for example a web browser. The applet must run in a container, which is provided by a host program, or through a plugin. It enables a variety of web browsers to accomplish many tasks, including viewing and manipulating images in many formats. When you use a Java technology-enabled browser to view a page that contains an applet, the applet's code is transferred to your system and executed by the browser's Java Virtual Machine (JVM).


Artifact: An error in the reconstructed image that does not correspond to the patient. There are three major forms of artifacts that can occur in MR imaging and contribute to poor image quality: geometric distortion, inhomogeneous signal intensity, and spurious signal.


ASSET: Array spatial sensitivity encoding technique

ASCII: ASCII is an industry standard which assigns letters, numbers, and other characters within the 256 slots available in the 8-bit code. ASCII defines codes for 33 non-printing control characters (which mostly affect how text is processed) plus 95 printable characters.

Aspect Ratio: The aspect ratio of an image is the proportion of the image's size given in terms of the horizontal dimension versus the vertical dimension. An aspect ratio of 4:3 indicates that the image is 4/3 times as wide as it is high. Maintaining aspect ratio is important when viewing images so that they do not appear ‘squished’ or ‘stretched’.

Attribute: An attribute is a defining characteristic of an object and is part of a tag. It can be set to different values.


Base Device:  A base device is one that produces primary image information. These devices include: digital fluoroscopy, digital ultrasound, MRI scanner, gamma camera acquisition, positron emission tomography (PET), CT scanning, CR and ddR radiographic equipment.


Batch Conversion: Batch conversion is the ability to convert large quantities or groups of images from one format to another. Batch conversion is usually done in an automated manner.


BI-RADS:  BI-RADS is an acronym for Breast Imaging-Reporting and Data System, a quality assurance tool originally designed for use with mammography.


Biophotonic Imaging: A novel approach to functional genomics, target validation, and drug screening and preclinical testing. Uses a bioluminescent reporter gene to tag a target of interest - which can be a gene, a cell, or a microorganism - in a whole mouse. Because light passes through tissue, the labeled mouse can be anesthetized and photographed with a camera capable of detecting the bioluminescence.


B0: Static magnetic field or main magnetic field Bandwidth: A range within a band of frequencies that an MRI system is "tuned" to receive. The received bandwidth of an image determines the number of frequencies encompassed in the image. The system’s bandwidth choice depends on the TE, matrix, and FOV selected.


CARET (Computerized Anatomical Reconstruction Toolkit): CARET is a software application for the structural and functional analysis of the cerebral and cerebellar cortex.


CDRH - FDA’s Center for Devices and Radiological Health:   One of the centers under the Food and Drug Administration (FDA) is the Center for Devices and Radiological Health and they regulate the manufacturer of electronic products that emit ionizing electromagnetic or particulate radiation
and assures they meet radiation safety standards. They make sure that new devices are safe and effective before they are marketed.


Chest Room - Dedicated: A specific or specialized radiographic room used for routine chest

X-rays and those radiographic procedures which can or should be performed in an upright




Chiller: A refrigeration unit that supplies cold water used to cool MRI components. Depending on the system configuration chillers are used to cool shield coolers, shim coils and sometimes the air conditioning.


Cine:  Movie Recording capability


Coil (MRI Coil): A coil consists of one or more loops of conductive wire, looped around the core of the coil. Coils are part of the hardware of MRI machines and are used to create a magnetic field or to detect a changing magnetic field by voltage induced in the wire. A coil is usually a physically small antenna. The perfect coil produces a uniform magnetic field without significant radiation.


Color Conversion: Color conversion is the process of changing from one color model to another.

Color Correction: Color correction is the process of removing unwanted casts or tints from an image.


Comparator: An established test against which a proposed test is compared to evaluate the effectiveness of the proposed test. A comparator usually means an agent or modality approved for a similar indication. (See also definition for reference product.)

Compile: Compiling is a process statement which turns a particular programming language into machine language or “code” that a computer’s processor uses. (e.g. an executable .EXE or .COM file that may run on a computer or virtual machine.)

Component Application: An application that performs a specific function and is designed in such a way to easily operate with other components and applications. The term is sometimes used interchangeably with applet.

Compression: Compression is a process of encoding an image or other data so that it occupies less memory or disk space than its uncompressed version. Image compression can be lossy or lossless. The goal is to achieve the best image quality at a given bit-rate (or compression rate). Compression techniques for 24-bit color images usually do not work well on 1-bit or bi-level images. Similarly, compression for 1-bit images do not compress well for 24-bit color images. Examples of compression formats include ABIC, Group3/Group4, JPEG, JPEG2000, JBIG, JBIG2, MMR, ZIP, and LZW. Snowbound's products handle image compression directly and rapidly without having to invoke a print driver or any other external application.
Compression Ratio The compression ratio is the ratio of a file’s uncompressed size compared to its compressed size. Because the user has control of the amount of loss, JPEG is one of the few formats that permits the user to control the compression ratio of the information.



Computed Tomography: The technique employing ionizing radiation to produce axial (cross

section) body section images. Data obtained by X-ray transmission through the patient are

computer analyzed to produce these images. The series of sectional, planar images may be

manipulated to produce different planar or volumetric view of the areas of interest and eliminate

overlying structures such as bone. Manipulations of data allows for the selective view of

either dense tissues such as bones or diffuse tissues such as the heart, brain, or lung. CT is

used for both head and body imaging and is applicable to diagnosis, biopsy, and therapy



Content Management System (CMS):  A content management system (CMS) is a computer software system for organizing and facilitating collaborative creation of documents and other content. A content management system is frequently a web application used for managing web sites and web content, though in many cases, content management systems require special client software for editing and constructing articles. Snowbound's FlexSnap web viewer can integrate with CMS systems enabling users to easily access, view, convert, manipulate, annotate, and print document and image formats within the repository through a single universal viewer.

Contrast: Contrast is the variation of the lightest or brightest in comparison to the darkest portions of an image. In imaging, contrast depends on the image source, the medium, and the ambient lighting. 


Contrast Resolution: An image function providing the ability to differentiate anatomical density differences with respect to surrounding anatomical regions.

Control Array: A control array allows you to dynamically add menu items to a Visual Basic form during program execution.

Coordinates: Coordinates are a pair of numbers that represents a specific location in a two-dimensional plane.


CRCPD - Conference of Radiation Control Program Directors:  The Conference of Radiation Control Program Directors is a non-profit, nongovernmental professional organization that brings together the radiation protection programs in all fifty states. It is an association of state and local
radiation control agencies and is an effective voice for the states when national and international issues are discussed. The CRCPD committees are responsible for a variety of public health, worker and environmental protection advances in radiation protection.


Cryoelectron Tomography:  A technology for taking three- dimensional pictures of a cell, providing insights into how the cell's machinery carries out some of the basic processes of life.  It works essentially like a doctor's CT scan; a computer constructs a 3-D image of a flash- frozen cell from a series of image "slices" created by penetrating electron beams.


Cryogens: Supercooled liquids that are used to keep magnets at super conducting temperatures. Most magnets use Liquid Helium (Lhe) and some use both liquid nitrogen (LN2) and Lhe.


Cryogen Meter: Sometimes called helium meter or nitrogen meter is used to monitor the cryogen level of Lhe or LN2 used in the magnet.

Crop: Cropping is an image processing method to remove a region of an image or text. It can be used to remove an extraneous information or subject matter to improve the final composition.


CT: A radiological test known as “computerized tomography” that can visualize areas in the body, such as the brain, and cannot be seen on regular x-ray examinations.  


CT pulmonary angiogram (CTPA):  A diagnostic test that employs computed tomography to obtain an image of the pulmonary arteries.


Daily Quality Assurance (DQA): A scan or procedure used by system operators to verify system operation.


Decompression: Decompression is the method or process of decoding image data which is stored in a compressed data stream or file. Decompression methods automatically detect the file format.


Depth: Depth is defined by the number of bits-per-pixel that can be displayed on a computer screen.


Device: Dependent Device dependent is the software written to work on a particular set of hardware platforms.


Device Driver: The device driver is the set of software routines that work with and control a specific hardware device. Each device including printers, keyboards, mouse, monitors, disk drives need to have a driver in order to work with the system.


Dewar: A large vacuum jacketed (double walled container) generally made out of stainless steel that is used to transport cryogens.


DEXA (DXA): Dual-energy X-ray absorptiometry - it is the best technique to measure bone density (DXA, previously DEXA[1][2]) is a means of measuring bone mineral density (BMD). Two X-ray beams with different energy levels are aimed at the patient's bones. When soft tissue absorption is subtracted out, the BMD can be determined from the absorption of each beam by bone. Dual-energy X-ray absorptiometry is the most widely used and most thoroughly studied bone density measurement technology.


DIB: A Device Independent Bitmap (DIB) is an image format specification independent of all hardware devices and platforms. 


Diffusion MRI:  A specific Magnetic Resonance Imaging (MRI) modality that produces in vivo images of biological tissues weighted with the local microstructural characteristics of water diffusion.


Digital radiography (DR):  A form of x-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce an image of similar contrast to conventional radiography.  There are two types of flat panel DR technology.  Direct Panel - which converts X-Rays into electrical current; and Indirect Panel - which in a two-step process converts X-Rays into light and shifts it to an electronic signal.  Direct panel is the older type and uses selenium material, which has a latency time for charging the place that makes it hard to take multiple images is cannot be used for Fluoroscopy.  Selenium has low X-Ray absorption rates and is highly sensitive to temperature (it is destroyed at temperatures below 5 degrees Celsius and above 45 degrees Celsius).  Selenium panels require a high voltage applied to the Selenium layer and this can contribute to early panel failure due to arcing.  For all these negatives, Selenium panels do offer a very high intrinsic resolution, making them ideal for Mammography.  The other type of flat Panel DR technology is Indirect Panel, which typically uses either Cesium Iodide or Ganolidium.  Both have a high Detective Quantum Efficiency (DQE - A measure of contrast resolution), for high image quality at low dose and allow for fluoroscopy.    Both also operate at lower voltages and are thus more likely not to be damaged by arcing.  These two elements are the most commonly used in DR flat panels.


Physically, the flat panel detectors are typically designed in a standard 14x17 configuration although some manufacturers have made them in different sizes.  The Selenium, Cesium Iodide or Ganolidium elements are usually put in layers of amorphous silicon thin-film transistors (TFT), which are typically deposited on a piece of glass.  Amorphous silicon photodiode circuitry and a scintillator form the top layers of the TFT.  The elements collect the X-Ray, convert it to light and photodiodes then convert it to a digital output signal.  Most flat panels are tethered via cable to a workstation but there are several wireless models.


DQE: Detective Quantum Efficiency is a measure of contrast resolution


Edge Detection: Edge detection is a method of locating and isolating an optical edge in a digital image. For instance, most high-speed scanners scan with a black background. An edge-detection algorithm will look for this black edge and remove it leaving only the original page data. The goal of edge detection is to mark the points in an image at which the intensity changes sharply.


EI – Exposure Index:  Exposure index (EI) is the measure of the amount of exposure received by the image receptor (IR). It is dependent on mAs, total detector area irradiated, and beam attenuation. The exposure index is indicative of the image quality. EI is derived from the mean detector entrance exposure which is in turn derived from the mean pixel value of the image. Although EI is always derived from the IR exposure, equipment manufacturers calculate the numeric value differently, resulting in different ranges and definitions.


Electron beam tomography: A specific form of computed axial tomography (CAT or CT) in which the X-Ray tube is not mechanically spun in order to rotate the source of X-Ray photons.  It is an effective tool for the study of subcellular structure at a range of resolutions. In many labs tomography is being used to understand the overall structure and interplay of sub-cellular organelles of eukaryotic cells. Such work is generally carried out on plastic-embedded, stained and sectioned samples. The resolution can be high enough to identify individual molecular complexes and even to understand conformational changes associated with their functions.

Encoding: Encoding is the format for storing uncompressed data, how it is packed, and the set of symbols used to represent the range of data items . File compression allows you to limit an image's size by encoding the image's data more concisely and efficiently.


Endorectal Coil Magnetic Resonance Imaging:  Endorectal coil MRI is a type of medical imaging in which MRI is used in conjunction with a coil placed into the rectum in order to obtain high quality images of the area surrounding the rectum

Encryption: Encryption is the conversion of data into a form that cannot be easily understood by unauthorized people. Encryption/decryption is a good idea for sending sensitive information over the web, such as an online credit-card purchase, patient records, and financial data.

Equalize: Equalize is an image-processing algorithm that redistributes the frequency of image pixel values allowing equal representation for any given continuous range of values.


ESE - Entrance Skin Exposure:  The Entrance Skin Exposure is an important dosimetric indicator of the radiation received by the patient in a single radiographic exposure. The ESE can be measured by either direct measurement on phantoms using an ionization chamber (or other appropriate dosimeter) or on patients using thermoluminescent dosimeters (TLDs), or by using calculations based on a mathematical model. Factors that can cause differences in measured values include instrument calibration, backscatter, collimation, estimation of focal spot location, choice of phantom, and location of dosimeter in the primary beam. The ESE is the benchmark of safety and is the measure of risk.


Extended Dynamic Range (EDR): An imaging enhancement that uses 32-bit processing instead of the conventional 16-bits to improve SNR.


Faraday's Law:  Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil. No matter how the change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc.


Fat/Water Suppression (F/W): An imaging enhancement technique that suppresses signal within the imaging volume from either fat or water by applying a frequency-selective saturation pulse


Ferrous or Ferromagnetic: A material containing iron having a magnetic property that produces a strong and powerful attraction between that object and the center of the magnet.


Field of View (Acquisition FOV): The area of the anatomy being imaged, usually expressed in centimeters. FOV image size is a function of the acquisition matrix times the pixel size.


FIESTA: Fast Imaging Employing Steady State Acquisition


Flip Angle: Flip angle is the rotational angle of the magnetization vector produced by a RF pulse relative to the longitudinal axis of the static magnetic field. Flip angle adjusts contrast.


Flow Axis: The orthogonal axis (S/I, R/L, A/P) for which flow has been encoded in a flow image

Flow Compensation (Flow Comp): An imaging enhancement using the system’s gradients to put flowing protons into phase with stationary protons, thereby reducing flow artifacts. Applied in the slice and frequency directions.

Flow Encoding: A technique used in MR to measure or display motion such as blood flow within vessels Flow Recon Type: A user-selectable option for selecting a Slab Dephasing Gradient and a Phase Correction technique. See Phase Difference, Complex Difference, and Flow Analysis.


Flow-Related Enhancement: A process by which the signal intensity of moving fluids, like blood or CSF, can be increased compared with the signal of stationary tissue. Occurs when unsaturated, fully magnetized spins replace saturated spins between RF pulses.


fMRI: Functional Magnetic Resonance Imaging:  The recent discovery that magnetic resonance imaging can be used to map changes in brain hemodynamics that correspond to mental operations extends traditional anatomical imaging to include maps of human brain function.


Fluoroscopy:  Imaging technique that enables physicians to obtain real-time, moving X-Ray images (typically 25-30 images per second) of the internal structures of the body.  The technique is commonly used for diagnostic and interventional procedures such as barium X-Rays and enemas, catheter insertions, angioplasty and angiography procedures, blood flow studies and orthopedic surgery.  A non-ionic contrast material is injected or consumed by the patient to enhance visualization of various organs.  A constant stream of radiation passes through the patient and strikes a fluorescent screen creating shadows of the opaque internal organs.  Induced

motion provides a continuous or nearly continuous evaluation of the visual effects of

that motion.  Images produced by this modality include upper and lower gastrointestinal series,

cystography, pyelography and esophageal mobility studies.


Gradient: The magnitude and direction of the rate of change in space of the magnetic field strength. In a MR system gradient amplifiers and coils are used to vary the magnetic field strength in the X, Y, and Z planes.


Gradient coil: a device used to produce deliberate variations in a magnetic field


GUI: A Graphical User Interface (GUI) is a computer interface that uses graphical objects. GUIs display visual elements such as icons, windows, and other gadgets.


Half-Value Layer: See HVL


HIPAA: The intent of the Health Information Portability and Accountability Act (HIPAA) is that all electronic transactions for which standards are specific must be conducted according to the standards. These standards were not imposed by the law, but instead were developed by a process which included significant private sector input. HIPAA also addresses the security and privacy of health data.

Histogram: A histogram shows the distribution of colors in an image. For a 256 color image, it shows how many times a particular pixel intensity occurred in that image. It is a graphical version of a table which shows what proportion of cases fall into each of several or many specified categories. The categories are usually specified as nonoverlapping intervals of some variable.


Homogeneity: Refers to the uniformity or consistency in the magnetic field. Proper homogeneity is required for optimum images.


HTS:  High Temperature Superconductor material (HTS).  It has been well demonstrated that the greater the number of coil elements in an array, the better the improvement in SNR.
Today, the coil elements are made of Copper (Cu) surface loops ranging in 2-4 inch sizes. With such small coil sizes, the dominant noise in MRI no longer arises from the body sample but rather from the coils themselves.  Therefore, the challenge arises - how to reduce the coil noise. The best solution is to change the Cu material with a material with lower resistance/noise characteristics. For this reason, High Temperature Superconductor material (HTS) becomes an ideal material of choice. 


HVL – Half-Value Layer: The half-value layer of an x-ray beam is that thickness of absorbing material, when introduced into the path of a given beam of radiation, reduces the X-ray intensity (quantity) to half its original value. The HVL is a measure of beam quality. The factors that directly affect X-ray quality are kilovoltage and filtration.


Interventional Radiology (IR): The clinical subspecialty that uses fluoroscopy, CT and ultrasound

to guide percutaneous (through the skin) procedures such as performing biopsies,

draining fluids, inserting catheters, or dilating or stenting narrowed ducts or vessels. IR Procedures are complex, requiring a team of doctors and technicians. As such, they are often

performed in the Surgical Suite, and scheduled in advance as they require special preparation.



IR / Special Procedure Room:  An IR / Special Procedure Room can be categorized as: Angiographic Room - an R/F system with rapid filming techniques including capabilities for performing angiographic procedures; Vascular / Neuro-radiology Room - a diographic/fluoroscopic system with rapid film changer and capabilities for performing a range of neuro, visceral, and peripheral procedures, single-plane or bi-plane.



Inversion Recovery (IR): A pulse sequence that inverts the magnetization and then measures the recovery rate as the nuclei return to equilibrium.


ISO - Independent Service Organization:  An organization, like MMI, that offers services for medical imaging systems independent from the OEM.


K: An algebraic equation and is a constant that includes the coil filling factor, coil resistance, noise power spectrum, pulse sequence, and tissue parameters (T1, T2, Proton Density or PD).


kV:  Kilovoltage (kV), which governs primarily the energy, or penetrability of the x-ray photons.  X- rays of adequate energy provide the required contrast to the image.


K-Shell: The orbital electron shell closest to the nucleus.


K-Space: A spatial frequency domain where the raw magnetic resonance signals are collected in the computer system before being processed for reconstruction.


Layer: The layer is the organization of programming into separate functional components that interact in some sequential and hierarchical way, with each layer usually having an interface only to the layer above it and the layer below it.

Library :The library is a collection of software functions that can be called by a higher level program. Most libraries are collections of similar routines such as those used for graphical or image processing.

Linear Interpolation: Linear interpolation is used for resizing an image. It takes 2 pixels, separated by x pixels, then averages the x + 2 pixels to create an intermediate value. This resulting value is then used to represent the entire range of pixels. Linear interpolation is not very effective for resizing 1-bit documents since much of the visual data is lost.


LITT: Laser induced interstitial thermotherapy

Look-up-table: A look-up-table is an indexed list of numbers used to change pixel values in a predefined way. A look-up-table is used to determine the colors and intensity values with which a particular image will be displayed.

Lossless Compression: Lossless compression is a method of image compression where there is no loss in quality when the image is compressed or uncompressed. Lossless compression is used when it is important that the original and the decompressed data be identical. Some image file formats, notably PNG, use only lossless compression.


LS – Lumbosacral: The low back officially begins with the lumbar region of the spine directly below the cervical and thoracic regions and directly above the sacrum. The sacral spine refers to the large irregular triangular shaped bone made up of the five fused vertebrae below the lumbar region.


mA:  Tube current (milli-Amperes, mA), which governs the number, or quantity of photons. Adequate  number  of  photons  decrease  image noise, and give it the required brightness.


mAs - Milliampere-second:  A unit determined by multiplying the milliamperes by the time the x-ray tube is generating x-rays. On many x-ray machines this is a technique factor selected by the operator that together with kVp determines the exposure of patient and image receptor.


Magnetic Field Gradient: A device for varying the strength of the static magnetic field at different spatial locations. This is used for slice selection and determining the spatial locations of protons being imaged. Also used for velocity encoding, flow comp, and in place of RF pulses during gradient echo acquisitions to rephase spins. Commonly measured in gauss per centimeter.


Magnetic Resonance (MR): The absorption or emission of electromagnetic energy by nuclei in a static magnetic field after excitation by a suitable RF pulse.


Magnetic Resonance Imaging (MRI): The creation of images using the magnetic resonance phenomenon. MRI has the ability to characterize and discriminate among tissues based on their physical and biochemical properties. Different types of tissue can be demonstrated in different colors on a MRA.  The current application involves imaging the distribution of hydrogen nuclei (protons) in the body. The image brightness in a given region usually depends jointly on the spin density and the relaxation times. Image brightness is also affected by motion such as blood flow.

Magnetic Resonance Signal: The electromagnetic signal (in the radio frequency range) produced by the precession of the transverse magnetization of the spins. The rotation of the transverse magnetization induces a voltage in the coil. This voltage is amplified by the receiver.


Magnetization Transfer: A technique that improves contrast by saturating the short T2 component of tissue such as gray/white matter and skeletal muscle.


Maximum Intensity Projections or Pixels (MIP or MIPS): A technique for producing multiple projection images from a volume of image data (i.e., 3D volume or a stack of 2D slices). The volume of image data is processed along a selected angle and the pixel with the highest signal intensity is projected onto a two-dimensional image.


Memory Buffer: The memory buffer is a temporary space in memory for working storage.

Memory Pointer: The memory pointer is a variable that points to the location in memory of some data. This is also known as indirect addressing.

Merge: Merging is the process of taking two or more images and combining them into one.


MHz: Mega hertz


Micro-coil: a type of wire in which current is generated by a moving magnetic field (permanent, implanted) cardiac pacemaker is a device that establishes the rhythm of the heartbeat


micro-PET: A dedicated PET scanner designed for high resolution imaging of small laboratory animals. It has been developed and built by a team of researchers at the Crump Institute for Biological Imaging, UCLA. The aim was to build a compact and relatively low cost PET scanner with unprecedented spatial resolution that would be useful to researchers in a wide range of biomedical research applications.


Microtomography: Uses x-rays to create cross-sections of a 3D-object that later can be used to recreate a virtual model without destroying the original model.


MRA: Magnetic resonance angiography


MRI:  See above Magnetic Resonance Imaging


MRS: Magnetic resonance spectroscopy


MRSI: Magnetic resonance spectroscopy imaging


MTF: Modulation Transfer Function 


Multi-Planar Gradient Echo (MPGR): A pulse sequence that represents a combination of Gradient Echo and Spin Echo sequences. Acquires data sequentially rather than slice-by-slice.

Multi-Slice, Multi-Phase (MSMP) Imaging: Multi-slice, multi-phase cardiac gating pulse sequence that produces images at multiple heart locations and several different cardiac phases at each location.


Multi-Slice, Single-Phase (MSSP) Imaging: Multi-slice, single-phase cardiac gating pulse sequence that produces images at multiple heart locations, each at a different phase of the cardiac cycle.


Nanoimaging: Real-time subcellular imaging of structure, function, properties and metabolism


Nanomagnetic: referring to the concept of using magnetic nanoparticles coated with a semiconductor layer as a base for the development of electromagnetic devices


Nanotomography: Nanotomography, much like its related modalities tomography and microtomography, uses x-rays to create cross-sections from a 3D-object that later can be used to recreate a virtual model without destroying the original model.


Near InfraRed spectroscopy NIR: A noninvasive technique that uses the differential absorption properties of hemoglobin and myoglobin to evaluate tissue oxygenation and indirectly can measure regional hemodynamics and blood flow. Near- infrared light (NIR) can propagate through tissues and at particular wavelengths is differentially absorbed by oxgenated vs. deoxygenated forms of hemoglobin and myoglobin.


Negative predictive value: The probability that a subject does not have the disease when the test result is negative. Synonyms include predictive value negative.


Noise: Noise consists of dark spots that can appear when using a digital camera with bad lighting conditions, or when there is static build-up on the scanning array element in a high speed scanner.


NEXT: Nationwide Evaluation of X-ray Trends.  The Nationwide Evaluation of X-ray Trends is a national program conducted jointly by the Conference of Radiation Control Program Directors and the FDA’s Center for Devices and Radiological Health, with financial support from the American College of Radiology since 1998, to measure the x-ray exposure that a standard patient receives for selected x-ray examinations.


OEM: Original Equipment Manufacturers (OEM’s)


Optical tomography:  A form of computed tomography that creates a digital volumetric model of an object by reconstructing images made from light transmitted and scattered through an object.


Orientation: Orientation determines which edge of the image is displayed in the positive X direction (up) and which edge is displayed in the negative Y direction (left).


PA – Posteroanterior: An x-ray picture in which the rays pass through the body from back-to-front.


PCA: Phase contrast angiography


PD: Proton density


Peak Skin Dose:  Peak skin dose (PSD) is known to be the most reliable estimate of risk to skin.  Fluoroscopy time, dose-area product (DAP), and cumulative dose at the interventional reference point are recorded during procedures.  The dose index is the ratio between PSD and cumulative dose.


Penetration Panel: This is the point of penetration of the MR system cables into the RF room. This panel contains filters and other connections required provide communication between the scan room and the rest of the system without allowing interference to pass.


PET: Positron emission tomography.  PET builds images by detecting energy given off by decaying radioactive isotopes.  PET is a noninvasive diagnostic imaging procedure that assesses the level of metabolic activity and perfusion in various organ systems of the human body. Images are obtained from positron-emitting radioactive tracer substances (radiopharmaceuticals) that are usually administered intravenously to the patient.


Positron-emitting radioisotopes were first discovered in the 1930’s. FDG PET has been evaluated for several decades in pre-clinical models, and is premised on basic research in biochemisty and biology that have established the basis of glucose metabolism in normal cell function, and it’s alteration in diseases like cancer, ischemic heart disease and some neurological disorders. The first PET scanners were developed in the United States in the 1970’s with the first scan of a human reported in 1978. Through the early 1980's, PET scans were used primarily in research and predominantly focused on the neurosciences because scanners were typically only large enough for head studies. Due largely to the emergence of two major commercial suppliers in the mid-1980’s, PET scanners have become capable of whole body imaging and increased computer processing capability. Improvements in the technology have had a significant impact on the quality of PET’s image reconstruction and display.


As a molecular diagnostic imaging modality, PET can detect rates of biological activity, as contrasted other imaging modalities such as x-ray films, computed tomography (CT), and magnetic resonance imaging (MRI), which depict the anatomical location of both normal and abnormal structures in the body.

pH: Power of hydrogen


Phase Difference: A flow reconstruction type for Phase Contrast Vascular imaging providing control of the Slab Dephasing Gradient and Phase Correction. Phase difference reconstructions have the Dephase Gradient off and Phase Correction on.

Phase Encoding: The act of localizing an MR signal by applying a gradient pulse to alter the phase of spins before signal readout.

Phase Field of View (PFOV): The phase field of view option provides faster scans by scaling down the size of the field of view in the phase direction by 3/4 or 1/2. The phase FOV option is not compatible with some PSD and imaging options.


Photoacoustic (PA) Computed Tomography: (PAT, or PACT) is based on the reconstruction of an internal PA source distribution from measurements acquired by scanning ultrasound detectors over a surface that encloses the source under study.


Photo Multiplier Tube PMT: A vacuum phototube with additional amplification by electron multiplication . It consists of a photocathode, a series of dynodes, called a dynode chain on which a secondary- electron multiplication process occurs, and an anode.


Photon: The quantum of electromagnetic energy at a given frequency. This energy, E=hv, is the product of the Planck constant (h) and the frequency of the radiation (v).


Photonics: The technology of transmission, control, and detection of light (photons). This is also known as fiber optics and optoelectronics.



Picture Archiving and Communication System (PACS):  The digital capture, transfer and

storage of diagnostic images. A PACS system consists of workstations for interpretation,

image / data producing modalities, a web server for distribution, printers for file records, image

servers for information transfer and holding, and an archive of off-line information. A

computer network is needed to support each of these devices.



Positron emission tomography (PET): a computerized image of the metabolic activity of body tissues used to determine the presence of disease


Positive predictive value: The probability that a subject has the disease when the test result is positive. Synonyms include predictive value positive.

PPM or ppm: Parts per million

PRESS: Point RESolved Spectroscopy


Precision: A measure of the reproducibility of a test, including reproducibility within and across doses, rates of administration, routes of administration, timings of imaging after product administration, instruments, instrument operators, patients, and image interpreters, and possibly other variables. Precision is usually expressed in terms of variability, using such measures as confidence intervals and/or standard deviations. Precise tests have relatively narrow confidence intervals (or relatively small standard deviations).


PROBE: Proton brain exam

PROSE: Prostate spectroscopy and imaging exam

Proton Density-Weighted (PD-weighted): PD-weighted images have contrast that is primarily due to the number of protons in the structures. PD-weighted images result when scan timing parameters are selected that minimize the T1 (long TRs) and the T2 (short TEs) contrast effects.


PSD: See Peak Skin Dose


PSL: Photostimulable Luminescence 


PSP: Photo-Stimulable Phosphor A radiographic screen containing a special class of phosphors which when exposed to X-rays, stores the latent image as a distribution of electron charges, the energy of which may later be freed as light by stimulation with a scanning laser beam. The light is directed to a photomultiplier tube, and the output electrical signal is digitized. The final result is a digital projection radiograph.  The photostimulable phosphor plate is also known as an imaging plate, storage phosphor imaging plate, and digital cassette.

Pulse Length or Width: The duration of a pulse expressed in milliseconds.


Pulsed Flouro: With C-Arms, The primary purpose of pulsed fluoro is for dose reduction. The secondary purpose is for reduction of blurring while imaging moving anatomy. On some systems like the Ziehm Vision, pulse mode may also be used with higher mA values to improve image quality. Pulsed Fluoro mA up to 6mA 0.2-6 mA 0.1 - 20 mA up to 75 mA


Pulsed gradient magnetic field: regular alterations in the force of a magnetic field (magnetic field

Pulse Sequence Database (PSD): A series of RF and gradient pulses and the intervals between them used in conjunction with gradient magnetic fields to produce magnetic resonance images.


Pulsed radio frequency field: alternating current that, when input to an antenna, generates an
electromagnetic, or radio frequency field suitable for wireless communications. The radio frequencies form a significant portion of electromagnetic radiation.


PWI: Perfusion weighted imaging


Radio Frequency (RF): The frequency (intermediate between audio and infrared frequencies) used in magnetic resonance systems to excite nuclei to resonance.


Radio frequency Pulse (RF Pulse): A burst of RF energy which, if it is at the correct Larmor frequency, will rotate the macroscopic magnetization vector by a specific angle dependent on the amplitude and duration of the pulse.


Radiography: The use of x-rays to view unseen or hard to image objects.


Radiotelemetry: automatic transmission and measurement of data from remote sources by radio
frequency energy


RBw: Receiver bandwidth


Readout Gradient: A gradient pulse applied when an MR signal is collected; used for frequency encoding.


Refocusing: The re-establishment of phase coherence via gradient or RF pulse. See Echo Rephasing, Gradient Echo, and Gradient Moment Nulling.

Relaxation Time: The time required for 63% of the nuclei to revert to their original state in the magnetic field after the RF pulse is turned off.

Repetition Time (TR): The time between successive excitations of a slice. That is, the time from the beginning of one pulse sequence to the beginning of the next. In conventional imaging, it is a fixed value equal to a user-selected value. In cardiac-gated studies, however, it can vary from beat to beat depending on the patient’s heart rate.

Rephasing Gradient: A gradient applied in the opposite direction of a recent selective excitation pulse, in order to correct for gradient-induced phase shifts.

RF: Radiofrequency


RF Coil: the "antenna" of the MRI system that broadcasts the RF-signal to the patient and/or
receives the return signal. RF coils can be receive only, in which case the body coil is used as a
transmitter; or transmit and receive (transceiver).


Reference product: An FDA-approved drug product having an indication similar to that of an investigational drug or biological product to which it is being compared for the purpose of evaluating the effectiveness of the investigational drug or biological product.


Rx: Radiotherapy


SAR: Specific absorption rate


Saturation (SAT): Repeated application of radio frequency pulses in a time that is short compared to the T1 of the tissue, producing incomplete realignment of the net magnetization with the static magnetic field.

Saturation Pulse: A slice-selective RF pulse applied, often followed by a dephasing gradient, to saturate spins and therefore minimize their signal. Used, for example, to minimize signal from flowing blood in the slice direction.

Scan Time: The amount of time needed to acquire data.

SCIC: Surface coil intensity correction


Sensitivity: The probability that a test result is positive or negative.


Sensor: a device that responds to a physical stimulus, such as thermal or electromagnetic energy,
by producing a signal, usually electrical


Shield Cooler: A water-cooled refrigeration system or heat pump used to reduce the shield temperatures of magnet Lhe or LN2 vessels. Lower shield temperatures reduce costly magnet boil off.


Shim Coils: Coils used to compensate for inhomogeneity (inconsistency) in the in the magnetic field caused by on site ferrous objects, impurities in the magnet and inconsistencies in magnet windings.

Shimming: The process of adjusting the magnetic field for inhomogeneities. There are four types: gradient, passive, resistive, and superconductive shimming


SID – Source-to-Image Distance:  The Source-to-Image Distance is also known as the focal film distance and is the distance from the source of radiation to the image receptor. The SID alters
the intensity of the beam reaching the image receptor, according to the inverse square law. The inverse square law affects density in inverse proportion to the square of the distance. When the distance is doubled, the quantity of radiation reaching the image receptor is reduced by one fourth. Resolution is improved when the SID increases and degraded when the SID decreases.


Signal-to-Noise Ratio (SNR): The ratio of signal amplitude to noise – i.e., the amplitude of signal emitted by the patient’s protons divided by the amount of patient noises and electronic noise inherent in any electronic instrument.

Slice Select: The scanning direction associated with the slice-select gradient. Usually corresponds to the direction of the scanning range.


Smart Contrast Agents: When smart contrast agents are injected into the body, they are undetectable. However, when they come into contact with tumor- associated enzymes called proteases, the smart agents change shape and become fluorescent. The fluorescent signal can then be detected using sophisticated imaging devices.


SNR: See Signal-To-Noise Ratio


Specificity: The probability that a test result is negative when the subject does not have the disease. Synonyms include true negative rate


Spin Echo Imaging (SE imaging): A magnetic resonance imaging technique in which the spin echo magnetic resonance signal rather than the free induction decay is used.


Spiral Computed Tomography: Computed tomography where there is continuous X-ray exposure to the patient while being transported through a rotating fan beam.

Spoiled Gradient Echo (SPGR): A gradient echo pulse sequence designed for acquiring T1-weighted images in 2D or 3D mode.

Spoiler Pulse: A gradient pulse applied to dephase spins and to minimize or eliminate residual signal.

SR: Spatial resolution

SS-EPI: Single slice - echo planar imaging


SSFSE - MRCP: Single shot fast spin echo - Magnetic resonance cholangiopancreatography

SSFSE: Single shot fast spin echo

Steady State Free Precession (SSFP): 1. A gradient echo pulse sequence designed for acquiring T2-weighted images in 3D mode. 2. A condition achieved by repeatedly exciting an MR sample with phase-coherent RF pulses at a repetition rate (TR) which is shorter than T2.



Stereotactic Mammography:  Imaging of the breast from two slightly angled directions in order

to identify a path to help guide a needle for breast biopsy. The procedure may be performed

upright or with the patient lying face down. Several stereotactic pairs of X-ray images

are made. Small samples of tissue are then removed from the breast using a hollow core

needle or vacuum-assisted biopsy device that is precisely guided to the correct location using

X-ray imaging and computer coordinates.



T-rays terahertz rays: Terahertz (THz) radiation is electromagnetic radiation in a frequency band from 0.1 to 10 terahertz between the infrared and microwave bands and is the next frontier in imaging science and technology.


T/R: Transmit/Receive

T: Tesla

T1: The characteristic time constant for the magnetization’s return to the longitudinal axis after being excited by an RF pulse. Also called spin lattice or longitudinal relaxation time.

T1-Weighted: Scan protocols that allow the T1 effects to predominate over the other relaxation effects.


T2*: The characteristic time constant for loss of transverse magnetization and MR signal due to T2 and local field inhomogeneities. Since such inhomogeneities are not compensated for by gradient reversal, contrast in gradient-echo images depends on T2*.

T2*-Weighted: Scan protocols that allow the T2* effects to predominate over the other contrast effects. There are three primary gradient echo pulse sequences that can be used to produce varying T2*-weighted images: gradient echo, SPGR, and SSFP.

T2: The characteristic time constant for loss of phase coherence among spins caused by their interaction and the resulting loss in the transverse-magnetization MR signal. Also referred to as spin-spin or transverse relaxation time.

T2-Weighted: Scan protocols that allow the T2 effects to predominate over the other contrast effects.


Time-of-Flight (TOF) Angiography: A 2D or 3D imaging technique that relies primarily on flow-related enhancement to distinguish moving from stationary spins in creating MR angiograms. Blood that has flowed into the slice will not have experienced RF pulses and will therefore appears brighter than stationary tissue.


Truth standard (gold standard): An independent method of measuring the same variable being measured by the investigational drug or biological product that is known or believed to give the true value of a measurement.


TRUS: Transrectal ultrasound


Tube Current:  (milli-Amperes, mA), which governs the number, or quantity of photons. Adequate  number  of  photons  decrease  image noise, and give it the required brightness.

US: Ultrasound

VBw: Variable bandwidth

Variable Bandwidth (VB or VBw): An imaging option that lets you narrow the system’s receiver bandwidth to increase SNR. Narrowing the bandwidth forces the system to detect signals from a small range of frequencies. This means the system discards more random electronic noise, improving SNR. The system narrows the Variable Bandwidth only as much as the selected TE allows.


Very Selective Saturation (VSS): Used in spectroscopy.

Volume Imaging: An acquisition technique in which signal is collected from an entire volume rather than individual slices. Permits reconstruction of extremely thin slices, and usually enhances SNR.


Water Suppression: The suppression of the water signal in a MR spectrum, usually by a specialized excitation sequence.


Weighted-Phase Images: Images that present flow data. Directional-flow images demonstrate flow along a single axis; speed-flow images combine all flow information into a single presentation.



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