Radiology, the medical specialty that uses imaging to diagnose and sometimes treat disease, is distinct from radiography, an imaging technique based on x-rays passing through tissue and emerging to “hit” film on the other side. Radiology comprises all types of medical imaging, including radiography. To help standardize nomenclature and abbreviations used in radiology, a short list of terms and their definitions and helpful resources is provided in this section.
14.17.1 Radiology Terms.
The following terms are commonly used in radiology.
b value: The “b value” (also occasionally referred to as the “b factor”) is associated with diffusion-weighted magnetic resonance imaging (diffusion-weighted MRI or DWI). It measures “strength (intensity and timing) of the diffusion gradient,”1,2 and the units are seconds per square millimeter.
maximum b value of 1221 s/mm2
Four gradient strengths were applied, resulting in b values of 0 and 1000 s/mm2 applied sequentially in the X, Y, and Z gradient directions.
boost: An additional dose of radiation delivered to a particular subset of the original treatment field, usually the tumor bed.2
density:Density should be used only in the photometric sense to refer to inherent characteristics of film or film blackening.2 For describing the appearance on radiographic images, in most cases density should be changed to opacity, which is an area of whiteness. For computed tomography (CT) and magnetic resonance imaging (MRI), see hyperattenuating and hyperintense, respectively.
Doppler: See 14.3.6, Echocardiography.
echo train: A sequence of 2 or more echoes generated by the application of radiofrequency pulses or gradients. Echo train is not a unit of measure2 but is expressed as in these examples:
echo train length 5
echo train length 18
echo train length 16
echo train length 20
a long echo-train—length 3-dimensional fast-spin echo sequence
excitations/signals: Change “number of excitations” to “number of signals acquired” (applies to MRI). A signal is the component of an electrical current that contains information, as opposed to noise.3
field of view: The rectangular region superimposed over the area of the body from which MRI data are acquired.4
field strength:Field refers to the magnetic field generated by the MRI magnet (eg, high-field-strength imaging).2
hyperattenuating, hypoattenuating: CT images are described in terms of the relative attenuation of what is being measured. A hyperattenuating (or high-attenuation) lesion is more dense than surrounding tissue and appears as an area of whiteness on the CT image, whereas a hypoattenuating (low-attenuation) lesion appears as an area of blackness.
hyperintense, hypointense: In MRI, the image contrast is measured in terms of signal intensity, where hyperintense indicates areas of whiteness and hypointense indicates areas of blackness.2
k-space: This term refers to mathematical space with frequency and phase, rather than spatial data, as coordinates.1
Our pulse sequences collected data spirally in k-space.
lucency, lucent, radiolucent: These terms refer to an area of blackness on a radiograph.2
opacity: An area of whiteness on a radiograph.2
radiofrequency ablation: A treatment technique that uses high-frequency alternating electrical current to destroy tissue cells by heating them.5
T1, T1ρ, T2, T2*: These are types of relaxation time in MRI.1,4 They need not be expanded.
spin-lattice or longitudinal relaxation time
spin-lattice relaxation time in the rotating frame
spin-spin or transverse relaxation time
time constant for loss of phase coherence among spins
TE: The time between the middle of 90° pulse and the middle of spin-echo production. Expand echo time (TE) as in this example:
Echo times (TEs) were 20 and 80 milliseconds.
TR: The time between the beginning of a pulse sequence and the beginning of the succeeding (essentially identical) pulse sequence. Expand repetition time (TR) as in this example:
Cardiac-gated repetition time (TR) was greater than 2400 milliseconds.
Available radiologic glossaries include the following:
■Thoracic radiology: glossary of terms for thoracic radiology6
■Breast imaging: American College of Radiology BI-RADS Atlas7
■Magnetic resonance: ACR Glossary of MRI Terms,4 glossary of magnetic resonance terms1
■Ultrasonography: Recommended Ultrasound Terminology3
■General, for laypersons and nonspecialists: RadiologyInfo glossary of terms5
In addition to the terms explained in this section, see 11.1, Correct and Preferred Usage of Common Words and Phrases, for terms such as radiography, radiology, radiograph, and film; 13.14, Radioactive Isotopes, and 17.0, for units such as H (Hounsfield) and keV (kiloelectron volt).
Principal Author: Cheryl Iverson, MA
Thanks to Jennifer Eberhart, Radiology, Oak Brook, Illinois, and Philip Sefton, MS, ELS, JAMA, for reviewing and providing comments.
1.Rinck PA. Glossary. In: Magnetic Resonance in Medicine: The Basic Textbook of the European Magnetic Resonance Forum. 11th ed. 2017. Accessed July 22, 2019. https://www.magnetic-resonance.org/ch/22-01.html
2.Lang D. Usage and nomenclature. In: Radiological Society of North America (RSNA) In-House Style Manual. RSNA; 2005.
3.Recommended Ultrasound Terminology. 3rd ed. American Institute of Ultrasound in Medicine; 2008.
4.Hendrick RE, Bradley WG Jr, Harms SE, et al. ACR Revised Glossary 2005 (ACR Glossary of MRI Terms). American College of Radiology. Accessed August 5, 2019. https://www.acr.org/-/media/ACR/files/radiology-safety/MR-safety/MRGlossary.pdf
5.Glossary of terms. RadiologyInfo. Accessed April 25, 2018. https://www.radiologyinfo.org/en/glossary/browse-glossary1.cfm
6.Hansell DM, Bankier AA, MacMahon H, McLoud TC, Müller NL, Remy J. Fleischner Society: glossary of terms for thoracic imaging. Radiology. 2008;246(3):697-722. doi:10.1148/radiol.2462070712
7.D’Orsi CJ, Sickles EA, Mendelson EB, et al. BI-RADS Atlas. 5th ed. American College of Radiology; 2013. Accessed April 25, 2018. https://www.acr.org/Quality-Safety/Resources/BIRADS