Glossary

A

Accession number

The order number for one exam. It links the images in PACS to the order and the report. Lesson 2.3

Addendum

A note added to a signed report to correct or add something. Lesson 2.4

ALARA

"As low as reasonably achievable": use radiation only when the scan is appropriate, and at the lowest dose that still answers the question. Lesson 2.1

Anechoic

On ultrasound, giving no echoes at all, so it looks black. Simple fluid is anechoic. Lesson 2.1

AP and PA

Directions of the X-ray beam on a chest X-ray. PA (back to front, standing) is the standard view; AP (front to back, often in bed) makes the heart look larger. Lesson 2.1

Appropriateness

Whether a scan is the right test, for the right patient, at the right time. The ACR Appropriateness Criteria rate tests from 1 (usually not appropriate) to 9 (usually appropriate). Lesson 2.1

Artifact

Something on an image that is not really in the patient, caused by the scanner, the patient (for example, movement) or the physics (for example, metal). Lesson 2.3

Atelectasis

Partial collapse of part of a lung. Lesson 2.4

Axial, coronal, sagittal

The three planes used to slice the body: axial cuts across like bread slices, coronal from front to back, sagittal from side to side. Lesson 2.1

C

Clinical decision support

Software in the ordering system that checks an order against guidelines and flags tests unlikely to help. Lesson 2.2

Contrast agent

A substance given, usually into a vein, to make vessels or organs stand out. Iodine-based for CT, gadolinium-based for MRI. Lesson 2.1

Critical result

A finding that needs action right away, such as a pulmonary embolism. The radiologist phones the treating team directly and documents the call. Lesson 2.2

CT (computed tomography)

X-ray measurements taken from every angle and reconstructed by a computer into cross-sectional slices. Lesson 2.1

CT number (Hounsfield unit, HU)

The number in each CT pixel, on a fixed scale where water is 0 and air is -1000. Bone is +1000 or more. Lesson 2.3

CTPA (CT pulmonary angiogram)

A CT with contrast timed to fill the lung arteries, used to look for a pulmonary embolism. Lesson 2.1

D

D-dimer

A blood test that is high when the body is breaking down blood clots. Lesson 2.2

De-identification

Removing names, record numbers, dates and other identifying details from images and headers before they are shared. Lesson 2.3

DICOM

Digital Imaging and Communications in Medicine: the standard file format and network language for medical images. Each file holds a header and the pixel data. Lesson 2.3

Doppler

An ultrasound technique that shows blood flowing through vessels. Lesson 2.1

E

EHR (electronic health record)

The patient's main chart: notes, medicines, results and orders. Where clinicians order scans and read reports. Lesson 2.2

F

FHIR

Fast Healthcare Interoperability Resources (said "fire"): a newer, web-style standard for exchanging health records, used by many apps and AI tools. Lesson 2.2

Filling defect

A dark gap inside a contrast-filled vessel. In a lung artery, it is the clot of a pulmonary embolism. Lesson 2.4

Fleischner Society guidelines

Guidelines for following up lung nodules found by chance, based on size, type and the patient's risk. Lesson 2.4

Fluoroscopy

Live X-ray video, for example to watch a swallow or guide a procedure. Lesson 2.1

H

Header (metadata)

The part of a DICOM file that describes the image: patient, exam, scanner settings and position in the body. Lesson 2.3

Hedging language

Phrases radiologists use to express how sure they are, such as "consistent with" or "cannot be excluded." Lesson 2.4

HIPAA

The U.S. Health Insurance Portability and Accountability Act, which sets the privacy rules for health information. Lesson 2.3

HL7

Health Level Seven: the standard for text messages between hospital systems, such as orders and reports. Lesson 2.2

Hyperdense, hypodense

On CT, brighter (denser) or darker (less dense) than the surrounding tissue. Lesson 2.1

Hyperechoic, hypoechoic

On ultrasound, giving more or fewer echoes (brighter or darker) than the surrounding tissue. Lesson 2.1

Hyperintense, hypointense

On MRI, brighter or darker signal than the surrounding tissue. What is bright depends on the sequence. Lesson 2.1

I

Impression

The radiologist's numbered conclusion at the end of the report, most important finding first. Lesson 2.4

Incidental finding

A finding unrelated to the reason for the scan, such as Mr. Diaz's lung nodule. Lesson 2.2

Interventional radiologist

A radiologist who uses images to guide needles and catheters for treatments and biopsies. Lesson 2.1

Ionizing radiation

Radiation with enough energy to damage DNA. Used by X-ray, CT, fluoroscopy and nuclear medicine; not by MRI or ultrasound. Lesson 2.1

K

Kernel (reconstruction kernel)

A CT reconstruction setting: sharp kernels make lung and bone edges crisp but grainy; smooth kernels suit soft tissue. Lesson 2.3

M

Millisievert (mSv)

The unit used to compare radiation doses. Natural background is about 3 mSv a year in the United States. Lesson 2.1

Modality

One kind of imaging tool, such as X-ray, CT, MRI, ultrasound or nuclear medicine. Lesson 2.1

MR Safe, MR Conditional, MR Unsafe

Labels for implants and objects: safe in the MRI room, safe only under stated conditions, or never allowed. Lesson 2.1

MRI (magnetic resonance imaging)

Imaging with a strong magnet and radio waves that picks up signal from hydrogen in water and fat. No ionizing radiation. Lesson 2.1

N

Noise

Graininess in an image, often from too little X-ray reaching the detector. Lesson 2.3

Nuclear medicine

Imaging that tracks a small dose of radioactive tracer to show what tissue is doing. Includes gamma camera scans, SPECT and PET. Lesson 2.1

O

Opacity, lucency

On an X-ray, a whiter area (opacity) or a darker area (lucency). Lesson 2.1

P

PACS

Picture archiving and communication system: stores the images and shows them on the radiologist's workstation. Lesson 2.2

PET (positron emission tomography)

Nuclear medicine slices made with a ring camera. The usual tracer, FDG, is made from sugar and collects in busy cells such as many cancers. Lesson 2.1

Pixel, voxel

A pixel is one square of an image grid; a voxel is the small block of tissue it stands for in a slice. Lesson 2.3

Pleuritic

Chest pain that is worse when breathing in. Lesson 2.4

Preliminary and final report

A preliminary report, often from a resident overnight, is later confirmed or corrected by an attending radiologist as the final report. Lesson 2.2

Prior

An earlier imaging exam used for comparison. Lesson 2.2

Protocol

The exact plan for how a scan is done: body part, contrast, timing. Chosen by a radiologist or technologist. Lesson 2.2

Pulmonary embolism (PE)

A blood clot that has travelled to the arteries of the lungs. Lesson 2.1

R

Radiograph

A flat X-ray image, sometimes called a film. Lesson 2.1

Radiologic technologist

Positions the patient and runs the X-ray, CT or MRI scanner. Also called a radiographer. Lesson 2.1

Radiologist

A physician who interprets medical images and writes the report. Lesson 2.1

RADS (Reporting and Data Systems)

ACR scoring systems such as BI-RADS (breast) and Lung-RADS that pair a category with a risk level and a next step. Lesson 2.4

Read-back

Repeating a critical result back to the person who gave it, to confirm it was heard correctly. Lesson 2.4

Reason for exam (indication)

The clinical question on the order that the scan should answer. Lesson 2.2

Reconstruction

The computer step that turns the signal collected by the scanner into images of the patient. Lesson 2.3

RIS (radiology information system)

Radiology's scheduling and tracking system. Lesson 2.2

S

Sequence (MRI)

One way of running an MRI scan. Each sequence, such as T1 or T2, shows tissues differently; fluid is dark on T1 and bright on T2. Lesson 2.1

Sonographer

Performs ultrasound exams and chooses which images to save. Lesson 2.1

SPECT

Single-photon emission computed tomography: a gamma camera circles the patient to make nuclear medicine slices, for example of blood flow to the heart. Lesson 2.1

STAT

Urgent, to be done or read now. Lesson 2.2

Structured report

A report written from a template with fixed headings and sometimes fixed choices. Lesson 2.4

Study and series

A study is one exam; a series is one set of images within it made in one way (for example, thin slices in a lung kernel). Lesson 2.3

T

Tracer

A small amount of radioactive substance given in nuclear medicine; the camera records where it collects. Lesson 2.1

U

Ultrasound

Imaging with sound waves and their echoes, shown live. No radiation. Lesson 2.1

W

Window and level

CT display settings: the level is the CT number shown as mid-gray, the width is the range spread from black to white. Lesson 2.3

Worklist

The radiologist's queue of exams waiting to be read, sorted by urgency. Lesson 2.2

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