Later pages use these terms without defining them. Image orientation is explained in more detail in 2.14 Image geometry: spacing, orientation and the affine.

Term notation/acronym Meaning
Radiologist A physician who interprets medical images and writes the report.
Radiographer The professional who operates the scanner and acquires the images; called a radiologic technologist in the US.
Pathologist A physician who diagnoses disease from tissue and cells, on glass slides or whole-slide images.
Picture archiving and communication system PACS The hospital system that stores images and sends them to viewing stations.
Examination, series, image One visit to a scanner (also called a study); one acquisition or reconstruction within it; one slice or frame of a series.
Case One patient examination together with everything acquired with it: images, reports, test results.
Screening Examining people without symptoms to find disease early, for example mammography for all women in an age range.
Diagnostic examination An examination of a patient with symptoms or an earlier abnormal finding.
Recall recall rate = (TP + FP) / N Calling a screened person back for further tests after a suspicious result. Not the machine learning metric.
Prevalence π = (TP + FN) / N The fraction of the examined population that has the disease.
Reference standard The best available answer against which a model is trained or evaluated, such as a biopsy, a consensus of readers or follow-up. Often called ground truth, although it can be wrong.
Lesion Any abnormal region of tissue, such as a tumor, cyst or scar.
Benign, malignant Not cancerous; cancerous.
Interval cancer A cancer diagnosed between two screening rounds, after a normal screening result.
Axial, coronal, sagittal The three standard image planes. Axial slices are perpendicular to the head-to-foot axis, coronal slices separate front from back, and sagittal slices separate left from right.
Anterior, posterior, superior, inferior A, P, S, I Toward the front, back, head and feet of the patient. Left and right always mean the patient's left and right.
Radiological convention Axial and coronal images are displayed as if the viewer faces the patient, so the patient's left appears on the right of the screen.
Contrast agent A substance given to the patient to make vessels or tissues stand out, such as iodine in CT and gadolinium in MRI.
Computed tomography CT X-ray imaging from many angles, reconstructed into a 3D map of how strongly each point attenuates X-rays.
Magnetic resonance imaging MRI Imaging of hydrogen nuclei in a strong magnetic field; the contrast depends on tissue properties and the chosen pulse sequence.
Ultrasound US Imaging with high-frequency sound reflected at boundaries between tissues.
Hounsfield unit HU The CT intensity scale, on which air is −1000 and water is 0.
Digital Imaging and Communications in Medicine DICOM The standard file format and network protocol for medical images.
Region of interest ROI A part of an image selected for analysis or annotation.
Breast Imaging Reporting and Data System BI-RADS The categories radiologists use to report breast findings, from 0 (incomplete) to 6 (known cancer).
True positive, false positive, true negative, false negative TP, FP, TN, FN; N = TP + FP + TN + FN Counts of cases by test result and true state: a true positive is a diseased case that the test flags, a false positive a healthy case that it flags, a true negative a healthy case that it clears and a false negative a diseased case that it misses. N is the total number of cases.
Sensitivity, specificity TPR = TP / (TP + FN); TNR = TN / (TN + FP) The fraction of diseased cases that a test flags; the fraction of healthy cases that it clears. Sensitivity is the recall of machine learning.
Positive predictive value PPV = TP / (TP + FP) The fraction of positive results that are truly diseased. It falls when prevalence falls.
Computer-aided detection CAD Software that marks suspicious regions for a reader to review.
Randomized controlled trial RCT A study that assigns participants at random to an intervention or a control; the strongest evidence that an intervention helps.
Retrospective, prospective study A study of data that were already collected; a study that collects new data under a plan fixed in advance.
Medical Device Regulation MDR The EU law that medical devices, including diagnostic software, must meet before they can be used clinically; compliant devices carry a CE mark.
Biopsy Removal of a tissue sample for examination under a microscope.
Whole-slide image WSI A digital scan of an entire glass slide at microscope resolution, often billions of pixels.
Hematoxylin and eosin H&E The standard tissue stain: hematoxylin colors nuclei blue-purple and eosin colors cytoplasm and stroma pink.
Immunohistochemistry IHC Staining with antibodies that shows where a specific protein is found in tissue.
Fluorescence microscopy Microscopy of light emitted by fluorescent labels bound to specific molecules, usually recorded as one channel per label.
Field of view FOV The region of space captured in one image.
High-content screening HCS Automated microscopy of many samples, such as cells treated with thousands of compounds, with image analysis to measure the effects.
Batch effect A systematic difference between samples processed at different times, at different sites or with different reagents, unrelated to the biologyPicture archiving and communication system