Imaging Data 101

What is a DICOM?

DICOM® (Digital Imaging and Communications in Medicine) is the international standard to transmit, store, retrieve, print, process, and display medical imaging information (source: Data is available in the DICOM format as produced by the imaging device. Each DICOM file contains extensive metadata in a header as well as pixel data for the image itself. The header portion of a DICOM file almost always contains PHI; pixel data may also contain PHI.

What is a header?

In the context of biomedical imaging, an image header represents embedded metadata. This metadata can include patient health information (PHI) such as patient name, medical record number, and date of birth, as well as image acquisition parameters such as image dimensions, voxel size, repetition time (TR), and voxel data type.  

What is an image?

An image is defined as one slice in an imaging series. There can be from one to hundreds of images in a given imaging series.

What is an imaging examination?

An imaging examination, more commonly abbreviated imaging exam or imaging study, contains all the images acquired in a given imaging protocol. An imaging examination can contain from hundreds of images to thousands depending on the imaging protocol. Each imaging examination is assigned a unique accession number on PACS.

AIR users are allowed to retrieve a set number of imaging examinations. This retrieval limit is dictated by the AIR Access Plan for a given IRB. Thus, the retrieval count represents the total number of imaging examinations one can retrieve, not the absolute number of images.

What is an imaging modality?                   

An imaging modality describes the imaging equipment and/or method used to acquire certain structural or functional information about the body. These include but are not limited to computed tomography (CT) and magnetic resonance imaging (MRI).

It is helpful to learn about the relationship between an imaging modality and the average amount of data each imaging exam for that respective imaging modality requires. As a general rule, the amount of data each imaging exam requires for storage increases as the number of images in that imaging exam increases. In the context of AIR, this relationship helps explain why some imaging exams take longer to queue and retrieve than others.

What is an imaging protocol?

An imaging protocol has three main components: imaging modality, anatomical region of interest, and acquisition parameters. Acquisition parameters dictate how each particular imaging series is collected. These include but are not limited to details describing image dimensionality (i.e. 3D vs 2D), perspective (axial vs coronal vs sagittal), and granularity (ex: slice thickness). This information is loaded on a scanner prior to scanning and can be modified under special circumstances.

What is an imaging series?

An imaging series describes the specific type of structural or functional imaging data captured by an imaging modality given a pre-determined set of acquisition parameters. An imaging series can contain from a few images to hundreds of images. There are typically a dozen imaging series in a whole imaging protocol.

What is PHI?

Protected health information (PHI) is any information in the medical record or designated record set that can be used to identify an individual and that was created, used or disclosed in the course of providing a health care service such as diagnosis or treatment (source: UCSF IRB). For more information, please see this page.