DICOM Architecture: Technical Guide to Medical Image Protocol

1. What is DICOM?

DICOM(Digital Imaging and Communications in Medicine) is more than just a file format. It’s the international standatd protocol for medical imaging since 1993. Unlike regular image files that only store pixel data, DICOM packs both the image and crucial metadata about who took it, when, where, what equipment was used, and under whar conditions.

Key points that make DICOM special:

• Integrates medical information with imaging data in a single file.
• Ensures compatibility across different medical devices.
• Serves as the gold standard in medical imaging.

2. Deep Dive into DICOM File Structure

A DICOM file consists of two main components: File Meta Information and Data Set.

2-1. File Meta Information

Think of this as the file’s ID card. Here’s what you’ll find:

2-1-1. File Preamble

• First 128 bytes of the file
• Usually filled with 0x00
• Reserved space for special purposes
• No specific use defined in the DICOM standard

  2-1-2. DICM Identifier

• Follows right after the preamble
• Literally spells out “DICM” in ASCII
• Acts as the file’s signature
• NO DICM = Not a valid DICOM file!

  2-1-3. Meta Elements (Group 0002)

  These elements are cruicial for file interpretation:

• (0002,0001): File Meta Information Version
• (0002,0002): Media Storage SOP Class UID
• (0002,0003): Media Storage SOP Instance UID
• (0002,0010): Transfer Syntax UID
• (0002,0012): Implementation Class UID
• (0002,0013): Implementation Version Name

2-2. Data Set

Here’s where things get interesting! The data set consists of Data Elements structured like this:

[Tag: 4bytes] [VR: 2bytes] [Length: 2 or 4bytes] [Value: variable length]

Each element has:

• Tag: Group Number(2bytes) + Element Number(2bytes)
• VR (Value Representation): Defines the data type (DA for dates, TM for time, etc.)
• Length: Size of the value field in bytes
• Value: The actual data

3. Components of DICOM Architecture

DICOM follows a hierarchical structure that looks like this:

Patient
└── Study
    └── Series
        └── Instance

3-1. Patient

Contains basic patient identification information

Tag	Item Name
(0010,0010)	Patient’s Name
(0010,0020)	Patient ID
(0010,0030)	Patient’s Birth Date
(0010,0040)	Patient’s Sex

• Patient ID: A unique identifier assigned by the healthcare facility. This ID should remain consistent across different visits and examinations.

3-2. Study

Information about specific examination/diagnosis session

Tag	Item Name
(0020,000D)	Study Instance UID
(0008,0020)	Study Date
(0008,0030)	Study Time
(0008,0050)	Accession Number
(0008,0080)	Institution Name
(0008,0090)	Referring Physician’s Name
(0032,1060)	Requested Procedure Description
(0008,0032)	Study ID
(0032,1032)	Requesting Physician

• Accssion Number: A unique identifier for the requested procedure, typically generated by the Radiology Information System (RIS).
• Study Instance UID: A globally unique identifier that distinguishes this study from all others in the world, following DICOM’s UID (Unique Identifier) format.

3-3. Series

• Collection of sequential images within a single examination

Tag	Item Name
(0020,000E)	Series Instance UID
(0020,0011)	Series Number
(0008,0060)	Modality
(0008,103E)	Series Description
(0008,1010)	Station Name
(0008,1070)	Operators’ Name
(0018,0015)	Body Part Examined
(0018,1030)	Protocol Name
(0054,0081)	Number of Slices
(0040,0002)	Status

• Modality: Type of imaging equipment used
  • CT (Computed Tomography)
  • MR (Magnetic Resonance)
  • US (Ultrasound)
  • CR (Computed Radiography)
  • DX (Digital Radiography)
  • MG (Mammography)
  • XA (X-Ray Angiography)
• Status: Indicates the current state of the series
  • SCHEDULED: Examination is planned but not yet started
  • IN PROGRESS: Currently being acquired
  • COMPLETE: Acquisition is finished
  • VERIFIED: Results have been reviewed and validated
  • DISCONTINUED: Series was stopped before completion
  • CANCLED: Series was cancled before starting

3-4. Instance

• Information about individual images

Tag	Item Name
(0008,0018)	SOP Instance UID
(0020,0013)	Instance Number
(0020,0032)	Image Position Patient
(0020,0037)	Image Orientation Patient
(0028,0010)	Rows
(0028,0011)	Columns
(0028,0100)	Bits Allocated
(0028,0101)	Bits Stored
(0028,0102)	High Bit
(0028,0103)	Pixel Representation
(0020,4000)	Image Comments

• SOP Instance UID: A globally unique identifier for each DICOM instance, essential for tracking, storing, and retrieving medical images across different systems.