dicom structure
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History• 1985-1988 :
• Joint effort between Radiologist and Manufacturers to specify ACR-NEMA 1.0 and 2.0• ACR : American College of Radiology• NEMA : National Electrical Manufacturer Association
• 1993 :• 9 parts of DICOM (3.0)
• 2007 :• 18 parts of DICOM - 126 Supplements
• DICOM is developed under joint efforts of• ACR (American College of Radiology) • NEMA (National Electrical Manufacturers Assoc.) …… also more than 25 vendors…
IntroductionDigital Imaging and COmmunication in Medicine
is a standard for handling, storing, printing, and transmitting information in medical imaging. It includes a file format definition and a network communications protocol. The communication protocol is an application protocol that uses TCP/IP to communicate between systems. DICOM files can be exchanged between two entities that are capable of receiving image and patient data in DICOM format.
DICOM File Format
DICOM File Meta Info
DICOM Dataset
File Preamble
PrefixData ElementData ElementData ElementData Element
Data Element
***
128 Bytes (Set to 00H by default)DICMAttribute Name Tag Typ
eGroup Length (0002,
0000)1
File Meta Info Version (0002, 0001)
1
Media Storage SOP Class UID (0002, 0002)
1
Media Storage SOP Instance (0002, 0003)
1
Transfer Syntax UID (0002, 0010)
1
Implementation Class UID (0002, 0012)
1
Implementation Version Name (0002, 0013)
3
Source Application Entity Title (0002, 0016)
3
Private Info Creator UID (0002, 0100)
3
Private Info (0002, 00102)
1C
Group 0002H elements are always encoded in Explicit VR Little Endian
DICOM File Format
Data ElementData ElementData ElementData Element
Data Element
***
PrefixPreamble
Explicit V R other than above
Element Number
Group Number
Value Length Value Field
2 bytes2 bytes 4bytes Value Length bytes
Implicit V R
Element Number
Group Number
Value Representat
ionValue
Length Value Field
2 bytes2 bytes 2 bytes 2 bytes Value Length bytes
Explicit V R of OB, OW, OF, OD, SQ, UC, UR, UT or UNElement Number
Group Number
Value Representat
ionValue Field
2 bytes2 bytes 2 bytes Value Length bytes
Reserved
2 bytes
Value Length4 bytes
Value Representation (V R)• Clinical data comes in a wide variety of formats.
• Ex. Distances measured in millimeters, time in seconds, • patient names are typically written in alphabetic characters,
and so on. • The DICOM standard defines 27 basic data types, known as
value representations (VRs), • which are designed to encapsulate all possible clinical data
types. • Each VR has its own abbreviated two-letter name, a definition
of what it represents, a description of what characters are allowed in its data, and a pre-scribed data length.
Value Representation•Free Form Text VR:• SH: Short String• LO: Long String• ST: Short Text• LT: Long Text• UT: Unlimited Text
•Math VR:• IS: Integer String• DS: Decimal String• US: Unsigned Short• SS: Signed Short• UL: Unsigned Long• SL: Signed Long• FL: Floating Point Single• FD: Floating Point Double
• Fixed Format VR:• DA: Date• TM: Time• DT: DateTime• PN: Person Name
• Other VR:• OB: Other Byte• OW: Other Word• OF: Other Float • SQ: Sequence• AE: Application Entity• AS: Age String• AT: Attribute Tag
• Other VR•CS: Code String•UI: Unique Identifier•UN: Unknown
Unique IDentifier• UIDs are internal DICOM mechanism to identify
Studies, Series, Images, SOP classes, etc.• A UID is a string up to 64 characters including digits
and “.”• example SOP Instance UID 1.2.840.113619.2.65.3.200583648570.2428.1178103577.1
• No Leading zeroes in UID components are not allowed.• This string is MUST be UNIQUE around the world.
Transfer Syntax• A transfer syntax is the encoding methodology used to
send data over network, or to write data to a physical medium. 01001000
01100101 01101100 01101100 01101111 00100000 01000100 01001001 01000011 01001111 01001101 00001010
Hello DICOM
Transfer Syntax• Big Endian
• Store the most significant byte in the smallest address• Little Endian
• store the least significant byte in the smallest address
Address Value
1000 901001 AB1002 121003 cd
Address Value
1000 CD1001 121002 AB1003 90
Transfer SyntaxTransfer Syntax UID Transfer Syntax Name
1.2.840.10008.1.2 Implicit VR Endian: Default Transfer Syntax for DICOM1.2.840.10008.1.2.1 Explicit VR Little Endian1.2.840.10008.1.2.1.99 Deflated Explicit VR Little Endian1.2.840.10008.1.2.2 Explicit VR Big Endian
Transfer Syntax UID Transfer Syntax Name1.2.840.10008.1.2.4.50 JPEG Baseline (Process 1):
Default Transfer Syntax for Lossy JPEG 8-bit Image Compression1.2.840.10008.1.2.4.51 JPEG Baseline (Processes 2 & 4):
Default Transfer Syntax for Lossy JPEG 12-bit Image Compression1.2.840.10008.1.2.4.57 JPEG Lossless, Nonhierarchical (Processes 14)1.2.840.10008.1.2.4.70 JPEG Lossless, Nonhierarchical, First- Order Prediction
Default Transfer Syntax for Lossless JPEG Image Compression1.2.840.10008.1.2.4.80 JPEG-LS Lossless Image Compression1.2.840.10008.1.2.4.81 JPEG-LS Lossy (Near- Lossless) Image Compression1.2.840.10008.1.2.4.90 JPEG 2000 Image Compression (Lossless Only)1.2.840.10008.1.2.4.91 JPEG 2000 Image Compression1.2.840.10008.1.2.4.92 JPEG 2000 Part 2 Multicomponent Image Compression (Lossless Only)1.2.840.10008.1.2.4.93 JPEG 2000 Part 2 Multicomponent Image Compression1.2.840.10008.1.2.5 RLE Lossless1.2.840.10008.1.2.4.94 JPIP Referenced1.2.840.10008.1.2.4.95 JPIP Referenced Deflate1.2.840.10008.1.2.6.1 RFC 2557 MIME Encapsulation1.2.840.10008.1.2.4.100 MPEG2 Main Profile Main Level1.2.840.10008.1.2.4.103 MPEG-4 AVC/H.264 BD-compatible High Profile / Level 4.11.2.840.10008.1.2.4.102 MPEG-4 AVC/H.264 High Profile / Level 4.1
SOP Class UIDSOP Instance UID
Patient NamePatient IDPatient Birth DatePatient SexStudy UIDStudy DateStudy IDReferring PhysicianAccession NumberSeries UIDSeries NumberModality TypeManufacturerInstitution Name
Image UIDImage NumberImage TypeImage Pixel AttributesWindow width Window Center
Patient
Study
Series Series Series
ImageImageImageImageImageImage
ImageImageImage
Other Studies
Information Object Definition
Patient EntityStudy EntitySeries EntityImage Entity
General Image
AttributesImage Pixel Attributes
Samples per PixelPhotometric Interpretation
RowsColumns
Bits AllocatedBits Stored
Pixel RepresentationPixel Data
Planar Configuration
Image DisplaySamples per Pixel
Photometric InterpretationRows
ColumnsBits Allocated
Bits Stored
Pixel RepresentationPixel Data
Planar Configuration
Un used
Bits AllocatedPixel Cell
High Bit
High Bit
Un used Pixel Cell Un
used Pixel Cell
Pixel Data Stream
Pixel Sample0111215
Bits Allocated = 16Bits Stored = 12High bit = 11
Image DisplayPixel Cell
Pixel sample value
Pixel sample value
Pixel sample value
Pixel sample value
Pixel sample value
Pixel sample value
….. …. …. …..
…. …. …. … ……. …. …. ……. …. …. … ……. …. …. … …
Rows
Columns
Image displayPixel data Apply LUT Render
Window Width / Window Centerwhere x is the input value, y is an output value with a range from y min to y max
c is Window Center (0028,1050) and w is Window Width (0028,1051):
If (x <= c - 0.5 - (w-1)/2), then y = y minelse if (x > c - 0.5 + (w-1)/2), then y = y max ,else y = ((x - (c - 0.5)) / (w-1) + 0.5) * (y max - y min )+ y min
VOILUT FunctionSIGMOID DescriptorIf the value of VOI LUT Function (0028,1056) is SIGMOID, the function to be used to convert the output of the (conceptual) Modality LUT values to the input of the (conceptual) Presentation LUT is given byOUT =whereIN is the input value of the LUT (i.e., the output of the (conceptual) Modality LUT).WC (resp. WW) is the Window Center (resp. Window Width) defined interactively by the useror by using the values provided in (0028,1050) (resp. 0028,1051).Output_range is the maximum output value
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