Structure of DICOM Image

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DICOM Digital Imaging Communications in Medicine

Transcript of Structure of DICOM Image

Page 1: Structure of DICOM Image

DICOMDigital Imaging Communicationsin Medicine

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Session Outline List of modalities and study typesCT/DX/US study structure Structure of DICOM image

DIOCM composite insatnce IOD information Module

How the dicom study came to PACS serverTransfer syntax for transfer study to PACS

Storage of DICOM in PACSStorage Services

Query/Retrieve from PACSPre Fetch Data

dcm File sections Imaging Data Imaging fundamental WW/WC Brightness and contrast

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List of Modalities and study types

• Modality Types• Modality CT• Modality CR• Modality US• Modality XA• Modality MR• Modality DX• Modality NM• Modality RF

Study Types-CT CRUSXAMRDXNMRFBIDGECGEMESGMHC VL

• MG• OP• OPM• OPR• OPV• PR• PX• RD• RG• RP• RS• RT• RTIMAG• SC• SM• SR

• LS• TG• VL• XC

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CT Study:

Study

Series

Instances

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DX Study:

Study

Series

Instances

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US study:

Study

Series

Instances & Frames

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Structure of DICOM Study

• The data model defines Information Entities (IE’s)• Patient• Study• Series • Image

• The classes of the DICOM Objects however are composites made of modules from different entities.

• The classes of the DICOM static data model are called SOP (Service Object Pair) Classes and are defined by IOD’s – Information Object Definition.

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DICOM Composite Instance IOD Information Model

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Secondary Capture Image IOD:IE Module UsagePatient Patient M

Clinical Trial Subject U

Study General Study M

Patient Study U

Clinical Trial Study U

Series General Series M

Clinical Trial Series U

Equipment General Equipment U

SC Equipment M

Image General Image M

Image Pixel M

Device U

Specimen U

SC Image M

Overlay Plane U

VOI LUT U

Modality LUT U

SOP Common M

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Attribute Name Tag Type Attribute DescriptionPatient's Name (0010,0010) 2 Patient's full name.

Patient ID (0010,0020) 2 Primary hospital identification number or code for the patient.

Patient's Birth Date (0010,0030) 2 Birth date of the patient.

Patient's gender (0010,0040) 2 Gender of the patient.

STUDY MODULE ATTRIBUTES:

PATIENT MODULE ATTRIBUTES:

Attribute Name Tag Type Attribute DescriptionStudy Instance UID (0020,0008) 1 Unique identifier for the Study.

Study Date (0008,0020) 2 Date the Study started.

Study Time (0008,0030) 2 Time the Study started.

Referring Physician's Name (0008,0090) 2 Name of the patient's referring physician

Study ID (0020,0010) 2 User or equipment generated Study identifier.

Accession Number (0008,0050) 2 A RIS generated number that identifies the order for the Study.

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Attribute Name Tag Type Attribute Description

Modality (0008,0060) 1 Type of equipment that originally acquired the data used to create the images in this Series.

Series Instance UID (0020,000E) 1 Unique identifier of the Series.

Series Number (0020,0011) 2 A number that identifies this Series.

Laterality (0020,0060) 2C Laterality of (paired) body part examined.

SERIES MODULE ATTRIBUTES:

Attribute Name Tag Type Attribute Description

Conversion Type (0008,0064) 1 Describes the kind of image conversion

Modality (0008,0060) 3 Source equipment for the image.

SC EQUIPMENT MODULE ATTRIBUTES:

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GENERAL IMAGE MODULE ATTRIBUTES:

Attribute Name Tag Type Attribute Description

Instance Number (0020,0013) 2 A number that identifies this image.

Patient Orientation (0020,0020) 2C Patient direction of the rows and columns of the image.

Content Date (0008,0023) 2C The date the image pixel data creation started.

Content Time (0008,0033) 2C The time the image pixel data creation started.

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IMAGE PIXEL MACRO ATTRIBUTES:

Attribute Name Tag Type Attribute Description

Samples per Pixel (0028,0002) 1 Number of samples (planes) in this image

Photometric Interpretation

(0028,0004) 1 Specifies the intended interpretation of the pixel data

Rows (0028,0010) 1 Number of rows in the image

Columns (0028,0011) 1 Number of columns in the image

Bits Allocated (0028,0100) 1 Number of bits allocated for each pixel sample. Each sample shall have the same number of bits allocated.

Bits Stored (0028,0101) 1 Number of bits stored for each pixel sample. Each sample shall have the same number of bits stored.

High Bit (0028,0102) 1 Most significant bit for pixel sample data. Each sample shall have the same high bit.

Pixel Representation (0028,0103) 1 Data representation of the pixel samples. Each sample shall have the same pixel representation.

Pixel Data (7FE0,0010) 1C A data stream of the pixel samples that comprise the Image.

Planar Configuration (0028,0006) 1C Indicates whether the pixel data are sent color-by-plane or color-by-pixel.

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SOP COMMON MODULE ATTRIBUTES:

Attribute Name Tag Type Attribute Description

SOP Class UID (0008,0016) 1 Uniquely identifies the SOP Class

SOP Instance UID (0008,0018) 1 Uniquely identifies the SOP Instance

Specific Character Set (0008,0005) 1C Character Set that expands or replaces the Basic Graphic Set.

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How the DICOM study send from modality to PACS

•  Auto forward is a configuration in modalities which facilitate the automatic transfer of images to the desired DICOM destination once the technician completes the study.

• In real life technologists may not want to send the complete study to the PACS or they may want to add another series which could be for example a series containing lung window or bone window of acquired study.

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Transfer Syntax for transfer study to PACS

• When sharing objects with other applications,

everyone should be able to use the same object. The

common solution for such problems is serialization.• Serialization is the process of writing a data structure

or object state to a format that can be stored in a file or transmitted across a network so it can be read on the other side of the same or by another process.

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Storage of DICOM study in PACS• The modality acquires the images in full resolution, i.e.,

uncompressed, and the PACS typically compresses the images in a lossless compressed format.

• Compression will be of 2 types- – Lossy: lossy compression reduces a file by permanently

eliminating certain information, especially redundant information.

– Lossless: This will compress every single bit of data that was originally in the file remains after the file is uncompressed. Ex-• JPEG2000• RLE • Even JPEG-LS

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Storage Services of DICOM in PACS

• The DICOM Storage service is a fundamental service in DICOM, as it allows exchange of data among multiple devices over the DICOM network.

• In DICOM Storage Commitment service SCU(Service class user) issues a normal DICOM Storage request to a SCP (service class provider) in order to transfer some DICOM data, and the SCP accepts this Storage request by returning a successful C-STORE-RSP message, there is the guarantee that the SCP has simply accepted the transferred DICOM data.

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Query/Retrieve Service• The Query phase: During the Query phase, the SCU sends a C-FIND-RQ (request) message to the SCP, also including eventual search parameters, and the SCP is expected to answer returning one or more C-FIND-RSP (response) messages to the SCU, conveying the items matching the search criteria. • The Retrieve phase: During the Retrieve phase, the SCU sends a C-MOVE-RQ (request) message to the SCP, specifying the items to be retrieved (normally, a Patient, a Study, a Series or a Instance). This request will trigger the transfer of the appropriate DICOM data through the DICOM Storage service (through C-STORE messages)

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Pre-fetch Data:Workflow automation mechanism, for fetching relevant prior studies of the Patient from Image Archives (PACS).This service is able to retrieve the DICOM objects back from the archive to a specific local file system.

Why Prefetch:– Required for diagnostic scenarios which need

comparison of studies acquired over time.

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dcm file sections :In a dcm file 3 sections will come-• Header- It stores demographic information about the patient,

study (imaging study, image dimensions) and information required by the computer to correctly display the image.

• Meta Data- It provide the information about image data, such as the size, dimensions, bit depth and equipment settings used to capture the image.

• Look up Table(LUT)- LUT transformation transforms the modality pixel values into pixel values which are meaningful for the user or the application. There are 3 types of lookup table (LUT) in dicom:

• Modality LUT• VOI LUT• Presentation LUT

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Imaging Data

• Study components:– Imaging data- A medical image is

the representation of the internal structure or function of an anatomic region in the form of an array of picture elements called pixels.

– Non imaging data - • A DICOM data object consists of

number of attributes-patient, study and series.

• It contains Structured Report(SR) also. This report is generate in modality.

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Imaging Fundamental

• Modality units- For instance, the original pixel values could store a device specific value that has a meaning only when used by the device that generated it.

• Imaging Units• Transformation-

• Linear- The rescale intercept and slope are applied to transform the pixel values of the image into values that are meaningful to the application.

• Non-Linear- When the transformation is not linear, then a LUT (lookup table) is applied.

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What is WW/WC • Window Center contains the input value that is the center of the

window. Window Width contains the width of the window.• The window width/center specify which pixels should be visible:

all the pixels outside the values specified by the window are displayed as black or white.

• To calculate the pixels to display using the window center/width:1.) lowest_visible_value = window_center - window_width / 22.) highest_visible_value = window_center + window_width / 2

• For instance, if the window center is 100 and the window width is 20 then all the pixels with a value smaller than 90 are displayed as black and all the pixels with a value bigger than 110 are displayed as white.

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What is Brightness Contrast

• Up to decrease brightness (window level goes up)

• Down to increase brightness(Window level goes down)

• Left to increase contrast (window width shrinks)• Right to decrease contrast (window width expands)

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Thank You!