DICOMDIR结构

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无论是在DICOM文件还是DICOM通信中，其信息都是由许多data element（数据单元)的集合所表示，每个data element表示一个属性，如病人姓名、图像类型等等。这些data element按照Tag值从小到大依次连接，类似于数据结构的链表或者数组(SQ类型有另外的编码方式,以后会讲到)，请看下图，一个data element包含四个字段Tag,VR,ValueLength,Value Field.

DICOMDIR 是一个可变长度迷你 database 文件。由 group (0002, xxxx) 和 group (0004, xxxx) 为主题。描述的是一个 4 层的树状结构 (tree structure)。

1. Patient
2. Study
3. Series
4. Image

将data element的数据结构编码为字节流时受以下几个因素影响:

1.传输语法： Implicit/Explicit VR, BIG/LITTLE Endian

2.VR

当采用implicit VR时，其编码如下，这个时候是没有VR字段的，它采用data dictionary默认的VR.

DICOMDir结构的delphi实现

///////////////////////////////////////////////////////////////////////////////
//
// Filename: uDICOMDIR.pas
//
// Summary:
//    DicomStation Source With Delphi7
//
// Modification History:
//    Date         By       Summary
//    --------     -------- ---------------------------------------------
//    07/24/2011   hegb     Original Creation
///////////////////////////////////////////////////////////////////////////////
unit uDICOMDIR;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
//Instance Class
TImageItem = class(TObject)
    NextDirRecordOffset: LongWord; //(0004,1400)
    RecordInUseFlag: Word; //(0004,1410)
    LowerLevelDirOffset: LongWord; //(0004,1420)
    DirRecordType: string; //(0004,1430)
    ReferenceFileID: string; //(0004,1500)
    ReferenceTransSyntaxUID: string; //(0004,1512)
    InstanceNumber: string; //(0020,0013)
public
    constructor Create;
    destructor Destroy; override;
end;

//Series Class
TSeriesItem = class(TObject)
    NextDirRecordOffset: LongWord; //(0004,1400)
    RecordInUseFlag: Word; //(0004,1410)
    LowerLevelDirOffset: LongWord; //(0004,1420)
    DirRecordType: string; //(0004,1430)
    Modality: string; //(0008,0060)
    SeriesInstanceUID: string; //(0020,000E)
    SeriesNumber: string; //(0020,0011)
private
    ImageList: TList; //Image for this Series
public
    procedure AddImage(pImage: TImageItem);

    constructor Create;
    destructor Destroy; override;
end;

//Study Class
TStudyItem = class(TObject)
    NextDirRecordOffset: LongWord; //(0004,1400)
    RecordInUseFlag: Word; //(0004,1410)
    LowerLevelDirOffset: LongWord; //(0004,1420)
    DirRecordType: string; //(0004,1430)
    StudyDate: string; //(0008,0020)
    StudyTime: string; //(0008,0030)
    AccessionNumber: string; //(0008, 0005) /////////(0008,0050) ===== SH
    StudyInstanceUID: string; //(0020,000D)
    StudyID: string; //(0020,0010)
private
    SeriesList: TList; //Series for this Study
public
    procedure AddSeries(pSeries: TSeriesItem);

    constructor Create;
    destructor Destroy; override;
end;

//Patient Structure
TPatientItem = class(TObject)
    NextDirRecordOffset: LongWord; //(0004,1400)
    RecordInUseFlag: Word; //(0004,1410)
    LowerLevelDirOffset: LongWord; //(0004,1420)
    DirRecordType: string; //(0004,1430)
    PatientName: string; //(0010,0010)
    PatientID: string; //(0010,0020)
private
    StudyList: TList; //Study for this Patient
public
    procedure AddStudy(pStudy: TStudyItem);

    constructor Create;
    destructor Destroy; override;
end;

//DicomDir Class
TDicomDir = class(TObject)
    GroupLength: LongWord; //(0002,0000)
    FileMetaVersion: string[2]; //(0002,0001)        ====OB====
    MediaSOPClassUID: string; //(0002,0002)
    MediaSOPInstanceUID: string; //(0002,0003)
    TransferSyntaxUID: string; //(0002,0010)
    ImplementClassUID: string; //(0002,0012)
    ImplementVersionName: string; //(0002,0013)
    FilesetID: string; //(0004,1130)
    RootDirFistRecord: LongWord; //(0004,1200)
    RootDirLastRecord: LongWord; //(0004,1202)
    FileSetConsFlag: Word;   //(0004,1212)
    DirRecordSequence: LongWord; //(0004,1220)     ====SQ====
    SOPClassUID: string; //(0008, 0016)
private
    PatientList: TList; //Patient for DICOMDIR
public
    procedure AddPatient(pPatient: TPatientItem);
    procedure ClearPatient;

    function WriteDicomDir(FilePath: string): Boolean;
    constructor Create;
    destructor Destroy; override;
end;

function GetEvenStr(const str: string): string;

var
g_pDICOMDIR: TDicomDir;

implementation

const
GroupTagLen = 2;   //Group Number -- 2bytes
ElementTagLen = 2; //Element Number -- 2bytes
// VR2 = 2;           //Explicit VR时，如果VR = OB,OW,OF,SQ,UT,UN时，VR占用2字节
// VR4 = 4;           //Explicit VR时，如果VR <> OB,OW,OF,SQ,UT,UN时，VR占用4字节
// VR_Len2 = 2;       //Explicit VR时，如果VR = OB,OW,OF,SQ,UT,UN时，Value Length占用2字节
// VR_Len4 = 4;       //Explicit VR时，如果VR <> OB,OW,OF,SQ,UT,UN时，Value Length占用4字节

var
DICOM_signature: array[0..131] of byte =
    (
       0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0,
       0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0,
       0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0,
       0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0,
       0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0,
       0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0,
       0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0,
       0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0, 0, 0, 0 , 0,
       68, 73, 67 , 77
    );

VR_Reserved: array[0..1] of Byte = (0, 0);

ItemBegin_Group: Word = $FFFE;
ItemBegin_Element: Word = $E000;
ItemEnd_Group: Word = $FFFE;
ItemEnd_Element: Word = $E00D;
ItemEnd_Sequence: Word = $E0DD;

ItemBegin_Value: LongWord = $FFFFFFFF;
ItemEnd_Value: LongWord = $00000000;

iOffSet: LongWord = 0;

procedure WriteDicomDir;
begin
end;

function SwapLong(Value: Cardinal): Cardinal;
asm
BSWAP EAX
end;

function GetEvenStr(const str: string): string;
begin
if Length(str) mod 2 <> 0 then
    Result := str + Char(0)
else
    Result := str;
end;