Analysis of DICOM Format of Medical Images

Medical Imaging

• Medical Imaging medical imaging is used to study the interaction between the human body by means of certain media (such as X-ray, electromagnetic field, and ultrasound), and shows the structure and density of tissue and organ in the human body as images, A scientific science that allows diagnostic physicians to evaluate human health by judging the information provided by images, including medical imaging systems and medical image processing.
• The main instruments include X-ray imaging instruments, CT (general CT, spiral CT), sub-scan (PET), ultrasound (B-ultrasound, color Doppler ultrasound, cardiac color Doppler ultrasound, three-dimensional color Doppler ultrasound) MRI, ECG, and EEG

 

DICOM Introduction

• DICOM (Digital Imaging and communications in medicine) is an international standard for medical imaging and communication. It is ISO 12052 ). It defines medical image formats that meet clinical needs for data exchange. DICOM has been widely used in radiology, cardiovascular imaging, and radiology diagnostic equipment (such as X-ray, CT, MRI, and ultrasound ), it has been widely used in ophthalmology, dental, and other medical fields. Among the tens of thousands of medical imaging devices, DICOM is one of the most widely deployed medical information standards. Currently, about 10 billion level DICOM-compliant medical images are used for clinical use.
• The current standard is dicom3.0. Its composition is as follows:

  Part 1: Overview

  Part 2: Compatibility

  Part 4: Service Description

  Part 3: Information Objects

  Part 1: media storage applications

  Part 5: Data Structure and definition

  Part 6: Data Dictionary

  Part 7: Information Exchange Network Operations

  Part 8: Network Support for TCP/IP

  Part 9: point-to-point communication

  Part 10: media storage and file format

  Other parts: special media formats and physical media, printing, and security mechanisms

DICOM file

• DICOM files are medical files stored according to DICOM standards. They generally consist of a DICOM file header and a DICOM data set.
• The DICOM file header contains information related to the identification data set. Each DICOM file must contain a file header:

1. The introduction of the file, which consists of 128 bytes.
2. DICOM prefix. You can determine whether the file is a DICOM file based on whether the 4-byte string is equal to "dicm.
3. File Information element

• The main component of the DICOM file is the dataset, which is composed of DICOM data elements in the specified order. For DICOM files, explicit transmission is generally used, and data elements are arranged in ascending order by TAG. The most basic unit is data element, which consists of four parts:

1. Tag: A 16-bit unsigned integer ordered pair. The first eight digits represent the group number, and the last eight digits represent the element number.
2. Indicates the data type in the data element.
3. Value length: A 16-bit or 32-bit unsigned integer that represents the length of the data field.
4. Data field: the data type of the value of this field is determined by the value representation of this data element, and its storage length is an even number of bytes.

Tag

Each data element can be segmented from the beginning to the end: file meta tag, common tag, and pixel tag.

 

• File meta tag (group number + 0000): It is always expressed in the display VR mode without being affected by the transmission syntax, because it defines the transmission syntax; The dataelement of the file meta tag, it doesn't make much sense. Its VF value is the byte length of all dataelements in the entire group. One DICOM can have only one file meta tag or multiple file meta tags.
• Common Tag: Except for the object meta tag and pixel tag, the rest are the common tag data. Including: image width, height, data transmission format, patient name, patient birthday, medical records Hospital, Medical Records Department, description of illness, and so on.
• Pixel tag (7fe0, 0010): indicates that dataelement stores the image data of medical records. For example, tag (,) determines whether the reading method of common tags is little byte or big byte, and implicit VR or display VR. It is determined by its value. Tag (7fe0, 0010) pixel data starting point. Other important tags are as follows.

 

 

DCM File

• Files that meet DICOM standards are usually suffixed with. DCM. When a DICOM file is selected for display, the extension name of the DICOM file is DCM or DCM. After checking the extension name of the file name, you can preliminarily determine whether the file is a DICOM file, however, if the suffix name meets the requirements, it does not mean a standard DICOM file. You need to open the file, skip the introduction of the 128-byte file, read four bytes, and check whether the data of these four bytes is "dicm ". When the requirements are met, a DICOM file can be judged.

Parse DICOM files

You can use Sante DICOM viewer to view DICOM data.

• Skip the introduction of the 128-byte file, read "dicm" Four bytes, and confirm that the file is in DICOM format.
• Read important data elements, such as transmission syntax. The group number 0010 describes the patient information, and the group number 0008 describes the feature parameters.
• Read the common tag until the ttag (7fe0, 0010), that is, the start of the pixel data. The storage sequence of pixel data, from left to right, from top to bottom.

 

Analysis of DICOM Format of Medical Images