The Structure of DICOMDIR

DICOMDIR acts as a "Directory" for DICOM file sets and holds a full 4 level hierarchy (PATIENT --> STUDY --> SERIES --> IMAGE) as shown below:

DICOMDIR files can be read using DicomDataSets.ReadDirectory method in DicomObjects and the complex structure of linked lists with offsets is held in a single DicomDataSet object.

Coronal, Sagittal & Transverse position calculation

To calculate frame position in terms of Sagittal, Coronal and Transverse position please see the attached code.


Transfer Syntax Control on the Network

How can I control the Transfer Syntax (compression) used when I send images over the network?

It is important first to understand how DICOM negotiation occurs in general.

Configuring a Web Server to send out DICOM files

Whilst the DicomObjects ReadURL method is extremely useful for web projects, some people have problems configuring their web servers to allow DICOM files to be sent. The solution is of course different for different web servers:


Before the DICOM format, NEMA (National Electrical Manufacturers Association) proposed two formats NEMA-1 and NEMA-2. (This is why DICOM is sometimes referred to as DICOM-3.) Several manufactures had there own proprietary variations on the NEMA format (e.g. SPI, IS&C).

Number of Overlays in Image

How overlay data is stored

There are two ways of storing overlays in DICOM Image:

  • Overlay data stored in unused bit planes of the Pixel Data (7FE0,0010) with Samples Per Pixel (0028,0002) of 1. This usage has now retired.
  • Overlay data stored in separate "Overlay pixel data" attribute (60xx,3000).

DICOM Error/Warning Code

Below is a list of common DICOM Error/Warning Code (not the complete list):


UnsharpLength and Enhancement

The DicomImage.UnsharpLength and DicomImage.UnsharpEnhancement parameters are documented in the help file. Basically, the UnsharpLength defines the size of the area (in image pixels) over which the enhancement is performed. Odd number is expected for UnsharpLength as it defines the area around the center pixel, which is then compared to those pixels around it to see if it should be enhanced up or down. Enhancement defines how much the difference should be increased/decreased.

Example 1:

If the pixels are as follows:

Transport Layer Security

DICOM Transport Layer Security (DICOM TLS) is derived from SSL 3.0 and is largely compatible with it.

For samples showing how to use DICOM TLS in DicomObjects (COM & .NET), please see the examples page

Please check part 15 of the DICOM standard for more information about TLS.


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