7.4.1.7 General Image#
This normative section contains extensions to DICOM tags defined in the General Image module which are relevant to orthodontic image acquisition.
References:
Extensions in Table 7.4.1.7-1 are from ADA Standard No. 1114 Rev. ??. Section 6.1
Attribute |
Tag |
Type |
Attribute Description |
|---|---|---|---|
Image Type |
(0008,0008) |
R+ |
See DICOM PS3.3: Section C.7.6.1.1.2. This is a multi-valued attribute; one of these value pairs shall be used:
(Note: When saving both the original and the derived image, the derived image will have to reference the original image making use of the General Reference Module.) |
Anatomic Region Sequence |
(0008,2208) |
O+ |
When applied to orthodontic photographs, the anatomic region is Mouth for intraoral views, and Head/Neck for extraoral views. See Section 7.2.1 for coded values taken from DICOM CID 4028 Craniofacial Anatomic Region 7.2.1 CID 4028 - Craniofacial Anatomic Region |
>Anatomic Region Modifier Sequence |
(0008,2220) |
O+ |
This modifier is used to clarify which side of the region is contained in the image. See Section 7.2.2 for coded values taken from DICOM CID 247 Laterality |
>>Primary Anatomic Structure Sequence |
(0008,2228) |
O+ |
For orthodontic photographs, the primary anatomic structure for extraoral views is designated as Face Structure (body structure). In contrast, intraoral views exhibit a broader range of variations. See Section 7.2.4 for coded values taken from CID 4061 7.2.4 CID 4061 - Head and/or Neck Primary Anatomic Structure. Head and/or Neck Primary Anatomic Structure |
>>>Anatomic Region Modifier Sequence |
(0008,2220) |
O+ |
This modifier is used to clarify which side of the structure is contained in the image.
|
Instance Number |
(0020,0014) |
R+ |
To ensure images are presented in a specific sequence, set the Instance Number (0020,0013) for each image in a series according to the desired order. See Section 7.4.1.7.1 7.4.1.7.1 Instance Number (0020,0013) Examples for guidance and examples. |
Patient Orientation |
(0020,0020) |
R+ |
Patient direction of the rows and columns of the image. Required because the IOD VL Photographic Image does not require Image Orientation (Patient) (0020,0037) or Image Position (Patient) (0020,0032), and the IOD VL Photographic Image does not require Image Orientation (Slide) (0048,0102). See Section 7.2.5 7.2.5 Patient Orientation for guidance and allowed values. |
Image Laterality |
(0020,0062) |
R+ |
See Section 7.2.3 cid_144 for guidance and allowed values. |
Image Comments |
(0020,4000) |
O+ |
According to DICOM, Image comments can be any string with a maximum lengthof 10240 characters. N ew lines and tabs are allowed. For orthodontic purposes, any kind of clinical comments for an image would normally go in the practice management software, or in a DICOM structured report. We recommend this field to be used to store the image view type with the following format: where:
An example string: |
Quality Control Image |
(0028,0300) |
O+ |
Indicates whether or not this image is a quality control or phantom image. In the orthodontic practice, a quality control image is usually an image that the staff acquires to ensure that the equipment is functioning as desired, or to test new settings (flash, exposure, …) on the camera. Under these circumstances, set the value to For regular production use, this value should always be set to |
Burned in Annotation |
(0028,0301) |
O+ |
According to DICOM, burned in annotation indicates whether or not an image contains sufficient burned in annotation to identify the patient and date the image was acquired. If this Attribute is absent, then the image may or may not contain burned in annotation. For orthodontic purposes, conventionally photographs do not contain any burned in annotations. If this were the case for your software, thisvalue could always be present and set to |
Lossy Image Compression |
(0028,2110) |
O+ |
Because of the varied nature of photographic capture equipment used for orthodontic purposes, this tag should be used. E.g, some cameras are configured to store images in raw and uncompressed format, others will save a compressed JPEG image. See Section 7.4.1.7.2 7.4.1.7.2 Lossy Image Compression (0028,2110) - Guidance for guidance on encoding this attribute. |
7.4.1.7.1 Instance Number (0020,0013) Examples#
To ensure images are presented in a specific sequence, set the Instance Number (0020,0013) for each image according to the desired order.
Examples:
For example, if you have a series of intraoral photographs, assign Instance Numbers incrementally:
(0020,0013) Instance Number: 1 # Frontal view
(0020,0013) Instance Number: 2 # Right lateral view
(0020,0013) Instance Number: 3 # Left lateral view
(0020,0013) Instance Number: 4 # Maxillary occlusal view
(0020,0013) Instance Number: 5 # Mandibular occlusal view
When generating DICOM files programmatically, set the Instance Number attribute for each image object:
# Example using pydicom
import pydicom
ds = pydicom.Dataset()
ds.InstanceNumber = 1 # Set according to the image order
# ... set other attributes ...
ds.save_as('image1.dcm')
Repeat for each image, incrementing the Instance Number as needed. This ensures that DICOM viewers and systems can display the images in the intended sequence.
Non-Sequential Instance Numbers
Instance Numbers do not have to be strictly sequential. For example, you may assign non-consecutive values to allow for future insertion of images or to match an external numbering scheme:
(0020,0013) Instance Number: 10 # Frontal view
(0020,0013) Instance Number: 20 # Right lateral view
(0020,0013) Instance Number: 30 # Left lateral view
DICOM viewers will still use the Instance Number to determine display order, regardless of whether the numbers are consecutive.
7.4.1.7.2 Lossy Image Compression (0028,2110) - Guidance#
7.4.1.7.2.1 Compression Use Cases#
Compression, in general, aims to reduce file size, with or without decreasing data quality of the original file. DICOM is a medical imaging file standard used to store multiple information such as information of the image itself (resolution, pixel data, bit allocation, compression type, etc.) . With the rising usage of imaging in clinical diagnosis, there is a need for a fast and secure method to share a large number of images between practitioners, and compression is used to facilitate interoperability.
The main purpose of compression techniques is memory efficiency, fast compression, and the generation of the best output. It can be divided into two types, lossless compression and lossy compression. Lossless compression is a type of data compression which does not remove any information from the initial data, while the lossy compression removes some of the information from the initial data.
Compression of image may compromise the diagnostic value of photographs and is therefore not the preferred method of storage. The main reasons to utilize compression in the past were related to storage costs and bandwidth speed, which, over time, have increased by orders of magnitude. In addition, each image is composed of single relatively small file (less then 20MB).
According to DICOM :
The Attribute Lossy Image Compression (0028,2110) conveys that the Image has undergone lossy compression. It provides a means to record that the Image has been compressed (at a point in its lifetime) with a lossy algorithm and changes have been introduced into the pixel data. Once the value has been set to “01”, it shall not be reset.
Note
If an image is compressed with a lossy algorithm, the Attribute Lossy Image Compression (0028,2110) is set to “01”. Subsequently, if the image is decompressed and transferred in uncompressed format, this Attribute value remains “01”. The value of Lossy Image Compression (0028,2110) in SOP Instances containing multiple frames in which one or more of the frames have undergone lossy compression shall be “01”.
For orthodontic purposes, this tag should be used, because of the varied nature of photographic capture equipment. Some cameras are configured to store images in raw and uncompressed format, others will save a compressed JPEG image. In order to correctly encode this information, the following three DICOM tags should be used.
In an orthodontic setting, the following use cases are to be considered:
Use Case |
(0028,2110) |
(0028,2112) |
(0028,2114) |
|
0 1 |
Photograph was acquired with a camera which saves the images in RAW uncompressed format, or a lossless compression method. For example: TIFF, RAW or PNG. |
00 |
not present |
not present |
0 2 |
Photograph was acquired with a camera which saved the image using a lossy compression scheme, for example JPEG. |
01 |
For a 30:1 compression ratio, set to 30. If unknown, do not add this tag. |
See Lossy IMage Compression Method below. |
0 3 |
Photograph was acquired with a camera using an unknown type of image format, and then converted into DICOM. |
If image is in a lossy compression format like JPEG, use 01 here and follow same indications as above use case 02. Otherwise don’t specify this tag at all. |
If image is in a lossy compression format like JPEG, follow same indications as above use case 02. Otherwise don’t specify this tag at all. |
If image is in a lossy compression format like JPEG, follow same indications as above use case 02. Otherwise don’t specify this tag at all. |
0 4 |
An existing DICOM image was modified and compressed with a lossy algorithm. |
01 |
For a 30:1 compression ratio, set to 30. If unknown, do not add this tag. |
See Lossy Image Compression Method below. |
0 5 |
Photograph was taken using an analog camera, and image was then converted into digital using a scanner. |
Use SC Secondary Capture IOD. Then set this tag following the same guidelines as use case 01 or 02 above, s ubstituting the camera with whatever imaging device was used to acquire or scan the analog photograph or slide. |
Use SC Secondary Capture IOD. Then set this tag following the same guidelines as use case 01 or 02 above, s ubstituting the camera with whatever imaging device was used to acquire or scan the analog photograph or slide. |
Use SC Secondary Capture IOD. Then set this tag following the same guidelines as use case 01 or 02 above, s ubstituting the camera with whatever imaging device was used to acquire or scan the analog photograph or slide. |
7.4.1.7.2.2 Lossy Image Compression(0028,2110) - Attribute Values#
Set to the string "00" if image is not compressed. Otherwise set to
the string "01".
In order to determine if an image is to be considered compressed or not,
one needs to be familiar with the algorithm used to store the image. As
an example, all forms of JPEG images are considered lossy compression
and should thus be tagged as "01".
7.4.1.7.2.3. Lossy Image Compression Ratio (0028,2112) - Attribute Values#
7.4.1.7.2.4. Lossy Image Compression Method (0028,2114) - Attribute Values#
Check DICOM Standard for most current defined terms.
At time of writing, allowed terms were:
ISO_10918_1for JPEG Lossy Compression [ISO/IEC 10918-1],ISO_14495_1for JPEG-LS Near-lossless Compression [ISO/IEC 14495-1]ISO_15444_1JPEG 2000 Irreversible Compression [ISO/IEC 15444-1]
All of the above terms are to be stored in this tag as a simple string (CS Codes String DICOM value representation allows only 16 uppercase characters or numbers here).