5.4. Orthodontic Imaging Data Model

5.4.1. Orthodontic Progress (Informative)

During orthodontic treatment, it is common for providers to monitor progress by regularly collecting records such as photographs or intra-oral surface scans [provide reference]. Identifying the timing of these records in relation to the treatment is crucial. Specifically, the provider needs to know if, at the time of acquisition, the patient:

• was undergoing treatment (progress photos)

• had never undergone treatment before (observation/pretreatment photos)

• had completed treatment (posttreatment photos)

Orthodontic photograph progress shall be stored in three key areas:

• Longitudinal Temporal Event Type (Registration, Treatment, Posttreatment)

• Longitudinal Temporal Offset From Event (in days)

• Study Description (0008,1030)

The mapping below provides a reference for translating orthodontic progress into codesets that DICOM can understand.

Orthodontic progress code mapping

orthodontic progress	description	event type	offset (days)
First Time Observation	Patient has just registered with the practice for the first time and has not agreed any treatment yet. The provider collects first time records.	SCT-184047000 Patient registration	0
Observation	Patient comes back for regular visits. The provider collects observation records.	SCT-184047000 Patient registration	Number of days past the day the patient registers.
Pretreatment	Images acquired before treatment starts. Only used when the patient and doctor have agreed to start a treatment. This should be treated as Observation above.	See Observation	See Observation
Initial	Patient and provider agreed to start treatment. Records are taken to mark the Baseline for comparison with treatment progress.	SCT-1332161000 Orthodontic Treatment started	0
Progress	Images taken during treatment.	SCT-1332161000 Orthodontic Treatment started	Number of days past the day the treatment started.
Final	Image taken at the end of active treatment (after appliance removal, if applicable). Sequence number is not required.	SCT-1340210007 Orthodontic Treatment stopped	0
Posttreatment	Image acquired after treatment.	SCT-1340210007 Orthodontic Treatment stopped	Number of days past the day the treatment ended (see Final above).

Note

Distinguishing Pretreatment from Observation is not always straightforward. In some cases, there may be a clear Pretreatment definition by the provider, which could be properly coded in the practice management system. However, in many other cases, it may not be clearly defined, or what was considered Pretreatment might not lead to treatment.

Consequently, the orthodontic domain experts of the working group have decided to disregard Pretreatment status and consider it as Observation.

5.4.2. Study Description (0008,1030)

This optional DICOM tag, part of the General Study module, can contain a Long String (up to 64 characters). In the context of orthodontic photographs, the Study Description is used to represent treatment progress as defined above.

Most PACS systems display the Study Description in search results when listing studies after a query. Therefore, it is recommended to include the information from the Concept Codes described in Longitudinal Temporal Event Type and Longitudinal Temporal Offset from Event here, in a more human-readable form. For example, you might choose a Study Description based on progress names defined by the main practice management system used by the practice that initially acquired the photographs. Examples include:

• Pre-treatment 1

• Initial

• Progress 12

• Final

Note

• The Study Description is typically used by the medical provider who treats the patient and acquires the images.

• Other software may also use the Study Description. But with the limit of 64 characters, it is advisable to keep the string under 16 characters to allow other systems to append their own text.

• When importing images from other institutions, the Study Description may not be relevant to the receiving practice.

• The Study Description is not a reliable tag for ensuring interoperability across systems and institutions.

• For reliable interoperability, refer to Acquisition Context codes as defined in Longitudinal Temporal Event Type and Longitudinal Temporal Offset from Event.

5.4.3. Image Views/Request Procedure Codes

Orthodontic photographs are typically taken in a standardized manner to ensure consistent and comparable results. The American Dental Association (ADA) has published a standard, ADA Standard No. 1100, which defines the views that could be taken for orthodontic photographs. These views are referred to as Image Views in that standard. However, in DICOM, these views are best represented as Scheduled Protocol Codes.

The orthodontic provider needs to be able to programmatically distinguish the different types of images, in order to compare them both with other images of the same series and over time to monitor treatment progress. While the types of images can be defined by their anatomical and other view type tags in DICOM, saving a coded version of the name of the type of image along with the image is useful both for human readability and for developers who need to programmatically process the images. When and if a code is available, that one can be used to identify the image (if known).

There is a distinction between the anatomical and view information defined in the DICOM tags and the type of image: the anatomical and view information is used to define what is in the image, while the type of image is used to define what the original intention of that image was. The image type code is therefore well suited to be used as a protocol for a scheduled procedure, and represents what the provider has scheduled before the acquisition of the image. Then, once the photograph is taken, the DICOM tags are used to define what was actually taken. The resulting DICOM image would thus contain both the scheduled protocol code, as well as the anatomical and view information in the DICOM tags. In the domain of orthodontics, these two should, for the vast majority of cases, match. It should thus be safe to make use of the protocol code to identify the image type.

When the provider schedules for an appointment, once the patient has arrived for that appointment, the practice management system can trigger the generation of a DICOM Modality Worklist, and populate it with the scheduled procedure codes. The imaging device can then use this information to pre-populate the fields in the DICOM image, including the scheduled procedure code. This code can then be used to identify the type of image that was taken.

Within the DICOM IOD (the DICOM image), the Scheduled Procedure Code Sequence (0040,0008) is contained within the Requested Attributes Sequence (0040,0275), in the General Series Module. Therefore, it cannot be used to define a specific type of image (instance). Instead, it must contain all the views that are part of the same series. This is because the Scheduled Procedure Code Sequence is shared by all instances in the series. Then Instance Number (0020,0013), which is part of the General Image module, is used to differentiate between the different views in the series. The Instance Number is a unique integer for each image in the series which can correspond to the index position of the Requested Procedure Code in the Requested Procedure Code Sequence.

In the orthodontic domain, it is expected for the photographs to be taken in a specific sequence in order to optimize the workflow. This order can be defined in the Scheduled Procedure Code Sequence, such that image acquisition devices (such as DICOM enabled cameras) can present the operator with the images in the same order. The Instance Number of each image, can then be used to refer to the index position of the Scheduled Procedure Code Sequence in the series. See Instance Number (0020,0013) for more information.