B-scan Slab Thickness Attribute
| Tag | (0022,1643) |
|---|---|
| Type | Required (1) |
| Keyword | BscanSlabThickness |
| Value Multiplicity | 1 |
| Value Representation | Single (FL) |
Nominal thickness of each B-scan slab, in mm. See Section C.8.17.16.2 for further explanation.
Section C.8.17.16.2
C.8.17.16.2 Ophthalmic Optical Coherence Tomography B-scan Volume Analysis Acquisition Parameters Expected Use
The acquisition technique of ophthalmic tomography B-scan volume analysis (e.g., OCT angiography blood flow information) is based on the same mechanism as used for ophthalmic tomography images. Therefore, B-scans are used for individual image frames of the acquired volume. The frames of the resulting volume are calculated based on a number of repeated B-scans at the same spatial location. So the frame of an Ophthalmic Tomography B-scan Volume Analysis SOP Instance is not a B-scan, but a data aggregation of B-scans from the raw data of the acquisition.
To convey the information about the acquisition of the raw data, which are not typically in the scope of DICOM, the OCT B-scan Analysis Acquisition Parameters Sequence (0022,1640) is used. The parameters are provided for the user to assess the quality of the resulting B-scan volume analysis as well as to provide a means to compare volumes created by different devices. Furthermore the user is able to identify if a vendor-recommended protocol has been used to acquire the raw data.
The OCT B-scan Analysis Acquisition Parameters Sequence contains at least one Item. It can contain more than one if multiple scan patterns have been used to acquire the raw data and are used to calculate the volume data.
Number of B-scans Per Frame (0022,1642) can be used to provide an indication about the resulting image quality. In principal, the more B-scans averaged the better but as a high number of scans slows down the acquisition process, the resulting data becomes prone to noise introduced by eye movements, which are not related to blood flow. Furthermore, the number of B-scans averaged can be used to determine whether the acquisition was based on a vendor-specific protocol, or if the user changed the protocol.
The B-scan Slab Thickness (0022,1643) and Distance Between B-scan Slabs (0022,1644) provide information about the density of the sampling pattern used to acquire the volume data. The calculation of the volume (Ophthalmic Tomography B-scan Volume Analysis SOP Instance) is based on this information.