Have you ever wondered why many CT files are not compatible with the CBCT softwares? The reasons could be multiple. Here we are going to provide a detailed explanation about the properties and step by step procedure to convert the files.
Why do we require CT files to convert into CBCT compatible files?
A common question that comes to mind when reading the title is: Why do we need to convert CT files to CBCT format? The main reason is to enable the use of CBCT-specific tools on CT images. Let me explain.
CBCT software offers specialized imaging tools such as panoramic reconstruction, trans-axial sectioning, and tangential view tools, volumetric tools, which are widely used in dental image analysis. These tools provide dental professionals with enhanced visualization capabilities essential for effective diagnosis and treatment planning.
If you only have CT scans, you can still utilize these advanced CBCT tools by converting your CT files into CBCT-compatible formats. This is particularly useful in situations where only small field-of-view CBCT machines are available in your area, making CT the primary imaging option. By converting CT files, you can view and analyze them using CBCT software, gaining access to critical diagnostic tools that might otherwise be unavailable.
The Basic differences
Most CT files are not compatible with CBCT software primarily due to differences in acquisition methods, image data structure, and DICOM metadata specifics between traditional CT and CBCT modalities. As a result the CT files become incompatible with many CBCT softwares, even though all the files are in DICOM format.
Different Imaging Geometry:
CT uses fan-beam geometry acquiring slices sequentially, while CBCT uses cone-beam geometry capturing volumetric data in a single rotation. This results in different data organization and image reconstructions that many CBCT softwares expect in a specific CBCT format.
DICOM Metadata Variations:
Although both CT and CBCT use DICOM formats, their header tags differ significantly. CBCT DICOM files contain modality-specific metadata such as different manufacturer tags, exposure parameters, and reconstruction algorithms. CBCT software often requires these specific tags to interpret the scan correctly.
Image Volume and Resolution Differences:
CBCT images tend to have isotropic voxels with high spatial resolution for dental or maxillofacial analysis, while CT scans may have anisotropic voxel sizes. Software tailored for CBCT expects this data format and may not handle CT data properly.
Software Vendor and Proprietary Formats:
Some CBCT machines save data in proprietary formats or with additional viewer software. These may not be readily importable by standard CBCT planning tools unless converted properly to CBCT-standard DICOM.
File Size and Compression:
CT images may use different compression or slice spacing, incompatible with CBCT workflow. CBCT files can be massive due to fine slices and different storage, demanding software that can handle this format efficiently.
| Feature | CT | CBCT |
|---|---|---|
| Volume size | Larger (whole body, head, neck) | Smaller (dental/maxillofacial region) |
| Acquisition method | Slice-by-slice with fan-beam geometry | Single rotation with cone-beam geometry |
| Voxel size | Anisotropic (thicker slices) | Isotropic (fine, small voxels) |
| Spatial resolution | Moderate, optimized for soft tissue and large volumes | High, optimized for bone and teeth detail |
| Image noise | Lower noise, better soft tissue contrast | Higher noise, less soft tissue detail |
DICOM Tags
DICOM tags are pieces of information embedded in medical image files that describe details about the image and the patient. They act like labels or data fields within the file, holding metadata such as the patient’s name, date of birth, the type of scan, the device used, and technical imaging parameters. Each tag has a unique identifier consisting of two hexadecimal numbers, often written like (XXXX,XXXX), which helps software recognize and organize this information consistently across different medical imaging systems.
In simpler terms, think of a DICOM tag as a specific label on a medical image file that tells you who the image belongs to, when and how it was taken, and other important details needed to understand and use the image properly in healthcare settings. This combination of image plus detailed metadata helps ensure the images can be shared, viewed, and analyzed accurately and safely across hospitals and software platforms.
Examples of DICOM tags include:
- Patient’s Name (e.g., “John”)
- Patient’s ID number
- Modality (CT, MRI, CBCT, etc.)
- Study Date
- Equipment Manufacturer
These tags allow medical professionals to manage and interpret imaging data efficiently without losing important patient or scan context. The standardization of DICOM tags is central to interoperability in medical imaging worldwide
How these tags differ in CT & CBCT?
DICOM tags in CT and CBCT images differ primarily due to the distinct imaging technologies, acquisition methods, and clinical purposes of these modalities. While both use the DICOM standard to store image data and metadata, certain tags or tag values reflect their modality-specific characteristics.
Key Differences in DICOM Tags Between CT and CBCT
- Modality Tag (0008,0060):
- CT files typically have the value “CT”.
- CBCT files often show “CBCT” or a vendor-specific code indicating cone-beam technology.
- Manufacturer and Model (0008,0070)/(0008,1090):
- Identify the scanner brand and model, which differ as CBCT and CT machines are distinct hardware.
- Acquisition Geometry and Parameters:
- Tags describing source-to-patient distance (0018,1111), X-ray tube settings (0018,0060 KVP), exposure time (0018,1120), and modulation type (0018,1151) vary due to fan-beam versus cone-beam geometry.
- Reconstruction Algorithm (0018,9310):
- CTs often use standard filtered back projection or iterative reconstruction, while CBCT uses algorithms tailored for cone-beam projections.
- Image Resolution and Voxel Size:
- Though not always stored in explicit tags, related metadata can show differing pixel spacing and slice thickness reflecting the isotropic voxels of CBCT versus anisotropic voxels in CT.
- Unique Identifiers and Series Information:
- Study and series Instance UIDs differ, reflecting separate acquisition systems and software workflows.
- Private Vendor Tags:
- Many CBCT manufacturers use proprietary private tags to store modality-specific information, such as FOV (field of view) size, bowtie filters, and dose-related details that differ from CT metadata.
These differences affect how software interprets the images, contributing to compatibility challenges when using CT data in CBCT-specific software.
How to convert the CT file into CBCT compatible file?
Certain image computational softwares like 3D slicer can be used. 3D Slicer is a free, open source software for visualization, processing, segmentation, registration, and analysis of medical, biomedical, and other 3D images.
How does 3D slicer convert the file?
There is a tool called “Create a DICOM Series” in 3D slicer to convert or reformat an existing CT folder’s DICOM files, even though they already come from the machine, can be explained as follows:
Reasons to Reformat Existing DICOM Files
Slice Order and Volume Type Adjustments: Changing slice order or resampling volumes might be necessary for proper visualization or following specific protocols.
Standardization and Consistency: Different scanners and manufacturers may produce DICOM files with varying metadata formats or inconsistencies. Using this module lets you standardize tags like patient ID, study description, series number, and timestamps for consistent downstream processing.
Custom Metadata Editing: You may want to modify or add specific DICOM tags (patient info, study details, clinical notes) that were not properly set or omitted in the original files to meet research or clinical workflow requirements.
Anonymization or De-identification: This process can be part of anonymizing sensitive patient data by changing or removing identifying tags in a controlled way before sharing or analysis.
File Organization and Naming: The module offers control over filename conventions, numbering, and folder organization, which can be important for managing large datasets or preparing data for specific software pipelines that expect a certain format.
Compression or Format Changes: You can convert the files to use compression or different pixel data encoding formats that may be more efficient for storage or compatible with certain analysis tools.
Linking and UID Control: The ability to set or regenerate unique identifiers (UIDs) helps in ensuring that the generated DICOM series is correctly linked within a study for multi-series datasets or cross-software compatibility.
STEP BY STEP PROCEDURE
Step 1: Download latest version of 3D Slicer here.
Step 2: Open 3D slicer and click on “Add DICOM Data”.
Step 3: Click on Import DICOM files > Select the folder> and click import.
Step 4: Select any one of the series and click “Examine”. Then select the generated data > click “Load”.
You will see a similar window.
Step 5: Click on the search symbol in top left corner, then type “DICOM” in the search bar. The following image will be displayed. Click on “Switch to module” button.
Step 6: Now select the input volume – the volume which you want to convert into CBCT compatible DICOMS.
Next, you select the output DICOM Directory – here select the folder where you want to save the converted DICOM > Click on “Apply”.
Now you have successfully save the converted DICOM files into a folder. These files are easily identified by your CBCT softwares.
But! Are these files reliable after conversion?
Did you get this question? Are the files reliable for image analysis, after conversion? The answer is “YES”!
Converting CT files to CBCT-compatible formats generally does not degrade the original image data since the process involves repackaging the existing image volume and modifying metadata (DICOM tags) rather than altering pixel values or image quality.
Reliability After Conversion
- Image Data Integrity: The actual voxel data from the CT scan remains unchanged during conversion. The conversion primarily updates metadata to match CBCT software requirements, so image content and resolution are preserved.
- Resampling Considerations: If resampling (e.g., to make voxels isotropic) is done, minimal interpolation occurs. This may introduce very slight smoothing but usually does not significantly impact image diagnostic reliability.
- Software Interpretation: The key advantage is enabling CBCT-specific tools designed for volumetric dental imaging to read and process the data correctly. This increases the practical usability of the images without compromising accuracy.
- Clinical Use: Converted images retain their diagnostic value as long as the original CT scan quality was adequate. However, the fundamental differences between CT and CBCT imaging physics remain; no new data or resolution enhancement occurs, just format compatibility.
FAQs
What is the main difference between CT and CBCT?
CT uses a fan-shaped X-ray beam capturing slice-by-slice images primarily for larger anatomical areas, while CBCT uses a cone-shaped beam capturing a volumetric scan of smaller regions, ideal for dental and maxillofacial imaging.
Why are CBCT images preferred in dental imaging?
CBCT provides high-resolution, isotropic voxels focused on teeth and bone with lower radiation dose and faster scan times compared to traditional CT, making it highly suitable for precise dental diagnostics.
What are DICOM tags and why do they matter?
DICOM tags are metadata fields embedded in medical image files that store patient info, modality, technical scan parameters, and more. They ensure interoperability and correct interpretation across medical software.
Why do some CT files not work with CBCT software?
Differences in imaging geometry, DICOM metadata, reconstruction algorithms, and proprietary formats mean CBCT software often expects specific tags and image formats that some CT files lack.
Does CBCT expose patients to more radiation than CT?
No, CBCT generally exposes patients to significantly lower radiation doses than conventional CT scanners, particularly when imaging localized regions like the dental arch.
Can CBCT provide good soft tissue images like CT?
CBCT typically has lower soft tissue contrast and more image noise due to its imaging physics, making CT preferable for detailed soft tissue visualization.
What makes CBCT scan times faster than traditional CT?
CBCT acquires a full volumetric dataset in a single rotation using a cone-shaped beam, while CT collects multiple slices sequentially, making CBCT scans quicker.
These FAQs provide clear, expert information for readers unfamiliar wi
With over a decade of experience in dentistry, I specialize in diagnosing a wide range of oral diseases and have developed a deep passion for dental imaging. My interest in CBCT reporting and digital implantology led me to become a pioneer in the concept of diagnostic 3D modelling. Throughout my career, I have supported and educated numerous dentists in mastering CBCT interpretation, virtual implant planning, and the latest advancements in 3D printing for dental applications. Read more about me on the “about me” page.
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