PET-CT Fusion Mode

Overview

The PET-CT fusion mode in OmegaAI enables integrated visualization of Positron Emission Tomography (PET) and Computed Tomography (CT) images within a single viewing environment. This mode overlays a color-mapped PET image onto the corresponding CT image, allowing users to correlate areas of increased FDG (fluorodeoxyglucose) uptake with precise anatomical structures.

PET-CT Fusion is especially useful for lesion localization, treatment planning, and diagnostic interpretation by combining functional and anatomical information in real time. This guide explains how to activate PET-CT Fusion mode and provides an overview of its interface and core functionality.

Activation of PET-CT Fusion Mode

1. Prerequisites

Before activating PET-CT Fusion mode, ensure the following:

• Two viewports are displayed side by side.

• One viewport contains the PET series, and the other contains the corresponding CT series from the same study.

2. Activating PET-CT Fusion Mode

• With the PET and CT series displayed side by side, the Fusion button appears in the viewport menu at the bottom center of the viewport.

• Click the Fusion button to enable the PET-CT Fusion mode.

Once activated, the PET image is fused with the CT image, providing a combined view for enhanced anatomical and functional assessment.

Interface Overview

1. Primary Fusion Viewport

• The primary fusion viewport occupies half the screen and displays the fused PET-CT image. Key features include the following:

• Default plane: Axial view on activation.

• Plane switching: Use the expand icon at the top-left corner of any MPR viewport to switch to sagittal or coronal views.

• This viewport serves as the main workspace for detailed diagnostic assessment.

2. Multi-Planar Reconstruction (MPR) Viewports

• Up to four secondary MPR viewports are displayed alongside the primary fusion viewport. These may show:

  • Alternative fused views (axial, coronal, or sagittal), or

  • Standalone PET or CT images, depending on the configuration.

• All MPR viewports are linked and synchronized, ensuring consistent navigation across planes. Moving the crosshair in any viewport automatically updates the corresponding anatomical location across all other views, supporting precise spatial correlation between PET uptake and CT anatomy.

3. Maximum Intensity Projection (MIP) View

The MIP view displays Maximum Intensity Projection images derived from the PET volumetric data. It provides:

• A whole-body PET overview for rapid visual assessment.

• Dynamic areas with increased radiotracer uptake will appear highlighted, facilitating the quick identification of potentially suspicious regions.

• Real-time updates based on navigation and fusion settings.

Mouse interaction: Scrolling the mouse wheel rotates the MIP view, enabling visualization from multiple angles.

4. Fusion Display Controls

Opacity Sliders

Located at the bottom of the fusion viewport, these sliders allow fine-tuning of the fused image display:

CT Opacity	Adjusts CT image visibility. Lower values emphasize PET uptake; higher values enhance anatomical detail.
PET Opacity	Controls the intensity of the PET overlay. Useful for balancing tracer uptake visibility against background anatomy.

5. PET Color Map Selection

• Multiple PET color palettes are available to optimize contrast and highlight subtle uptake patterns.

• Switching color maps does not affect the underlying quantitative data.

Probe Tool SUV Measurement

The Probe tool enables volumetric Standardized Uptake Value (SUV) measurements directly on the fused PET-CT image. It is designed for rapid quantitative assessment of radiotracer uptake at specific anatomical locations without requiring a manually drawn ROI contour.

Accessing the Probe Tool

The Probe tool can be activated in any of the following ways:

• Image Control Wheel --- Right-click on the viewport to open the wheel and select Probe.

• Toolbar — Click the Probe icon in the toolbar (availability depends on toolbar customization).

• Keyboard shortcut --- Press Q to activate the tool instantly.

How It Works

Once activated, place a probe marker on any area of interest within the fusion viewport. The tool immediately calculates and displays SUV metrics at that location.

Depending on the area selected, the probe will return one of two results:

• Measurable uptake --- SUV metrics are displayed directly on the image overlay next to the probe marker.

• No measurable uptake --- The label "SUV: no measurable uptake" is shown, indicating background or low-uptake regions.

Auto-Volumetric SUV Measurement

When a probe is placed on a region of increased FDG uptake, OmegaAI automatically computes volumetric SUV metrics without requiring the user to manually draw an ROI contour.

The system segments the uptake region and calculates the full suite of SUV metrics ---SUVmax, SUVmean, SUVpeak, and Vol (cc) ---based on the automatically defined volume. This significantly reduces manual effort during lesion assessment and supports consistent, reproducible quantification across studies.

Displayed Metrics

Each probe measurement displays the following values on the image and in the Measurements panel:

SUVmax	Highest SUV values recorded within the segmented region.
SUVmean	Arithmetic mean of SUV values across all voxels in the region.
SUVpeak	Mean SUV values within a 1 cm³ sphere centered on the SUVmax voxel.
Vol (cc)	Total lesion volume, calculated as voxel count × voxel spacing product.

• Placed probe markers can be repositioned at any time by clicking and dragging the marker (yellow circle) to a new location, SUV values update automatically.

• Multiple probes can be placed simultaneously in the same study.

Save Measurements in Fusion Mode

• All ROI measurements performed in Fusion mode in the study can be automatically saved within the active session.

• Measurements taken in the Fusion Mode would remain preserved even after exiting the mode.

• When the same study is reopened in Fusion mode, the saved measurement details are displayed on both the image overlay and the Measurements panel on the right.