Image Rendering Techniques in Postmortem Computed Tomography: Evaluation of Biological Health and Profile in Stranded Cetaceans

This study aims to assess different image rendering techniques in the postmortem computed tomography for the evaluation of biological health and profile in stranded cetaceans in Hong Kong waters. This helps guide radiologists, clinicians, and veterinarians through the often difficult and complicated realm of the postmortem computed tomography image rhetoric and review. Eight image rendering techniques consist of both 2-D and 3-D rendering are routinely applied to each stranded cetaceans for the biological health and profile investigation.

The first one is multiplanar reconstruction, MPR. Display the default MPR from axial view, coronal view, and sagittal view after loading the series left click hold mouse button on the centers of MPR cross hairs to concurrently adjust the region of interest and slice in three MPR images click rotate, left click hold mouse button and drag the mouse to rotate the MPR images. Click pen, left-click hold mouse button and drag the mouse to adjust the location of image inside the panel.

Click zoom, left click hold mouse button and drag the mouse to magnify or minimize the image. Select the appropriate present windows levels by clicking app one, app two, head, lung, bone, in the window leveled mini toolbar, depending on the region of interest, click window level left click hold mouse button and drag the mouse to adjust the window width and window level of CT slice manually. Click slice, left click hold mouse button and drag mouse to evaluate the virtopsy datasets from the first image to the last image slice by slice.

The second one is curve planar reformation, CPR. Design the area of anatomical interests left click hold mouse button on the centers of MPR cross hairs to the particular region of interest. View the MPR from three different views, ensure MPR cross hairs placed in a correct location.

Adjust MPR cross hairs if it is not. Select one display panel from axial, coronal, or sagittal view as a study panel. For example, aiming to view the flipper from an axial view depending on the study panel, adjust the extended line of MPR cross hairs from the coronal view perpendicularly to the region of interest by left click hold mouse button on the rotation point of extended line, adjust another extended line of MPR cross hairs from sagittal view parallel to the region of interest by left click hold mouse button on the rotation point of extended line.

View the axial view to check whether the region of interest is adjusted correctly. Adjust the extended lines if it is not. Evaluate the virtopsy datasets using four main functions of rotations, panning zooming, and window level changes.

The third one is maximum intensity projection, MIP. Change the rendering mode to MIP by clicking MIP in the rendering mode mini toolbar adjust the slab thickness on the right upper corner by clicking the green annotation and select a new thickness to visualize the region of interest. Evaluate the virtopsy datasets using four main functions of rotations, panning, zooming, and window level changes.

The fourth one is minimum intensity projection, MinIP. Change the rendering mode to MinIP by clicking MinIP in the rendering mode mini toolbar. Adjust the slab thickness on the right upper corner by clicking the green annotation and select a new thickness to visualize the region of interest.

Evaluate the virtopsy datasets using four main functions of rotations, panning, zooming, and window level changes. The fifth is direct volume rendering, DVR. As one of the default display interface of two-by-two, DVR shows the 3-D rendered images of carcass.

The default DVR template setting is AAA, giving a gross skeletal structures of the carcass. Automatically adjust the rendering settings via clicking template under the viewers and select the appropriate DVR templates. For example, gray, 10%and fracture.

Use four main functions of rotations, panning, zooming, and window level changes for further corrections. The six is segmentation and region-of-interest, ROI, editing. Segment the CT slice using three different tools.

Slab and cubed view tool, FreeROI tool, and dynamic region growing tool. For slab and cubed view tool, click slab under tool, giving a parallel display line. Adjust the slab location by relocating the MPR cross hairs from corresponding MPR views.

Change the slab thickness via the slab thickness bar resulting in a segmentation of 3-D rendered images of carcass. For FreeROI tool, click FreeRO under tool. Hold on the shift key on keyboard to exclude or include a region of interest from the MPR views and DVR.

For dynamic region growing tool, click region under tool. Hold on the shift keys on keyboard, left click hold mouse button and scroll middle button of mouse giving a highlighted region. Click exclude to delete the region.

The seventh is transfer functions, TF.Click 3-D settings under viewer. Select copies to create a new 3-D reconstructed model. In the new 3-D reconstructed model click FreeRO or region under tool.

Hold on the shift keys on keyboard and use 3-D VR all to include a region of interest. Then click select, right click one of the sliders in the color slide bar for changing the color of DVR. Select change color, and define a custom color from the color pallettes, if needed.

The eighth is perspective volume rendering, PVR. To launch the fly-through module, right click on the selected series and select fly-through from the right click menu. Choose the primary 3-D of reading style preference wizard for primary view selection.

Click the two-by-two screen layout, and okay. Resulting in automatically PVR. Make sure that the region of interest is selected.

Building a flight path by placing the start and end of control points by drawing a path. Correct the path by clicking the edit connection or edit path radio button in the tool panel. If there is a broken path or missing structure, add it the control points for smoother sections of the curve or correct the problems.

Create new control points by clicking on the flight path. Once the flight path is correct, click okay. View the fly-through window displayed showing a main fly-through window, MPR views and flat view.

Use 3-D tools by clicking the tools panel located on the right side of the screen to evaluate the luminal structure. Adjust the speed and direction of the fly-through using fly backward, pause, flight forward, slow down fly-through, and speed up fly-through under the 3-D tools. From January 2014 to May 2020, a total of 193 cetaceans stranded in Hong Kong waters were examined by the postmortem computed tomography.

Here are the results for each image rendering techniques applied in in the biological health and profile investigations of stranded cetaceans. MPR function displaying a diseased Indo-Pacific humpback dolphin in axial, reconstructed 3-D, reconstructed coronal, reconstructed sagittal views. Linear and area measurements for the diagnosis of atlanto-occipital dislocation are also demonstrated.

CPR function displaying curved structures in the flipper of a diseased Indo-Pacific Venus Porpoise in point of view. MIP function highlighting hyper-attenuated pulmonary nodules appeared as intense white dots in both lungs of a diseased Indo-Pacific Venus porpoise. MinIP function highlighting hyper-attenuated guest view structures which is the tracheobronchial trees in both lungs of a diseased Indo-Pacific Venus Porpoise.

DVR function, displaying different components of a diseased Indo-Pacific Venus porpoise. Vasculature overlaid with skeletal system are highlighted by AAA. Respiratory system is highlighted by lung.

Skeletal system including the vertebral physio plates is highlighted by bone plus plates. Hyper-attenuated ear bones and fish hooks are highlighted by hardware. ROI editing function displaying a diseased Indo-Pacific Venus porpoise, with the CT couch and with the CT couch removed.

TF function displaying different components of a diseased Indo-Pacific Venus porpoise. Sand in air sac is highlighted in cyan. Stomach content is highlighted in green.

Parasitic granulomatous mastitis lesion is highlighted in red. PVR function demonstrating a virtual enteroscopy of a diseased Indo-Pacific humpback dolphin with the fly-through function. Based on our experience, the listed eight rendering techniques were able to identify most of the postmortem findings in stranded cetaceans, and serve as a tool to investigate their biological health and profile while other rendering techniques were disputed in the present study due to their uncommon usage and limited usefulness.

A proper utilization of rendering techniques could improve the postmortem diagnosis and effectively relate such complicated information, such as the underlying pathology and atomic structures, as well as skeletal morphology and taxonomy to other referring veterinarians, clinicians, and researchers in a better and easier understanding manner.