Name: image rendering techniques in postmortem computed tomography: evaluation of biological health and profile in stranded cetaceans
Uploaded: 2020-09-27T15:00:00
Description: Watch this Scientific Journal Video about Image Rendering Techniques in Postmortem Computed Tomography: Evaluation of Biological Health and Profile in Stranded Cetaceans at JoVE.com

The authors would like to thank the Agriculture, Fisheries and Conservation Department of the Hong Kong Special Administrative Region Government for the continuous support in this project. Sincere appreciation is also extended to veterinarians, staff, and volunteers from the Aquatic Animal Virtopsy Lab, City University of Hong Kong, Ocean Park Conservation Foundation Hong Kong and Ocean Park Hong Kong&#160;for paying great effort on the stranding response in this project. Special gratitude is owed to technicians in CityU Veterinary Medical Centre and Hong Kong Veterinary Imaging Centre for operating the CT and MRI units for the present study. Any opinions, findings, conclusions or recommendations expressed herein do not necessarily reflect the views of the Marine Ecology Enhancement Fund or the Trustee. This project was funded by the Hong Kong Research Grants Council (Grant number: UGC/FDS17/M07/14), and the Marine Ecology Enhancement Fund (grant number: MEEF2017014, MEEF2017014A,&#160;MEEF2019010 and MEEF2019010A), Marine Ecology Enhancement Fund, Marine Ecology &#38; Fisheries Enhancement Funds Trustee Limited. Special thanks to Dr. Mar&#237;a Jos&#233; Robles Malagamba for English editing of this manuscript.

NOTE: In the framework of the Hong Kong cetacean virtopsy stranding response program, stranded cetaceans were routinely examined by PMCT. The authors were in charge of virtopsy scanning, data postprocessing (e.g., image reconstruction and rendering), data interpretation, and virtopsy reporting1. This advanced technology emphasizes attentive findings and gives insights on the initial investigation of PM findings prior to conventional necropsy (https://www.facebook.com/aquanimallab).
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	<li>Tsui, H. C. L., Kot, B. C. W., Chung, T. Y. T., Chan, D. K. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Virtopsy+as+a+revolutionary+tool+for+cetacean+stranding+programs:+Implementation+and+management.">Virtopsy as a revolutionary tool for cetacean stranding programs: Implementation and management.</a> Frontiers in Marine Sciences. , (2020).</li><li>Jacobsen, C., Bech, B. 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For the clear visualization of virtopsy datasets, 8 image rendering techniques, consisting of both 2D and 3D rendering, were routinely applied to each stranded carcass for the PM investigation of their biological health and profile. These rendering techniques included MPR, CPR, MIP, MinIP, DVR, segmentation, TF, and PVR. Diverse rendering techniques are complementarily used together with windowing adjustment. The concepts of each image reformation technique and advantages are also described.
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Virtopsy, also known as postmortem (PM) imaging, is the examination of a carcass with advanced cross-sectional imaging modalities, including postmortem computed tomography (PMCT), postmortem magnetic resonance imaging (PMMRI), and ultrasonography1. In humans, PMCT is useful in investigating traumatic cases of skeletal alterations2,3, foreign bodies, gaseous findings4,5,6, and pathologies of the vascular system7,8,9. Since 2014, virtopsy has been routinely implemented in the Hong Kong cetacean stranding response program1. PMCT and PMMRI are able to depict patho-morphological findings on carcasses that are too decomposed to be evaluated by conventional necropsy. The non-invasive radiological assessment is objective and digitally storable, allowing second opinion or retrospective studies years later1,10,11. Virtopsy has become a valuable alternative technique to provide new insights of PM findings in stranded marine animals12,13,14,15,16. Combined with necropsy, which is the gold standard to explain the pathophysiological reconstruction and cause of death17, the biological health and profile of the animals can be addressed. Virtopsy has been gradually recognized and implemented into stranding response programs worldwide, including but not limited to Costa Rica, Japan, Mainland China, New Zealand, Taiwan, Thailand and USA1.
Image rendering techniques in radiology use computer algorithms to transform numbers into information about the tissue. For example, radiological density is expressed in conventional X-rays and CT. The vast quantity of volumetric data is stored in the Digital Imaging and Communications in Medicine (DICOM) format. CT images can be used to produce isotropic voxel data using two-dimensional (2D) and three-dimensional (3D) image rendering in a postprocessing 3D workstation for high resolution visualization18,19. Quantitative data and results are mapped to transform serially acquired axial images into 3D images with gray-scale or color parameters19,20,21. Choosing an appropriate data visualization method from diverse rendering techniques is an essential technical determinant of the visualization quality, which significantly affects the analysis and interpretation of radiological findings21. This is particularly critical for stranding work that involves personnel without any radiology background, who need to understand the results in different circumstances17. The goal of implementing these image rendering techniques is to enhance the quality on the visualization of anatomical details, relationships and clinical findings, which boosts the diagnostic value of imaging and allows an effective rendition of the defined regions of interest17,19,22,23,24,25.
Although the primary axial CT/MRI images contain most information, they may limit accurate diagnosis or documentation of pathologies as structures cannot be viewed in various orthogonal planes. Image reformation at other anatomically aligned planes permits visualization of structural relationships from another perspective without having to reposition the body26. As medical anatomy and forensic pathology data are predominantly 3D in nature, color-coded PMCT images and 3D reconstructed images are preferred to gray-scale images and 2D slice images in view of improved understandability and suitability for courtroom adjudications27,28. With the advances in PMCT technology, a concern of visualization exploration (i.e., the creation and interpretation of 2D and 3D image) in cetacean PM investigation has been raised12,29. Various volumetric rendering techniques in the radiology workstation allow radiologists, technicians, referring clinicians (e.g., veterinarians and marine mammal scientists), and even laymen (e.g., stranding response personnel, government officers and general public) to visualize and study the regions of interest. Yet, the choice of a suitable technique and confusion of terminology remain a major issue. It is necessary to understand the basic concept, strengths and limitations of the common techniques, since it would significantly influence the diagnostic value and interpretation of radiological findings. Misuse of techniques may generate misleading images (e.g., images that have distortions, rendering errors, reconstruction noises or artefacts) and lead to an incorrect diagnosis30.
The present study aims to assess 8 essential image rendering techniques in PMCT that were used to identify most of the PM findings in stranded cetaceans in Hong Kong waters. Descriptions and practical examples of each technique are provided to guide radiologists, clinicians, and veterinarians worldwide through the often difficult and complicated realm of PMCT image rendering and review for the evaluation of biological health and profile.

<table>
	<tbody>
		<tr>
			<td>Aquarius iNtuition workstation</td>
			<td>TeraRecon Inc</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Siemens 64-row multi-slice spiral CT scanner Somatom go.Up</td>
			<td>Siemens Healthineers</td>
			<td>NA</td>
			<td></td>
		</tr>
	</tbody>
</table>

image rendering techniques in postmortem computed tomography: evaluation of biological health and profile in stranded cetaceans

With 6 years of experience in implementing virtopsy routinely into the Hong Kong cetacean stranding response program, standardized virtopsy procedures, postmortem computed tomography (PMCT) acquisition, postprocessing, and evaluation were successfully established. In this pioneer cetacean virtopsy stranding response program, PMCT was performed on 193 stranded cetaceans, providing postmortem findings to aid necropsy and shed light on the biological health and profile of the animals. This study aimed to assess 8 image rendering techniques in PMCT, including multiplanar reconstruction, curved planar reformation, maximum intensity projection, minimum intensity projection, direct volume rendering, segmentation, transfer function, and perspective volume rendering. Illustrated with practical examples, these techniques were able to identify most of the PM findings in stranded cetaceans and served as a tool to investigate their biological health and profile. This study could guide radiologists, clinicians and veterinarians through the often difficult and complicated realm of PMCT image rendering and reviewing.

From January 2014 to May 2020, a total of 193 cetaceans that stranded in Hong Kong waters were examined by PMCT, including 42 Indo-Pacific humpback dolphins (Sousa chinensis), 130 Indo-Pacific finless porpoises (Neophocaena phocaenoides) and 21 other species. A whole-body scan was performed on 136 carcasses while 57 were partial scans on skulls and flippers. Anatomical features and pathologies commonly observed were illustrated with the 8 image rendering techniques for the evaluation of the stranded cet...

Watch this Scientific Journal Video about Image Rendering Techniques in Postmortem Computed Tomography: Evaluation of Biological Health and Profile in Stranded Cetaceans at JoVE.com

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

The Hong Kong cetacean stranding response program has incorporated postmortem computed tomography, which provides valuable information on the biological health and profile of the deceased animals. This study describes 8 image rendering techniques that are essential for the identification and visualization of postmortem findings in stranded cetaceans, which will help clinicians, veterinarians and stranding response personnel worldwide to fully utilize the radiological modality.

With 6 years of experience in implementing virtopsy routinely into the Hong Kong cetacean stranding response program, standardized virtopsy procedures, ...

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.

Research

JoVE Journal

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