Accuracy and reliability of cetacean cranial measurements using computed tomography three dimensional volume rendered images

Abstract

Computed tomography (CT) has become more readily available for post-mortem examination, offering an alternative to cetacean cranial measurements obtained manually. Measurement error may result in possible variation in cranial morphometric analysis. This study aimed to evaluate the accuracy and reliability of cetacean cranial measurements obtained by CT three-dimensional volume rendered images (3DVRI). CT scans of 9 stranded cetaceans were performed. The acquired images were reconstructed using bone reconstruction algorithms. The reconstructed crania obtained by 3DVRI were visualized after excluding other body structures. Accuracy of cranial measurements obtained by CT 3DVRI was evaluated by comparing with that obtained by manual approach as standard of reference. Reproducibility and repeatability of cranial measurements obtained by CT 3DVRI were evaluated using intraclass correlation coefficient (ICC). The results demonstrated that cranial measurements obtained by CT 3DVRI yielded high accuracy (88.05%– 99.64%). High reproducibility (ICC ranged from 0.897 to 1.000) and repeatability (ICC ranged from 0.919 to 1.000 for operator 1 and ICC range from 0.768 to 1.000 for operator 2) were observed in cranial measurements obtained by CT 3DVRI. Therefore, cranial measurements obtained by CT 3DVRI could be considered as virtual alternative to conventional manual approach. This may help the development of a normative reference for current cranial maturity and discriminant analysis studies in cetaceans.

Postmortem Neuroimaging of Cetacean Brains Using Computed Tomography and Magnetic Resonance Imaging

“…Virtopsy using postmortem computed tomography (PMCT) and postmortem magnetic resonance (PMMR) imaging (PMMRI) has been implemented in the pioneering virtopsydriven cetacean stranding response program in Hong Kong (HK) waters, to provide vital or additional information for conventional necropsy (Kot et al, 2016(Kot et al, , 2018(Kot et al, , 2019(Kot et al, , 2020Chan et al, 2017;Yuen et al, 2017). Stranded cetacean carcasses found in HK waters are often badly degraded (Jefferson et al, 2002) as high temperature and humidity accelerate autolysis (Klein et al, 2016), hampering stranding response personnel and veterinarians in the documentation of postmortem findings and tissue sampling (Tsui et al, 2020).…”

Morphological analysis of the foramen magnum in finless porpoise (genusNeophocaena) using postmortem computed tomography 3D volume rendered images

“…, Yuen et al . ), including FM. Reconstructed CT 3DVRI also allows researchers to undertake detailed morphometrical analysis of the FM and occipital condyle region without the process of skeletal excarnation (Brough et al .…”

“…Cranial measurements obtained by CT 3DVRI have proved to be accurate and reliable (Yuen et al . ), and considered as virtual alternative to the conventional manual approach in the present study. Eight measurements of the FM and adjacent occipital indices, including foramen magnum height (FMH), foramen magnum width (FMW), dorsal notch height (DNH), foramen magnum index (FMI), occipital triangle height (OCH), occipital triangle height (without foramen magnum) (OCHW), intercondylar width (ICW), and occipital condyle thickness (OCT), were obtained from CT 3DVRI of each specimen by operator 1 (AY), with reference to the cranial measurement definitions from Yahaya et al .…”

“…A growing body of digitally stored anatomical data has become available to assist with biological health and profile investigation. Reconstructed cetacean CT three-dimensional volume rendered images (3DVRI) can be sectioned in any plane and rotated in space, allowing 3D insights of dedicated cranial characters (Fatterpekar et al 2006, Yuen et al 2017, including FM. Reconstructed CT 3DVRI also allows researchers to undertake detailed morphometrical analysis of the FM and occipital condyle region without the process of skeletal excarnation (Brough et al 2013).…”

Diagnosis of atlanto-occipital dissociation: Standardised measurements of normal craniocervical relationship in finless porpoises (genus Neophocaena) using postmortem computed tomography

“…In the course of the pioneering virtopsy-driven stranding response program in Hong Kong and adjacent waters, virtopsy using PMCT and postmortem magnetic resonance imaging (PMMRI) have been implemented to provide supplementary or complementary information to conventional necropsy 24 , 25 . Kot and his team suspected a high incidence of abnormal diastasis of AOJ in stranded cetaceans using PMCT 26 .…”