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The use of Diagnostic Imaging for Identifying Abnormal Gas Accumulations in Cetaceans and Pinnipeds.

Dennison S, Fahlman A, Moore M - Front Physiol (2012)

Bottom Line: Lung compression and alveolar collapse that terminate gas-exchange before a depth is reached where supersaturation is significant and bradycardia with peripheral vasoconstriction affecting the distribution, and dynamics of blood and tissue nitrogen levels.Published accounts of gas and fat emboli and dysbaric osteonecrosis in marine mammals and theoretical modeling have challenged this view-point, suggesting that decompression-like symptoms may occur under certain circumstances, contrary to common belief.The presence of gas may be asymptomatic and must be interpreted cautiously alongside all other available data including clinical examination, clinical laboratory testing, gas analysis, necropsy examination, and histology results.

View Article: PubMed Central - PubMed

Affiliation: Marine Mammal Radiology San Francisco, CA, USA.

ABSTRACT
Recent dogma suggested that marine mammals are not at risk of decompression sickness due to a number of evolutionary adaptations. Several proposed adaptations exist. Lung compression and alveolar collapse that terminate gas-exchange before a depth is reached where supersaturation is significant and bradycardia with peripheral vasoconstriction affecting the distribution, and dynamics of blood and tissue nitrogen levels. Published accounts of gas and fat emboli and dysbaric osteonecrosis in marine mammals and theoretical modeling have challenged this view-point, suggesting that decompression-like symptoms may occur under certain circumstances, contrary to common belief. Diagnostic imaging modalities are invaluable tools for the non-invasive examination of animals for evidence of gas and have been used to demonstrate the presence of incidental decompression-related renal gas accumulations in some stranded cetaceans. Diagnostic imaging has also contributed to the recognition of clinically significant gas accumulations in live and dead cetaceans and pinnipeds. Understanding the appropriate application and limitations of the available imaging modalities is important for accurate interpretation of results. The presence of gas may be asymptomatic and must be interpreted cautiously alongside all other available data including clinical examination, clinical laboratory testing, gas analysis, necropsy examination, and histology results.

No MeSH data available.


Related in: MedlinePlus

A CT image of the head at the level of the eyes from a bycatch gray seal (Halichoerus grypus). The image was acquired using a bone reconstruction algorithm and displayed on a wide window that results in only gas being displayed as dark gray or black. Normal gas accumulations in the nasopharynx (*) and oral cavity (white circle) are observed. Abnormal gas accumulations within tissues and vasculature, some demonstrated by black arrows, are also present.
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Figure 3: A CT image of the head at the level of the eyes from a bycatch gray seal (Halichoerus grypus). The image was acquired using a bone reconstruction algorithm and displayed on a wide window that results in only gas being displayed as dark gray or black. Normal gas accumulations in the nasopharynx (*) and oral cavity (white circle) are observed. Abnormal gas accumulations within tissues and vasculature, some demonstrated by black arrows, are also present.

Mentions: Like DR and CR, CT utilizes x-rays to produce an image with tomography referring to the fact that images are acquired as slices or sections. CT is superior to conventional screen-film CR and DR as superimposition of structures is almost eliminated, depending on operator-selected parameters. CT has greater sensitivity for small differences in attenuation that allows distinction of structures that are indistinguishable on DR, CR, or conventional screen-film radiography (Gore et al., 2000; Bushberg et al., 2002). Different generations of CT scanner exist that utilize varying technologies but the typical scanners currently in use have a CT tube and detector(s) that circle the patient whom is positioned within the gantry. Beams of x-rays pass through the patient through 360°. Different tissues attenuate the x-ray beam to varying degrees and therefore the number of photons (x-rays) that reach the detector at each scanning point around the patient will be different, determined by the tissues passed through. Once all data for an image have been acquired, reconstruction algorithm selections are applied to produce a recognizable displayed image. Usually reconstruction algorithms for both bone and soft tissue optimization are applied, resulting in the production of two series for the same area. Each pixel in the image has a designated shade of gray that represents an attenuation value. Attenuation is quantitative and is measured in Hounsfield units (HU). Average attenuations for fat are −100 HU, soft tissues are +30 to +50, and cortical bone are +1000 to +3500 HU (Bushberg et al., 2002). Essentially gas does not affect the x-ray beam as it passes through, resulting in a very negative HU value and a pixel coloration that is very dark gray to black, Figure 3.


The use of Diagnostic Imaging for Identifying Abnormal Gas Accumulations in Cetaceans and Pinnipeds.

Dennison S, Fahlman A, Moore M - Front Physiol (2012)

A CT image of the head at the level of the eyes from a bycatch gray seal (Halichoerus grypus). The image was acquired using a bone reconstruction algorithm and displayed on a wide window that results in only gas being displayed as dark gray or black. Normal gas accumulations in the nasopharynx (*) and oral cavity (white circle) are observed. Abnormal gas accumulations within tissues and vasculature, some demonstrated by black arrows, are also present.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3368393&req=5

Figure 3: A CT image of the head at the level of the eyes from a bycatch gray seal (Halichoerus grypus). The image was acquired using a bone reconstruction algorithm and displayed on a wide window that results in only gas being displayed as dark gray or black. Normal gas accumulations in the nasopharynx (*) and oral cavity (white circle) are observed. Abnormal gas accumulations within tissues and vasculature, some demonstrated by black arrows, are also present.
Mentions: Like DR and CR, CT utilizes x-rays to produce an image with tomography referring to the fact that images are acquired as slices or sections. CT is superior to conventional screen-film CR and DR as superimposition of structures is almost eliminated, depending on operator-selected parameters. CT has greater sensitivity for small differences in attenuation that allows distinction of structures that are indistinguishable on DR, CR, or conventional screen-film radiography (Gore et al., 2000; Bushberg et al., 2002). Different generations of CT scanner exist that utilize varying technologies but the typical scanners currently in use have a CT tube and detector(s) that circle the patient whom is positioned within the gantry. Beams of x-rays pass through the patient through 360°. Different tissues attenuate the x-ray beam to varying degrees and therefore the number of photons (x-rays) that reach the detector at each scanning point around the patient will be different, determined by the tissues passed through. Once all data for an image have been acquired, reconstruction algorithm selections are applied to produce a recognizable displayed image. Usually reconstruction algorithms for both bone and soft tissue optimization are applied, resulting in the production of two series for the same area. Each pixel in the image has a designated shade of gray that represents an attenuation value. Attenuation is quantitative and is measured in Hounsfield units (HU). Average attenuations for fat are −100 HU, soft tissues are +30 to +50, and cortical bone are +1000 to +3500 HU (Bushberg et al., 2002). Essentially gas does not affect the x-ray beam as it passes through, resulting in a very negative HU value and a pixel coloration that is very dark gray to black, Figure 3.

Bottom Line: Lung compression and alveolar collapse that terminate gas-exchange before a depth is reached where supersaturation is significant and bradycardia with peripheral vasoconstriction affecting the distribution, and dynamics of blood and tissue nitrogen levels.Published accounts of gas and fat emboli and dysbaric osteonecrosis in marine mammals and theoretical modeling have challenged this view-point, suggesting that decompression-like symptoms may occur under certain circumstances, contrary to common belief.The presence of gas may be asymptomatic and must be interpreted cautiously alongside all other available data including clinical examination, clinical laboratory testing, gas analysis, necropsy examination, and histology results.

View Article: PubMed Central - PubMed

Affiliation: Marine Mammal Radiology San Francisco, CA, USA.

ABSTRACT
Recent dogma suggested that marine mammals are not at risk of decompression sickness due to a number of evolutionary adaptations. Several proposed adaptations exist. Lung compression and alveolar collapse that terminate gas-exchange before a depth is reached where supersaturation is significant and bradycardia with peripheral vasoconstriction affecting the distribution, and dynamics of blood and tissue nitrogen levels. Published accounts of gas and fat emboli and dysbaric osteonecrosis in marine mammals and theoretical modeling have challenged this view-point, suggesting that decompression-like symptoms may occur under certain circumstances, contrary to common belief. Diagnostic imaging modalities are invaluable tools for the non-invasive examination of animals for evidence of gas and have been used to demonstrate the presence of incidental decompression-related renal gas accumulations in some stranded cetaceans. Diagnostic imaging has also contributed to the recognition of clinically significant gas accumulations in live and dead cetaceans and pinnipeds. Understanding the appropriate application and limitations of the available imaging modalities is important for accurate interpretation of results. The presence of gas may be asymptomatic and must be interpreted cautiously alongside all other available data including clinical examination, clinical laboratory testing, gas analysis, necropsy examination, and histology results.

No MeSH data available.


Related in: MedlinePlus