MFR PAPER 1047 



Investigation of Blubber Thickness in a 

 Gray Whale Using Ultrasonography 



MICHAEL P. CURRAN and WILLIAM M. ASHER 



ABSTRACT 



A captive juvenile i;ray whale. Eschrichtius robustus. was studied with tdtra- 

 soiind using A-mode technique. Measurements of hiuhher and fat titickness by 

 means of selected tissue interfaces were made. Suture implantation depths were 

 also measured. Ultrasound woidd he a reliable method for measiirini; hiuhher 

 and fat thicknesses to .y/ic insiiiht to a marine moiitmal's nutritional status. 



PROBLEM 



A captive yearling gray whale was 

 considered for ultrasound study 1) to 

 measure blubber and fat thickness to 

 reflect on nutritional status, and 2) 

 to measure depth of polyethylene 

 suture implantations being used for an 

 attachment of a radio transmitter de- 

 vice on the animal's dorsal surface. 



PROPOSAL 



Using an ultrasound beam with 

 A-mode technique, it was proposed to 

 measure skin, blubber, fat. and muscle 

 depth. Tissues of varying density will 

 reflect ultrasound echoes from their 

 respective interfaces. A porpoise. Tur- 

 siops truncutus. model was proposed 

 for correlation. 



BACKGROUND 



Ultrasound is a relatively new sci- 

 ence which is meeting with intense 

 interest and enthusiasm for medical 

 diagnostic and research purposes. It 

 has proven effective in detecting brain 

 midline shifts with the echoencephalo- 

 gram. Examinations of the heart to 

 predict cardiac output, mitral valve 

 activity, and presence or absence of 

 pericardial effusions are made. B-scan 

 examination of the abdomen to localize 

 and characterize various masses and 

 organs in the peritoneal cavity and 

 retroperitoneal space is accepted prac- 



tice. Obstetrics has found valuable 

 use for ultrasound in evaluating 

 gestational age. placental location, 

 and pelvic masses. 



In the field of veterinary medicine 

 this technique has made it possible 

 to select breeding stock by determina- 

 tion of the fat and muscle interfaces, 

 allowing identification of those ani- 

 mals with the best commercial poten- 

 tial. This latter application suggested 

 measurements for marine animals to 

 evaluate nutrition. 



MATERIALS AND METHODS 



Utilizing commercially available 

 pulsed ultrasound equipment designed 

 for medical application, multiple 

 measurements of the echo interfaces 

 of the gray whale were obtained at 

 selected positions along the dorsal- 

 lateral aspect and axilla. Additional 

 measurements were obtained over the 

 polyethylene sutures to determine the 



Lt. Conidr. Michael P. Curran, 

 MC. USNR, and Lt. Comdr. 

 William M. Asher, MC, USN, 

 are both from the Department 

 of Ultrasound and the Clinical 

 Investigation Center, Naval Hos- 

 pital, San Diego, CA 92134. 

 The opinions or assertions con- 

 tained herein are those of the 

 authors and are not to be con- 

 strued as official nor as reflecting 

 the views of the Navy Depart- 

 ment. 



suture depth. All of this material was 

 displayed on a cathode ray oscillo- 

 scope with a linear scale divided into 

 millimeter increments. As an in vitro 

 correlation to provide information as 

 to which structures were providing 

 the echo interfaces observed in the 

 live mammal, a porpoise model with 

 necropsy section was obtained. Using 

 a direct visual placement of the trans- 

 ducer in similar areas to that of the 

 gray whale, the echo interfaces were 

 photographed on the oscilloscope. 

 Direct linear measurements and ana- 

 tomical identification of the structures 

 traversed were performed. These echo 

 patterns correlated highly with the 

 similar patterns obtained from the 

 gray whale and indicated which struc- 

 tures were providing these echoes. 

 Thin section radiographs were ob- 

 tained of the porpoise model, further 

 demonstrating the density differences 

 of tissue between the skin lines, blub- 

 ber, areolar fat, muscle, and fascial 

 surfaces. In all cases the measurements 

 corresponded exactly to the visual 

 interpretation of the fascial, fat, bone, 

 and skin interfaces. 



DISCUSSION 



Elementary Ultrasound Physics 



Although ultrasonic technology in 

 medicine is relatively new, the earliest 

 experiments date back to the I800"s 

 when attempts to produce high fre- 

 quency sounds were performed. In 

 1883 Gallon developed an ultrasound 

 whistle which was capable of produc- 

 ing vibrations as high as 25,000 cycles 

 per second. In modern terminology, 

 the frequency of vibrations is assigned 

 the term "Hertz"' and 25,000 cycles 

 per second is abbreviated as 25 kilo- 

 heriz (25 kHz). In 1929 Sokolov de- 

 scribed an ultrasonic method for de- 

 tecting flaws in metals. Following 

 this, in l')47. this new modality was 

 utilized in medical diagnosis when 

 early workers such as Keksell. in 

 Sweden, demonstrated the ability to 

 delect the midline of intracerebral 

 structures. 



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