Computed tomography of the thorax and abdomen of the clinically normal common marmoset (Callithrix jacchus)

Abstract

The aim of this study was: 1) to describe the computed tomographic thoracic and abdominal anatomy in the clinically normal common marmoset; 2) to describe the normal reference range of Hounsfield units (HU) of major abdominal and thoracic organs; 3) to refine the computed tomography (CT) protocol; 4) to compare abdominal CT to other imaging modalities such as radiography and ultrasound (US). Eight clinically healthy mature common marmosets ranging from 12 to 48 months and 235 to 365 g bodyweight were anesthetised and pre- and post-contrast CT examinations were performed using different CT settings. In 3/8 common marmosets radiography was performed at the same time. Diagnostic quality images could be obtained in the common marmoset despite its small size and high respiration rate using a dual slice CT scanner. Quantitative and qualitative assessments of major thoracic and abdominal structures were obtained. The HU of major abdominal and thoracic organs differed from small animals. Representative cross-sectional images were selected and relevant anatomy was labeled. None of the thoracic lymph nodes were detected and separation of individual lung lobes besides the accessory was only occasionally seen. Identification and delineation of abdominal organs greatly improved with i.v. contrast. A high frequency algorithm with edge enhancement proved to be particularly beneficial for the evaluation of thoracic and to a lesser degree abdominal CT. Due to their size and species specific anatomy (also reflected in their different normal range of HU of individual organs), standard small animal CT protocols need to be critically assessed and adapted for exotics, such as the common marmosets. Imaging findings differed from described anatomic findings (such as positioning of kidneys in relationship to lumbar vertebrae) and could either be due to different study population, imply more mobility of kidneys similar to cats, or emphasize that CT might be better for certain aspects of anatomic descriptions than actual anatomy studies, since it is done in vivo versus the traditional post-mortem approach. This study established normal reference ranges for the thoracic and abdominal computed tomographic anatomy of clinically healthy common marmosets, including adapted CT protocols. This baseline study should facilitate CT examinations of marmosets in a clinical set-up and it is anticipated that diagnostic proficiency will be facilitated. The decision to perform advanced imaging is multi-factorial and highly dependent on patient factors, user experience with the modality and species, emotional value to the owner, availability and accessibility of equipment will be important decision criteria in developing decision strategies in clinical settings. Under ideal circumstances US is recommended as the screening tool of choice for the abdomen in the common marmoset. Radiography still plays an important role as a baseline imaging modality for the abdomen, particularly as whole body radiography in the common marmoset, providing simultaneous information about the thorax and the skeletal system; however its limitations must be considered. In cases where further work-up would be required or in certain clinical presentations, CT should be recommended and should always be combined with i.v. contrast.