Pitfalls in interpreting rat knee joint magnetic resonance images and their histological correlation.
BACKGROUND
Magnetic resonance (MR) imaging has been increasingly used as an investigational tool for assessing the structure and function of animal joint disease models, while to date MR tomographic knowledge of laboratory animal skeletal microanatomy remains limited.


OBJECTIVE
To describe pitfalls in interpreting rat knee joint MR images and their histological correlation.


METHODS
MR scans of the right knee of five 3-month-old Sprague-Dawley (SD) rats were carried out using a 4.7T magnet, using a fat-suppressed three-dimensional (3D) gradient echo sequence with a spatial resolution of 59 x 117 x 234 microm. Histology assessment with hematoxylin and eosin staining and Safranin O staining was carried out in the five 3-month-old SD rats and two SD rats of 1 month and 6 months old, respectively. MR images were analyzed by a radiologist, and histology data were assessed by a radiologist and a pathologist.


RESULTS
Though the MR images were acquired in normal rats, many signs unfamiliar to radiologists were noted, including notch-like bright signal areas in the epiphysis, gray signal areas in the epiphysis, and fuzzy joint surface of the epiphysis of the femur and tibia. Detailed inspection of the histology specimen showed more unfamiliar features of rat knee microanatomy, including curvy or dipped surface of the femur/tibia epiphysis, areas composed of a mixture of cartilage and bone components, normal notch structure, cyst-like structure, and cavity between cortical lamellae under the joint cartilage.


CONCLUSIONS
There are a number of normal microstructures of the rat knee joint that can be potentially misinterpreted as arthritic changes on MR images. Recognizing these rat knee microstructures can help correct image reading during biomedical research.
Department of Oncological Surgery, First Affiliated Hospital, College of Medicine, Zhejiang University, Zhejiang Province, Hangzhou, China.
Hao-Hao
HH
Wang
Yi-Xiang J
YX
Wang
J F
JF
Griffith
Yan-Lin
YL
Sun
Ge
G
Zhang
Chun-Wai
CW
Chan
Ling
L
Qin
A T
AT
Ahuja
Li-Song
LS
Teng
D000818:Animals; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley