Computer aided vertebral visualization and analysis: a methodology using the sand rat, a small animal model of disc degeneration

Spontaneous age-related cervical disc degeneration in the sand rat

BACKGROUND

Disc space narrowing, osteophytes, and disc degeneration are common and increase with aging. Few animal models are appropriate for the study of spontaneous age-related cervical disc degeneration.

QUESTIONS/PURPOSES

We used the sand rat, a member of the gerbil family with well-recognized age-related lumbar disc degeneration, to determine whether spontaneous cervical disc degeneration differed from lumbar degeneration when evaluated by (1) radiologic and (2) histologic measures. Animals 2 to 25 months of age were used in these analyses.

METHODS

Cervical and lumbar discs of 99 sand rats were analyzed with radiology, and cervical discs of 67 sand rats were studied with histology. Lateral digital radiographs of cervical and lumbar spines were scored for presence or absence of wedging, disc space narrowing, osteophytes, end plate calcification, and irregular disc margins at C2-C3 through C6-C7 and T12-L1 through L7-S1. Percentages for presence were calculated and statistically analyzed for younger (range, 2-11.9 months old) versus older (range, 12.0-25 months old) animals.

RESULTS

Cervical discs in younger animals exhibited a greater proportion of irregular margins compared with lumbar sites (94% versus 83%; p = 0.02; 95% CI for difference, 2.7, 19.0%). In older animals, cervical discs showed a greater proportion of osteophytes than did lumbar discs (7% versus 0%; p < 0.0001). The incidence of disc space narrowing was greater in cervical versus lumbar sites (99% versus 90%; p = 0.0008). Cervical spine sites which contained osteophytes morphologically showed irregular disc margins and revealed an extrusion of herniated disc material in the osteophytes.

CONCLUSIONS

Radiologic and morphologic studies confirmed age-related disc degeneration in the cervical spine of the sand rat.

CLINICAL RELEVANCE

Clinical cervical aging studies have shown that 14% of asymptomatic subjects younger than 40 years have abnormal MRI scans with an increase to 50% by 50 years old. We studied an economic rodent model for cervical age-related spontaneous disc.

An entropy-based automated cell nuclei segmentation and quantification: application in analysis of wound healing process

The segmentation and quantification of cell nuclei are two very significant tasks in the analysis of histological images. Accurate results of cell nuclei segmentation are often adapted to a variety of applications such as the detection of cancerous cell nuclei and the observation of overlapping cellular events occurring during wound healing process in the human body. In this paper, an automated entropy-based thresholding system for segmentation and quantification of cell nuclei from histologically stained images has been presented. The proposed translational computation system aims to integrate clinical insight and computational analysis by identifying and segmenting objects of interest within histological images. Objects of interest and background regions are automatically distinguished by dynamically determining 3 optimal threshold values for the 3 color components of an input image. The threshold values are determined by means of entropy computations that are based on probability distributions of the color intensities of pixels and the spatial similarity of pixel intensities within neighborhoods. The effectiveness of the proposed system was tested over 21 histologically stained images containing approximately 1800 cell nuclei, and the overall performance of the algorithm was found to be promising, with high accuracy and precision values.

N-acetyltransferase 2 (Nat2) polymorphism in the sand rat Psammomys obesus

Human arylamine N-acetyltransferase 1 (NAT1) and its homologue in rodents (Nat2) are polymorphic xenobiotic metabolizing enzymes and also seem to play a role in endogenous metabolism. NAT1 and Nat2 polymorphism was associated to cancers under xenobiotic procarcinogens metabolism as well as under endogenous substrate metabolism. This study investigated the p-aminobenzoic acid (PABA) -Nat2 catalytic activity and its polymorphism in liver homogenates of adult sand rats Psammomys obesus Cretzschmar, 1828. These Saharian sand rats develop high incidence of spontaneous cancers under standard laboratory diet. The average value of PABA-Nat2 specific activity tested in nine sand rats was significant (2.96 ± 2.16 nmoles/min/mg). The N-acetylation exhibited a bimodal distribution. There was a significant difference (p<0.01) between PABA-Nat2 activity in the fast acetylators group (4.10 ± 1.67 nmol/min/mg) and slow acetylators group (0.7 ± 0.27 nmol/min/mg). The percentage of the fast acetylator group was 66.66%. These results support the presence of Nat2 polymorphism in the liver of the strain sand rats Psammomys obesus. This strain is useful for investigating the role of Nat2 polymorphisms in susceptibility to cancers related to arylamine carcinogen exposures as well as to endogenous substrate metabolism.

Vertebral endplate and disc changes in the aging sand rat lumbar spine: cross-sectional analyses of a large male and female population

STUDY DESIGN

Lumbar vertebral segments from a large cross-sectional population of male and female sand rats were assessed for quantitative determination of lumbar endplate bone mineral density (BMD) and radiologic features.

OBJECTIVE

To determine radiologic and BMD characteristics in the lumbar spines of males and females ranging in age from 1.5 to 46.0 months.

SUMMARY OF BACKGROUND DATA

The sand rat provides an excellent economical model in which disc degeneration is reliable and well characterized. A major advantage of this model is that disc degeneration is spontaneous and does not need to be induced by stab surgical procedures. Previous work has only examined a small group of male sand rats for radiologic and BMD features of the lumbar spine; more complete data on both genders and a wider age range are lacking.

METHODS

BMD data were obtained for 99 male or female sand rats aged 1.5 to 46.0 months using the GE Lunar PIXImus bone densitometer; results were assessed for changes related to age, weight, gender, lumbar vertebral site, and radiologic characteristics of disc degeneration (disc space narrowing, wedging, and endplate calcification). Four age groups were studied: Group 1, 1 to 3.9 months of age; Group 2, 4 to 11.9 months of age; Group 3, 12 to 23.9 months of age, and Group 4, 24 to 46 months of age.

RESULTS

Group 1 females showed a greater incidence of radiologic disc space narrowing and wedging at L1-L2, L2-L3, L3-L4, L4-L5, and of wedging at sites L5-L6, L6-L7, and L7-S. Group 2 females had significantly greater disc space narrowing at L3-L4 and L4-L5. By the time animals reached the age of Groups 3 and 4, males showed more wedging at L1-L2 and L3-L4. BMD data showed that Group 1 females had significantly lower BMD than Groups 2, 3 and 4 at all lumbar levels, and Group 4 had significantly higher BMD than Group 3. For males, there were no differences in younger animals, but older Group 3 and 4 animals had significantly greater BMD than Groups 1 and 2. Caudal BMD values were generally significantly higher than cranial values. Averaged BMD levels correlated significantly with both age and body weight, but the correlation with age at each lumbar level accounted for much more of the variation than did weight. Averaged BMD was significantly greater in disc sites showing disc space narrowing than in sites without narrowing for L1-L2 and L3-L4 through L7-S (P < or = 0.002 for each spinal level).

CONCLUSION

Results expand our understanding of the association of age and gender to endplate sclerosis patterns in the lumbar spine, and support the hypothesis that endplate sclerosis may play a role in disc degeneration.

Automated Spine Survey Iterative Scan Technique

Institutional review board approval, with waived consent, was obtained to develop a spine-labeling algorithm with retrospectively obtained deidentified HIPAA-compliant data. An automated magnetic resonance (MR) imaging technique to rapidly survey the entire spine and provide definitive numbering of disks and vertebrae was compared with neuroradiologist assignments in 50 cases. Contiguous two-station sagittal fast gradient-recalled-echo sequences with 35-cm fields of view (FOVs) were preprogrammed for full cervical, thoracic, and lumbar spine coverage (combined 70-cm FOV, seven sections, 15 mm left of to 15 mm right of midline, 4-mm section thickness, 1-mm intersection gap, 512 x 352 matrix, 58/2.0 [repetition time msec/echo time msec], 30 degrees flip angle, 15.6-kHz bandwidth, 42-second acquisition time). In all cases, the neuroradiologist could visualize and definitively number all cervical, thoracic, and lumbar levels on automated spine survey iterative scan technique localizer studies. Automated disk-vertebra detection and numbering were concordant with neuroradiologist assignments in all cases. The entire spine can be surveyed with subminute, submillimeter in-plane resolution MR imaging. Cervical, thoracic, and lumbar vertebrae and disks can be readily identified and definitively numbered by means of visual inspection or semiautomated computer algorithm.