Imaging Sci Dent.  2014 Mar;44(1):43-52. 10.5624/isd.2014.44.1.43.

A magnetic resonance imaging study on changes in rat mandibular bone marrow and pulp tissue after high-dose irradiation

• Lee W
• Lee BD
• Lee KK
• Koh KJ

• KMID: 1974473
• DOI: http://doi.org/10.5624/isd.2014.44.1.43

Abstract

PURPOSE
This study was designed to evaluate whether magnetic resonance imaging (MRI) is appropriate for detecting early changes in the mandibular bone marrow and pulp tissue of rats after high-dose irradiation.
MATERIALS AND METHODS
The right mandibles of Sprague-Dawley rats were irradiated with 10 Gy (Group 1, n=5) and 20 Gy (Group 2, n=5). Five non-irradiated animals were used as controls. The MR images of rat mandibles were obtained before irradiation and once a week until week 4 after irradiation. From the MR images, the signal intensity (SI) of the mandibular bone marrow and pulp tissue of the incisor was interpreted. The MR images were compared with the histopathologic findings.
RESULTS
The SI of the mandibular bone marrow had decreased on T2-weighted MR images. There was little difference between Groups 1 and 2. The SI of the irradiated groups appeared to be lower than that of the control group. The histopathologic findings showed that the trabecular bone in the irradiated group had increased. The SI of the irradiated pulp tissue had decreased on T2-weighted MR images. However, the SI of the MR images in Group 2 was high in the atrophic pulp of the incisor apex at week 2 after irradiation.
CONCLUSION
These patterns seen on MRI in rat bone marrow and pulp tissue were consistent with histopathologic findings. They may be useful to assess radiogenic sclerotic changes in rat mandibular bone marrow.

Keyword

Magnetic Resonance Imaging; Mandible; Bone Marrow; Irradiation

MeSH Terms

Animals
Bone Marrow*
Incisor
Magnetic Resonance Imaging*
Mandible
Rats*
Rats, Sprague-Dawley

Figure

• 

  Fig. 1 Target volume of the right mandible including the ramus and condyle in CT scans are set prior to high-dose irradiation. 100% isodoses are marked in yellow. Pre-irradiated planning enables setting a one-sided application of radiation and minimizing the change in adjacent tissues, especially the brain.

• 

  Fig. 2 Coronal fat-suppressed T2-weighted MR image. In order to locate the same plane every week, the axial (pulp floor of molar teeth), sagittal (midline of face), and coronal (first molar including two roots) planes were adjusted. The location of the region of interest (ROI) was used to measure the signal intensity in the mandibular first molar area. The ROIs included the alveolar bone marrow between the first molar and the incisor, and the adjacent muscles.

• 

  Fig. 3 The ROI of the incisor pulp tissue below the molar teeth on the modified sagittal section is obtained along the long axis of the incisor.

• 

  Fig. 4 Coronal fat-suppressed T2-weighted MR image. The image shows an example of a mandibular ramus height (condyle to mandibular angle) measurement using the Tapeline tool in the OnDemand3D program.

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  Fig. 5 A. The MR images show the changes during the 4 weeks after irradiation. The SI of the irradiated tissues around the right incisor pulp has increased (arrowhead). The changes in the MR images in Group 2 are prominent. B. The diagram shows the SI of the bone marrow versus the time curve. In the control group, the SI of the bone marrow has decreased. The SI of the irradiated right bone marrow has also decreased. The irradiated groups show a lower level of SI than that of the control group. These differences appear from the first week. However, a small difference can be seen between the Groups 1 and 2.

• 

  Fig. 6 A. The MR images show the changes during the 4 weeks after irradiation. A modified sagittal view is obtained along the long axis of the incisor. The size and SI of pulp of incisor have decreased (arrow) in Group 2. However, the SI of the MR images in the Group 2 is high at the apex of the incisor from week 2 after irradiation (arrowhead). B. The diagram shows the SI of the pulp tissue versus the time curve. The SI of the irradiated pulp tissue has decreased until week 3 after irradiation. There are differences among the groups at week 3.

• 

  Fig. 7 A. The MR images show the changes during the 4 weeks after irradiation. There is a mandibular asymmetry due to the retardation of the growth on the right side (arrowhead). B. The diagram shows the mandibular ramus height versus the time curve. The height of the irradiated ramus is shorter than the contralateral and control side.

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  Fig. 8 Histopathologic examination of the alveolar bone below molar tooth (H&E stain, 100×). At the irradiated sites, the histopathologic changes show increasing trabecular bone formation and bone sclerosis in the irradiated groups, prominent in the molar region in Group 2.

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  Fig. 9 Histopathologic changes show the atrophic incisor pulp tissue due to irradiation. The enlarged vessels and hemorrhagic changes are visible. The formation of dental hard tissue is inhibited, but it shows new bone formation (Group 2 at week 4 after irradiation. H&E stain, 100×).

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