Guldberg Lab

MICRO-CT IMAGING

[cell-based therapies] [biomaterials] [biomechanics]

Imaging of cartilage and bone during development or degradation.

Soft tissues such as cartilage are generally undetectable by micro-CT due to their low X-ray attenuation. We have developed a new micro-CT technique that relies on the equilibrium partitioning of an ionic contrast agent (EPIC-µCT), which can provide direct in situ analysis of both bone and cartilage during joint development, degeneration, or repair. We have validated and applied EPIC-µCT for assessment of 3D articular cartilage morphology and proteoglycan composition with high precision and accuracy in the rat model.

Rat femora were scanned after incubation with Hexabrix contrast agent. The following image shows: (A) Cartilage (white) overlayed on bone (grey) in these images of 4, 8, and 16wk old rat femora. (B) EPIC-µCT thickness mappings for the cartilage layers. (C) Sagittal sections showing attenuation distribution in the femoral condyles.

In addition, with safranin-O staining, we show that areas of low X-ray attenuation correspond to areas of high sGAG content, and high attenuation corresponds with low sGAG content. This can be seen in the following images for normal and chondroitinase ABC-digested cartilage.

We have also assessed damage in bone and cartilage in a monosodium iodoacetate (MIA) induced rat arthritis model. Some composition changes were seen as early as 1 week after injection of MIA in the knee joints. Morphological changes in femoral articular cartilage and underlying trabecular bone were seen 3 weeks after injection of MIA in the joint space of rats (shown below: control limb on the left, arthritic limb on the right, M = medial, L = lateral).

Assessment of vascular anatomy.

We have developed novel imaging methodologies for evaluating vascular growth in small animal models. In these procedures, an injectable radio-opaque contrast agent is perfused through the vasculature of mice and rats and micro-CT is used to provide quantitative, 3-D analysis of blood vessel morphology. We have used this technique to image and quantify vessel development and remodeling in several growth and injury models including murine hindlimb ischemia, murine fracture healing, and rat segmental defect. Additionally, considering the large number of transgenic mice currently available, this technique can be highly valuable in determining the role of specific factors in vascular growth.

This movie generated from micro-CT images depicts the entire hindlimb vasculature of a mouse from one of the hindlimb ischemia studies.

In the following images also from a mouse hindlimb ischemia study, hindlimb vasculature is described via the color-coded diameter scale (in microns) below. Further quantitative characterization of control and surgery hindlimbs demonstrates that excision of the femoral artery stimulates reconstitution of vascular volume through a highly connected network of small, closely spaced, and isotropically oriented vessels.

Other micro-CT applications.

Some other areas where we have applied micro-CT imaging include vascular growth and remodeling, cardiovascular prosthetics and implants, biomaterials, fracture and defect healing, evolutionary biology, and engineering materials.

Calcified pericardial valve implant, excised from a human patient:

Haversian canal space from a baboon mandible bone specimen (inverted image):

Allografts with gelfoam and adeno-associated virus treatments for accelerating bone healing in a rat femoral defect. Left: full image, middle: allograft only, right: new mineral formation.

A silicate foam with embedded iron particles:

Evolutionary study of cichlid fish pharyngeal jaw. Left: greyscale slice. Right: segmented 3-D image.

Copyright © 2004 Parker H. Petit Institute for Bioengineering and Bioscience
All rights reserved. Last modified on December 17, 2008