Micro-CT of a Stained Mouse Heart

Unravelling the intricacies of the heart is an ongoing process for researchers, and micro-CT imaging adds to our understanding of heart tissue. As one looks at the heart it seems to be made of complex muscle fibers and interactions that can appear quite confusing. Yet, if we image the heart with micro-CT and trace the interconnectivity of the muscle fibers, we can see that the heart is made of one long muscle folded onto itself in a helical fashion. Through high resolution micro-CT imaging we see how this is made visible in a mouse heart scan.

Understanding the heart myocardium with staining and micro-CT imaging

The myocardium, which makes up the bulk of the heart wall structure, is muscle consisting of cardiac myocytes, which in turn consist of bundles of myofibrils. The myocytes and myofibrils are connected to each other through collagen connective tissue. The best way to understand the myocyte structure is to hold a bunch of pencils in your hand. Your hand would be a myocyte and each of the pencils would be the myofibrils. All the air space between your hands and the pencils would be the connective tissue.1

The collagen is the key to understanding the muscles of the heart with micro-CT imaging because it is easily stained with phosphor-tungstic acid (PTA). PTA is known to bond to fibrin and collagen in muscle tissue, and due to the tungsten in the chemical, PTA allows more absorption of X-rays. This extra absorption of X-rays in the collagen causes the myocytes to become more prominent as individual strands, allowing us to see the cardiac muscle layout in more detail.

Why is seeing myocytes important?

Orientation of the myocytes is critical to understanding how the heart contracts as one single unit. Because of the staining, high resolution micro-CT scans show the orientation of the myocytes in a mouse heart and how they propagate throughout the heart. As others have investigated, these fibers are one continuous helical band if they were to be unraveled. When wrapped around each other, the myocytes adhere to themselves to shape the heart. When the heart contracts these fibers constrict and twist, similar to the wringing out of a towel. As the heart contracts, blood is squeezed through the ventricles. The myocytes make it possible to see the heart as one big muscle that contracts and twists (Figure 2).2

 

Fig 2
Figure 2. Orientation of myocytes to understand the contraction in a mouse heart (left). As the myocytes contract the heart also twists, which causes constriction and pumping of the blood through the heart (right). Sample courtesy of Dr. Steven Phillips, Temple University.

Conclusion

We hope this image of the month demonstrated something new to you about heart structure. This study has been an enjoyable experience for us. We want to thank Dr. Steven Phillips from Temple University for providing the mouse heart for this imaging, as well as all the knowledge he has shared with us over the years. We look forward much more collaboration in the future.

If you have an image of the month sample, or know of someone that is interested in getting micro-CT imaging done on their sample, we are always looking for new and exciting projects. Please feel free to call Brandon Walters at 610-366-7103 or e-mail brandon@microphotonics.com to learn more about what micro-CT can offer you.

 

SCAN SPECIFICATIONS

System

SkyScan 1272 Micro-CT

Voltage

50kV

Current

200µA

Pixel Size

2.7um

Rotation Step:

0.1

Scan Time

4:41:31 (HH:MM:SS)

Software

NRecon, DataViewer, CTVox

Location

Micro Photonics Imaging Laboratory, Allentown, PA

Works Cited

  1. Sherwood, L. (2006). Fundamentals of Physiology: A Human Perspective. Belmont, CA: Thomson Brooks/Cole.
  2. Masood, S.; Yang, G. (2001). Macroscopic Structure and Physiology of the Normal and Diseased Heart. London SW7 2BZ, UK. Retrieved from: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.22.7988&rep=rep1&type=pdf

 

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