MicroCT for comparative morphology: simple staining methods allow high-contrast 3D imaging of diverse non-mineralized animal tissues.
BioMed Central Physiology, 9:11, 2009
Brian D Metscher
Department of Theoretical Biology, University of Vienna, Austria
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High-contrast 3D imaging of diverse non-mineralized tissues
1. MicroCT for comparative morphology: simple staining
methods allow high-contrast 3D imaging of diverse
non-mineralized animal tissues
Brian D Metscher
Department of Theoretical Biology, University of Vienna, Austria
BioMed Central Physiology, 9:11, 2009
Arun Torris
2. Overview:
⢠Introduction
⢠Methods
MCT imaging systems
Sample preparation
Illustrations
⢠Results & Discussion
Vertebrates
Embryos
Insects
Invertebrates
⢠Conclusion
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3. Introduction
Methods of 3D visualizations:
I. Serial sections
⢠Laborious process
⢠Specimen sectioning
⢠Destructive
II. Whole-volume imaging
⢠Non-destructive
⢠Imaging instrumentation
E.g.: Micro-MRI, OPT
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8. Micro-CT units
⢠Lab-based scanner
â Commercial x-ray source
â 120,000 to 400,000 Euro
⢠Synchrotron systems
â Much finer resolution
â Requires beamline
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9. Limitations in comparative morphology:
Low x-ray contrast of non-mineralized
tissues
Only few techniques for imaging soft tissues
Organically-bound iodine
Osmium staining
Reduced-silver
Contrast resin perfusion
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10. Major Contributions so farâŚ..
⢠Imaging of mouse and rabbit â de Crespigny et al, 2008.
⢠Phenotyping mouse embroys â Johnson T J et al, 2006.
⢠Honeybee brains â Ribi W et al, 2008.
⢠Drosophila brains â Mizutani R et al, 2007.
⢠Arthropod vasculature â Wirkner et al, 2007.
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11. What it can offer ?
⢠Linear and volumetric size changes in development
⢠Comparison between control and genetically manipulated
specimens
⢠Quantitative data for modeling of developmental and
evolutionary changes
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12. Methods
Micro-CT imaging systems used in the study
SkyScan 1174 scanner
Xradia MicroXCT System 30Âľm to 6Âľm
5Âľm to 500nm
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13. Imaging Parameters
⢠No single optimal set of constants
⢠Requirements of investigation determines
⢠Lower voltage provides higher projection exposure
Specimens
⢠Vertebrates
⢠Vertebrate embryo
⢠Insects
⢠Insect pupae
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14. Object Fixation, Storage Stain Voltage Time Voxels
Polyodon Head Bouin's, 70% ethanol PTA 60 kV, 8 W 2.2 hrs 5.6 Îźm
Polyodon Sections Bouin's, 70% ethanol PTA 80 kV, 8 W 2.8 hrs 4.3 Îźm
Grayling Section formalin PTA 40 kV, 8 W 12 hrs 2.1 Îźm
Axolotl glyoxal, 70% ethanol PTA 60 kV, 8 W 3 hrs 9.6 Îźm
Pike Hatchling formalin IKI 30 kV, 6 W 4 hrs 4 Îźm
Lamprey formalin, 70% ethanol I2E 50 kV, 8 W 4.2 hrs 15 Îźm
Polyodon Head formalin, methanol I2M 80 kV, 8 W 2.6 hrs 5.1 Îźm
Sturgeon Pectoral Fin Dent's, methanol I2M 40 kV, 8 W 2 hrs 9.2 Îźm
Xenopus Embryos formalin PTA 60 kV, 8 W 4 hrs 2.1 Îźm
Mouse Embryo paraform-aldehyde IKI 80 kV, 8 W 2.6 hrs 9 Îźm
Mouse Embryo paraform-aldehyde PTA 80 kV, 8 W 3 hrs 9.6 Îźm
Mouse Embryo EM fix, resin block OsO4 -- -- 8.2 Îźm
Insect Thorax Bouin's, 70% ethanol I2E 60 kV, 5 W 4 hrs 4.3 Îźm
Insect Head Bouin's, 70% ethanol I2E 60 kV, 5 W 16 hrs 2 Îźm
Insect Tibia Bouin's, 70% ethanol PTA 60 kV, 4 W 8 hrs 0.9 Îźm
Fly Pupa hot ethanol PTA 50 kV, 8 W 2.75 hrs 7.7 Îźm
Falcidens EM fix, resin block OsO4 60 kV, 8 W 1 hr 3.2 Îźm
Bryozoan Cristatella Bouin's PTA 40 kV, 8 W 1 hr 4.2 Îźm
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Squid Hatchlings gluteraldehyde PTA IKI 90 kV, 4W 3 hrs 4 Îźm
15. Contrast stains
⢠Inorganic iodine in alcohol
â Diffuses rapidly into fixed tissues
â Ability to stain in few hours
⢠PTA â Phosphotungstic acid
â Larger molecule
â Require overnight incubation
â Binds heavily to proteins and connective tissue
â Electron energy matches x-ray source emissions
⢠PMA â Phosphomolybdic acid
⢠Osmium Tetroxide
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16. Stain Stock Solution Staining Procedure
Mix 30 ml 1% PTA solution + 70 ml absolute ethanol to
make 0.3% PTA in 70% ethanol.
1% (w/v) Keeps indefinitely. Take samples to 70% ethanol.
PTA phosphotungstic Stain overnight or longer.
acid in water
Change to 70% ethanol. Staining is stable for months.
Scan samples in 70% â 100% ethanol
1% iodine metal Dilute to 10% in water just before use.
(I2) + 2% Rinse samples in water.
IKI
potassium iodide Stain overnight. Wash in water.
(KI) in water Can be scanned in water or dehydrated to alcohol.
Use at full concentration or dilute in absolute alcohol.
1% iodine metal Take samples to 100% alcohol.
(I2) dissolved in
I2E, I2M Stain overnight or longer. Wash in alcohol.
100% ethanol (I2E)
or methanol (I2M) Stain does not need to be completely washed out before
scanning.
Same as routine EM processing.
Osmium standard EM post- Osmium-stained samples can be scanned in resin
tetroxide fixation blocks, with some loss of contrast. 16
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17. Fixatives
⢠Neutral-buffered formalin
⢠Paraformaldehyde
⢠Gluteraldehyde
⢠Bouin's fluid
⢠Alcoholic Bouin's
⢠Glyoxal
⢠Dent's fixative
⢠Hot alcohol
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18. Fixative Notes
neutral-buffered Formalin = 37% formaldehyde solution (aq.). in phosphate buffer at pH
formalin (10% NBF) 7.0. The most common, but rarely the best fixative.
paraformaldehyde Polymerized formaldehyde, usually dissolved in buffer (e.g. PBS) at 4%
w/v when a chemically-controlled fixative is required. Similar to 10% NBF.
gluteraldehyde Strong cross-linking fixative, often prepared in cacodylate buffer or a less
toxic alternative such as HEPES. Common fixative for electron microscopy.
4F1G 4% (or 3.7%) formaldehyde + 1% gluteraldehyde in phosphate buffer.
Common fixative for electron microscopy.
Bouin's fluid 75 parts (v/v) saturated aqueous picric acid, 25 parts formalin (37%
formaldehyde), 5 parts glacial acetic acid.
A standard and excellent histological fixative
alcoholic Bouin's Refers to either a mixture of Bouin's fluid and ethanol (1:1), or to the
fixative also known as Bouin-Duboscq-Brasil. The alcoholic solutions
penetrate more readily and are sometimes favored for arthropods.
Glyoxal A cross-linking dialdehyde prepared in acidic buffers and marketed as
formalin substitute. Much less volatile and toxic than formaldehyde.
Very good tissue preservation; especially good for immunostaining.
Dent's fixative 80% methanol, 20% DMSO. Rapid dehydrating fixative. Expect some tissue
shrinkage. Often used for immunostaining.
hot alcohol 2009
10 September
Samples are dropped into 70% ethanol at about 60°C. Mainly used for
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fixing soft-bodied animals, such as insect larvae and pupae.
19. Sample mounting
⢠Scanned in liquid media
⢠Polypropylene tubes
â Low x-ray absorption
â Conical shape
⢠Absolute alcohol
â Fewer bubbles
â Better tissue contrast
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20. Preparation of illustrations
⢠3D viewing and imaging software's
⢠Transparency function
â to show both internal and external features
⢠Arranged with Photoshop CS3
⢠False color was added to the volume renderings
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21. SpecimensâŚ..
European grayling â
Thymallus thymallus
Paddle Fish â Polydon spathula
Pike - Esox lucius
Axolotl â Ambystoma mexicanum
Green sturgeon -
Acipenser medirostris
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22. SpecimensâŚ..
Diptera â
Calliphora vicinia
Lamprey â Lampetra
genus Sysira
Xenopus embryos
Squid - Ideosepius pygmeus Bryozoan Cristatella mucedo
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24. Results & Discussion
⢠Vertebrates â Paddle Fish (Polyodon spathula)
⢠Lateral line receptors
⢠Nasal capsules and
muscles
5.6 Îźm voxels
Multiple views from a single scan of a 7-day post hatching paddlefish
Fixed in Bouin's, stored in 70% ethanol, stained with PTA.
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25. Paddle Fish Paddle Fish
4 days post-hatching 27mm length
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27. Axolotl (Ambystoma mexicanum)
o Muscles and
nervous tissues.
o Sensory organs.
o Nasal capsules.
o Neuromasts.
9.6 Îźm voxels
Scale = 500 Îźm
External views from the dorsal
Glyoxal-fixed, stored in 70% ethanol, PTA stained.
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28. Pike (Esox lucius) o Layers in the brain.
o Jaw adductor
muscles.
o Gill-arch cartilages.
o Retinal layers.
o Connections with
optic nerves, lenses.
4.0 Îźm voxels
Scale = 500 Îźm
Volume renderings and virtual sections - fishâs head
Fixed in formalin and stained with IKI.
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30. Juvenile lamprey (Lampetra)
o The effects of previous
dehydration are evident
Fixed in formalin and stained with I2E after storage Îźm voxels
15
in alcohol (10 cm)
Top: Ventral View; Central: Club
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External View; Bottom: 30
Section
31. Xenopus embryos, stage ca. 27
o Pharyngeal pouches
o Optic vesicles
o Ciliated epidermal
cells.
o Neural tube.
2.1 Îźm voxels
Scale = 100 Îźm
Fixed in formalin and stained with PTA (left) and IKI (right).
Fixed in formalin and stained with IKI.
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32. Mouse embryos
Left: Paraformaldehyde-fixed and IKI-stained 9.0 Îźm voxels
Center: PTA-stained; Right: Osmium-stained 9.6 Îźm voxels
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8.2 Îźm voxels
33. 2D sections of Mouse embryo
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34. Volume Reconstruction
Mouse embryo Mouse embryo
Theiler stage 21 Theiler stage 22
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35. A neuropteran insect (genus Sisyra)
o Musclature.
o Chitinous and soft
tissues
4.3 Îźm voxels
2 Îźm voxels
Fixed in Bouin's fluid and stained with I2E Scale = 100 Îźm
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36. Tibia of a mantophasmid insect
o Scolopidial organ
o Sensory cells and
fiber
o Muscle fibers
o Single blood cells
0.9 Îźm voxels
Stereo pair for convergent (cross-eyed) viewing.
Shows the vibration-sensitive scolopidial organ
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37. Pupa of the flesh fly Calliphora vicinia (Diptera)
o Metamorphosis
o Near-adult
morphology
7.7 Îźm voxels
Scale = 1 mm
Fixed in hot ethanol and stained with PTA.
Pupae must be perforated for PTA to penetrate
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38. A caudofoveate mollusc (Falcidens sp).
Stained with osmium tetroxide and embedded
3.2 Îźm voxels
in Spurr's resin, scanned in resin block
Left: a low-resolution scan (1.4mm); 1.6 Îźm voxels
Center: High resolution, Right: Section Scale = 1 mm
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39. Bryozoan Cristatella mucedo
o Extraction of soft tissue
characters important for study
of the diversification of life
[systematics]
4.2 Îźm voxels
Fixed in Bouin's and stained with PTA.
Scanned in alcohol (2 mm)
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40. Squid hatchlings, Ideosepius pygmeus, ca. 2 mm long
o Emphasizing
the importance
of testing
different stains
on each new
kind of sample
4 Îźm voxels
4.4 Îźm voxels
Fixed in gluteraldehyde, stored in cacodylate buffer,
and stained with PTA (left) and IKI (right).
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41. Discussion
⢠Examples are intended to illustrate some possibilities for
microCT investigations of diverse problems that require or
will benefit from 3D morphological data
⢠Each new type of sample must be tested with different
fixations and stains to find the best treatment for the
imaging required
Accurately calibrated 3D images of musculoskeletal systems
can be also used to quantify
Muscle fiber numbers and cross sectional areas,
Muscle attachment areas,
Bone or cartilage sizes and shapes, and
Facilitate functional modeling
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42. Discussion
PTA Vs Iodine stain
The PTA and iodine stains were found to impart strong tissue
contrast to fish and amphibian samples
Especially PTA staining of Bouin's or glyoxal-fixed material
with IKI staining after formalin-fixation
PTA is known to bind to collagen, proteins and musculature
Cartilage does not stain strongly with PTA, but appears as gaps in
volume renderings
It is worth noting that iodine did not stain effectively in 70%
alcohol, and so samples had to be transferred to 100% alcohol
before staining
Nervous tissues are also demonstrated well with PTA & IKI, and
different layers of the brain can be distinguished easily.
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43. Discussion
Osmium staining
Most common contrast stain,
Has electron binding energies favorable for strong x-ray
absorption
Bind to cell membranes and other lipid-rich structures
including nerves
Very toxic
Penetration is slow
Expensive to dispose of
Does not stain well if samples have been in alcohol
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44. Discussion
PTA staining
Penetrates tissues slowly
Far less toxic
Much simpler to use
Effectively stain alcohol-stored samples
PTA did not readily penetrate the cuticle
Inorganic iodine readily penetrates all soft tissues tested so far,
and it has proven to be versatile and robust contrast stain.
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