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Flashcards in Non-invasive analysis of skeletal structures Deck (52):
1

What are the reasons to image bone?

Clinical investigations
Research
Forensic purposes

2

What are examples of clinical investigations of bone?

Diagnosis of pathologies
Identification of fractures
Pre-surgical visualisation

3

What are examples of research purposes of bone?

Investigation of bone structure
Cortical and trabecular bone comparisons:
-within inidividuals
-between ontogenetic developmental groups
-between comparative species

4

What are examples of forensic purposes of bone?

Assessment of microscopic trauma
Skeletal observation without destryong (CBRN - chemical, biological, radiological, nuclear)

5

What are the types of 2D imaging techniques?

Plane plate radiography
Modified plane plate radiography
Ultrasonography

6

What are examples of 3D imaging techniques?

CT - computed tomography
MRI

7

How is 3D image data produced?

All based on 2D image capture
'Slices' are produced at each scanning interval along a subject and then combined

8

What are 'slices' comprised of?

Pixels
X x Y

9

What is 3D data comprised of?

Voxels
X x Y x Z

10

What is resolution?

Pixel size divided by voxel size

11

Properties of Radiography

2D representation of 3D structures - no depth
Superimposition is a problem - overlying/underlying or dense structures obscure details and features
Very useful clinically - cheap, fast (almost instant), low radiation dosage
Difficult to make accurate measurements - magnifaction

12

How does the source of radiography work?

A beam of x-rays is produced by an x-ray generator
The beam is directed towards an object, which comprises materials of differing densitites
A proportion of x-rays are absorbed by the dense material of the object

13

How does the detector of Radiography work?

Remaining x-rays reach a detector where they are viewed as an image

14

Historically what was used to capture x-rays?

Photographic film sensitive to x-rays

15

What is modernly used to capture x-rays?

Digital plates containing diode arrays

16

What are the benefits of the modern day x-ray equipment?

Re-usable
Processed instantly using computer software

17

What is the process of macro-radiography?

Method of enlarging radiographs - increases the size of the image relative to that of the object

18

How does macro-radiography work?

By increasing the object-film distance relative to focal-film distance
Object further from detector = bigger picture

19

What is macro-radiography useful for?

Observing fine details such as:
-carpals
-petrous temporal
-lacrimal system

20

Why is macro-radiography outdated?

Modern digital detectors give very high resolution images
Can be magnified digitally

21

What are CT scans based on?

Based on x-ray radiography and digital detectors

22

How do CT scans work?

X-ray source and detectors mounted on a ring on opposing sides
Rotates 360 degrees around the subject capturing data in intervals

23

What do CT scans produce?

They don't produce an image
They measure transmission levels of a thin beam of xrays through a full scan of the body

24

How is an image produced from a CT scan?

Detectors transmit measurement data to a PC
Computer uses mathematical algorithms for image reconstruction
Collates each interval to form a 'slice'
Series of slices is collected from the length of the subject

25

What is the attenuation coefficient?

A quantitiy that characterises how easily a material or medium can be penetrated by a beam of light, sound, particles or other energy/matter

26

What are the units of attenuation coefficient?

Hounsfield units

27

What are the hounsfield units of air, fat, water and compact bone?

Air = -1000 HU
Fat = -60 to -120 HU
Water = 0 HU
Compact bone = +1000 HU

28

Why are CTs useful in clinical settings?

Can be interpreted and displayed in innumerable ways:
-2D slices
-Multi-planar reconstruction
-3 volume or surface rendering
No superimposition
High tolerance for tissue determination

29

What are the pros of CT?

Availability - most modern hospitals have facilities
Large gantry sizes - up to whole body scans
Relatively quick scan and reconstruction - depends on computing power

30

What are the cons of CT?

Poor spatial resolution
'Streak' artefacts associated with bone
Higher radiation dose
Relatively high running costs - hardware, facilities, operators, maintenance

31

What was introduced in 1970s by Hounsfield?

Computed Tomography

32

What was introduced by Feldkamp et al in 1989?

Micro computed tomography

33

What is micro computed tomography specifically designed for?

High-resolution imaging of bone

34

What is the difference in spatial resolution of CT and micro CT?

CT - >0.3mm
Micro CT - 0.01mm

35

How does micro CT work?

Specimen mounted on rotating stage and positioned between fixed X-ray source and detector
X-ray projections acquired by phosphor detector then released through fibre optic taper
Taper output feeds into charged coupled device image sensor which converts photons to electrons

36

What does the fibre optic taper do?

Acts as a funnel to reduce size of image

37

What are the pros of micro CT?

Great for quantification of structural indices which aid explainng bone form
Indispensable tool for bone analysis
High spatial resolution achievable
Good contrast in dry bone

38

What are the cons of micro CT?

Gantry size does not allow imaging of whole bones
Larger specimens result in lower resolution and loss of detail
Mostly carried out on animals, not suited for in-vivo humans
Long scan and reconstruction time
Artefact production if specimen outside field of view

39

How can micro CT be applied?

Initially for study of trabecular bone architecture
Regarded as gold standard for assessment of trabecular bone
Assessment of animal models
Recently applied to investigation of ontogenetic development in human skeletal collections

40

What is the magnetic resonance imaging based on?

Excitation of hydrogen nuclei in water

41

What do detectors of magnetic resonance imaging do?

Pick up energy emissions during movement
Produce a 3D image based on slices
Protons in different tissue return to their normal alignment at different rates so scanner can distinguish among tissues

42

What type of radiation is used in magnetic resonance imaging?

Non-ionising radiation

43

What can micro-MRI be applied to?

Visualisation of trabecular bone

44

What does micro-MRI rely on?

Free protons

45

What does bone require for micro-MRI?

Ideally the presence of soft tissue

46

How is a good picture still achieved from micro MRI?

Bone mineral lacks free protons, so limited MR signal
Soft tissue has a high water content
Although bone images poorly, good definition can be achieved due to the obvious contrast between hard and soft tissue

47

What are the pros of micro MRI?

Good contrast between tissue types
Non ionising

48

What are the cons of micro-MRI?

Good but limited resolution for trabecular analysis
Limited resonator size
Lengthy scan time
Scan artefacts
Powerful magnetic field

49

What are the applications for micro MRI?

Predominantly research based, due to specimen size limitations
Investigation of bone architecture when in the presence of soft tissue
Investigation of anatomical compartments in animal models

50

What did Bolliger et al study in 2008?

Virtual autopsy using imaging
Implementation of modern imaging techniques to augment current examination techniques or offer alternative means of analysis

51

What is Bolliger et al's 2008 study useful for?

Non-invasive analysis of the skeleton in both the living and deceased

52

What was dedouit et al's study in 2007?

Virtual anthropology and forensic identification
Charred body found in house, identification unknown
CT performed to assess potential of radiolgogical anthropological bone identification