Flashcards in Non-invasive analysis of skeletal structures Deck (52):
What are the reasons to image bone?
What are examples of clinical investigations of bone?
Diagnosis of pathologies
Identification of fractures
What are examples of research purposes of bone?
Investigation of bone structure
Cortical and trabecular bone comparisons:
-between ontogenetic developmental groups
-between comparative species
What are examples of forensic purposes of bone?
Assessment of microscopic trauma
Skeletal observation without destryong (CBRN - chemical, biological, radiological, nuclear)
What are the types of 2D imaging techniques?
Plane plate radiography
Modified plane plate radiography
What are examples of 3D imaging techniques?
CT - computed tomography
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
What are 'slices' comprised of?
X x Y
What is 3D data comprised of?
X x Y x Z
What is resolution?
Pixel size divided by voxel size
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
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
How does the detector of Radiography work?
Remaining x-rays reach a detector where they are viewed as an image
Historically what was used to capture x-rays?
Photographic film sensitive to x-rays
What is modernly used to capture x-rays?
Digital plates containing diode arrays
What are the benefits of the modern day x-ray equipment?
Processed instantly using computer software
What is the process of macro-radiography?
Method of enlarging radiographs - increases the size of the image relative to that of the object
How does macro-radiography work?
By increasing the object-film distance relative to focal-film distance
Object further from detector = bigger picture
What is macro-radiography useful for?
Observing fine details such as:
Why is macro-radiography outdated?
Modern digital detectors give very high resolution images
Can be magnified digitally
What are CT scans based on?
Based on x-ray radiography and digital detectors
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
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
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
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
What are the units of attenuation coefficient?
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
Why are CTs useful in clinical settings?
Can be interpreted and displayed in innumerable ways:
-3 volume or surface rendering
High tolerance for tissue determination
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
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
What was introduced in 1970s by Hounsfield?
What was introduced by Feldkamp et al in 1989?
Micro computed tomography
What is micro computed tomography specifically designed for?
High-resolution imaging of bone
What is the difference in spatial resolution of CT and micro CT?
CT - >0.3mm
Micro CT - 0.01mm
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
What does the fibre optic taper do?
Acts as a funnel to reduce size of image
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
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
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
What is the magnetic resonance imaging based on?
Excitation of hydrogen nuclei in water
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
What type of radiation is used in magnetic resonance imaging?
What can micro-MRI be applied to?
Visualisation of trabecular bone
What does micro-MRI rely on?
What does bone require for micro-MRI?
Ideally the presence of soft tissue
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
What are the pros of micro MRI?
Good contrast between tissue types
What are the cons of micro-MRI?
Good but limited resolution for trabecular analysis
Limited resonator size
Lengthy scan time
Powerful magnetic field
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
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
What is Bolliger et al's 2008 study useful for?
Non-invasive analysis of the skeleton in both the living and deceased