General Flashcards
What is an Image?
A representation of the external form of a person or thing in art / 2D representation of a 3D object
What sort of factors can be represented by a medical image?
- Brightness, colour
- Emission, transmission
- Electrical impedance
- Magnetic moment
What are the purposes of anatomical imaging?
- Structural imaging of the body
- What is and isn’t present in an area
- How organs vary in their
composition - How organs vary in their
location/size/shape
What are the purposes of Functional/Physiological imaging?
- How organs are functioning within the body (4d gating)
- How are biological pathways functioning (DaTSCAN)
- Uptake of pharmaceuticals within organs and lesions (MAG3 kidney scan)
Explain x-ray radiographs
anatomical and functional imaging (fluroscopy - barium meal)
Utilise x-ray photons to measure variations in attenuation coefficient
Explain CT
anatomical and functional imaging (triple phase liver scans)
2D slices displayed to form a 3D stack - can be rendered to appear 3D
Utilise photons to measure differences in attenuation coefficient
* Different anatomy – different attenuation
Higher dose and higher contrast
Explain Nuc Med
Planar (2D) and SPECT/PET (3D)
Allows for functional imaging (technicium bone scan )
Measuring uptake/location of an emission from a radionuclide
Relatively high dose as patients are active from moment of injection
to clearance/decay of radionuclide
Explain MRI
3D imaging (2D slices from 3D stack)
Functional (fMIR) and structural imaging
Measure variation of magnetisation or magnetic moment of protons
in different environments
Explain Ultrasound
2D and 3D real-time imaging
Utilise reflective acoustic boundary between materials
- Functional (e.g. Doppler imaging) or structural (lesion detection)
Name 3 other types of medical imaging
Thermography (non-ionising precursor to mammo)
Electrical Impedance (monitor lung ventilation)
Optical
(naked eye, endoscopy, microscopy)
Explain how a Technicium-99 bone scan works
The 99mTc is chemically bound to a compound -methylene diphosphonate (MDP) to form technetium-99m MDP
It emits gamma rays
Tc-99 MDP is injected intravenously
Tracer accumulates in bones by diffusing and binding to hydroxyapatite crystals in bone tissue
scintillation crystal in gamma camera detects radiation emitted and generates flashes of light
Gamma camera rotates around pt to get images from multiples angles for 3d reconstruction later
photomultiplier tube detects and converts these flashes into electrical signals
Reconstruction allows for visualizing areas of abnormal radiotracer uptake, indicating potential bone abnormalities or diseases.
Increased uptake may suggest conditions such as bone infections, tumors, or fractures, while decreased uptake may indicate areas of decreased blood flow or bone turnover.
Why Tc-99?
Emits Gamma rays
140keV (High energy) Gamma - better pt penetration - efficient imaging
6-Hour (Short) half life, decays fast - sufficient imaging time but minimises pt exposure
Tc-99 MDP gives excellent skeletal uptake, high bone-to-soft-tissue contrast, and low soft-tissue background signal. This results in clear and accurate visualization of bone abnormalities.
Tc-99 is readily available from on-site generators - parent isotope molybdenum-99
whats an example of MRI functional Imaging?
fMRI measures changes in blood oxygenation and flow in the brain, which are related to neural activity
- study brain function and connectivity.
when a particular brain region is more active, there is an increased demand for oxygenated blood in that region. This increased blood flow leads to changes in the level of oxygenation in the blood, which can be detected using MRI.
During the scan, the pt can be asked to do cognitive or motor task
scanner captures a series of images over time, showing the changes in blood oxygenation in different brain regions.
data is then analyzed to see regions that are most active
Also used to investigate resting-state brain activity,
used in neurology to study cognitive processes
Important cases of image formation
If h(ro,ri,kf(ro)) = kh(ro,ri,f(ro)) for any k linear system
* Contribution to the image from any point is proportional to the strength of signal at
that point
- If h(ro,ri,f(ro)) = h(ro,-ri,f(ro)) for any ro,-ri shift invariant
- PSF depends only on the relative displacement of the points in the image and object
What are the 4 main image properties
Spatial Resolution
Contrast
Noise
Geometric intensity
