Food imaging Flashcards
what do mechanistic studies show
correlations between imaging parameters and physiological or behavioural endpoints
what does there need to be an interaction between to image inside the body
electromagnetic radiation and body/food
interaction capable of carrying information that can be detected outside body and analysed
what is the ionizing radiation for energy
120eV - 120keV
how do x-rays travel and how does the body affect it
straight lines, human tissue attenuates the beam
what information does an x-ray have when comes out other side
comes out other side
carries spatial absorption information on tissues and structures
converts this into light for film or digital capture
what must food and beverages be mixed with in order to be able to do a radiographic assessment
mixed with radiopaque materials
e.g. bisumuth salts, barium sulphate
what is the benefit of using radiographic x-ray technology
relatively cheap
accessible as study of digestion is considered limited
what are the negatives of using radiographic x-ray technology
ionizing radiation can break chemical bonds in tissue = biological damage
many foods and beverages must be mixed with radiopaque material
what is gamma scinitigraphy
use radioactive elements mixed with food and liquids
radioactive decay emits gamma rays can be detected outside body
what is the problem with gamma rays being used
gamma rays come out in many directions - difficult to understand
need to use a collimator
what is the benefit of using gamma rays
very sensitive so amount of radiation needed for detection is small - use less radiation
what does magnetic resonance imaging use
radio waves
principally water - hydrogen protons from water give a signal that can be transmitted
what is the richness in MRI signal dependent on
T1 and T2
depends on mobility of water molecules
why is MRI so useful
can be tuned to highlight many different characteristics of food, chime, tissue such as water density
what are the benefits of MRI
good spatial resolution (mm)
image selectively the fat and water in body or meal
how do fluids appear in an MRI scan and why - which image is used
T2 weighted
very bright - water has protons which are very mobile in fluid so have a very long T2 relaxation time constant
how do organs appear in an MRI T2 weighted image
dark as most of their signal will have decayed by time MRI image taken
how is gastric emptying measured
measure serial image stacks across abdomen at intervals
volume of meal (+/- gas) measured at each time point by drawing round boundaries of stomach and summing across all slices
what happens if we eat the same food but with different physical properties e.g. blended
changes hormone peptide response and satiety change
what occurs in the small bowel
bolus transport - propulsive
mixing/digestion - segmental
what is colonic gas
poorly digested carbohydrates
thought to ferment in the colon and be the cause of some peoples bloating
what colour is intestinal gas on MRI and why
black as contains no water - no protons
what is used for constiptation
insoluble fibre - swells and trap water carrying it into the colon
which has higher mixing frequency
- colon
- small bowel
small bowel
