Food imaging

Question 1

what do mechanistic studies show

Answer 1

correlations between imaging parameters and physiological or behavioural endpoints

Question 2

what does there need to be an interaction between to image inside the body

Answer 2

electromagnetic radiation and body/food

interaction capable of carrying information that can be detected outside body and analysed

Question 3

what is the ionizing radiation for energy

Answer 3

120eV - 120keV

Question 4

how do x-rays travel and how does the body affect it

Answer 4

straight lines, human tissue attenuates the beam

Question 5

what information does an x-ray have when comes out other side

Answer 5

comes out other side
carries spatial absorption information on tissues and structures
converts this into light for film or digital capture

Question 6

what must food and beverages be mixed with in order to be able to do a radiographic assessment

Answer 6

mixed with radiopaque materials

e.g. bisumuth salts, barium sulphate

Question 7

what is the benefit of using radiographic x-ray technology

Answer 7

relatively cheap

accessible as study of digestion is considered limited

Question 8

what are the negatives of using radiographic x-ray technology

Answer 8

ionizing radiation can break chemical bonds in tissue = biological damage
many foods and beverages must be mixed with radiopaque material

Question 9

what is gamma scinitigraphy

Answer 9

use radioactive elements mixed with food and liquids

radioactive decay emits gamma rays can be detected outside body

Question 10

what is the problem with gamma rays being used

Answer 10

gamma rays come out in many directions - difficult to understand
need to use a collimator

Question 11

what is the benefit of using gamma rays

Answer 11

very sensitive so amount of radiation needed for detection is small - use less radiation

Question 12

what does magnetic resonance imaging use

Answer 12

radio waves

principally water - hydrogen protons from water give a signal that can be transmitted

Question 13

what is the richness in MRI signal dependent on

Answer 13

T1 and T2

depends on mobility of water molecules

Question 14

why is MRI so useful

Answer 14

can be tuned to highlight many different characteristics of food, chime, tissue such as water density

Question 15

what are the benefits of MRI

Answer 15

good spatial resolution (mm)

image selectively the fat and water in body or meal

Question 16

how do fluids appear in an MRI scan and why - which image is used

Answer 16

T2 weighted

very bright - water has protons which are very mobile in fluid so have a very long T2 relaxation time constant

Question 17

how do organs appear in an MRI T2 weighted image

Answer 17

dark as most of their signal will have decayed by time MRI image taken

Question 18

how is gastric emptying measured

Answer 18

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

Question 19

what happens if we eat the same food but with different physical properties e.g. blended

Answer 19

changes hormone peptide response and satiety change

Question 20

what occurs in the small bowel

Answer 20

bolus transport - propulsive

mixing/digestion - segmental

Question 21

what is colonic gas

Answer 21

poorly digested carbohydrates

thought to ferment in the colon and be the cause of some peoples bloating

Question 22

what colour is intestinal gas on MRI and why

Answer 22

black as contains no water - no protons

Question 23

what is used for constiptation

Answer 23

insoluble fibre - swells and trap water carrying it into the colon

Question 24

which has higher mixing frequency

• colon
• small bowel

Answer 24

small bowel

Question 25

how does the colon move chyme along

Answer 25

intervals approximately every 2-hrs

colon undergoes high amplitude propagating contractions (HAPCs)