chapter 1

Question 1

what is the equation for image resolution?

Answer 1

image resolution (mmpixel^-1)= actual size (mm)/ number of pixels (pixel)

Question 2

what is a pixel?

Answer 2

the smallest thing you can resolve in a digital image

Question 3

what is the wave equation?

Answer 3

velocity= frequency x wavelength

Question 4

how are x-rays produced?

Answer 4

high speed electrons are fired onto a photographic cassette through the body. Bones absorb the radiation more than the less dense soft tissue and so a negative image is shown on the picture

Question 5

how do MRI’S work?

Answer 5

Magnetic resonance imaging- you lie in a strong magnetic field and radio-frequency waves are directed at your body. The water molecules in your body act was tiny magnets which are very sensitive to magnetic fields- the protons line up in the same direction.Short bursts of radio waves are sent to certain areas of the body, knocking protons out of alignment.when the radio waves are turned off, the protons realign and in doing so send out radio signals which are picked up by receivers. Different tissues form different relaxation times so that areas of the body can be distinguished on the image

Question 6

how do gamma ray tracers work?

Answer 6

a radioactive source is injected or swallowed into/by the patient. this radiation penetrates the body tissues and can be detected externally. The areas which absorb lots of glucose eg the thyroid emit more radiation and so are detected

Question 7

how does an STM work?

Answer 7

Scanning Tunneling Microscope. Non- optical microscope that works by scanning an electrical probe top over the surface of a sample at a constant spacing. This allows for a 3D picture of the surface to be created.

Question 8

wavelength of visible light?

Answer 8

400nm (4x10^-7)-> 700nm(7x10^-7)

red–> violet

Question 9

protons and neutrons are made of what?

Answer 9

quarks

Question 10

what is the size of quarks/electrons?

Answer 10

10^-18m

Question 11

order of the electromagnetic spectrum?

Answer 11

radio waves, microwaves, infra-red waves, visible light, UV, x-rays, gamma

Question 12

wavelength of microwaves?

Answer 12

10^-1 -> 10^-3 m

Question 13

wavelength of radiowaves?

Answer 13

10^6–> 10^-1 m

Question 14

wavelength of infrared?

Answer 14

10^-3–> 10^-6 m

Question 15

wavelength of uv?

Answer 15

10^-7 –> 10^-8 m

Question 16

wavelength of x-rays?

Answer 16

10^-8 –> 10^-10 m

Question 17

wavelength of gamma rays?

Answer 17

10^-10–> 10^-12 m

Question 18

define period

Answer 18

the time taken for 1 complete wave

Question 19

frequency=

Answer 19

1/T

Question 20

how does ultrasound imaging work?

Answer 20

a change in density shows how much will be transmitted and how much will be reflected so you put a gel on the stomach with the same density as the skin so that the ultrasound can pass through and not be reflected. short pulses of sound are sent out from the scanner which is held in contact with the mother’s belly.
the pulses are reflected back where the density of the tissue changes. bone is a good reflector of sound.sound comes back to the scanner from the different parts of the baby, each part producing its own characteristic reflection

Question 21

what’s acoustic independence (AI)?

Answer 21

dependent on the density of the material in which sound is propagated- the greater the independence the denser the material

Question 22

where do reflections come from in ultrasound imaging?

Answer 22

from the interface of different AI’s- the greater change pf the AI, the more signal reflected

Question 23

what’s a transducer?

Answer 23

transmits and receives the ultrasound waves?

Question 24

what produces ultrasound waves? how?

Answer 24

ultrasound pulse is a pulse containing just a few oscillations produced by a piezoelectric crystal. Ultrasound is generated by rapid electric oscillations applied to a piezoelectric crystal. When the ultrasound pulse returns and vibrates the crystal, it produces a signal that is picked up by the scanner

Question 25

what type of waves are ultrasound waves?

Answer 25

longitudinal

Question 26

can you explain how the darkness level on the grey scale is determined by the imaging method?

Answer 26

the number for each pixel decides what shade of grey that pixel will be printed. Darker regions correspond with larger numbers in the array (the date for the image)

Question 27

what's the speed of sound in air?

Answer 27

330-340 ms^-1

Question 28

what is the speed of sound in soft human tissue?

Answer 28

1500ms^-1 (0.67 micro s per mm)

Question 29

why must the frequency of the ultrasound wave be greater than 1MHz?

Answer 29

because the depths to be 'sounded' are only about 100mm, and ultrasound travels at high speed taking about 70 micro seconds to go 100mm in soft tissue. Thus the delay times are short. The pulses must be only about 1 micro second long if returning pulses are not to overlap outgoing ones. The time of an oscillation of the wave cannot be longer than the time the pulse exists so the frequency must exceed 1MHz= 1million oscillations per second

Question 30

why is ultrasound ultra-inaudible?

Answer 30

because the highest frequency you can hear is about 20KHz

Question 31

what's ultrasounds frequency and wavelength?

Answer 31

high f and short wavelength

Question 32

in binary what does 1 represent?

Answer 32

a signal being on- high voltage

Question 33

in binary what does 0 represent?

Answer 33

a signal being off- low voltage

Question 34

what is a single binary digit called?

Answer 34

a bit

Question 35

what is a group of 8 binary digits called?

Answer 35

a byte - the smallest meaningful units of computer memory

Question 36

what does the number of bits in a string (I) determine?

Answer 36

how many alternatives that string can code for

Question 37

how many alternatives does a single bit have?

Answer 37

2 alternatives (0 and 1)

Question 38

how many alternatives does on byte (8 bits) have?

Answer 38

256 alternatives

Question 39

number of alternatives=

Answer 39

2 ^ Number of bits or N= 2^I

Question 40

number of bits=

Answer 40

log2 (number of alternatives) or I =log2N

Question 41

1 pixel in a black and white image=

Answer 41

1 bit

Question 42

in a grey scale image 1 pixel=

Answer 42

8 bits

Question 43

how many shades of grey are there?

Answer 43

2^8= 256

Question 44

what are the primary colours of light?

Answer 44

red, green and blue

Question 45

for a colour image how many bits for each pixel?

Answer 45

256/8 = 24

Question 46

how many different colours are there?

Answer 46

2^24= 16777216

Question 47

what will add values to the pixel number?

Answer 47

increasing the brightness of an image

Question 48

what does adding a fixed positive value do to the image?

Answer 48

it makes it brighter,but it doesn't change the difference between the dark and light regions (contrast)

Question 49

what does multiplying by a fixed value greater than 1 do to the image?

Answer 49

makes the image brighter and increases the contrast

Question 50

what reduces noise?

Answer 50

replace each pixel with the median of itself and the 8 pixels surrounding it- the result is that any 'odd' (very high or low) values are removed and the image is smoother

Question 51

what is noise?

Answer 51

unwanted interference affecting a signal. in images this is usually bright or dark spots on the picture

Question 52

which parts of the eye are involved in bending the light?

Answer 52

cornea - transparent curved front surface and the lens which adjusts the focus to produce a sharp image on the retina

Question 53

what are the light sensitive elements in the eye?

Answer 53

cones and rods- emit signals that go to the brain. cones detect colours and work best in bright light.rods are sensitive to dim light but do not distinguish colours

Question 54

how many rods in the eye?

Answer 54

more than 100million

Question 55

what is the function of the fovea?

Answer 55

only cones, where the eye detects fine detail- central vision eg reading and driving

Question 56

what does the lens look like when light is from a near object?

Answer 56

short and fat

Question 57

what does the lens look like when light is from a distant object?

Answer 57

longer and thinner

Question 58

when light comes from a distant source, what happens to the rays and wavefronts?

Answer 58

they are parallel to each other

Question 59

draw a ray reflected off a mirror including the normal, incident ray, reflected ray and the wave fronts

Answer 59

look in book

Question 60

draw a virtual image

Answer 60

look in book

Question 61

when will the image be at the focal point?

Answer 61

when the light source is distant and wavefronts are parallel

Question 62

when won't the image be at the focal point?

Answer 62

if it's a close source then the image will be further away than the len's focal point

Question 63

what happens if the source is at the focal point?

Answer 63

there will be no curvature after and will produce parallel wavefronts and there would be a very distant image of the source which won't be seen

Question 64

power of lens (d), Dioptres=

Answer 64

1/f, the focal length has to be in metres as dioptres =m^-1

Question 65

curvature before the lens=

Answer 65

1/u where u is the object distance - from source to lens

Question 66

curvature after the lens=

Answer 66

1/v where v is the image distance

Question 67

1/v=

Answer 67

1/u + 1/f

Question 68

greater focal length means the lens has less

Answer 68

curvature

Question 69

how do you find the refractive index of a material that is not air/.

Answer 69

n1sinQ1=nsinqQ2

Question 70

snell's law:

Answer 70

n=sini/sinr

Question 71

refractive index=

Answer 71

speed in free space 3x 10^8m/s / speed in the medium | n= ci/cr

Question 72

define refraction

Answer 72

when light passes from air into a more dense medium it slows down. this causes the light to bend. the ratio of the speed of light in air to its speed in the medium is called the refractive index of the medium

Question 73

when a ray passes into a denser medium why does the ray bend towards the normal?

Answer 73

because one edge of the wave will slow down before the others which will keep travelling faster so will change direction

Question 74

define linear magnification

Answer 74

defined as the ratio of the image height to the object height m=v/u

Question 75

what does short-sighted mean and how is it corrected?

Answer 75

difficulty focusing on distant objects as they form an image before the retina as it's adding too much curvature. They need a diverging lens to correct it which removes curvature before the lens.

Question 76

what does long-sighted mean and how is it corrected?

Answer 76

difficulty focusing on near objects as they form an image after the retina as there's not enough curvature. Need a convex (converging) lens to focus the image on the retina

Question 77

what is the laplace rule?

Answer 77

method to finding edges: 1-multiply a pixel by 4 2- subtract the value of the pixels immediately above, below and to the left and right of it the result is that any pixel not on an edge goes black so you're left with just the edges