50-62;EM spectrum/CT scans/Laser/Holography

Question 1

EM spectrum

Answer 1

Radiowaves
Microwaves
Infrared
Visible
Ultraviolet
X-ray
Gamma

Transverse waves w/ characteristic freq/wavelengths/amplitudes = divided into several bands of increasing freq

Question 2

plane polarised light

Answer 2

all electric field vectors of light are in 1 plane in space

EG sunlight in unpolarised since waves oscillate in all directions to its propagation direction

Question 3

quantum theory of light

Answer 3

light exhibits particle properties in interactions on atomic scale

Question 4

how was quantum theory of light experimented

Answer 4

photoelectric effect = light falls on surface of metals = metal ions ejected from surface = energy from light given to e-s = enables ions to escape forces holding them to metal

time lag expected for metals to heat before escaping BUT e- ejected instantaneously

increased light intensity should increase no. of e-s ejected BUT max velocity stays the same

SO changing to blue light = increasing focal ability = increases max speed of ejected e-s

Question 5

photons

Answer 5

light thought to exist in form of quanta = photons that have definite amount of energy

visualised as tiny packets of energy travelling though space

photon of blue light has MORE energy than photon of red light

Question 6

de broglie equation shows

Answer 6

wavelength of particle w/ mass moving w/ velocity

Question 7

e- microscope

Answer 7

e-s used to form images similar to light microscope

e- gun produces high energy beam = magnetic fields focus e-s = e-s refracted, reflected and focused from specimen at certain angles = forms image on fluorescent screen

good due to increased resolution, observing small organisms and structures on cells that are too small for optical microscopes

Question 8

pauli exclusion principle

Answer 8

no 2 e-s can have the same set of quantum numbers, so no 2 e-s can be in the same state

Question 9

interaction of EM waves w/ matter

Answer 9

study of selective absorption of EM waves done by spectroscopy

EG. Emission spectrum of H2
H2 places in sealed glass container = subjected to high voltage = emits pink light along electrical discharge - emits blue light in other parts of container - emits series of bright lines of diff colours through diffraction

freq determined by quantised energy levels that H2 e- occupy

Question 10

when energy is given off in the form of photon how to determine freq of light given off

Answer 10

EG H2 e-

n=1 ground state
when excited = e- tend to jump up to higher energy level = then drop down to lower energy state till reaches ground state = gives off energy in form of photon = quantum of light

Question 11

spectral lines

Answer 11

spectral lines used to identify element emitting them, even when mixed w/ spectra from other elements

the freq of spectral lines for a given element are unique and precisely reproducible

Question 12

EG of absorption spectroscopy

Answer 12

• Fingerprints from emission spectrum used in spectrochemical analysis = check for presence of quantities of toxic elements (arsenic or lead)
• to identify chemical elements in starts via wavelength

Question 13

clinical applications of EM waves

Answer 13

EM waves have diff physiological effects
= body transparent to RW but opaque as freq increases to visible ligh then transparent again to XR

diff caused by diff quantum energies (E=hf) that produce diff types of physical interactions and how strongly radiation is absorbed

Question 14

absorbance of diff EM waves

Answer 14

tissue has few ways to absorb low RW so they pass thru

MW region, the E of photons large enough to cause molecular rotation and torsion = heat

IR = molecular vibration = periodic stretching/torsion on internal molecular bonds = absorbed STRONGLY

Vis/UV = large quantum energy to excite e- to higher energy state = absorbed STRONGLY by don’t penetrate skin

UV photon energy so dense that UV is absorbed by v thin outside layer of skin

Question 15

describe medical applications of the lower freq of EM spectrum

Answer 15

500kHz-2500MHz
lower = RW
upper = MW

= penetrates body = raises temp throughout portion of body exposed to radiation = heat therapy = Diathermy

Question 16

diathermy

Answer 16

therapeutic effectiveness of R/MW by penetration and raising temp of body

relief of muscular pain, inflammation of skeleton and warming deep tissues

NO chem changes in bodys, XR could produce internal burns w/ XS exposure

Question 17

Infrared radiation

Answer 17

infrared = broad range of freq
upper = communications/near infrared range

lower= far infrared range = separation from vis light region

hot object gives off IR

Question 18

near infrared range

Answer 18

7500 - 30000 A

most medical appl use this

originated from accelerated charged particles near surface of object = emits radiation = thermally agitated charges produce continuous spectrum of radiation

Question 19

wein’s displacement law

Answer 19

for black- body curve! for diff temp peaks at diff wavelengths inversely proportional to T

increasing T at peak of distribution shifts to a shorter wavelength

higher temp = object has more U to be released via EM waves = brightness increases

Question 20

IR use in medicine

Answer 20

Infrared lamps used for heat therapy

IR = molecules vibrate = radiated energy is absorbed v quickly

good cos = doesn’t penetrate v far into body, penetrates more deeply than visible light

= used in infrared photography = veins/pattern of healing of scabs/eye diagnostic

Question 21

thermograph

Answer 21

sensitive Infrared detector = scans over successive small strips of area to convert infrared intensity into electrical signal to be displayes

examine burns/frostbite for analysis of type of skin graft to be used

Question 22

UV

Answer 22

ranges upwards in freq/QE from high freq end of VL - low freq end of XR

absorbed strongly by matter

doesn’t penetrate into tissues deeper than 1mm = used for skin treatments EG psoriases /acne

Question 23

high energy UV

Answer 23

excites to higher levels

ejects e- from atoms to from ions

dissociate molecules into constituent atoms or produce other chem changes

Can cause ionisation = skin cancer/sunburn

kills fungi/bacteria on skin/instrument (sterilisation)

Question 24

X rays

Answer 24

EM waves w/ wavelength 100 - 0.1 Angstrom units

Question 25

x-ray tube

Answer 25

= accelerates e-s thru high voltages 20-200kV near metal atom = high speed e- is strongly repelled = decelerated by e- cloud of atom = loses Ek = most E goes into heating metal target, 1% given off as x-rays w/ wide spread of wavelengths

2 distinct patterns:

• continuous broad spectrum = depends on V applied to tube
• series of sharp, intense lines = depends on nature of target material = accelerating V exceeds certain threshold range

Question 26

Bremsstrahlung

Answer 26

continuous radiation also called braking radiation

= EM radiation produced by deceleration of charged e- when deflected by another charged particle = produces short wavelength radiation

no particular wavelength since many e-s aren’t stopped in a single collision = produces production of continuous spectrum

Question 27

what is x-ray attenuation

Answer 27

QE of XR photon so great = not strongly absorbed by ordinary tissue

atoms w/ low probability can absorb XR photon and be disrupted = ejects an e- in photoelectric process = this e- has enough energy to ionise other atoms

Question 28

EGs of XR attenuation

Answer 28

photoelectric effect, compton scatter and pair production

Question 29

why is XR attenuation observed

Answer 29

Ionising capability of XR is what makes it diff to other lower freq EM waves

disruptive ionisation events can cause biological damage

Soft tissues transparent to XR than bony structures = used to form shadow pattern
- To increase contrast = introduce air/gas to fluid cavity so less XR is absorbed into air than into tissue = provides contrast

=OR we can add barium sulfate to increase contrast

Question 30

how are we protected from XR

Answer 30

using heavy elements like lead as shield = its energy levels in inner shells have separations comparable to XR photon energies = readily absorb XR

Question 31

angiography

Answer 31

process of injecting dye heavy element that absorbs XR into blood vessel = enhances XR contrast to tissue backgrounds

Question 32

digital subtraction angiography

Answer 32

digitized process
XR taken before dye injected into blood vessel - repeated w/ dye = 1st image subteacted from 2nd = leaves only changed part of image

Question 33

Computed Tomography scan/ CT scan

Answer 33

Thin beam of XR passed thru section of tissue no. of times from diff direction at common crossing point = results in detailed evaluation of XR absorption at that point

w/ multiple detectors/modern scanners = collect info about 1000s of points w/i sec of exposure time = constructs 2D view of XR absorption of section of body

ADV

• presents cross sectional image of tomograph = accurate relative location of absorbers
• using computer = eliminate distortion of image, can display on screen
• detects changes in XR absorption 100 x smaller than on conventional XR photographs

Question 34

LASER and properties

Answer 34

Light Amplification by Stimulated Emission of Radiation

properties =
collimation (confining of XR to given area) of light in v narrow beam = focused to microscopic point = yields enormous energy density in area of focus = absorption/stimulated emission

Question 35

spontaneous and stimulated emission of radiation

Answer 35

emission of light by a material associated w/ transition of atomic e- from high energy state to lower level = leads to spontaneous emission of photon of energy E-=hf=E2-E1

If photon of Energy E interacts w/ atom whose e- is in E1(lower level) then may be absorbed to raise e- to energy E2

if photon interacts w/ atom when e- is in E2 = may cause it to make downward transition sooner than it would spontaneously = stimulated emission

=== so large no. of photon of this E are incident upon the material = both absorption(most freq) and stimulated emission occurs

Question 36

population inversion

Answer 36

process of achieving greater population of higher energy state compared to lower energy state

used for light amplification and laser operation

we need to use 3 energy levels, using only 2 atomic energy levels = photons sent into excite e-s to higher energy level can equally cause transition out of upper level

the excited states of atoms have v short lifetimes 10^-8s

Question 37

metastable state

Answer 37

Usually E2

atomic excited states have longer lifetimes to several mins before the e- makes downwards transition

1. e-s pumped to higher energy level = E3 supplies energy in form of light electric discharge/high energy molecular collision
2. elevated e-s drop quickly to E2/MS by spontaneous emission/loss of energy thru collisions
3. large population inversion obtained = e- remains in E2 for long time = stimulates trapped e- to emit photon

Question 38

structure and operational principle of lasers

Answer 38

precisely aligned parallel mirrors placed at ends of laser medium several times - 1 mirror totally reflective, other partially reflective to let some light out upon each reflection

parallel laser beam rays of 1 wavelength focused to 1 extremely tiny spot

= amplifies light passing thru = improves efficiency of laser

Question 39

medical applications of laser

Answer 39

photocoagulation of retina = laser emitted in short bursts = haemorrhages treated by focusing intense light thru lens of eye

bean can be focused on fovea = smaller area for photocoagulation

treat retinal tears/detachments

removal of tattoos or birthmarks/bloodless surgery/cauterising effect due to enormous energy density = precise focusing of laser beam

Question 40

holography

Answer 40

photographic process, film is exposed to reflected light from object instead of FORMING focused image on film

1. Part of laser light reflected from mirror
2. directed towards film
   3.mixes w/ reflected light from object
3. film records interference btw 2 beams of light
   = photographic pattern of irregular fringes
   = wavefront reconstructed by passing laser light thru film = 3D image perceived in space behind film

Question 41

can hologram be made w/ ordinary light

Answer 41

no, ordinary light is incoherent and laser light must be coherent

Question 42

use of holography

Answer 42

provides 3D recording of microscopic events

improved resolution than standard microscope