Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

*FRCR1 Physics > Leicester Course > Flashcards

Leicester Course Flashcards

1
Q

1Proton mass = 1.67 × 10-27 kilograms
= 5000 x electron mass

Electron mass = 9.1 × 10-31 kilograms

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Mass number = equivalent term to nucleon number

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Pair production = higher energies than diagnostic xrays

Diagnostic range = 50 - 100 kEv

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Compton scatter
E>50kEV
<10MeV

A

Varies with density BUT INDEPENDANT OF ATOMIC NUMBER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Direction of compton scatter is more BACKWARDS than FORWARDS.

Higher energies = more back scattering / larger angles

A

So UNDERCOUCH will mean BACKSCATTER will go towards your feet rather than your body.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Tungsten Z = 74

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Anode angle = 7 - 18 degrees

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Increasing focal spot = reduces resolution.

A

Larger anode angle = less anode heel effect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Auger electrons = electron ejection after a lower shell vacancy is filled = no radiation

A

More likely to occur with lower atomic numbers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Average energy = 1/3 to 1/2 of MAX value

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

mA = photon number = does not change relative attenuation or energy levels = so changes quantity NOT quality

A

kVp = increases quantity and quality (area under graph and shifts spectrum to the right)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

CONSTANT potential = higher INTENSITY and AVERAGE energy than full wave (on/off)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Added filtration = preferential absorption of lower energies

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

LEGAL REQUIREMENT for filtration

Mammoraphy <30kev 0.5 mm Aluminium
XRays <=70vV 1.5mm
Xrays >70kV = 2.5 mm

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Bit Depth = no of discrete image levels determined by bits

A

Higher bit depth = less digitation error but more storage required.

Bit depth = 8 = 2^8 shades of grey
So better CONTRAST resolution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Quantum noise = stochastic nature of photons interacting with matter.

A

Other noise = electronic, structural and digitisation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Digital image processing

Point operations = adjusting each pixel e.g. window or level

Segmentation = nulling a range of values

A

Histogram equalisation = histogram to bin up the distribution = you increase the spread of a concentrated distribution to tease out more detail.

Mean filter = your image can get smaller if you don’t pad the edges

Edge enhancement = smooth - subtract from original = Edges, then add to original = smooth and edge enhanced.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Median filters = remove defective pixels or lines in the image

A

Median of adjacent pixel elements

Median NOT swayed by extreme values

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Temporal Averaging
= Frame average in fluoroscopy
= average over consecutive frames - with MOST emphasis on the most recent frames.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Spatial Frequency Filtering

Line pairs per mm = SPATIAL FREQUENCY

High pass filter:
removes low spatial frequencies
Edge enhancement
BUT Higher noise - reduces SNR

A

Low Pass:
Removes higher spatial frequencies
Allows low filter = large objects
Gives SMOOTHING.
Increases SNR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Advanced techniques:

  1. Image fusion
  2. Dual Energy Subtraction
  3. Computer aided diagnoses
  4. Tomosynthesis
A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

CR’s = Indirect conversion using STORAGE PHOSPHORS (PSPs)

Luminescence:
Emission of light as a a result of excitation of atoms by energy other than heat

A

Phosphorescence = DELAYED READOUT with RED LASER STIMULATION (out of electron trap)

  • scatter susceptibility

(NOT Fluorescence = immediate release)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Layers of PSPs

Primary material used as a storage phosphor is

Barium Fluorobromide doped with Europium (BaFBr:Eu2+)

A

Protective surface
Light reflective layer
Conductive layer = protects against static build up, static collection and mechanical damage.
Colour layer
Support layer
Backing layer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

CR artifacts

  1. Fogging from background scatter
  2. Back to front or bent plate
  3. GHOSTING of previous images if not bleached with white light
A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

DR - Indirect detectors

= CsI Needle Phosphors

Proportion of Fill factor - light sensitive area / element area

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

DR - direct

= Amorphous Selenium photoconductor, Z=34 -e’s swept out by electric field

A

Special use case:
LOW kV for low Z

LOW dose
GOOD spatial resolution

4x faster

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Imaging systems are inherently low pass filters

Take an image of a line
Perform a Fourier transform

MTF = 1 = Perfect

A

Direct = best

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Noise Power Spectrum = Amplitude of different frequencies = monitor for system degradation.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Low Energies = Kerma and Absorbed dose are similar

Radiotherapy = higher energies = need to correct for Kerma and Absorbed dose. (MV not kV so energy can get out)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

DAP = measured using transparent flat bed ion chamber with xray collimator

Gy cm^2

A

INDEPENDANT OF DISTANCE FROM source.

As dose falls away with distance but area goes up!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

ESD = absorbed dose at skin

  • includes backscatter, backscatter factor (BSF) 1.2 - 1.4
A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

CT - pencil ionisation chamber

x length
x slice thickness

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Stochastic - Linear no threshold

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Threshold for cataract = 0.5 Sv

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Hereditable disease risk is 1 in 200 000 per mGy

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

IRR
- STAFF and PUBLIC
- Reg by HSE
- Risk Assessment for any new or change to working with radiation.
- Local Rules
- ALARP
- Information, instruction and training

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

RPS
- MAIN JOB: ENSURES LOCAL RULES ARE FOLLOWED.
- Personal monitoring
- Changes to work or equipment that may affect safety notified to RPA

A

Run new methods by RPS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Permanent signs = permanent controlled area

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

RPA
- controlled and supervised areas
- Examination of plans for installers
- Regular checking of engineer controls
- Calibration of equipment

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

Leakage MUST BE
<1mGy PER HOUR AT ONE METRE

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

Local Rules
- Identification and description of areas
- Names of RPS, RPA and head of department
- Work instruction summary
- Copy of contingent arrangements
- Dose investigation levels

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Controlled:
Under 6mSv a year
3/10 18+ annual dose limit

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

Carers and comforters = willingly, knowingly and NOT as part of their job.

SO NO DOSE LIMIT.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

Designating classified workers:

Subject to paragraph (2), the employer must designate as classified persons those of its employees who are likely to receive

  • an effective dose greater than 6 mSv per year
  • or an equivalent dose greater than 15 mSv per year for the lens of the eye
  • or greater than 150 mSv per year for the skin or the extremities and must immediately inform those employees that they have been so designated.

https://www.legislation.gov.uk/uksi/2017/1075/part/5#:~:text=%E2%80%94(1)%20Subject%20to%20paragraph,skin%20or%20the%20extremities%20and

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

Dose limits for age groups:

https://www.legislation.gov.uk/uksi/2017/1075/schedule/3

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

IRMER 2017

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q
  • Informing patient and representative, practitioner and referral of any clinically significant raiation incident
  • Dose constraints to comforters and carers
  • Protocols for every standard radiological practice
A

2024 IRMER AMENDMENTS
- Making and Cancelling referrals
- Following up on actions related to clinical audit.
- Co-operation of employers involved in different parts of the system - all different imaging and reporting parties are aware of their responsibilities.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

IRMER PROCEDURES

  • ID referrer, practitioner, operator
  • ID pregnancy
  • Quality Assurance programmes (audit, incident)
  • Patient dose assessment and recording
  • Giving info and written instructions
A
  • Carrying out and recording exposure evaluations
  • DRLs = diagnostic reference levels
  • Ensuring accidental exposures conform to ALARP (equipment maintenance, dealing with incidents)
  • Carrying out non-medial imaging
  • Research dose constraints
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

EPR - Regulated by Environmental Agency
- Dose calculation to sewers, sewage workers, farming family

A
50
Q

CDG - Carriage of dangerous goods
Regulated by ONR - Office of nuclear regulation

A
51
Q

Flat plane image intensifiers
Evacuated electron-optical device- Glass or ceramic envelope surrounding metal housing

  • NON- MAGNETIC
  • PREVENTS STRAY light

LARGE FIELD - typical input 35 - 40 cm diameter.

A

3 Main Components:

  1. Input screen: window, phosphor and photocathode
  2. Electron optics - focus and direct electron beam to output screen
  3. Output screen - Electrons onto photocathode, with conversion into electrical signal sent to monitor.
52
Q

Input Window:
- Must withstand vacuum
- Thin enough to keep dose low
- Low Z material - aluminium or Titanium
- Titanium foil allow 90% transmission of incident x-ray photons.

A

Input Phosphor:
- Thin fluorescent material on a thin metal layer as primary XR detector
- SODIUM ACTIVATED CAESIUM IODIDE - thin crystals MINIMISE SPREAD.

About 200-400 micrometres
Average diameter < 5 micrometres.

Fractional absorption is 0.5-0.8
K edge of Cs 36keV and I 33eV

Each XR photon - yields 3000 light photons

53
Q

Photocathode layer

Converts light photos emitted by input phosphors into electrons
A layer of Caesium Antimonide well matched to blue light emitted by the input phosphor.

A

Output fluorescent screen
- Concentrates electron pattern over a smaller area from the photocathode layer
- Electrons accelerated 25-35 keV
- Voltage is applied to CYLINDRICAL ANODE structure to the II output

Curvature of input screen:
- means all electrons are the same path

54
Q

Additional focusing electrodes 0 metal rings with negative charge
- Act as an ELECTRON LENS (hence electron optics)
- Can alter the focussing to the central region - ABC = automatic brightness control

A
55
Q

Output phosphor Window:
- Bombarded by these high energy electrons- Very thin fine grain phosphor
- Electrons have a limited range.

Can capture high quality static images under ABC control (fluorourography).

23-35mm in diameter.

A

ACCELERATION and MINIMISATION results in AMPLIFICATION of IMAGE BRIGHTNESS

Thin 0.5 micrometres from prevents back scatter of light into image intensifier.

56
Q

CCD Cameras
- TV camera produces an analogue converter that needs to be converted to digital

  • CCD’s have use amorphous silicon *sane as (Digital Radiography Direct conversion in mammography) - divided into pixels.
  • Charge readout row-by-row sufficient for 30fps
  • Avoids stroboscopic effects.
A
57
Q

Image Intensifier GAIN:
- Ratio of brightness of input and output phosphors
- Generally 1 light photo from input = 1 electron from photocathode
- Image flux gain

Mininification gain = ration of the areas of the two screens

A

Conversion factor deteriorates with time

YOU DO NOT GET THIS WITH FLAT PLANE DETECTORS.

58
Q

Image Intensifier Magnification - change voltages of focusing electrons to move electron cross over point nearer to the input

  • Results in more limited of the area of the input projected on the screen
  • BUT AT EXPENSIVE OF BRIGHTNESS
  • So…DOSE MUST BE INCREASED via ABC .
A

ABC
- feedback intensity of the central portion of output
- Increases kVp and.or mA

  • Paediatrics - use a LOW kV
  • If using Iodine - may hold kV 60 - 65 kV. Limited to increase mA up to a point.
59
Q

AGC - Automatic grain control

DOES NOT FEEDBACK TO ADJUST EXPOSURE FACTORS
- At expense of HIGH NOISE

A
60
Q

DOSE RATES

  • lower input dose to intensifier = HIGHER NOISE in the image
  • ## brightness reduces in proportion to MAGNIFICATION
A

INTERNATIONAL ABSOLUTE LIMIT OF

100 MILLIGRAYS PER MINUTE
UK REMEDIAL LEVEL set at 50mGy/min

(see rest of slide)

61
Q

Modern Fluro

Cardiac systems - Cu filters to harden beam
- same input dose to detector
- less dose to patient
- reduced contrast as higher AVERAGE kV

A

Dose Settings
- vary with manufacturer and model or software!

Low dose
- more filtration, high kV, less pulses/sec

High contrast
- less filtration, lower kV, higher pulses/sec

62
Q

Flat Panel Fluoroscopy

  • Phosphor coupled to TFT - Indirect conversion
  • a-Se/TFT array - Direction conversion flat panels

High quality dynamic and static image
No distortions like II
NO GENUINE MAGNIFICATION - Resolution fixed by pixel pitch

A

Use Automatic Exposure Control

  • set level exposure required for adequate image.
  • doses generally lower (not always depending on operator training) on modern flat panel detectors compare to IIs.
63
Q

DSA and NOISE

Quantum noise in subtraction image is GREATER than noise in either the mask or contrasts images

Signals subtract but noises reinforces, thus reducing SNR

A

Noise can be reduced by obtaining and storing sequence of images

Random noise tends to average out
Loose temporal resolution

64
Q

Mammography

  • Microcalcifications 100 micrometres in size
  • High inherent contrast

Large areas of lower contrast

Focal Spot Size 0.3 - 0.4,mm
(smaller than normal focal spot about 0.8mm)

Total filtration > 0.3 mmAl

mA 100 broad and 30 fine.

Target angle is 22 degrees
Nipple region 60% of maximum intensity

A

Photoelectric effect
Ideally want monoenergetic 18-20keV.

Mo or Rh targets

K edges:
Mo - 29
Rh - 23.2

Or Tungsten - BUT WITH FILTER

Mo/Mo - Characteristics XRs 17-19keVs.

1 - 6.5mGy with limit of45 mm breast thickness

65
Q

Typical line pair resolutions

Digital 7 lp/mm
CR 7 lp/mm
Film Screen 15-20 lp/mm
CT 10 lp/cm

A

So CT HAS A SIGNIFICANTLY POOR LINE PAIR RESOLUTION.

66
Q

Assume speed of sound in soft tissue 1540 m/s

A

Assume speed of sound in soft tissue 3500 m/s

67
Q

Frame rate is ~ 20fps

Human eye can resolve ~ 40ms

A
68
Q

Ultrasound range

A

> 20kHz

69
Q

Speckle = scattered echoes that echotexture.

A

Rayleigh scatters occur if wavelenth&raquo_space;d
Backscatter power proportional to
diameter, d^6 x frequency, f^4

Isotropic spread (all directions).

70
Q

Anisotropy = non-uniformity in density and stiffness - different reflective behaviours depending on what direction the sound is coming from.

A
71
Q

reverberation - between two linear surfaces

A

Edge refraction = edge shadowing artefact

72
Q

Strong or weaker attenuators compared to average of tissue = acoustic shadowing or enhancement.

A
73
Q

if aperture < wavelength = divergent wave = diffraction

A

If aperture > wavelength = waves parallel to aperture.

74
Q

Fresnel diffraction in NEAR FIELD

A

Fraunhofer diffraction in FAIR FIELD.

75
Q

Average size of microbubbles 2 - 6 micrometres
Behave as RAYLEIGH SCATTERERS

A

Linear backscatter - fundamental imaging

~100kPa
Non-linear backscatter - Harmonic & Pulse Inversion

~1 MPa
Transient scattering - Triggered imaging (fill/refill dynamics)

76
Q

Rarefraction = microbubble cavitation = implosion

A
77
Q

Contrast harmonic imaging

A

Soft tissue harmonic imaging

78
Q

Layers:
Frequency decided by circuit
Backing layer - DAMPING
Piezoelectric signal set at = λ / 2
Matching layer set at = λ /4 - can have multiple
Lens

A
79
Q

PZT is 20 x Z of soft tissue = 80% reflection at skin without gel.

A
80
Q

Dampening = lowers quality factor, increases BW, but allows for shorter pulse repetition times.

A
81
Q

Linear stepped array width = 1.3 λ
Array height = 30 λ

A
82
Q

Electronic steering can steer the beam +/- 45 degrees.

A
83
Q

Phased array = elements are packed in to almost a point source are also thinner = 0.5 λ

A
84
Q

Harmonic imaging - using the central intense part of the beam

  • loose side lobes
  • better resolution
A

Use a broad transducer, filter out the original / fundamental frequency and just keep the higher degree harmonic.

85
Q

Spatial compounding: Extension of a steered-linear technique

  • gets rid of steered beam artefact
  • reduces speckle
A
86
Q

Acoustic Power - measured using a FORCE BALANCE device.

A
87
Q

Spatial Peak Intensity = max

A

Spatial average intensity

87
Q

Thermal effects

Organogenesis up to 8/40
Mineralisation of developing bones
Spinal Cord
Eyes

A
88
Q

WFUMB 1998 - max temp rise of no more than 1.5 degrees C above 37 may be used without reservation

A

Diagnostic exposure that elevates embryonic tissue >4 degrees above 37 i,e, >41 degrees

89
Q

No requirement to display when
TI < 0.4
MI <0.4

A
89
Q

1992 AIUM and the NEMA define the published “Output Display Standard” (ODS)

A
90
Q

TI = Thermal index

A
91
Q

MI <0.3 No restriction
MI > 0.3 potential damage to neonatal lung and intestine

Mi > 0.7

A
92
Q

US Quality Assurance

A
93
Q

Pulse wave is used to sample in discreet areas
- timing allows you to set a received gate
- but susceptible to aliasing

A

Spectral broadening - range of velocities - slower along the wall, faster in the centre.

Established by Fast Fourier Transform of the received signal to establish the spread of the involved frequencies.

94
Q

Larger angles of insonation will result in larger degree of spectral broadening.

A

Hence the inaccuracy when you reach angles above 60 degrees.

95
Q

Colour doppler

Multiple echoes are sent out - autocorrelation technique
The relative phase shift is used to determine the relative velocities

A
95
Q

I T = 10,000 Gaus
1 Gauss = 1mT

Surface of the earth 0.5 Gauss

A

Limit for general safe access = 0.5 Gauss / 0.5 mT
PART OF CONTROLLED AREA

Typical clinical system 1.5 - 3T

96
Q

Gyromagnetic ratio of hydrogen

A

42.5 MHz per tesla

97
Q

B1 in the x-y plane are 90 degrees and in the order of a few micro Tesla.

A
98
Q

The smaller the surface receiver coil the less noise it picks up = BETTER SNR

A
99
Q

Shimming coils to even out B0 nonuniformity

A
100
Q

Liquids =higher frequency of molecular / Brownian motion.

As tissues become MORE solid, frequency of movement is CLOSER to the LARMOUR frequency. - So more RESONANT transfer. T1 relaxation is FASTER.

As you become more solid beyond this point difference in movement frequency is a lot slower the Lamour frequency, T1 increases again due to LESS resonant transfer.

T1 WILL ALWAYS TAKE LONGER THAN T2

A

The more SOLID, the SHORTER the T2.

101
Q

As you INCREASE the magnetic field

  • T1 always increases
  • T2 always decreases
A
102
Q

Contrast agents

SHORTEN T1

SHORTEN T2

SHORTEN T2*

A

Metals:
Gadolinium
Iron - particularly affects T2*

103
Q

HASTE - all echoes in one RF 90, heavily T2 weighted

A

Radient echo version = ECHO PLANER IMAGING

104
Q

Inversion recovery sequencies are independent of magnetic field inhomogeneities / T2*

A
105
Q

Spin echo - flow void - black blood

A

Gradient echo

Large flip angle α to T1-weight and suppress background

Inflow of blood is not T1 weighted - BRIGHT BLOOD

106
Q

Integration of volume flow rate in order to measure cardiac output.

A
107
Q

Thinner slices = more noise = lower SNR

A
108
Q

IF you try to fill few phase encoding lines and move further out = FOV SMALLER = WRAP AROUND ARTEFACT

A
109
Q

A single corrupt point in k space can corrupt the whole image. Depending on where, you will get lines across the image.

A

Movement gives you a REPLICATION ARTIFACT

110
Q

Plants / implants causing distortion - spin echo is much more robust.

A
110
Q

Gibbs ring or truncation artefact. You are not collecting an infinite amount of data.

A

Causes ripples along the cord when there is a sharp change between the cord and the CSF.

111
Q

IF FOV too big for scanner.
Gradients tail off at either tend i.e. are no longer linear.

So FOV is compressed at either end.

A
112
Q

Chemical shift artefact
- Higher field strengths in the frequency encoding area minimise the relative differences in frequency.

A
113
Q

MRI resolution = 1mm normal scan
2mm fast scan
0.7mm REALLY LONG SCAN

A
114
Q

Easy to remove wrap around artefact in the frequency encoding direction by over sampling.

A

Phase Encoding for minimising artefact.

115
Q

Susceptibility weighted imaging - GE with long TE to allow for inhomogeneity to become incoherent.

A
116
Q

SAFETY LIMIT of 0.5 mT for general public.

Bo field - missile effect, magnetophspheses

A

MR unsafe
MR Safe - no scanning restrictions
MR Conditional = safe to use provided certain conditions determined during safety testing

117
Q

Gradient field
Gradient SWITCHING is what counts
Peripheral nerve stimulation
Pain
Causes limb twitching
Cardiac nerve stimulation at very high switching rates

A

Other factors to be aware of

What to do in case of pregnancy - not in first trimester
Magnet quench
Pacemakers
Implants
Acoustic noise
NSF

*FRCR1 Physics (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions