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MRCOG Part one > Biophysics > Flashcards

Biophysics Flashcards

1
Q

In the ECG what represents
I) Atiral repolarisation
II) Ventricular repolarisation

A

i) Not as during ventricular polarisation (QRS)

II) T wave

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2
Q

The large squares on an ECG (measuring 5mm) represent what time period

1mm wide small square

A
  1. 2seconds

0. 04seconds

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3
Q

Which leads are the inferior leads

A

III, aVF, II

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4
Q

Which leads are the anterior leads

A

V1-v4

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5
Q

Which leads are the lateral leads

A

aVL, 1, V5&V6

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6
Q

Which leads are the right atrium and left ventricle leads

A

aVr and V1

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7
Q

What is the normal QT interval

A

0.3-0.43 seconds (0.3-0.45 in women) - time for depolarisation and repolarisation of the ventricles

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8
Q

Sound waves above what hertz are termed ultrasound?

A

20kHz

Most medical ultrasound is the low MHz range.

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9
Q

In ultrasound how is the pressure wave created?

A

Piezoelectric crystal within a transducer - the piezoelectric crystal converts electrical energy into mechanical energy & vica versa (with high voltage current the crystal oscillates)

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10
Q

What is the pulse repetition frequency?

A

indicates the number of ultrasound pulses emitted by the transducer over a designated period of time.

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11
Q

What is the acoustic impedance

A

the tissue property that determines the degree of reflection

the greater the difference of acoustic impedance between 2 tissues the greater the degree of reflection.

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12
Q

What it the equation to calculate acoustic impedance

A

acoustic appendance = density x velocity of ultrasound

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13
Q

When does scatter occur?

A

When the ultrasound interacts with a structure with a similar dimensions (or smaller) then the length of the ultrasound wavelength e.g. blood cells and parenchyma

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14
Q

What direction is the ultrasound scatter in? How does it appear

A

360 degree

speckled appearance

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15
Q

What happens to the intensity of scatter as the frequency of ultrasound is increased

A

scatter increases very quickly putting an upper limit on ultrasound

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16
Q

What is absorption in ultrasound? For safety what is the upper limit of ultraounds

A

Conversion of mechanical every into heat or internal molecular energy producing heat.
Absorption increases with high frequencies - upper limit of 20MHz

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17
Q

Typically how many beams produce one image

A

200

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18
Q

What is the function of power in ultrasouns

A

The electric voltage used to generate the ultrasound pulses

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19
Q

What is the gain

A

The recieved signal is amplified to useful levels

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20
Q

What is attenuation?

How does this change with different frequencies and how does this impact clinical practice?

A

The amplitude and intensity of ultrasound waves decrease as they travel through tissue, a phenomenon known as attenuation. Given a fixed propagation distance, attenuation affects high frequency ultrasound waves to a greater degree than lower frequency waves. This dictates the use of lower frequency transducers for deeper areas of interest, albeit at the expense of resolution.

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21
Q

What is time gain compensation?

A

Amplify (increased gain) for deeper depths to adjust for attenuation

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22
Q

What are the limitations of real time B-mode scanning

A 
inadequate spatial resolution
inadequate penetration 
poor image quality 
low frame set
compromised field of view
low line density
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23
Q

What is spatial resolution?

A

Minimum distance between two reflectors or scattering surfaces to be able to distinguish between 2 signals

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24
Q

What are the two main components of spatial resolution and how are they impacted?

A

Axial resolution: determined by pulse length, shorter at high frequency (higher frequency is better axial resolution)
Lateral resolution: determined by beam width

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25
What affects penetration os USS
Absorbtion and scatter - both increased with high frequency. Lower frequency for deeper penetraion but at cost of resolutino n
26
What information can doppler ultrasound tell us?
The speed at which a target is moving direction of movemen Direction of movement Calculated using principles of doppler frequency shift
27
What is the colour coding system on dopplers
Red: towards transducer Blue: away from transducer Dark hues: low level velocity Light hues: high level velocity
28
What measurement is used to account for possibility of bio effects of from heating.
Thermal index | TI soft tissues/bone/cranium
29
The mechanical index is to minimised the risk of...?
Cavitation - gas filled cavities can oscilllate or collapse under pressure of USS
30
What is the wavelength of XRAY? | How does this compare to ultraviolet and gamma rays?
10-0.01nm | Longer than gamma, shorter than ultra violet
31
How are XRAY images produced?
Accelerating electrons made to collide with a metal target. Body creates a shadow, as XRAYs are attenuated by dense tissue, dense appears white.
32
What is real-time X-ray procedures?
Radioopaque contrast agents are used to highlight organs or vessels depending on where they are injected.
33
What is hysterosalpingography | When is it performed
To assess tubal patency | performed 1st 10 days of menstrual pregnancy to avoid exposure in early pregnancy
34
Benefits of HSG
minimally invasive, rare complications, quick, valuable information on uterine cavity and potency of tubes
35
Disadvantages HSG
Radiation exposure 1mSv (4 months background radiation) - small risk of cancer Risk flare of undiagnosed chronic pelvic pain. Exposure of unsespectant pregnancy
36
In electrosurgery why does low frequency current cause neuromuscular stimulation whilst high frequency does not?
At low frequency the cyclic polarisation/depolrisation allows transmembrane exchange of ions →neuromuscular stimulation High frequency so fast ions do not have time instead collision of intracellular ions/materials producing heat
37
Do grounded (meaning current returns back to the unit via earth) or isolated systems risk burning the patient if the electrode is faulty or poorly applied?
Grounded
38
Difference between monopolar and bipolar?
Monopolar: One electrode in operators hand and return electrode is attached to the patient - the return electrode is attached tot eh diathermy machine. Bipolar: Current flows between forceps - manymachines have a anticoagulation function where the machine sense optium degree of anticoagulation - no cutting function
39
What waveform is used for a cutting current?
Continous unmodulated with relatively low voltage, use tip of the electrode → creates high temp which vaproises the cells.
40
What waveform is used for coagulation?
High voltage applied intermittently, modulated to a duty cycle of about 6% → tissue can cool between heating bursts, no vaporisation
41
What is dessication?
Extreme drying, where by caogulation happens but at a high heat 70-100, requires contact with the active electrode & tissue, usually achieve on cutting mode 100% duty cycle - forms a coagulum
42
What is fulguration?
High powered current is used to produce sparks - not touching tissue, produces deeper coagulation than soft coagulation
43
What is direct coupling ?
Electrode is activated in close proximity or direct contact with another conductive instrument within the body
44
What is capacitive coupling?
Current between o conductors that are separated by an insulator
45
Safe electrosurgery practices
Check instruments insulation before surgery Lowest power and voltage for desired effect Active electrode only when needed Never active the electrode when close or in contact ieth metal or conductive object
46
In endoscopic surgery, what does laser stand for?
Light amplification by stimulated emission of radiation.
47
What does the laser device emit?
Light photos (electromagnetic radiation) - a process called stimulated emission to vaporise, dissect and coagulate
48
Why is laser associated with less post op pain? Other benefit
Laser beams seal nerve endings, also natural sterilisation as they evaporate bacteria, viruses and fungi
49
What are the main types of laser devices?
CO2 gas Argon ions Solid-state lasers
50
How do CO2 gas laser works | What is a good use for this in gynaecology
Absorbed to high degree by soft tissues containing water - enables precise cutting/dissection with miinmal lateral damage - Removal of endometriosis, especially near ureters
51
Disadvantage of CO2 laser
Expensive Difficult to clean Invisable to human eye - second laser needed Depth is limited, unsuitable for most laproscopic sugery
52
How are solid lasers commonly made?
'doping; a crystalstalline solid host with ions that provide the require energy state e.g. Nd:YAG → deeply penetrating The beam passes through KTP potassium titanic phosphate for more disired effect → penetrate 1-2mm, vaporise cut & coagulated
53
The amount of radiation used in radiotherapy is called? | How does work?
Gray (Gy) | Damages cellular DNA - caused by photons, electrons, proteins, neutrons or ions
54
When radiationg works by indirect actions what is happening
H20 is ionised generating free radical H+ and OH- that damage DNA
55
What is the effect of tissue hypoxia on the effects of radiation?
Increases resistance
56
Why are portions (positive charged particles) prefered to photons (soft X-RAY)
Release energy at point of impact, rapid fall off, adverse effects are minimised
57
What are the main tyoes of external radiotherapy
Linear accelerator - 2D beans from 1-4 directions Conformal radiotherapy CRT - 3D, multiple beams shaped to fit profile or target Intensity modulated radiation therapy (IMRT) - intensity of each beam can be modulated
58
Main limitations of external beam radiotherapy?
Unable to indenitfy microscopic disease difficulty immobilising person/tumour tumour shrinkage with Tx
59
What are the 2 main types of internal beam therapy?
Sealed source radiotherapy and non-sealed radiotherapy
60
What is the main type of sealed course radiotherapy, benefits?
Brachytherapy, sealed radioactive material is placed into or next to tumour. Works over short distances, passing through less health tissue, lower energy radiotherapy.
61
What is unsealed source radiotherapy - give an example
Radioisotope is delivered by injection e.g. Iodine 131 for thyroid Ca/thyrotoxicosis - new developments monoclonal antibody conjugated with radioisotope molecule to Tx non Hodgkin lymphoma.
62
Name some acute adverse effects of radiotherapy
Damage to epitheilal surfaces (skin, oral, bowel) Oedema & swelling of soft tissues Infertility - damage to radiation sensitive gonads Generalised fatigue (80%) N+V (60%) Diarrhoea (60%)
63
Long term effects
``` Fibrosis hair loss dryness as result of damage to salivary glands or vaginal dryness dmaage to cerival glands Fatigue + lethargy cancer secondary to irridation death ```
64
What is the typical magnetic field strength of an MRI scanner used routinely in UK hospitals?
The majority of MRI scanners in UK hospitals are 1.5 to 3.0T.
65
What frequency would typically be used for monopolar diathermy?
The frequency must be greater than 100 KHz. 500 KHz is typically used. Below this depolarisation (electric shock) can occur. Household frequency is around 60 KHz.
66
Early pregnancy USS: | What gestation can you see the gestational sac - how big is it
4 weeks + 3 Days
67
Early pregnancy USS: What gestation can you see the yolk sac how big is the gestational sac
5- 5+3 weeks | 10mm
68
Early pregnancy USS: What gestation can you see the embryonic pole how big is the gestational sac
5+3-6 weeks | 16mm
69
At what gestation does the fetal heart first become detectable on ultrasound?
6 weeks
70
The yolk sac reaches its maximum diameter at what week of gestation?
10 weeks
71
What are the definitions of oligohydraminos and polyhydramions on measurement of the AFI?
AFI involves measuring the depth of amniotic fluid pockets in all 4 quadrants. Oligohydramnios AFI< 5cm or deepest amniotic fluid pocket < 2cm Polyhydramnios AFI > 25cm or deepest amniotic fluid pocket > 8cm
72
How much radiation is in an chest XRAY compared to background radiation
A chest XRAY iss equivalent to 2.4 days natural background radiation.
73
What is the normal dose of external radiothe
Total dose varies between tumour type and stage but typical regimes involve 1.8-2.0 Gy fractions delivered over a number of weeks with total dose accumulating to reach around 50 Gy

MRCOG Part one (28 decks)

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