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MRCOG part 1 > Biophysics > Flashcards

Biophysics Flashcards

1
Q

What size does the gestational sac need to be to see the embryonic pole

When is the yolk sac visible

A

Typically when the GS is 16mm.

However, miscarriage not diagnosed until GS >25mm and fetal pole not seen

Yolk sac typically visible when GS 10mm

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2
Q

What are the following units measuring:

Grey
Sievert
Becquerel
Hertz
Tesla
Weber

A

Grey - unit of absorbed dose
Sievert - unit of equivalent dose
Becquerel - unit of radioactive decay
Hertz - frequency
Tesla - unit of magnetic field strength
Weber - magnetic flux

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3
Q

What is an XRAY?

How much radiation does a CXR give you?

How much radiation does an abdo CT give you?

A

Ionising Electromagnetic radiation

Frequency of 30 petahertz to 30 exahertz

CXR - 2.4 days natural background radiation

CT AP - 2.7 years

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4
Q

RADIOTHERAPY

How does radiotherapy work?

What are the most common side effects?

What are radiosensitisers?

What are radioprotectors?

What is radiotherapy dosing in?

What is the typical dose of RT?

A

Kills cells.
There are multiple beams to direct most of the radiation to the unheathy tissue rather than damaging healthy tissue.

Brachytherapy - localised RT

Acute side effects:
- Fatigue in 80%
- N&V 60%
- In pelvic - diarrhoea in 70%
- Moist skin desquamation

Chronic side effects:
- Fatigue in 30%
- Lymphoedema
- Fibrosis
- Myelodisplastic syndroes - about 10% of MDS is due to RT/chemo

Radiosensitisers - enhance effect of RT: PHOB
- Pramidines (halogenated)
- Hypoxic cell sensitisers
- Oxygen
- Bioreactive agents

Radioprotectors - not used much because risk of enhancing cancers. e.g. a Radioprotective would be a HYPOXIC environment because oxygen is radiosensitive

RT dosing is in Gray

Typical dose of RT is 1.8-2 Gy fractions over a number of weeks to delivery approx 50 Gy

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5
Q

With MRI, what is the SI unit measurement of:

  • Magnetic field strength
  • Magnetic flux
A

MFS - Tesla

MF - Weber

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6
Q

MRI

How does it work?

What is the unit of measurement?

What is T1/T2 and how does it appear on an MRI scan

How much does an MRI magnet generate a field of?

A

NON-IONISING RADIATION

A magnetic field is applied to tissue and this causes the protons to align. Radiofrequency waves are then sent throughout a tissue which causes the protons to spin. When radiofrequency waves are stopped they slow down and stop spinning. This happens at different rates depending on the tissue they are within. As they relax they release radiowaves of different frequencies. This is picked up by the MRI scanner.

Unit of magnetic field strength = Tesla
Unit of Magnetic flux = Weber

T1 = dark image
T2 = light image

MRI magnets generate a field of 0.5-3.0 tesla

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7
Q

What does the P, QRS, T and U represent in an ECG

A

P wave = Atrial depolarisation

QRS complex = Ventricular depolarisation

T wave = Ventricular repolarisation

U wave = repolarisation of the interventricular septum

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8
Q

What are the typical ECG features of:

Hyperkalaemia

Hypokalaemia

Hypercalcaemia

Hypocalcaemia

A

Hyperkalaemia:
- TTT waves
- Wide QRS
- Prolonged PR
- Flat P wave

Hypokalaemia
- Flat T waves
- U waves
- ST depression

Hypercalcaemia
- Short QT

Hypocalcaemia
- Long QT

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9
Q

What type of lasers are used in:

  • precancerous genital lesions
  • TTTS
A

Precancerous genital lesions/VIN - CO2 lasers

TTTS - Diode or ND:YAG

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10
Q

When does the yolk sac reach maximum diameter?

What is the maximum diameter? What if it gets bigger than this?

Can you see it on the 20 week scan?

A

Maximum diameter at 10 weeks

6mm

If >6mm ???failed pregnancy

Usually gone by 20 weeks scan

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11
Q

What is the maximum diameter of a follicle before it ovulates

A

25mm

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12
Q

What is the gestation when heart becomes visible?

A

6 weeks

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13
Q

Which of the following imaging methods are ionising:

Ultrasound
PET
CT
MRI
Xray
Laser
Iodine 131

A

Xray
CT
PET
Iodine 131

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14
Q

How does Ultrasound work

A

Sending high freuqency sound waves through tissue.

These waves are created by putting a voltage across a piezoelectric crystal.

The transducer directs the waves produced.

Different tissue reflect varying amounts of the waves based on density (or acoustic impedence).

Doppler uses direction to produce colour. The coloured image is called a duplex image.

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15
Q

How does CT work?

Contrast the radiation of an abdo CT with a CXR

A

Significant ionisation. Uses multiple XRAYS to create 3D image

Abdo CT = 400 CXRs

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16
Q

How does PET scanning work?

A

Uses a radioactive tracer, usually FDG which gets taken up by areas of high metabolism in the body - e.g. cancer. The tracer then emits gamma rays which are picked up by the PET scanner

FDG is an analogue of glucose

17
Q

DIATHERMY

What is monopolar vs bipolar diathermy?

What can cause tissue burns?

What is the frequency used for diathermy?

A

Monopolar - current passed between two electrodes. One is the diathermy tip and the other is the plate on the patient (on the leg)
- COAG
- CUT

Bipolar - both electrodes are help by surgeon. E.g. forceps
- ONLY COAG

Tissue burns can happen if the plant is not applied correctly. It means that the surface area the current is spread over is not as big so can be condensed and cause tissue burns.

The frequency has to be over 100 kHz because otherwise cell depolarisation can occur and cause electric shock. Surgery typically uses 500 kHz

18
Q

How is hysterosalpingography performed?

Who is it an appropriate test for?

What about for hx of PID?

Who is it contraindicated in?

When should it be performed?

What is the main alternative to HSO?

A

Uses Xrays with contrast. Can see moving image to assess patency of the tubes. Iodine based contrast

It is an appropriate test for people with no suggestion of tubal issue.

For people with hx suggestive of tubal issue - laparoscopy with dye testing is the test of choice

Contraindiacations:
- Pregnancy
- Active pelvic infection

Should be performed in follicular phase. After menses but before ovulation

The main alternative if a HYCOSY
- Uses ultrasound
- Uses iodine based contrast or saline based

19
Q

What gestation does the gestational sac become visible on TVS?

How about yolk sac?

How about the embryonic pole?

How about heart beat?

A

4+3 weeks

5 weeks

5+3 weeks

6 weeks

20
Q

Desrcibe the 3 modes of USS and their advantages/disadvantages

A

Power
- No information related to velocity or direction
- Detects flow in smaller vessels
- Better penetration
- Not angle dependant

Colour and Pulse
- Gives info about velocity and direction
- Worse penetration
- Angle dependant

21
Q

Short PR and delta waves?

A

WPW

22
Q

How do DEXA scans work?

A

TWO beams - hence the dual, with different freuqncies are directed at the same bone area. The higher the density, the more of the beam gets absorbed. The rest of the beam is picked up on a plate behind. The BMD is calculated minusing the soft tissue density

23
Q

What is the doppler effect

A

How the waves re changed as they move away from trnsducer

24
Q

What are the initial invetigations for urinary incontinence?

A

Hx and exam
Bladder diary 3 days
Post-void bladder scan
Urine dip

25
Q

When are urodynamics indicated?

A

Before surgery in women who have:

  1. When symptoms suggest OAB
  2. OR symptoms suggest difficulty voiding

MRCOG part 1 (30 decks)

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