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Part 1 MRCOG > Medical physics > Flashcards

Medical physics Flashcards

1
Q

USS signs: DCDA/ MCDA twins

A

DCDA twins: lamda sign (part of placenta)
MCDA twins: T sign (thinner amniotic demarcation)

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2
Q

When can FH be detected on USS?

A

5+2 gestation or CRL>6mm

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3
Q

When can gestational sac be seen? How does it grow?

A

TV: 4+3 weeks (2-3mm)
TA: 5+3 weeks

Grows 1mm/ day in diameter

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4
Q

Yolk sac- when should it be seen and how big?

A

Visible in chorionic cavity (TV) at 5 weeks (3-4mm).
Should be seen in all pregnancies with gestation sac >12mm.
Reaches max of 6mm (at 10 weeks)

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5
Q

Embryonic pole- when is it visible?

A

When gestational sac diameter >18mm
Can be seen TV at 37 days (2-3mm)

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6
Q

How do US waves interact with tissues?

A

Reflection: change of direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originates.
Strength of reflection from an object depends on its acoustic impedance.

Refraction: change in direction of a wave due to a change in its speed as it passes from one medium to another

Diffraction: bending of waves around small obstacles and spreading out of waves past small openings (occurs when a wave encounters an obstacle that has a diameter comparable to its wavelength)

Scatter

Absorption: direct conversion of sound energy into heat as it travels through a medium

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7
Q

Nd: YAG laser & uses

A

Crystal, solid state laser

Used in hysteroscopic ablation/ endometriosis ablation/ treatment of TTTS

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8
Q

CO2 laser

A

Highest power continuous wave laser. Microscopic precision with high degree of clinical efficacy.

Preferred for endometriosis because minimal tissue damage without lateral thermal spread

Used for CIN treatment

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9
Q

What is in an USS transducer?

A

Piezoelectric crystals

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10
Q

Type of atom released during MRI to generate image?

A

Hydrogen

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11
Q

Type of treatment where device is inserted into vagina to deliver radioactive substance?

A

Brachytherapy

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12
Q

Type of electrosurgery used in laparoscopy where a pad is placed on the patient?

A

Monopolar diathermy

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13
Q

Monopolar vs bipolar

A

With the monopolar device, the current passes from the active electrode to the target lesions through the patient’s body and finally exits the patient via a return electrode. With the bipolar device, the current only passes through the tissue between the two electrodes of the instrument

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14
Q

USS process causing lysis of cell and damage?

A

Heating

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15
Q

3 biological effects of USS

A
  1. Cavitation (i.e. growth, oscillation and decay of small gas bubbles under the influence of an ultrasound wave)
  2. Microstreaming (formation of small local fluid circulations and can be both intra- and extracellular)
  3. Heating
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16
Q

USS phase with best resolution

A

Axial

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17
Q

USS features of complete/ partial molar pregnancy/ choriocarcinoma

A

Complete:
- Solid collection of echoes with numerous small anechoic spaces (snowstorm/ granular appearance/ honeycomb texture)
- Bunch of grapes sign (swelling of trophoblastic villi)
- Normal interface between abnormal trophoblastic tissue & myometrium
- No identifiable fetal tissue or gestational sac

Partial mole:
- enlarged placenta with multiple diffuse anechoic lesions
- Fetus with severe structural abnormalities or growth restriction
- Oligohydramnios or deformed gestational sac

Choriocarcinoma
- Large irregular haemorrhage mass, invading myometrium (20% occur after TOP)

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18
Q

A CXR/ CT abdomen is equivalent to how many days of natural background ratiation?

Radiation dose of CT pelvis?

A

CXR: 2.4 days
CTA: 2.7 years (0.8-3rad; 9-30mGy)
CTP: 2.5-8rad; 25-80mGy)

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19
Q

When are urodynamics (multi-channel filling and voiding cystometry) indicated?

A

Before surgery in women who have:
- Symptoms of OAB leading to clinical suspicion of detrusor overactivity
- Symptoms suggestive of voiding dysfunction
- Anterior compartment prolapse
- Previous surgery for stress incontinence

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20
Q

On TVS USS, at what gestation are the following structures visible from:
- Gestational sac
- Yolk sac
- Embryonic pole

A
  • Gestational sac: 4+3
  • Yolk sac: 5- 5+3 (gestational sac should be 10mm when yolk sac visible)
  • Embryonic pole: 5+3 to 6 wks (gestational sac should be 16mm when embryonic pole visible)
21
Q

What is the maximum normal diameter of the yolk sac on TVUS?

A

6mm (around 10th week)

Yolk sac >6mm is suspicious of failed pregnancy

22
Q

Monopolar vs Bipolar diathermy

What frequency is typically used?

A

Monopolar: current passed from small electrode held by surgeon and returned to a large area plate via patient’s tissues

Bipolar: current passes between two electrode held by surgeon as forceps. Used to coagulate rather than cut.

Frequency must be >100kHz (500kHz is typically used), below this, depolarisation (electric shock) can occur

200kHz-3.3MHz

23
Q

Key abnormalities on ECG for hyper/ hypokalaemia, hyper/hypocalcaemia

A

Hyperkalaemia: Tall T waves, wide QRS, flat p waves, prolonged PR, bradycardia

Hypokalaemia: flat T waves, U waves, increased amplitude of p waves, long PR, ST depression

Hypercalcaemia: Short QT, long PR, Osborn waves (also caused by hypothermia)

Hypocalcaemia: Long QT, reduced PR, narrow QRS, T wave flattening/ inversion, ST depression

24
Q

When is lap and dye more appropriate than HSG for assessing tubal patency?

A

Lap & dye if history of pelvic surgery or PID

25
Q

MRI
- Principle
- T1 vs T2
- SI unit for magnetic field/ flux

A

Principle: Uses strong magnetic fields to cause protons to align with the magnetic field. Radio frequency pulses then cause the protons to excite or ‘spin’. When they relax back into alignment of the field, they release radio waves which are detected by MRI sensors.

T1 weighted: fluid is dark
T2 weighted: fluid is bright

MRI magnets typically generate fields of 0.5 to 3.0 Tesla

Tesla = SI unit for magnetic field

Weber is the SI unit for magnetic flux

26
Q

Radiotherapy dosing

A

Dosing is in Gray (Gy)

Total dose varies between tumours and stage but typical regimes involve 1.8-2.0 Gy fractions delivered over a number of weeks with total doses accumulating to reach around 50Gy

27
Q

Principle of PET scan

A

Uses radioactive tracer, usually fluorodeoxyglucose (FDG), an analogue of glucose. Is given to patients and taken up in areas of high metabolism. The tracer emits gamma rays, detected by the scanner.

Uses ionising radiation

28
Q

Types of LASER

A

Gas LASER:
- CO2
- Argon
- Helium- neon

Solid state LASER
- Nd YAG
- Neodynium
- Titanium sapphire

Liquid
- Rodamine
- Stibene
- Coumarin

Semiconductor
- Diode

29
Q

SI units:
Gray
Sievert
Becquerel

A

Gray- SI unit of absorbed dose of ionising radiation

Sievert- SI unit of equivalent dose of ionising radiation

Becquerel- SI unit of radioactive decay

30
Q

USS:
- Doppler effect
- Refraction
- Scatter
- Diffraction
- Attenuation

A
  • Doppler effect: frequency change when an observer moves towards or away from an object
  • Refraction: the change in wave direction as it passes from one medium to another
  • Scatter: the effect when the sound waves are greater than the structure they come into contact with causing uniform amplitude waves in all directions with little or no reflection returning to the transducer
  • Diffraction: bending of waves around small obstacles
  • Attenuation: decreasing intensity of a sound wave as it passes through a medium. Due to a combination of absorption of sound waves, conversion into heat energy and loss of scattered and reflected sound waves.
31
Q

SI unit of diathermy power?

A

Watt

32
Q

Oligo/ Polyhydramnios diagnosis

A

Oligo: AFI <5cm or deepest fluid pocket <2cm

Poly: AFI >25cm or deepest fluid pocket >8cm

AFI = measuring depth of fluid pockets in all 4 quadrants

33
Q

Laser of choice for ablation in TTTS

A

Diode or ND: YAG

34
Q

LASER of choice for CIN/ genital warts treatment

A

CO2

35
Q

DEXA scan principles

A

Measures bone density by: Measuring absorption from two different XRAY beams with different energy peaks at the same time

Soft tissue absorption subtracted to give BMD measurement

36
Q

What are radio-sensitisers and the 4 main groups?

Radioprotectors

A

Radio-sensitisers increase the effect of a given dose of radiation
4 main groups:
- Oxygen
- Hypoxic cell sensitizers
- Halogenated pyrimidines
- Bioreductive agents

e.g. metronidazole, cisplatin, cetumixab

Radioprotectors are agents that reduce the effects of radiation e.g. amifostine. Limited use in clinical practise due to possible protection of tumours

37
Q

At what gestation is the FH first detectable on US

A

6 weeks

38
Q

Main advantages/ disadvantages of power doppler mode?

A

Adv: Good penetrance and able to detect flow in small vessels

Dis: No information on direction of flow or velocity of flow

39
Q

What are the 3 doppler modes?

A

Power
Pulse
Colour

Pulse & colour give flow and direction information, but are angle dependent and have poorer penetration than power mode

40
Q

USS features consistent with miscarriage

A

Mean gestation sac diameter >=25mm (with no obvious yolk sac or fetal pole).
OR
Fetal pole & CRL >=7mm & no evidence of FH activity

41
Q

USS features in keeping with molar pregnancy

A

Complete mole:
- Enlarged uterus
- Solid collection of echoes with numerous small (3-10mm) anechoic spaces (snowstorm or granular appearance)
- Bunch of grapes sign, which represents hydronic swelling of trophoblastic villi

Partial mole:
- Placenta enlarged containing areas of multiple, diffuse anechoic lesions
- Foetus with severe structural abnormalities, growth restriction, oligohydramnios or a deformed gestational sac may be noted
- Colour doppler may show high velocity, low impedance flow

42
Q

B & M rules in IOTA USS guidance on ovarian masses

A

B rules (Benign)
- Unilocular cysts
- Presence of solid components where largest solid component <7mm
- Presence of acoustic shadowing
- SMooth multilocular tumour with largest diameter <100mm
- No blood flow

M- rules (malignant)
- Irregular solid tumour
- Ascites
- At least 4 papillary structures
- Irregular multilocular solid tumour with largest diameter 100mm
- Very strong blood flow

43
Q

Non-reassuring and abnormal features on CTG (NICE classification)

A

Variability:
NR: <5bpm for 30-50min, >25bpm for 15-15min

Ab: <5bpm for >50min, >25bpm for >25min

FHR range:
NR: 100-109 or 161-180

Ab: <100, >180

Accelerations:
NR/Ab: Absence is of uncertain clinical significance

Decelerations:
NR:
Variable decels with no concerning characteristics for >90min
OR
Variable decels with any concerning characteristics in up to 50% of contractions for >30min
OR
Variable decels with any concerning characteristics in >50% contractions for <30min
OR
Late decels in >50% of contractions for <30min with no maternal or fetal clinical risk factors like vaginal bleeding or significant meconium

Ab:
Variable decels with any concerning characteristics in >50% contractions for 30 mins (or less if any maternal/ fetal clinical risk factors)
OR
Late decels for 30 min (or less if any maternal/ fetal clinical risk factors)
OR
Acute bradycardia, or single prolonged deceleration lasting >=3 min

*Concerning characteristics: lasting >60s, reduced baseline variability within the decel, failure to return to baseline, biphasic (W) shape, no shouldering

44
Q

USS frequencies & those used in medical imaging

A

> 20kHz

Medical imaging: 2MHz to 15 MHz

(1MHz = 1000kHz)

45
Q

What frequency is used for trans-abdominal US vs TVUS?

A

Trans-abdominal: 3-3.5 MHz

TVUS: 5-7.5 MHz

46
Q

Approximate dose of radiation to breast tissue when performing CTPA in pregnancy vs to foetus

How does this effect risk of breast cancer

A

10-20mGy to breast

0.1mGy to fetus

Increases lifetime risk from 12% to 13.6%

47
Q

SI unit for power generated by electrosurgery units

A

Watts
Often 50-400 watts

48
Q

Absolute CI to MRI/ relative CI

A

Absolute contraindications
- Implanted electric and electronic devices especially heart pacemakers (especially older types)
- insulin pumps
- implanted hearing aids
- neurostimulators
- intracranial metal clips
- metallic bodies in the eye

Relative contraindications
- Metal hip replacements, sutures or foreign bodies in other sites are relative contraindications to the MRI
- The first trimester of pregnancy

Part 1 MRCOG (13 decks)

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