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RANZCOG - Core sciences 2024 > Clinical imaging > Flashcards

Clinical imaging Flashcards

1
Q

Discuss USS
-ALAR principles (6)
-USS frequencies and use in pregnancy and gynaecology

A
  1. ALAR - as low asreasonably achievable
    -Only use USS when clinically indicated
    -Minimal time of exposure
    -Be cautious with pulse wave doppler
    -Don’t rest the transducer on the skin when not scanning
    -Don’t scan using a non-obstetric setting during pregnancy as the power setting is too high
    -Use low power and high gain to ensure USS exposure is minimised
  2. USS frequency prinicples
    -High frequency = less penetration but greater resolution. TV USS
    -Low frequency = deeper penetration but poor resolution
    -Curved array good for obstertics
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2
Q

How should MSD be measured
-How to measure
-How to distinguish from pseudo sac
-Expected growth rate

A
  1. Meaure in longitudinal, transverse adn AP planes and take average
  2. Measure sac from inner to inner aspect of Sac
  3. Gestational sac has bright ring and is on one side of the endometrium cf pseudo sac which is central, less brigth and can dissapate during scan
  4. Average growth rate 1mm / day (0.7mm - 1.5mm)
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3
Q

How should CRL be measured - 4 points

A
  1. Dating is based on CRL
  2. <7 weeks measure the longest length of the embryo
  3. 9-13 weeks measure in sagittal plane
  4. Don’t include yolk sac
  5. Only date on CRL if
    -Unsure of LMP or if >7 days discrepency between scan and LMP then use scan
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4
Q

What are the USS findings of a miscarriage
-Incomplete
-Complete

A
  1. Heterogenous material in cavity
  2. Incomplete miscarrige ET >15mm
  3. Complete miscarriage ET <15mm
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5
Q

Describe USS findings of ectopic pregnancy (5)

A
  1. Empty uterus
  2. Pseudo sac, thickened endometrium, multiple cystic spaces
  3. Echogenic free fluid or blood clot in POD
  4. Adnexal mass. Beware of CL - can be on contralateral side in 30% of cases
  5. Ectopic tubal ring
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6
Q

Describe USS findings of corpus luteum (7)

A
  1. Present in all 1st Trimester pregnancies
  2. May be >1 if twin pregnancy
  3. Mean diameter 19mm (8-55mm)
  4. Appearences
    -Peripheral ring of vascularity on doppler 92%
    -Solid mass (34%)
    -Thick walled cyst with anechoic centre (27%)
    -Thin simple walled cyst (15%)
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7
Q

Discuss nuchal transluceny scan
-When to perform (2)
-How to measure (2)
-Measures which suggest abnormalies (2)

A
  1. Perform
    -If CRL >55mm
    -12 - 13+6
  2. How to measure
    -Measure the lymphatic fluid behind back of neck
    -Don’t include skin
    -Take several measures
  3. Abnormalities
    - >3mm - 10% risk of abnormality
    - > 3.5mm refer to MFM
    - >6mm 90% change of abnormality
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8
Q

Discuss deterimination of chorionicity and amnioicity
-When to assess
-Signs for dichorionic twins (3)
-Signs for monochorionic twins (3)

A
  1. Best to assess between 10-12+6 weeks
  2. Signs of dichorionic twins
    -2 seperate placentas (100% sensitivity)
    -Lambda sign
    -Fetuses with different genders
  3. Signs of monochorionicty
    -Tau sign sensitivity of 100% specificity of 98%
    -Thickness of membrane <1.5mm
    -Absence of membranes = MCMA twins
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9
Q

Discuss anatomy scan
-% of major structural abnormalities in pregnancies
-Detection rate for
-Abnormalities
-Major abnormalities
-Minor abnormalities

A
  1. 2-3.5% of pregnancies have major abnormalities
  2. Anatomy scan detects:
    -60% of all abnormalities
    -73% of major abnormalities
    -45% of minor abnormalities
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10
Q

Describe how the following should be measured on USS
-BPD
-HC
-FL
-AC

A
  1. BPD
    -midline horizontal including falx cerebrum, CSP, thalami
    -Measure from outer skull margin to inner skull margin perpendicular to midline through widest point
  2. HC
    -Measure in same plane as BPD
    -Measure outer parimeter of bone in an elipse
    -Exclude subcutaeneous tissue
  3. FL
    -Choose upper most leg
    -Obtain horizontal impage parallel to probe
    -Exclude cartilaginous epiphyses in the measurement
    -Make sure lower limb by identify spine or bladder
  4. AC
    -Measure transverse section of abdo
    -Include stomach and umbi vein and spine
    -Include whole of rib to ensure avoiding oblique view
    -Measure with spine at 3 or 9 o’clock
    -measure at skin edge
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11
Q

Discuss the assessment of gestational age
-Most accurate time to assess
-Margin of error at 6 weeks
-Margin of error at 12-22 weeks
-Margin of error at 36 weeks

A
  1. Most accurate time = 6-13 weeks
  2. Margin of error at 6 weeks - 3 days
  3. Margin of error at 12 - 22weeks - 7 days
  4. Margin of error at 36 weeks - 24 days
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12
Q

Discuss measurements for assessing gestational age at:
-Up to 11 weeks
-11-13 weeks
-14 weeks
-From 20 weeks

A
  1. Up to 11 weeks = CRL
  2. 11-13 weeks CRL + BPD
  3. 14 weeks BPD HC and FL
  4. 20 weeks HC most accurate
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13
Q

Discuss measurement of liquor volume
-How to assess
-Normal range of liquor
-AFI vs SDVP

A
  1. Measure SDVP
  2. Normal range 2-10cm for SDVP, 5-25cm for AFI
  3. AFI of <5 or SDVP of < 2cm = oligohydramnios
    -AFI better at predicting dx of oligohydramnios
    -AFI has increased CS, IOL but no difference on apgar UA pH or perinatal outcomes
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14
Q

Discuss umbillical artery doppler
-What it estimates
-Pathophysiology of UA doppler
-How changes progress in early and late FGR
-How it should be used
-What are the causes of acute deterioration (3)

A
  1. UA doppler measures infomation on the fetal side of the placenta reflecting downstream resistance at the placental stem and terminal villi
  2. Pathophysiology
    -Abnormal spiral artery remodelling results in reduced oxygen delivery to the fetal surface.
    -This results in vasoconstriction of the stem villi increasing resistance to flow.
    -Resistance should get lower a gestation increases in normal anatomy
  3. Changes
    -Progression is from increased resistance to AEDF to REDF
    -In Early onset FGR the progession can remain stable for weeks between AEDF and REDF
    -In Late onset IUGR the progression is faster
    -In Early onset IUGR persisting AEDF may be due to higher placental resistance and an immature fetal heart rather than acidemia
  4. How should it be used
    -Is a primary screen in SGA fetus
    -Use of UA dpolers in SGA babies reduces perinatal mortality
    -In SGA/FGR babies with normal dopplers do fortnightly
    -Where dopplers are abnormal do 2 x weekly if not for delivery
    -If AEDF or REDF do daily
  5. Causes of acute deterioration in dopplers
    -PET
    -Sudden thrombotic event
    -Sudden haemorrhagic event (Abruption)
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15
Q

Describe the uterine artery dopplers
-What does it meausure
-How should it be used (2)

A
  1. Uterine artery doppler measures resistance at the maternal interface of the placenta
    -Reflects the conversion of spiral arteries and invasion of trophoblasts
  2. Uses
    -Not usful for growth surveillance
    -Differentiates between early onset FGR and SGA
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16
Q

Discuss Middle cerebral artery
-What it measures
-Pathophysiology
-Uses

A
  1. What it measures
    -Measures fetal circulation
    -It reflects chronic hypoxemia but not acidemia or adverse outcomes
    -In early onset FGR almost alwasy seen with abnormal UAPI but not in third trimester
  2. Pathophysiology
    -Normally shows high resistance flow pattern.
    -In palcental insufficency there is high diastolic velocities thus a low PI.
    -Results in brain sparing where the fetus is prioritising local perfusion
  3. Uses
    -Abnormal MCA PI should not be used to time delivery in pre-term
    -If abnormal MCA PI delivery at 37 weeks
    -Useful for differential diagnosis of SGA
17
Q

Discuss cerebral placental ratio
-What it measures
-Uses (3)

A
  1. Ratio between MCA PI and UAPI
  2. Uses
    -May be better predictor of adverse outcomes
    -Might help to identify at risk fetus early when the individual parameters are normal
    -Might be useful in predicting which babies will tolerate labour
18
Q

Describe ductus venosus
-What it measures
-Pathophysiology
-Wave form
-When should be done
-Uses

A
  1. What it measures
    -Shows cardiac redistribution
  2. Pathophysiology
    -The ductus venosus shunts oxygenated blood to the IVC bypassing the liver
    -Hyperaemia causes increased shunting to ductus venosus for preferential redistribution mechanism
    -As increasing myocardia hypoxia occurs due to failing compensatory mechanisms the right heart has reduced contractility
    -This leads to increased resistance in the DV and this deteriorates into absent or reversed a wave
  3. Wave form
    - first peak = systole
    -Second peak - early diastole
    -A wave - R atrial contraction
  4. Should be done if UAPI is abnormal
  5. Uses
    -Use for timing of delivery in pre-term FGR babies
    -Best predictor of acidemia at birth and perinatal outcomes in severe early onset FGR
19
Q

Discuss ionising radiation exposure during pregnancy
-Maximum recommended exposure
-Level of radiation in the following
-USS, MRI, CXR, CTPA, CTAP

A
  1. Maximum recommended level of exposure during pregnancy = 50mGy (5 rads)
  2. Level of radiation
    -MRI - nil
    -USS - nil
    -CXR - <0.1
    -CTPA <0.1
    -CTAP 10-50
20
Q

Discuss the risks of exposure to radiation in pregnancy
-Short term risks (4)
-Long term risks (1)

A
  1. Short term risks - thought unlikely if <100mGy
    -Growth and developmental problems
    -Malformations esp 3-8 weeks
    -Pregnancy loss - miscarriage, still birth
    -Erythema, cataracts, hair loss
  2. Long term risks
    -Radiation induced cancer
21
Q

What is the risk of fetal cancer for the following examination types
-CXR, CT head, CTPA
-AXR, CT Chest
-Lumbar XR, CT Abdo, lumbar
-CT pelvis

A
  1. <1: 1 000 000
  2. 1: 100 000 - 1:10 000
  3. 1: 10 000 - 1:1000
    4: 1: 200 - 1:1000

RANZCOG - Core sciences 2024 (9 decks)

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