Ultrasound - Ede 1 Study Notes By Chris Krause

Front 1

Define frequency, penetration, and resolution. What is their relationship?

Back 1

Resolution - the ability to distinguish between two objects at different depths (i.e. to determine if one big blob is actually two small blobs).
Frequency - the number of cycles per second (in MHz) of the ultrasound wave employed by a given probe.
Penetration - the depth to which the the ultrasound beam can "look" into a patient's body.

The higher the frequency, the higher the resolution, but the LOWER the penetration.
The lower the frequency, the lower the resolution, but the HIGHER the penetration.

Front 2

Regarding ultrasound probes, what does "format" mean? What are the two formats?

Back 2

Format refers to the shape of the ultrasound beam generated by the probe. The two formats are "linear" and "sector."
"Linear" format sends parallel beams and creates a rectangular image on the screen.
"Sector" format has a curved surface and creates a wedge-shaped image.

Front 3

Regarding ultrasound probes, what does "array" mean? What are the types of arrays?

Back 3

Array refers to the way that the crystals are arranged, INSIDE the probe.
The two types of arrays are "phased" and "linear" - but not linear like the linear format.

At this point just stop learning.

Front 4

List and explain 3 common types of artifact encountered with ultrasound.

Back 4

1) Shadowing: When something hard stops the ultrasound waves (or greatly diminishes them), everything behind that thing appears black (or at least very dark).

2) Refraction, aka "edge artifact": When the US waves pass near a large, curved, fluid-filled structure, the waves are deflected, creating a small wedge-shaped sliver of darkness on either side of the structure where the US waves would have gone but didn't because they were deflected.

3) Enhancement: If the US waves travel through something which transmits them very efficiently, e.g. fluid, the tissue on the other side can appear unexpectedly brighter because so little of the US signal has been lost (the opposite of shadowing).

Front 5

What is the "dead zone"?

Back 5

When using a low-frequency probe, the first few cm of the image are a "dead zone" containing NO useful information.

Never try to interpret what you see in the dead zone.

Front 6

List the Areas of Interest for all the basic EDE indications.

Back 6

All Areas of Interest are WHITE in Basic EDE

AAA - aortic wall

Cardiac - pericardium

Abdominal (upper abdomen) - interface between "double density" kidney and liver (or spleen)
Abdominal (pelvic) - the edges of the bladder (white membrane surrounding a dark circle).

Obstetrical - endometrial strip (if there is a gestational sac, minimum 5mm thick white lining inside the uterus around the sac).

Front 7

List 5 steps in the EDE evaluation of the aorta.

Back 7

1) Place the probe just caudal to the xiphoid process, taking care to maintain the TRUE TRANSVERSE plane.

2) Identify the spine.

3) Identify the aortic WALL - the WALL is the Area of Interest.

4) Center the aorta by decreasing the depth.

5) SLIDE the probe caudally until the iliac bifurcation.

Front 8

The aortic should be visualized from the _____ to the ____ in order to rule out AAA.

Back 8

From the DIAPHRAGM to the ILIAC BIFURCATION.

Front 9

List 4 features that allow you to identify the aorta.

Back 9

1) Location - it should be immediately near-field to, and up against, the spine.

2) Wall thickness - it should have a thick, echogenic wall - thicker and more echogenic than the IVC.

3) Non-compressibility - it's, like, non-compressible.

4) Lack of respiratory variability - the IVC will collapse slightly when the patient inspires.

Front 10

What criteria would constitute a positive scan of the aorta?

Back 10

A diameter of 3cm or greater. Remember to scan all the way down even if you see a 3cm aneurysm - the diameter may be even greater farther down.

Front 11

What 2 criteria should you NOT use to identify the aorta?

Back 11

1) Pulsatility - the IVC is also pulsatile.

2) Sidedness

Front 12

What are the 5 steps of cardiac EDE?

Back 12

1. Place the probe flat on the abdomen, just cephalad to the umbilicus.

2, SLIDE the probe up the midline of the abdomen.

3. Identify the heart and centre it on the screen.

4. Identify the pericardium.

5. Perform an anterior-posterior SWEEP of the heart.

Front 13

Which side of the heart is not surrounded by pericardium? Why? Where is that on the ultrasound image?

Back 13

The part that has no pericardium is the "top right" side of the heart, because that is where the great vessels enter and exit.
That corresponds to the far-field, screen-left area on the US image.

Front 14

What are the two positive findings for cardiac EDE?

Back 14

1) Cardiac standstill (vs. "normal cardiac activity")

2) Pericardial effusion.

Front 15

How far do you have to sweep on cardiac EDE to have an acceptable scan?

Back 15

You must sweep until you see the septum join the inferior wall - which the book very confusingly describes as the "pericardium touching the septum".

Either way, just remember you have to visualize the "corner" of the "7".

Front 16

How big of a pericardial effusion (PCE) must there be for it to be present posteriorly throughout the cardiac cycle?

How much fluid for it to be present anteriorly AND posterior?

Back 16

100-300cc - present (posteriorly) throughout the cardiac cycle.

>300cc - visible anteriorly and posteriorly.

Front 17

How can you distinguish between a PCE and an epicardial fat pad?

Back 17

Epicardial fat pad will always appear ANTERIOR, whereas a PCE should be posterior if anywhere.

Also, the fat pad is unlikely to be completely black, whereas the PCE is extremely likely to be totally black.

Front 18

Where is Morrison's pouch? What is its significance in abdominal EDE?

Back 18

Morrison's pouch, aka the hepatorenal space, is the area most likely to provide a positive scan in the case of abdominal free fluid.

This is because
1) It is the 2nd-lowest area of the supine abdomen,
2) the pelvis quickly overflows into the RUQ if there is a clinically significant amount of fluid, and
3) if there is a splenic bleed it will track to the RUQ via some ligaments which I hope we don't have to memorize.

Front 19

List the 5 steps of abdominal EDE.

Back 19

1. Place the probe on the posterior axillary line at the level of the xiphoid process, in the longitudinal plane.

2. SLIDE the probe posteriorly and anteriorly to locate the kidneys, the landmark for the organ/kidney interface.

3. SLIDE the probe in the longitudinal plane to identify and centre the interface.

4. Decrease the depth to magnify the image.

5. Sweep the interface to look for free fluid.

Front 20

Provide a mnemonic that summarizes the steps of abdominal EDE (upper abdomen).

Back 20

PALMS:
PA - slide the probe Posteriorly and Anteriorly to locate the kidney
L - slide the probe in the Longitudinal plane to centre the kidney
M - magnify the area of interest
S - sweep the area of interest

Front 21

What is the lowest point in the supine LUQ? What is the implication for EDE scans of the LUQ?

Back 21

It's the subdiaphragmatic space, NOT the spleen-renal interface.

The implication is that, in additional to sweeping through the kidney, any scan of the LUQ must also visualize the diaphragm from 6 o'clock to 9 o'clock.

Front 22

What can do you to improve a sub-optimal pelvic view during abdominal EDE?

Back 22

The bladder must be full for an optimal scan. If it is empty, you can insert a catheter and instill 250cc of saline, then clamp it.

Front 23

What constitutes a positive scan in the abdominal EDE?

Back 23

1) In the upper quadrants, it's black stuff along the kidney-organ interface.

2) In the pelvic area, it's black stuff OUTSIDE the wall of the bladder - generally in the RECTOVESICULAR POUCH (for men), or the RECTOUTERINE POUCH (aka POUCH OF DOUGLAS) in women.

Front 24

List the steps in performing the pelvic part of the abdominal EDE scan.

Back 24

1. Place the probe in the transverse plane immediately cephalad to the symphysis pubis.

2. Identify the bladder.

3. Sweep the bladder in a caudad-cephalad direction, looking for free fluid.

4. (Not always necessary) Rotate the probe to sweep in the longitudinal plane to corroborate a finding, if needed.

Front 25

List 2 sources of false negatives in abdominal EDE.

Back 25

1) Adehesions - will affect where the blood collects - surgical scars = possible false negative.

2) Delayed presentation - blood may have clotted after a period of time and the blood will have an echogenic appearance.

Front 26

List the steps in performing an abdominal OB EDE.

Back 26

1. Place the probe in the longitudinal plane in the midline, just above the symphysis pubis.

2. Identify the bladder and uterus. You may need the SLIDE the probe left and right to get the uterus to appear as large as possible.

3. Centre the uterus by adjusting the depth, and heeling the probe cephalad or caudad.

4. Sweep through the uterus and the endometrial stripe(about 30 degrees in each direction).

5. Rotate the probe and sweep through the uterus in the transverse plane.

Front 27

List the steps in performing a transvaginal OB EDE.

Back 27

1. Insert the probe in the vagina in the saggital plane (with the indicator up).

2. Identify the bladder by pushing the handle DOWN (thus lifting the business end of the probe up).

3. Sweep left and right to Identify the uterus and centre it on the screen. If you don't see it, push the handle UP (i.e. the business end DOWN) and sweep again.

4. Sweep through the uterus and endometrial stripe.

5. Rotate the probe and sweep through the uterus in the coronal plane.

Front 28

What three structures must be identified in order to diagnose an IUP?

Back 28

1) Decidual reaction - white lining in the uterus around the gestational sac.

2) Gestational sac - A black area inside the decidual reaction.

3) Yolk sac - a white ring inside the gestational sac.

OR

4) Fetal pole with fetal cardiac activity can replace the yolk sac as the third element.

Front 29

What is a blighted ovum? What are the EDE findings?

What is a pseudogestational sac?

Back 29

A blighted ovum is when a fertilized egg implants normally but no baby grows. The presence of an empty gestational sac > 25mm in diameter confirms a blighted ovum and rules out ectopic just like the finding of an IUP.

A pseudogestational sac is when a small fluid collection develops inside the uterus in response to an ECTOPIC pregnancy. Don't assume that just because there is SOMETHING in the uterus, that means the pregnancy is intra-uterine.

Front 30

What does a molar pregnancy look like on EDE?

Back 30

It appears to be a dense cluster of cysts and junk inside the uterus.

Front 31

How can you differentiate an interstitial or cornual pregnancy from a true IUP?

Back 31

An IUP should have a layer of myometrium around it measuring at LEAST 5-8mm in thickness. If there is an interstitual or cornual pregnancy the layer of myometrium will be thinner.

Front 32

What is the discriminatory threshold? What should be visible if the BHCG is beyond the threshold?

Back 32

According to the EDE text, it's 3000 abdominally and 1500 trans-vaginally. This is when you should see the GESTATIONAL sac. The yolk sac may not appear yet at these levels.
So, if the beta is past the threshold with...
No gestational sac - HIGHLY suspicious for ectopic until proven otherwise.
No yolk sac - might not have appeared yet.

Front 33

What is the expected orientation of the screen when performing TV OB EDE in the saggital plane (i.e. what is left, right, near, far)? How should the uterus look?

Back 33

Transvaginal EDE in the sagittal plane should look like this:
Screen left (i.e. anterior) - bladder
Screen right (i.e. posterior) - rectouterine pouch (i.e. pouch of Douglas)??
Near field is caudad
Far field is cephalad

The uterus should look PEAR-SHAPED with the fundus pointing to SCREEN LEFT (if anteverted uterus). If retroverted it may point far field or sometimes even to screen right.

Front 34

What is the expected orientation of the screen when performing TV OB EDE in the coronal plane (i.e. what is left, right, near, far)? How should the uterus look?

Back 34

Transvaginal EDE in the coronal plane should look like this:
Screen left - patient right
Screen right - patient left
Near field - caudad - should be bladder
Far field - cephalad

The uterus should look like a CIRCLE with the endometrial stripe (or decidual reaction and gest. sac) in the centre.