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EDE 1 Review
| Question | Answer |
|---|---|
| Define frequency, penetration, and resolution. What is their relationship? | Resolution - the ability to distinguish between two objects at different depths Frequency - the number of cycles per second by a given probe. Penetration - the depth to which the the ultrasound beam can see |
| What is the relationship between frequency, penetration, and resolution? | 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. |
| Regarding ultrasound probes, what does "format" mean? What are the two formats? | Format refers to the shape of the ultrasound beam generated by the probe. "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. |
| Regarding ultrasound probes, what does "array" mean? What are the types of arrays? | 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. |
| List 3 common types of artifact encountered with ultrasound. | 1) Shadowing 2) Refraction 3) Enhancement |
| Define shadowing | When something hard stops the ultrasound waves (or greatly diminishes them), everything behind that thing appears black (or at least very dark). |
| Define 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. |
| Define enhancement | When 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). |
| What is the "dead zone"? | 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. |
| List the Areas of Interest for all the basic EDE indications. | AAA - aortic wall Cardiac - pericardium Abdominal - interface between kidney and liver/spleen Pelvic - the edges of the bladder Obstetrical - endometrial stripe |
| List 5 steps in the EDE evaluation of the aorta | 1) Place probe just caudal to the xiphoid process, maintain the TRUE TRANSVERSE plane 2) Identify the spine 3) Identify the aortic WALL 4) Center the aorta by decreasing the depth 5) SLIDE the probe caudally until the iliac bifurcation |
| The aortic should be visualized from the _____ to the ____ in order to rule out AAA. | From the DIAPHRAGM to the ILIAC BIFURCATION. |
| List 4 features that allow you to identify the aorta. | 1) Location - it should be immediately near-field to, and up against, the spine. 2) Wall thickness - it should have a thicker and more echogenic than the IVC. 3) Non-compressibility 4) Lack of respiratory variability (unlike the IVC) |
| What criteria would constitute a positive scan of the aorta? | 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. |
| What 2 criteria should you NOT use to identify the aorta? | 1) Pulsatility - the IVC is also pulsatile. 2) Sidedness |
| What are the 5 steps of cardiac EDE? | 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 |
| Which side of the heart is not surrounded by pericardium? Why? Where is that on the ultrasound image? | 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. |
| What are the two positive findings for cardiac EDE? | 1) Cardiac standstill (vs. "normal cardiac activity") 2) Pericardial effusion |
| How far do you have to sweep on cardiac EDE to have an acceptable scan? | 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". |
| 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? | 100-300cc - present (posteriorly) throughout the cardiac cycle. >300cc - visible anteriorly and posteriorly. |
| How can you distinguish between a PCE and an epicardial fat pad? | 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. |
| Where is Morrison's pouch? What is its significance in abdominal EDE? | Morrison's pouch, aka the hepatorenal space, is the area most likely to provide a positive scan in the case of abdominal free fluid. |
| Why is MOrrison's pouch most likely to provide a positive scan? | 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 3) Splenic bleeds will track to the RUQ via some ligaments which I hope we don't have to memorize. |
| List the 5 steps of abdominal EDE. | 1) Place probe longitudinally at post axil line at the level of the xiphoid 2) SLIDE probe post and ant to locate the kidneys 3) SLIDE probe longitudinally to identify the interface. 4) Decrease depth/magnify 5) Sweep interface to look for free fluid. |
| Provide a mnemonic that summarizes the steps of abdominal EDE (upper abdomen). | 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 |
| What is the lowest point in the supine LUQ? What is the implication for EDE scans of the LUQ? | 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. |
| What can do you to improve a sub-optimal pelvic view during abdominal EDE? | 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. |
| What constitutes a positive scan in the abdominal EDE? | 1) In the upper abdomen, it's BLACK along the kidney-organ interface. 2) In the pelvic area, it's BLACK OUTSIDE the wall of the bladder - generally in the RECTOVESICULAR POUCH (for men), or the RECTOUTERINE POUCH (aka Pouch of Douglas) in women. |
| List the steps in performing the pelvic part of the abdominal EDE scan. | 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. Rotate the probe to sweep longitudinally if needed |
| List 2 sources of false negatives in abdominal EDE. | 1) Adhesions - 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. |
| List the steps in performing an abdominal OB EDE. | Place probe midline longitudinally above symphysis pubis Identify bladder-uterus juxtaposition Centre uterus by adjusting depth and fan cephalad-caudad. Sweep +/-30deg through uterus and endometrial stripe Rotate and sweep through uterus transversly |
| What three structures must be identified in order to diagnose an IUP? | 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 Fetal pole with cardiac activity) |
| What is a blighted ovum? What are the EDE findings? | 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. |
| What is a pseudogestational sac? | 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. |
| What does a molar pregnancy look like on EDE? | It appears to be a dense cluster of cysts and junk inside the uterus. |
| How can you differentiate an interstitial or cornual pregnancy from a true IUP? | 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. |
| What is the discriminatory threshold? What should be visible if the BHCG is beyond the threshold? | At 3000 abdominally and 1500 trans-vaginally you should see the GESTATIONAL sac (not necessarily the yolk sac) So, if the beta is past the threshold with... No gestational sac - HIGHLY suspicious for ectopic until proven otherwise. |
| What is the expected orientation of the screen when performing TV OB EDE in the sagittal plane (i.e. what is left, right, near, far)? | 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 |
| How should the uterus look in proper orientation when performing TV OB EDE in the sagittal plane? | 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. |
| 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)? | 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 |
| How should the uterus look in proper orientation when performing TV OB EDE in the coronal plane? | The uterus should look like a CIRCLE with the endometrial stripe (or decidual reaction and gest. sac) in the centre. |
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deanis
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