Intro to Radiology

Question 1

PA vs AP setups

Answer 1

Question 2

Which setup makes the heart appear larger than it really is? AP, or PA?

Answer 2

AP makes the heart appear larger, since it is farther away from the screen.

Remember, AP is A Portable X-ray, which has the screen placed behind the patient while the patient is in bed.

Question 3

Good inspiration on a CXR

Answer 3

Diaphragm should be between the 8th and 10th posterior rib

Question 4

Dorsal vs ventral ribs on CXR

Answer 4

Question 5

When placing a central line, where do you want it to end up?

Answer 5

The cavo-atrial junction (where the SVC meets the right atrium)

Question 6

How do you find the cavo-atrial junction on a CXR?

Answer 6

It is approximately at the location where the right main stem bronchus meets the heart.

Question 7

Endotracheal tubes should be placed. . .

Answer 7

. . . in the trachea, above the level of the carina.

If one is improperly placed, the lung it favors will likely be hyperinflated relative to the other lung.

Question 8

How far should an NG tube be placed?

Answer 8

10 cm into the stomach beyond the approximate EG junction

Question 9

“Danger zones” on CXR

Answer 9

Areas that are hard to see and often harbor pathology

The apices of the lungs and behind the heart

Question 10

What is more dangerous? A left-sided pneumothorax, or a right-sided pneumothorax?

Answer 10

A right-sided pneumothorax, because the lower-pressure vascular systems are all on the right.

Question 11

If you are having trouble telling whether or not an X-ray shows pneumothorax, the best place to look is the. . .

Answer 11

. . . intervertebral squares: the areas in-between the posterior and anterior rib shadows that should clearly show normal lung markings.

Question 12

When you see an opacified hemithorax on imaging, think. . .

Answer 12

. . . atelectasis, pneumonia, or pleural effusion.

Question 13

What finding suggests atelectasis on CXR with an opacified hemithorax?

Answer 13

Deviation of the heart towards the collapsed side.

Question 14

What finding suggests pleural effusion on CXR with an opacified hemithorax?

Answer 14

1. Deviation of the heart away from the opacified side
2. Sharp line boundaries indicating a fluid-air interface
3. Occupation of the costodiaphragmatic recess

Question 15

What finding suggests pneumonia on CXR with an opacified hemithorax?

Answer 15

Lack of heart deviation

Question 16

Straight line vs meniscus on pleural effusion

Answer 16

Meniscus = uncomplicated pleural effusion

Straight line = air-liquid-interface, ergo, hydropneumothorax

Question 17

Most frequent cause of airway deviation

Answer 17

Thyroid goiter

Question 18

If you see a rib fracture on CXR, you should always go back and double-check the area for. . .

Answer 18

. . . pneumothorax

Question 19

Tissue-weight factors in radiation exposure

Answer 19

Accounts for density and replicative capacity of different tissues.

Used to noramlize “effective dose” of radiation

Question 20

In radiology, radiation dosage is measured in. . .

Answer 20

. . . millisivierts (mSv)

Question 21

Radiation exposure diagram

Answer 21

Question 22

If in doubt, how do you determine what imaging protocol is appropriate for a given scenario?

Answer 22

The American College of Radiology Appropriateness criteria

Or, call your radiology team!

Question 23

Whenever you image a patient with and without contrast. . .

Answer 23

. . . you are giving double the dose of radiation.

If you are ordering an abdominal CT, that is a LOT of radiation (~6 years worth of background radiation)

Question 24

When fat is inflammed, . . .

Answer 24

. . . it appears brighter on CT!

Question 25

Characteristics of contrast-induced nephropathy

Answer 25

* Serum creatinine elevated to ~50% above baseline 1-3 days after contrast injection * Elevation peaks at ~7-10 days post-injection * Usually returns to baseline within 2 weeks

Question 26

Generally speaking, when is it safe vs unsafe to give contrast?

Answer 26

If creatinine is \< 1.5, it is fine. If cretinine is between 1.5 and 2, it might be okay with adequate hydration and monitoring. If creatinine is \> 2, absolutely not.

Question 27

Contrast allergy

Answer 27

* Not well understood * Not a true IgE-mediated effect * Thought to be a direct effect of contrast on mast cells

Question 28

Contrast and shellfish allergy overlap

Answer 28

IS A MYTH This is BS, but some clinicians still believe it.

Question 29

If a patient has questions about preparing for a study and what it will entail, where should you refer them?

Answer 29

radiologyinfo.org This is a good reference for students as well. Includes info about dietary restrictions prior, protocols, etc.

Question 30

The frequency of diagnostic ultrasound is on the order of. . .

Answer 30

. . . **10⁶ Hz**

Question 31

Essential mechanism of ultrasound

Answer 31

Ultrasound devices utilize piezoelectric crystals such as quartz to create ultrasound waves (by applying a rapidly alternating current) and receive sound waves (by generating current from compression). Over 128 crystals are measured spread over the face of the ultrasound tool. The received information is used to digitally reconstruct an image.

Question 32

Static vs dynamic guidance

Answer 32

Static: Get imaging, then use this to figure out location and angle for needle insertion Dynamic: Live imaging to guide insertion of needle with visualization of the needle tip in real time

Question 33

In-plane vs out-of-plane ultrasound guidance

Answer 33

Question 34

FAST exam sensitivity and specificity

Answer 34

**Sensitivity of 73 to 99%, a specificity of 94 to 98%**, and an overall accuracy of 90 to 98% for **clinically significant intraabdominal injury in trauma**

Question 35

Angles examined in FAST exam

Answer 35

Question 36

"Lung point" sign

Answer 36

Visualized on ultrasound and 100% specific for pneumothorax. The parietal and visceral pleura of the lung stops sliding at a certain point on ultrasound. This correlates with a "barcode" or "stratosphere" sign on time-resolved ultrasound, also highly specific for pneumothorax.

Question 37

B lines

Answer 37

Correlates with the presence of an **air-liquid interface** on ultrasound, and usually means **fluid is present in the alveoli**, often from alveolar edema or acute respiratory distress syndrome. In the emergency care setting, the presence of B lines on pleural ultrasonography predicts fluid overload, adding diagnostic accuracy to the physical examination and measurement of brain natriuretic peptide

Question 38

Low frequency vs high frequency in ultrasound

Answer 38

* Low frequency has a rounded top, travels farther, see more depth, used for cardiac and abdomen * High frequency has a flat top, better resolution, but less depth, used for superficial visualization

Question 39

A lines

Answer 39

Ultrasound artifact indicating the normal lung surface

Question 40

The liver is normally slightly more dense on CT (higher Hounsfield units) relative to the spleen. What might cause this ratio to change?

Answer 40

If there is hepatic steatosis, increased fat content in the liver decreases the density by HU, making it less dense than the spleen. Diatnostically, liver HU \< 40 or liver HU \< (Spleen - 10) are sufficient for diagnosing hepatic steatosis.