0. Basics of XRAY, Nuclear Medicine, US, CT

Question 1

What type of radiation is XRAY?

Answer 1

Electromagnetic, IONIZING radiation

Question 2

How are X rays generated?

Answer 2

Through a vacuum tube that uses high voltage to accelerate electrons released by a cathode to a high velocity - those electrons collide with a metal target, the anode, creating the XRAY

Question 3

Examples of anode metals

Answer 3

• Molybdenum (used in mammography)
• Wolfram

Question 4

Types of X-Ray images

Answer 4

• static snapshot (photography)
• dynamic / functional imaging (“movie”)
• continuous XRAY radiation

Question 5

What does the attenuation of XRAY depend on?

Answer 5

It depends on atomic number, density and thickness - dense structures appear brighter.
(it’s the opposite in fluoroscopy)

Question 6

How is XRAY resolution?

Answer 6

• Excellent spatial resolution
• Poor soft tissue resolution

Question 7

How can we visualize pneumoperitoneum in XRAY?

Answer 7

By layin the patients in lateral decubitus position for their XRAY, we can detect air-fluid levels and free peritoneal air

Question 8

What is dense breast on mammography?

Answer 8

Dense fibroglandular tissue with less adipose tissue - makes it harder to see cancer & microcalcification

Question 9

What is the fat-pad sign on XRAY?

Answer 9

Luscent crescent of fat that indicates join effusion after trauma (aka fracture)

Question 10

What is the significance of posterior fat pad on XRAY?

Answer 10

Supracondylar fracture or intra-articular fracture

Question 11

What is the GI contrast agent for XRAY?

Answer 11

Barium, but if contraindicated it can be switched out for iodine-based contrast agentsW

Question 12

When and why can barium be contraindicated?

Answer 12

• It is contraindicated in cases of GI postoperative bleeding, perforation…
• Because it causes severe peritonitis or mediastinitis if it gets in contact with the peritoneum or pleura

Question 13

What is a small bowel follow through exam?

Answer 13

• First a non contrast XRAY is taken
• Then patient drinks iodine-based contrast agent
• Images are taken after every 30-60 minutes to follow advancement of contrast agent

Question 14

Advantages of XRAY

Answer 14

• Accessible
• Quick
• Can use contrast agents
• Specific signs in certain diseases

Question 15

Disadvantages of XRAY

Answer 15

• Ionising radiation
• 2D
• Summation image
• Not good for soft tissues
• Can’t detect many diseases

Question 16

Can we use XRAY to detect kidney stones?

Answer 16

No, it’s not sensitive enough, the gold standard is low dose enhanced abdominal CT

Question 17

What is nuclear medicine ?

Answer 17

medical activities using unsealed radioactive isotopes in diagnosis, treatment, and research of diseases

Question 18

Types of radiations used in diagnostics and therapy

Answer 18

Diagnostic : 99mTc (gamma - SPECT), 18F (positron - PET)
Therapy : alpha or beta emitting isotopes

Question 19

Half life of Technetium-99m

Answer 19

6 hours

Question 20

What does SPECT detect?

Answer 20

Gamma emitting radioisotopes

Question 21

Which has the best resolution and sensitivity between PET and SPECT?

Answer 21

PET

Question 22

Advantages of PET/SPECT

Answer 22

• Sensitive
• More specific than CT
• Gives metabolic information

Question 23

Disadvantages of PET/SPECT

Answer 23

• Lower resolution
• Lack of precise localization
• Longer acquisition time

Question 24

What radioisotope is used in bone scintigraphy and why?

Answer 24

Tc99m-diphosphonate - adsorbs to bones in proportion to osteoblast activity

Question 25

Advantages and disadvantages of bone scintigraphy

Answer 25

- Very sensitive : can detect lesions before XRAY - Not specific : fractures, inflammation, primary tumors...

Question 26

What radioisotope is used in thyroid scintigraphy and why?

Answer 26

Tc99m-pertechnetate - taken up by thyroid cells through Na-I symporter (so same as iodine)

Question 27

What are some tumors that cannot take up FDG?

Answer 27

Prostate, hepatocellular, some neuroendocrine tumors...

Question 28

What 3 components does the creation of sonographic images depend on?

Answer 28

- production of high frequency sound waves - reception of reflected waves - conversion of that echo into the actual image

Question 29

Frequency of probes in US

Answer 29

- Curvilinear : 3-5MHz - Linear : 7-10MHz

Question 30

How can you get better resolution and penetrability in US?

Answer 30

Higher frequency results in better resolution, while lower frequency results in better penetrability

Question 31

What is the most used type of ultrasound in diagnostics?

Answer 31

B-mode

Question 32

What is an echodense tissue?

Answer 32

A tissue that reflects all echo. It will be bright with a posterior acoustic shadowing

Question 33

What is M-mode used for?

Answer 33

To visualize moving structures, like heart valves in echocardiography

Question 34

What is power doppler used for?

Answer 34

More sensitive than color doppler, so it' sused for flow with low velocity

Question 35

What is the ultrasound contrast agent?

Answer 35

Microbubbles : bubbles with a shell made up from albumins, galactose, lipids and polymers

Question 36

What is US used for in kidneys?

Answer 36

To detect hydronephrosis. The ureters are difficult to visualize on US, so we would use CT instead

Question 37

Why is a full bladder necessary for US?

Answer 37

To provide an acoustic window, to avoid the air filled bowels when assessing prostate or pelvic structures

Question 38

What is ureteric jet?

Answer 38

Detecting normal periodic flux of urine from ureters into the bladder - to exclude renal tract obstruction

Question 39

What is US used to detect in the thyroid gland?

Answer 39

- Vascularization - Nodules

Question 40

Normal lymph node on US

Answer 40

- Fatty hyperechoic hilum - Hypoechoic cortex

Question 41

What is the modality used to screen stenosis?

Answer 41

Doppler ultrasound

Question 42

What affects the risk of rupture of an aneurysm?

Answer 42

Its size (4-5cm have 25% risk of rupture)

Question 43

What is the screening of choice to check for aortic aneurysm?

Answer 43

US - blood will be anechoic, thrombus will be echogenic

Question 44

HOw do we check for deep vein thrombosis on US?

Answer 44

Veins containing thrombus will not completely collapse after compression, and the thrombus is echogenic

Question 45

What does FAST US stand for?

Answer 45

Focused Assessment With Sonography in Trauma

Question 46

What are the 5 main points of focus of FAST?

Answer 46

- Heart - IVC - Morrison's pouch (x3) - Aorta - Lungs

Question 47

Classical sign of pneumothorax on M mode FAST US?

Answer 47

Normal lung sign would be "seashore" but in PTX, there is just beach : only static

Question 48

Benefit of helical / spiral CT

Answer 48

Multiple regions can be scanned during a single breath-hold, in just a couple of seconds

Question 49

What is bright vs dark in CT?

Answer 49

Dark : hypodense - low density regions like air, fat Light : hyperdense - dense structures like metal, bone

Question 50

GI contrast agents in CT

Answer 50

- Iodine based, like gastrografin (bowel leaks, fistulae) - Water or macrogol -hypodense, useful in suspected bowel ischemia)

Question 51

Phases of contrast enhancement

Answer 51

1. No contrast phase 2. Arterial phase / angiography 3. Late arterial / renal cortical phase 4. Hepatic / late portal phase 5. Nephrogenic / venous phase 6. Excretory / delayed phase

Question 52

Do we always measure the GFR before contrast CT?

Answer 52

No, not in emergency situations - kidney function is measured after the examination

Question 53

Advantages of CT

Answer 53

- 3D image - Good spatial resolution - Good for soft tissues - Fast - Can visualize calcifications and lung tissue

Question 54

Disadvantages of CT

Answer 54

- High ionizing dose - Less good than MRI for soft tissue - Contraindications (pregnancy, kidney failure)