Imaging of Circulatory Disturbances

Question 1

What are some anatomical vascular imaging?

Answer 1

Plain radiographs, catheter angiography, ultrasound and CT/MRI

Question 2

What are some functional vascular imaging?

Answer 2

Radionuclide imaging, MRI functional imaging and ultrasound

Question 3

Explain a catheter angiography

Answer 3

Vessel punctured and catheterised. Is a sterile procedure.
contrast is injected using pump injector
Rapid series of image acquisition

Question 4

Explain a scintigraphy

Answer 4

Looking for perfusion/ventilation mismatch
Can show filling defect or PE

Question 5

What are the challenges of vascular imaging?

Answer 5

Soft tissue contrast, cant see important structures well - blood vessels or lumen of hollow viscera, functional significance of lesions and cant see if treatment is effective

Question 6

Describe radiographic contrast

Answer 6

Densities of different tissues - bone brightest and air is darkest
Vessels and their lumens poorly seen against soft tissue

Question 7

What are you trying to see in a vascular image?

Answer 7

The anatomy, if there is a blockage, occlusion or stenosis, is there a leak and can these be fixed

Question 8

What can a CT 3D be useful for?

Answer 8

Volume rendering can be used prior to a surgery or dissection
Can also be used for planning of aortic aneurysm repair and lower limb arterial stenting/bypass

Question 9

What are some causes for a blockage?

Answer 9

Thrombus in stroke, thrombus of superior mesenteric artery for mesenteric ischaemia (bowel pain and septic shock) and venous sinus thrombosis

Question 10

What are some causes for a leak?

Answer 10

Aortic aneurysm rupture, lower gastrointestinal haemorrhage and intracranial aneurysm

Question 11

What are the limitations of CT in showing leaks and blockages?

Answer 11

Wont identify small volume leaks, is snapshot images so cannot exclude intermittent bleeding
Cant differentiate between acute and chronic thrombosis (if new or old)

Question 12

What are the different phases of a CT scan?

Answer 12

Non-contrast, arterial phase, venous phase, nephrogenic phase and delayed phase
(native phase then nephrogram phase then excretory phase)

Question 13

What are the ideal properties of man-made contrast agent in radiology?

Answer 13

Attenuation comparable to surrounding soft tissue, inexpensive, inert, equal distribution, painless and easy to use

Question 14

How do we visualise the vessels?

Answer 14

Intravenous contrast

Question 15

Describe intravenous contrast

Answer 15

High density (iodine), inert, stable in body compartments, painless, cheap, easy to use, injected during different phases and speed using pressured pump

Question 16

Explain the problems with iodinated contrast

Answer 16

Major allergic reaction, renal dysfunction, disturbance of thyroid metabolism, disturbance of clotting mechanism, seizures, pulmonary oedema
Can be uncomfortable and metallic taste

Question 17

What are important considerations before using contrast?

Answer 17

Previous contrast images, asthma/atopy, poor renal function, and diabetics

Question 18

Explain metformin as a consequences of contrast

Answer 18

Rare complication causes renal failure - continuous consumption of medication results in lactic acidosis
Consider with holding dose after administration of contrast agent for 24-4hrs for those at risk

Question 19

What are some contrast reactions - dose related?

Answer 19

Dose related - nausea, itching, flushing and possible seizures and arrhythmias
Management is supportive if mild

Question 20

What are some anaphylaxis (IgE mediated/ non-mediated) contrast reaction?

Answer 20

Hypotension, pulmonary oedema, bronchospasm and convulsions
Management is by anaphylaxis guidelines or salbutamol if less severe

Question 21

Describe the process of an ultrasound

Answer 21

Electricity - ultrasound waves - reflects off boundaries in tissues - turned back into electricity - converted into pictorial form
Piezoelectric crystal is the basis of US images

Question 22

Explain B-mode (brightness/ 2D mode)

Answer 22

Scans an anatomical plane
Gives anatomical representation of structures
Used in almost all types of ultrasound scans

Question 23

Explain M-mode (motion mode)

Answer 23

Less commonly used. Fixed plane overtime.
Assess heart valve movement as well as heart chamber dimension and function

Question 24

Explain doppler imaging

Answer 24

Flow alters frequency of US waves returning to probe
Shows velocity and direction of flow
Common clinical use is in detection of DVT
Blue means flow away and red means flow towards flow

Question 25

Describe the ultrasound contrast

Answer 25

Made from microbubbles, stable gas surrounding by a shell
Indications include - characterising lesions, organ perfusion, delineating organ edge for irregularity of heart valves and is alternative to CT/MRI if allergic to contrast forms

Question 26

What is the benefit of spiral CT?

Answer 26

Enables acquisition in single breath hold and better coordination with IV contrast
Much quicker, enables multi-planar imaging and can reduce patients radiation dose

Question 27

What are the principles of CT?

Answer 27

Uses attenuation of radiation in multiple planes to generate images
More projections - more accurate images
Uses standardised arbitrary unit, representing density of structures

Question 28

Explain windowing

Answer 28

Changes the shading of pixels to make easier for human eye
Window level refers to CT unit assigned as midpoint of the scale
Window range refers to values around this which are shaded, before complete black or white