Imaging of Circulatory Disturbances Flashcards
What are some anatomical vascular imaging?
Plain radiographs, catheter angiography, ultrasound and CT/MRI
What are some functional vascular imaging?
Radionuclide imaging, MRI functional imaging and ultrasound
Explain a catheter angiography
Vessel punctured and catheterised. Is a sterile procedure.
contrast is injected using pump injector
Rapid series of image acquisition
Explain a scintigraphy
Looking for perfusion/ventilation mismatch
Can show filling defect or PE
What are the challenges of vascular imaging?
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
Describe radiographic contrast
Densities of different tissues - bone brightest and air is darkest
Vessels and their lumens poorly seen against soft tissue
What are you trying to see in a vascular image?
The anatomy, if there is a blockage, occlusion or stenosis, is there a leak and can these be fixed
What can a CT 3D be useful for?
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
What are some causes for a blockage?
Thrombus in stroke, thrombus of superior mesenteric artery for mesenteric ischaemia (bowel pain and septic shock) and venous sinus thrombosis
What are some causes for a leak?
Aortic aneurysm rupture, lower gastrointestinal haemorrhage and intracranial aneurysm
What are the limitations of CT in showing leaks and blockages?
Wont identify small volume leaks, is snapshot images so cannot exclude intermittent bleeding
Cant differentiate between acute and chronic thrombosis (if new or old)
What are the different phases of a CT scan?
Non-contrast, arterial phase, venous phase, nephrogenic phase and delayed phase
(native phase then nephrogram phase then excretory phase)
What are the ideal properties of man-made contrast agent in radiology?
Attenuation comparable to surrounding soft tissue, inexpensive, inert, equal distribution, painless and easy to use
How do we visualise the vessels?
Intravenous contrast
Describe intravenous contrast
High density (iodine), inert, stable in body compartments, painless, cheap, easy to use, injected during different phases and speed using pressured pump
Explain the problems with iodinated contrast
Major allergic reaction, renal dysfunction, disturbance of thyroid metabolism, disturbance of clotting mechanism, seizures, pulmonary oedema
Can be uncomfortable and metallic taste
What are important considerations before using contrast?
Previous contrast images, asthma/atopy, poor renal function, and diabetics
Explain metformin as a consequences of contrast
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
What are some contrast reactions - dose related?
Dose related - nausea, itching, flushing and possible seizures and arrhythmias
Management is supportive if mild
What are some anaphylaxis (IgE mediated/ non-mediated) contrast reaction?
Hypotension, pulmonary oedema, bronchospasm and convulsions
Management is by anaphylaxis guidelines or salbutamol if less severe
Describe the process of an ultrasound
Electricity - ultrasound waves - reflects off boundaries in tissues - turned back into electricity - converted into pictorial form
Piezoelectric crystal is the basis of US images
Explain B-mode (brightness/ 2D mode)
Scans an anatomical plane
Gives anatomical representation of structures
Used in almost all types of ultrasound scans
Explain M-mode (motion mode)
Less commonly used. Fixed plane overtime.
Assess heart valve movement as well as heart chamber dimension and function
Explain doppler imaging
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
Describe the ultrasound contrast
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
What is the benefit of spiral CT?
Enables acquisition in single breath hold and better coordination with IV contrast
Much quicker, enables multi-planar imaging and can reduce patients radiation dose
What are the principles of CT?
Uses attenuation of radiation in multiple planes to generate images
More projections - more accurate images
Uses standardised arbitrary unit, representing density of structures
Explain windowing
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
