Imaging of Circulatory Disturbances Flashcards
What is catheter angiography?
Vessels are punctured and catheterised.
A sterile procedure.
Contrast injected via pump injector.
Rapid series of image acquisition.
What investigations are done for pulmonary embolisms?
Normal lung scintigraphy.
V/Q scans.
What are the challenges of vascular imaging?
Soft tissue contrast - blood vessels and the lumen of hollow viscera are difficult to see.
Functional significance of lesions.
Effectiveness of treatment.
What is radiographic contrast?
Checks densities of different tissues. Vessels and lumens are poorly seen against soft tissue.
What is CT 3D volume rendering used for?
Planning AAA repair, or lower limb arterial stenting/bypasses.
What cause leaks in the body?
Aortic aneurysm ruptures.
Intracranial aneurysms.
Lower GI haemorrhages.
What are the limitations of CT?
Cannot identify small volume leaks or intermittent bleeding (snapshot images).
Differentiation between acute and chronic thrombosis is difficult.
Difficult to convey anatomy to non-radiologists.
What is a CT taken before contrast used for?
Urinary tract calculi.
Arterial calcifications.
What is the arterial phase of a CT scan?
Used to see abdominal bleeding, aortic aneurysm, arterial stenosis/occlusions, or hypervascular liver mets.
20secs PI - contrast has not enhanced organs or soft tissues.
40secs PI - optimal enhancement of portal vein and structures that get vascular supply from arteries.
What is the venous phase of a CT scan?
Used for hypovascular liver mets, abscesses, or venous thromboses.
80secs PI - enhancement of liver parenchyma, including medullae.
What is the nephrogenic phase of a CT scan?
Nephrogenic - kidneys tumours / trauma.
100secs PI - enhancement of renal parenchyma, including medullae.
What is the delayed phase of a CT scan?
Ureteral obstruction/leaks, characterisation of liver tumours.
10mins PI - wash out of contrast in all abdominal structures, except for fibrotic tissues.
What are the ideal properties of contrast agents?
Has an attenuation comparable to surrounding soft tissues.
Equal distribution in and out of selected body compartments.
Cheap, inert, painless, easy to use.
What is IV contrast?
For high density (iodine).
Stable in different compartments.
Differential x-ray attenuation.
Injected during different phases, speed using a pressurised pump.
Cheap, inert, painless, and easy to use.
What are the problems with iodinated contrast?
Major allergic reactions; renal dysfunction; disturbance of thyroid metabolism and clotting; seizures; pulmonary oedema.
Warmth sensation, discomfort, nausea, metallic taste, feels like urination.
What are the considerations of contrast?
Previous contrast allergies, stolid diseases, poor renal function.
Metformin - renal failure (rare), lactic acidosis (with continuous consumption).
What are the chemo-toxic reactions to contrast?
Dose-related- nausea, itching, flushing, seizures, arrhythmias. Supportive management if mild.
What are the anaphylactic reactions to contrast?
Hypotension, pulmonary oedema, bronchospasm. Management per anaphylaxis guidelines; antihistamines or salbutamol if less severe.
What is US B-Mode?
Brightness, 2D mode.
Scans an anatomical plane, and gives an anatomical representation of structures.
Used in almost all types of US.
What is US M-Mode?
Motion, 2D mode (less common).
A fixed plane over time.
Used to assess heart valve movement, and heart chamber dimension and function.
What is doppler imaging?
Flow altered the frequency of US waves returning to the probe.
Shows direction/velocity of flow.
Common use - detecting DVT.
What is US contrast?
Made from microbubbles of an inert gas, surrounded by a shell.
An alternative to CT/MRI, if unable to tolerate or allergic to other forms of contrast.
What are the indications for US contrast?
Characterising lesions (dynamic uptake pattern).
Assessing organ perfusion (liver cirrhosis).
Delineating organ edge (irregular heart valves).
What is spiral CT?
Enables acquisition in one breath hold.
Less motion artefacts, better coordination with IV contrast, higher patient throughput, and reduced radiation dose.
