Imaging of circulatory disturbances Flashcards
Describe options available to image vascular system.
Anatomical: Use of plain radiographs, catheter angiography, ultrasound and CT/MRI.
Functional: Radionuclide imaging, MRI functional imaging and ultrasound.
Describe the use of catheter angiography.
Catheter angiography - Vessel punctured and catheterised, sterile procedure, contrast injected using pump injector, rapid series of image acquisition.
What are the challenges of vascular imaging.
Challenges with vascular imaging:
- Soft tissue contrast: We cant see important structures very well such as blood vessels or lumen of hollow viscera.
- Functional significance of lesions.
- Is treatment effective.
Describe the indications of blockages when looking at a scan.
- Thrombus in stroke,
- thrombus of superior mesenteric artery for mesenteric ischemia,
- venous sinus thrombosis
Describe indications of leaks when looking at scan.
- Aortic aneurysm rupture,
- lower gastrointestinal haemorrhage,
- intracranial aneurysm.
Describe the limitations of CT in terms of identifying blockages and leaks.
Leaks - wont identify small volume leaks, snapshot images, cannot exclude intermittent bleeding.
Blockages - can’t always differentiate between acute and chronic thrombosis.
Anatomy - can be difficult to convey anatomy to non-radiologists.
What are contrast agents used for.
Contrast aides visualisation of vascular structures.
Describe the ideal properties of man made contrast agents in radiology.
Has an attenuation comparable to surrounding soft tissues,
inexpensive,
inert,
equal distribution in and out of selected body compartments,
painless,
ease of use.
Describe problems with iodinated contrast
major allergic reactions,
renal dysfunction,
disturbance of thyroid metabolism,
disturbing of clotting mechanism,
seizures,
pulmonary oedema.
What are important considerations before using contrast.
Important considerations before using contrast: any previous contrast allergies, asthma/atopy, poor renal function, metformin.
Describe different types of contrast reactions and their management.
Dose related/chemo-toxic - nausea, itching, flushing, (seizures, arrhythmias), management is usually supportive if mild.
Anaphylaxis/anaphylactoid (IGE/ non-IGE mediated) - causes hypotension, pulmonary oedema, bronchospasm and convulsions. Management is as per anaphylaxis guidelines or antihistamines/salbutamol if less severe.
Explain the principles of ultrasound.
Piezoelectric crystal - basis of ultrasound images. Electricity goes into piezoelectric crystal, creates ultrasound waves, travels through body and reflects off boundaries and tissues, turned back into electricity, converted into pictorial form (related to timing of signal return).
Describe the B-Mode, M-mode and Doppler ultrasound scanning.
B-mode (brightness mode) - most commonly used mode - Scans an anatomical plane, gives anatomical representation of structures, used in almost all types of ultrasound scans.
M-mode (motion mode) - less commonly used, fixed plane over time, to assess heart valve movement as well as heart chamber dimension and function.
Doppler imaging - flow alters frequency of ultrasound waves returning to the probe, to show direction/velocity of flow, common clinical use include detection of deep vein thrombosis.
Illustrate indications and contrast agents in ultrasound.
Contrast made from microbubbles - inert gas, surrounded by a shell.
Indications to use -
when characterising lesions,
assessment of organ perfusion,
delineating organ edge,
Alternative to CT/MRI if unable to tolerate/allergic to other forms of contrast.
Explain principles of CT
CT scanner with the X ray source and detectors shown in three positions.
Uses attenuation of radiation in multiple planes to generate image.
