Imaging Flashcards
Anatomical imaging
Plain films
Contrast angiography
Ultrasound
CT / MRI
Functional imaging
Radionuclide Imaging
MRI functional imaging
Ultrasound
Problems with vascular imaging
Soft tissue contrast
Functional significance of lesions
Is treatment effective
What are the ideal properties of a man-made contrast agent in radiology?
Has an attenuation the same as the surrounding tissues
Inexpensive
Inert
Equal distribution in and out of selected body compartments
Painless
Easy to use
Iodinated Contrast
Differential X Ray attenuation Inert Stable in selected body compartments Painless Easy to use Cheap
Problems with Iodinated Contrast
Major Reactions Renal Dysfunction Disturbance of Thyroid Metabolism Disturbance of Clotting Seizures Pulmonary oedema
Parenteral Iodinated Contrast side effects
Metallic Taste Feeling of warmth Arterial injections Micturition (urination) discomfort Rarely nausea Previous contrast allergy Asthma / atopy Poor renal function Remember Metformin (interaction)
Catheter Angiography
Vessel punctured and catheterised
Sterile procedure
Contrast injected using pump injector
Rapid series of images acquired
Interventional Radiology can be used for..
Minimal invasive treatment of lots of things Angiography / Angioplasty Embolisation Catheter thrombolysis Drainage of abscesses Nephrostomy Vertebroplasty
When to use Angioplasty
Short stenoses or occlusions
Sessile (fixed)/ concentric plaques (all around)
Iliac > sfa > popliteal > crural
“Not as long lasting as surgery but not as dangerous”
Carbon Dioxide
as a contrast
A negative contrast agent
Useful in patients with poor renal function or sensitivity to iodinated contrast agents
Angioplasty : Problems
Occlusion Dissection Embolisation Rupture Infection
Limitations of CT
Leaks
Won’t 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
Contrast Reactions
Dose-related / chemotoxic Nausea Itching Flushing (Seizures, arrhythmias)
Management is usually supportive, if mild
Anaphylaxis / anaphylactoid (IgE / non-IgE mediated)
- Hypotension
- Pulmonary oedema
- Bronchospasm
- Convulsions
Management is as per anaphylaxis
Or antihistamines / salbutamol if less severe
Ultrasound
piezoelectric crystal produces waves via electricity
B-Mode US
(Brightness / 2D mode)
Scans an anatomical plane,
gives anatomical representation of structures
Used in almost all ultrasound practice
M-mode US
Motion mode
Less commonly used – fixed plane over time
Can be used to assess heart valve movement, and heart chamber dimension / function
Doppler Imaging
Flow alters frequency of ultrasound waves returning to the probe
Can be used to show direction / velocity of flow
Used clinically primarily for detection of DVT
Ultrasound Contrast
Indications
Contrast made from microbubbles
Inert gas, surrounded by a shell
Characterising lesions (dynamic pattern of uptake)
Assessment of organ perfusion, e.g. in liver cirrhosis
Delineating organ edges, e.g. for irregularity of heart valves
Alternative to CT / MRI, if unable to tolerate, or allergic to other forms of contrast
Spiral CT
Enables acquisition in single breath hold
Less motion artefact
Better coordination with IV contrast
Much quicker -> higher patient throughput
Enable multiplanar image reconstruction (coronal, axial, sagittal)
Can reduce patient radiation dose (depending on other technical factors)
CT (Hounsfield) units
Standardised arbitrary unit, representing the density of structures
Air = -1000 Fat= -60 to -120 water= 0 Soft tissue= 20 to 70 bone= 1000
Windowing in CT
Windowing changes the shading of pixels to make easier for human eye to appreciate particular structures
Window level refers to the CT unit assigned as the midpoint of the scale
Window range refers to the range of values around this, which are shaded, before complete black or white
