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Questions and Answers
What is a characteristic feature of hyperacute and late subacute phases in isotropic/trace DWI images?
What is a characteristic feature of hyperacute and late subacute phases in isotropic/trace DWI images?
How do the ADC values compare in different stages of haematoma evolution?
How do the ADC values compare in different stages of haematoma evolution?
What happens to the T1 and T2 signal characteristics during the acute stage of haematoma as it evolves?
What happens to the T1 and T2 signal characteristics during the acute stage of haematoma as it evolves?
What can confound attempts at reliably dating the age of an extracranial haemorrhage?
What can confound attempts at reliably dating the age of an extracranial haemorrhage?
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What effect does the presence of blood products in a cavity have on the utility of diffusion restriction for diagnosing pus in an abscess?
What effect does the presence of blood products in a cavity have on the utility of diffusion restriction for diagnosing pus in an abscess?
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What imaging characteristic depends on the oxygenation state of hemoglobin?
What imaging characteristic depends on the oxygenation state of hemoglobin?
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Which type of hemoglobin has a strong paramagnetic effect due to the presence of unpaired electrons?
Which type of hemoglobin has a strong paramagnetic effect due to the presence of unpaired electrons?
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How does methaemoglobin affect T2* weighted sequences on MRI?
How does methaemoglobin affect T2* weighted sequences on MRI?
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Which MRI sequence is primarily affected by the presence of red blood cell lysis?
Which MRI sequence is primarily affected by the presence of red blood cell lysis?
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What is the primary characteristic of oxyhemoglobin in terms of its magnetic properties?
What is the primary characteristic of oxyhemoglobin in terms of its magnetic properties?
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What factor primarily influences the appearance of hemorrhage on MRI over time?
What factor primarily influences the appearance of hemorrhage on MRI over time?
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In which state is hemoglobin mostly found in arterial blood?
In which state is hemoglobin mostly found in arterial blood?
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What effect does the presence of blood proteins have on T1 signals during hyperacute and acute hemorrhages?
What effect does the presence of blood proteins have on T1 signals during hyperacute and acute hemorrhages?
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Study Notes
Haemorrhage on MRI Imaging Characteristics
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Haemorrhage appearance on MRI varies significantly, dependent on several factors:
- Blood age
- Haemoglobin type (oxy-, deoxy-, or met-)
- Red blood cell wall integrity (intra- vs. extracellular)
- MRI sequence used
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MRI is often considered insensitive to acute haemorrhage, but newer sequences can detect it.
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Haemorrhage presentation changes over time; therefore, precise age estimation is challenging.
Physiology of Blood on MRI
- Haemoglobin oxygenation state significantly impacts MRI signal:
- Oxyhaemoglobin (95% arterial, 70% venous): weakly diamagnetic, minimal effect on T2* and T1.
- Deoxyhaemoglobin: strongly paramagnetic, substantial signal loss on T2* sequences (e.g., SWI), creating blooming artifacts.
- Methemoglobin: strongly paramagnetic, similar to deoxyhaemoglobin in its effect on T2* sequences.
MRI Sequences and Haemorrhage
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T1-weighted sequences: little effect from oxy- and deoxyhaemoglobin; blood proteins result in intermediate signals in hyperacute/acute haemorrhages.
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T2-weighted sequences (e.g., SWI, gradient-echo):* primarily affected by haemoglobin oxygenation and cell lysis.
- Within RBCs, deoxy/met-hemoglobin leads to signal loss.
- After cell lysis, even distribution of paramagnetic effects reduces signal loss.
- Haemosiderin/ferritin ingestion by monocytes/macrophages result in uneven, paramagnetic effects causing signal loss.
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Diffusion-weighted imaging (DWI):
- Apparent diffusion coefficient (ADC) maps: substantially lower values than normal white matter in all stages except chronic.
- Isotropic/trace DWI images: High signal hyperacute and late subacute phases due to combined T2 and diffusion effects
Stages of Haematoma Evolution
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Hyperacute (1-14 days):
- Periphery: Hypointense on T1, T2, and SWI (rim).
- Centre: Isointense on T1, hyperintense on T2; low DWI, high ADC, variable SWI.
- Ageing blood appearance factors: influenced by the extracranial/intracranial location, and heterogeneous appearance affecting the reliability of dating extracranial haemorrhage.
Practical Considerations
- Extracranial vs. Intracranial Haemorrhages: Extracranial blood products age differently than intracranial ones, and have a more heterogeneous appearance.
- Subacute/Chronic Blood: appear hypointense and show blooming on T2* weighted sequences (e.g., SWI).
- Blood in cavities: result in low ADC values; making diffusion restriction not useful for differentiating blood from an abscess.
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Description
Explore the imaging characteristics of haemorrhage on MRI. This quiz covers factors such as blood age, haemoglobin type, and the effect of various MRI sequences. Delve into the physiology of blood and the impact of oxygenation on MRI signals.
