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Virtual ischaemic map images in acute ischaemic stroke
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  1. Ronni Mikkelsen,
  2. Christian Rahbek and
  3. Lasse Speiser
  1. Department of Neuroradiology, Aarhus University Hospital, Aarhus, Denmark
  1. Correspondence to Dr Ronni Mikkelsen; ronni.mikkelsen{at}rm.dk

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Description

An unresponsive woman in her 80s was admitted to the emergency department and received directly in the CT scanner. The patient was last known well approximately 3 hours earlier. The initial assessment of the non-contrast CT (NCCT) (figure 1A) revealed no signs of haemorrhage or acute ischaemia; however, after reviewing the subsequent virtual ischaemia maps (VIM, figure 1B,C—grey scale and colour coded, respectively) a large infarction in the left, middle cerebral artery (MCA) territory was suspected. A clinical reevaluation of the patient revealed right hemiparesis and aphasia, triggering a stroke call. The patient was rushed to the neuroradiology department where a subsequent MRI of the brain confirmed a large acute (fluid-attenuated inversion recovery (FLAIR)-negative) infarction mirroring what was suspected from the initial CT (DWI, ADC, FLAIR, figure 1D–F, respectively), along with slow-flow in several MCA vessels. Unfortunately, given the low Alberta Stroke Program Early CT (ASPECT) score, the patient was beyond endovascular therapy.

Figure 1

Non-contrast CT (A), VIM-greyscale (B) and VIM-colour coded (C) of the primary CT showing acute ischaemic infarct in the left MCA Territory more clearly on the VIM images and very subtle on the non-contrast CT. Subsequent MRI FLAIR (D) DWI (E), ADC (F) also visualising the acute MCA infarct. FLAIR, fluid-attenuated inversion recovery; MCA, middle cerebral artery; VIM, virtual ischaemia maps.

VIM imaging was first described by Wolman et al,1 who validated it against CT perfusion and 24-hour post-treatment DWI lesion seen on MRI. VIM images are constructed using data from a non-contrast dual-energy CT scan, making it possible to separate individual tissue components. Using a mathematical reconstruction called three-material decomposition, it is possible to get a more uniform attenuation between the grey and white matter in the brain, making the total water content of the tissue clearer, thereby highlighting the cytotoxic oedema in the core of an acute ischaemic infarct.1

At our department, VIM imaging is now a standard part of the emergency NCCT brain protocol. With this case we wish to illustrate the added value VIM images could have to NCCT in the acute setting of stroke imaging.

Learning points

  • Virtual ischaemia maps (VIM) images may aid in the detection of acute infarcts on non-contrast CT.

  • VIM-images can be made using Dual Energy CT scanning.

Ethics statements

Patient consent for publication

Acknowledgments

We owe a great thanks to radiographers Ulrich Veje and Mia Hougaard Christiansen for their tireless efforts in constantly improving our CT scanner and protocols.

Reference

Footnotes

  • Contributors RM prepared the image, collected consent and drafted the manuscript. CR and LS provided feedback and corrected the manuscript. All authors came up with the concept of the article.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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