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Brain Protection in Cardiac Surgery pp 65–72Cite as

Imaging of the Brain in Cardiac Surgery as a Tool in Brain Protection Studies

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Abstract

Computed tomography (CT) is based on the absorption of X-rays in tissue. Tissue density is correlated with the amount of radiation being absorbed. Tissue absorption values are expressed as Hounsfield units (HU). Per definition, water has an HU of 0. In brain tissue, acute hemorrhage results in an increase of absorption caused by the cellular components of the blood. In contrast to normal absorption values of brain tissue (35–45 HU), acute hemorrhage features absorption values of approximately 60–70 HU. Thus, acute hemorrhage appears as a hyperdense lesion (that is, bright lesion compared with brain tissue) with a mass effect. Due to the marked difference in tissue density, CT features a high sensitivity in the detection of blood and is the method of choice to rule out acute hemorrhage. In acute ischemic infarction of the brain, diagnosis on CT is based on increased water content in brain tissue resulting in a decrease of tissue density. Thereby, acute cerebral infarction presents as hypodense (i.e., dark) lesion relative to brain parenchyma. In the hyperacute phase (i.e., <2 h), acute cerebral infarction, in general, escapes diagnosis from CT since water shifts from the extra- to the intracellular space precede a significant increase in absolute water content. Large territorial infarction later on presents as hypodense space-occupying lesions 2 h after onset at the earliest, whereas small ischemic lesions may be identified only at later stages or not at all, especially if preexisting microangiopathy of the brain with diffuse white matter hypodensity is present. Therefore, CT, in general, is not suitable in monitoring the overall ischemic lesion load in studies assessing brain protection in cardiac surgery.

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Author information

Authors and Affiliations

  1. Department of Neuroradiology, University of Heidelberg, Heidelberg, Germany

    Martin Bendszus (Director)

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  1. Martin Bendszus
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Correspondence to Martin Bendszus .

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Editors and Affiliations

  1. Dept. Cardiothoracic Surgeon, Queen Elizabeth Hospital, Birmingham, B15 2TH, United Kingdom

    Robert S. Bonser

  2. Cardiothoracic Surgery, Beaumont Road 208, Birmingham, B30 1NX, United Kingdom

    Domenico Pagano

  3. Klinik für Herz-, Thorax-,, Transplantations- und Gefäßchirurgie, Medizinische Hochschule Hannover (MHH), Carl-Neuberg-Str. 1, Hannover, 30625, Germany

    Axel Haverich

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Bendszus, M. (2011). Imaging of the Brain in Cardiac Surgery as a Tool in Brain Protection Studies. In: Bonser, R., Pagano, D., Haverich, A. (eds) Brain Protection in Cardiac Surgery. Springer, London. https://doi.org/10.1007/978-1-84996-293-3_8

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  • DOI: https://doi.org/10.1007/978-1-84996-293-3_8

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  • Print ISBN: 978-1-84996-292-6

  • Online ISBN: 978-1-84996-293-3

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