title: Human cerebral blood volume (CBV) measured by dynamic susceptibility contrast MRI and 99mTc-RBC SPECT.
abstract: BACKGROUND
  Patients with elevated intracranial pressure risk compromising their cerebral blood flow, resulting in ischemia. Lowering of the raised intracranial pressure, is therefore, mandatory. Reduction of the cerebral blood volume (CBV) might be target. In finding ways to do so, one has to be able to measure CBV. Measurement of CBV is, however, difficult. Radio(99mTc-)labeled erythrocytes (99mTcRBC) single photon emission computer-aided tomography (SPECT) is one established method used for CBV measurement. Recently, dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI), has also been successfully used for this purpose. The aim of this study was to validate the use of DSC-MRI for the measurement of CBV by the investigation of the correlation between the regional distributions of 99mTc-RBC SPECT and DSC-MRI measurement of CBV in humans. If possible, the aim was also to find a conversion constant that will enable the DCS-MRI to be interpreted as CBV (percent of brain volume).
  
  
  METHODS
  CBV of 8 volunteers were studied under normocapnic and hypocapnic conditions. CBV was measured with both 99mTc-RBC SPECT and DSC-MRI.
  
  
  RESULTS
  There were significant correlations between the regional distributions of CBV measured by 99mTc-RBC SPECT and DSC-MRI (rest: F=4.53, P<0.05; hypocapnia: F=9.61, P<0.005). The derived conversion factor between DSC-MRI voxel values and 99mTc-RBC SPECT CBV (percent of brain volume) at rest was 0.0059+/-0.0013. Global CBV during normocapnia was 4.3%+/-0.6% of brain volume as measured by SPECT of brain volume and 4.5%+/-0.9% as measured by MRI. Decreasing the end-tidal pCO2 by 1.8 kPa by spontaneous hyperventilation reduced the global CBV significantly to 3.9%+/-0.5% in the SPECT group and to 3.5%+/-0.6% in the MRI group.
  
  
  CONCLUSIONS
  The comparison of 99mTc-RBC SPECT and DSC-MRI measurements in our study indicates that DSC-MRI can be a useful method to measure CBV as a percent of brain volume.
authors.affiliation: Department of Anesthesiology, University Hospital, Lund, Sweden. christian.engvall@skane.se
authors.forename: Christian
authors.initials: C
authors.lastname: Engvall
authors.forename: Erik
authors.initials: E
authors.lastname: Ryding
authors.forename: Ronnie
authors.initials: R
authors.lastname: Wirestam
authors.forename: Stig
authors.initials: S
authors.lastname: Holtås
authors.forename: Kaj
authors.initials: K
authors.lastname: Ljunggren
authors.forename: Tomas
authors.initials: T
authors.lastname: Ohlsson
authors.forename: Peter
authors.initials: P
authors.lastname: Reinstrup
mesh_terms: D000328:Adult; D001810:Blood Volume / Q000502:physiology; D001811:Blood Volume Determination / Q000379:methods*; D001921:Brain / Q000000981:diagnostic imaging*; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004912:Erythrocytes / Q000000981:diagnostic imaging*; D006801:Humans; D006985:Hyperventilation / Q000378:metabolism; D016857:Hypocapnia / Q000000981:diagnostic imaging; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D013667:Technetium; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D002245:Carbon Dioxide; D013667:Technetium