Quantification of normal cerebral oxygen extraction and oxygen metabolism by phase-based MRI susceptometry: evaluation of repeatability using two different imaging protocols.
BACKGROUND
Global oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2) were quantified in a test-retest study. Cerebral blood flow (CBF) data, required for CMRO2estimation, were obtained using dynamic susceptibility contrast MRI (DSC-MRI). OEF and CMRO2were quantified using two separate data sets, that is, conventional high-resolution (HR) gradient echo (GRE) phase maps as well as echo planar imaging (EPI) phase maps taken from the baseline (precontrast) part of the DSC-MRI time series. The EPI phase data were included to elucidate whether an extra HR-GRE scan is needed to obtain information about OEF and CMRO2, or if this information can be extracted from the DSC-MRI experiment only.


METHODS
Twenty healthy volunteers were scanned using 3 T MRI on two occasions. Oxygen saturation levels were obtained from phase data measured in the great cerebral vein of Galen, based on HR-GRE as well as EPI phase maps. In combination with DSC-MRI CBF, this allowed for calculation of OEF and CMRO2.


RESULTS
High-resolution-gradient echo- and EPI-based phase images resulted in similar OEF spread and repeatability, with coefficients of variation/intraclass correlation coefficients of 0·26/0·95 and 0·23/0·81, respectively. Absolute OEF values (HR-GRE: 0·40 ± 0·11, EPI: 0·35 ± 0·08) were consistent with literature data. CMRO2showed similar repeatability, somewhat increased spread and reasonable absolute values (HR-GRE: 3·23 ± 1·26 ml O2/100 g min-1, EPI: 2·79 ± 0·89 ml O2/100 g min-1).


CONCLUSIONS
In general, the results obtained by HR-GRE and EPI showed comparable characteristics. The EPI methodology could potentially be improved using a slightly modified DSC-MRI protocol (e.g. with regard to spatial resolution and slice gap).
Department of Medical Radiation Physics, Lund University, Lund, Sweden.
Robin
R
Kämpe
Department of Medical Radiation Physics, Lund University, Lund, Sweden.
Emelie
E
Lind
Department of Medical Radiation Physics, Lund University, Lund, Sweden.|Diagnostic Radiology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
Freddy
F
Ståhlberg
Diagnostic Radiology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.|Imaging and Function, Skåne University Health Care, Lund, Sweden.
Danielle
D
van Westen
Department of Medical Radiation Physics, Lund University, Lund, Sweden.
Linda
L
Knutsson
Department of Medical Radiation Physics, Lund University, Lund, Sweden.
Ronnie
R
Wirestam
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D001921:Brain / Q000098:blood supply* / Q000000981:diagnostic imaging* / Q000378:metabolism; D002560:Cerebrovascular Circulation; D005260:Female; D064368:Healthy Volunteers; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010108:Oxyhemoglobins / Q000378:metabolism; D055420:Perfusion Imaging / Q000379:methods*; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D013997:Time Factors
D015415:Biomarkers; D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin; D010100:Oxygen
brain; magnetic resonance imaging; oxygen consumption; oxygen saturation; perfusion