SUSCEPTIBILITY CONTRAST IMAGING OF CO2-INDUCED CHANGES IN THE BLOOD-VOLUME OF THE HUMAN BRAIN

Purpose: To investigate changes in the regional cerebral blood volume (rCBV) in human subjects during rest and hypercapnia by MR imaging, ac id to compare the results from contrast-enhanced and noncontrast-enhan ced susceptibility-weighted imaging. Material and Methods: Five health y volunteers (aged 24-29 years) were studied during inhalation of atmo spheric air and 7% CO2. A bolus injection of Gd-DTPA was given during the acquisition of a series of susceptibility-weighted, fast gradient echo images (TRWTE=27/22 ms). The images were converted to Delta R(2) maps, and CBV was calculated pixelwise by fitting a gamma-variate fun ction to the data. The tissue concentration vs time curves were deconv oluted using an input function obtained by arterial sampling. Results: The ratio of gray to white matter CBV (1.9-2.5) as well as the fracti onal increase in rCBV during hypercapnia (about 30%) was found to be i n accordance with results obtained by other methods. Noncontrast funct ional MR (fMR) imaging showed signal increases in gray matter, but als o inconsistent changes in some white matter regions. Conclusion: In th is experiment, contrast-enhanced imaging seemed to show a somewhat hig her sensitivity towards changes in cerebral hemodynamics than noncontr ast-enhanced imaging. The results of the deconvolution analysis sugges ted that perfusion calculation by conventional tracer kinetic methods may be impracticable because of nonlinear effects in contrast-enhanced MR imaging.