Kenichi Kashikura PHD, Presenter: Nothing to Disclose

Functional magnetic resonance imaging (fMRI) using blood oxygenation level-dependent (BOLD) contrast is based on the coupling between neural activity and deoxy-Hb concentration changes. However, the deoxy-Hb concentration changes depend on the complex interaction between cerebral blood flow (CBF), cerebral blood volume (CBV), and cerebral metabolic rate for oxygen (CMRO2). In this study, we investigated the relationship between BOLD contrasts and total hemoglobin (total-Hb) concentrations correspoding to CBV in human primary visual cortex (V1) during graded visual stimulation using fMRI and near-infrared spectroscopy (NIRS).

Seven healthy volunteers were studied using a 3T MRI scanner (GE Signa Horizon LX) and a near-infrared spectroscopy (NIRS) system (Hitachi ETG-100). The same visual stimuli were used for both fMRI and NIRS experiments. Subjects were given three different photic patterns. Each pattern was reversed at frequencies of 1, 3.9, 7.8 and 15.5 Hz. For the fMRI studies, a T2*-weighted single-shot EPI sequence was applied with TR = 2 sec, TE = 30 msec, Flip Angle = 70°, and Matrix size = 64 x 64. Twenty-three axial slices were acquired. A pixel by pixel cross-correlation was performed with an expected time course (r=0.4). We defined a region of interest (ROI) in V1 according to the activation area and anatomical T2-weighted images. All pixels within the ROI were averaged and used to calculate the mean percentage change. For the NIRS studies, sixteen probes were placed in a 4 x 4 array covering the primary and associated visual cortices. The magnitude of the response was estimated as the area under the averaged integral curve above or below zero.

The computed linear regression lines and correlation coefficients between BOLD and NIRS signal changes were: y = 20.7x, R2= 0.99 for oxy-Hb, y = 13.5x, R2 = 0.94 for |deoxy-Hb|, and y=9.3x, R2=0.56 for total-Hb (n=7).

Our results showed that: 1) there was a linear relationship between BOLD response and total-Hb concentrations during graded visual activation, and 2) a strong linear correlation was found between oxy-Hb, |deoxy-Hb|, and total-Hb concentration changes.

Kashikura, K, Measurements of BOLD and Total-Hb by fMRI and Near-Infrared Spectroscopy (NIRS) during Graded Visual Stimulation.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4405590.html