Comparison of methods for detecting nondeterministic BOLD fluctuation in fMRI Vesa Kiviniemi a, *, Juha-Heikki Kantola a , Jukka Jauhiainen b , Osmo Tervonen a a Department of Diagnostic Radiology, University of Oulu, Oys, Finland b Oulu Polytechnic, Institute of Technology, Oys, Finland Received 19 April 2003; accepted 2 September 2003 Abstract Functional MR imaging (fMRI) has been used in detecting neuronal activation and intrinsic blood flow fluctuations in the brain cortex. This article is aimed for comparing the methods for analyzing the nondeterministic flow fluctuations. Fast Fourier Transformation (FFT), cross correlation (CC), spatial principal component analysis (sPCA), and independent component analysis (sICA) were compared. 15 subjects were imaged at 1.5 T. Three quantitative measures were compared: (1) The number of subjects with identifiable fluctuation, (2) the volume, and (3) mean correlation coefficient (MCC) of the detected voxels. The focusing on cortical structures and the overall usability were qualitatively assessed. sICA was spatially most accurate but time consuming, robust, and detected voxels with high temporal synchrony. The CC and FFT were fast suiting primary screening. The CC detected highest temporal synchrony but the subjective detection for reference vector produced excess variance of the detected volumes. The FFT and sPCA were not spatially accurate and did not detect adequate temporal synchrony of the voxels. © 2004 Elsevier Inc. All rights reserved. Keywords: BOLD; Fluctuation; Thiopental; ICA; Child 1. Introduction The T2*-weighted blood oxygen level dependent (BOLD) images have been mainly used in detecting prede- termined neuronal activations in the functional brain regions [1]. Spontaneous BOLD signal fluctuation related to phys- iologic changes were first demonstrated in fMRI data set in 1993 [2]. The nondeterministic fluctuations of the BOLD signal have gained interest as a method for detecting func- tional connectivity of inter-hemispheric pathways [3]. Spontaneous vasomotor fluctuation is another source of BOLD signal variation especially evident in anesthetized and sedated subjects [4,5]. The analysis of nondeterministic BOLD signal is focused on detecting physiological, patho- logic, and drug related changes in spontaneous blood oxy- genation noise structure [3– 8]. The very low frequency vasomotor fluctuation has been previously localized with Fast Fourier Transformation (FFT), by color-encoding the spectral power of a fluctuation frequency onto a MR image [4,5]. The cross-correlation (CC) of a detected fluctuating signal has also been also utilized [3,4]. These methods were sensitive to artifacts and did not clearly separate areas of varying phases of the fluctuation. BOLD voxel time domain signal is affected by multiple signal sources, either purely physiological, aliased artifacts, or a mixture of them [9,10]. Spatial independent component analysis (sICA) has successfully been used in separating the statistically independent BOLD signal sources related to controlled activation and nondeterministic neurovascular phenomena [10,11]. Principal component analysis (PCA) of the BOLD signal has been used to order fluctuating signal sources based on variance [12]. The differences between the methods of detecting non- deterministic VLF fluctuation have not been analyzed be- fore. The aim of this study was to compare qualitative and quantitative differences between the analysis methods. The goal was to determine the application areas for the different tools of nondeterministic BOLD signal analysis. 2. Materials and methods There were 15 child patients aged between 2 to 9.5 years (aver 5.2) imaged under thiopental anesthesia with fMRI * Corresponding author. Tel.: +358-0-8-3152462; fax: +358-0-8- 3152112. E-mail address: vkivinie@mail.student.oulu.fi (V. Kiviniemi). Magnetic Resonance Imaging 22 (2004) 197–203 0730-725X/04/$ – see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.mri.2003.09.007