Harald E. Möller1
1Max Planck Institute for Human Cognitive and Brain Sciences, Germany


While the BOLD contrast is widely applied to map brain activity, it is also fundamentally limited as it provides only an indirect measure of neural activation that cannot be straightforwardly quantified and is inherently limited in its spatial specificity. Consequently, alternative methods have evolved to address such limitations. Here, we will primarily focus on measurements of CBF and CBV changes as currently popular ‘non-BOLD’ contrasts in human fMRI studies of the neurovascular coupling or at laminar resolution.

Target Audience

Researchers and clinicians interested in cutting-edge fMRI acquisitions and contrast mechanisms that complement BOLD-based fMRI.


While blood oxygenation level-dependent (BOLD) contrast is widely applied to map brain activity—predominantly, with rapid gradient-echo (GE) imaging—it is also fundamentally limited:
  • Being based on the related hemodynamic response, it is only an indirect measure of neural activation [1].
  • A complex interplay of different physiological and metabolic parameters hampers its quantitative interpretability [2,3].
  • Oxygenation changes in draining veins reduce the effective spatial resolution [4].
Consequently, alternative methods have evolved as presumably being more direct, quantitative, or spatially specific. Measures of cerebral blood flow (CBF), cerebral blood volume (CBV), or the cerebral metabolic rate of oxygen (CMRO2) have received increasing attention [5]. Other substitutes proposed for detecting neural activation include, for example, intravoxel incoherent motion (IVIM) [6], water diffusivity [7,8], intermolecular multiple-quantum coherences (iMQC) [9,10], temperature [11], electric activity [12], manganese-enhanced MRI (MEMRI) [13], MR elastography [14], hyperpolarized 129Xe inhalations [15], or metabolic information obtained with magnetic resonance spectroscopy (MRS) [16]. Here, we will primarily focus on measurements of CBF and CBV changes as currently popular ‘non-BOLD’ contrasts in human studies of the neurovascular coupling [17] or laminar fMRI [18,19].

CBF-Based fMRI

The most promising method to detect activation-induced CBF changes is arterial spin labeling (ASL) [20]. The main approaches are pulsed ASL (PASL), continuous ASL (CASL), and pseudo-continuous ASL (pCASL), which primarily differ in the specific labeling procedure [21]. PASL techniques employ a (single) radiofrequency (RF) pulse (order of ms) to invert arterial water spins in a thick slab upstream to the imaging region, which is typically followed by additional saturation pulses to control the width of the labeled bolus (e.g., with QUIPPS II [22]). In CASL, RF is applied ‘continuously’ (order of 1-3 s) to achieve flow-driven adiabatic inversion [20]. The labeling mechanism is similar for pCASL, however, the continuous RF application is replaced by a train of shaped RF pulses (e.g., 1/ms) [23]. At routine field strengths (≤ 3T), pCASL outperforms PASL and CASL regarding sensitivity. At higher field, however, its performance is currently limited by an increased specific absorption rate (SAR), suggesting PASL for 7T experiments targeted at ‘laminar fMRI’ [24].

CBV-Based fMRI

Early pioneering studies with exogenous contrast agents have demonstrated functional CBV changes [25], and applications of iron-oxide nanoparticles are a method of choice for fMRI in animals [26]. In humans, however, the entirely non-invasive principle of vascular space occupancy (VASO) [27,28] is the most widely applied CBV-sensitive fMRI technique. It employs an inversion-recovery scheme to take advantage of the (subtle) T1 difference between blood and surrounding tissue by nulling the blood signal while maintaining parts of the tissue signal. The (relative) VASO signal intensity can, thus, be considered to be proportional to 1−CBV (in the absence of BOLD contamination), and increased CBV in activated brain regions lead to a signal reduction. Potentially limited spatial coverage due to the requirement of a consistent blood-nulling time has been effectively addressed through simultaneous multi-slice acquisitions [29].

Comparison of CBF- and CBV-Based fMRI to BOLD-fMRI

Sensitivity is typically the most limiting factor of non-BOLD fMRI. With ASL, this is primarily due to the relatively small signal difference between control and label conditions, resulting in approximately 10-20% of the temporal signal-to-noise ratio (tSNR) that can be achieved achieved with BOLD-fMRI [5]. The VASO signal stability is affected by gray-matter signal attenuation during the blood-nulling condition, with a tSNR in the order of 40-70% compared to BOLD-fMRI [5]. However, such sensitivity comparisons should also consider the complementary aspect of specificity, in particular, as the sensitivity of GE-BOLD-fMRI is known to be driven by an undesired signal from large vessels. Estimations for 7T suggest that the macrovascular GE-BOLD signal originating in ascending and pial veins exceeds that from microvessels by an order of magnitude [30]. Signal changes detected with ASL primarily arise from permeable capillaries, suggesting a spatial specificity matching that of the neurovascular coupling [31]. VASO is also sensitive to depth-dependent microvessels but additionally, to some extent, to unspecific diving and pial arteries indicating that its spatial specificity is reduced in comparison to ASL but better in comparison to BOLD-fMRI. Both ASL and VASO provide quantitative estimates of the vascular response. Although VASO signal changes may be converted to biophysical units, ASL is probably more directly quantifiable given that information about the baseline blood flow is straightforwardly accessible.
While the temporal efficiency of BOLD-fMRI is largely defined by gradient performance and achievable acceleration, ASL and VASO share limitations arising from the underlying concepts of T1 contrast generation: Absolute CBF estimates require interleaved label and control acquisitions leading to temporal resolutions above 4 s. With VASO, interleaved acquisition schemes are typically employed to achieve a correction for BOLD contaminations, with a temporal resolution of about 3 s. Since non-BOLD contrast mechanisms do not rely on detecting susceptibility effects, the shortest possible echo time is advantageous [32]. For high-resolution studies, multi-shot 3D readouts have been advocated due to moderate SAR constraints at high field and favorable tSNR [33].


No acknowledgement found.


  1. N. Logothetis. What we can do and what we cannot do with fMRI. Nature 2008; 453: 869–878.
  2. R. Buxton. Dynamic models of BOLD contrast. NeuroImage 2012; 62: 953–961.
  3. M. Lauritzen, C. Mathiesen, K. Schaefer, K.J. Thomsen. Neuronal inhibition and excitation, and the dichotomic control of brain hemodynamic and oxygen responses. NeuroImage 2012; 62: 1040–1050.
  4. R. Turner. How much cortex can a vein drain? Downstream dilution of activation-related cerebral blood oxygenation changes. NeuroImage 2002; 16: 1062–1067.
  5. L. Huber, K. Uludağ, H.E. Möller. Non-BOLD contrast for laminar fMRI in humans: CBF, CBV, and CMRO2. NeuroImage 2019; 197: 742–760.
  6. A.W. Song, M.G. Woldorff, S. Gangstead, G.R. Mangun, G. McCarthy. Enhanced spatial localization of neuronal activation using simultaneous apparent-diffusion-coefficient and blood-oxygenation functional magnetic resonance imaging. NeuroImage 2002; 17: 742–750.
  7. D. Le Bihan, S.-i. Urayama, T. Aso, T. Hanakawa, H. Fukuyama. Direct and fast detection of neuronal activation in the human brain with diffusion MRI. Proc. Natl. Acad. Sci. USA 2006; 103: 8263–8268.
  8. K.L. Miller, D.P. Bulte, H. Devlin, M.D. Robson, R.G. Wise, M.W. Woolrich, P. Zezzard, T.E.J. Behrens. Evidence for a vascular contribution to diffusion FMRI at high b value. Proc. Natl. Acad. Sci. USA 2007; 104: 20967–20972.
  9. W. Richter, M. Richter, W.S. Warren, H. Merkle, P. Andersen, G. Adriany, K. Ugurbil. Functional magnetic resonance imaging with intermolecular multiple quantum coherences. Magn. Reson. Imaging 2000; 18: 489–494.
  10. A. Schäfer, H.E. Möller. Functional contrast based on intermolecular double-quantum coherences: Influence of the correlation distance. Magn. Reson. Med. 2007; 58: 696–704.
  11. D.A. Yablonskiy, J.J.H. Ackerman, M.E. Raichle. Coupling between changes in human brain temperature and oxidative metabolism during prolonged visual stimulation. Proc. Natl. Acad. Sci. USA 2000; 97: 7603–7608.
  12. N. Petridou, D. Plenz, A.C. Silva, M. Loew, J. Bodurka, P.A. Bandettini. Direct magnetic resonance detection of neuronal electrical activity. Proc. Natl. Acad. Sci. USA 2006; 103: 16015–16020.
  13. Y.-J. Lin, A.P. Koretsky. Manganese ion enhances T1-weighted MRI during brain activation: An approach to direct imaging of brain function. Magn. Reson. Med. 1997; 38: 378–388.
  14. S. Patz, D. Fovargue, K. Schregel, N. Nazari, M. Paloti, P.E. Barbone, B. Fabry, A. Hammers, S. Holm, S. Kozerke, D. Nordsletten, R. Sinkus. Imaging localized neuronal activity at fast time scales through biomechanics. Sci. Adv. 2019; 5: eaav3816.
  15. M.L. Mazzanti, R.P. Walvick, X. Zhou, Y. Sun, N. Shah, J. Mansour, J. Gereige, M.S. Albert. Distribution of hyperpolarized xenon in the brain following sensory stimulation: Preliminary MRI findings. PLoS ONE 2011; 6: e21607.
  16. S. Magia, F. Giove, I. Tkáč, N.K. Logothetis, P.-G. Henry, C.A. Olman, B. Maraviglia, F. Di Salle, K. Uğurbil. Metabolic and hemodynamic events after changes in neuronal activity: Current hypotheses, theoretical predictions and in vivo NMR experimental findings. J. Cereb. Blood Flow Metab. 2009; 29: 441–463.
  17. L. Huber, J. Goense, A.J. Kennerley, D. Ivanov, S.N. Krieger, J. Lepsien, R. Trampel, R. Turner, H.E. Möller. Investigation of the neurovascular coupling in positive and negative BOLD responses in human brain at 7 T. NeuroImage 2014; 97: 349–362.
  18. L. Huber, J. Goense, A.J. Kennerley, R. Trampel, M. Guidi, E. Reimer, D. Ivanov, N. Neef, C.J. Gauthier, R. Turner, H.E. Möller. Cortical lamina-dependent blood volume changes in human brain at 7 T. NeuroImage 2015; 107: 23–33.
  19. L. Huber, D.A. Handwerker, D.C. Jangraw, G. Chen, A. Hall, C. Stüber, J. Gonzalez-Castillo, D. Ivanov, S. Marrett, M. Guidi, J. Goense, P.A. Poser, P.A. Bandettini. High-resolution CBV-fMRI allows mapping of laminar activity and connectivity of cortical input and output in human M1. Neuron 2017; 96: 1253–1263.
  20. J.A. Detre, J.S. Leigh, D.S. Williams, A.P. Koretsky. Perfusion imaging. Magn. Reson. Med. 1992; 23: 37–45.
  21. D.C. Alsop, J.A. Detre, X. Golay, M. Günther, J. Hendrikse, L. Hernandez-Garcia, H. Lu, B.J. MacIntoshL.M. Parkes, M. Smits, M.J.P. van Osch, D.J.J.Wang, E.C. Wong, G. Zaharchuk. Recommended implementation of arterial spin-labeled perfusion MRI for clinical applications: A consensus of the ISMRM Perfusion Study group and the European Consortium for ASL in Dementia. Magn. Reson. Med. 2015; 73: 102–116.
  22. W.-M. Luh, E.C. Wong, P.A. Bandettini, J.S. Hyde. QUIPSS II with thin-slice TI1 periodic saturation: A method for improving accuracy of quantitative perfusion imaging using pulsed arterial spin labeling. Magn. Reson. Med. 1999; 41: 1246–1254.
  23. W. Dai, D. Garcia, C. de Bazelaire, D.C. Alsop. Continuous flow-driven inversion for arterial spin labeling using pulsed radio frequency and gradient fields. Magn. Reson. Med. 2008; 60: 1488–1497.
  24. D. Ivanov, A. Gardumi, R.A.M. Haast, J. Pfeuffer, B.A. Poser, K. Uludağ. Comparison of 3 T and 7 T ASL techniques for concurrent functional perfusion and BOLD studies. NeuroImage 2017; 156: 363–376.
  25. J.W. Belliveau, D.N. Kennedy, R.C. McKinstry, B.R. Buchbinder, R.M. Weisskoff, M.S. Cohen, J.M. Vevea, T.J. Brady, B.R. Rosen. Functional mapping of the human visual cortex by magnetic resonance imaging. Science 1991; 254: 716–719.
  26. J.B. Mandeville. IRON fMRI measurements of CBV and implications for BOLD signal. NeuroImage 2012; 62: 1000–1008.
  27. H. Lu, X. Golay, J.J. Pekar, P.C.M. van Zijl. Functional magnetic resonance imaging based on changes in vascular space occupancy. Magn. Reson. Med. 2003; 50: 263–274.
  28. L. Huber, D. Ivanov, S.N. Krieger, M.N. Streicher, T. Mildner, B.A. Poser, H.E. Möller, R. Turner. Slab-selective, BOLD-corrected VASO at 7 Tesla provides measures of cerebral blood volume reactivity with high ratio. Magn. Reson. Med. 2014; 72: 137–148.
  29. L. Huber, D. Ivanov, M. Guidi, R. Turner, K. Uludağ, H.E. Möller, B.A. Poser. Functional cerebral blood volume mapping with simultaneous multi-slice acquisition. NeuroImage 2016; 125: 1159–1168.
  30. K. Uludağ, B. Müller-Bierl, K. Uğurbil. An integrative model for neuronal activity-induced signal changes for gradient and spin echo functional imaging. NeuroImage 2009; 48: 150–165.
  31. A.L. Vazquez, M. Fukuda, J.C. Crowley, S.-G. Kim. Neural and hemodynamic responses elicited by forelimb- and photo-stimulation in channelrhodopsin-2 mice: Insights into the hemodynamic point spread function. Cereb. Cortex 2014; 24: 2908–2919.
  32. S. Hetzer, T. Mildner, H.E. Möller. A modified EPI sequence for high-resolution imaging at ultra-short echo time. Magn. Reson. Med. 2011; 65: 165–175.
  33. L. Huber, D. Ivanov, D.A. Handwerker, S. Marrett, M. Guidi, K. Uludağ, P.A. Bandettini, B.A. Poser. Techniques for blood volume fMRI with VASO: Form low-resolution matting towards sub-millimetre layer-dependent applications. NeuroImage 2018; 164: 131–143.
Proc. Intl. Soc. Mag. Reson. Med. 28 (2020)