After reading this chapter, you should be able:
- To describe the microcirculatory parameters measured in cerebral perfusion MRI
- Explain the principles of first pass perfusion MRI:
- role of the contrast agent
- adapted imaging sequences
- optimization of acquisition quality
- Present the methods of perfusion MRI by spin labeling, their advantages and drawbacks
- List the main clinical applications of cerebral perfusion MRI
Perfusion MRI provides a relative and/or absolute measurement of the parameters of cerebral microvascularisation: regional blood volume, mean transit time, regional blood flow.It relies on the use of a tracer that may be exogenous (contrast agent: Gadolinium) or endogenous (spin labeling)The first pass technique exploits the magnetic susceptibility effect of the Gadolinium chelates, either with T2 weighting or with T2*weighting, in SE-EPI or GE-EPI sequences. The quality of the injection and the timing of acquisition are of prime importance in obtaining a good examination. The drop in the signal during the first pass of the product allows perfusion parameters to be extracted after post-processing.In spin labeling technique, it is the saturated blood just upstream of the slice of interest which serves as a tracer. This saturation provokes a variation in the signal received in relation to an acquisition without prior saturation. An estimate of the local hemodynamic parameters can be deduced by comparing these two signals. Different labeling techniques are possible and imaging is carried out in echo planar sequence. It is restricted to the exploration of a limited region of the brain and produces only a weak signal-to-noise ratio.The main applications of first pass perfusion MRI are vascular pathologies (ischemic strokes, vasospasm) and tumoral pathologies. Progress in sequences and the very high fields should lead to improvements in spin labeling technique.
- Barbier, Lamalle. Methodology of brain perfusion imaging. J Magn Reson Imaging. 2001 Apr;13(4):496-520.
- Detre and Alsop. Perfusion magnetic resonance imaging with continuous arterial spin labeling: methods and clinical applications in the central nervous system. European journal of radiology. 1999 May;30(2):115-24.
- Luypaert, Boujraf. Diffusion and perfusion MRI: basic physics. European journal of radiology. 2001 Apr;38(1):19-27.
- Ostergaard. Principles of cerebral perfusion imaging by bolus tracking. J Magn Reson Imaging. 2005 Dec;22(6):710-7.
- Wu, Ostergaard. Technical aspects of perfusion-weighted imaging. Neuroimaging clinics of North America. 2005 Aug;15(3):623-37, xi.
- Buxton. Quantifying CBF with arterial spin labeling. J Magn Reson Imaging. 2005 Dec;22(6):723-6.
- Wong. Quantifying CBF with pulsed ASL: technical and pulse sequence factors. J Magn Reson Imaging. 2005 Dec;22(6):727-31.
- Duyn, van Gelderen. Technological advances in MRI measurement of brain perfusion. J Magn Reson Imaging. 2005 Dec;22(6):751-3.
- Grand, Lefournier. [MR and CT perfusion imaging of the brain: principles and clinical applications.]. Journal de radiologie. 2007 Mar;88(3 Pt 2):444-71.