MR Perfusion Overview
What are the differences between DSC, DCE and ASL perfusion methods used in MRI?
|
|
Three methods are commonly used to measure perfusion using MRI: Dynamic Susceptibility Contrast (DSC), Dynamic Contrast Enhanced (DCE), and Arterial Spin Labeling (ASL). Both DSC and DCE require intravenous bolus administration of gadolinium, while ASL is performed without exogenous contrast. These techniques will be briefly described below, with more detailed explanations in subsequent Q&A's.
Gadolinium-enhanced T1-weighted image of malignant brain tumor
|
Dynamic Susceptibility Contrast (DSC) map of cerebral blood volume
|
Dynamic Contrast Enhanced (DCE) map of transfer constant (Ktrans)
|
Arterial Spin Labeling (ASL) map of cerebral blood flow (CBF)
|
Dynamic Susceptibility Contrast (DSC) Perfusion MRI
DSC perfusion imaging begins with a bolus of gadolinium chelate injected intravenously, followed by a series of rapidly acquired gradient or spin echo images over the organ of interest. As the gadolinium first passes through the regional circulation, it remains largely confined to the intravascular space. Due to its paramagnetic properties, gadolinium creates a local magnetic field distortion around vessels, with T2 (T2*) dephasing and loss of signal as the bolus passes. By measuring signal intensity as a function of time and fitting to a mathematical model, various perfusion parameters (e.g., blood volume, blood flow, mean transit time) can be extracted. Because DSC imaging depends only on the first pass of the contrast agent, it is sometimes known as bolus tracking MRI. Image acquisition time is therefore very short (~2 min).
Dynamic Contrast Enhanced (DCE) Perfusion MRI
Like DSC imaging, DCE also requires exogenous administration of a gadolinium-based contrast agent. DCE, however, exploits the T1 shortening effects of gadolinium, acquiring repeated T1-weighted images over an approximately 5-10 minute interval. During this time frame, gadolinium contrast accumulates within the tissue extracellular space at a rate determined by perfusion, capillary permeability, and surface area. The image data may be analyzed visually or semiquantitatively. Full quantification may be obtained by applying a compartmental model allowing several physiological parameters to be derived, including the transfer constant (Ktrans), fractional plasma volume (vp), and fractional volume of the tissue extracellular space (ve).
Arterial Spin Labeling (ASL)
Unlike DSC and DCE perfusion MRI, ASL does not require the administration of gadolinium contrast. Instead, the patient's own water molecules serve as an endogenous diffusible tracer. This is accomplished by "magnetically labeling" water molecules in proximal blood vessels with radiofrequency pulses. As these molecules flow into the organ of interest they reduce tissue signal intensity in proportion to perfusion. In the typical ASL pulse sequence, images are acquired both with and without labeling pulses, then subtracted. By applying a mathematical model, various perfusion parameters (principally blood flow) can be obtained. The signal-to-noise of ASL techniques is inherently low, and so multiple signal averages must be acquired resulting in 3-5 minute minimum imaging times to obtain useful data. Because it is signal-to-noise limited, ASL performs significantly better at 3T than 1.5T.
More detailed descriptions of DSC, DCE, and ASL are provided in subsequent Q&A's. A summary table comparing the techniques is provided below.
References
Borogovac A, Asllani I. Arterial spin labeling (ASL) fMRI: advantages, theoretical constrains and experimental challenges in neurosciences. Int J Biomed Imaging 2012; Article ID 818456:1-13.
Diebler AR, Pollock JM, Kraft RA, et al. Arterial spin-labeling in routine clinical practice, Part 1: techniques and artifacts. AJNR Am J Neuroradiol 2008; 29:1228-1234.
Essig M, Shiroishi MS, Nguyen TB, et al. Perfusion MRI: the five most frequently asked technical questions. AJR Am J Roentgenol 2013; 200:24-34.
Ferré J-C, Bannier E, Raoult H, et al. Arterial spin labeling (ASL) perfusion: techniques and clinical use. Diagn Interv Radiol 2013; 94:1211-1223
Jahng G-H, Li K-L, Ostergaard l, Calamante F. Perfusion magnetic resonance imaging: a comprehensive update on principles and techniques. Korean J Radiol 2014; 15:554-577. (good recent review).
McGehee BE, Pollock JM, Maldjian JA. Brain perfusion imaging: how does it work and what should I use? J Magn Reson Imaging 2012; 36:1257-1272.
Tofts PS. T1-weighted DCE imaging concepts: modelling, acquisition and analysis. MAGNETOM Flash 2010; 3:30-35.
Zaharchuk G. Theoretical basis of hemodynamic MR imaging techniques to measure cerebral blood volume, cerebral blood flow, and permeability. AJNR Am J Neuroradiol 2007; 28:1850-8.
Borogovac A, Asllani I. Arterial spin labeling (ASL) fMRI: advantages, theoretical constrains and experimental challenges in neurosciences. Int J Biomed Imaging 2012; Article ID 818456:1-13.
Diebler AR, Pollock JM, Kraft RA, et al. Arterial spin-labeling in routine clinical practice, Part 1: techniques and artifacts. AJNR Am J Neuroradiol 2008; 29:1228-1234.
Essig M, Shiroishi MS, Nguyen TB, et al. Perfusion MRI: the five most frequently asked technical questions. AJR Am J Roentgenol 2013; 200:24-34.
Ferré J-C, Bannier E, Raoult H, et al. Arterial spin labeling (ASL) perfusion: techniques and clinical use. Diagn Interv Radiol 2013; 94:1211-1223
Jahng G-H, Li K-L, Ostergaard l, Calamante F. Perfusion magnetic resonance imaging: a comprehensive update on principles and techniques. Korean J Radiol 2014; 15:554-577. (good recent review).
McGehee BE, Pollock JM, Maldjian JA. Brain perfusion imaging: how does it work and what should I use? J Magn Reson Imaging 2012; 36:1257-1272.
Tofts PS. T1-weighted DCE imaging concepts: modelling, acquisition and analysis. MAGNETOM Flash 2010; 3:30-35.
Zaharchuk G. Theoretical basis of hemodynamic MR imaging techniques to measure cerebral blood volume, cerebral blood flow, and permeability. AJNR Am J Neuroradiol 2007; 28:1850-8.
Related Questions
How do you perform a brain DSC perfusion study?
How do you perform a brain DSC perfusion study?