Arterial input function

Also the method used for post-processing can influence the CBV The reliability and stability of the results depend among other things on the fact, whether or not curve fitting is used to fit the concentration time curve of tissue and arterial input function (Smith et al. 2000b). As long as there is no universally accepted procedure for PI measurement... 

Many methods for measurement of tumor blood flow are based on quantifying the tumor uptake of a systemically administered tracer. Such uptake will obviously be a function of regional blood flow, but it will also depend on the arterial input function and the efficiency with which the tracer is extracted from the blood during passage through the microvasculature. The latter parameter is defined as the extraction ratio (ER) ... 

The radioligand not only has to satisfy this large array of demanding criteria, but also has to present pharmacokinetics that can be modelled biomathematically to deliver accurate binding parameters (e.g., binding potential). A particular administration protocol may be needed to achieve this aim, based on one, two or three separate injections of radioligand, usually at varied specific radioactivity. If the biomathematical model requires an arterial input function, information on the appearance of radioactive metabolites in plasma may be required in each PET experiment. 

Arterial input function, (AIF), C (t) Concentrafion of tracer in the feeding vessel to the voxel of interest at time t. 

Arterial input function (AIF) A small ROI (typically 2 X 2 x4 pixels in area) is placed over the central portion of a large intracranial artery, preferably an artery orthogonal to the imaging plane in order to minimize dilutional effects from volume averaging. An attempt should be made to select an arterial ROI with maximal peak contrast intensity. 

Calamante, E, M. Morup, L.K. Hansen, Defining a local arterial input function for perfusion MRI using independent component analysis. Magn Reson Med, 2004. 52(4) p. 789-97. 

Fig. 8.3 Idealized and actual perfusion experiments. In aU of the above graphs, time is depicted on the x axis and concentration of contrast material on the y-axis. In an idealized perfusion experiment, the entirety of a bolus of contrast material would be delivered instantaneously to brain tissue via a feeding artery. This is depicted in the arterial input function in the upper left hand comer. In this case, the tissue concentration-vs.-time curve (upper right) is a residue function, reflecting the amormt of contrast bolus remaining in the tissue...

CBV (whose calculation does not require deconvolution) is proportional to the area under the curve. Deconvolution using a separately measured arterial input function (AIF) allows computation of a residue function, which describes the fraction of a hypothetical instantaneous contrast bolus that would remain at each time after injection. The peak of the residue function is proportional to CBF. CBV is divided by CBF to yield MTT... 

Use a deconvolution algorithm that attempts to shift tissue curves in time, removing arrival delays Use local arterial input functions Choose a global arterial input function that is as close as possible to the ischemic tissue... 

Fig. 8.12 Choice of different arterial input functions. The patient is 39-year-old female with a history of right internal carotid artery dissection and left-sided weakness, who was imaged at 8 h after symptom onset. When the left middle cerebral artery (MCA) stem is chosen as the arterial input function (AIF), there is longer delay between the AIF and the tissue sam-...

Thijs VN, Somford DM, Bammer R, Robberecht W, Moseley ME, Albers GW. Influence of arterial input function on hypoperfusion volumes measured with perfusion-weighted imaging. Stroke. 2004 35 94-98... 

Lorenz C, Benner T, Chen PJ, Lopez CJ, Ay H, Zhu MW, Menezes NM, Aronen H, Karonen J, Liu Y, Nuutinen J, Sorensen AG. Automated perfusion-weighted MRl using localized arterial input functions. J Magn Reson Imaging. 2006 24 1133-1139... 

Indirect or summary parameters, such as bolus arrival time, time-to-peak (TTP), and full-width at half maximum concentration, are easy to calculate, but are thought to be less accurate than parameters derived from deconvolution with an arterial input function (AIF). Deconvolution corrects for bolus delay and dispersion up to the level of the AIF [114], However, recent studies suggest that both approaches provide quahtatively similar results [115-117] and may be vaUd for clinical purposes [112,118,119],... 

Parker, G.J., Roberts, C., Macdonald, A., Buonaccorsi, G.A., Cheung, S., Buckley, D.L., et al. Experimentally-derived functional form for a population-averaged high-temporal-resolution arterial input function for dynamic contrast-enhanced MRI. Magnetic Resonance in Medicine Official Journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine 56(5), 993—1000 (2006)... 

PCT data are analyzed at an imaging workstation. Post-image-collection processing involves semi-au-tomated definition of an input artery and a vein. In acute stroke patients, selection of different arterial inputs has been demonstrated to have no significant effect on PCT results for an individual patient (Wintermark et al. 2007a). As a result, we routinely use the anterior cerebral artery as the arterial input function to provide standardization and facilitate intersubject comparison. In patients with chronic cerebral vascular disease, the situation is different, and we select for each vascular territory its own, specific arterial input function. 

The quantitative accuracy of the PCT CBF results is debated. PCT CBF results were demonstrated in a few small studies to be highly correlated with PET (Kudo et al. 2003) and xenon-CT (Wintermark et al. 2001b) quantitative values. As mentioned above, this however requires appropriate selection of accurate arterial input functions (Wintermark et al. 2007a). 

For application of 40-50 ml contrast agent at a flux of 5-10 ml/s, a central venous catheter or an 18-gauge injection catheter at the cubital vein is mandatory. Using a saline pusher at the same injection speed directly after contrast agent administration improves the quality of the arterial input function. 

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