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Open Access Original research

Dual time point based quantification of metabolic uptake rates in 18F-FDG PET

Jörg van den Hoff12*, Frank Hofheinz1, Liane Oehme2, Georg Schramm1, Jens Langner1, Bettina Beuthien-Baumann12, Jörg Steinbach1 and Jörg Kotzerke12

Author Affiliations

1 PET Center, Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, 01328, Germany

2 Department of Nuclear Medicine, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, 01307, Germany

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EJNMMI Research 2013, 3:16  doi:10.1186/2191-219X-3-16

Published: 13 March 2013

Abstract

Background

Assessment of dual time point (DTP) positron emission tomography was carried out with the aim of a quantitative determination of Km, the metabolic uptake rate of [18F]fluorodeoxyglucose as a measure of glucose consumption.

Methods

Starting from the Patlak equation, it is shown that <a onClick="popup('http://www.ejnmmires.com/content/3/1/16/mathml/M1','MathML',630,470);return false;" target="_blank" href="http://www.ejnmmires.com/content/3/1/16/mathml/M1">View MathML</a>, where mt is the secant slope of the tissue response function between the dual time point measurements centered at t = t0. <a onClick="popup('http://www.ejnmmires.com/content/3/1/16/mathml/M2','MathML',630,470);return false;" target="_blank" href="http://www.ejnmmires.com/content/3/1/16/mathml/M2">View MathML</a> denotes arterial tracer concentration, <a onClick="popup('http://www.ejnmmires.com/content/3/1/16/mathml/M3','MathML',630,470);return false;" target="_blank" href="http://www.ejnmmires.com/content/3/1/16/mathml/M3">View MathML</a> is an estimate of the Patlak intercept, and τa is the time constant of the ca(t) decrease. We compared the theoretical predictions with the observed relation between <a onClick="popup('http://www.ejnmmires.com/content/3/1/16/mathml/M4','MathML',630,470);return false;" target="_blank" href="http://www.ejnmmires.com/content/3/1/16/mathml/M4">View MathML</a> and Km in a group of nine patients with liver metastases of colorectal cancer for which dynamic scans were available, and Km was derived from conventional Patlak analysis. Twenty-two lesion regions of interest (ROIs) were evaluated. ca(t) was determined from a three-dimensional ROI in the aorta. Furthermore, the correlation between Km and late standard uptake value (SUV) as well as retention index was investigated. Additionally, feasibility of the approach was demonstrated in a whole-body investigation.

Results

Patlak analysis yielded a mean Vr of <a onClick="popup('http://www.ejnmmires.com/content/3/1/16/mathml/M5','MathML',630,470);return false;" target="_blank" href="http://www.ejnmmires.com/content/3/1/16/mathml/M5">View MathML</a> ml/ml. The patient averaged τa was 99 ± 23 min. Linear regression between Patlak-derived Km and DTP-derived Ks according to Ks = b · Km + a yielded b = 0.98 ± 0.05 and a = -0.0054 ± 0.0013 ml/min/ml (r = 0.98) in full accordance with the theoretical predictions b = 1 and <a onClick="popup('http://www.ejnmmires.com/content/3/1/16/mathml/M6','MathML',630,470);return false;" target="_blank" href="http://www.ejnmmires.com/content/3/1/16/mathml/M6">View MathML</a>. Ks exhibits better correlation with Km than late SUV and retention index, respectively. <a onClick="popup('http://www.ejnmmires.com/content/3/1/16/mathml/M7','MathML',630,470);return false;" target="_blank" href="http://www.ejnmmires.com/content/3/1/16/mathml/M7">View MathML</a> is proposed as a quantitative estimator of Km which is independent of patient weight, scan time, and scanner calibration.

Conclusion

Quantification of Km from dual time point measurements compatible with clinical routine is feasible. The proposed approach eliminates the issues of static SUV and conventional DTP imaging regarding influence of chosen scanning times and inter-study variability of the input function. Ks and <a onClick="popup('http://www.ejnmmires.com/content/3/1/16/mathml/M8','MathML',630,470);return false;" target="_blank" href="http://www.ejnmmires.com/content/3/1/16/mathml/M8">View MathML</a> exhibit improved stability and better correlation with the true Km. These properties might prove especially relevant in the context of radiation treatment planning and therapy response control.

Keywords:
Whole-body PET; Dual time point; Metabolic rate of FDG; PET quantification; Tracer kinetic modeling