Plasma and blood data
The concentration of the unchanged (non-metabolized) tracer in arterial plasma (or blood, depending on the tracer) is the gold standard input function (IF) in quantitative PET data analysis. This is often referred to as plasma time-activity curve (PTAC).
Correction of vascular radioactivity requires the measurement of total radioactivity concentration in the blood (BTAC).
Arterial blood can be measured
- by manual or automated sampling of arterial blood: arterial catheterization is safe (Jons et al., 1997) and reliable, but burdensome;
- noninvasively from dynamic PET image, if heart, arch of aorta, abdominal aorta or other large artery is visible in the image;
- by sampling arterialized venous blood: hand is warmed to increase blood flow and shunting; or
- as a combination of these.
Arterial sampling from small animals is difficult, but possible: Croteau et al. (2014) compared arterial IFs obtained from rat femoral and tail artery, either manually, or using microvolumetric blood counter with dispersion correction. Huang et al. (2017) have inserted catheter into the femoral artery of rat, kept it in place for 1.5 months, conducting several FDG PET studies for the same animals, with arterial blood sampling using microfluidic blood sampler. Sijbesma et al. (2016) collected manual samples from catheter placed into femoral artery of the rat, repeating the procedure later by placing the catheters to the other hind limb. Online blood sampling system can produce reliable BTAC in rat studies (Roehrbacher et al., 2015). Pump-driven arteriovenous shunt allows measurement of BTAC without the problems of reduced amount of circulating blood in the small animal and background activity that affect intra-arterial probes (Weber et al., 2002; Warnock et al., 2011).
Plasma
Plasma can be separated from blood samples by adding anti-coagulants, followed by centrifugation, for measurement of the total radioactivity concentration in it. Plasma sample can also be used in analysis of parent tracer fraction for metabolite correction.
Serum
If no anticoagulant is added to the blood collection tube and the blood is allowed to clot, the supernatant fluid is called the serum. Serum is less viscous than plasma, and lacks clotting proteins such as fibrinogen and prothrombin. In PET studies plasma is more common than serum.
File format
Plasma and blood data files are stored in ASCII format (File format of time-radioactivity curves).
See also:
- Preprocessing arterial input data
- Blood sampling
- Time-delay correction
- Extraction of blood TAC from PET image
- Metabolite correction
- Compartmental models
- Plotting TACs
- Units of PET data
- Erythrocytes
- PET study design
References
Bentourkia M, Bol A, Ivanoiu A, Michel C, Coppens A, Sibomana M, Cosnard G, De Volder AG. A standardized blood sampling scheme in quantitative FDG-PET studies. IEEE Trans Med Imag. 1999; 18(5): 379–384.
Eriksson L, Kanno I. Blood sampling devices and measurements. Med Prog Technol. 1991; 17(3-4): 249-257.
Greuter HN, Boellaard R, van Lingen A, Franssen EJ, Lammertsma AA. Measurement of 18F-FDG concentrations in blood samples: comparison of direct calibration and standard solution methods. J Nucl Med Technol. 2003; 31(4): 206-209.
Jons PH, Ernst M, Hankerson J, Hardy K, Zametkin AJ. Follow-up of radial arterial catheterization for positron emission tomography studies. Hum Brain Mapping 1997; 5: 119-123.
Krebs HS. Chemical composition of blood plasma and serum. Annu Rev Biochem. 1950; 19: 409-439. doi: 10.1146/annurev.bi.19.070150.002205.
Warnock G, Bahri MA, Goblet D, Giacomelli F, Lemaire C, Aerts J, Seret A, Langlois X, Luxen A, Plenevaux A. Use of a beta microprobe system to measure arterial input function in PET via an arteriovenous shunt in rats. EJNMMI Res. 2011; 1(1):13. doi: 10.1186/2191-219X-1-13.
Tags: Input function, Blood, Plasma, PTAC, BTAC
Updated at: 2018-01-06
Created at: 2014-04-08
Written by: Vesa Oikonen