Renal blood flow using [15O]H2O and dynamic PET
[15O]H2O bolus model
The analysis method of renal blood flow (RBF) is based on one-tissue compartment model with parameters RBF (renal blood flow), p (partition coefficient, and RBV (renal blood volume). Measurement of perfusion with[15O]H2O is based on the principle of exchange of inert gas between blood and tissues (Kety and Schmidt, 1945).
RBF can be estimated from regional time-activity concentration curves (TACs), or from dynamic PET image to produce perfusion map. The methods presented below use blood curve from arterial line as their input. The non-linear method for regional TACs is based on the study by Nitzsche et al. (1993), but recovery correction is presently not applied, leading to slower RBF estimates. The linearized method for calculation of RBF image is based on the publication Alpert et al. (2002), except that also RBV is included in the present model; Alpert et al. (2002) ignored RBV, which causes overestimation of RBF (TPCMOD0032).
Processing of arterial blood data from on-line sampler
Arterial blood data, collected using on-line sampling system, must be calibrated and corrected for physical decay, dispersion and time delay. Please note: Do NOT use countrate curve or head curve for time delay correction, because aorta or even the heart, where high radioactivity concentration appears considerably sooner than in the kidneys, is also located in the PET image. Although it may cause extra work, renal TACs must be used in time delay correction instead.
- Draw ROIs on kidneys (ROIs need not be accurate)
- Calculate the renal TACs from these ROIs. Make sure that TAC datafiles do not contain aortic TACs!
- On MS Windows PC in TPC network, do the corrections for blood data using water_input script. Alternatively, these corrections can also be done using a series of low-level commands on both Solaris and Windows platforms.
- Check visually that the corrected blood TAC is fine and that time delay correction has moved it to start to rise at the same time as the renal TACs. Previous water_input command made a graph of these curves in postscript format (*.ps). Alternatively you can create the plot by yourself.
Calculation of RBF image:
RBF image can be calculated using imgflow, version 0.8.2 or later, in MS Windows command prompt window or Solaris terminal window on SUN or PC platform.
For example, if the dynamic PET image filename is us0345dy1.img, and the corrected arterial blood curve is us0345ab.kbq, you would enter the following command:
imgflow us0345ab.kbq us0345dy1.img 180 us0345rbf.img -va=us0345rbv.img
This command will create an RBF image us0345rbf.img and RBV image us0345rbv.img. Unit of RBF is [ml blood * min-1 * (ml renal tissue)-1] and unit of RBV is [ml blood * (ml renal tissue)-1]. These parametric images can be processed further as needed.
Calculation of RBF from renal TACs
After ROIs have have been drawn and average time-activity concentration curves have been calculated from dynamic PET images, the regional RBF can be estimated using fit_h2o, version 4.1.0 or later, in MS Windows command prompt window or Solaris terminal window on SUN or PC platform.
For example, if the renal TAC filename is us0345dy1.dft, and the corrected arterial blood curve is us0345ab.kbq, you would enter the following command:
fit_h2o -ml us0345ab.kbq us0345dy1.dft 180 us0345rbf.res
This command will create a result file
us0345rbf.res, which contains regional RBF, p, and RBV values. If you remembered to
put the option -ml to the command line, the unit of RBF is
[ml blood * min-1 * (ml renal tissue)-1]
Sometimes you may need to specify lower and upper limits for the parameters. For this purpose a parameter file needs to be created. It is a text file, which has to be created only once,
using for example Notepad in MS Windows or textedit in Solaris or from the command line with call:
fit_h2o -i=rbf.par
Suitable contents for RBF calculation are:
K1_lower := 0 K1_upper := 600 K1k2_lower := 0.2 K1k2_upper := 1 Va_lower := 0 Va_upper := 40 Delay_lower := 0 Delay_upper := 0
After this, the program is called with following command:
fit_h2o -i=rbf.par -ml us0345ab.kbq us0345dy1.dft 180 us0345rbf.res
