This is the same model as the C14 Autoradiography, except that a correction for the changing of plasma glucose during the experiment is included [1].
The autoradiographic experiment is performed as follows:
1.The 14C-labeled deoxyglucose is injected.
2.Blood is sampled and counted until the end of the experiment.
3.The glucose concentration in plasma is measured for several samples.
4.After 50 minutes the deoxyglucose has been trapped and the animal is sacrificed.
5.The brain is isolated, then frozen, and sectioned into very thin slices.
6.The slices are put onto a flat support and mounted into a radioactivity counter together with reference sheets of known activity concentration.
7.The radioactivity is counted during several days.
The result is a set of images either on a conventional film or as a digital file in one of the popular graphic formats. These images can be turned into radioactivity units by a translation table which needs to be obtained from the reference sheets.
Acquisition and Data Requirements
Image Data |
A data set representing the autoradiographical slices in arbitrary units. Select 1/1 as the loading units as the values are transformed into nCi/g during the model calculations. An appropriate translation table must be derived from the image representation of the reference sheets and supplied as the TAC1 curve in the model preprocessing panel. Note that the duration of the acquisition must be specified as the time from injection until sacrificing the animal. |
Input curve |
Plasma activity of blood sampled at a peripheral artery from the time of injection until sacrificing the animal. Important: Select 1/1 as the units and ensure that the values in the data file are already in nCi/g. |
Blood Preprocessing
Model Preprocessing
The parameters applied in the autoradiographic calculation of MRGlu must be entered in the model pre-processing dialog
Lumped constant |
It is used to account for the difference in uptake between normal glucose and DG. |
K1 |
Unidirectional transfer of DG into tissue. |
k2 |
Clearance of DG from the tissue. |
k3 |
Phosphorylation rate in tissue. |
As mentioned before it is assumed that the input images are in arbitrary units and must be converted to radioactivity. This is done by the application of a translation table which must be specified as File for image pixel value -> nCi transformation on the Model Preprocessing panel (C14translation.crv). The contents of this text file should look like :
Graphic[1/1] Activity[1/1]
46 0
48 34
57 84
66 126
72 157
82 233
86 270
95 323
95 391
102 433
111 497
121 549
126 585
136 688
159 916
So in the above example the image pixel values have an original range up to 159, and the resulting activity values range up to 916 nCi/g.
Note: Please use the FILE option for specifying the conversion table with 1/1 units for time and value. The model will NOT work with TAC DB.
Additionally a File containing the course of Plasma glucose over time in mg/100ml must be specified (C14plasmaGlucose.crv). This text file should look like :
time[seconds] glucose[1/1]
0 115.2
2700 97.2
Note that linear interpolation is applied between the tabulated values in the look-up files.
Model Configuration
MRGlu |
Metabolic Rate of Glucose in [μmol/min/100ml], the actual result of the model. It is calculated according to eq. (7) in [23]. |
nCi/g |
This is just a utility parameter showing the activity in the pixels after application of the conversion table. |
Reference
1.Savaki HE, Davidsen L, Smith C, Sokoloff L: Measurement of free glucose turnover in brain. J Neurochem 1980, 35(2):495-502.