[Gate-users] TOF differences in GATE.

[KB]

Hello All,

     I was looking at the TOF values with a gate simulation and I
noticed that there is a significant difference between the time as
calculated with distances and that with the time stamps.

Here is part of my root file:

                Float_t		SOL_MM_PER_PS=0.299792458;

		dist1 = sqrt(TMath::Power( (SPX1-GPX1),2)+
				TMath::Power( (SPY1-GPY1),2)+
				TMath::Power( (SPZ1-GPZ1),2)
			    );

		dist2 = sqrt(TMath::Power( (SPX1-GPX2),2)+
				TMath::Power( (SPY1-GPY2),2)+
				TMath::Power( (SPZ1-GPZ2),2)
			    );

		TOF_from_dist = (dist1-dist2)/SOL_MM_PER_PS;
	
                time1=time1*1e12; //Convert to ps
		time2=time2*1e12;

                TOF=time1-time2;

                printf("%f\t%f\t%.13f\t%.13f\n",dist1,dist2,TOF_from_dist,TOF);

And the output is:

453.940308      452.199921      5.8053059577942 5.0950469970703
459.470947      455.000916      14.9104204177856        11.3311767578125
448.798157      453.128357      -14.4439926147461       -17.9815368652344
459.725372      450.393494      31.1277961730957        33.6613769531250
455.757416      459.803253      -13.4954605102539       -15.4542427062988
457.842651      450.991852      22.8518066406250        23.3282699584961
455.239349      452.293945      9.8248100280762        10.6857109069824
459.894775      453.933655      19.8841571807861        94.1573410034180
448.406433      449.142334      -2.4547009468079        -1.4030494689941
451.955017      457.242065      -17.6356945037842       -13.6032714843750

Why the difference between column 3 and 4? I made sure that I was
looking at only true events, with no scatter in the phantom.
Does this come from the timing dispersion due to scatter within the
crystal? If so, it looks like a rather long path within the crystal
(20 mm, LYSO).


Thanks in advance for any explanation.


Karthik.