Table 2. Linear regression results of the ⁶⁸Ga-FAPi-04 and ¹⁸F-FET PET semiquantitative parameters with different thresholds for lesion delineation.

Delineation threshold	Parameter	Coefficient	P value	95% confidence interval	VIF
20% lesion FAPi SUVmax	MTVFAPi:MTVFET ratio	4.142	0.027*	0.572 to 7.712	5.02
	TLUFAPi/TLUFET ratio	−2.672	0.032*	−5.057 to −0.288	3.94
	TBRmax-FAPi	0.008	0.044*	0.000 to 0.016	2.75
	TBRmax-FET	−0.589	0.114	−1.347 to 0.169	1.65
30% lesion FAPi SUVmax	MTVFAPi:MTVFET ratio	5.484	0.052	−0.045 to 11.013	3.97
	TLUFAPi:TLUFET ratio	−3.095	0.067	−6.447 to 0.257	3.59
	TBRmax-FAPi	0.007	0.081	−0.001 to 0.015	2.45
	TBRmax-FET	−0.747	0.047*	−1.482 to −0.012	1.36
40% lesion FAPi SUVmax	MTVFAPi:MTVFET ratio	8.974	0.049*	0.044 to 17.903	3.28
	TLUFAPi:TLUFET ratio	−3.678	0.098	−8.174 to 0.818	2.87
	TBRmax-FAPi	0.007	0.082	−0.001 to 0.015	2.42
	TBRmax-FET	−0.601	0.104	−1.351 to 0.149	1.41
50% lesion FAPi SUVmax	MTVFAPi:MTVFET ratio	14.732	0.065	−1.131 to 30.596	2.82
	TLUFAPi:TLUFET ratio	−4.179	0.194	−10.857 to 2.500	2.49
	TBRmax-FAPi	0.006	0.116	−0.002 to 0.014	2.38
	TBRmax-FET	−0.428	0.279	−1.261 to 0.406	1.65

*, P<0.05. ⁶⁸Ga-FAPi-04, gallium-68 fibroblast activation protein inhibitor 04; ¹⁸F-FET, fluoride 18 fluoroethyl-L-tyrosine; PET, positron emission tomography; VIF, variance inflation factor; FAPi, fibroblast activation protein inhibitor; SUVmax, maximal standardized uptake value; MTV, metabolic tumor volume; TLU, total lesion tracer uptake; TBRmax, maximal tumor-to-brain ratio; FET, fluoroethyl-L-tyrosine.