Estimation of 15O PET in healthy volunteers with automated ROI analysis by FineSRT

Introduction

Under the conditions of major cerebral arterial stenosis, increased OEF is reported to play an important role as a major risk factor for cerebral infarction and return to normal after revascularization therapy. Consequently, measurement of OEF and CMRO2 is useful for determination of indication for revascularization therapy. However, anatomical constitution of the OEF images, which were generated by the calculation using CBF images, was not so clear as those of the CBF images, which were directly generated by kinetic analysis of dynamic PET data and arterial input functions. Therefore, the results of the conventional ROI (region of interest)analysis of the OEF and CMRO2 images had serious problems in the objectivity and reproducibility. We already established the automated constant ROI analysis software for the cerebral gray matter named “FineSRT”. In this study we tried to estimate OEF and CMRO2 images of the normal volunteers using FineSRT.

Materials and methods

Nine healthy volunteers (age range 44−58 years, mean 51. 8 years, 9 men) were enrolled. The parametric images of CBF, OEF and CMRO2 were calculated according to the method of autoradiography. Using FineSRT, the OEF and CMRO2 images of each subject were anatomically standardized first with the same moving parameters determined by the CBF image and CBF PET template image under SPM99 algorithm. The standardized images were consequently analyzed using the constant ROI template, which was composed of 1394 ROIs grouped into 41 areas corresponding to respective cerebral convolutions as shown in the Table, and area-weighted mean value for each of the 41 areas based on the PET count in each ROI were calculated. The mean and standard deviation (SD) of the respective area-weighted mean OEF, CMRO2 and CBF values of all subjects' 41 areas were calculated and compared.

Results

Significant correlation was expectedly not shown between OEF and CBF values (Figure 1; r=0. 038, R2=0.001) but between CMRO2 and CBF (Figure 2; r=0.908, R2=0.825). As shown in the Table, the mean and SD of 41 OEF values were 42.56± 3.27 mL/100gr/min (range 31.64–46.68), and OEF values of the caudate tail (31.64), the hippocampus (35.75), the amygdaloid body (34.82) and the thalamus (37.34) were conspicuously lower than those of the other areas.

Figure 1

Scatter plot of CBF as measured by OEF

Figure 2

Scatter plot of CBF as measured by CMR O₂

Conclusion

FineSRT enables objective quantification of each cerebral gyrus of PET images. The normal OEF values of almost all gyri were observed around 42.56 irrespective of their CBF values, but lower threshold was needed for the evaluation of caudate tail, hippocampus, amygdaloid body and thalamus.

Table 1

Mean and SD of the nine volunteers' area-weighted average of OEF, CMRO₂ and CBF

SuperiorFrontal	MedialFrontal	ParacentralLobule	AnteriorCingulate	Subcallosal	Orbital	Rectal	MiddleFrontal	InferiorFrontal	Precentral	Postcentral
OEF	42.76±3.95	42.66±3.43	43.34±3.65	39.39±2.94	41.63±3.52	46.20±3.41	43.81±2.76	43.71±3.24	42.84±3.44	42.93±4.24	43.51±3.64
CMRO2	2.62±0.48	3.20±0.53	3.37±0.97	3.07±0.38	3.71±0.56	3.86±0.63	4.05±0.55	3.01±0.44	3.09±0.35	2.82±0.50	2.83±0.46
CBF	37.74±4.63	45.98±6.06	46.78±11.89	47.85±5.02	53.57±6.43	49.80±5.85	54.64±5.71	41.73±4.62	43.98±4.27	40.46±6.23	39.92±5.64

	Insula	SuperiorParietal	InferiorParital	Supramarginal	Angular	SuperiorTemporal	MiddleTemporal	InferiorTemporal	TransverseTemporal	SuperiorOccipital	MiddleOccipital
OEF	42.20±2.87	45.35±3.90	44.38±3.01	44.25±2.42	45.89±3.08	41.52±3.34	44.22±3.00	45.05±3.13	40.38±3.18	46.11±3.36	46.42±2.89
CMRO2	3.41±0.44	2.77±0.56	3.00±0.47	3.01±0.39	3.38±0.44	3.08±0.33	2.98±0.35	2.82±0.35	3.86±0.64	3.09±0.40	2.96±0.45
CBF	48.73±5.86	37.56±6.12	41.40±4.98	41.60±4.89	44.43±5.40	45.21±4.79	41.25±4.42	38.64±4.47	56.72±8.89	40.77±4.62	38.82±4.88

	InferiorOccipital	PrecuneusLower	Cuneus	Hippocampus	Fusiform	Lingual	Parahippocampal	AmygdaloidBody	Thalamus	Putamen	GlobusPallidus
OEF	46.68±3.56	44.93±3.09	44.66±3.31	35.75±2.71	45.23±3.16	44.18±3.03	39.71±2.52	34.82±3.46	37.34±2.79	45.05±3.20	44.29±2.97
CMRO2	3.40±0.51	4.41±0.76	3.86±0.61	2.41±0.35	3.45±0.49	4.04±0.60	2.66±0.41	2.63±0.56	2.76±0.41	3.57±0.60	3.08±0.47
CBF	43.89±6.91	56.86±6.58	50.91±6.09	42.38±4.80	46.01±5.93	53.84±6.69	41.58±5.17	46.50±7.75	44.72±4.55	47.22±6.71	42.92±5.35

	CaudateHead	CaudateTail	PrecuneusUpper	Cingulate	PosteriorCingulate	Vermis	AnteriorLobe	PosteriorLobe			Average
OEF	43.48±4.29	31.64±4.96	44.37±3.04	41.03±2.91	42.58±3.32	39.95±2.97	39.46±3.30	41.28±3.21			42.56±3.27
CMRO2	2.06±0.44	1.46±0.38	3.58±0.93	3.35±0.55	4.07±0.75	3.62±0.75	3.19±0.54	4.50±0.82			3.22±0.60
CBF	30.00±3.87	30.45±4.02	46.89±8.35	49.12±6.63	54.27±5.48	54.26±9.71	48.65±6.78	63.43±10.48			45.65±6.90