13N-NH3: a selective contrast-enhancing tracer for brain tumor.
OBJECTIVE
The purpose of this study is to determine whether there is a qualitative and quantitative relationship between the breakdown of the blood-brain barrier, defined radiologically by the contrast enhancement of MRI, and the uptake of N-NH3 in brain tumors.


METHODS
The results of N-NH3 PET in 42 patients suspected of having brain tumors were compared with the findings of contrast-enhanced MRI. A histopathological diagnosis was carried out in 33 patients, and a clinical diagnosis was performed in the remaining patients. PET and MRI images were visually inspected, and the contrast index (CI) of MRI and the uptake index (UI) of N-NH3 were measured.


RESULTS
Contrast enhancement of MRIs was seen in 20 of 29 brain tumors (69%). Increased uptake of N-NH3 was seen in 24 of 29 brain tumors (83%). Nineteen of 20 contrast-enhancing brain tumors exhibited the increased uptake of N-NH3 (95%). Areas of the increased N-NH3 uptake corresponded to areas enhanced on MR images in the majority of cases. Five out of nine nonenhancing tumors exhibited increased uptake of N-NH3 (56%). The contrast enhancement of MRIs was seen in nine of 13 nonneoplastic lesions (69%). None of the nonneoplastic lesions showed increased uptake of N-NH3, yielding a specificity of 100% for brain tumors (0 of 13). CI for tumor tissue was 1.46+/-0.64. UI of N-NH3 for tumor tissue was 1.64+/-0.71. CI and UI for tumor tissue were significantly correlated (r=0.86, P<0.01). A statistically significant difference in uptake levels of N-NH3 between contrast-enhancing tumors and nonenhancing tumors (1.88+/-0.66, n=20 vs. 1.11+/-0.52, n=9, P<0.01) was observed. UI was higher in brain tumors compared with the nonneoplastic lesions (1.64+/-0.71 vs. 0.71+/-0.19, P<0.01).


CONCLUSIONS
N-NH3 is a potential selective contrast-enhanced tracer for brain tumor, and may prove especially useful for evaluating the contrast-enhancing lesions on MRI to distinguish brain tumors from nonneoplastic lesions.
Xiangsong
Zhang
Z
Department of Nuclear Medicine, Sun Yat-sen University, Guangzhou, China. sd_zh@163.net
Xinjian
Wu
W
Yong
Zhang
Z
Weian
Chen
C
D000293:Adolescent; D000328:Adult; D000368:Aged; D001254:Astrocytoma / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D001812:Blood-Brain Barrier / Q000378:metabolism; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D002648:Child; D003287:Contrast Media / Q000493:pharmacokinetics; D005260:Female; D005909:Glioblastoma / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009590:Nitrogen Radioisotopes / Q000737:chemistry; D049268:Positron-Emission Tomography; D000644:Quaternary Ammonium Compounds / Q000737:chemistry* / Q000493:pharmacokinetics; D011849:Radioactive Tracers; D012680:Sensitivity and Specificity; D055815:Young Adult
D003287:Contrast Media; D009590:Nitrogen Radioisotopes; D000644:Quaternary Ammonium Compounds; D011849:Radioactive Tracers