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MRI. [56] Furthermore FDOPA PET fused with MRI for benign conditions such as infections and nonspecific
anatomic localization provides accurate localization of inflammatory tissue. [45,79] In viral encephalitis FDG
tracer uptake taking advantage of both techniques. [71] PET usually demonstrates hypermetabolism but focal
areas of hypometabolism may also be observed. [80]
3’-deoxy-3’-[18F]-fluorothymidine is a PET tracer Brain abscess may also exhibit FDG hypermetabolism
developed for imaging cellular proliferation. In patients making the differential diagnosis between a metastatic
with histologically diagnosed primary brain tumors the tumor and abscess in a patient with systemic cancer
FLT uptake by the primary tumor could correlate with impossible with only this test. [81,82] Tuberculomas may
[72]
the grade of malignancy and proliferation index, but also exhibit FDG hypermetabolism in the periphery
occasionally it could result in false positive diagnoses, and hypometabolism in the center. [83]
especially in cases of benign lesions with blood-brain
barrier disruption, for example postoperative Even though, most of the newer PET tracers demonstrated
granuloma. [57] Comparison of FLT PET to MRI with enhanced tumor-specificity compared with FDG, they
and without contrast in 19 patients with recurrent also had certain limitations; for example, (11)C-choline
glioma treated with bevacizumab in combination with can be accumulated in various inflammatory processes,
irinotecan indicated that both early (1-2 weeks post MET in brain abscesses and (18)F-FLT in nonmetastatic
treatment) and late FLT PET responses (6 weeks) were reactive lymph nodes. [45]
more significant predictors of overall survival compared
with the MRI responses. In this study, metabolic response CONCLUSION
was defined as more than 25% reduction in tumor FLT
[58]
uptake compared with baseline. Furthermore, when (18)F-flurodeoxyglucose PET, as well as PET with other
compared to FDG PET, FLT PET was reported better in tracers, may be useful for diagnosis of cerebral gliomas
imaging recurrent high-grade tumors, correlating with in patients that present with a brain mass and no
Ki-67 values, and predicting tumor progression and involvement of other organs in conventional imaging. In
[18]
patient survival. Similarly, comparison of FDG with addition, PET/CT is helpful in selecting the appropriate
FDOPA and FLT PET in 15 patients with untreated or site for stereotactic biopsy and in monitoring response
recurrent low-grade gliomas demonstrated that clearly to various therapeutic interventions. Finally, upon re-
FDOPA was the tracer of choice for tumor delineation growth of the tumor after the initial treatment, PET/
[17]
compared with the other 2 tested tracers. However, CT can differentiate between glioma recurrence vs.
another small study in 15 patients with recurrent gliomas necrosis from the employed radiation therapy and
reported no advantage of FLT PET compared with FDG guide further therapeutic management.
PET in discriminating between tumor recurrence and
radiation necrosis. [19] REFERENCES

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