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18f_positron_emission_tomography

18F positron emission tomography

see also Fluoroethyl Tyrosine Positron Emission Tomography

Besides the advantages of hybrid positron emission tomography-computed tomography imaging, this dual-modality scanning may produce their own specific artifacts due to different causes, such as metallic implants, respiratory motion, contrast medium and truncation. Proper patient preparation is required to minimize the potential artifactual uptake patterns that make reporting difficult. It is important to learn about proper quality control, imaging and reconstruction and to be familiar with potential artifacts and, pitfalls for the accurate interpretation of “F-fluorodeoxyglucose positron emission tomography-computed tomography 1).

It is a highly sensitive and specific modality for detection of bone metastases in patients with high-risk prostate cancer. It is more specific than 18F-Fluoride PET alone and more sensitive and specific than planar and SPECT bone scintigraphy (BS). Detection of bone metastases is improved by SPECT compared with planar BS and by 18F-Fluoride PET compared with SPECT. This added value of 18F-Fluoride PET/CT may beneficially impact the clinical management of patients with high-risk prostate cancer 2) PET scanning with the tracer fluorine-18 (F-18) fluorodeoxyglucose (FDG), (FDG-PET), is widely used in oncology. This tracer is a glucose analog that is taken up by glucose-using cells and phosphorylated by hexokinase (whose mitochondrial form is greatly elevated in rapidly growing malignant tumours).

A typical dose of FDG used in an oncological scan has an effective radiation dose of 14 mSv.

Because the oxygen atom that is replaced by F-18 to generate FDG is required for the next step in glucose metabolism in all cells, no further reactions occur in FDG. Furthermore, most tissues (with the notable exception of liver and kidneys) cannot remove the phosphate added by hexokinase. This means that FDG is trapped in any cell that takes it up, until it decays, since phosphorylated sugars, due to their ionic charge, cannot exit from the cell. This results in intense radiolabeling of tissues with high glucose uptake, such as the brain, the liver, and most cancers. As a result, FDG-PET can be used for diagnosis, staging, and monitoring treatment of cancers, particularly in Hodgkin's lymphoma, non-Hodgkin lymphoma, and lung cancer. Many other types of solid tumors will be found to be very highly labeled on a case-by-case basis—a fact that becomes especially useful in searching for tumor metastasis, or for recurrence after a known highly active primary tumor is removed.

Because individual PET scans are more expensive than “conventional” imaging with computed tomography (CT) and magnetic resonance imaging (MRI), expansion of FDG-PET in cost-constrained health services will depend on proper health technology assessment; this problem is a difficult one because structural and functional imaging often cannot be directly compared, as they provide different information. Oncology scans using FDG make up over 90% of all PET scans in current practice.

Bone metastasis

Temporal lobe epilepsy

Several studies using 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) or diffusion tensor imaging (DTI) have found both temporal and extratemporal abnormalities in patients with mesial temporal lobe epilepsy with ipsilateral hippocampal sclerosis (MTLE-HS).

Patients with MTLE-HS have widespread metabolic and microstructural abnormalities that involve similar regions. The distribution patterns of these gray and white matter abnormalities differ between patients with left or right MTLE, but also with the extent of the 18F-FDG-PET hypometabolism along the epileptogenic temporal lobe. These findings suggest a variable network involvement among patients with MTLE-HS 3).

The area of predominant perifocal 18F positron emission tomography hypometabolism and reduced [11C]flumazenil (11C-FMZ) -binding on PET scans is currently considered to contain the epileptogenic zone and corresponds anatomically to the area localizing epileptogenicity in patients with temporal lobe epilepsy (TLE).

High grade glioma

The precise definition of the post-operative resection status in high-grade gliomas (HGG) is crucial for further management. We aimed to assess the feasibility of assessment of the resection status with early post-operative positron emission tomography (PET) using [18F]O-(2-[18F]-fluoroethyl)-L-tyrosine ([18F]FET).

25 patients with the suspicion of primary HGG were enrolled. All patients underwent pre-operative [18F]FET-PET and magnetic resonance imaging (MRI). Intra-operatively, resection status was assessed using 5-aminolevulinic acid (5-ALA). Imaging was repeated within 72h after neurosurgery. Post-operative [18F]FET-PET was compared with MRI, intra-operative assessment and clinical follow-up.

[18F]FET-PET, MRI and intra-operative assessment consistently revealed complete resection in 12/25 (48%) patients and incomplete resection in 6/25 cases (24%). In 7 patients, PET revealed discordant findings. One patient was re-resected. 3/7 experienced tumor recurrence, 3/7 died shortly after brain surgery.

Early assessment of the resection status in HGG with [18F]FET-PET seems to be feasible 4).

Case series

2016

A study included 71 patients who had a presurgical evaluation workup performed due to drug resistant epilepsys, who underwent epilepsy surgery, and who were histopathologically diagnosed with focal cortical dysplasia (FCD). Relationships involving MRI and FDG-PET findings and clinical data from pathological subgroups and patients were assessed.

According to the International League Against Epilepsy (ILAE) classifications of FCD, 28 of the patients were type I and 43 were type II. FCD was visible on the MRI scans of 53 patients, and a majority of this group was classified as type II FCD (n=34). Of these 53 patients, FCD was located in the temporal area of 21 patients, the extratemporal area of 29 patients. Of the patients who exhibited FDG-PET hypometabolism (PET-positive), 23 were classified as temporal, 17 as frontal, 11 showed involvement of the posterior cortex. The age of seizure onset was younger in PET-positive patients (p=0.032), and histopathological analyses revealed that 23 patients had type I FCD and 30 patients had type II FCD.

PET scans reveal a lesion by showing hypometabolism in patients who have refractory epilepsy and an early age of onset with FCD. The lesions of MRI-negative/PET-positive FCD patients tend to be localized in the temporal lobe and that FCD may be localized in the frontal lobe of MRI-negative/PET-negative patients. However, the histopathological examinations of MRI-positive/PET-positive, MRI-negative/PET-positive, and MRI-negative/PET-negative patients did not exhibit a particular histopathological subtype 5).

1)
Mihailovič J, Matovina E, Nikoletič K. 18F-fluorideoxyglucose positron emission tomography/computed tomography imaging: artifacts and pitfalls. Med Pregl. 2015 Jan-Feb;68(1-2):41-8. PubMed PMID: 26012243.
2)
Even-Sapir E, Metser U, Mishani E, Lievshitz G, Lerman H, Leibovitch I. The detection of bone metastases in patients with high-risk prostate cancer: 99mTc-MDP Planar bone scintigraphy, single- and multi-field-of-view SPECT, 18F-fluoride PET, and 18F-fluoride PET/CT. J Nucl Med. 2006 Feb;47(2):287-97. PubMed PMID: 16455635.
3)
Aparicio J, Carreño M, Bargalló N, Setoain X, Rubí S, Rumià J, Falcón C, Calvo A, Martí-Fuster B, Padilla N, Boget T, Pintor L, Donaire A. Combined (18)F-FDG-PET and diffusion tensor imaging in mesial temporal lobe epilepsy with hippocampal sclerosis. Neuroimage Clin. 2016 May 6;12:976-989. PubMed PMID: 27995064.
4)
Kläsner B, Buchmann N, Gempt J, Ringel F, Lapa C, Krause BJ. Early [18F]FET-PET in Gliomas after Surgical Resection: Comparison with MRI and Histopathology. PLoS One. 2015 Oct 26;10(10):e0141153. doi: 10.1371/journal.pone.0141153. eCollection 2015. PubMed PMID: 26502297.
5)
Halac G, Delil S, Zafer D, Isler C, Uzan M, Comunoglu N, Oz B, Yeni SN, Vatankulu B, Halac M, Ozkara C. Compatibility of MRI and FDG-PET findings with histopathological results in patients with focal cortical dysplasia. Seizure. 2016 Dec 6;45:80-86. doi: 10.1016/j.seizure.2016.11.024. [Epub ahead of print] PubMed PMID: 27960132.
18f_positron_emission_tomography.txt · Last modified: 2016/12/23 09:04 (external edit)